No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Maerl-associated macroalgae in the bay of Brest (Brittany, France)
Abstract
Maerl beds are unique marine habitats hosting a great diversity of organisms while macroalgae are a major component of this diversity. The bay of Brest is one of the most studied coastal ecosystems in the world; in addition, it has a significant background concerning historical seaweeds checklists associated to maerl beds. However, no recent work aimed at compiling and completing these data. In this study, a total of 7 subtidal and 3 intertidal maerl beds have been surveyed between 2020 and 2022. These data complete 4 previous inventories, giving the most accurate description of seaweeds colonizing maerl beds in the bay of Brest. The total number of macroalgal species reaches 170 among which 127 are Rhodophyta, 22 Phaeophyceae, and 21 Ulvophyceae, with 51 additions to the French and 19 additions to the European maerl beds checklist. A comparison with other maerl beds of the northeastern Atlantic coasts is compiled. It appears that the maerl beds from the bay of Brest are the most diverse in Atlantic France and among the most diverse in Europe. A description of the stratification of maerl beds and the associated macroalgal communities is proposed. It includes maerl species, encrusting species, maerl-entangling species, erect isolated species, and free-living species. In addition, specimens of the rarely recorded Rytiphlaea tinctoria, reaching its northernmost population in the bay, a possible introduced species/relict population, are described.
... In the northeast Atlantic Ocean, macroalgal communities associated with maerl beds are mostly dominated by Rhodophyta (BIOMAERL, 1999;Peña and Bárbara, 2010), and some species are only found in this habitat and can be considered maerl-specialists (Maggs and Guiry, 1987;Leliaert et al., 2009;Peña, 2010). In Europe, 368 macroalgae species are found associated with maerl beds (representing 30 % of the area's macroalgal diversity), with at least 170 species occurring in the bay of Brest (Peña et al., 2014;Helias and Burel, 2023). Maerl beds are characterized by a marked seasonality, with higher macroalgal biomass during summer, particularly in temperate waters (Grall et al., 2006;Peña and Bárbara, 2010;Qui-Minet et al., 2018). ...
... The effects of anthropogenic pressures on the macrofaunal communities are well known in the area (Grall, 2003;Tauran et al., 2020). Yet, studies focusing on maerl-associated flora often rely on the grey literature, mainly focusing on species lists (Peña et al., 2014;Helias and Burel, 2023). ...
... They were then grouped into morphoanatomical groups (cartilaginous, blades, fine foliaceous, filamentous and others) to investigate the influence of morphological groups on the variability. This morphofunctional approach is based on previous classifications made by Steneck and Dethier (1994), Ar Gall and Le Duff (2014) and Helias and Burel (2023). ...
Background and Aims:
Maerl-associated communities have received considerable attention due to their uniqueness, biodiversity and functional importance. Although the impacts of human activities are well documented for maerl-associated macrofauna, the spatio-temporal variations of macroalgae have comparatively been neglected, and the drivers that influence their dynamics are poorly known. We investigate the links between maerl-associated macroalgal communities, anthropogenic pressures and environmental conditions, and hypothesize that sites under human pressure would exhibit different dynamics when compared to reference site.
Methods:
In order to better understand community variation through space and time, four subtidal maerl beds under different pressures were consistently monitored over one year in the bay of Brest, Brittany, France. Both macroalgae communities monitoring and environmental data were acquired through field sampling and
available models.
Key Results:
Higher macroalgal biomass was observed within eutrophic sites, especially in summer (more than 10 times higher than in Unimpacted site), caused by free-living forms of opportunistic red macroalgae. The Dredged site also exhibited distinct macroalgal communities during summer from the Unimpacted site. Nutrient concentrations and seasonality proved to be key factors affecting the macroalgal community composition, although dredging and its effects on granulometry also had strong influence. Over the long term, less than half of the species identified during historical surveys were found, indicating major temporal changes.
Conclusions:
Human pressures have strong impact on maerl-associated macroalgal communities. Nutrient concentrations and dredging pressure appear as the main anthropogenic factors shaping maerl-associated macroalgal communities. Additionally, our results suggest historical changes in maerl-associated macroalgal
communities over 25 years in response to changes in local human pressure management. This study suggests that maerl-associated macroalgal communities could be used as indicators of anthropogenic-driven changes in this habitat
... These species often lack a nucleus, the main reason why many now consider only such forms as maerl (sensu stricto). At least 13 different maerl-forming species have been identified in the NE Atlantic with many different growth forms (Peña et al. 2013Pardo et al. 2014;Qui-Minet et al. 2021;Helias and Burel 2023). The term maerl sensu lato has sometimes been Table S1. ...
... In the GET definition, only nongeniculate coralline algae are included; however, the ecosystem properties, resources, ambient environmental conditions, disturbance regimes and biotic interactions used to define them could also be applied to free-living geniculate coralline algae (Keith, Fragkopolou, et al. 2022). For instance, rhodolith and maerl beds are grouped on the basis of moderate productivity (Martin et al. 2005;Riosmena-Rodríguez 2017;Qui-Minet et al. 2022), high associated biodiversity Boyé et al. 2019;Helias and Burel 2023) and high structural complexity (Jardim et al. 2022;Bélanger and Gagnon 2023;Cabrito et al. 2024). Although understudied and possibly rare, articulith beds probably share most of these characteristics, are formed through similar processes and face similar pressures (Tâmega et al. 2017(Tâmega et al. , 2021. ...
Linguistic uncertainty is a prime source of uncertainty pervading ecology and conservation. Coralline algae are a widespread and diverse group of calcifying red macroalgae that underpin coastal ecosystem function and service provision. Recent increasing interest in coralline algae in the scientific literature has revealed a diverse but confusing terminology at organism to habitat scales. Coralline algal research and conservation are international and multidisciplinary, so there are geographic and disciplinary imbalances in research and conservation efforts. To reach consensus and reduce uncertainty, we propose a unified terminology. We review trends in cultural and scientific use of coralline algal terms and propose a system based on six morphologies: (1) attached, (2) free-living geniculate, (3) encrusting and free-living nongeniculate coralline algae, the latter either being (4) This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
... Maerl beds are biogenic habitats founded on a few species of free-living non-geniculate coralline algae that form structurally complex nodules called rhodoliths or maerl (herein used as synonyms) that can aggregate to high densities in soft substrates. These worldwide distributed habitats present high macrofaunal diversity and abundance (Barbera et al. 2003, Grall et al. 2006, Riosmena-Rodríguez et al. 2017, Schubert et al. 2020) as well as rich algal communities (Qui-Minet et al. 2018, Helias andBurel 2023), harbouring around 30% of the macroalgae diversity of the NE Atlantic (Peña et al. 2014). However, maerl beds face several conservation challenges globally due to anthropogenic threats (Barbera et al. 2003, Wilson et al. 2004, Ragueneau et al. 2018. ...
Habitat complexity (HC) promotes species richness and abundance. Aquatic environments are faced with intense pressures that threaten the 3D structure of the seafloor, with cascading effects on ecosystem functioning and biodiversity. Maerl or rhodolith beds are marine biogenic habitats created by few species of free-living non-genicu-late coralline algae that aggregate and form complex structures. Although their high biodiversity has been attributed to the HC provided by coralline algal nodules, the mechanisms through which HC modification affect associated communities remains uncertain in face of numerous confounding factors. Hence, we tested how changes in the extent and nature of maerl complexity drive changes in biodiversity. Using long-term monitoring data from ten maerl beds in Brittany (France) over 12 years, we investigated the links between structural complexity, environmental conditions and benthic macrofaunal communities. HC was quantified at the coralline algal nodule and bed level, through morphometrics and density, and its effects on local diversity and on communities spatial and temporal variability were evaluated. HC promoted species richness and density of most taxa regardless of other environmental factors. These relationships were linear and no limiting threshold of complexity was found at a regional scale. HC played a more important role in driving regional diversity patterns than other measured environmental constraints individually, and beds with relatively lower HC were the most distinct in terms of community composition and structure. Species replacement was the main component of temporal variability and HC promoted community stability. While overall facilitative, the effects of HC might be taxa and trait-dependent, justifying comprehensive trait-based approaches. Our results reiterate the need to protect complex biogenic habitats.
... Peña et al. (2014) and Helias et al. (2024) document the high diversity and distinct assemblages of macroalgae on maerl. To date, 174 macroalgal species have been recorded on Breton maerl, which is an outstanding 42% of the total regional seaweed diversity (Helias and Burel 2023;Helias et al. 2024). Normally (but see the eutrophication section below), the biomass of noncalcified seaweeds on maerl remains low due to grazing and mobility of the surface layer, although kelp can be conspicuous and transports clumps of maerl in its holdfasts in storms. ...
Most ecoregions lack data on maerl distribution and ecological status, so this needs fundamental research for conservation. Brittany, NW France, is an exception and has extensive research on maerl species, associated biodiversity, human-induced impacts and protection efforts. Breton maerl habitats host exceptionally high species richness and functional diversity, surpassing all other coastal habitats in the region. The meiofauna and microflora of maerl beds and the role of these habitats as carbon stores remain poorly known. Bans on direct exploitation in Europe have led to environmental improvements, although maerl extraction has begun in other regions of the world. In Europe, serious maerl conservation problems persist, particularly due to scallop and clam dredging, eutrophication and mariculture impacts. Not enough has been done to curb these issues, which are proven to severely degrade maerl, its biodiversity and ecosystem functions. Conservation measures for maerl beds should be strengthened and codesigned with local stakeholders as these habitats take millennia to form and are inadequately protected by current strategies.
... For instance, northeast Atlantic maerl beds host at least 349 associated macroalgal species, including 232 Rhodophyta, 72 Heterokontophyta and 45 Chlorophyta, making up about 30% of the total macroalgal diversity in the region . Likewise, Helias & Burel (2023) recorded 170 macroalgal species, belonging to Rhodophyta, Ochrophyta and Chlorophyta in rhodolith beds from the Bay of Brest, 108 of which were found growing exclusively on rhodoliths, while 14 occurred only as epiphytes on other species, indicating two and three levels of co-occurring habitat-formers. In Brazil, local estimates (across areas of tens of km 2 ) of seaweed diversity in rhodolith beds range from 44 to 67 species, with regional estimates (i.e. ...
