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Temperature effect on survival, growth, and triacylglycerol content during the early ontogeny of Mytilus edulis and M. Trossulus
Abstract
Temperature is a major factor contributing to the biogeography of intertidal poikilotherms. The population dynamics of intertidal invertebrates like mussels are strongly dependent on larval supply and larval mortality. Unlike adults, which are resistant to fluctuating environmental conditions, larvae are highly sensitive to the physicochemical conditions of the pelagic zone. The effects of rearing temperature on larval and post-larval performance of 2 coexisting mussels species, Mytilus edulis and M. trossulus, were examined in this study. In the first experiment, larvae of both species were reared separately at constant temperatures of 10, 17, and 24 degrees C from D-larvae to the dissoconch stage. In the second experiment, pediveligers were reared under the same experimental conditions as the larvae for 2 wk. Survival, growth, and lipid composition (triacylglycerol [TAG] and sterol [ST] contents) were used to compare the performance of both species. The first experiment showed a species-specific thermal tolerance range, reflecting the biogeography of the species. M. trossulus larvae showed a preference for water at 10 and 17 degrees C, corresponding to the more northerly distribution of this species, whereas M. edulis preferred temperatures of 17 and 24 degrees C. Moreover, the TAG content in larvae of both species varied with temperature, supporting the hypothesis of a positive correlation between energy reserve content and the survival of mussel larvae. In contrast, the species-specific characteristics of thermal tolerance were not observed during post-larval development, suggesting that the selective effect of temperature on mussel species occurs during early ontogeny.
... Temperatures outside of the tolerance window reduce fitness and physiological stability, and thus increase the risk of mortality (Hoegh-Guldberg and Bruno, 2010). The degree of thermal tolerance for bivalves is species-specific and fluctuates by developmental stages, with larval stages showing narrower temperature tolerance ranges than juveniles and adults (Rayssac et al., 2010;Zippay and Helmuth, 2012;Gosling, 2015a;Pörtner et al., 2017). The thermal window (maintaining aerobic metabolism) for blue mussel (Mytilus edulis, L. 1758) usually ranges from 5 to 20 • C, whereas the optimal temperature for growth is between 10 and 20 • C (Widdows, 1973;Bayne, 1976;Incze et al., 1980;Almada-Villela et al., 1982;Stirling and Okumuş, 1994;Comeau et al., 2008;Hiebenthal et al., 2013). ...
... We tested for the presence of thermal selectivity on peri-(< 1 mm) and post-metamorphic (> 1 mm) mussels. We suggest that the selective pressure could be more effective around metamorphosis because of the sensitivity of this stage (Pechenik, 2006;Rayssac et al., 2010;Jenewein and Gosselin, 2013;Gosling, 2015a). We needed to mimic mussel farming practises because mussel stock performance had been observed on spat settled on artificial collectors (Sénéchal et al., 2008;Myrand et al., 2009aMyrand et al., , 2009bGuillou et al., 2020). ...
... Collectors were stored and treated as already described. The first 3000 individuals sampled with undamaged shells ranging from 300 to 1000 μm were placed into a large downweller for acclimation (Ø = 25 cm, 209 μm Nitex bottom mesh, 20 cm seawater column height) at 18 • C to respect the optimal conditions for post-larval blue mussel development (Lutz and Kennish, 1992;Rayssac et al., 2010). Post-larvae stayed in acclimation condition until to reach the targeted experimental sizes. ...
Our previous work confirmed that the higher survival, growth, and commercial performance of a mussel stock collected from a specific lagoon have been maintained over the last 25 years at a microgeographic scale despite intensive transfers of its spat to other local mussel sites. The objective of this study was to identify potential selection mechanisms supporting the quality of this stock. We used a mesocosm approach to examine the effect of maximum seawater temperature measured in the field on the different ontogenic stages of Mytilus edulis to simulate similar patterns in the laboratory. We demonstrated that thermal selection did not affect the development of peri-metamorphic stages (< 1 mm) since no effects were observed on growth, survival, or prodissoconch II size under natural thermal variations. However, our experimental results clearly indicated the existence of a thermal selective pressure (24 °C for 85 h) on 4.5–7 mm juvenile mussels, with growth performance enhanced in surviving individuals. Mortality was 37% higher compared to the control group, suggesting the elimination of more sensitive and less performant mussels. Interestingly, surviving individuals showed improved shell and tissue growth rates, by 22 and 51%, respectively. Our results support the hypothesis that the thermal selection of highly performant stock is size-dependent. The selective pressure demonstrated in this study along with our previous work highlighting the physiological and genetic differences between local stocks constitute the key mechanisms leading to the observed stable production performance over decades at a microgeographic scale.
... Les avantages démontrés sont que le milieu offshore propose des conditions d'élevage plus stables pour la mytiliculture, notamment en termes d'exposition aux stress environnementaux (e.g. stress thermique), avec des répercussions directes sur les taux de mortalité, les taux de croissance, l'état de santé des stocks à la récolte et donc sur la qualité de la production (Cheney et al., 2010;Langan, 2012;Gallardi et al., 2017;Steeves et al., 2018; (Mallet & Carver, 1995;Rayssac et al., 2010;Tremblay & Landry, 2016). (1) ponte des moules établies dans le milieu naturel au mois de juin & installation des collecteurs dans le site de captage, (2) larves en dispersion dans le milieu pélagique, (3) fixation-métamorphose des larves sur les collecteurs, (4) retrait des collecteurs en octobre-novembre, (5) boudinage du naissain récupéré, (6) installation des boudins en site de grossissement, (7) récolte partielle du stock, moules âgées de ~18 mois, (Bayne, 2004;Toupoint et al., 2012a;2012b;Gosling, 2015d ...
... De plus, leurs tailles varient en fonction du stade de vie de l'organisme ( Figure 7b), mais aussi selon la localisation géographique de la population à laquelle il appartient (Pörtner, 2002;Jones et al., 2009;Pörtner, et al., 2017). Les premiers stades ontogéniques des bivalves ont effectivement une sensibilité thermique plus accrue que les juvéniles (Rayssac et al., 2010;Zyppay & Helmuth, 2012;Gosling, 2015b), du fait des comportements induisant l'utilisation des réserves en énergie ( Figure 5). Une hausse des températures entraine une augmentation de la vitesse des réactions chimiques et enzymatiques, et agît sur la fluidité membranaire et la structure des protéines (Hochachka & Somero, 2002). ...
... Pörtner, 2002;Pörtner, et al., 2017). (Bayne, 1965;Rayssac et al., 2010). Au stade adulte, la fenêtre optimale peut s'étirer de 17 à 20 °C, selon Lutz & Kennish (1992). ...
... Thermal tolerance is species specific (Rayssac et al., 2010), with each species occupying a particular thermal niche of optimal functioning outside which it may fail to survive. Within a thermal range, temperature controls various essential features of an ectothermic organism's physiology, as it alters chemical and enzymatic reactions, rates of diffusion, membrane fluidity, and protein structure (reviewed in Sokolova, 2021), resulting in performance variability. ...
... Recently, Foret et al. (2020) showed that rearing temperature modulates the fatty acid profile of V. verrucosa, as juveniles reared at 20°C contained largely less energetic (neutral) lipids than those reared at 15°C. As the main energetic reserve in marine bivalve larvae are the neutral lipids (Holland and Spencer, 1973;Gallager et al., 1986;Whyte et al., 1991), they positively correlate with their survival (Rayssac et al., 2010). Thus, temperature modulation could have long-term impacts on fitness. ...
... et al., 2023). Temperature mainly influences the physiological state of bivalve larvae by modifying the lipid composition (Pernet et al., 2007;Rayssac et al., 2010;Barret et al., 2016) and thereby could impact larval development, particularly the success of metamorphosis. Lipid accumulation (neutral) and membrane fatty acid (polar) composition acting on membrane fluidity are modified by temperature exposure and modulate the responses to stressors. ...
Noise is now recognized as a new form of pollution in marine coastal habitats. The development of marine renewable energies has introduced new sonorous perturbations, as the wind farm installation requires pile driving and drilling operations producing low frequency sounds at high sound pressure levels. Exponential expansion of offshore wind farms is occurring worldwide, making impact studies, particularly on benthic species highly abundant and diverse in the coastal area used for wind farming, a necessity. As larval recruitment is the basis for establishing a population, we conducted an experimental study to assess the interactive effects of pile driving or drilling sounds and larval rearing temperature on the endobenthic bivalve Venus verrucosa. In ectothermic animals, temperature modifies the organism’s physiology, resulting in performance variability. We hypothesize that temperature modulation could change larval responses to noise and explore the potential interacting effects of temperature and noise. Using two distinct rearing temperatures, physiologically different batches of larvae were produced with contrasting fatty acid content and composition in the neutral and polar lipid fractions. Without defining any absolute audition threshold for the larvae, we demonstrate that the effects of temperature and noise were ontogenic-dependent and modulated larval performance at the peri-metamorphic stage, acting on the metamorphosis dynamic. At the pediveligers stage, a strong interaction between both factors indicated that the response to noise was highly related to the physiological condition of the larvae. Finally, we suggest that underwater noise reduces the compensatory mechanisms established to balance the temperature increase.
... Sperm and eggs were collected separately, and spawning was induced by thermal shock (Rayssac et al. 2010). Briefly, mussels were put in individual flasks of 500 ml, each flask containing one mussel, to allow sperm and eggs to be collected separately, thus preventing unwanted fertilization. ...
... If triploid levels were <5%, the larval batches were discarded. Larval mussels were reared in a batch system (Rayssac et al. 2010). Briefly, after embryogenesis, fully shelled ˝D˝ veligers (D-larvae) were reared at 18°C in 2.5 L glass culture Fernbach at a ratio of 5 larvae ml −1 . ...
... Water was changed every 2 days with filtered (1 µm), ultraviolet (UV)-treated seawater provided. When >50% of the larvae reached the pediveliger stage, they were transferred to flow-through downwellers supplied with water at 18-20°C and 27 PSU (Rayssac et al. 2010). The larvae were fed continuously and Skeletonema costatum was included in their diet at 1:1:1:1:1 equivalent biomass estimated by culture algal dry weight. ...
Recently, there is a greater interest for the development of mussel Mytilus edulis hatcheries, particularly for the production and commercialization of triploid bivalves. The aims of this study were to examine the efficiency of inducing triploid mussels by various treatments and to determine the effect of triploidy on larval development. To produce triploids, extrusion of the second polar body of fertilized eggs was inhibited by 6-(dimethylamino)purine (6-DMAP), cold-shock, or heat-shock treatments. Triploidy was detected by flow cytometry for all the treatments. Treatment with 6-DMAP was the most efficient with a rate of triploidy of 90%, followed by heat-shock (56%) and cold-shock (30%) treatments. No survival differences were observed between diploids and 6-DMAP-induced triploid larvae from the D-shape stage up to their settlement. Moreover, increased growth was observed in triploid larvae compared to diploid larvae. Overall, this study showed that 6-DMAP is a highly efficient method to induce triploidy in mussels, with triploid larvae having faster growth compared to diploid.
... Although extensive literature on the importance of the lipid composition on the nutrition during larval stages of bivalves is available (da Costa et al., 2011, da Costa et al., 2015b, Delaunay et al., 1993, Kheder et al., 2010, Pernet et al., 2005, Pernet et al., 2004, Rayssac et al., 2010, so far few examples of lipidomics on invertebrate hatchery procedure have been produced. An example of lipidomics investigation on a relevant invertebrate aquaculture species is provided by Rey et al. (2015), who studied the lipidome during larval development in crabs (Carcinus maenas and Necora puber). ...
... Lipids can provide information regarding the development of a larval culture. An increase in the TG content in scallops and mussel larvae was correlated with metamorphosis success and batch quality (Pernet et al., 2006, Rayssac et al., 2010. C. gigas larvae challenged by Vibrio coralliilyticus reduced their feeding regime resulting in a significant decrease in their TG and increase in NMI FA in membrane lipids (Genard et al., 2013). ...
... For example, exposure to low temperatures results in lower levels of membrane sterols (Crocket, 1998), whilst high temperature influenced content of PUFA in PC, PE and PI phospholipids (Fokina et al., 2017). Exposure to higher temperatures resulted in a decreasing of storage lipids as TG (Pernet et al., 2007b, Rayssac et al., 2010, due to the higher metabolic requirements (Navarro et al., 2000). Shifts between PC and PE are also observed as a response to temperature fluctuations due to the stabilizing effect of choline head compared with the smaller size of ethanolamine (Ernst et al., 2016). ...
... Two blue mussel species, Mytilus edulis L. (1758) and M. trossulus Gould (1850), and their hybrids were identified in the mussel beds in Kandalaksha Bay of the White Sea (Katolikova, Khaitov, Väinölä, Gantsevich & Strelkov, 2016;Väinölä & Strelkov, 2011). It is known that M. edulis and M. trossulus adults and larvae differ in their tolerance to thermal effects (Koehn, 1991;Rayssac, Pernet, Lacasse & Tremblay, 2010). Unlike M. trossulus mussels, M. edulis are less tolerant to low-temperature effects (Koehn, 1991;Rayssac et al., 2010). ...
... It is known that M. edulis and M. trossulus adults and larvae differ in their tolerance to thermal effects (Koehn, 1991;Rayssac, Pernet, Lacasse & Tremblay, 2010). Unlike M. trossulus mussels, M. edulis are less tolerant to low-temperature effects (Koehn, 1991;Rayssac et al., 2010). It is assumed that differences in thermal tolerance determine the biogeographical distribution of these mussels (Koehn, 1991;Rayssac et al., 2010). ...
... Unlike M. trossulus mussels, M. edulis are less tolerant to low-temperature effects (Koehn, 1991;Rayssac et al., 2010). It is assumed that differences in thermal tolerance determine the biogeographical distribution of these mussels (Koehn, 1991;Rayssac et al., 2010). Similarly, M. trossulus is not found to occur in all mussel beds in Kandalaksha Bay (Katolikova et al., 2016;Väinölä & Strelkov, 2011). ...
The lipid composition of blue mussels Mytilus edulis L. living under different environmental conditions (in the intertidal zone and in aquaculture) was studied to detect origin-related differences in seasonal modifications of lipids, and their fatty acid composition in gills and digestive glands. In early May, the gills and digestive glands of intertidal mussels contained higher amounts of total lipids, chiefly phospholipids and sterols, which appear to perform a protective function as maintenance of membrane integrity. Seasonal modifications in lipid composition of both intertidal and aquaculture mussels were related to environmental factors (mainly low temperature), reproductive processes and food availability. We show that seasonal changes in membrane lipid composition of both intertidal and aquaculture mussels reflect the process of membrane lipid remodelling (namely changes in phosphatidylethanolamine proportion and in the fatty acid composition of phospholipids) required for homeoviscous adaptation in low-temperature conditions. In particular, the unsaturation index and chain fluidity index of phospholipids increased in gills and digestive glands of mussels collected in early May and in November. Similar seasonal changes in the triacylglycerol levels and its fatty acid composition were observed in gills and digestive glands of both intertidal and aquaculture mussels collected in late May and August.
... Cette hypothèse a été le plus souvent appliquée pour expliquer la relation entre l'ichtyofaune et le zooplancton (Fortier & Gagne 1990, Gotceitas et al. 1996, Johnson 2000, Beaugrand et al. 2003, mais elle fut aussi validée chez les invertébrés marins (Bos et al. 2006a, Ouellet et al. 2007 Parmi les facteurs abiotiques, l'hydrodynamisme est un facteur primordial pour la dynamique des populations des animaux marins benthiques car il influence l'advection des larves (Incze et al. 2000), le contact avec le substrat dans la couche limite benthique (Eckman 1983, Butman 1987 -Brenko & Calabrese 1969, Lough 1974, Incze et al. 1980, Pechenik 1990) et le comportement larvaire (Bayne 1965, Beaumont & Budd 1982. La gamme de tolérance thermo-haline est variable d'une espèce à l'autre et ces facteurs environnementaux sont déterminants pour le métabolisme des organismes (Rico-Villa et al. 2009, Ben Kheder et al. 2010a, Rayssac et al. 2010. Finalement, les concentrations en oxygène et en polluants sont également susceptibles d'affecter le recrutement en agissant sur le métabolisme, la croissance et la métamorphose (Widdows 1991, Alfaro 2005 Enfin, la disponibilité de la ressource trophique semble pouvoir influencer le succès de recrutement chez certains groupes taxonomiques à phase larvaire planctotrophique (Olson & Olson 1989). ...
... Behavior is influenced by larval physiological condition (quality), which depends on the energy acquired from food (Tremblay et al. 2007) to meet metabolic needs that are influenced by temperature (Rayssac et al. 2010). The energetic costs of the metamorphosis are provided by biochemical reserves accumulated during the larval phase (Videla et al. 1998). ...
... search for another suitable substrate for the adult life according to the primary-secondary settlement theory (Bayne 1964a, Erlandsson et al. 2008 inter-and intra-specific relations (Petersen 1984, Porri et al. 2008a), and physiological conditions (Tremblay et al. 2007, Rayssac et al. 2010. ...
The rate of settlement-metamorphosis is one of the determinant factors for the
recruitment success, and thus the populations’ renewal , in benthic marine invertebrates
with bentho-pelagic life-cycle. Related to the abundance and behavior of perimetamorphic
stages (competent larvae and post-larvae), the settlement rate is regulated
by the interaction of multiple endo- and exogenous factors. Pre-required for the vital
functioning of heterotrophic organisms, the trophic resource is an important exogenous
biotic factor as it affects their physiological conditions. Its influence on recruitment is
often considered in a quantitative point of view whereas laboratory researches certify
the importance of its lipid quality. In such context, the main objective of the present
study is to evaluate the influence of the trophic resource quality on the recruitment
success, using the blue mussel (Mytilus edulis, L 1758) as biological model.
The research concentrated on the potential food resources available for the perimetamorphic
stages, such as the plankton and the biofilm. A particular emphasis is
given to polyunsaturated (PUFA) and essential fatty acids (EFA), which are largely
recognized to be indispensable for aquatic organisms. Moreover, studies dealing wit h
recruitment show a bentho-pelagic decoupling between larvae and recruits, an
important spatio-temporal variability of the settlement, and settlement peak
synchronization. Even if larval availability and behavior are often incriminated factors,
origins of such phenomenon still remain uncertain. Thus, the present study proposes to
provide additional response elements by producing a fine analysis of the spatiotemporal
variability during the larval ontogeny.
