Article

Population structure, mortality and growth of Pinna nobilis Linnaeus, 1758 (Mollusca, Bivalvia) at different depths in Moraira bay (Alicante, Western Mediterranean)

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Abstract

An investigation to characterize the causes of Pinna nobilis population structure in Moraira bay (Western Mediterranean) was developed. Individuals of two areas of the same Posidonia meadow, located at different depths (A1, −13 and A2, −6 m), were inventoried, tagged, their positions accurately recorded and monitored from July 1997 to July 2002. On each area, different aspects of population demography were studied (i.e. spatial distribution, size structure, displacement evidences, mortality, growth and shell orientation). A comparison between both groups of individuals was carried out, finding important differences between them. In A1, the individuals were more aggregated and mean and maximum size were higher (A1, 10.3 and A2, 6 individuals/100 m2; A1, x = 47.2 ± 9.9; A2, x = 29.8 ± 7.4 cm, P < 0.001, respectively). In A2, growth rate and mortality were higher, the latter concentrated on the largest individuals, in contrast to A1, where the smallest individuals had the higher mortality rate [A1, L = 56.03(1 − e−0.17t ); A2, L = 37.59(1 − e−0.40t ), P < 0.001; mean annual mortality A1: 32 dead individuals out of 135, 23.7% and A2: 16 dead individuals out of 36, 44.4%, and total mortality coefficients (z), z A1(−30) = 0.28, z A1(31–45) = 0.05, z A1(46−) = 0.08; z A2(−30) = 0.15, z A2(31–45) = 0.25]. A common shell orientation N–S, coincident with the maximum shore exposure, was observed in A2. Spatial distribution in both areas showed not enough evidence to discard a random distribution of the individuals, despite the greater aggregation on the deeper area (A1) (A1, χ 2 = 0.41, df = 3, P > 0.5, A2, χ 2 = 0.98, df = 2 and 0.3 < P < 0.5). The obtained results have demonstrated that the depth-related size segregation usually shown by P. nobilis is mainly caused by differences in mortality and growth among individuals located at different depths, rather than by the active displacement of individuals previously reported in the literature. Furthermore, dwarf individuals are observed in shallower levels and as a consequence, the relationship between size and age are not comparable even among groups of individuals inhabiting the same meadow at different depths. The final causes of the differences on mortality and growth are also discussed.

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... It occurs in coastal areas, between 0.5 and 60 m depth, mainly on soft sediments colonized by seagrass meadows (Basso et al., 2015b), but also on other type of substrata such as bare sand (Katsanevakis, 2007;Rabaoui et al., 2007;Richardson et al., 1999), mud (Richardson et al., 1999), rhodolith beds (García-March and Kersting, 2006), pebbly bottoms (Richardson et al., 1999;Zavodnik, 1967) or among boulders (García-March and Kersting, 2006). Density values in P. nobilis populations are around 1 individual 100 m À2 (Coppa et al., 2010;García-March et al., 2007a;Guallart and Templado, 2012;Siletic and Peharda, 2003), however higher densities have been reported in many areas (Basso et al., 2015b;Prado et al., 2014). ...
... Growth rates have been assessed both through direct measurements (Acarli et al., 2011;García-March et al., 2007a;Moreteau and Vicente, 1982) and indirect approaches (Galinou-Mitsoudi et al., 2006;García-March et al., 2011a;Katsanevakis, 2007;Richardson et al., 2004Richardson et al., , 1999Siletic and Peharda, 2003), being described as some of the highest in bivalves (Richardson et al., 2004). ...
... Without the protection given by the cages, mortality by predation increases significantly, being enhanced by the presence of many other predators, from cephalopods to fishes (e.g. García-March et al., 2007a;Katsanevakis, 2007). Furthermore, the Columbretes Islands Marine Reserve is well known for its success in the conservation and restoration of many invertebrates and fishes (Stobart et al., 2009;Templado and Calvo, 2002), including many known P. nobilis predators such as Sparus aurata whose abundances are noteworthy (Templado and Calvo, 2002;authors' pers. ...