Rhodolith beds are diverse and globally distributed habitats. Nonetheless, the role of rhodoliths in structuring the associated species community through a hierarchy of positive interactions is yet to be recognised. In this review, we provide evidence that rhodoliths can function as foundation species of multi-level facilitation cascades and, hence, are fundamental for the persistence of hierarchically structured communities within coastal oceans. Rhodoliths generate facilitation cascades by buffering physical stress, reducing consumer pressure and enhancing resource availability. Due to large variations in their shape, size and density, a single rhodolith bed can support multiple taxonomically distant and architecturally distinct habitat-forming species, such as primary producers, sponges or bivalves, thus encompassing a broad range of functional traits and providing a wealth of secondary microhabitat and food resources. In addition, rhodoliths are often mobile, and thus can redistribute associated species, potentially expanding the distribution of species with short-distance dispersal abilities. Key knowledge gaps we have identified include: the experimental assessment of the role of rhodoliths as basal facilitators; the length and temporal stability of facilitation cascades; variations in species interactions within cascades across environmental gradients; and the role of rhodolith beds as climate refugia. Addressing these research priorities will allow the development of evidence-based policy decisions and elevate rhodolith beds within marine conservation strategies.
... Brittany has been extensively studied over the last decade and is well known for being a diversity hotspot characterised by various intertidal and subtidal habitats (Gallon et al. 2017, Boyé et al. 2019, Hily et al. 2022, Helias & Burel 2023, Toumi 2023. This study aimed to estimate the diversity associated with Breton sandy beaches through a long-term monitoring program. ...
Although knowledge of sandy beaches has increased recently, the benthic diversity of macrotidal sandy beaches in the northeastern Atlantic Ocean (more specifically, the western Channel and the northern Bay of Biscay) is poorly known. Here, we present a regional-scale account of the species diversity, both observed and estimated, of the macrobenthic fauna of Brittany based on an analysis of a species-level data set from 18 sandy beaches in Brittany that were sampled annually for 13 yr on the lower shore. In total, 526 species were identified, including 210 Annelida, 167 Arthropoda, 103 Mollusca, 19 Echinodermata and 27 species of other phyla. Four distinct habitats were distinguished based on their benthic communities and characterised using environmental variables. Sediment heterogeneity appeared to enhance diversity, as heterogeneous muddy sand harboured significantly more species than (muddy) fine sand. The role of environmental variables as structuring factors of benthic communities was investigated using redundancy analysis and variance partitioning. Beach morphodynamics and sediment structure explained most diversity variations (25.40 and 24.91%, respectively) followed by wave characteristics (13.46%).
Finally, we offer some habitat-specific reference values regarding species richness and the Shannon index for M-AMBI computation during Water Framework Directive and Marine Strategy Directive evaluations for a more reliable characterisation of the ecological status of sandy beaches.
... These habitats have a worldwide distribution and typically thrive in shallow waters where conditions of light, temperature and sedimentation are favourable for photosynthetic, respiratory and calcification processes (Riosmena-Rodriguez et al., 2016). Coralline algae are recognized as bioengineers, forming complex three-dimensional habitats that foster highly diverse macroalgal communities and serve as nursery grounds and shelter for a wide range of invertebrates and fishes, including commercially important species (Barbera et al., 2003;Hall-Spencer, 1998;Helias & Burel, 2023;Neill et al., 2015;Nelson, 2009;Peña et al., 2014;Sciberras et al., 2009;Stelzer et al., 2021;Teichert, 2015). Additionally, maerl beds are one of the most important producers of calcium carbonate in temperate marine environments, thus exerting a significant role in the global carbon cycle within shallow coastal waters (Tuya et al., 2023;van der Heijden & Kamenos, 2015). ...
1. Effluents resulting from fish farming activities can alter the structure and functioning of benthic ecosystems. In Norway, recent technological advances within the salmon industry have facilitated the expansion of aquaculture into shallower locations, leading to additional pressures upon coastal habitats.
2. Maerl/rhodolith beds are important bioengineers in coastal waters—supporting highly diverse associated macrofaunal communities—and are likely to be particularly at risk.
3. This study aims to investigate the environmental changes induced by fish farms in their vicinity and their impact on the structure and functioning of maerl bed macrofaunal communities.
4. High dissolved nutrients and organic enrichment levels were observed close to the cages, associated with lower live maerl cover.
5. Overall, the most substantial impact of salmon farms on macrofaunal communities was observed within 100 m from the cages. Nevertheless, changes in the structure and functioning of assemblages were evidenced up to 300 m.
6. In the vicinity of the cages, communities were characterized by the dominance of endobenthic subsurface deposit feeders and opportunistic species, notably the polychaetes Chaetozone sp., Capitella sp. and Scoloplos armiger. Conversely, sites situated farther away from the cages exhibited higher abundances of epibenthic taxa, including crawlers, grazers and species sensitive to organic enrichment.
7. Sites unaffected by the presence of fish farms were described by high abundances of the ophiuroid Ophiura robusta, the polychaete Proclea graffi and ostracods, reflecting more favourable environmental conditions.
8. Such changes in macrofaunal communities highlight the vulnerability of maerl beds to the impacts of aquaculture, thus emphasizing the importance of rigorous site selection when establishing new fish farming facilities.
... maiteae (Santos et al., 2016), and several endemic coral (Cavalcanti et al., 2013;Pereira-Filho et al., 2015Amado-Filho et al., 2016;Negrão et al., 2021) and fish species . In the Mediterranean, the endemic deep-water kelp Laminaria rodriguezii (Barbera et al., 2003) and several species of endemic sponges (Longo et al., 2020) can be found on rhodolith beds, while in the NE-Atlantic the rare kelp L. ochroleuca and several rare rhodolith-associated seaweeds have been recorded (Peña et al., 2014;Braga-Henriques et al., 2022;Helias and Burel, 2023). At Cocos Island, Costa Rica, a new and endemic octocoral species, Rhodolitica oculta, has been found in association with rhodoliths (Breedy et al., 2021). ...
Global marine conservation remains fractured by an imbalance in research efforts and policy actions, limiting progression towards sustainability. Rhodolith beds represent a prime example, as they have ecological importance on a global scale, provide a wealth of ecosystem functions and services, including biodiversity provision and potential climate change mitigation, but remain disproportionately understudied, compared to other coastal ecosystems (tropical coral reefs, kelp forests, mangroves, seagrasses). Although rhodolith beds have gained some recognition, as important and sensitive habitats at national/regional levels during the last decade, there is still a notable lack of information and, consequently, specific conservation efforts. We argue that the lack of information about these habitats, and the significant ecosystem services they provide, is hindering the development of effective conservation measures and limiting wider marine conservation success. This is becoming a pressing issue, considering the multiple severe pressures and threats these habitats are exposed to (e.g., pollution, fishing activities, climate change), which may lead to an erosion of their ecological function and ecosystem services. By synthesizing the current knowledge, we provide arguments to highlight the importance and urgency of levelling-up research efforts focused on rhodolith beds, combating rhodolith bed degradation and avoiding the loss of associated biodiversity, thus ensuring the sustainability of future conservation programs.
Share Link:
https://authors.elsevier.com/c/1hGaZB8ccyZih
... Plants of P. morrowii collected in Brittany can be found as epiliths in tidepools or on pontoons, growing up to 25-30 cm (Figure 8a), and as a floating mass of freeliving entangled filaments in marinas. The species was also found in intertidal maerl beds, growing on Lithothamnion corallioides (Helias and Burel 2023). In transverse section, plants of P. morrowii have a central cell surrounded by four periaxial cells (Figure 8d). ...
Non-indigenous seaweed species have been introduced to the coasts of Brittany, France for decades, with an increasing arrival rate since the 1970s due to both the introduction of the Pacific oyster and increased maritime traffic. In this study, seven species of red macroalgae originating from the Pacific Ocean were found in new locations around the coasts of Brittany between 2018 and 2022. The seaweed species belong to four different orders: Ceramiales (Antithamnion hubbsii, Polysiphonia morrowii, and Symphyocladiella dendroidea), Halymeniales (including Pachymeniopsis lanceolata and Polyopes lancifolius), Rhodymeniales (Botryocladia wrightii), and Gigartinales (Solieria sp.). The dispersal mode and putative invasive potential of each species were examined, and the species were described in terms of their macroscopic and microscopic appearance and habitat. These finds result from a combination of citizen science and long-term monitoring. Used together, these two approaches can aid in the detection of these species on other European coasts and in understanding their dispersion.
One of the various seaweed species with biostimulating properties is Lithothamnion sp., a calcareous seaweed recognized for its nutritional attributes. This review article aimed to gather information on Lithothamnion sp. and its applications in agricultural cultivation, focusing on identifying and analyzing its biostimulant effects. The practical use of this biostimulant in farming has been confirmed by studies highlighting its efficiency, which varies according to the source material (deposit and particle fraction), application methodology (dosage, methods and frequency) and specific crop (genotype and development stages). Lithothamnion sp. is notable for promoting vegetative growth and has established itself as an invaluable biostimulant in producing seedlings of various species. Its application, either via soil or by foliar methods, has led to improvements in the yield and quality of vegetables, fruits, oilseed crops, grains and forage plants. Although the underlying mechanisms need further investigation, the results suggest that Lithothamnion sp. contributes to amplifying photosynthesis, water-use efficiency and phytoalexin production.