Three principal research axes constitute the project where we define the settlement as
the process by which individuals associate to the substrate, and the recruitment as the
number of individuals present at a time t of the benthic life:
i) Considering the Cushing « match/mismatch » theory, we hypothesize that EFA
concentration in the food influence the success of both settlement and recruitment. We
simultaneously monitored the larval development and the trophic conditions during
two successive reproductive seasons (2007 and 2008);
ii) Considering biofilm as potential trophic resource, we hypothesize that the
settlement rate increases with the biofilm age and its EFA content. We conditioned
and performed a fine characterization of biofilms in order to test their influence on
mussels’ settlement success ;
iii) Considering the important role of behavior and physiological conditions in peri -
metamorphic stages, we hypothesized an important microscale spatial variability, a
bentho-pelagic decoupling, and a physiological advantage during the settlement peak. We monitored the larval development in several sites, and also the lipid
quality of post-larvae and of their trophic resources.
Our results highlight the predominant control of phytoplanktonic communities on the
blue mussel recruitment success via two innovative processes: i) the match/mismatch
with the planktonic lipid quality, and ii) the trophic settlement trigger (TST).
Nutritional role of PUFA/EFA seems to be important for the recruitment of the year,
but their concentration in benthic and pelagic compartments seems not to insofar as
affect behavior and physiology of young mussels during the season. The latest seems
to strongly respond to variations in autotrophic picoplankton (picoeukaryotes, < 2 μm)
abundance within both compartments. Finally, our results show a bentho-pelagic coupling
between larvae and recruits, and suggest for the first time that decoupling depends on the
two typical behavioral traits of bivalves: the metamorphosis delay and the bysso-pelagic
drifting.
This research provides new lines of thinking about the benthic invertebrates ecology and
highlights the need to consider planktonic compartment, and behavior during the larval and
post-larval ontogeny when working on the population dynamics in the field. A special
emphasis should be given to the trophic resources lipid quality and taxonomical
composition, and the separation of the different developmental stages appears necessary to
understand populations dynamic. The notion of TST constitute the major point of the study
as it would rely on a cue independent from the prospected habitat that would synchronize
the settlement behavior, whatever substratum quality and/or individual historic life.
... Cette hypothèse a été le plus souvent appliquée pour expliquer la relation entre l'ichtyofaune et le zooplancton (Fortier & Gagne 1990, Gotceitas et al. 1996, Johnson 2000, Beaugrand et al. 2003, mais elle fut aussi validée chez les invertébrés marins (Bos et al. 2006a, Ouellet et al. 2007 Parmi les facteurs abiotiques, l'hydrodynamisme est un facteur primordial pour la dynamique des populations des animaux marins benthiques car il influence l'advection des larves (Incze et al. 2000), le contact avec le substrat dans la couche limite benthique (Eckman 1983, Butman 1987 -Brenko & Calabrese 1969, Lough 1974, Incze et al. 1980, Pechenik 1990) et le comportement larvaire (Bayne 1965, Beaumont & Budd 1982. La gamme de tolérance thermo-haline est variable d'une espèce à l'autre et ces facteurs environnementaux sont déterminants pour le métabolisme des organismes (Rico-Villa et al. 2009, Ben Kheder et al. 2010a, Rayssac et al. 2010. Finalement, les concentrations en oxygène et en polluants sont également susceptibles d'affecter le recrutement en agissant sur le métabolisme, la croissance et la métamorphose (Widdows 1991, Alfaro 2005 Enfin, la disponibilité de la ressource trophique semble pouvoir influencer le succès de recrutement chez certains groupes taxonomiques à phase larvaire planctotrophique (Olson & Olson 1989). ...
... Behavior is influenced by larval physiological condition (quality), which depends on the energy acquired from food (Tremblay et al. 2007) to meet metabolic needs that are influenced by temperature (Rayssac et al. 2010). The energetic costs of the metamorphosis are provided by biochemical reserves accumulated during the larval phase (Videla et al. 1998). ...
... search for another suitable substrate for the adult life according to the primary-secondary settlement theory (Bayne 1964a, Erlandsson et al. 2008 inter-and intra-specific relations (Petersen 1984, Porri et al. 2008a), and physiological conditions (Tremblay et al. 2007, Rayssac et al. 2010. ...
thèse sur articles déposée en Février 2012 Langue: Français/Anglais
... We examined the PII region of the larval shell to determine the size of individual settlers at the time of settlement and metamorphosis. Since larval shell length changes linearly with time (Sprung 1984;Pechenik et al. 1990;Galley et al. 2010;Rayssac et al. 2010), we could thus estimate a range of the period of PLD based on the maximum and minimum planktonic growth rates observed in laboratory experiments at similar water temperatures (Bayne et al. 1975;Beaumont & Budd 1982;Sprung 1984;Pechenik et al. 1990;Beaumont et al. 2004;Hayhurst & Rawson 2009;Rayssac et al. 2010). Sixteen individuals (when available) less than 475 µm in total length were randomly chosen from each of 4 collectors used for the weekly samples in experiment 2 (the size criterion was applied to avoid including secondary settlers; see above). ...
... We examined the PII region of the larval shell to determine the size of individual settlers at the time of settlement and metamorphosis. Since larval shell length changes linearly with time (Sprung 1984;Pechenik et al. 1990;Galley et al. 2010;Rayssac et al. 2010), we could thus estimate a range of the period of PLD based on the maximum and minimum planktonic growth rates observed in laboratory experiments at similar water temperatures (Bayne et al. 1975;Beaumont & Budd 1982;Sprung 1984;Pechenik et al. 1990;Beaumont et al. 2004;Hayhurst & Rawson 2009;Rayssac et al. 2010). Sixteen individuals (when available) less than 475 µm in total length were randomly chosen from each of 4 collectors used for the weekly samples in experiment 2 (the size criterion was applied to avoid including secondary settlers; see above). ...
... For primary settlers collected weekly at Pointe-Mitis in 2008, mean (±SD) PII size ranged from 284 ± 16 µm (4 August, n = 51) to 319 ± 28 µm (25 August, n = 71), with individual values varying from 242 to 384 µm (Fig. 7). Using values of planktonic larval growth rates ranging from 3 to 8 µm day -1 (= water temperature from 6 to 15°C; see above) and an initial prodissoconch I shell ('D-shell') length of 110 µm after 3 days of post-fertilization development (Bayne et al. 1975;Sprung 1984;Pechenik et al. 1990;Beaumont et al. 2004;Hayhurst & Rawson 2009;Rayssac et al. 2010), we estimated PLD to be 38 days on average with a growth rate of 5.5 µm day -1 (range: 27 to 67 days for growth rates of 8 and 3 µm day -1 , respectively, for a 302 µm settler, the overall average size in 2008). In 2008, for the first 6 weeks, mean PII length did not vary significantly (p > 0.05, group d, Tukey's test), but by late August (25 August and 1 September) PII size was significantly larger than previously observed (p < 0.001, ANOVA; group a, Tukey's test). ...
Connectivity of marine populations represents a key element of metapopulation demography, as it links local populations. For marine invertebrates with a bentho-pelagic life cycle, connectivity occurs during the dispersive larval stage, which is primarily driven by marine currents. The main objective of this study was to show the variability of connectivity within marine metapopulations, especially for Mytilus spp. populations in the St. Lawrence maritime estuary. The secondary objective was to further analyse the spatiotemporal variations of settlement and recruitment in this system, since these processes are essential for connectivity. (1) Different methods to assess the variability of connectivity are described, as well as their applicability to different systems. Following a description of the main factors influencing connectivity, the drivers of variability and their implications for marine metapopulations and biodiversity management are discussed. (2) In addition, field studies were conducted and revealed seasonal and inter-annual variability of Mytilus spp. settlement in the boreal St. Lawrence marine ecosystem. These observations showed that settlement, following the initial larval dispersal phase (i.e. large spatial scale), occurred during one or two short periods of time (1 to 2 weeks) during the reproductive season. Moreover, there was also evidence for a secondary post-metamorphic settlement phase (juneniles) that extended over the entire reproductive season and represented a major part of the total settlement, particularly during weeks following primary larval settlement events and storms. (3) Finally, a geostatistic method, based on the relationship between adult biomass and recruitment in different local populations, identified homogeneous demographic coupling at scales from 12-24 km over a five year study, in the direction of the main current. Overall, this study empirically confirms the importance of variations in adult biomass, settlement, and recruitment in determining the variability of connectivity in marine metapopulations and supports theoretical studies considering such fluctuations.
... data), and individuals cannot be readily distinguished morphologically. We thus considered this complex as a whole because environmental conditions are comparable among sites (Ouellet et al. 2011), and similar larval growth rates have been observed within this complex for temperatures typical of this region (Rayssac et al. 2010). The Gaspé Current, the dominant current in this area, runs downstream (west to east) along the shore towards the Gulf of St. Lawrence (Sheng 2001). ...
... We examined the PII region of the larval shell to determine the size of individual settlers at the time of settlement and metamorphosis. Since larval shell length changes linearly with time (Sprung 1984, Pechenik et al. 1990, Galley et al. 2010, Rayssac et al. 2010), we could thus estimate a range of the period of PLD based on the maximum and minimum planktonic growth rates observed in laboratory experiments at similar water temperatures (Bayne et al. 1975, Beaumont & Budd 1982, Sprung 1984, Pe chenik et al. 1990, Beaumont et al. 2004, Hayhurst & Rawson 2009, Rayssac et al. 2010. Sixteen individuals (when available) < 475 µm in total length were randomly chosen from each of 4 collectors used for the weekly samples in Expt 2 (the size criterion was applied to avoid including secondary settlers; see above). ...
... We examined the PII region of the larval shell to determine the size of individual settlers at the time of settlement and metamorphosis. Since larval shell length changes linearly with time (Sprung 1984, Pechenik et al. 1990, Galley et al. 2010, Rayssac et al. 2010), we could thus estimate a range of the period of PLD based on the maximum and minimum planktonic growth rates observed in laboratory experiments at similar water temperatures (Bayne et al. 1975, Beaumont & Budd 1982, Sprung 1984, Pe chenik et al. 1990, Beaumont et al. 2004, Hayhurst & Rawson 2009, Rayssac et al. 2010. Sixteen individuals (when available) < 475 µm in total length were randomly chosen from each of 4 collectors used for the weekly samples in Expt 2 (the size criterion was applied to avoid including secondary settlers; see above). ...
Recruitment has often been cited as a key factor regulating population abundance and community structure in benthic marine ecosystems, where the life cycle of many species includes a dispersive planktonic phase. Still, the patterns and causes of temporal heterogeneity in the recruitment process, from daily to annual scales, are poorly understood for most taxa. We conducted weekly (2008) and biweekly (i.e. every 2 wk; 2008-2009) assessments of settlement of the marine mussels Mytilus spp. in the St. Lawrence maritime estuary, and differentiated between primary (metamorphosis) and secondary (post-metamorphosis movements) settlers. At a biweekly temporal resolution, recruitment in 2008 occurred over a 2 mo period with a single peak in August. A more complex pattern of recruitment involving multiple peaks of primary and secondary settlement was, however, revealed at a weekly resolution. In 2009 the biweekly settlement rates were an order of magnitude lower, with again only a single peak. In both years, secondary settlement was observed throughout most of the season and contributed as much or more (50-81%) than primary settlement for several peaks. Based on prodissoconch II size and estimated larval growth rates, the mean planktonic larval duration was estimated to be 38 d, but may have ranged from 27 to 67 d depending on the actual growth rate. The importance of secondary settlement increased over time and was a major contributor to local recruitment dynamics. Variation in primary and secondary settlement as well as inter-annual variations could strongly affect estimates of recruitment rates, local dynamics and the spatial scales of connectivity among coastal populations, and thus our understanding of local population regulation and metapopulation dynamics.
... One question is how the dynamics of species composition differ between different rocky shores. Different rocky shores should have experienced different abiotic and biotic environmental factors (Raffaelli and Hawkins 1996). Especially, rocky shores affected by different sea currents should have experienced considerably different environmental changes, considering the reports that different sea currents have been exposed to different patterns of climate change (Levitus et al. 2000;IPCC 2007). ...
... Therefore, the positions of quadrats may have shown a marked random shift on many shores. This shift should have caused inaccurate estimate of density for each mollusk species, because densities of benthic animals often change at the scales exceeding several centimeters (Underwood 1979;Raffaelli and Hawkins 1996). The error, in turn, may have resulted in apparent increases in the southern species dominance and latitude of species range. ...
... The warming of the Kuroshio area would favor the southern species, as species geographically distributed at lower latitudes tend to be adapted to higher temperatures (Lomolino et al. 2005). Higher temperatures can improve probability of recruitment, reproductive output, and survival and growth rates in the southern species, as is suggested for intertidal and shallow-water mollusks (Zacherl Gilman et al. 2006;Moore et al. 2007;Hilbish et al. 2010;Rayssac et al. 2010). It should be noted, however, that the influences of increased temperatures would be altered by synergetic effects with other factors (Harley et al. 2006;Parmesan 2006). ...
Increases of low-latitude species in various sea areas and poleward shifts of ranges of many species have been reported and
linked to warming environments. To examine the generality of these trends for mollusks, we conducted 7 quadrat surveys during
1978–2006 on Pacific rocky shores in Japan (26.6–45.0°N). Results showed that the dominance of southern species increased
on 11 of the 15 shores in a southern, warming sea area but on only 1 of the 6 shores in a northern area with no warming trend.
The latitudes of species ranges increased on average but showed large interspecific variations which showed a weak, positive
correlation with interspecific taxonomic distance. The differences of these results from the previously reported trends are
discussed in relation to the unique current patterns in our study area and the phylogenetic constraints of species-specific
responses to a warming environment.
... There are interactions between organisms of different species where predation and parasitism can kill the organism or affect its growth. There are responses to external factors such as temperature [15,16] and salinity [17,18], which change the rate of growth of an organism as well as many others. This paper uses fundamental mathematical principles to account for these factors and creates a biologically informed model of growth rather than the approach of fitting expected growth to statistical representations of marine growths [9,19]. ...
... where Φ(t, z) is the growth factor, T(t, z) is the temperature at a given depth and time, T H is the upper temperature tolerance of the mussels, and T L is the lower temperature tolerance of the mussels. The temperature growth curve created from Equation (3) and shown in Figure 1a has an optimal temperature T 0 for growth at 17 • C [15,16]. Above and below this temperature, growth is slower. ...
There are several factors to account for marine growth including but not limited to temperature, salinity, chlorophyll-a content, existing species in the environment and predating. This paper proposes a model of biological growth for hard species on marine structures, which can be compatible with site-specific and realistic ecology while also being able to translate the results for analyses linked to lifetime hydrodynamic or structural effects via commercial software or computing. The model preserves fundamentals of ecological aspects rather than using heuristics or random sampling to data fitting on sparsely collected information. The coefficients used in the proposed model align to the real world, with location-specific values, and can be adapted to new information. The growth model is demonstrated for Mythulis Edulis (blue mussel) colonisation to assess the lifetime hydrodynamic effects for the West Coast of Ireland and the Gulf of Guinea. The model can be extended to any hard growth approach.
... The hybrid zones between them are usually considered as stable, with hybrids being less fit than purebreds (Väinölä and Strelkov, 2011;Katolikova et al., 2016;Wenne et al., 2020). MT is less thermophilic: it does not spread as far south as ME in the Atlantic (Wenne et al., 2020 and references therein) and shows a poorer physiological performance at elevated temperatures (Rayssac et al., 2010;Fly and Hilbish, 2012;Bakhmet et al., 2022). ME and MT appear to play similar ecological roles in their native oceans, and their differences can only be assessed in sympatry (Riginos and Cunningham, 2004). ...
... Again, the only factor which seems to be correlated with this change is the mean annual temperature, which increased during the study period. Indeed, MT is a more stenothermal species than ME (Rayssac et al., 2010;Fly and Hilbish, 2012). In field experiments in the White Sea, adult MT have shown an increased heart rate and hence a poorer physiological performance than ME at water temperatures above 16°C (Bakhmet et al., 2022). ...
Subarctic populations of “cryptic” blue mussel species Mytilus edulis (ME) and M. trossulus (MT) are less studied than Arctic and boreal populations. Ecological features of ME and MT in sympatry are poorly known everywhere. We studied the habitat segregation of ME and MT and the interannual dynamics of their mixed settlements at the Murman coast of the Barents Sea, the northeastern boundary of the Atlantic littoral mussel communities. Previous data on mussels from this area are 50-100 years old. The 3-km-long Tyuva Inlet (Kola Bay) was used as the study site. Mussels were found in the littoral and the sublittoral down to a depth of 4 m. Their characteristic habitats were sandbanks, littoral rocks, sublittoral kelp forests and “the habitat of the mussel bed” in the freshened top of the inlet. The main spatial gradients explaining the variability of demographics of the settlements (abundance, age structure, size) were associated with the depth and the distance from the inlet top. ME and MT were partially segregated by depth: ME dominated in the sublittoral and MT, in the littoral. In addition, ME dominated throughout the mussel bed. The ratio of species in the mixed settlements varied over time: between 2004 and 2010 the proportions of MT decreased everywhere, by 22% on average. The habitat distribution of mussels apparently changed with time: we found that mussels were abundant in kelp forests, where they had rarely been observed in the 20th century. We suggest that the spatial and temporal dynamics of subarctic mussels can be partly explained by the competition between ME and MT and their differing sensitivity to environmental factors.
... In our case we dealt with local adaptation to the unique characteristics (winter temperature as low as − 1.5 о С and 25 PSU salinity). Another problem is that the comparative analyses of the responses of the native and the invasive species are often based on short-term observations lasting not more than a month (Gardner and Thompson, 2001;Rayssac et al., 2010;Thyrring et al., 2017). ...
... A reduced ability of M. trossulus to temperature acclimation agrees with the experimental results showing that the spat of M. trossulus has a higher mortality at 20 • C compared to the spat of M. edulis (Hayhurst and Rawson, 2009). In addition, larval thermal preferences determined in another study were 10-17 о С for M. trossulus and 17-24 о С for M. edulis (Rayssac et al., 2010). To note, 50% mortality of M. edulis and M. trossulus occurred at 25.1 and 23.7 • C, respectively (Fly and Hilbish, 2013). ...