Article
A long-term experimental approach was undertaken to assess viability and resilience of the endangered Mediterranean fan mussel Pinna nobilis. Artificial and natural recruitment, mortality, population traits and juvenile growth were assessed in seasonal and annual surveys. In the Columbretes Islands, P. nobilis thrives in differing substrate types, from coarse sand to boulders, in Cymodocea nodosa meadows and among rhodoliths, and is always found sharing habitat with the less abundant sibling species P. rudis. In artificial collectors larval settlement occurred over a several months period, concentrating its peak in September and resulting from two separated spawning events. Recruitment in the collectors showed high inter-annual variability and was independent of depth, but positively correlated with seasonal water temperature increase in June. Natural recruitment of P. nobilis was low and showed little variability, evidencing the existence of intense post-settlement processes. Adult mortality was also low, thus leading to slow population dynamics and to the species' vulnerability to catastrophic events. Population size structure suggests the existence of a refuge size above 45 cm shell length. The fast growth during the first years of life would help shortening this vulnerability period. Altogether, essential information and tools for the species' conservation are provided, which will be critical in the current context of mass mortalities affecting P. nobilis.
... (1 -e -K(t-t°) ) Equation (1) where L t is length at time t (age); L ∞ (asymptotic length) is the theoretical maximum length that an organism would reach at an infinite age; K (Growth constant) is the rate at which the organism approaches its L ∞ ; and t 0 (theoretical time at which L t = 0) positions the growth curve horizontally (Sparre and Venema 1998;Anthony et al. 2001). The VBG equation has been used to examine growth characteristics in a number of bivalve species (Nolan and Clarke 1993;Sparre and Venema 1998;Urban 2000;Anthony et al. 2001;Maronas et al. 2003;Smith 2011), including pinnids (Garcia-March et al. 2007a). While this equation is generally used to describe growth rates where length-at-age data have been collected, the parameters L ∞ and K can be estimated using simple mark-and-recapture techniques to construct a Ford-Walford plot (Anthony et al. 2001). ...
... In similar studies examining the growth of P. nobilis in the Mediterranean, K values ranged between 0.16-0.40 (Richardson et al. 1999;Siletic and Peharda 2003;Garcia-March et al. 2007a). ...
... A number of exogenous factors have been reported to affect absolute growth in pinnids (Rabaoui et al. 2007). These include depth, temperature, food availability, sediment type, predation, hydrodynamics and the impact of anthropogenic influences, such as disturbance from boating, fishing and pollution (Butler et al. 1993;Garcia-March et al. 2007a;Garcia-March et al. 2007b;Rabaoui et al. 2007). Endogenous factors, such as those associated with reproductive activity (e.g. ...
Article
Anecdotal reports suggest that populations of razor clams, Pinna bicolor, have increased substantially in Lake Macquarie, New South Wales over the last 5-10 years. This has raised concerns about the ecology of the Lake and human safety. As a first step to providing information to inform management, between August 2009 and August 2010, we examined growth, population density, recruitment and the morphometrics of marked razor clams in a permanently marked grid in the southern reaches of the Lake. Growth increments of 61 P. bicolor were used to construct a Ford-Walford plot, from which von Bertalanffy growth parameters were calculated (K = 0.409 and L∞ (dorso-ventral measurement) = 235.192 mm). During the study period 24 P. bicolor recruited to the grid, increasing the population density from 0.15 m -2 to 0.20 m -2. Recruits ranged in size (antero-posterior measurement) from 177-241 mm, with a mean (± SE) of 215.4 ± 4.1 mm. Morphological variation was observed and was evident within the linear regression of shell length on shell height (r 2 = 0.631). These observations confirmed that growth, density and recruitment, as well as the degree of morphological variation within a population of P. bicolor in the warm temperate waters of New South Wales, is similar to that recorded for populations in South Australia and Western Australia. © 2011 malacological society of australasia & society for the study of molluscan diversity.
... Eventually, the nacre below the calcite is also abraded, leaving the myostracum in contact with the exterior in the anterior portion of the shell. At the tip of the valve, the myostracum is also abraded leaving n2 in contact with the environment in the outer side of the shell (García-March and Marquez-Aliaga, 2007;García-March et al., 2007a). As a consequence, the myostracum crosses the anterior portion and extends partly into the inner side of the shell. ...
... The ELL is observed from a wedge between nacre and calcite close to the posterior terminus of the first LL to the most posterior terminus of the ELL itself. Within the wedge, the calcitic outer shell layer interdigitates with the nacreous shell layer over a distance not exceeding 1 cm (García-March et al., 2007a). In the first-formed adult couplet, LL1 attaches to the nacreous middle shell layer and FL1 attaches partially to the nacreous layer and partially to an aragonitic irregular simple prismatic ligamental ridge (LR1) sensu Carter (1990), or pseudonymph. ...