KEYWORDS:
Coralline algae; rhodolite; biofertilizers
Maerl beds are ecologically important marine biogenic habitats founded on a few species of free-living coralline algae that aggregate and form highly complex rhodoliths. The high biodiversity found in these habitats have been mainly justified by the structural complexity that they provide. However, few attempts to quantify this complexity have been made. Maerl species distribution, density, rhodolith growth forms, and shapes vary with environmental conditions. Hydrodynamics and depth have been shown to drive morphology. Using species-specific metrics such as sphericity and branching density, as well as diameter and fractal dimension at the rhodolith level, and maerl density at the habitat level, we quantified the habitat complexity within ten maerl beds at a regional scale (along ∼400 km of the coastline of Brittany in Western France). Using both long-term monitoring data and environmental models, we investigated how maerl habitat complexity varies among beds and which environmental conditions drive those differences. The effects of currents, exposure to wind-generated waves, temperature and sediment granulometry were evaluated. We confirmed variations in complexity in maerl beds at the habitat and rhodolith levels at local and regional scales, which might have ecological and conservational implications for their associated biodiversity. The analysed environmental conditions drive around a third of the variance in habitat complexity. Sediment granulometry is the main driver of maerl habitat complexity in Brittany, while the isolated effects of depth and hydrodynamics accounted for less than 5% of the variability each. Our results have important implications for paleoecology, and we suggest that maerl facies should be interpreted carefully. Our study provides a first attempt at explicitly quantifying maerl habitat complexity, and further contributes to the understanding of this fundamental ecological question.
En esta guía se describen las principales especies de macroalgas y fanerógamas marinas presentes en las costas del Mediterráneo occidental. Estos organismos pertenecen mayoritariamente a cuatro grandes grupos taxonómicos: las algas pardas o feofíceas, las algas rojas o rodófitos, las algas verdes o clorófitos, y las fanerógamas. Aunque el área abarcada por esta guía es únicamente el Mediterráneo occidental, el libro puede
ser utilizado con la debida precaución en todo el Mediterráneo puesto que la biota del conjunto es relativamente homogénea. Aun así, no se incluyen algunas especies, abundantes en la cuenca oriental, que están ausentes en la cuenca occidental.
In temperate and subarctic regions of the Northern Hemisphere, green algae of the genus Blidingia are a substantial and environment-shaping component of the upper and mid-supralittoral zones. However, taxonomic knowledge on these important green algae is still sparse. In the present study, the molecular diversity and distribution of Blidingia species in the German State of Schleswig-Holstein was examined for the first time, including Baltic Sea and Wadden Sea coasts and the offshore island of Helgo-land (Heligoland). In total, three entities were delimited by DNA barcoding, and their respective distributions were verified (in decreasing order of abundance: Blidingia marginata, Blidingia cornuta sp. nov. and Blidingia minima). Our molecular data revealed strong taxonomic discrepancies with historical species concepts, which were mainly based on morphological and ontogenetic characters. Using a combination of molecular, morphological and ontogenetic approaches, we were able to disentangle previous mis-identifications of B. minima and demonstrate that the distribution of B. minima is more restricted than expected within the examined area. Blidingia minima, the type of the genus name Blidingia, is epitypified within this study by material collected at the type locality Helgoland. In contrast with B. minima, B. marginata shows a higher phenotypic plasticity and is more widely distributed in the study area than previously assumed. The third entity, Blidingia cornuta sp. nov., is clearly delimited from other described Blidingia species, due to unique characters in its ontogenetic development and morphology as well as by its tufA and rbcL sequences.
Maerl beds form highly complex three-dimensional biogenic habitats that support a very important biodiversity. These habitats are very vulnerable and the negative impact of bivalve dredging on these ecosystems is well known. This study aims to experimentally assess the impact of two fishing intensities and three dredges commonly used in the Bay of Brest (north-western France) on maerl beds using a BACI (Before – After – Control – Impact) approach on a one-year time period. Sampling occurred from April 2016 to April 2017, on four occasions and at eight zones, which resulted in 480 photographs of quadrats and 288 grab samples. One-way Anova or Kruskal-Wallis tests were used to test for differences on biodiversity and habitat structure descriptors and a non-metric multidimensional scaling analysis was performed to assess the habitat temporal evolution. The initial impact of each gear and the time to recover were estimated using a weighted linear mixed-effects model with restricted maximum-likelihood estimator. The results were consistent with the literature and showed an immediate impact of dredging resulting in increased mud cover and loss in species richness and density of individuals. The queen scallop dredge was responsible for the largest depletion of both abundance and species richness followed by the clam dredge and the king scallop dredge. Significant impacts of the experimental dredging were still visible after one year and estimated times of recovery all exceeded 1.5 years. At high fishing intensity, the pressure level appeared as the principal structuring factor of the maerl habitat while at low intensity the impacts were mostly dependant on the gears used. Considering the rate at which fishing activities occur in the Bay of Brest (every 6 months), these results question (1) the ability of maerl beds to recover from such perturbations and (2) the current techniques for the assessment of bivalve dredging impacts. It therefore indicates the need to take into consideration fishing intensity and gears’ specificities when dealing with management measures.
La crépidule (Crepidula fornicata) est une espèce invasive des côtes européennes. Hermaphrodite protandre, cette espèce grégaire forme des chaines d’individus qui s’accumulent en forte densité sur les fonds. Longtemps considérée comme un envahisseur néfaste, la crépidule est aussi un ingénieur de l’écosystème, modifiant physiquement et biologiquement son habitat. Elle constitue un modèle biologique pour étudier comment les espèces invasives et ingénieurs peuvent structurer et modifier l’écosystème qu’elles colonisent. Dans le cadre de cette thèse, ces effets ont été examinés à travers le fonctionnement trophique des habitats à crépidules, en lien notamment avec la production primaire benthique. Il a été mis en évidence expérimentalement une stimulation du microphytobenthos (MPB) subtidal grâce à l’activité biologique de la crépidule. La niche trophique de C. fornicata a été redéfinie suite à la découverte de la présence de sphérules de carbonates dans ses tissus, surestimant la contribution du MPB dans son régime alimentaire. L’utilisation de différents marqueurs trophiques (pigments, acides gras, isotopes) a révélé que les jeunes individus mobiles étaient susceptibles de brouter le MPB associé au biofilm présent sur les coquilles. Les adultes sessiles, sont des filtreurs opportunistes, où la matière détritique mais aussi du MPB contribuent à leur régime alimentaire. L’analyse de différents suspensivores inféodés à cet habitat, a démontré que la crépidule n’était pas un compétiteur trophique pour des espèces commercialement importantes (pétoncle noir et huître plate) dû à leurs mécanismes de sélection trophique. À l’échelle du réseau trophique, la crépidule en très forte densité peut conduire à une homogénéisation du réseau trophique global dû à l’enrichissement en matière organique. Au contraire, un banc mort de crépidules montre une complexité trophique similaire à celle d’un banc de maërl, écosystème à forte biodiversité. Cette thèse, en plus d’avoir caractérisé le fonctionnement trophique des bancs de crépidules, montre qu’une espèce invasive, en facilitant certains compartiments biologiques (MPB, suspensivores), peut contribuer à la richesse d’un écosystème comme celui la rade de Brest.
The use of molecular tools often shows that regional species diversity differs from what we know from assessments based on morphological identifications. The seaweed flora of the British Isles has been well established over a long period from foundational work published during the xviii-xix centuries to more recent revisions based on molecular tools. The application of these tools (primarily rbcL sequences), alongside morphological observations, to the study of the tribes Streblocladieae and Polysiphonieae in the British Isles led us to three new records of species, as well as two species that require taxonomic revision. Polysiphonia morrowii Harvey, P. delicata Díaz-Tapia and Vertebrata tripinnata (Harvey) Kuntze are recorded for the first time in the British Isles. Finding P. morrowii and P. delicata, which are considered introduced or cryptogenic in Europe, is not surprising and these new records improve our knowledge of their distribution. Vertebrata tripinnata had previously been recorded in southern Europe and collecting it on the northern coast of Ireland considerably expands its known distribution. We also found that rbcL and cox1 sequences for the morphologically divergent V. simulans (Harvey) Kuntze and P. ceramiiformis P.Crouan & H.Crouan(which has never been transferred to Vertebrata) from the British Isles were identical, and we propose to reduce the latter to a synonym of the former. Finally, we found two pseudo-cryptic species represented in specimens morphologically assigned to V. fruticulosa (Wulfen) Kuntze, and we propose the resurrection of V. martensiana (Kützing) Piñeiro-Corbeira, Maggs & Díaz-Tapia. This work further evidences the relevance of reassessing red algal species diversity using molecular tools, even in regions where floras are considered well-known.
Made up of calcareous coralline algae, maerl beds play a major role as ecosystem engineers in coastal areas throughout the world. They undergo strong anthropogenic pressures, which may threaten their survival. The aim of this study was to gain insight into the future of maerl beds in the context of global and local changes. We examined the effects of rising temperatures (+3ºC) and ocean acidification (-0.3 pH units) according to temperature and pH projections (i.e. the RCP 8.5 scenario), and nutrient (N and P) availability on three temperate maerl species (Lithothamnion corallioides, Phymatolithon calcareum, Lithophyllum incrustans) in the laboratory in winter and summer conditions. Physiological rates of primary production, respiration and calcification were measured on all three species in each treatment and season. The physiological response of maerl to global climate change was species-specific and influenced by seawater nutrient concentrations. Future temperature-pH scenario enhanced maximal gross primary production rates in P. calcareum in winter and in L. corallioides in both seasons. Nevertheless, both species suffered an impairment of light harvesting and photo-protective mechanisms in winter. Calcification rates at ambient light intensity were negatively affected by the future temperature-pH scenario in winter, with net dissolution observed in the dark in L. corallioides and P. calcareum under low nutrient concentrations. Nutrient enrichment avoided dissolution under future scenarios in winter and had a positive effect on L. incrustans calcification rate in the dark in summer. In winter conditions maximal calcification rates were enhanced by the future temperature-pH scenario on the three species, but P. calcareum suffered inhibition at high irradiances. In summer conditions, the maximal calcification rate dropped in L. corallioides under the future global climate change scenario, with a potential negative impact on CaCO3 budget for maerl beds in the Bay of Brest where this species is dominant. Our results highlight how local changes in nutrient availability or irradiance levels impact the response of maerl species to global climate change and thus point out how it is important to consider other abiotic parameters in order to develop management policies capable to increase the resilience of maerl beds under the future global climate change scenario.