In this study we compared some aspects of the physiology of the invasive blue mussel species Mytilus trossulus and the native Mytilus edulis in the White Sea. We registered the heart activity of M. edulis, M. trossulus and the hybrids in situ for two years and tested their thermal tolerance in a laboratory experiment. In situ monitoring showed that the heart rate, as well as its variability, was greater in the invasive species and the hybrids than in the native mussel species. At the same time, the native species showed a higher thermal tolerance in the laboratory experiment. Our results suggest that, when it comes to adaptation to increased temperature, M. edulis has a greater physiological potential than M. trossulus. In a warming climate, the invasive species may lose in competition with the native one due to a higher level of metabolism.
... For all species, the renewal of populations is strongly linked to the success of recruitment, which will itself rely on several pre-and post-settlement processes (Pineda 2000). The importance of recruit-ment on population structure of benthic invertebrates is strongly related to higher susceptibility of larvae and newly settled juveniles to stressful conditions and predation (Hunt & Mullineaux 2002, Qiu et al. 2002, Rayssac et al. 2010, Jenewein & Gosselin 2013. Recruitment can be influenced by several biotic factors, such as food availability and biological interactions such as predation, but also on abiotic factors related, for example, to hydrodynamics or substrate characteristics (Hunt & Scheibling 1997, Olivier & Retière 1998, Pineda et al. 2009). ...
... The physiological state of bivalve larvae and post-larvae is essentially controlled by the abiotic and biotic conditions to which they are exposed (Pechenik 1990, Pernet et al. 2007a. Their lipid composition is therefore mainly in fluenced by their diet (Nevejan et al. 2003, Pernet et al. 2005, Gagné et al. 2010) but also by temperature (Pernet et al. 2007b, Rayssac et al. 2010, Barret et al. 2017. The influence of temperature on the accumulation of TAG varies according to species and their thermal preferences. ...
Secondary dispersal (= migration) of bivalves occurs after metamorphosis and is a key recruitment process that can radically change patterns of primary settlement. An example of secondary dispersal is active migration behavior of bivalve recruits such as in bysso-pelagic drift. We hypothesize that these active migrations represent an energy cost for recruits and that the ability to actively migrate will depend upon the recruit’s physiological profile (quantity and quality of energy reserves). In lab experiments, we hatched 4 batches of recruits of Venus verrucosa with different physiological profiles by varying rearing temperature and diet composition. We then introduced these recruits into a fall velocity tube (5 m height) to estimate their vertical fall velocity as a proxy of their dispersal potential: slower fall velocity implies enhanced dispersal potential. We also compared alive vs. passive (dead) recruits to assess behavioral differences. Fall velocity increased logarithmically with recruit volume for each treatment, and no differences between active and passive individuals were observed for batches reared at 20°C with a mixture of Tisochrysis lutea and Chaetoceros gracilis . By contrast, active recruits in 2 other treatments ( T. lutea at 20°C and a mix of C. gracilis and T. lutea at 15°C) significantly decreased their fall velocity regardless of their volume. Moreover, the ability of recruits to control their fall velocity by their behavior was correlated with triglyceride content. Recruits with the highest energy reserves had the greatest capacity to decrease their fall velocity, which suggests a major role of physiological conditions on potential secondary dispersal. We also used a benthic flume to test the substrate selection ability of recruits depending on their physiological profile and found no differences between physiologically different batches. However, V. verrucosa recruits preferred fine sediments, unlike adults, which live mainly in coarse sediment habitats; such difference in substrate preference suggests potential secondary migrations between nursery and adult areas.
... Temperature exerts a strong selective pressure upon marine populations distributed over various spatial scales, from small cm-scales to broad latitudinal scales (e.g. Bertness and Gaines, 1993;Rayssac et al., 2010;Peck, 2011). Marine invertebrates inhabiting tropical shores are exposed to both extremely hot and highly thermally variable conditions, and most are already living close to their thermal tolerance limit (Helmuth and Hofmann, 2001;Nguyen et al., 2011;Kasten and Flores, 2013). ...
... The ability to tolerate the harsh thermal conditions that prevail in the intertidal depends on the tolerance of early settlement stages, which are thought to be the most sensitive to temperature (Foster, 1969;Gosselin and Qian, 1997;Hunt and Scheibling, 1997;Pineda et al., 2009;Collin and Chan, 2016). Early tolerance depends on both genetic factors and past embryonic and larval experiences (Emlet and Sadro, 2006;Rayssac et al., 2010;Freuchet et al., 2015). Growing evidence suggests that variability in the physiological condition of settling larvae can give rise to cohort-specific differences in the fitness of juveniles and adults (Jarrett and Pechenik, 1997;Olivier et al., 2000;Emlet and Sadro, 2006;Tremblay et al., 2007;Thiyagarajan, 2010). ...
Marine invertebrates inhabiting low-latitude shores are exposed to both extremely hot and highly variable conditions. Further changes in habitat temperature may pose a risk to these populations. In this study, we examined the early life stage response of foundation species from subtropical and tropical latitudes to changes in the thermal habitat. We manipulated the color of settling surfaces for barnacle species that occupy the same ecological niche, Chthamalus bisinuatus (southeastern coast of Brazil), and Chthamalus proteus (northwestern coast of Panama). Using an in situ experimental approach, we assessed: 1) the combined effects of temperature and other abiotic parameters, and 2) the significance of larval and early juvenile traits in determining post-settlement performance for the first three days of benthic life. We found that the biological outcomes differed for the two species, according to the local thermal regime experienced. C. bisinuatus juveniles responded positively to higher temperatures, through a positive interaction between larval energetic condition, post-metamorphic size and temperature on their initial growth. Conversely, C. proteus juveniles grew slower at higher temperatures, although a positive effect of size at settlement was found. Continuous air-and sea-surface temperature measurements revealed that the tropical chthamalids experienced temperatures ≈6 °C higher than their subtropical congeners, as well as harsher thermal conditions during aerial exposure. This suggests that manipulated temperatures likely exceeded the tolerance of the Caribbean population, already living on the edge of their thermal threshold. Our findings contribute to the understanding of the factors underpinning the critical post-settlement events that drive patterns of abundance and distribution of barnacles in low-latitude systems.
... For all species, the renewal of populations is strongly linked to the success of recruitment, which will itself relates on several pre-and post-settlement processes (Pineda 2000). The importance of recruitment on population structure of benthic invertebrates is strongly related to higher susceptibility of larvae and newly settled juveniles to stressful conditions and predation (Hunt and Mullineaux 2002, Qiu et al. 2002, Rayssac et al. 2010, Jenewein and Gosselin 2013. Recruitment can be influenced by several biotic factors, such as food availability, biological interactions, but also abiotic factors related for example to hydrodynamics or substratum characteristics (Hunt and Scheibling 1997, Olivier and Retière 1998, Pineda et al. 2009). ...
... The physiological state of bivalve's larvae and post-larvae relate essentially on the abiotic and biotic conditions to which they are submitted (Pechenik 1990, Pernet et al. 2007a. Their lipid compositions are therefore mainly influenced by their diet (Nevejan et al. 2003, Pernet et al. 2005, Gagné et al. 2010) but also by temperature (Pernet et al. 2007b, Rayssac et al. 2010, Barret et al. 2016. The influence of temperature on the accumulation of TAG varies according to the species probably and to their thermal preference. ...
Le recrutement est un processus clé du cycle de vie des invertébrés marins benthiques, dont les bivalves. Si la phase larvaire et l’étape de fixation/métamorphose sont largement étudiées, les processus post-fixation, dont font partie les migrations secondaires, restent relativement ignorés ou du moins sous-estimés.Ces migrations secondaires ou post-fixations résultent de processus hydrodynamiques modulés par des réponses éco-éthologiques.Le présent projet proposait d’étudier les mécanismes de migrations secondaires des recrues de bivalves en développant une approche éco-étho-physiologique afin de répondre à trois objectifs : i) Estimer le poids potentiel des migrations secondaires dans les habitats de sédiments grossiers ii) Identifier des facteurs environnementaux, et plus spécifiquement ceux de l’environnement trophique en relation avec l’hydrodynamisme, qui contrôlent ces processus iii) Évaluer les potentielles interactions entre migrations secondaires et physiologie des recrues. Dans un premier temps, nous avons développé une étude in-situ des migrations secondaires des recrues de bivalves dans un habitat de sédiments grossiers dans l’archipel de Chausey (Normandie, France) via l’utilisation de pièges à recrues. En parallèle, un suivi de nombreux paramètres environnementaux (conditions hydrologiques, hydrodynamiques et trophiques) a été mis en place. Puis, nous avons étudié en conditions expérimentales, le potentiel de dispersion post-fixation de différentes espèces de bivalves exploitées et l’influence de la physiologie (en termes de réserves énergétiques) sur les migrations secondaires. Pour ce faire, nous avons utilisé des outils innovants, tels un tube de vitesse de chute et un canal hydrodynamique tout en développant la zootechnie de l’élevage larvaire et poste-larvaire de la praire, Venus verrusosa. Nos résultats mettent en évidence l’importance des migrations secondaires des recrues de bivalves dans les habitats de sédiments grossiers avec près de 24 taxons différents de bivalves identifiés en migration. Certaines de ces migrations post-fixations correspondraient à des changements ontogéniques d’habitats, et les habitats de sédiments grossiers constitueraient une zone de nurserie pour plusieurs espèces. De plus, ce projet démontre, pour la première fois, le rôle de la physiologie et de l’environnement trophique dans le contrôle des migrations secondaires et cela à différents niveaux. Nous avons observé une synchronisation entre un événement massif de migrations secondaires actives et un changement de la composition de la communauté phytoplanctonique, plus particulièrement un bloom de nanoeucaryotes. Cette réponse des recrues de bivalves à un signal trophique pélagique («trophic migration trigger», TMT), pourrait être due au coût énergétique supplémentaire associé aux comportements actifs de migration. En effet, nous avons ensuite constaté en conditions expérimentales que la capacité des recrues à contrôler leur dispersion par leur comportement est directement corrélée avec leur profil physiologique. Les recrues avec le plus de réserves énergétiques ont une meilleure capacité d’accroître leur potentiel de dispersion par leur comportement. Aussi les recrues migreraient quand leur principale source de nourriture est disponible dans le milieu afin de mieux supporter le coût des comportements de migrations secondaires actives comme la dérive byssopélagique. De plus, le potentiel de migration post-fixation apparait comme fortement lié à la synchronicité entre la période d’arrivée de la larve sur le sédiment et le cycle de marée (morte-eau ou vive-eau), mais également aux taux de croissance post-larvaires qui dépendent eux-mêmes de l’environnement trophique. Les patrons de migrations secondaires des recrues bivalves résultent donc d'un étroit couplage physico-biologique impliquant l'hydrodynamique, mais aussi des réponses éco-éthologiques modulées par des processus physiologiques en lien avec l’environnement trophique.
... 19 releases at a 5-day interval were performed every year, while approx. 200 000 particles were inserted into the model per release and allowed to drift for 450 degree days (temperature in°C * time in days), an interval that roughly corresponds to the larval phase of Mytilus trossulus and Mytilus edulis within their natural thermal window (Rayssac et al. 2010). Particle tracking was performed assuming a mortality depending on the number of degree days (calculated as per cent mortality per degree day = 0.0011 (temperature in°C) 2 -0.0329 (temperature in°C) + 0.3204) (average mortality for M. edulis and M. trossulus derived from Fig. 1 in Rayssac et al. 2010). ...
... 200 000 particles were inserted into the model per release and allowed to drift for 450 degree days (temperature in°C * time in days), an interval that roughly corresponds to the larval phase of Mytilus trossulus and Mytilus edulis within their natural thermal window (Rayssac et al. 2010). Particle tracking was performed assuming a mortality depending on the number of degree days (calculated as per cent mortality per degree day = 0.0011 (temperature in°C) 2 -0.0329 (temperature in°C) + 0.3204) (average mortality for M. edulis and M. trossulus derived from Fig. 1 in Rayssac et al. 2010). No further assumptions with respect to mortality were made (e.g. ...
While secondary contact between Mytilus edulis and M. trossulus in North America results in mosaic hybrid zone formation, both species form a hybrid swarm in the Baltic. Despite pervasive gene flow, Baltic Mytilus species maintain substantial genetic and phenotypic differentiation. Exploring mechanisms underlying the contrasting genetic composition in Baltic Mytilus species will allow insights into processes such as speciation or adaptation to extremely low salinity. Previous studies in the Baltic indicated that only weak interspecific reproductive barriers exist and discussed the putative role of adaptation to environmental conditions. Using a combination of hydrodynamic modelling and multilocus genotyping we investigate how oceanographic conditions influence passive larval dispersal and hybrid swarm formation in the Baltic. By combining our analyses with previous knowledge we show a genetic transition of Baltic Mytilus species along longitude 12°-13°E, i.e. a virtual line between Malmö (Sweden) and Stralsund (Germany). Although larval transport only occurs over short distances (10-30 km), limited larval dispersal could not explain the position of this genetic transition zone. Instead, the genetic transition zone is located at the area of maximum salinity change (15 to 10 psu). Thus, we argue that selection results in weak reproductive barriers and local adaptation. This scenario could maintain genetic and phenotypic differences between Baltic Mytilus species despite pervasive introgressive hybridization. This article is protected by copyright. All rights reserved.
... This result may provide some indications that the high experimental water temperature of 25 • C can occur on a regular basis in most bays in the southern Gulf of St-Lawrence, and particularly in the studied sites. The thermal tolerance of mussel larvae is species-specific with M. trossulus larvae having a lower survival success at 24 • C (Rayssac et al. 2010). Low survival of M. trossulus larvae at high temperatures is reflected by the distribution of these two species, with M. trossulus having a more northerly distribution compared to the more temperate distribution of M. edulis (Gosling 1992). ...
... Low survival of M. trossulus larvae at high temperatures is reflected by the distribution of these two species, with M. trossulus having a more northerly distribution compared to the more temperate distribution of M. edulis (Gosling 1992). In contrast, the survival of juveniles at high temperatures is similar between the two species (Rayssac et al. 2010). Therefore, the absence of M. trossulus on artificial collectors at all sampling sites, except Caraquet likely reflects the effect of elevated summer seawater temperature that are not tolerated by M. trossulus larvae. ...
The bivalve’s aquaculture industry is an important component of the economy in Eastern Canada. Seed collection is an initial and critical activity in most bivalve aquaculture industries including mussel farming in Prince Edward Island, production is entirely dependent on natural spat collection. Although seed supply is not a concern from a quantitative standpoint, there are growing concerns about the quality of natural seed. The general objective of this study was to identify and assess mussel seed quality criteria on the basis of physiological and biochemical status under laboratory and field conditions. The performance, as estimated by metabolic measurements, lipid class composition, multi-locus heterozygosity (MLH) and survival to stressful environment of seed from 6 different stocks sources was first compared under laboratory conditions at 12 °C and 25 °C. Results showed that MLH varied among the six sources of mussels in a way which is consistent with the physiological and biochemical indicators of seed quality. Mussels from Shippagan (New Brunswick) and Tracadie (Prince Edward Island) were found to have the highest quality scores and the best adaptive capacity to extreme water temperature under laboratory conditions. The results of the stock-site reciprocal field studies are in general agreement with those of the laboratory experiments with higher survival of mussels from Shippagan, Tracadie and St. Peters Bays in the various study sites. Our results suggest that the measure of MLH and survival curves at stressful temperature could be a good criteria combination to identify the improved survival potential of mussels stocks.
... They are sedentary suspension feeders and are often used as sentinel organisms in monitoring studies of aquatic ecosystems (Goldberg 1986;Gosling 1992). Mussel species in the genus Mytilus vary in their resistance to various abiotic factors (Koehn 1991;Rayssac et al. 2010). The attached lifestyle of bivalves prompts them to develop a set of adaptations at different levels of biological organisation, including lipid-profile remodelling (Hochachka and Somero 2002;Munro et al. 2015). ...
Context
Owing to the multiple functions of lipids and fatty acids in organisms, lipid composition can be used as an environmental biomarker of the health status of sentinel organisms in monitoring studies of aquatic ecosystems.
Aims
To study the lipid profile of the mussel Mytilus galloprovincialis from the Black Sea and to identify lipid compounds as environmental biomarkers.
Methods
Lipid and fatty acid compositions in the gills and digestive glands of mussels were analysed by chromatography.
Key results
Membrane-state fatty acid indices in phospholipids were quite stable in all the mussels examined. The fatty acid composition of triacylglycerols is primarily an indicator of the food source for mussels. The selective retention of arachidonic acid as well as the accumulation of non-methylene-interrupted fatty acids in mussels are assumed to be biomarkers of environmental stress.
Conclusions
The presence of regulatory mechanisms ensuring the stability of the membrane structure was confirmed in all studied mussels.
Implications
The content of minor phospholipid fractions (namely, phosphatidylinositol and sphingomyelin) and the distribution of some fatty acids and their indices among lipid classes in the gills and digestive glands of M. galloprovincialis can be used in the assessment of the health status of sentinel organisms.
... Larval formation after embryonic development has a significant energetic cost in bivalves, which determines normal development of a shell and of structures to enable swimming and feeding (Rusk et al., 2017;Zardus and Martel, 2002). Lipids have been recognised as the main energy substrate to fuel this critical phase of development in mussels, scallops, oysters and clams (Bayne et al., 1975;Farias et al., 2003;Rayssac et al., 2010;Sánchez-Lazo and Martínez-Pita, 2012;Whyte et al., 1990;Whyte et al., 1991). In this study, both lipid quantification methods were successful in detecting differences in the lipid content among the larval groups analysed. ...
... All experiments were carried out at the UQAR-ISMER wet laboratory facilities (Rimouski, Qc, Canada). Mussels, Mytilus edulis, from St. Peter's Bays, Prince Edward Island (Canada) were spawned and reared according to Rayssac et al. (2010). Briefly, spawning was induced by thermal shock and the larvae were reared in three 60 L conical tanks. ...