... The initial ligamental ridge is physically continuous with the early formed myostracum, which has the same aragonitic irregular simple prismatic microstructure. With continued shell deposition, however, this initial prismatic pseudonymph is cut off from the pallial myostracum as it becomes covered internally by the nacreous inner shell layer (García-March et al., 2007a). ...
Article
Body size (weight per individual) is an important concept in ecology. It has been studied in the deep sea where a decrease in size with increasing depth has often been found. This has been explained as an adaptation to food limitation where size reduction results in a lowered metabolic rate and a decreased energetic requirement. However, observations vary, with some studies showing an increase in size with depth, and some finding no depth correlation at all. Here, we collected data from peer-reviewed studies on macro- and meiofaunal abundance and biomass, creating two datasets allowing statistical comparison of factors expected to influence body size in meio- and macrofaunal organisms. Our analyses examined the influence of region, taxonomic group and sampling method on the body size of meiofauna and macrofauna in the deep sea with increasing depth, and the resulting models are presented. At the global scale, meio- and macrofaunal communities show a decrease in body size with increasing depth as expected with the food limitation hypothesis. However, at the regional scale there were differences in trends of body size with depth, either showing a decrease (e.g. southwest Pacific Ocean; meio- and macrofauna) or increase (e.g. Gulf of Mexico; meiofauna only) compared to a global mean. Taxonomic groups also showed differences in body size trends compared to total community average (e.g. Crustacea and Bivalvia). Care must be taken when conducting these studies, as our analyses indicated that sampling method exerts a significant influence on research results. It is possible that differences in physiology, lifestyle and life history characteristics result in different responses to an increase in depth and/or decrease in food availability. This will have implications in the future as food supply to the deep sea changes as a result of climate change (e.g. increased ocean stratification at low to mid latitudes and reduced sea ice duration at high latitudes).
... Eventually, the nacre below the calcite is also abraded, leaving the myostracum in contact with the exterior in the anterior portion of the shell. At the tip of the valve, the myostracum is also abraded leaving n2 in contact with the environment in the outer side of the shell (García-March and Marquez-Aliaga, 2007;García-March et al., 2007a). As a consequence, the myostracum crosses the anterior portion and extends partly into the inner side of the shell. ...
... The ELL is observed from a wedge between nacre and calcite close to the posterior terminus of the first LL to the most posterior terminus of the ELL itself. Within the wedge, the calcitic outer shell layer interdigitates with the nacreous shell layer over a distance not exceeding 1 cm (García-March et al., 2007a). In the first-formed adult couplet, LL1 attaches to the nacreous middle shell layer and FL1 attaches partially to the nacreous layer and partially to an aragonitic irregular simple prismatic ligamental ridge (LR1) sensu Carter (1990), or pseudonymph. ...
... The initial ligamental ridge is physically continuous with the early formed myostracum, which has the same aragonitic irregular simple prismatic microstructure. With continued shell deposition, however, this initial prismatic pseudonymph is cut off from the pallial myostracum as it becomes covered internally by the nacreous inner shell layer (García-March et al., 2007a). ...
Article
Full-text available
The pen shell Pinna nobilis (also known as the fan mussel) is an endemic bivalve of the Mediterranean Sea. Threatened by human activities, it has been listed as an endangered and protected species under the European Council Directive 92/43/EEC since 1992. The ecological role of this species is of importance because it filters and retains large amounts of organic matter from suspended detritus contributing to water clarity. In addition, as a hard substrate in the soft-bottom seafloor, it provides a surface that can be colonized by other (floral and faunal) benthic species. Here, we provide an overview of all available published studies on the pen shell, compiling available data and summarizing current knowledge on the conservation status and viability of populations over the full range of the Mediterranean Basin. Additionally, we discuss the different practices in applied methodology and identify gaps and new research areas in order to render conservation programmes of the species more effective. © 2015 Elsevier Ltd. All rights reserved.
... The majority of the population in the Gulf of Erdek is characterized by the predominance of small-sized (juvenile) individuals (Fig. 6), which were found in almost all sites, indicating successful recruitment in specific areas. Fan mussels grow fast in the first years of life, sizes show extreme variation among different stocks or even among groups of individuals inhabiting multiple depths at a similar habitat (Katsanevakis, 2006;García-March et al., 2007b;Kersting & García-March, 2017). P. nobilis population in the Gulf of Erdek is composed of smaller individuals (H t ranged from 11.8 to 31.4 cm) when contrasted to the other Mediterranean populations (Katsanevakis, 2006;Centroducati et al., 2007;García-March et al., 2007b;Theodorou et al., 2017;Ruitton & Lefebvre, 2021). ...