Continuando con los estudios para la actualización del inventariado de la flora bentónica marina del Atlántico Ibérico.En este trabajo se incluye nueva información de distribución para 18 especies (3 Cyanobacteria, 9 Rhodophyta, 4 Ochrophyta, 2 Chlorophyta) de algas bentónicas marinas, recolectadas en el intermareal y submareal de 46 localidades del atlántico ibérico norte. Atendiendo a la distribución de las especies recolectadas, cabe destacar una nueva cita para Europa (Plocamium cf. ovicorne), 3 nuevas citas para Galicia (Calothrix consociata, Lyngbya martensiana y Centroceras gasparrinii), 14 nuevas citas provinciales y 8 segundas citas provinciales. Además dos especies (Spermothamnion strictum y Punctaria plantaginea) son excluidas de la flora de Galicia después, de estudiar el único material de herbario testigo de las citas.et al. 2005a-b, 2006, 2008, 2012, 2014, 2015, 2016), se presentan nuevas citas y correcciones florísticas que completan el actual inventario de la biodiversidad marina de Galicia (Bañón 2017). La mayoría de las muestras se conservaron en formalina al 4% y la conservación definitiva se realizó en pliegos de herbario, depositados en el herbario de la Universidad de Santiago de Compostela (SANT), así como en preparaciones semipermanentes en Karo®. También se estudiaron pliegos de herbario del Nationaal Herbarium Nederland, para la verificación o corrección de citas antiguas. Paralelamente, se conservaron fragmentos sin formolar de algunas especies en gel de sílice para estudios moleculares.
The present study gives an updated list of macroalgal species from the Channel and Atlantic coasts of France. It includes a total of 707 macroalgal species with their taxonomic treatment.
Rhodoliths are the main hard substrata for the attachment of benthic macroalgae in the NW Gulf of Mexico rubble habitats that are associated with salt domes, unique deep bank habitats at ~50–90 m depth on the continental shelf offshore Louisiana and Texas. With the advent of additional sequencing technologies, methodologies for biodiversity assessments are now rapidly shifting to DNA metabarcoding, i.e., High Throughput Sequencing (HTS) of environmental DNA mixtures with standardized molecular markers, such as 16S V4, for rapid, cost-effective biodiversity measurement. We newly tested 16S V4 metabarcoding on endolithic portions of mesophtic rhodoliths exhibiting low phototroph colonization that revealed a hidden, cryptic algal diversity targeting spores, propagules, and unsuspected life history stages. We explored cryo-SEM as a potentially more informative method than regular SEM to minimize artifacts of sample preparation in the study of endolithic cell inclusions which brought to light a suite of microalgal stages. We were able to differentiate floridean starch from cellular inclusions. We associated the effect of anatomical growth pattern on presence or absence of cellular inclusions in biogenic rhodoliths. Analyses of combined 16S V4 metabarcodes and 16S Sanger sequences of two red algal orders, the Halymeniales and Bonnemaisoniales, increased the established record of diversity in the region. We view rhodoliths as marine biodiversity hotspots that may function as seedbanks, temporary reservoirs for life history stages of ecologically important eukaryotic microalgae, and macroalgae or as refugia for ecosystem resilience following environmental stress.
Abstract
1.
Maerl beds occur worldwide and are formed by an accumulation of unattached calcareous red algae (Rhodophyta).
2.
Maerl‐forming algae grow in a superficial living layer on sediments within the photic zone.
3.
Maerl beds are spatially complex habitats with a high degree of species and trophic group diversity.
4.
The European Commission's ‘Habitats Directive’ mandates the conservation management of two of the main European maerl‐forming species, Phymatolithon calcareum and Lithothamnion corallioides.
5.
Mediterranean maerl beds are to be considered for inclusion in national inventories of sites of conservation interest, as required by the SPABIM Protocol of the Barcelona Convention.
6.
In spite of their importance, and the requirement for their conservation management, European maerl grounds suffer a variety of anthropogenic perturbations including direct exploitation through extraction, fishing impacts and chemical pollution by organic matter and excess nutrients.
7.
The ecology of northeast Atlantic and Mediterranean maerl beds has received little attention, in contrast to other marine communities (e.g. kelp forests, sea‐grass meadows).
8.
Key conservation and management measures proposed include: the recognition that maerl beds are non‐renewable resources and cannot sustain direct exploitation; prohibitions on the use of towed gear on maerl grounds; moratoria on the issue of further permits for the siting of aquaculture units above maerl grounds; monitoring of existing exploited or impacted maerl beds; the designation of ‘no‐take’ reserves; measures to limit the impacts that might affect water quality above maerl beds; a programme of monitoring of the ‘health’ of European maerl beds; an awareness campaign on the biological importance of maerl beds; a higher conservation status for maerl habitats and maerl‐forming species in European legislation; and further research on maerl ecosystems.
Predicted ocean acidification and warming are likely to have major implications for marine organisms, especially marine calcifiers. However, little information is available on the response of marine benthic communities as a whole to predicted changes. Here, we experimentally examined the combined effects of temperature and partial pressure of carbon dioxide (pCO2) increases on the response of maerl bed assemblages, composed of living and dead thalli of the free-living coralline alga Lithothamnion corallioides, epiphytic fleshy algae, and grazer species. Two 3-month experiments were performed in the winter and summer seasons in mesocosms with four different combinations of pCO2 (ambient and high pCO2) and temperature (ambient and +3 ∘C). The response of maerl assemblages was assessed using metabolic measurements at the species and assemblage scales. This study suggests that seasonal variability represents an important driver influencing the magnitude and the direction of species and community response to climate change. Gross primary production and respiration of assemblages was enhanced by high pCO2 conditions in the summer. This positive effect was attributed to the increase in epiphyte biomass, which benefited from higher CO2 concentrations for growth and primary production. Conversely, high pCO2 drastically decreased the calcification rates in assemblages. This response can be attributed to the decline in calcification rates of living L. corallioides due to acidification and increased dissolution of dead L. corallioides. Future changes in pCO2 and temperature are likely to promote the development of non-calcifying algae to the detriment of the engineer species L. corallioides. The development of fleshy algae may be modulated by the ability of grazers to regulate epiphyte growth. However, our results suggest that predicted changes will negatively affect the metabolism of grazers and potentially their ability to control epiphyte abundance. We show here that the effects of pCO2 and temperature on maerl bed communities were weakened when these factors were combined. This underlines the importance of examining multi-factorial approaches and community-level processes, which integrate species interactions, to better understand the impact of global change on marine ecosystems.
The taxonomy of the Cladophoraceae, a large family of filamentous green algae, has been problematic for a long time due to morphological simplicity, parallel evolution, phenotypic plasticity and unknown distribution ranges. Partial large subunit (LSU) rDNA sequences were generated for 362 isolates, and the analyses of a concatenated dataset consisting of unique LSU and small subunit (SSU) rDNA sequences of 95 specimens greatly clarified the phylogeny of the Cladophoraceae. The phylogenetic reconstructions showed that the three currently accepted genera Chaetomorpha, Cladophora and Rhizoclonium are polyphyletic. The backbone of the phylogeny is robust and the relationships of the main lineages were inferred with high support, only the phylogenetic position of both Chaetomorpha melagonium and Cladophora rupestris could not be inferred unambiguously. There have been at least three independent switches between branched and unbranched morphologies within the Cladophoraceae. Freshwater environments have been colonised twice independently, namely by the freshwater Cladophora species as well as by several lineages of the Rhizoclonium riparium clade. In an effort to establish monophyletic genera, the genera Acrocladus and Willeella are resurrected and two new genera are described: Pseudorhizoclonium and Lubrica. This article is protected by copyright. All rights reserved.
Hill numbers (or the effective number of species) have been increasingly used to quantify the species/taxonomic diversity of an assemblage. The sample‐size‐ and coverage‐based integrations of rarefaction (interpolation) and extrapolation (prediction) of H ill numbers represent a unified standardization method for quantifying and comparing species diversity across multiple assemblages.
We briefly review the conceptual background of H ill numbers along with two approaches to standardization. We present an R package iNEXT (i N terpolation/ EXT rapolation) which provides simple functions to compute and plot the seamless rarefaction and extrapolation sampling curves for the three most widely used members of the H ill number family (species richness, S hannon diversity and S impson diversity). Two types of biodiversity data are allowed: individual‐based abundance data and sampling‐unit‐based incidence data.
Several applications of the iNEXT packages are reviewed: (i) Non‐asymptotic analysis: comparison of diversity estimates for equally large or equally complete samples. (ii) Asymptotic analysis: comparison of estimated asymptotic or true diversities. (iii) Assessment of sample completeness (sample coverage) across multiple samples. (iv) Comparison of estimated point diversities for a specified sample size or a specified level of sample coverage.
Two examples are demonstrated, using the data (one for abundance data and the other for incidence data) included in the package, to illustrate all R functions and graphical displays.
We quantitatively assessed the relative contribution of the rhodolith form of Lithothamnion muelleri, a likely foundation species, to macroorganism diversity in a community also inhabited by the large fucalean Sargassum horridum at a site near Cabo Los Machos at the mouth of Bahía Concepción, Baja California Sur, Mexico. The composition and abundance of seaweeds, epibenthic invertebrates, and fish were estimated in March and October 2003, and invertebrates within rhodoliths (cryptofauna) in March 2003. Rhodoliths and Sargassum horridum had the highest cover of all organisms within the 0.5-km2, 2-8-m-deep cobble-sand site. A total of 29 species of seaweeds, 40 taxa of benthic invertebrates, and 33 species of fish were sampled in transects and quadrats. Macroalgal and fish diversity were similar between sampling times as a result of loss and replacement of taxa, but benthic invertebrate diversity declined without replacement from March to October. Rhodolith cover was similar at both sampling times. The cover and density of S. horridum were highly seasonal, and the non-rhodolith flora changed from abundant S. horridum (35% cover) in March to abundant red algal turf in October (22% cover). The sea urchin Arbacia incisa, tunicates, and polychaetes were the most abundant epibenthic invertebrates in March, but declined by October, the former to zero. Grunts (Haemulon maculicauda) and porgies (Calamus brachysomus) were the most abundant fish at both sampling times, but there were large temporal changes in some other species, especially schooling fishes. Rhodolith density in March was 24 ind m-2, with numerous individuals >8 cm diameter. Fifteen rhodoliths from a range of size classes contained 114 cryptofaunal taxa with an average of 40 taxa /individual in the largest rhodoliths. These results show the importance of rhodolith habitat to diversity, the large temporal changes in some assemblages, and the exceptionally high diversity of this subtropical community.