Anthropogenic noise is a pervasive feature of the coastal ocean soundscape and is intensifying as vessel traffic activity increases. Low-frequency sounds from wave action on coastal reefs or anthropogenic noise have been shown to initiate larval settlement of marine invertebrates and accelerate metamorphosis to juvenile stages. These results suggest that some planktonic species can perceive and be impacted by anthropogenic sound. Hence, we tested the hypothesis that vessel noise has an impact on the feeding behavior of blue mussel (Mytilus edulis) veligers and of the copepod Eurytemora herdmani as well as on the growth of the rotifer Brachionus plicatilis. The results show that microalgae and feeding behavior of early life stages of mussels and copepods are not influenced by the presence of vessel noise. The growth of the rotifers was similar between the two sound treatments, but rotifers’ egg production in the absence of vessel noise was higher and eggs were also larger. Our results suggest that the effects of noise on plankton are complex; much more work is needed to unravel these often subtle effects.
... Mussels, M. edulis, from St. Peters Bay, Prince Edward Island (Canada) were transferred to ISMER-UQAR wet laboratory facilities for larval rearing as described in Rayssac et al. (2010). Spawning was induced on 30 individuals by thermal shock and gametes from different parents were used in a pool-cross design to produce one random larval family. ...
The uncontrolled colonization of benthic organisms on submerged surfaces, also called biofouling, causes severe damage in the shipping and aquaculture industries. Biofouling starts with a benthic biofilm composed of a complex assemblage of microbes, bacteria and benthic diatoms, called microfouling, on which macrofouling invertebrate species settle and grow. Invertebrate larvae may use natural soundscapes to orientate inshore and choose their optimal habitat. Recent studies have demonstrated that ship sounds enhance the larval settlement and growth of several invertebrate species, such as mussels, associated with biofouling. Among invertebrates, effects of sound generated by offshore human activities are still poorly studied. This study aims to assess the effect of pile driving, drilling and vessel sounds on model species associated with micro and macrofouling. First, the biofilm development of Navicula pelliculosa and Amphora coffeaeformis was assessed, then, the larval development of the blue mussel (Mytilus edulis) was evaluated from the D-veliger to the postlarval stage. Mussel larvae and microalgae were exposed 12 h each day in tanks (Larvosonic) adapted to sound experiments under controlled conditions. All anthropogenic sounds induced a thinner N. pelliculosa biofilm coupled with a lower microalgae concentration. The drilling sound had a stronger effect on the biofilm thickness. The drilling sound significantly reduced the pediveliger settlement and the postlarvae clearance rate by 70.4% and tended to diminish settler sizes compared to control sound. Contrary to our expectation, pile driving tended to enhance larval recruitment by 22% (P=0.077) and the boat sound did not stimulate larval settlements or recruitment. Drilling sound generated a stressful acoustic environment for pediveliger settlements and postlarvae seem to maintain their shell valves closed to preserve energy. We identify potential causes and mechanisms involved in these impacts of anthropophony on larval ecology and microfouling dynamics.
... We consider that its aggregation in the middle part of the intertidal helped not to exceed the environment temperature due to shorter exposure time, which favored not affecting its metabolic processes. In bivalves such as Mytilus edulis Linnaeus, 1758 and Mytilus trossulus A. Gould, 1850, a higher growth rate was observed in warm temperatures; however, this depended on the fact that the body temperature did not reach or exceed the ambient temperature because their growth decreased (Rayssac et al. 2010). ...
The density, dispersion, size, growth, longevity, natural mortality, and recruitment of Chama coralloides Reeve, 1846, a bivalve captured in artisanal fisheries, were studied. Sample collection was carried out in November 2016, March 2017, and February 2018 at eight sites in the rocky intertidal zone, located in the south-central region of the Mexican Transitional Pacific. Using a 1 x 1 m quadrat, 10 random quadrats were conducted at each site. Density was determined with Pennington's method of Δ distribution. The dispersion was estimated with the Morisita index and modal groups with multinomial analysis. Growth, natural mortality, and recruitment parameters were estimated with FiSAT II. Variable density between sampling dates and sites was observed, with the highest densities found at sites 1 and 4. The largest interquartile range of lengths was observed at site 6, and the smallest at site 5. Five modal groups were determined in November 2016 and March 2017, and four in February 2018. Estimated growth parameters were L∞= 74.5 mm and K= 0.63; longevity was A.95 = 4.4 and A.99= 6.9 years, growth performance index ∅′= 3.5 and natural mortality M = 1.05 yr–1. Continuous recruitment was observed with a maximum peak in summer.
... Many studies demonstrated that a thermal tolerance threshold above 20 • C was associated with stressful conditions for M. edulis larval development, recruitment, metabolism, growth, and survival (Widdows, 1973;Incze et al., 1980;Myrand et al., 2000;Rayssac et al., 2010;Hiebenthal et al., 2013;Cottrell et al., 2016;Clements et al., 2018). Hiebenthal et al. (2013) experimentally demonstrated that mortality rates in mussels cultivated at 7.5, 10, 16 and 20 • C did not significantly increase (< 5%), whereas culture at 25 • C impacted survival by 25%. ...
Bivalve aquaculture in nearshore sites has expanded worldwide. Mussel farming productivity is commonly assumed to depend on survival and growth performance, which can be highly variable among spat stocks originating from different sites, even at a microgeographical scale. Using a traditional two-year production cycle, we monitored the productivity of neighbouring blue mussel (Mytilus edulis) spat stocks that had been cultivated in such contrasted environments that are shallow lagoons and open sea sites. We demonstrated that mussels collected in the nearshore, Bassin du Havre-Aubert (BHA) lagoon, exhibited the best survival rate (≥ 90%) in both nearshore and offshore sites, while other stocks experienced mortality as high as 60% under the same conditions. At spat recovery, the BHA spat stock showed higher gene expression levels for catalase and heat shock protein 70 (HSP70), which are involved in antioxidant defenses and the cellular stress response, respectively. Offshore conditions clearly enhanced overall growth performance independently of stock origin, as shown by the higher condition indexes, higher energy lipids (triacylglycerol), and generally higher glycogen content in mussels at the end of the production cycle. These observations of improved performance at the more favourable open-water conditions, particularly during summer, confirmed the importance of site-related environmental factors for productivity. The observed survival (+ 23%) and growth (+ 27%) trends support the hypothesis that offshore cultivation represents a valuable strategy for mussel aquaculture development. Considering current social, environmental, economic, and resource constraints, offshore mussel cultivation may be a viable alternative strategy for aquaculture development.
... Each downweller had mussels from one larval tank to follow the same stock through ontogeny and was in a raceway tank of 120 L (2 m × 0.5 m × 0.12 m). The seawater was pre-filtered at 10 μm at a flow-rate of 100 L h − 1 , temperature controlled at 18 • C and post-larvae fed continuously with the same nutritional treatment added of Skeletonema costatum (1:1:1:1:1) at 10 × 10 9 cell day − 1 until they reached a length of >2-cm (1 year old) (Rayssac et al., 2010;Bassim et al., 2014). The ploidy of each group (triploid and diploid) was measured in triplicate. ...
... For example, in mesocosm experiments, warm winter temperatures increased sea star metabolic rates but sea stars did not increase their feeding rates on mussels, in part because mussel body condition declined (Melzner et al., 2020). Mussels' greater resistance to high temperatures compared with some of their intertidal algal space competitors (Weitzman et al., 2021), combined with the benefits mussels may experience from increased temperature during their larval and juvenile stages (Almada-Villela et al., 1982;Rayssac et al., 2010) could enable them to maintain dominance in the intertidal as long as temperatures remain within mussel's tolerance windows. However, mussels are also susceptible to ocean acidification. ...
Mussels occupy a key middle trophic position in nearshore food webs linking primary producers to predators. Climate‐related environmental changes may synergistically combine with changes in predator abundance to affect intertidal ecosystems. We examined the influence of two major events on mussel (Mytilus trossulus) abundance in the northern Gulf of Alaska: the recent Pacific marine heatwave (PMH, 2014–2016) and an outbreak of sea star wasting (SSW). We investigated how mussel abundance changed since the onset of SSW and whether the density of predatory sea stars or PMH‐related temperature metrics explain variation in mussel abundance. Sea stars and mussels were surveyed since 2005 approximately annually in four regions of the northern Gulf of Alaska: Katmai (KATM), Kachemak Bay (KBAY), Kenai Fjords (KEFJ) and western Prince William Sound (WPWS). Mussel percent cover in the mid‐intertidal increased 1–3 years after declines in sea stars at all regions and in the low‐intertidal at KATM, KBAY, and KEFJ, but not at WPWS. After the onset of SSW, large (≥20 mm length) mussel density and mussel bed width increased at KATM but not the other regions. Total mussel densities, including recruits, did not differ before and after the onset of SSW. The total number of sea stars significantly explained variation in mussel metrics, but the proportions of the three sea star species examined did not. We did not find strong evidence for direct effects of temperature on mussels. The effects of the PMH and the SSW outbreak appear to have combined, with increased temperatures indirectly benefiting mussels in concert with relaxed top‐down pressure from sea stars, allowing for increased mussel abundance. Changing mussel abundance may affect intertidal local productivity and the abundance or performance of other nearshore consumers of mussels.
... En utilisant l'huître creuse Crassostrea gigas comme modèle biologique, nous avons testé l'hypothèse que la variabilité de la taille des coquilles de prodissoconque II (la taille de PII se réfère à la taille à la métamorphose) dépend du fonctionnement écologique de l'écosystème. We suggest that these impacts may be accentuated in the first development stages of bivalves, as larvae and newly settled juveniles have been widely shown to be the most susceptible to stressful conditions (Jenewein & Gosselin 2013;Qiu et al. 2002;Rayssac et al. 2010). Their susceptibility can be expressed in many ways, but is usually reflected in growth and survival. ...
Les lagunes méditerranéennes hébergent de nombreux usages anthropiques dont la conchyliculture depuis le début du 20ème siècle. Importée en 1970, l’huître creuse, Crassostrea gigas, s’y est adaptée parfaitement et a permis un développement ostréicole important jusqu’en 2008, année d’apparition des surmortalités de naissain liées à l’émergence d’un variant du virus OsHv1. La raréfaction du naissain et la spéculation sur ce produit ont modifié régionalement les pratiques culturales et les modes d’approvisionnement en juvéniles, avec notamment la volonté de développer une activité locale de captage. Mais le cycle de reproduction de l’espèce et le recrutement de juvéniles étaient mal connus en milieu lagunaire. Dans ce contexte, l’objectif de cette thèse est de caractériser la variabilité de la reproduction et du recrutement de l’huître creuse en lagune méditerranéenne. La configuration lagunaire offre des atouts de productivité pour le cheptel de géniteurs et de connectivité hydrodynamique pour les larves. Cependant, il apparaît que le fonctionnement écologique du système à la base de la production primaire joue un rôle essentiel sur les apports trophiques pour le succès de la reproduction des huîtres. Ce travail s’inscrit, en outre, dans le contexte d’un écosystème en voie de restauration écologique entamant un processus d’oligotrophisation dont nous décrivons les premiers effets sur le cycle de reproduction de l’huître.
... Temperature directly affects physiological rates and thus every aspect of the biology and ecology of mussels [67,82,83]. Although [84] established that the scope for growth remains stable between 10 °C and 20 °C, other studies demonstrated that temperatures greater than a 20 °C threshold are associated with stressful conditions for recruitment, metabolism, growth, and survival of M. edulis [21,[85][86][87]. Cheney et al. [8] affirmed that the stable temperature of offshore waters results in lower stress and a faster growth. ...
Bivalve aquaculture is an important component of the economy in eastern Canada. Because of current social, environmental, economic, and resource constraints, offshore mussel cultivation seems to be a promising strategy. With the objective of optimizing farming strategies that support the sustainability and development of the mussel industry at a microgeographic scale, we evaluated, after a traditional two year production cycle, the commercial performance of spat from several mussel (Mytilus edulis) stocks originating from sites separated by less than 65 km and cultivated at two different grow-out sites (shallow lagoon and offshore waters). The spatiotemporal variation in spat performance was studied through a multiyear in situ “stock-site” spat transfer design. The spat supply originating from the Bassin du Havre-Aubert lagoon systematically exhibited a larger size at sleeving time when compared to other stocks, and a better productivity level when harvested. Nevertheless, an alternative strategy would be to collect spat from the Havre-aux-Maisons lagoon, mostly because of the important commercial volumes of spat that can be collected there. Commercial performance (net income) was three times higher in the deep offshore grow-out site than in the shallow lagoon site. This better productivity in the open sea confirms the highly valuable strategy of offshore mussel farming in this area, where it was hypothesized that the less stressful environmental conditions positively influence reproduction, survival, and growth trends.
... Furthermore, surface water temperatures in excess of 25°C are in creasingly being recorded in the Baltic (Siegel & Gerth 2019). High water temperatures cause irreversible protein denaturation, reduce byssal thread production, and decrease the survival rate of M. trossulus larvae (Hofmann & Somero 1995, Rayssac et al. 2010. The future of this key Baltic Sea habitat therefore seems uncertain (Vuorinen et al. 2015, Wester bom et al. 2019. ...
Mytilid mussels form abundant, species-rich reefs on rocky substrates, but the role of this key habitat in carbon (C) cycling remains poorly understood. We performed a seasonal study on a 5 m deep photic Mytilus trossulus reef in the Central Baltic Sea to investigate pathways and rates of organic C flow. Reef gross primary production (GPP) and respiration ( R ) were estimated seasonally using underwater O 2 eddy covariance on hourly and daily timescales. Photogrammetry and biotic sampling were used to quantify reef rugosity and mussel coverage, and to derive mussel filtration and biodeposition. Mussels were highly abundant, reaching ~50000 ind. m ⁻² , and the reef structure increased the seabed surface area by 44%. GPP hourly was up to 20 mmol O 2 m ⁻² h ⁻¹ and GPP daily was up to 107 mmol O 2 m ⁻² d ⁻¹ , comparable to a nearby seagrass canopy. Hourly eddy fluxes responded linearly to light intensity and flow velocity, with higher velocities enhancing reef O 2 uptake at night. Reef R daily exceeded GPP daily on 12 of 13 measurement days, and R annual (29 mol O 2 m ⁻² yr ⁻¹ ) was 3-fold larger than GPP annual . The reef sustained a productive community of microbes and fauna whose activities accounted for ~50% of R annual . Horizontal water advection promoted food supply to the reef and likely facilitated substantial lateral C export of mussel biodeposits. Our analyses suggest that a reduction in mussel reef extent due to ongoing environmental change will have major implications for the transport and transformation of C and nutrients within the coastal Baltic Sea.
... En utilisant l'huître creuse Crassostrea gigas comme modèle biologique, nous avons testé l'hypothèse que la variabilité de la taille des coquilles de prodissoconque II (la taille de PII se réfère à la taille à la métamorphose) dépend du fonctionnement écologique de l'écosystème. We suggest that these impacts may be accentuated in the first development stages of bivalves, as larvae and newly settled juveniles have been widely shown to be the most susceptible to stressful conditions (Jenewein & Gosselin 2013;Qiu et al. 2002;Rayssac et al. 2010). Their susceptibility can be expressed in many ways, but is usually reflected in growth and survival. ...
The Mediterranean lagoons host many anthropogenic uses including shellfish aquaculture since the beginning of the 20th century. Imported in 1970, the Pacific oyster, Crassostrea gigas, has adapted perfectly and has allowed an important development of oyster’s industry until 2008, the year of occurence of spat outbreak related to the emergence of an Ostreid Herpes-virus μvar. The scarcity of spat and the speculation on this product changed regionally cultural practices and the supply of juveniles, with in particular the wish of developing a local activity of spat collection. However the cycle of reproduction of the species and the recruitment of juveniles were poorly known in lagoon environments. In this context, the objective of this thesis is to characterize the variability of the reproduction and the recruitment of the cupped oyster in Mediterranean lagoon. The lagoon configuration offers the advantages of productivity for the broodstock and hydrodynamic connectivity for the larvae. However, it appears that the ecological functioning of the system at the base of the primary production plays an essential role on the trophic resources for the success of oyster reproduction. This work takes place in the context of the ecological restoration under oligotrophication, which first effects we describe on the oyster's reproductive cycle
... In other words, while the overall quantity of potential food sources varied consistently through time at sites separated by a few km, the lipid budget, which has been shown to be critical for a number of invertebrate larvae (e.g. Phillips, 2002;Pernet et al., 2004;Rayssac et al., 2010) is far more erratic. ...
Oligotrophic conditions may impose a nutritional challenge for the larval and early post-larval development of bivalves during the search for a suitable benthic habitat. Here we investigated what settlement cues might be important for mytilid populations in southeastern Brazil. Our results point to a trophic trigger mediating larval settlement that may include an effect of saturated fatty acids, probably linked to organic detritus and bacterial production deriving from terrestrial inputs. The prevalence of drifting in this population suggests it may be a strategy for individuals to delay final settlement until encountering favorable trophic environmental conditions.
... The temperature rise in the Danish Straits was accompanied with decreasing nutrient inputs, which had a negative synergetic effect on the biomass of phytoplankton (food for mussels) that decreased twofold (Henriksen 2009). Although both M. edulis and M. trossulus in the wider framework are boreal-arctic species, physiological experiments on North American mussels have suggested that M. trossulus is indeed more cold-adapted than M. edulis (Hayhurst and Rawson 2009;Rayssac et al. 2010;Fly and Hilbish 2013). Along the Northwest Atlantic coast the southern limit of M. trossulus is in the eastern Gulf of Maine, and it is completely substituted by M. edulis to the south of that (Hayhurst and Rawson 2009). ...
In a temporal comparison over 18 years, we documented changes in the position and structure of the North European blue mussel hybrid zone in the Öresund strait, between Mytilus edulis of the marine Kattegat and Mytilus trossulus of the brackish Baltic Sea. In 1987 the midpoint of the 140-km wide multilocus allozyme cline in shallow-water populations was estimated to be located half-way along the strait. In 2005, it was shifted 25 km towards the Baltic end of the Öresund, and was located near the fixed link (bridge) that was built across the strait meanwhile in the 1990s. The cline also appeared to have become narrower and the extent of hybridity among individuals decreased. Factors that theoretically can control the position and shape of a clinal hybrid zone involve environmental gradients between habitats that differentially favor the two hybridizing taxa, or barriers to geographical dispersal of the organism. We consider two alternative hypotheses to explain the movement of the mussel hybrid zone. (1) Environmental change related to climate warming: the more stenothermal M. trossulus was pushed out from the Öresund towards the cool Baltic by elevated temperatures. (2) Change of dispersal dynamics: the construction of the fixed link locally affected mussel dispersion which attracted the zone. We raise the question whether similar changes have taken place also in the other euryhaline taxa where genetic clines between Baltic vs. Kattegat populations occur.