... Fan mussels grow fast in the first years of life, sizes show extreme variation among different stocks or even among groups of individuals inhabiting multiple depths at a similar habitat (Katsanevakis, 2006;García-March et al., 2007b;Kersting & García-March, 2017). P. nobilis population in the Gulf of Erdek is composed of smaller individuals (H t ranged from 11.8 to 31.4 cm) when contrasted to the other Mediterranean populations (Katsanevakis, 2006;Centroducati et al., 2007;García-March et al., 2007b;Theodorou et al., 2017;Ruitton & Lefebvre, 2021). Size ranges of the fan mussel population from Dardanelles Strait are consistent with our results. ...
Article
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This study presents the results of the first broad-scale assessment of the spatial distribution of the fan mussel (Pinna nobilis Linnaeus, 1758) population in the Gulf of Erdek (Sea of Marmara, Turkey), based on underwater surveys. The population density and structure of mussels were estimated by diving along strip transects between the shoreline and a depth of 15.8 m, in a study area of 9080 km2. A total of 2164 mussels were counted, of which 78.8% were alive, and 21.2% were dead in 29 sites. The mean density was calculated as 18.3 ± 3.3 ind•100 m-2, and recorded densities reached 71.2 ind•100 m-2 among the studied sites. Although mussel density was very high (>15 ind•100 m-2) in nine regions, dead mussels were also recorded in the gulf. Benthic habitats, depth range, and exposure levels seem to play a crucial role in the spatial distribution and survival of fan mussels. The average height (± SE) was calculated as 19.5 ± 0.35 cm and 24.9 ± 0.37 cm for alive and dead mussels, respectively. The percentage of juveniles (≤20 cm) was 57% in the population, and they dominated in seagrass meadow beds and shallow waters. Despite many deaths due to uncertain causes, the results indicate a partially promising scenario for the fan mussel population in the Gulf of Erdek and highlight the existence of many alive juveniles that could play a primary role in the sustainability of the population. This situation is not static, as anthropogenic changes and human activities could affect population welfare in the future. These high-density sites need to be protected, and protection measures in these locations should include all effects that may cause incidental mortality.
... Pinna nobilis typically inhabits meadows of Posidonia oceanica (e.g. Altaba 2006;García-March et al. 2007;Katsanevakis and Thessalou-Legaki 2009). Modern population density of P. nobilis is commonly in the order of ten individuals per 100 m 2 in open waters, but may rise to six individuals per square metre in sheltered settings (García-March et al. 2007), which probably comes close to the densities observed in the fossiliferous layers at Cape Vigli. ...
... Altaba 2006;García-March et al. 2007;Katsanevakis and Thessalou-Legaki 2009). Modern population density of P. nobilis is commonly in the order of ten individuals per 100 m 2 in open waters, but may rise to six individuals per square metre in sheltered settings (García-March et al. 2007), which probably comes close to the densities observed in the fossiliferous layers at Cape Vigli. ...
Article
Pliocene (Zanclean to mid Piacenzian) marine deposits from Cape Vigli on southwestern Rhodes (Mediterranean Sea, Dodecanes, Greece) are described, and assigned to the newly defined Cape Vigli Formation. Highly fossiliferous sandy to silty mudstones contain a diverse parautochthonous mollusc assemblage dominated by articulated specimens of the bivalves Pinna nobilis and Megaxinus ellipticus, and by abundant Persististrombus coronatus gastropods. These taxa formed part of a seagrass community. Combined with sedimentological evidence and microfossil assemblages (foraminifera, calcareous nannofossils), they indicate a very shallow (<5 m deep) depositional environment in a sheltered marine embayment close to the coast. The fossil community is characterised by the occurrence of several Late Miocene to Pliocene warm-water mollusc taxa, which had their acme in the Zanclean and have become extinct in the Mediterranean in the early Piacenzian. Consequently, these molluscs testify to a Zanclean to mid Piacenzian age. This assignment is corroborated by the calcareous nannofossil assemblages of the deposits, which support a potential latest Miocene (latest Messinian) to Early Pleistocene (early Gelasian) age (calcareous nannofossil zones NN12 to NN17). The occurrence of marine Pliocene deposits on Rhodes indicates that the depositional history of the island is more intricate than previously assumed. The shallow marine nature of the studied strata provides new evidence to reconstruct the position of the palaeo-coastline during Pliocene times, when Rhodes was still connected to Anatolia. So far, fossiliferous shallow marine strata of Zanclean to mid Piacenzian age in the eastern Mediterranean had been documented from Hatay Province (southern Turkey) and Agia Triada (southwestern Peloponnese, Greece). The newly discovered locality of Cape Vigli thus provides a significant, novel dataset, which helps to evaluate the palaeobiogeography of Pliocene biota.