A revision of the check-list of the red (Rhodophyta), green (Chlorophyta) and brown (Ochrophyta, Phaeophyceae) seaweeds of Britain has been compiled and revealed 644 taxa, mostly at species level but including infraspecific taxa: 348 reds, 110 greens and 186 browns. There were 30 additions to the list, notably five newly described species and five new non-native additions. In addition to the check-list, an updated list of non-native species was compiled based on a stringent review of the available evidence. We have listed 31 non-native species (~5% of the flora), although the numbers may be considerably higher and probably include species that are effectively naturalized and perceived to be part of the indigenous flora. The check-list is discussed in relation to the impact of molecular techniques on the identification, taxonomy and phylogeny of species, and points to the need for a comprehensive, in-depth study on the identity and relationships of the seaweeds of Britain.
DNA sequences from type material in the non-geniculate coralline genus Lithophyllum were used to unambiguously link some European species names to field-collected specimens, thus providing a great advance over morpho-anatomical identification. In particular, sequence comparisons of rbcL, COI and psbA genes from field-collected specimens allowed the following conclusions: The generitype species, L. incrustans, occurs mostly as subtidal rhodoliths and crusts on both Atlantic and Mediterranean coasts, and not as the common, NE Atlantic, epilithic, intertidal crust reported in the literature. The heterotypic type material of L. hibernicum was narrowed to one rhodolith belonging in Lithophyllum. As well as occurring as a subtidal rhodolith, L. hibernicum is a common, epilithic and epizoic crust in the intertidal zone from Ireland south to Mediterranean France. A set of four features distinguishes L. incrustans from L. hibernicum, including epithallial cell diameter, pore canal shape of sporangial conceptacles and sporangium height and diameter. An rbcL sequence of the lectotype of Lithophyllum bathyporum, which was recently proposed to accommodate Atlantic intertidal collections of L. incrustans, corresponded to a distinct taxon hitherto known only from Brittany as the subtidal, bisporangial, lectotype, but also occurs intertidally in Atlantic Spain. And specimens from Ireland and France morpho-anatomically identified as L. fasciculatum and a specimen from Cornwall likewise identified as L. duckerae were resolved as L. incrustans and L. hibernicum, respectively.
Maerl beds worldwide face habitat destruction (e.g. from dredging, fishing gear and fish farms), the combined pressures of ocean warming and acidification, and the spread of invasive species. Maerl beds have high conservation status in European legislation, yet their associated flora is poorly known. Here we evaluate the known macroalgal diversity of NE Atlantic maerl beds from Svalbard to Portugal. Maerl beds occur from the low intertidal down to 51 m in the clearest waters. To date, 349 macroalgal species have been recorded on maerl in the NE Atlantic (67% are Rhodophyta), a remarkable 30% of the total seaweed diversity in this region. Eleven non-native species have been recorded on Atlantic European maerl beds, the most widely distributed being phases of Bonnemaisonia hamifera (“Trailliella intricata”), Asparagopsis armata (“Falkenbergia rufolanosa”), Antithamnionella spirographidis and Heterosiphonia japonica. The flora of maerl beds off Iceland and Norway is poorly known, but maerl beds off Britain, Ireland, France and Spain have been surveyed extensively and support several species that are maerl specialists (viz. Cruoria cruoriaeformis, Cladophora rhodolithicola, Gelidiella calcicola). Our observations of G. calcicola and Gelidium maggsiae are new records for Portugal. Maerl beds in the Algarve have many of the same macroalgal species as Mediterranean maerl beds but they are not as floristically diverse as those in Galicia because they are confined to deeper water. Our census provides a baseline that can be used to assess changes to these habitats over the coming years.
The most widely recorded maerl-forming species in the NE Atlantic are Lithothamnion corallioides, L. glaciale, L. tophiforme and Phymatolithon calcareum although maerl formed by Lithophyllum spp. is occasionally found. Here, we studied two of the forms (incrassata and complanata) described for Lithophyllum fasciculatum that we collected in Brittany. Samples were identified using molecular techniques (DNA barcoding) and examined with scanning electron microscopy (SEM). Lithophyllum fasciculatum were globular to sub-globular unattached thalli up to 10 cm in diameter that formed maerl beds at 0 to 2 m depth in the eastern part of the Bay of Brest. All anatomical features matched the literature. Reproductive structures were only observed in one encrusting specimen overgrowing Mimachlamys varia in the Bay of Brest. Other than in Brittany, L. fasciculatum maerl was recorded in Kingstown Bay, Ireland, at 0-3 m depth. In the Irish beds, L. fasciculatum co-occurs with the closely similar maerl species Lithophyllum dentatum. The taxonomy of NE Atlantic maerl-forming Lithophyllum spp. continues to be messy and their ecology has not been studied yet; we are only certain that they are rare and warrant urgent conservation focus.
In recent years (2007–2009), the distribution and associated flora of maerl beds in southern Portugal (Algarve) were investigated by dredging and SCUBA diving (12–30 m depth). The present work provides the first data on the non-coralline crustose flora associated with maerl beds in Portugal. Peyssonnelia bornetii is a new record for Atlantic European coasts, and new records for Portugal are “Rhododiscus pulcherrimus” (sporophyte phase of Atractophora hypnoides), Contarinia peyssonneliaeformis, “Cruoria rosea” (sporophyte phase of Halarachnion ligulatum), Peyssonnelia armorica, and “Aglaozonia chilosa” (sporophyte phase of Cutleria chilosa). In addition, the records of three other species (Hildenbrandia crouaniorum, Peyssonnelia dubyi, and Peyssonnelia harveyana) completed the distribution gap between the North Iberian Peninsula and the Macaronesian region. The female and carposporangial structures of C. peyssonneliaeformis and P. bornetii are described for the first time. The diversity and species composition observed are compared with previous studies from maerl beds in the northwestern Iberian Peninsula (Galicia) and neighboring areas in the Atlantic Ocean and Mediterranean Sea. In order to facilitate and promote further studies of the crustose flora of subtidal habitats along European coasts, an identification key is provided for the 26 crustose taxa associated with maerl and gravel beds of the Atlantic coast of the Iberian Peninsula.
We studied crustose seaweeds associated with subtidal maërl beds and gravel bottoms in the Galician rías (NW Iberian Peninsula). Each species is described as well as its habitat and occurrence in maërl beds and gravel bottoms. We con-firmed the great crustose species richness associated with European Atlantic maërl beds. We report a new species for the Atlantic Ocean (Contarinia peyssonneliaeformis) and six new records for the Iberian Peninsula (Atractophora hyp-noides stage ''Rhododiscus pulcherrimus'', Peyssonnelia immersa, Scytosiphon lomentaria stage ''Microspongium gelatinosum'', Petroderma maculiforme, Pseudolithoderma roscoffense and Phycocelis foecunda). Peyssonnelia armo-rica is a new record for the Atlantic Iberian Peninsula and Peyssonnelia harveyana is a new record for the Galician coast. We provide for the first time observations on sper-matangial structures in Cruoria cruoriaeformis occurring on the Atlantic Iberian Peninsula. The Galician crustose algal flora of subtidal maërl beds and gravel bottoms is increased up to 23 species (15 Rhodophyta and 8 Ochrophyta). Peys-sonnelia rubra is excluded from the Galician flora.
Abstract The CIESM Atlas of Exotic Species covers the marine macrophytes. A total of 110 species (22 Chromobionta, 71 Rhodobionta, 16 Chlorobionta and 1 Magnoliophyta) are listed. Several other exotic species only known,on the NE Atlantic coast are listed in the Annex. The kinetics of species introduction into the Mediterranean Sea is exponential since the late 19, century. As far as the number,of introduced macrophytes is concerned, the main donor area is the Indo-Pacific region, and the main vectors of introduction are the shellfish aquaculture, followed by the ship traffic and the Suez Canal. Diagnostic features, biological information, references and a distribution map are given for each species. Keywords : Algae, Species Introduction, Suez Canal, Aquaculture. The CIESM Atlas of Exotic Species is the first attempt to provide a com- prehensive, group by group, survey of recent marine "immigrants" in the Mediterranean Sea, which is witnessing drastic and rapid changes in its biota. The present volume, which follows the publication of the first three Atlases (Fish, Crustaceans decapods/stomatopods and Molluscs), covers the marine macrophytes. As far as Macrophytes are concerned, the Mediterranean is the sea harbouring the greatest number,of exotic species worldwide. In this volume, we drew a list as broad as possible of the exotic macroflora on the basis of recent checklists and unpublished data [1-6], considering as "exotic" a species being a relative newcomer to the Mediterranean Sea (e.g.: not having appeared before 1869, date of the opening of the Suez Canal, for species originating from the Red Sea). Sev- eral species reported before this date and assumed,to be native by some authors [2] (e.g.: Asparagopsis taxiformis) have nevertheless been in- cluded because recent and fast changes in their Mediterranean distribution give evidence to a recent introduction of either a cryptic species similar to the Mediterranean one or an exotic genotype from remote population. A total of 110 species (22 Chromobionta, 71 Rhodobionta, 16 Chlorobionta and 1 Magnoliophyta) constitute the main core of this CIESM Atlas. Con- sidering the high risk of secondary,introduction into the Mediterranean Sea of exotic species present on the NE Atlantic coast, 12 other exotic species until now unknown,in the Mediterranean are briefly listed in the Annex. Each species is classified within the following categories accord-
A detailed study of the type specimen of Plocamium cartilagineum and other original material of European species of Plocamium revealed that the nomenclatural reorganization proposed by Saunders & Lehmkuhl in 2005 must be revised. The main consequences of the new interpretation are: (1) the use of Plocamium lyngbyanum to name their molecular entity EUR1 (previously considered to be equivalent to P. cartilagineum s.s.); and (2) adopting P. cartilagineum for their molecular entity EUR2, which renders P. subtile Kützing a taxonomic synonym. Using a combination of morphological, anatomical and molecular information (barcoding), we conclude that the colour and consistency of the thallus, the number of ramuli per series, the morphology and arrangement of the tetrasporangial stichidia, the length of the tetrasporangia, and the type of habitat are the most reliable characters of classical taxonomy for discriminating between the species of Plocamium occurring in northern Europe.