Full text online: http://rdcu.be/xx8R
... Mortality in mussel larvae is inherently high and increases considerably when larvae are stressed and larval duration is increased (Bayne 1965, Young 1990, Widdows 1991. Several studies have shown that larval stages are more sensitive than juvenile or adult mussels to changing environments (Hrs-Brenko and Calabrese 1969, Qiu et al. 2002, Gazeau et al. 2010, Rayssac et al. 2010, possibly resulting from high-energy demands for growth (Sprung 1984) or increased surface-area to volume ratio (Manahan 1983). Despite the importance of larval settlement to sustaining populations and, thereby dictating the distributions of adult mussels, little research has addressed the genetic and attendant physiological capacity of larvae to tolerate various environmental stressors. ...
In this study, we compared the osmotic stress response of larval and juvenile blue mussels (Mytilus edulis) at the transcriptomic, metabolomic, and whole organism levels. Blue mussels inhabit coastal areas, where they face climate-induced reductions in nearshore salinity. Despite their ecological and economic importance, scientists do not fully understand the underlying transcriptomic and cellular mechanisms of the osmotic stress response in blue mussels or how the ability to respond to stress changes throughout development. Blue mussels spend the first weeks of life developing through several larval stages in the plankton. These early life history stages are more vulnerable to environmental stress than juvenile or adult mussels, yet these stages are grossly understudied. Thus, an increased knowledge of how mussels at all developmental stages cope with low salinity is imperative for predicting how climate change will affect the distribution of M. edulis. In a series of experiments, we evaluated adjustments of molecular, cellular, and physiological processes in larval and juvenile blue mussels during short-term, low salinity exposure to elucidate stage-specific divergence in the osmotic stress response. We found that larval mussels differ from juveniles in the composition of their metabolome and in the differential expression of genes involved in the stress response. These differences in the larval response to low salinity exposure likely play a role in the increased susceptibility of these stages to stress and suggest that larvae may need to expend more energy relative to juvenile or adult mussels to mount a response. Additionally, we evaluated the effects of larval stress on later developmental stages and found that larval stress carries through metamorphosis and yields smaller juvenile mussels, potentially affecting the subsequent growth and size distributions of adult mussels. While larval exposure to low salinity generally had negative impacts on juvenile growth, there was evidence the previous exposure to stress may condition juvenile mussels for future low salinity events, depending on the timing of exposure. More studies on larval tolerance and the impacts of larval stress on juvenile fitness will be necessary for making accurate predictions of the effects of climate change on M. edulis distribution and abundance.
... The cosmopolitan Mediterranean mussel, Mytilus galloprovincialis (L.), is a sessile broadcast spawner, so their responses to environmental fluctuations are largely unmitigated by behavior. Their geographic and upper intertidal distributions are likely constrained by physiological limits such as thermal tolerance (Gardner 1992;Anestis et al. 2007;Jansen et al. 2009;Rayssac et al. 2010). Indeed, the range of M. galloprovincialis is limited to the southern half of the Australian coastline below 32°S latitude and throughout the intertidal zone (Suchanek 1978;Dias et al. 2014). ...
Oceans are a huge sink for the increased heat associated with anthropogenic climate change, and it is vital to understand the heat tolerance of marine organisms at all life stages to accurately predict species’ responses. In broadcast spawning marine invertebrates, reproduction is a vulnerable process in which sperm and eggs are released directly into the open water. Gametes are then exposed to fluctuating environmental conditions that may impact their fertilizing capacity. Using the broadcast spawning Mediterranean mussel, Mytilus galloprovincialis, as a model species, we performed blocks of factorial mating crosses to assess the variance in fertilization rates among individuals under both ambient and elevated temperatures. Overall, we found a small, but significant decline in fertilization rates with elevated temperatures. However, there was substantial plasticity in responses, with particular mussels having increased fertilization under elevated temperatures, although the majority showed decreased fertilization rates. Our results suggest possible future reproductive costs to ocean warming in M. galloprovincialis, although it is also possible that genetic variation for thermal sensitivity may allow for adaptation to changing environmental conditions.
... In another modelling exercise in St. Peter's Bay (PEI, Guyondet et al., 2015), the predicted temperatures reached~25°C, which could cause physiological stress, affect estuarine dynamics and impact aquaculture production. In addition, the thermal and salinity tolerance range being smaller in larvae comparatively to juveniles and adults (Qiu et al., 2002;Rayssac et al., 2010), and the impact of CC for the recruitment success of both species could be different than the growth effect simulated in this study. This increased risk should be considered in any management decision regarding mussel aquaculture. ...
Coastal embayments are at risk of impacts by climate change drivers such as ocean warming, sea level rise and alteration in precipitation regimes. The response of the ecosystem to these drivers is highly dependent on their magnitude of change, but also on physical characteristics such as bay morphology and river discharge, which play key roles in water residence time and hence estuarine functioning. These considerations are especially relevant for bivalve aquaculture sites, where the cultured biomass can alter ecosystem dynamics. The combination of climate change, physical and aquaculture drivers can result in synergistic/antagonistic and nonlinear processes. A spatially explicit model was constructed to explore effects of the physical environment (bay geomorphic type, freshwater inputs), climate change drivers (sea level, temperature, precipitation) and aquaculture (bivalve species, stock) on ecosystem functioning. A factorial design led to 336 scenarios (48 hydrodynamic × 7 management). Model outcomes suggest that the physical environment controls estuarine functioning given its influence on primary productivity (bottom-up control dominated by riverine nutrients) and horizontal advection with the open ocean (dominated by bay geomorphic type). The intensity of bivalve aquaculture ultimately determines the bivalve-phytoplankton trophic interaction, which can range from a bottom-up control triggered by ammonia excretion to a top-down control via feeding. Results also suggest that temperature is the strongest climate change driver due to its influence on the metabolism of poikilothermic organisms (e.g. zooplankton and bivalves), which ultimately causes a concomitant increase of top-down pressure on phytoplankton. Given the different thermal tolerance of cultured species, temperature is also critical to sort winners from losers, benefiting Crassostrea virginica over Mytilus edulis under the specific conditions tested in this numerical exercise. In general, it is predicted that bays with large rivers and high exchange with the open ocean will be more resilient under climate change when bivalve aquaculture is present.
... The very low presence of M. trossulus and hybrids in St. Anne's could be explained by specific environmental conditions in this bay. Experimental works have demonstrated that M. trossulus larvae do not survive at high temperature comparatively to M. edulis [7,54] , and reflect the general distribution of these two species, with M. trossulus having a more northerly distribution compared to the more temperature distribution of M. edulis [55] . However, M. trossulus larvae showed higher resistance to low salinity than M. edulis [56] . ...
... As shown in the current study, delay of metamorphosis can be inferred and measured when examining time series of the PII size of young postlarval or early juvenile specimens. Rayssac et al. (2010) conducted laboratory culture of Mytilus edulis larvae kept at 17-25°C and originating from Iˆles-de-la-Madeleine, and estimated that larval growth was about 8.4 mm/day. Using this value, we can estimate, using the observed means for PII size, that each summer a significant number of veligers typically delay their metamorphosis in natural conditions for about 10-15 days (22 days if we use the smallest and the largest PII values observed: 236 mm and 422 mm). ...
Examination of the larval shell (prodissoconch) of molluscs with planktotrophic development can provide valuable information on their planktonic and early benthic life. We examined temporal variability of abundance and size among11,994 veligers of the blue mussel (Mytilus edulis) in a coastal lagoon during settling periods between 1995 and 2009. Size and dateat metamorphosis during the recruitment season were determined for 1,925 postlarvae (shell length, 255–900 mm) withprodissoconch II (PII) measurements. Emphasizing the recurrence of metamorphosis delay in the field, our study reveals a netincrease in mean size at metamorphosis through time, with means for PII size ranging from 255–288 mm early in summer (afterpeak spawning events) to 400–422 mm(PII) during late July to early September. By estimating the ‘‘true’’ settlement date using theamount of dissoconch secreted after metamorphosis, such time-series analyses appropriately recapitulated the temporal pattern of mean pediveliger (competent larvae) size in the plankton. Our results demonstrate that greater settlement success rates wererelated to small size at metamorphosis—in particular, less than 320 mm. Seasonal increase in mean PII size occurring during thelatter part of the settling period may be explained by competent veligers remaining adrift and delayed metamorphosis as a result ofthe lack of favorable encounters with a suitable substrate or the absence of specific trophic signals, or cues, required forstimulating settlement, thus forcing larvae to continue planktonic growth. The difference between the smallest and largest meansfor PII size corresponds to 122 mmof larval shell growth, or 47.8%, potentially representing a 322% difference in larval body massat settlement.
... As shown in the current study, delay of metamorphosis can be inferred and measured when examining time series of the PII size of young postlarval or early juvenile specimens. Rayssac et al. (2010) conducted laboratory culture of Mytilus edulis larvae kept at 17-25°C and originating from Iˆles-de-la-Madeleine, and estimated that larval growth was about 8.4 mm/day. Using this value, we can estimate, using the observed means for PII size, that each summer a significant number of veligers typically delay their metamorphosis in natural conditions for about 10-15 days (22 days if we use the smallest and the largest PII values observed: 236 mm and 422 mm). ...
Examination of the larval shell (prodissoconch) of molluscs with planktotrophic development can provide valuable information on their planktonic and early benthic life. We examined temporal variability of abundance and size among 11,994 veligers of the blue mussel ( Mytilus edulis ) in a coastal lagoon during settling periods between 1995 and 2009. Size and date at metamorphosis during the recruitment season were determined for 1,925 postlarvae (shell length, 255-900 µm) with prodissoconch II (PII) measurements. Emphasizing the recurrence of metamorphosis delay in the field, our study reveals a net increase in mean size at metamorphosis through time, with means for PII size ranging from 255-288 µm early in summer (after peak spawning events) to 400-422 µm (PII) during late July to early September. By estimating the "true" settlement date using the amount of dissoconch secreted after metamorphosis, such time-series analyses appropriately recapitulated the temporal pattern of mean pediveliger (competent larvae) size in the plankton. Our results demonstrate that greater settlement success rates were related to small size at metamorphosis?in particular, less than 320 µm. Seasonal increase in mean PII size occurring during the latter part of the settling period may be explained by competent veligers remaining adrift and delayed metamorphosis as a result of the lack of favorable encounters with a suitable substrate or the absence of specific trophic signals, or cues, required for stimulating settlement, thus forcing larvae to continue planktonic growth. The difference between the smallest and largest means for PII size corresponds to 122 µm of larval shell growth, or 47.8%, potentially representing a 322% difference in larval body mass at settlement.
... Most benthic marine invertebrates have planktonic larvae (Thorson 1950), and successful delivery and settlement of larvae often drive population dynamics (Caputi and Brown 1986;Hughes et al. 2000;Roughgarden et al. 1988;Steneck and Wilson 2001;Underwood and Fairweather 1989). Temperature sensitivity is thought to be a major driver of biogeography in ectothermic marine organisms (Pörtner 2001), and the thermal sensitivity of larvae in particular may define the range of some species, such as fiddler crabs (Uca pugnax) (Sanford et al. 2006) and mussels (Mytilus spp.) (Rayssac et al. 2010). Larvae settling in water temperatures near their physiological thermal limits are essentially exposed to a reduced habitat quality, which may lead to slower development, smaller size, and higher mortality (Anger 2001) and thus decrease recruitment to adult populations. ...
We examined the potential for bottom temperatures ≤12 °C to inhibit successful recruitment of planktonic lobster postlarvae to the benthos. In laboratory trials, postlarvae held at 11 °C exhibited higher mortality, slower development, and reduced size increase at molt relative to postlarvae held at 13 °C. We sampled at field sites within Machias Bay, Maine (mean bottom temperature 12.39 °C, 46.1 degree-days ≥12 °C) and at the mouth of the bay (mean bottom temperature 11.57 °C, 5.1 degree-days ≥12 °C), where temperature was influenced by the cold Eastern Maine Coastal Current (EMCC). We found significantly higher settlement at the warm inshore site but, the abundance of competent planktonic postlarvae was not significantly different between sites, indicating a disconnect between postlarval abundance and settlement. Regional sampling of newly settled lobsters revealed a pattern of higher settlement at inshore sites extending across a broader coastal region impacted by the EMCC. Our results suggest that small differences in water temperature may shape settlement patterns through either behavioral avoidance of colder settlement sites or elevated postsettlement mortality of postlarvae settling at colder sites.
Ocean acidification (OA) caused by increased atmospheric carbon dioxide is affecting marine systems a globally and is more extreme in coastal waters. A wealth of research to determine how species will be affected by OA, now and in the future, is emerging. Most studies are discrete and generally do not include the full life cycle of animals. Studies that include the potential for adaptation responses of animals from areas with different environmental conditions and the most vulnerable life stages are needed. Therefore, we conducted experiments with the widely-distributed blue mussel, Mytilus edulis, from populations regularly exposed to different OA conditions. Mussels experienced experimental conditions prior to spawning, through embryonic and larval development, a highly vulnerable stage. Survivorship to metamorphosis of larvae from all populations was negatively affected by extreme OA conditions (pH 7.3, Ωar, 0.39, pCO2 2479.74), but, surprisingly, responses to Mid OA (pH 7.6, Ωar 0.77, pCO21167.13) and Low OA (pH 7.9, Ωar 1.53, pCO2 514.50) varied among populations. Two populations were robust and showed no effect of OA on survivorship in this range. One population displayed the expected negative effect on survivorship with increased OA. Unexpectedly survivorship in the fourth population was highest under Mid OA conditions. There were also significant differences in development time among populations that were unaffected by OA. These results suggest that adaptation to OA may already be present in some populations and emphasizes the importance of testing animals from different populations to see the potential for adaptation to OA.
Subarctic populations of blue mussels represented by 'cryptic' species Mytilus edulis (ME) and M. trossulus (MT) have been studied less intensively than Arctic and boreal populations. Ecological features of ME and MT in sympatry are poorly known everywhere. The knowledge about mussels at the northeasternmost boundary of the Atlantic littoral communities on Murman coast of the Barents Sea is based on data obtained 50-100 years ago. Our study provides the first insight into the long-term dynamics of the Barents Sea mussels, the habitat segregation of ME and MT, and the interannual dynamics of their mixed settlements. The Tyuva Inlet (Kola Bay), which is 3 km long, was used as the study site. Mussels were found everywhere in the littoral and the sublittoral down to a depth of 4 m. Their characteristic habitats were sandbanks, littoral rocks, sublittoral kelp forests and 'the habitat of the mussel bed' in the freshened top of the inlet. The main spatial gradients explaining the variability of demographics of the settlements (abundance, age structure, size) were associated with the depth and the distance from the inlet top. ME and MT were partially segregated by depth: ME dominated in the sublittoral and MT, in the littoral. In addition, ME dominated both in the littoral and in the sublittoral parts of the mussel bed. The ratio of species in the mixed settlements varied over time: between 2004 and 2010 the proportions of MT decreased everywhere, by 22 % on average. Historical data indicate that the abundance of the Murman mussels declined sharply between the 1960s and the 1970s, which coincided with the cooling of the Arctic. It seems that the populations have not completely recovered in the abnormally warm recent decades. The habitat distribution of mussels apparently changed with time, too: unlike today, in the 20th century mussels were rarely observed in kelps. We suggest that the spatial and temporal dynamics of subarctic mussels can be partly explained by the competition between ME and MT combined with their differing sensitivity to environmental factors.
The physiological response of two species of mussels ( Mytilus edulis and M. galloprovincialis ) and two species of oysters ( Crassostrea gigas and Ostrea edulis ) to temperature, oxygen levels and food concentration, factors likely to vary as a result of climate change, was determined experimentally. Bivalves of similar size from different origins were exposed to six temperatures (3, 8, 15, 20, 25 and 30 °C) at two food regimes (2 and 10 μg Chl a L ⁻¹ ) for 6 weeks. In a parallel running experiment M. edulis from the same batches were exposed to three different temperatures (15, 20 and 25 °C) and three different oxygen levels (30, 50 and 100%) at two food regimes (2 and >8 μg Chl a L ⁻¹ ) for 3–4 weeks. Survival during the experiment ranged from 93% to 100% except for the mussels exposed to 30 °C which showed 100% mortality after three to 32 days. Higher food conditions showed higher optimal temperatures for growth of mussels and oysters. In addition, at the high food treatment, reduced O 2 saturation resulted in lower growth of mussels. At the low food treatment there were no differences in growth among the different O 2 levels at the same temperature. At high food concentration treatment, M. edulis growth was higher with low temperature and high oxygen level. Condition index was higher at higher food concentrations and decreased with increasing temperature. In addition, condition was lower at low oxygen saturation. Lower clearance rates were observed at high food concentrations. At 100% saturation of oxygen, mussel clearance rate increased with temperature at High food regime, but not at Low food regime. Mussel clearance rates were significantly reduced with low oxygen concentrations together with high temperature. Oxygen consumption significantly increased with temperature. Oxygen saturation was the main factor affecting mussel clearance rate. High temperature and low oxygen concentration combined significantly reduced clearance rate and increased oxygen consumption. These response curves can be used to improve parameterisation of individual shellfish growth models taking into consideration factors in the context of climate change: temperature, food concentration, oxygen concentration and their interactions. The observation that abiotic factors interact in affecting mussels and oysters is an important result to take into account.
This chapter deals with reproduction, larval development, settlement, metamorphosis, post‐larval dispersal, larval identification and abundance estimates. Included are sex identification and determination, annual cycles in a wide range of marine mussel species, exogenous and endogenous regulation of gametogenesis and spawning, annual storage cycles and energy storage of glycogen, lipids and protein in mantle tissue cells. The act of settlement involves descent from the plankton to the sea bottom, followed by a sequence of swimming and crawling behaviour that culminates in attachment once a suitable substrate is chosen. Metamorphosis then follows, and this heralds the end of the pelagic larval phase and the start of benthic life. Recruitment refers to the process of successful colonisation and implies the lapse of some period of time during which some post‐settlement mortality will normally have occurred. The main causal factors are delay of metamorphosis, biological disturbance, physical disturbance and hydrodynamics, physiological stress, competition and predation, the later being the best‐documented cause; other possible causes are developmental insufficient energy reserves, disease and parasitism.