... oceanica) meadows that determine the intensity of drag forces (García-March et al., 2007a, b;Hendriks et al., 2011). The species can be found from ca. 5-60 m (Butler et al., 1993;García-March et al., 2007b), although higher abundances are usually reported from 10 m to up to 38 m (García-March et al., 2007b;Rouanet et al., 2015). In contrast, confined waters provide a more sheltered environment, and populations have been found to peak at less than 1 m (Zakhama-Sraieb et al., 2011;Russo, 2017;Prado et al., 2014), 2-5 m (Coppa et al., 2013) and up to 11-13 m depth (Katsanevakis, 2007), possibly depending on the influence of local geomorphology in recruitment patterns (see Prado et al., 2020a). ...
... oceanica) meadows that determine the intensity of drag forces (García-March et al., 2007a, b;Hendriks et al., 2011). The species can be found from ca. 5-60 m (Butler et al., 1993;García-March et al., 2007b), although higher abundances are usually reported from 10 m to up to 38 m (García-March et al., 2007b;Rouanet et al., 2015). In contrast, confined waters provide a more sheltered environment, and populations have been found to peak at less than 1 m (Zakhama-Sraieb et al., 2011;Russo, 2017;Prado et al., 2014), 2-5 m (Coppa et al., 2013) and up to 11-13 m depth (Katsanevakis, 2007), possibly depending on the influence of local geomorphology in recruitment patterns (see Prado et al., 2020a). ...
Article
We examined a disease outbreak of the fan mussel, Pinna nobilis (L.), in the Alfacs Bay (South Ebro Delta, Spain) during a period of two years in three zones exposed to a summer salinity gradient resulting from agricultural freshwater discharges and distance to the open sea. Long-term monitoring was also conducted in Fangar Bay (North Ebro Delta), featuring lower salinities and no evidence of disease. Results showed that the salinity gradient of Alfacs Bay (37.4 to 35.7) was associated to cumulative mortality (100% near the mouth, 43% in middle regions, and 13% in inner regions), thus hindering the spread of pathogens. Young specimens showed to be more tolerant to disease than large adults but become vulnerable over time. In Fangar Bay, lower salinities (30.5 to 33.5) prevented the disease but individuals were highly vulnerable to Storm Gloria which caused 60% mortality in 3 weeks, and ∼100% in 6 weeks.
... Pinna nobilis (Linnaeus, 1758) with a common name "fan mussel" is an endemic species of the Mediterranean Sea and one of the largest bivalve in the world (Garcia-March et al., 2007). It can reach lengths up to 120 cm (Zavodnik et al., 1991) in addition it is a long living species (Butler et al., 1993) which has reports of 45-50 years old individuals (Rouanet et al., 2015). ...
... Pinnids are fast growing bivalves. Fan mussels living in deep waters show slower growth than individuals that live in shallow waters while deep water individuals can reach longer lengths (Garcia-March et al., 2007;Basso et al., 2015). They are naturally spread out on soft sandy bottoms of shallow coasts (0.5-60 m) covered by Posidonia oceanica (Linnaeus) Delile 1813 meadows (Katsanevakis, 2005). ...