Gelidiella calcicola sp. nov. (Gelidiales, Gelidiaceae) is described from plants growing on loose-lying subtidal coralline algae and shells on southern, western and northern shores of the British Isles, and from Roscoff in Brittany, France. The species forms narrow, creeping axes attached at intervals by peg-like rhizoidal holdfasts. Irregularly pinnate branches arise at the points of attachment, arc downwards, and become attached and pinnately branched. No erect axes are formed; in all other described species of the genus Gelidiella at least some erect axes are formed from the creeping base. Internal rhizines, considered to be characteristic of all the genera of the Gelidiales except Gelidiella, are present in the medulla, but only at the attachment points. Surface cortical cells are large and usually arranged in chevron-like transverse rows. Tetrasporangia, formed only in the winter months, occur in lateral stichidia in chevron-like rows of 8–10 per row; they are spherical and apparently tetrahedrally or irregularly divided. Gametangial and carposporangial plants have not been found; these are known in only one species of the genus. Attempts to induce reproduction in vegetatively isolated plants in culture by subjecting them to a wide range of temperature and photoperiodic regimes in various enriched sea-water media strengths were unsuccessful. The new species is compared with Gelidium pusillum from the British Isles, and with the 21 previously described species of Gelidiella. The status of the family Gelidiellaceae is assessed and it is concluded that it should be merged with the Gelidiaceae. Some doubts are expressed as to the validity of the criteria used to delimit the genus Gelidiella.
A study of three shallow Atlantic maërl beds (3–6 m depth) in NW Spain (Galicia) sampled beds every 1.5 months for a year. At each study site, temporal variation in the associated flora and two parameters, temperature and photosynthetic photon flux density (PPFD), were recorded in situ and means were calculated for each period. The range of mean periodic temperatures was 11.9–17.5°C, increasing in late spring–summer and decreasing to <12°C in winter. Mean PPFD was 24–160 µmol photons m−2 s−1; the maximum was recorded in spring (up to 571 µmol photons m−2 s−1). The variation in temperature and PPFD was correlated with seasonal changes in the flora. The composition of the associated flora at Benencia Island (Ría de Arousa) showed a strong correlation with day length while at Tambo Island (Ría de Pontevedra), it was correlated with temperature. A total of 127 species was recorded (in seven functional groups), annual algae being the most abundant group. The highest species richness and total percentage cover occurred in spring and summer, and the lowest in autumn and winter. Significant seasonal differences were detected at each site, particularly between summer and autumn–winter, due to variation in cover of the foliose species Ulva rigida and Dictyota dichotoma. We propose that future monitoring of European Atlantic maërl beds should include several study areas and two sampling seasons (preferably summer and late autumn–winter).
The distribution, abundance and feeding behaviour of sea urchins (Paracentrotus
lividus,
Psammechinus
miliaris,
Sphaerechinus
granularis) and the macro-algal biomass were assessed in two maerl beds within a north-east Atlantic coastal ecosystem (Bay of Brest, Brittany, France). To study the possible control of herbivorous sea urchins on the macrophytic algae, one maerl bed under the influence of urban sewage (northern site) was compared to one less influenced by urban and industrial outlets (southern site). Macrophytic biomass in the northern site was estimated as 40-fold higher than in the southern site where sea urchins were, on average, 38-times more numerous. Preliminary results support the hypothesis that grazing of sea urchin, even in low densities, can be a factor regulating the macrophytic biomass on maerl beds except in too nutrient enriched environments. So in the northern basin of the Bay, data pointed out the role of anthropogenic impacts on macrophytic biomass increase which was concomitant with the progressive disappearance of sensitive herbivorous species like sea urchins, both processes result in change in the ecosystem.
In this review, using examples drawn from field observations or experimental studies, our goals are (i) to briefly summarize the major changes, in terms of species composition and functional structure, occurring in phyto and zoobenthic communities in relation to nutrient enrichment of the ecosystems; particular interest is given to the major abiotic and biotic factors occurring during the eutrophication process, (ii) to discuss the direct and indirect influences of benthic organisms on eutrophication and whether the latter can be controlled or favoured by benthos; most benthic species play a major role in the process of benthic nutrient regeneration, affecting primary production by supplying nutrients directly and enhancing rates of pelagic recycling; experimental studies have shown that the impact of benthic fauna on benthic–pelagic coupling and nutrient release is considerable. Thus, once the eutrophication process is engaged—that is, high organic matter sedimentation—it may be indirectly favoured by benthic organisms; benthos should always be considered in eutrophication studies, (iii) to evaluate the limits of our observations and data, highlighting the strong need for integrated studies leading to new concepts. Coastal ecosystems and benthic communities are potentially impacted by numerous human activities (demersal fishing, toxic contaminants, aquaculture…); in order to design strategies of ecosystem restoration or rehabilitation, we have to better understand coastal eutrophication and develop tools for quantifying the impacts; in order to achieve this goal, some possible directions proposed are: integrated studies leading to new concepts, model development based on these concepts and finally comparison of various ecosystems on a global scale.
In order to trace the introduction history of the western Pacific species Heterosiphonia japonica to and within Europe, information on distribution pattern of the species in Europe, oyster import and shipping activity has been compiled and analyzed. Additionally survival of fragments of H. japonica during a simulated journey in ballast water from Asia (Korea) to Europe (France) has been observed. The species was first recorded in Europe near an oyster culture area in Brittany (France) in 1984. Since then, it has spread quickly in Europe. The first introduction into Europe and secondary dispersal in southern Europe has most likely been trough movement of the Pacific oyster Crassostrea gigas. However, survival of H. japonica in temperatures varying from 14 to 28 degrees during a simulated 28-days journey in ballast water was demonstrated, and an introduction by ships from the Pacific Ocean may thus be considered as possible. Spreading of the species in the North Sea area and Scandinavia is most likely due to transport by ships, e.g. as attached to ships hulls, as fragments in ballast water or entangled e.g. in fishing gear.
1.Maerl beds occur worldwide and are formed by an accumulation of unattached calcareous red algae (Rhodophyta).2.Maerl-forming algae grow in a superficial living layer on sediments within the photic zone.3.Maerl beds are spatially complex habitats with a high degree of species and trophic group diversity.4.The European Commission's ‘Habitats Directive’ mandates the conservation management of two of the main European maerl-forming species, Phymatolithon calcareum and Lithothamnion corallioides.5.Mediterranean maerl beds are to be considered for inclusion in national inventories of sites of conservation interest, as required by the SPABIM Protocol of the Barcelona Convention.6.In spite of their importance, and the requirement for their conservation management, European maerl grounds suffer a variety of anthropogenic perturbations including direct exploitation through extraction, fishing impacts and chemical pollution by organic matter and excess nutrients.7.The ecology of northeast Atlantic and Mediterranean maerl beds has received little attention, in contrast to other marine communities (e.g. kelp forests, sea-grass meadows).8.Key conservation and management measures proposed include: the recognition that maerl beds are non-renewable resources and cannot sustain direct exploitation; prohibitions on the use of towed gear on maerl grounds; moratoria on the issue of further permits for the siting of aquaculture units above maerl grounds; monitoring of existing exploited or impacted maerl beds; the designation of ‘no-take’ reserves; measures to limit the impacts that might affect water quality above maerl beds; a programme of monitoring of the ‘health’ of European maerl beds; an awareness campaign on the biological importance of maerl beds; a higher conservation status for maerl habitats and maerl-forming species in European legislation; and further research on maerl ecosystems. Copyright © 2003 John Wiley & Sons, Ltd.
Maerl beds are composed of unattached red calcareous coralline algae. When located in shallow ecosystems, these calcareous macroalgae provide substrates for the development of fleshy epiphytic macroalgae, which contribute to the productivity of maerl beds. To assess the importance of their contribution, we estimated the primary production of the main taxa of fleshy epiphytic macroalgae (Solieria chordalis or Rhodomelaceae), growing in two distinct Lithothamnion corallioides maerl beds of the Bay of Brest (Brittany, France) characterized by different depths and incident irradiances. We estimated epiphytic algal photosynthetic parameters derived from photosynthesis-irradiance curves calculated from incubations in photo-respirometry chambers at different irradiances and in the dark. A comparison with results previously obtained in L. corallioides showed that, in the two studied maerl beds, there were no differences between maerl and its fleshy epiphytic macroalgae in terms of photo-acclimation to low irradiances. However, fleshy epiphytic macroalgae had higher photosynthetic efficiencies and photosynthetic rates per unit of biomass or chlorophyll a than the maerl species. Estimations of net primary production per surface area of maerl bed indicated that fleshy epiphytic macroalgae account for 25% of maerl bed productivity. Interactions between L. corallioides and its fleshy epiphytic macroalgae may affect their respective contributions. In the deepest maerl beds, shading by fleshy epiphytic macroalgae may have a detrimental impact on L. corallioides net primary production, whereas in the shallowest maerl beds, fleshy epiphytic macroalgae may protect maerl from photoinhibition under high irradiances.