This study quantified the effects of temperature on reproduction and maternal provisioning of the ectoparasite, Neobenedenia girellae (Platyhelminthes: Monogenea), a species known to cause detrimental impacts to aquaculture fishes in tropical and subtropical environments worldwide. At 20 and 25 °C, parasites exhibited relatively slower production of larger eggs that were energy-dense. In contrast, parasites at 30 °C attained sexual maturity faster, were reproductively active over a shorter period, grew to a smaller size and laid smaller, less energy-rich eggs at a faster rate. As such, parasites exhibited two distinct reproductive patterns in response to temperature: parasites at lower temperatures produced larger eggs with higher energy content, while those at the higher temperature had a higher rate of egg production. Larger eggs produced under cooler conditions were better provisioned with energetic reserves and important, membrane-bound lipids that would likely facilitate larval longevity and development success. This is commensurate with previous observations of epizootics of this parasite species in aquaculture systems during winter. Meanwhile, eggs produced at 30 °C contained higher proportions of saturated fatty acids compared with polyunsaturated fatty acids, likely reflecting metabolic regulation of cell membrane fluidity, which is necessary for larvae to survive warm conditions. This study demonstrates that fish ectoparasites have evolved substantial reproductive and metabolic flexibility to maximise infection success under variable environmental conditions.
Reproduction and recruitment of benthic invertebrates are influenced by the climate and by the ecological structure of marine ecosystems, along with local anthropogenic pressures such as eutrophication or oligotrophication. Using the Pacific oyster Crassostrea gigas as a biological model, we tested the hypothesis that the variability in prodissoconch II (PII) size (i.e. size at metamorphosis) depends on ecological functioning. Settlement and recruitment were assessed at 5 sampling sites on the French Mediterranean shellfish farmed Thau lagoon during the main summer recruitment events in 3 consecutive years (2012−2014). Hydrobiological and planktonic analyses were conducted at 3 sampling sites. Our results showed that recruitment was extremely heterogeneous, ranging from 0 to 260 ± 27 SE ind. dm⁻² throughout the ecosystem and was linked with variability in PII size, which ranged from 180 to 296 µm. The annual temporal pattern of PII sizes appeared to be controlled by temperature during the settlement period, whereas the spatial pattern depended on phytoplankton biomass and on the trophic functioning of the ecosystem. Smaller PII sizes were significantly correlated with the highest phytoplankton biomass, while larger PII sizes were positively correlated with mixotrophic cryptophyte abundance. We found an inverse relationship between PII size and survival after metamorphosis, showing that recruitment success was associated with smaller PII sizes. Regional climate conditions and local trophic functioning appear to be key factors in metamorphosis and consequently contribute to recruitment heterogeneity. Further studies should be performed in other ecosystems following an oligotrophication trajectory to generalize this result.
Ocean acidification severely affects bivalves, especially their larval stages. Consequently, the fate of this ecologically and economically important group depends on the capacity and rate of evolutionary adaptation to altered ocean carbonate chemistry. We document successful settlement of wild mussel larvae (Mytilus edulis) in a periodically CO2-enriched habitat. The larval fitness of the population originating from the CO2-enriched habitat was compared to the response of a population from a nonenriched habitat in a common garden experiment. The high CO2–adapted population showed higher fitness under elevated Pco2 (partial pressure of CO2) than the non-adapted cohort, demonstrating, for the first time, an evolutionary response of a natural mussel population to ocean acidification. To assess the rate of adaptation, we performed a selection experiment over three generations. CO2 tolerance differed substantially between the families within the F1 generation, and survival was drastically decreased in the highest, yet realistic, Pco2 treatment. Selection of CO2-tolerant F1 animals resulted in higher calcification performance of F2 larvae during early shell formation but did not improve overall survival. Our results thus reveal significant short-term selective responses of traits directly affected by ocean acidification and long-term adaptation potential in a key bivalve species. Because immediate response to selection did not directly translate into increased fitness, multigenerational studies need to take into consideration the multivariate nature of selection acting in natural habitats. Combinations of short-term selection with long-term adaptation in populations from CO2-enriched versus nonenriched natural habitats represent promising approaches for estimating adaptive potential of organisms facing global change.
Les lipides jouent un rôle de réserve d'énergie pour les organismes marins, ainsi qu'un rôle structural majeur en tant que composant de la membrane cellulaire. Nous verrons dans cette synthèse qui mêle écologie, physiologie, et épidémiologie, ce que l'analyse des lipides nous apprend sur le fonctionnement des organismes et des écosystèmes marins. Dans la première partie consacrée à l’écologie trophique et à la nutrition, nous verrons en quoi les lipides sont des indicateurs trophiques qui peuvent plus largement être utilisés comme témoins de la qualité de l’environnement. Dans la deuxième partie dédiée à l’adaptation et l’acclimatation des organismes marins aux changements de température du point de vue biochimique, nous aborderons les effets de la température sur le remodelage des lipides membranaires et le métabolisme énergétique. Enfin, dans la troisième partie consacrée à l’étude des relations hôtes-pathogènes-environnement, nous verrons comment la nutrition lipidique, l’énergétique et la température influence la réceptivité de l’huître vis-à-vis du virus OsHV-1, qui chaque année depuis 2008, décime les jeunes huîtres. Chaque partie comporte un état de l’art, une présentation de quelques études choisies et des perspectives.
Two size groups (20–30 and 45–55 mm) of Mytilus edulis and Mytilus trossulus were assessed from May to December 1992 at two locations in Nova Scotia. The two species were classified using electrophoresis based on mannose phosphate isomerase, and a discriminant function based on shell morphometry. The discriminant function misclassified less than 5% of the mussels and of these, 1% of the M. edulis were misclassified as M. trossulus, and 10% of the M. trossulus were misclassified as M. edulis. In general, both size groups of M. edulis tended to have higher shell growth rates than M. trossulus. Overall mortality was 6% and occurred primarily from mid-August to mid-September; M. edulis exhibited a slightly lower survival and for a given shell length had a higher average tissue and shell weight, as well as a greater shell height, than M. trossulus. Mytilus trossulus had a significantly lower tissue weight during the summer and was eliminated at a significantly higher rate during commercial grading trials than M. edulis. We estimated from the information on individual weight, survival, and grading losses that the economic value of M. edulis was 1.7 times higher than that of M. trossulus.
Understanding larval transport mechanisms is important to coastal ecosystem dynamics.
However, the relationships between nearshore larval abundance, onshore supply and settlement
remain poorly understood. We investigated instantaneous versus integrated methods to quantify barnacle
and mussel larval distributions as larvae traverse the last 100s of m of water, are delivered and
eventually settle onshore. Using the shore’s edge at low tide as a horizontal reference (~0 m), we sampled
at the following distances: >100s of m (offshore; Stn 1), >1 to 5 m (nearshore; Stn 2) and –10 to
–15 m (onshore; Stn 3). Offshore we used integrated collectors on moorings, nearshore instantaneous
pump samples were taken and onshore integrated plankton traps and collectors were deployed. All
sampling methods captured spatiotemporal variability but each sampled a different part of the water
column and potentially, larval life history. As larvae moved across the shore, distributions varied by
taxon, depth and sampling method. Offshore, mussel settlement varied between sites and depth.
Nearshore, mussel and barnacle larval abundances were coherent between sites. Mussel larvae were
well mixed vertically while barnacle larvae were stratified (higher abundances at 1 m). Onshore
(Stn 3) larval supply (traps) differed between sites for mussels only and settlement differed for barnacles.
Temporal coherence was high for the settlement, larval abundance and onshore supply of mussels,
as well as onshore barnacle settlement. Each sampling method was useful for examining larval
distributions in a different part of the environment. Used in concert, these methods provide a powerful
approach for linking oceanographic processes with nearshore larval abundance, onshore delivery
and replenishment of benthic communities.
▪ Abstract The majority of marine populations are demographically open; their replenishment is largely or exclusively dependent on a supply of juveniles from the plankton. In spite of much recent research, no consensus has yet been reached regarding the importance of recruitment relative to other demographic processes in determining local population densities. We argue 1. that demographic theory suggests that, except under restrictive and unlikely conditions, recruitment must influence local population density to some extent. Therefore, 2. the question as to whether the size of a particular population is limited by recruitment is misguided. Finally, 3. the effect of recruitment on population size can be difficult to detect but is nonetheless real. A major weakness of most existing studies is a lack of attention to the survival of recruits over appropriate scales of time and space. Acknowledgment of the multifactorial determination of population density should guide the design of future experimental studie...
Mytilus trossulus Gould and M. edulis L. coexist in mixed populations in Atlantic Canadian waters. Although there is evidence that the two species hybridize in
natural populations and that hybrids produce progeny through backcrosses, no study of the microgeographic distribution of
the two forms and their hybrids has been made. Here we examine subtidal samples of mussels taken in July 1997 from two locations
in eastern Newfoundland (Canada) and from wave-exposed and protected environments within each location. Shell lengths ranged
from 15 to about 90 mm. Mussels were classified as pure forms or hybrids (F1, F2 and from backcrosses) based on four diagnostic markers, two allozyme loci (Mpi and Est-D) and two nuclear PCR-based DNA markers (ITS and Glu-5). In addition, a PCR-based mtDNA marker (COIII) was used to characterize the distribution of mtDNA mitotypes among pure and hybrid individuals. There were differences in
the proportions of pure M. edulis and M. trossulus between sites and between environments at one location. M. trossulus was the predominant species at one of the two exposed sites. In all four samples, M. trossulus was also the predominant form among small individuals. The frequency of hybrids was 26% overall and did not differ among
samples. Hybrids consisted mostly of backcrosses that were M. trossulus-biased among small mussels and M. edulis-biased among large ones. We conclude that both intrinsic genetic factors and extrinsic environmental factors influence the
relative frequency of M. edulis, M. trossulus and their hybrids.
Genetic relationships among Mytilus populations throughout the North Atlantic region, including the Mediterranean and the Baltic Sea, were studied using enzyme electrophoresis. Three distinct groups of populations, each of a remarkably wide distribution, can be recognised on the basis of their multilocus allelic composition: (1) M. galloprovincialis Lmk. of the Mediterranean and western Europe; (2) a genetically distinct form of M. edulis L. from both the Baltic Sea and some localities in the Canadian Maritime Provinces (here provisionally termed the "trossulus type mussel"); and (3) the traditional "Atlantic" M. edulis populations of northwestern European coasts and most of eastern North America.
These groups are regarded as representing three relatively old evolutionary lineages, which all deserve separate and equal systematic status. The main part of the differentiation at most of the loci studied is accounted for by this major systematic pattern, but considerable geographical differentiation within each of the three principal groups was also detected. At single loci, different electromorphs were found to prevail in disjunct populations of M. galloprovincialis (Mediterranean/Britain) and of the trossulus-type mussel (Baltic/eastern Canada). Within the Atlantic M. edulis, a major part of the differentiation is transoceanic. At one locus (Ap), geographic differentiation appeared to be relatively independent of the systematic boundaries; the possible role of interlineage hybridisation in contact areas in regulating the pattern of geographical variation is discussed.
Ingestion, growth and metamorphosis of Pacific oyster, Crassostrea gigas, larvae were studied under controlled conditions of food density and temperature using a combination of a flow-through rearing system and a hydrobiological monitoring device. In a first experiment larvae were exposed to three different phytoplankton densities (12, 20 and 40 cells μl-1) while in a second trial larvae were reared at five different temperatures (17, 22, 25, 27 and 32°C). Both food concentration and temperature significantly affected the larval physiology throughout the entire development from D-veliger to young spat. Larvae survived over a wide range of both environmental parameters with high survival at the end of experiments. The feeding functional response provided the maximal ingestion rate (50 000 cells larva-1 day-1) which occurred at an algal density of 20 cells μl-1 surrounding the larvae and 25 °C. At the highest temperature (32 °C), maximal growth and metamorphosis performances were reached in less than 2 weeks while the lowest temperature (17°C) consistently inhibited ingestion and growth over the entire larval period. The estimate of the Arrhenius temperature (TA) was 11000 K for C. gigas larvae. Larval development could be divided on the basis of feeding activity into an initial mixotrophic period with a lower and constant ingestion over the first days (from D- stage to early umbonate larva of ≈110 μm length) followed by an exotrophic phase characterized by a sharp increase in ingestion (umbonate to eyed of ≈ 300 μm length) and, finally, a third period for larvae 300 μm during which ingestion decreased suddenly because of metamorphosis. Optimum larvaldevelopment and settlement of the oyster C. gigas occurred at 27 °C and an increasing food supply as the larvae were growing. A food density of ≥20 cells μl-1 of T-ISO + CP or CG (1:1 cells number) in the culture water was required to maximise growth and metamorphosis success.
Temperature is a major factor contributing to the latitudinal distribution of species. In the Northern Hemisphere, a species is likely to be living very close to its upper thermal tolerance limits at the southern limit of its biogeographic range. With global warming, this southern limit is expected to shift poleward. Moreover, intertidal ecosystems are expected to be especially strongly affected, mostly due to their large daily and seasonal variations in temperature and exposure. Hence, these are model systems in which to conduct experiments examining the ecological effects of climate change. In this study we determined the upper lethal thermal limits, for both air and water, of the blue mussel Mytilus edulis via laboratory experiments. Tolerances vary seasonally, with a difference between media of 0.7 degrees C in June and 4.8 degrees C in November, as well as a decrease with multiple exposures. Measured lethal limits were then compared to field measurements of environmental temperature and concurrent measurements of mortality rates. Field results indicate that mortality in the intertidal occurs at rates expected from laboratory responses to elevated temperature. Hindcasts, retrospective analyses of historical data, indicate that high rates of mortality have shifted 51 and 42 days earlier in Beaufort, North Carolina, and Oregon Inlet, North Carolina, respectively, between 1956 and 2007. The combined data suggest that the historical southern limit of M. edulis near Cape Hatteras, North Carolina, is indeed the result of intolerance to high temperature, and that this range edge is shifting poleward in a manner indicative of global warming.
We examined the seasonal variation in environmentally induced protein damage in natural populations of the intertidal mussel Mytilus trossulus. In order to compare the state of protein pools during seasonal variations in environmental temperature, we used solid-phase immunochemical analysis to quantify ubiquitin conjugate concentrations and relative levels of the stress protein hsp70. The two biochemical indices were selected for their cellular roles in irreversible and reversible protein denaturation, respectively. Proteins that are ubiquitinated are irreversibly damaged and are degraded by intracellular proteases; stress proteins act as molecular chaperones to re-fold thermally denatured proteins and, thus, indicate degrees of reversible protein damage. Comparisons involved mussels collected in February and August from two study sites: an intertidal site which subjected animals to a wide range of body temperatures (from approximately 10 to 35 C in summer), and a subtidal site where animals remained submerged throughout the tidal cycle. Our results show that quantities of ubiquitin conjugates and hsp70 were greater in gill tissue from summer-collected mussels than in gills of winter-collected specimens. Ubiquitin conjugate and hsp70 levels were also greater in mussels collected from an intertidal location than in mussels from a submerged population. Our results show that the high summer temperatures normally experienced in the field are sufficient to cause increased denaturation of cellular proteins. Despite increases in the concentrations of heat shock proteins in summer-acclimatized mussels, elevated levels of irreversibly denatured, i.e. ubiquitinated, proteins were still observed, which indicates that the heat shock response may not be able to rescue all heat-damaged proteins. The energy costs associated with replacing heat-damaged proteins and with maintaining the concentrations and activities of heat shock proteins may contribute substantially to cellular energy demands. These increased energy demands may have an impact on the ecological energetic relationships of species, e.g. in the allocations of energy for growth and reproduction, and, as a consequence, may contribute to determining their distribution limits.
The blue mussel Mytilus galloprovincialis, a native of the Mediterranean Sea, has invaded the west coast of North America in the past century, displacing the native blue mussel, Mytilus trossulus, from most of its former habitats in central and southern California. The invasive success of M. galloprovincialis is conjectured to be due, in part, to physiological adaptations that enable it to outperform M. trossulus at high temperatures. We have examined the structure and function of the enzyme cytosolic malate dehydrogenase (cMDH) from these species, as well as from the more distantly related ribbed mussel, Mytilus californianus, to characterize the effects of temperature on kinetic properties thought to exhibit thermal adaptation. The M. trossulus cMDH ortholog differs from the other cMDHs in a direction consistent with cold adaptation, as evidenced by a higher and more temperature-sensitive Michaelis-Menten constant for the cofactor NADH (Km(NADH)). This difference results from minor changes in sequence: the M. trossulus ortholog differs from the M. galloprovincialis ortholog by only two substitutions in the 334 amino acid monomer, and the M. californianus and M. trossulus orthologs differ by five substitutions. In each case, only one of these substitutions is non-conservative. To test the effects of individual substitutions on kinetic properties, we used site-directed mutagenesis to create recombinant cMDHs. Recombinant wild-type M. trossulus cMDH (rWT) has high Km(NADH) compared with mutants incorporating the non-conservative substitutions found in M. californianus and M. galloprovincialis - V114H and V114N, respectively - demonstrating that these mutations are responsible for the differences found in substrate affinity. Turnover number (kcat) is also higher in rWT compared with the two mutants, consistent with cold adaptation in the M. trossulus ortholog. Conversely, rWT and V114H appear more thermostable than V114N. Based on a comparison of Km(NADH) and kcat values among the orthologs, we propose that immersion temperatures are of greater selective importance in adapting kinetic properties than the more extreme temperatures that occur during emersion. The relative warm adaptation of M. galloprovincialis cMDH may be one of a suite of physiological characters that enhance the competitive ability of this invasive species in warm habitats.