Article
Spat recruitment of a large bivalve species endemic to the Mediterranean Sea and naturally found at İzmir, Turkey (Urla, Karantina Island), the fan mussel Pinna nobilis (Linnaeus, 1758), has been researched. The study was carried out between May and October 2012. The aim of this study was to determine the spat recruitment of the fan mussel. Collector systems were prepared with onion bags and pvc pipes. Collectors were deployed at two different depths (1 m and 8 m). Every month a new collector system was deployed at the study site and previous collectors were recovered. Length and weight of attached spats were recorded. Water temperature, salinity, chlorophyll-a and particulate matter were measured monthly. Surface collectors gathered 60.6 % of total spats. It was observed that, June, July and August were the most appropriate months to deploy fan mussel spat collectors for this site. Our results also showed that the main recruitment period of Pinna nobilis spat at the study site was between July and September. Résumé : Recrutement du naissain de Pinna nobilis (Linnaeus, 1758), bivalve menacé, à deux profondeurs différentes dans la baie d'Izmir, Turquie Cette étude vise à déterminer le recrutement des naissains de la grande nacre Pinna nobilis (Linnaeus, 1758), un grand bivalve endémique de Méditerranée qui se reproduit naturellement sur les côtes d'İzmir en Turquie (Urla, île de Karantina). Ce travail a été réalisé entre mai et octobre 2012. Des sacs d'oignons et des tuyaux en PVC ont servi de collecteurs pour recueillir les naissains du bivalve. Ceux-ci ont été installés à deux profondeurs différentes (1 et 8 m). Chaque mois, un nouveau système de collecte a été déployé et les anciens systèmes prélevés pendant toute la durée de l'étude. La longueur, la largeur, l'épaisseur et le poids de chaque naissain par collecteur ont été enregistrés. La température et la salinité de l'eau, les concentrations de chlorophylle et de matières en suspension ont également été mesurées mensuellement. 60,6 % du maissain a été récolté sur les collecteurs de surface (-1 m) sur toute la durée de l'étude. Le plus grand nombre de naissains de P. nobilis a été aux mois de juin, juillet et août. Il est alors établi que la meilleure période pour le captage de naissain de la grande nacre en cette région se situe entre juillet et septembre.
... Pinna nobilis is predated mainly by Octopus vulgaris, Hexaples trunculus and Sparus aurata (e.g., García-March 2007a, Addis et al. 2009, Zhakama-Sraieb et al. 2011, Kersting and García-March 2017 but also by sea turtles (Caretta caretta) in Cyprus, Lebanon and Turkey (M. Draman and M. Bariche pers. ...
... Larval settlement and the occurrence of resistant recruits should be monitored as well in order to assess recruitment potential in the impacted areas. Currently, there is enough information on how to assess larval settlement and recruitment in P. nobilis both in the field and by means of larval collectors (e.g., García-March et al. 2007a, Cabanellas-Reboredo et al. 2009, Kersting and García-March 2017. Additional information on the construction and installation of P. nobilis larval collectors can be found in Kersting and Hendriks (2019). ...
Article
Full-text available
This long-lived bivalve is endemic to the Mediterranean Sea, where it has a range from Spain to Turkey along the northern and southern coasts and coasts of the Mediterranean islands. Since 2016, a devastating and geographically widespread mass mortality event (MME) has impacted P. nobilis populations throughout the Mediterranean Sea. Previous to the MME, the species was widespread and locally abundant in some locations. The mortality is caused by a pathogen (H. pinnae) and the associated die-offs have rapidly spread from the western (starting in Spain) to the eastern Mediterranean Sea in less than three years, causing mortality rates of 80-100% of the individuals in most locations, including those with long-term P. nobilis monitoring programmes. There are a few populations (less than ten subpopulations) that are known to remain pathogen-free and these are geographically isolated and located in sites characterized by very specific environmental conditions (lagoons with little access to the sea and differing salinities). The presence of the pathogen throughout the environment hinders potential population recoveries through recruitment, which opens a highly worrying scenario. Fan mussels strongly rely on the survival of adults for the maintenance of populations and the slow population dynamics and low recruitment could seriously hinder recoveries following catastrophic events. In the past, major threats were very localised and came from illegal fishing, habitat loss, boat anchoring, invasive species and most recently climate change. However none of these threats had led to the extremely widespread and rapid population declines in the species. The percentage of population size reduction over the last ten years is ≥80%, and the pathogen that has caused the MME is still present in the environment, with continuing declines expected. Therefore, this species is listed as Critically Endangered, mainly supported by criteria A2be and A4be. Continuous monitoring of the species populations is mandatory, as well in those sites where the species has recently disappeared in order to detect potential recruitment in the future. This assessment should be re-evaluated in five years to include additional information and particularly related to the evolution of the disease and the potential occurrence of resistant individuals and recruitment. for citation Kersting, D., Benabdi, M., Čižmek, H., Grau, A., Jimenez, C., Katsanevakis, S., Öztürk, B., Tuncer, S., Tunesi, L., Vázquez-Luis, M., Vicente, N. & Otero Villanueva, M. 2019. Pinna nobilis . The IUCN Red List of Threatened Species 2019: e.T160075998A160081499.