The known distribution of seaweed species often requires updating after findings of new records outside the known range. The green algal family Halimedaceae is predominantly distributed in tropical and subtropical regions. Flabellia petiolata was considered endemic to the Mediterranean, but has also been recorded in the Canary Islands and Cape Verde. Recent marine biodiversity surveys by the citizen science group Seasearch in England led to the surprising discovery of plants that morphologically resemble F. petiolata. In this work we aimed to clarify the taxonomic identity of these specimens using morphological and molecular data. We obtained two rbcL and four tufA sequences for the English specimens that were identical to the two and nine sequences, respectively, available in GenBank for Mediterranean specimens of F. petiolata. This result is in agreement with morphological observations. Therefore, molecular and morphological data confirm that F. petiolata is established in southern England. Whether it is a new introduced species or a relict population is uncertain and we conclude that it is a cryptogenic species in England. This study provides an example of the contribution of citizen science to the better understanding of marine biodiversity.
Sequence data generated during a Canadian barcode survey (COI-5P) of the tribes Polysiphonieae and Streblocladieae, a large and taxonomically challenging group of red algae, revealed significant taxonomic confusion and hidden species diversity. Polysiphonia pacifica Hollenberg, P. paniculata Montagne, P. stricta (Dillwyn) Greville and Vertebrata fucoides (Hudson) Kuntze were all complexes of two or more genetically distinct yet overlooked species. One variety of P. pacifica was elevated to the rank of species as P. determinata (Hollenberg) Savoie & Saunders, stat. nov. Several new additions to the Canadian flora were recorded including P. kapraunii Stuercke & Freshwater and P. morrowii Harvey. Subsequent multi-gene (COI-5P, LSU and rbcL) phylogenetic analyses confirmed that the genus Polysiphonia Greville was polyphyletic, and currently assigned species resolved with many other genera. Polysiphonia sensu stricto was restricted to a group of species that formed a monophyletic lineage with the type, Polysiphonia stricta. Carradoriella P.C.Silva was resurrected based on the South African species Carradoriella virgata (C.Agardh) P.C.Silva. Species previously attributed to Polysiphonia were transferred to Carradoriella, Leptosiphonia and Vertebrata as well as to three new genera described here: Acanthosiphonia gen. nov., based on A. echinata (Harvey) comb. nov.; Eutrichosiphonia gen. nov. for E. confusa (Hollenberg) comb. nov. and E. sabulosia (B.Kim & M.S.Kim) comb. nov.; and Kapraunia gen. nov., which includes K. schneideri (Stuercke & Freshwater) comb. nov. and three additional species.
Large stands of free living (calcareous) coralline algae — called maerl beds — play a major role as ecosystem engineers in coastal areas throughout the world. They are also subject to strong anthropogenic pressures at global and local scales, which threaten their survival. However, the macroalgal epiphytes growing on maerl may benefit from these pressures, developing to the detriment of maerl algae. Here, we sought to gain insight into how maerl beds and their epiphytic algae are disturbed by variations in the local environment, and how these variations affect their capacity to respond to global change. In 2015, we monitored three maerl beds located in the Bay of Brest (Brittany, France). Sites with contrasting conditions were selected, with one station lying in a zone close to the harbor (northern basin S1) and two stations (S2 and S3) located in areas away from the main urban effluents but subject to other sources of local change: higher currents at S3 (PREVIMER Ocean Forecast) and higher sedimentation rates at S2 (Ehrhold et al., 2016). We observed significant temporal variations of physico-chemical parameters, on an annual but also on a daily basis. Results showed that S2 differentiated itself from the other stations, this station experienced higher fluctuations of salinity, nutrient concentrations and carbonate system parameters and hosted the lowest (living) maerl biomass (4.38 ± 1.54 kg DW m⁻²). S3 observed the highest living maerl biomass (14.56 ± 1.61 kg DW m⁻²) and the lowest non-calcareous epiphytic macroalgal abundance (0.1–7.9 g DW m⁻²). S1 displayed the highest heterogeneity in terms of living maerl biomass (it varied from 0.8 to 8.6 kg DW m⁻²), and the highest Chl a content. However, we did not record differences in terms of physico-chemical parameters between S1 and S3. No positive relationship was observed between nutrient enrichment and macroalgal epiphyte abundance, but epiphyte abundance was higher at stations with lower maerl biomass (S1 and S2) (mean value ranged from 4.6 to 49.0 g DW m⁻² at S1 and from 7.4 to 23.7 g DW m⁻² at S2). Our results highlight the importance of local changes on the development, survival and capacity to adapt to global change of maerl beds.
During our sampling surveys of the tribes Polysiphonieae and Streblocladieae in Spain and Australia, three previously unrecorded species were collected. Based on molecular and morphological evidence they are proposed as new species. Polysiphonia delicata sp. nov. and Polysiphonia radiata sp. nov. belong to the Polysiphonieae and share the synapomorphy in this group, rhizoids in open connection to pericentral cells. They differ from other members of this group either by rbcL sequence divergences greater than 4.5% and/or by morphological characters. The third species is placed in Melanothamnus (tribe Streblocladieae), as Melanothamnus pseudoforcipatus sp. nov. In agreement with the morphological delineation of the genus, it has plastids lying only on the radial walls of pericentral cells. It can be separated from most other members of the genus by having naked segments between trichoblasts or branches and/or rbcL sequence divergences higher than 4%. In Galicia, Spain, both Polysiphonia species were mainly collected in marinas, while M. pseudoforcipatus was found at a site close to oyster aquaculture facilities. Polysiphonia delicata was also found in Victoria, Australia, and the potentially non-native status of these three species in relation to their known distribution is discussed.
Coralline algae are expected to be adversely impacted by global warming and ocean acidification, although there has been no synthesis of these effects on habitat-forming species. We compiled published responses of maërl and rhodolith-forming species to ocean acidification and warming. Although the response is variable among species, their recruitment, growth, health and survival are usually negatively affected under elevated CO2. Most studies show that coralline algal calcification is adversely affected under near-future ocean acidification scenarios and that in combination with a 1–3 °C increase in seawater temperature this has an even larger impact. Most research has involved relatively short-term experiments on single species, which makes it difficult to predict long-term effects at the ecosystem level because the impact of global changes on coralline algal habitats will depend on the direct impacts on individual species and the indirect effects of altered interspecific interactions. Studies in areas with naturally high CO2 levels show that coralline algae are adversely affected by long-term acidification through increased competition from non-calcified competitors. Coralline algal habitats such as vermetid reefs, coralligene and beds of rhodoliths or maerl are likely to decline in the near future as higher CO2 levels benefit fleshy algae and corrosive waters reduce calcareous habitat complexity and associated biodiversity.
Phymatolithon lusitanicum is a new maerl species described based on an integrative systematic approach including molecular (COI-5P, psbA) and morphological data obtained from recent collections, as well as comparison of type material from the morphologically and ecologically alike NE Atlantic species P. lamii and P. laevigatum. Molecular analyses including type material of P. lamii and P. laevigatum were congruent in delimiting P. lusitanicum as an independent lineage from these crustose species. The three species shared a common external morphology of multiporate asexual conceptacles, but P. lusitanicum has been detected only unattached as maerl while P. lamii and P. laevigatum are crustose. Phymatolithon lusitanicum is particularly abundant in subtidal maerl beds of the Atlantic Iberian Peninsula (Galicia and the Algarve); however it has also been detected northwards in Ireland intertidally and in Western Mediterranean Sea (Alborán Sea, Balearic Islands) down to 64 m. Phymatolithon lusitanicum differs from other Phymatolithon species reported for the European coasts mainly by the external shape of the multiporate asexual conceptacles (pore plate flush with surface or slightly sunken without a conspicuous thick raised rim) and its unattached habit as maerl/rhodolith. In addition, the lectotype of Lithothamnion hamelii turned out to be conspecific to Phymatolithon calcareum, therefore this taxon is proposed as a heterotypic synonym of P. calcareum. Finally, our molecular analyses detected cryptic diversity within the European collections of Phymatolithon, while collections identified as P. lenormandii from Canada or P. repandum from New Zealand were resolved as unrelated to the remaining Phymatolithon. In the light of these results, it is clear that further work is necessary to resolve species diversity within the genus Phymatolithon and its relationship with related genera.
Los estimadores no paramétricos permiten comparar la riqueza estimada de conjuntos de datos de origen diverso. Empero, como su comportamiento depende de la distribución de abundancia del conjunto de datos, la preferencia por alguno representa una decisión difícil. Este trabajo rescata algunos criterios presentes en la literatura para elegir el estimador más adecuado para macroinvertebrados bentónicos de ríos y ofrece algunas herramientas para su aplicación. Cuatro estimadores de incidencia y dos de abundancia se aplicaron a un inventario regional a nivel de familia y género. Para su evaluación se consideró: el tamaño de submuestra para estimar la riqueza observada, la constancia de ese tamaño de submuestra, la ausencia de comportamiento errático y la similitud en la forma de la curva entre los distintos conjuntos de datos. Entre los estimadores de incidencia, el mejor fue Jack1; entre los de abundancia, ACE para muestras de baja riqueza y Chao1, para las de alta riqueza. La forma uniforme de las curvas permitió describir secuencias generales de comportamiento, que pueden utilizarse como referencia para comparar curvas de pequeñas muestras e inferir su comportamiento –y riqueza– probable, si la muestra fuera mayor. Estos resultados pueden ser muy útiles para la gestión ambiental y actualizan el estado del conocimiento regional de macroinvertebrados.
Two terete species of gracilarioid algae are described for the British Isles. Gracilaria gracilis comb. nov. and Gracilariopsis longissima comb. nov. (Gracilariopsis verrucosa nom. rej. prop.) are superficially similar species long confused under the name Gracilaria verrucosa (Hudson) Papenfuss (= G. confervoides (Stackhouse) Greville), until recently regarded as the type species of the genus Gracilaria Greville. They occur regularly on southern British coasts, often in the same locality, both inter- and subtidally. Gracilariopsis longissima is also recorded for the first time from France and Spain. A lectotype is selected for Gracilaria gracilis, Gracilariopsis longissima is neotypified, and new descriptions are given, including field characters and new details of vegetative and cystocarp structure obtained by sectioning in standard planes, using metachromatic dyes. The British record for Gracilariopsis lemaneiformis (Bory) Dawson, Acleto et Foldvik is not confirmed. Revision of those definitions of agar which include an incorrect specific name is recommended.