Field studies demonstrate that the population structure of the barnacle Balanus glandula differs between locations of high and low larval settlement rate. These observations, together with results from a model for the demography of an open, space-limited population, suggest that the settlement rate may be a more important determinant of rocky intertidal community structure than is presently realized. Locations with a low larval settlement rate exhibit a generally low abundance of barnacles that varies slightly within years and greatly between years, reflecting yearly differences in settlement. Locations with a high-settlement rate exhibit a generally high abudance of barnacles. However, the abundance varies greatly within years with a significant oscillatory component (period, 30 weeks) and only slightly between years regardless of yearly differences in settlement. At the low-settlement location mortality of barnacles is independent of the area occupied by barnacles. At the high-settlement location mortality is cover-dependent due to increased predation by starfish on areas of high barnacle cover. In both locations the cover-independent component of mortality does not vary with age during the first 60 weeks. As assumed in the demographic model, the kinetics of larval settlement can be described as a process in which the rate of settlement to a quadrat is proportional to the fraction of vacant space within the quadrat. Generalizations that the highest species diversity in a rocky intertidal community is found at locations of intermediate disturbance, and that competition causes zonation between species of the barnacle genera Balanus and Chthamalus, seem to apply only to locations with high-settlement rates.
A temperature decrease usually induces an ordering effect in membrane phospholipids, which can lead to membrane dysfunction. Poikilotherms inhabiting eurythermal environments typically counteract this temperature effect by remodeling membrane lipids as stipulated in the homeoviscous adaptation theory (HVA). Hard clams, Mercenaria mercenaria, can suffer high overwintering mortalities in the Gulf of St Lawrence, Canada. The selectively bred M. mercenaria var. notata can have higher overwintering mortalities than the wild species, thus suggesting that the two varieties have different degrees of adaptation to low temperatures. The objective of this study was to investigate the changes in lipid composition of soft tissues in wild and selected hard clams in relation to their metabolic and genetic characteristics. Clams were placed at the northern limit of their distribution from August 2003 to May 2004; they were exposed to a gradual temperature decrease and then maintained at <0 degrees C for 3.5 months. This study is the first to report a major remodeling of lipids in this species as predicted by HVA; this remodeling involved a sequential response of the phospholipid to sterol ratio as well as in levels of 22:6n-3 and non-methylene interrupted dienoic fatty acids. Hard clams showed an increase in 20:5n-3 as temperature decreased, but this was not maintained during overwintering, which suggests that 20:5n-3 may have been used for eicosanoid biosynthesis as a stress response to environmental conditions. Selectively bred hard clams were characterized by a higher metabolic demand and a deviation from Hardy-Weinberg equilibrium at several genetic loci due to a deficit in heterozygote frequency compared with wild clams, which is believed to impose additional stress and render these animals more vulnerable to overwintering mortality. Finally, an intriguing finding is that the lower metabolic requirements of wild animals coincide with a lower unsaturation index of their lipids, as predicted by Hulbert's theory of membranes as pacemakers of metabolism.
We compared lipid dynamics and the physiological responses of blue mussels Mytilus edulis, a cold-adapted species, and oysters Crassostrea virginica, a warmer-water species, during simulated overwintering and passage to spring conditions. To simulate overwintering, animals were held at 0°C, 4°C and 9°C for 3 months and then gradually brought to and maintained at 20°C for 5 weeks to simulate spring–summer conditions. Changes in lipid class and fatty acid composition were related to clearance rate and oxygen consumption.
We found major differences between species in triglyceride (TAG) metabolism during overwintering. Mussels used digestive gland TAG stores for energy metabolism or reproductive processes during the winter, whereas oysters did not accumulate large TAG stores prior to overwintering. Mussel TAG contained high levels of 20:5n-3 compared to levels in oysters and in the diet. This may help to counteract the effect of low temperature by reducing the melting point of TAG and thus increasing the availability of storage fats at low temperature. Mussels seemed better able to mobilise 20:5n-3 and 18:4n-3 than other fatty acids.
We also found that both bivalves underwent a major remodelling of membrane phospholipids. The unsaturation index decreased in the gills and digestive glands of both species during the early stages of warming, principally due to decreases in 22:6n-3 and 20:5n-3. In digestive glands, the unsaturation index did not increase with decreasing temperature beyond a threshold attained at 9°C whereas a perfect negative relationship was observed in gills, as predicted by homeoviscous adaptation. The presence of digestive enzymes and acids in the digestive gland microenvironment may lead to specific requirements for membrane stability. That oysters had lower metabolic rates than mussels coincides with a lower unsaturation index of their lipids, as predicted by Hulbert's theory of membranes as metabolic pacemakers. Both species showed increased 20:4n-6 levels in their tissues as temperature rose,suggesting an increasing availability of this fatty acid for eicosanoid biosynthesis during stress responses.
The contrast between the species in TAG dynamics and the similarity of their phospholipid remodelling emphasises the essential functional role of membrane phospholipid structure and the contrasting use of TAG by oysters and mussels during overwintering.
The hydrophobic nature of lipids provides a convenient means of separating them from other compounds in an aqueous sample matrix. Extraction in nonpolar solvents is universally employed and is the basis of the operational definition of lipids. This approach is used routinely in algal biosynthetic studies in which the fate of a radiolabeled precursor is followed into the lipid pool. By adding 14C bicarbonate to a sample from the field (Wainman and Lean, 1992) or a culture (Rai, 1995) and then later extracting the sample with a water-immiscible organic solvent, the “lipid fraction of carbon fixation” (LFCF) can be determined (Wainman and Lean, 1992). By performing a chromatographic separation before counting, this procedure can be further refined to determine the subclasses in which the 4C ends up (Smith and D’ Souza, 1993). Subfractionation is important when a differentiation between allocation to lipid storage and membrane synthesis is required. The radiolabeling approach is convenient, sensitive, and not prone to contamination. However, many ecological studies are not amenable to this approach, and so chemical analysis of the constituents of lipid extracts has to be performed.
Techniques for the induction of spawning of Mytilus edulis, the delay of spawning and the rearing of the larvae are described.
Hochachka P.W., Somero G.N. (2002) Biochemical adaptation: mechanism and process in physiological evolution. New York: Oxford University Press. 466 p.
We examined the species composition of eleven blue mussel populations in eastern and central Maine, USA using a set of PCR-based genetic markers. Previous reports suggested that mussel populations in the Gulf of Maine were composed of only a single species, Mytilus edulis. In contrast, our results clearly indicate that the range of a congener, M. trossulus, extends well into the Gulf. The two blue mussels are sympatric in eastern Maine populations, including all of those we sampled within Cobscook Bay, ME. The frequency of M. trossulus, however, declines dramatically in the vicinity of Little Machias Bay, ME, so that populations along the coast of central Maine are composed predominantly of M. edulis mussels. Among populations containing a mixture of M. edulis and M. trossulus-specific alleles we observed a low but significant frequency of mussels with hybrid genotypes including putative backcross genotypes, indicating the potential for introgression between these two species. We suggest that larval supply and recruitment, thermal tolerance and perhaps the interplay of these factors likely delimit the southern extent of the range of M. trossulus and influence the species composition of blue mussel populations in the northwest Atlantic.
Food uptake of marine mussel larvae (Mytilus edulisL.) was estimated in relation to larval size, temperature (6, 12, 18°C) and food concentration (1, 2, 5, 10, 20 and 40 Isochrysis galbana cells 1r1-I). Filtration rates were maximal at low food concentrations (between 1 and 5 cells 1r1-l). This was called 'filtration capacity' and expressed as a function of larval size. Ingestion rates reached a plateau with increasing food concentration above 10 cells p1-l. Maximum rates were called 'ingestion capacity' and expressed as weight and volume of particles passed through the gut. When previously starved larvae enter a food suspension of more than 10 cells p1 l , ingestion rate overshoots the ingestion capacity level for up to 1.5 h at 12°C. This is caused by filling of the gut, because it was not paralleled by a n overshoot of the filtration rate above the filtration capacity level Particles between 1 and 9 ktm diameter were taken up, with maximum retention efficiency at about 3.5 pm particle diameter.
Lipid classes in solvent extracts of marine dissolved and particulate matter, benthic invertebrates, net-caught zooplankton, and freshwater sediment trap material were measured with the Chromarod–latroscan (thin-layer chromatography (TLC/flame ionization detector (FID)) system. As many as 11 classes were identified in these samples by combining multiple development schemes with the partial scanning facility in the latroscan. Part of the latroscan's circuitry was modified to include a scan-interruptor switch to further facilitate partial scanning. Quantitative aspects of the TLC/FID system were improved with the use of a syringe fitted with a repeating dispenser for sample application, and by maximizing the detector's response. High FID responses were obtained with double developments and high hydrogen flow rates and FID scan rates. Under these conditions an analytical precision of 10% was attained for most compounds with only about five analyses on different Chromarods, and the range in mean FID response to different compounds was significantly narrowed. An intercalibration was performed to test TLC/FID accuracy: the latroscan gave lipid values which were about 85% of true gravimetric values.
The lipid biochemistry of environmentally stressed larval fish, bivalves and crustaceans is presented to illustrate the utility of a larval condition index based on lipid composition. Larvae under environmental stress are often unable to obtain sufficient energy from exogenous sources and, as a result, endogenous energy reserves are catabolised to maintain basal metabolism. The storage lipid triacylglycerol (TAG) is of particular importance in this respect, TAG content consequently correlating with the physiological condition of a larva. However, absolute TAG content cannot be directly correlated with larval condition because of its dependency on larval size. It is proposed that TAG content can be correlated with larval condition when expressed in the form of a TAG-sterol ratio that accounts for the size dependency of TAG content. This proposition is supported by data that illustrate a highly positive correlation between sterol content and dry weight for larval herring and larval American lobster. Examples of TAG-sterol ratios are calculated from a survey of studies relating to the lipid class composition of nutritionally and pollutant stressed larvae of some marine fish and crustaceans.
The effect of salinity (5 to 25 ppt) on Mytilus edulis and M. trossulus that co-exist in Atlantic Canada was examined in 2 laboratory experiments. The first experiment tested the effect of salinity on survival and duration of development from fertilization to settlement in the 2 species. Hyposalinity reduced survivorship and percent metamorphosis, and lengthened duration of development. At 5 and 10 ppt, all early stages of both species died. At 25 ppt, >90% of individuals of both species survived through the oocyte to swimming embryo and swimming embryo to D-veliger stages, but only ca. 40 % survived through the D-veliger to eyed-veliger stage, and 30 to 42 % of eyed-veligers successfully metamorphosed. At 15 ppt, the 2 species significantly differed in survival rate, duration of development, and metamorphosis, M. edulis did not develop through any of the 3 stages from oocyte to eyed-veliger, No AT edulis eyed-veligers metamorphosed. In contrast, in M. trossulus, 26 % of oocytes and 15 % of swimming embryos developed into swimming embryos and D-veligers, respectively, and 13 % of eyed-veligers metamorphosed into plantigrades. At 20 ppt, some M. edulis developed through each of the 4 stages, but the development time was longer and there was a lower percentage than for the corresponding stage of M, trossulus. The second experiment examined the effect of salinity on survival of juveniles and adults. The 2 species responded to hyposaline stress similarly. Survival ranged from 0 at 5 ppt to 100 % at 20 to 25 ppt. At 10 ppt, reproductive status affected mortality, with <5 % mortality in juveniles and post-spawning individuals, but 60 to 67 % mortality in reproductive mussels, A similar situation occurred at 15 ppt except there was lower mortality for reproductive individuals, Thus, we found that only in the early ontogenetic stages was M. edulis less tolerant to low salinity stress than M trossulus. Such difference suggests that selective mortality against M edulis in early ontogenetic stages rather than post-settlement stage may be responsible for the persistence of a few pure M trossulus populations along the Gaspe Peninsula. We also found that the ability to tolerate hyposalinity was weakened during the reproductive period, which indicates that salinity may also act as a selective factor in determining the abundance and size structure of wild mussel populations.
The purpose of this study was to examine the lipid class content of larval stages of the sea scallop Placopecten magellanicus during development and to examine the potential effects of varying feeding regimes on larval lipid content, growth, survival, settlement behavior, and survival of postlarval stage. The potential of lipid class ratios to forecast larval growth, .survival, settlement behavior, and success was examined. At the start of exogenous feeding (day 4) three diets, which differed in triacylglycerol (TAG) content, were applied. Diet A consisted of Isochrysis sp. and Pavlova lutheri, diet B was a mix of Isochrysis sp. and Chaetoceros muelleri, and diet C consisted of the same two species, but C. muelleri was grown under silicate deprivation to enhance TAG accumulation. Larvae were periodically sampled for lipid class analysis, growth measurement and survival assessment. Behavior of pediveliger larvae for each diet was recorded using an endoscopie camera during settlement. Experiments were replicated twice and repeated 1 mo later. Our study shows that TAG level in larval food was positively correlated with growth rate, larval TAG content and, as a consequence, larval "quality," as measured by TAG-sterol (ST) or TAG-phospholipid (PL) ratios, prior to settlement. A positive relation between number of competent larvae produced and larval quality at day 8 was found, suggesting that survival at competency was partly explained by the recovery efficiency of energetic reserves as TAG after embryogenesis. Higher growth rates obtained with the diet enriched with TAG reflect its high caloric content and the presence of sufficient essential fatty acids. TAG-ST ratio of competent larvae was negatively correlated with settlement success (day 40). High quality larvae explore the same period of time whatever their age, whereas low quality larvae decrease exploration time with age. Consequently, the low settlement success observed in our experiments with high quality larvae might reflect delayed metamorphosis in response to poor environmental conditions.
The aim of this study was to test the validity of a lipid based indicator of larval quality of sea scallop Placopecten magellanicus. Objectives were 2-fold: (1) to determine the link between lipid class content and reproductive state of adults in the field and in the laboratory and (2) to follow lipid class content, growth, and survival during embryonic and early larval development. Adult scallops were periodically sampled during gametogenesis for lipid class and histological analysis of the gonads in the field at two locations and in the laboratory after feeding three different diets. Females were induced to spawn and lipid class content, larval growth, and survival of five hatches of eggs were followed for 8 days after fertilization. Site, diet, and time had significant effects on lipid class composition of male and female gonads and gametogenesis of females. Triacyglycerol accumulation during vitellogenesis was characteristic of female gonads and explained respectively 56.4% and 71.3% of the variability in maturity and egg size. When spawning was induced, no major effect of location or diet on lipid composition of gonad and subsequent eggs was detected. Nevertheless, the mean number of eggs produced by females increased with atresia level in gonad, suggesting that egg quantity was incompatible with egg quality. Lipid class composition during embryogenesis and young larval development showed a high demand for triacyglycerol.
Mytilus edulis and M. trossulus are the two molluscan species co-occurring along the Gaspé coast, eastern Canada. Few studies examine the effects of environmental factors (temperature, salinity, tidal height and wave action) on the local or regional distribution of these two species in areas where they co-occur. This study is designed precisely to examine the niche of each of the two species, particularly in relation to environmental factors in the northeastern part of the Gulf of St. Lawrence, Canada. Mussels were sampled on rocky shores according to a factorial design including six locations, 3 degrees of wave exposure (exposed, semi exposed and sheltered) and 2 intertidal levels (mid and low). Species were distinguished with polymerase chain reaction amplification using a diagnostic DNA marker (Glu-5). Relative frequencies of each species showed no clear patterns of distribution with wave exposure or tidal height. A pattern of distribution at the regional scale does occur, but this pattern could not be related to salinity or temperature gradients observed.
The larvae of three species of bivalve molluscs, Crassostrea virginica (Gmelin), Ostrea edulis (L.) and Mercenaria mercenaria (L.) were cultured under a variety of temperature and food species regimes in the laboratory. Data were collected on growth, survival, total lipid content and lipid class composition of both healthy and starved larvae. Subsamples were stained specifically for lipid content with the lipid-specific stain Oil Red O. Newly formed straight hinge larvae of all three species exhibited small lipid droplets dispersed throughout the tissues. These were resorbed within 4 days of the initiation of feeding while the digestive gland filled with exogenously supplied lipid. Embryogenesis took place at the expense of 69 and 71% of parentally derived total lipid, 92.8 and 68.3% of which was composed of triacylglycerols (M. mercenaria and C. virginica, respectively). After 8 days of feeding on Isochrysis aff. galbana (clone T-ISO), total lipid had increased 2.7-fold in larvae of C. virginica grown at 25°C, 37.6-fold in larvae of M. mercenaria grown at 22°C, and 1.7-fold in larvae of O. edulis grown at 25°C. Shell growth in larvae of C. virginica grown at 30°C was initially higher than that at 25°C, but lipid was accumulated 2.5 times slower and survival of pediveliger larvae through metamorphosis was considerably reduced at this elevated temperature. The lipid class composition of healthy larvae of C. virginica and M. mercenaria was dominated by triacylglycerols and phospholipids in approximately equal proportions; however, triacylglycerols were preferentially catabolized during starvation and were responsible for greater than 80% of the total lipid loss. Color photographs of larvae stained with Oil Red O are presented that illustrate lipid levels in developing larvae in both healthy and poor condition. From these, a visual index of lipid content was developed to allow comparisons between larval survival and lipid levels. In general, high survival was always accompanied by a high lipid index but a high lipid index did not guarantee good survival. We suggest that the lipid index may be used to document visually the lipid content in individual bivalve larvae as an indicator of physiological condition and potential for successful metamorphosis.
The mussels Mytilus edulis L. and Mytilus galloprovincialis Lamark hybridise naturally in the wild along the Atlantic coast of Europe producing a patchwork of mixed pure species and hybrid populations. Individuals of both species were spawned in the laboratory and were hybridised in a series of reciprocal crosses. After 72 h, the proportion of eggs which developed into larvae (%yield) and the proportion of those larvae which had a normal veliger morphology (%normality) were estimated and compared between pure species and hybrid families. There were no significant differences in %yield or %normality between pure species and hybrids, but significant differences were evident between the offspring from different parents irrespective of whether they were hybrids or pure species. Therefore confirmation of hybrid heterosis in laboratory studies should not be based on a single, or a few reciprocal crosses. Hybrid and pure species veliger larvae were grown for approximately 4 weeks at 10, 14 or 20 °C. In all trials, pure M. galloprovincialis larvae grew significantly faster at 20 °C than either reciprocal hybrid or pure M. edulis larvae. Irrespective of temperature, in general, hybrid larvae grew slower than larvae of either pure species. Increased exposure to planktonic predation due to slow growth can be interpreted as selection against hybrids and this may play a role in the structure and distribution of mixed pure species and hybrid populations.