Two terete species of gracilarioid algae are described for the British Isles. Gracilaria gracilis comb. nov. and Gracilariopsis longissima comb. nov. (Gracilariopsis verrucosa nom. rej. prop.) are superficially similar species long confused under the name Gracilaria verrucosa (Hudson) Papenfuss (= G. confervoides (Stackhouse) Greville), until recently regarded as the type species of the genus Gracilaria Greville. They occur regularly on southern British coasts, often in the same locality, both inter- and subtidally. Gracilariopsis longissima is also recorded for the first time from France and Spain. A lectotype is selected for Gracilaria gracilis, Gracilariopsis longissima is neotypified, and new descriptions are given, including field characters and new details of vegetative and cystocarp structure obtained by sectioning in standard planes, using metachromatic dyes. The British record for Gracilariopsis lemaneiformis (Bory) Dawson, Acleto et Foldvik is not confirmed. Revision of those definitions of agar which include an incorrect specific name is recommended.
Le Lithophyllum fasciculatum (Lamarck) Foslie est une espèce localisée en de rares points de la Manche et des côtes d'Irlande. Une étude anatomique de la croûte basale et des branches a été effectuée en vue de permettre une meilleure connaissance de l'espèce. Elle a été complétée par une comparaison rapide avec la structure du L. dentatum (Kützing) Foslie. Cette étude a montré l'importance de l'amplitude des variations anatomiques et la nécessité de leur mention pour la description des espèces. Les organes reproducteurs sexués, qui n'avaient jamais été observés, ont été décrits.
Mesophyllum sphaericum sp. nov. is described based on spherical maërl individuals (up to 10 cm) collected in a shallow subtidal maërl bed in Galicia (NW Spain). The thalli of these specimens are radially organized, composed of arching tiers of compact medullary filaments. Epithallial cells have flattened to rounded outermost walls, and they occur in a single layer. Subepithallial initials are as long as, or longer than the daughter cells that subtend them. Cell fusions are abundant. Multiporate asexual conceptacles are protruding, mound‐like with a flattened pore plate, lacking a peripheral raised rim. Filaments lining the pore canal and the conceptacle roof are composed of five to six cells with straight elongate and narrow cells at their base. Carposporangial conceptacles are uniporate, protruding, and conical. Spermatangial conceptacles were not observed. Molecular results placed M. sphaericum near to M. erubescens, but M. sphaericum is anatomically close to M. canariense. The examination of the holotype and herbarium specimens of M. canariense indicated that both species have pore canal filaments with elongate basal cells, but they differ in number of cells (five to six in M. sphaericum vs. four in M. canariense). Based on the character of pore canal filaments, M. canariense shows similarities with M. erubescens (three to five celled). The outermost walls of epithallial cells of M. canariense are flared compared to the round to flattened ones of M. erubescens, the latter being widely accepted for the genus Mesophyllum. The addition of M. sphaericum as new maërl‐forming species suggests that European maërl beds are more biodiverse than previously understood.
Dense assemblages of macrophytes, mainly Rhodophyceae, grew on sandy mud sediments. Sediments were essentially covered by marl beds of the calcareous red alga Lithothamnion corallioides and various shell substrates. Five main algal assemblages extended along a west-east decreasing gradient of hydrodynamic activity (tidal currents, waves and turbidity). The high frequency of storms during the year is the main feature which disturbs both flora and epifauna. Interactions between flora and fauna were either direct, eg grazing and spatial competition, or indirect, most of the substrata occupied by macrophytes being shells of dead bivalves and gastropods. Attachment of algae was largely dependent on population dynamics of shell species living in the area. As a consequence, in the most disturbed area, the macrophytes found were opportunistic species (Polysiphonia fibrillosa and Polysiphonia urceolata). In areas where the assemblage was unstructured, which prevented development of herbivorous species, the animal assemblage was then dominated by suspension feeders (Ficulina ficus and Phallusia mammillata) which competed for space with the macrophytes. In the last disturbed area, herbivorous species dominated the fauna assemblage while flora assemblage had a high level of organization. However, in these places eutrophication and high turbidity prevented establishment of many algal species, causing the ubiquitous ones to dominate (Ulva sp., Ceramium rubrum). Between these extreme areas, the living Lithothamnion beds were more developed and were defined as a characteristic assemblage of diversified Rhodophyceae species such as Chylocladia verticillata, Halarachnion ligulatum and Crytopleura ramosa. The role of wave disturbance as the main factor controlling algal assemblages of shallow soft-bottom sediments is discussed. -from Authors
Around the Glenan Islands of Southern Brittany the depth of the maerl deposits was found to vary with the site, as did the substrate topography. At two out of five sites examined, the maërl was present in a ridge and furrow system, in which there was a greater proportion of living plants in the furrows than in the ridges. The maerl was found to be composed almost entirely of Phymatolithon calcareum. Other algal species found growing along with the maerl are listed. Analysis of maërl for calcium and magnesium contents showed no significant difference in the values obtained for living and dead plant material. The calcium content, calculated as Ca++, varied from 25.5% to 33.3% of the dry weight and the magnesium content, calculated as Mg++, varied from 1.7% to 3.3%. The major component of maerl was found to be calcite with magnesium carbonate present as a solid solution in the calcite structure at a concentration of about 8%. Aragonite was shown to comprise about 10—15% of the total material.
The Plocamiaceae currently includes two genera: the free-living Plocamium and the adelphoparasite, Plocamiocolax. Plocamium includes ca. 40 species that are widely distributed throughout the world's oceans. Most species are clearly defined anatomically and biogeographically; however, the type species Plocamium cartilagineum (type locality: considered northern Europe) is an exception. Although reportedly cosmopolitan in distribution, our investigations unequivocally indicate that there is substantial genetic diversity among isolates from different geographic locations and that there are at least eight divergent cryptic species currently included in P. cartilagineum. In this investigation we focused on populations of P. cartilagineum from northern Europe. We used a combination of molecular and morphological characters in order to establish boundaries between four cryptic species in this geographical area. Our molecular results not only resolve these four entities as distinct, but also indicate that they are among the most divergent of all Plocamium species worldwide. As a result, we now recognize P. cartilagineum, Plocamium subtile, Plocamium nanum sp. nov. and Plocamium maggsiae sp. nov. in northern Europe. A preliminary assessment of ‘P. cartilagineum' in other geographical areas is provided.
Maerl beds are highly biodiverse biogenic substrata that have been receiving increasing attention in the last decade. Although maerl beds represent important nursery areas for commercial fishes and molluscs, little is known on the trophic web of their communities. Community structure parameters of maerl bed of the Bay of Brest (species richness, abundance, biomass and dominating species) were studied in parallel with the carbon and nitrogen isotopic composition of their main benthic species (macrofaunal, and megafaunal organisms) in order to assess the trophic levels and differences in the potential food sources of maerl inhabitants. The major potential sources of energy were identified to originate either from epiphytic macroalgae and microphytobenthos both growing on maerl thalli, together with sedimenting (sedimentary) particulate organic matter (POM) originating from the water column. The majority of the macro- and megafaunal organisms investigated were filter feeders, selective-deposit feeders and predators/scavengers. Filter feeders fall into three different groups representing different trophic pathways (i) sponges feeding directly on POM (water column filter feeders I), (ii) ascidians and holothurians feeding on POM and probably captured pelagic preys (water column filter feeders II), and (iii) filter feeding molluscs and crustaceans were hypothesised to feed on microphytobenthos or on decaying sedimented POM (Interface filter feeders). Selective deposit feeders were also divided into two subgroups. Carnivores were also distinguished between those with scavenging habits and true predators. Coupling of the trophic levels observed with the community biomass structure revealed that most of the benthic biomass derives its food from detritic sedimented POM and/or microphytobenthos, with interface filter feeders (23% of the biomass), selective deposit feeders (12%). Carnivores made up to 14% of the total biomass. Generally stable isotopes ratio mean values overlap and cover a large range within feeding types, indicating a strong overlap in food sources and a high degree of complexity of the food web presumably due to the diversity of the potential food sources.
Strains of Gracilaria foliifera (Forsskål) Børgesen isolated into culture from Ireland (where the species would appear to be introduced), England and the Atlantic coast of France were interfertile. Strains of G. foliifera from Texas and North Carolina, U.S.A. were similarly interfertile but did not cross with the European strains. The North Carolina strain was distinctly flattened in culture and superficially resembled G. foliifera from Europe whereas the Texas strain was terete or slightly flattened. Both of the American strains were interfertile with an isolate of G. tikvahiae McLa-chlan from the type locality of this species in northern Nova Scotia, Canada. It seems likely from these data that G. foliifera is not represented on the coast of North America and that G. tikvahiae is a highly morphologically variable species widely distributed from Nova Scotia south to the Caribbean. Examination of type material of Gracilaria foliifera and G. multipartita (Clemente) Harvey, together with phyto-geographical considerations, suggests that the species known as G. foliifera on eastem Atlantic masts should be known as G. rnultipartita, and that G. foliifera s. str. is probably confined to the Red, Arabian, and Indian Seas.
The tribe Amansieae is composed mostly of genera with dorsiventrally flattened thalli with only a few species that are terete or sub-terete in cross-section. Two of these comprise the monotypic genera Rytiphlaea and Halopithys, both natives of the Mediterranean Sea and the northeastern Atlantic Ocean. An investigation of the relationships of these two species to each other and to the remaining terete or sub-terete species, Enantiocladia schottii and Protokuetzingia australasica, was carried out. The monotypic genus Digeneopsis from Mozambique and South Africa, which has been previously placed in the tribe Polysiphonieae, was also studied. No generic distinction was supported between Digeneopsis subopaca, Enantiocladia schottii and Halopithys incurva, and consequently all species have been included in Halopithys. Rytiphlaea tinctoria was shown to be generically distinct. Using molecular phylogenetic analysis, Rytiphlaea and Halopithys were shown to be closely related to each other but to have no particularly close affinity to Protokuetzingia.