Individuals of two species of blue mussels,Mytilus trossulus (Gould, 1850) andM. galloprovincialis (Lamarck, 1819), that have different latitudinal distributions, were collected from two locations on the Pacific coast of the USA where their distributions do not overlap. To determine if the congeners were differentially sensitive to thermal stress, we first held individuals of each species at 13C for 8 wk and then examined three biochemical indices of thermal damage to cellular proteins: relative levels of the stress protein hsp 70, quantities of ubiquitin conjugates and the induction of stress-protein synthesis. The results provide evidence that the northern species,M. trossulus, was more thermally sensitive than the southern species,M. galloprovincialis. Relative levels of hsp 70 and amounts of ubiquitin conjugates were higher in gill tissue fromM. trossulus than in gill fromM. galloprovincialis, which suggests thatM. trossulus was more susceptible to reversible and irreversible protein damage, respectively, thanM. galloprovincialis. In addition, the patterns of stress-protein expression as measured by in vitro radiolabeling experiments using isolated gill tissue, were significantly different, as follows: (1) the threshold induction temperatures for hsp 70 synthesis were 23 and 25C forM. trossulus andM. galloprovincialis, respectively; (2) the overall intensity of synthesis and induction was greater inM. galloprovincialis than inM. trossulus, particularly at the higher incubation temperatures of 28 and 30C; (3)M. galloprovincialis expressed a 30 kdalton, stress protein that was not induced in the northern species,M. trossulus. Thus, after an 8 wk exposure to a common temperature, the twoedulis-like mussel congeners appeared to be physiologically distinct with respect to thermal damage to proteins. Due to the energetic cost that is probably associated with environmentally-induced protein damage and maintaining pools of stress proteins, differential organismal thermotolerances and protein stabilites may contribute to setting species distribution-limits. Our data support conclusions of other workers thatM. trossulus is a more cold-adapted species thanM. galloprovincialis.
There is significant differentiation at five polymorphic loci ofMytilus edulis among certain geographical areas of the Atlantic coast of North America. Non-metric multidimensional numerical methods distinguished three population groups: (I) populations south of Cape Cod, (II) populations throughout the Gulf of Maine, Gulf of St. Lawrence, areas of both southern and northern Newfoundland, and southern Hudson Bay, and (III) populations in southeastern Nova Scotia, northern Newfoundland and Hudson Strait, Quebec. Each subset consists of populations that exhibit characteristic multilocus, multiple allele genotypes. Populations in Groups II and III are spatially interdigitated among each other. At least one geographical area of mixing between genetically distinct populations occurs in northeastern Newfoundland. There is no evidence for interbreeding among genetically distinct individuals in mixed populations, suggesting the possibility that populations in the Atlantic Canadian Provinces and areas of northern Canada may consist of two distinct species.
Allopatric populations of Mytilus species show distinct shell morphology which may be due to genetic and/or environmental effects. Sympatric populations of
Mytilus species show similar shell morphology which may be due to hybridization eroding morphological differences and/or the influence
of common environmental conditions. The present study examined shell morphology and shell shape from 16 sites in eastern Newfoundland
where M. edulis L. and M. trossulus Gould coexist in common environments with limited hybridization. Shell morphology was based on measurements of eight characters,
and shell shape was quantified by elliptic Fourier analysis of shell outlines. Significant differences were observed between
species for both shell morphology and shell shape across 16 sites sampled. The relatively small differences in morphology
and shape between the species were probably due to exposure to common environments rather than hybridization. Shell shape
for M. edulis was more eccentric compared to M. trossulus which was more elongated. Shell shape analysis of a range of size classes at one site showed a change from an eccentric to
an elongated shape going from the smaller to the larger size classes. Both species showed a similar trend, with the larger
M. edulis more eccentric and the larger M. trossulus more elongated.
Under homogeneous salinity and temperature conditions and uniform daylight, the early larvae of the Pacific mussel Mytilus trossulus (blastulae and trochophores) accumulated in the uppermost layer of water column, while the late larvae tend to concentrate at the bottom. In a water column with a temperature or salinity gradient, the early larvae accumulated at the surface even when the salinity and temperature conditions were incompatible with their life activity. The distribution of the late larvae was different as they were able to leave water of unfavorable temperature and salinity and accumulate at the bottom.
Blue mussels representing two nominal species (Mytilus trossulus Gould, 1850 and Mytilus galloprovincialis Lamarck, 1819 were collected from 28 intertidal locations along the Pacific coast of the USA in 1990–1991 (total N=1255) and examined for variation at 15 allozyme loci. Twelve samples, mostly from a region of suspected hybridization, were analyzed for variation in seven shell characters. Principal-components analysis of allozyme data revealed three groups based on first principal-component scores, which were identified as M. trossulus, M. galloprovincialis, and hybrids. Canonical discriminant analysis of shell characters was less successful in separating mussels into discrete groups. Each location was characterized for four environmental variables: (1) temperature, (2) salinity, (3) tidal height and (4) degree of exposure to wave action, which were then used as independent variables in a series of multiple-regression analyses, with the proportions of the two species as dependent variables. Temperature and salinity had significant (PM. trossulus was more abundant at locations with lower temperatures and greater salinity variation than M. galloprovincialis. The two species appear to be ecologically distinct, and their genetic integrity is at least partly the result of environmental heterogeneity.
Many authors have considered the common mussels in temperate waters of the Northern and Southern Hemispheres to be a single cosmopolitan species,Mytilus edulis Linnaeus, 1758. Others have divided these mussels into several subspecies or species. Samples of mussels were collected from 36 locations in the Northern Hemisphere and nine locations in the Southern Hemisphere. Electrophoretic evidence from eight loci indicates that the Northern Hemisphere samples consist of three electrophoretically distinguishable species:M. edulis from eastern North America and western Europe;M. galloprovincialis Lamarck, 1819 from the Mediterranean Sea, western Europe, California, and eastern Asia; andM. trossulus Gould, 1850 from the Baltic Sea, eastern Canada, western North America and the Pacific coast of Siberia. Mussels from Chile, Argentina, the Falkland Islands and the Kerguelen Islands contain alleles characteristic of all three Northern Hemisphere species, but because they are most similar toM. edulis from the Northern Hemisphere, we suggest that they tentatively be included inM. edulis. These South American samples are morphologically intermediate between Northern HemisphereM. edulis andM. trossulus. Mussels from Australia and New Zealand are similar in allele frequency and morphometric characters toM. galloprovincialis from the Northern Hemisphere. FossilMytilus sp. are present in Australia, New Zealand and South America, which suggests that the Southern Hemisphere populations may be native, rather than introduced by humans. Morphometric characters were measured on samples which the allozyme data indicated contained a single species. Canonical variates analysis of the morphometric characters yields functions which distinguish among our samples of the species in the Northern Hemisphere.
This study reports the effect of additions of dietary microspheres of triacylglycerol (TAG, extracted from the diatom Chaetoceros muelleri) on larval development and settlement of Mytilus sp. The first experiment showed that mussel larvae successfully ingested TAG microspheres as soon as they acquired the ability to feed from exogenous sources. In a second experiment, larvae were fed for 28days on diets consisting of 0, 1, 20, or 50% TAG microspheres (based on the cell concentration of a full algal ration) added as partial replacements for a ration of Isochrysis sp. (T-ISO). Lipid content and growth of larvae fed on a diet composed of 20% TAG were higher than those of the control groups, whereas survival was negatively affected. No growth or survival effect was detected with larvae fed on a diet composed of 1% TAG, whereas high mortality after 14days was observed for larvae fed on a diet composed of 50% TAG microspheres. In a third experiment, 22-day-old larvae were fed on rations of Isochrysis sp. supplemented with 0, 1, 10, 20, 50, and 100% TAG for 2days and allowed to settle for a 7-day period. TAG content of the larvae increased with TAG added to the diet until a saturation threshold was reached between a 20 and 50% supplementation level. Similarly, free fatty acid (FFA) content increased with TAG level in the diet and was linearly correlated with TAG content of larvae. Increased levels of FFA in larvae were attributed to digestion of TAG supplements. Settlement success and survival of larvae were not affected by diet; however, regression analysis revealed that TAG level in pre-metamorphic larvae explained 28% of survival variability among cultures.
Adaptivity to short-term and long-term changes in water temperature and salinity was studied in larvae of the bivalve mollusk
Mytilus trossulus. It was shown that water temperature of 4°C mostly suppressed growth and development of larvae. A temperature of 20°C promoted
an enhanced larval growth and development. Though a temperature of 20°C caused enhanced larval growth, the temperature was
not optimal, while its effect caused quality diversity of larval development, owing to the difference in their growth rates.
Such diversity was not observed at moderate temperatures of 10 and 15°C. At 20°C, fast-growing mussel larvae were very sensitive
to temperature drops. Growth of slowly-growing individuals did not depend on temperature in the range of 10 to 20°C. Daily
temperature variations by 3–8°C did not markedly affect growth and development of the larvae. A continuous 24-h exposure to
temperature drops by 3–8°C did not influence these very important physiological characteristics either. A salinity drop down
to 8‰ exerted an adverse effect only on early larvae. Later on, the larvae showed their ability to adapt to such a strong
desalination. The negative effect of reduced salinity (to 8‰) upon mussel larvae was increased at a temperature increase to
20°C.
It has been nearly 15 years since the genetics of Mytilus was the subject of a comprehensive review. In this period, our understanding of the nature of genetic variation in this group has been substantially altered. Studies on the extent of individual variation have demonstrated that genotype (i.e., multiple locus heterozygosity) has a significant effect on energy metabolism, producing significant statistical correlations between genotype and measures of both metabolic energy demand and productivity, particularly growth rate. These correlations can be mitigated by a number of factors, including age, reproductive state, the specific genes under study and ecological conditions.Studies of within-population variation have repeatedly noted marked deficiencies of heterozygotes, but no satisfactory explanation for this observation has yet been identified. Deficiencies are locus-specific and multilocus disequilibria have been described, suggesting a combination of larval mixing with additional forces such as selection, aneuploidy or molecular imprinting.Early work suggested substantial genetic differentiation between spatially proximate populations. Populations are now known to be relatively homogeneous, even over vast geographical distances. Genetic differences between proximate populations generally represent taxonomic differentiation among mytiliid species, not population differences.Studies of allozymes, morphology and (to some degree) mitochondrial genotype among world-wide samples have demonstrated the existence and geographic distributions of four species in the genus: Mytilus californianus, M. edulis, M. trossulus and M. galloprovincialis. Data for the three latter species are presented along with the geographic distribution of each.
Five independent batches of Pecten maximus (L.) larvae, reared under the same standard hatchery conditions, showed different growth rates, ranging from 1.9 to 6.6 μm·day−1. A standard lipid profile was defined based on the fast-developing larvae and variations to this standard were seen when abnormal growth performances occurred. The lipid class composition was determined during the development of D-larvae to Day 23 using chromarods and flame ionization detection. Phospholipids and triglycerides were the main lipid classes in P. maximus larvae as reported for other cultured bivalve larvae (accounting for 50 and 37% of total lipids, respectively). Sterols and free fatty acids formed 10 and 3% of the total lipids, respectively. These relative proportions of lipid classes were constant during development of fast developing larvae. The triglyceride:organic matter ratio (TG:OM) stabilized after an initial decline during 3 days after the first feeding and the increase of triglycerides after this time indicated that the catabolism of endogenous triglycerides was rapidly offset by the food intake during the nutritional transition. The comparison of this lipid class pattern with those from larvae which exhibited a lower growth rate revealed that: (i) no stability of the lipid class composition was apparent throughout development; (ii) the triglyceride:total lipid (TG:TL) ratio in D-larvae was not related to the subsequent growth; (iii) a low TG:OM ration in D-larvae was related to poor growth while higher levels did not correspond necessarily to better growth rates; (iv) both the degree and the duration of the TG:OM ration decline for all these batches during the 1st wk can be related to the ability of the larvae to overcome the nutritional transition from trochophore to veliger rapidly and allow for subsequent successful growth. The possible influence of uncontrolled genetic or environmental factors is suggested.
The growth of the shell of Mytilus edulis L. was measured at 16 different constant temperatures over short periods. Growth increased logarithmically between 3 and 20 °C; above 20 °C the growth rate declined sharply. Fluctuating temperatures appeared to promote growth above the levels corresponding to the lowest temperatures of the fluctuating regimes used and unexpectedly, in some cases even above the upper levels. Animals exposed to sinusoidal temperature changes achieved better growth than those subjected to abrupt changes. The long-term response of the growth of the shell of Mytilus was followed over a period of 3 wk and the general trend was similar to that found in the short-term experiments. At lower temperatures (3 and 5 °C) growth rates were constant but very low. There was a tendency for growth at the higher temperatures, after initial increase, to return to the ambient growth level after several days.
The relationship between growth rate, rate of morphological development, and length of larval life, was examined for larvae of the blue mussel Mytilus edulis L. The larvae were reared at phytoplankton (Isochrysis galbana, clone T-ISO) concentrations between 0.5 × 104 and 30 × 104 cells · ml−1 at either 12 or 16°C. Growth rates generally increased with increasing food concentration and were highest at the higher temperature; maximum shell growth rate was ≈ 8 μm · day −1. The number of days required for larvae to develop recognizable eyespots sometimes varied proportionately with changes in growth rate, but often did not; temperature was especially effective at uncoupling rate of growth from rate of morphological development. Maintained in clean glass dishes at 16°C, many eyespotted larvae survived until the end of the study, as long as 8 wk after they first developed eyespots (≈80 days after fertilization). Nearly 30% of those larvae that survived under these conditions eventually metamorphosed in the absence of filamentous substratum, suggesting that metamorphosis can be postponed at least 45 days at 16°C. Food concentration had no effect on 1.(1)the time elapsed between eyespot development and noninduced attachment;2.(2) the average shell length of individuals that did attach; or3.(3) the mean size of larvae remaining at the end of the study.
A broad zone of sympatry between two morphologically and ecologically similar blue mussels Mytilus trossulus (Gould) and M. edulis (L.) extends from the Canadian Maritimes into the Gulf of Maine. The zone boundary and the southern range limit of M. trossulus coincide with the position of the Eastern Maine Coastal Current (EMCC). This current has not been recognized as a biogeographic
boundary. However, the flow field associated with the EMCC essentially divides the eastern and western Gulf during the part
of year when mussel populations in the eastern portion of the Gulf are reproductively active and thus may be a hydrodynamic
barrier to the westward dispersal of M. trossulus larvae. Alternatively, a strong gradient in water temperature associated with the EMCC may create a physiological barrier
to M. trossulus larvae. We examined spatial variation in the abundance of M. trossulus and M. edulis along the coast of Maine using two diagnostic DNA-based markers. Although we detected M. trossulus in mussel populations in offshore locations in central Maine that were directly in the path of the EMCC, the abundance of
this species declines dramatically at sites beyond the influence of this current. Variation in the abundance of adults, however,
cannot differentiate between the effects of the EMCC on larval transport vs physiological tolerance. Thus, we also conducted a temperature challenge experiment investigating the species-specific variation
in larval survival at temperatures ranging from 5°C to 20°C. We found that larval mortality was generally higher for M. trossulus relative to M. edulis larvae when exposed to 20°C early during development. These results suggest that differences in larval thermal tolerance
help to structure the southern range limit for M. trossulus in the Gulf of Maine.
We have used the polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) techniques to design two genetic markers for blue mussels in the Mytilus edulis species complex. Both of these markers target the gene encoding the mussel polyphenolic adhesive protein. The first marker, Glu-5', is highly differentiated among and can be used to identify the three blue mussel species, M. edulis, M. galloprovincialis and M. trossulus. The second marker, Glu-3', can identify M. edulis and M. galloprovincialis. Using these markers we have demonstrated that hybrid mussels from Whitsand Bay, UK carry alleles for this gene that are the products of intragenic recombination. The high frequency (10 per cent) of these recombinant alleles within the hybrid population suggests that recombination is fairly frequent within this gene or that hybridization between M. edulis and M. galloprovincialis is substantial and has been occurring over considerable evolutionary time. The two novel genetic markers, Glu-5' and Glu-3' will be invaluable in additional studies regarding the importance of hybridization among blue mussels.
The three species of blue mussels, Mytilus trossulus Gould 1850, M. edulis Linnaeus 1758 and M. galloprovincialis Lamarck 1819, have distinct global distribution patterns that are hypothesized to reflect differences in their tolerances of temperature and salinity. We examined effects on heart rate (beats min–1) of acute exposure and acclimation to different combinations of temperature and salinity to test this hypothesis and, in the context of the invasive success of M. galloprovincialis, to gain insights into the factors that may explain the replacement of the temperate Pacific native, M. trossulus, by this Mediterranean Sea invader along much of the California coast. Heart rate of M. trossulus was significantly higher than that of M. galloprovincialis, consistent with evolutionary adaptation to a lower habitat temperature (temperature compensation) in the former species. Heart rates of M. trossulus/M. galloprovincialis hybrids were intermediate between those of the parental species. Following acclimation to 14°C and 21°C, heart rates of all species exhibited partial compensation to temperature.
Heart rate increased with rising temperature until a high temperature was reached at which point activity fell sharply, the high critical temperature(Hcrit). Hcrit increased with increasing acclimation temperature and differed among species in a pattern that reflected their probable evolutionary adaptation temperatures: M. galloprovincialis is more heat tolerant than the other two congeners. Ability to sustain heart function in the cold also reflected evolutionary history: M. trossulus is more cold tolerant than M. galloprovincialis.
Heart rates for all three congeners decreased gradually in response to acute reductions in salinity until a low salinity (Scrit)was reached at which heart rate dropped precipitously. Scrit decreased with decreasing salinity of acclimation and was generally lowest for M. galloprovincialis. Mortality during acclimation under common garden conditions was greatest in M. trossulus and was highest at high acclimation temperatures and salinities. These intrinsic differences in basal heart rate, thermal and salinity responses, acclimatory capacity, and survivorship are discussed in the contexts of the species' biogeographic patterning and, for the invasive species M. galloprovincialis, the potential for further range expansion along the Pacific coast of North America.
Lipid reserves and energy metabolism in the larvae of benthic marine invertebrates Biochemical and biophysical perspectives in marine biology The bases for temperature zonation in geographical distribution
- Dc Malin
- Sargent
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Physiological responses to temperature in two latitudinally separated populations of the mussel, Mytilus edulis
- R J Thompson
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temperature in two latitudinally separated populations of
the mussel, Mytilus edulis. In: Gibbs PE (ed) Nineteenth
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Lipid reserves and energy metabolism in the larvae of benthic marine invertebrates
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