... Pinna nobilis is predated mainly by Octopus vulgaris, Hexaples trunculus and Sparus aurata (e.g., García-March 2007a, Addis et al. 2009, Zhakama-Sraieb et al. 2011, Kersting and García-March 2017 but also by sea turtles (Caretta caretta) in Cyprus, Lebanon and Turkey (M. Draman and M. Bariche pers. ...
... Larval settlement and the occurrence of resistant recruits should be monitored as well in order to assess recruitment potential in the impacted areas. Currently, there is enough information on how to assess larval settlement and recruitment in P. nobilis both in the field and by means of larval collectors (e.g., García-March et al. 2007a, Cabanellas-Reboredo et al. 2009, Kersting and García-March 2017. Additional information on the construction and installation of P. nobilis larval collectors can be found in Kersting and Hendriks (2019). ...
Article
Full-text available
This long-lived bivalve is endemic to the Mediterranean Sea, where it has a range from Spain to Turkey along the northern and southern coasts and coasts of the Mediterranean islands. Since 2016, a devastating and geographically widespread mass mortality event (MME) has impacted P. nobilis populations throughout the Mediterranean Sea. Previous to the MME, the species was widespread and locally abundant in some locations. The mortality is caused by a pathogen (H. pinnae) and the associated die-offs have rapidly spread from the western (starting in Spain) to the eastern Mediterranean Sea in less than three years, causing mortality rates of 80-100% of the individuals in most locations, including those with long-term P. nobilis monitoring programmes. There are a few populations (less than ten subpopulations) that are known to remain pathogen-free and these are geographically isolated and located in sites characterized by very specific environmental conditions (lagoons with little access to the sea and differing salinities). The presence of the pathogen throughout the environment hinders potential population recoveries through recruitment, which opens a highly worrying scenario. Fan mussels strongly rely on the survival of adults for the maintenance of populations and the slow population dynamics and low recruitment could seriously hinder recoveries following catastrophic events. In the past, major threats were very localised and came from illegal fishing, habitat loss, boat anchoring, invasive species and most recently climate change. However none of these threats had led to the extremely widespread and rapid population declines in the species. The percentage of population size reduction over the last ten years is ≥80%, and the pathogen that has caused the MME is still present in the environment, with continuing declines expected. Therefore, this species is listed as Critically Endangered, mainly supported by criteria A2be and A4be. Continuous monitoring of the species populations is mandatory, as well in those sites where the species has recently disappeared in order to detect potential recruitment in the future. This assessment should be re-evaluated in five years to include additional information and particularly related to the evolution of the disease and the potential occurrence of resistant individuals and recruitment. https://www.iucnredlist.org/species/160075998/160081499
... We use the pen shell Pinna nobilis as a model species, a Mediterranean endemic and endangered bivalve. The pen shell can reach more than 1 m length 9 and is ecologically important in providing hard substratum for colonization by many benthic species in its soft natural habitat, Posidonia oceanica meadows 10 . Consequently, any population disruption could have cascading effects on the associated benthic community 11 . ...
... The sampling method was specific for P. nobilis, preventing killing: valves of each fan mussel were maintained open with a special aluminium clip, while a Hartman alligator forceps was used to take a small portion of mantle tissue (20 mg approx.). This opening device was designed to obtain a maximum aperture of 1.2 cm, according to the natural range of shell aperture of P. nobilis 9 . The mantle tissue of individuals was preserved in 95% ethanol and stored in 1.5 ml eppendorf tubes. ...
Article
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For marine meta-populations with source-sink dynamics knowledge about genetic connectivity is important to conserve biodiversity and design marine protected areas (MPAs). We evaluate connectivity of a Mediterranean sessile species, Pinna nobilis. To address a large geographical scale, partial sequences of cytochrome oxidase I (COI, 590 bp) were used to evaluate phylogeographical patterns in the Western Mediterranean, and in the whole basin using overlapping sequences from the literature (243 bp). Additionally, we combined (1) larval trajectories based on oceanographic currents and early life-history traits and (2) 10 highly polymorphic microsatellite loci collected in the Western Mediterranean. COI results provided evidence for high diversity and low inter-population differentiation. Microsatellite genotypes showed increasing genetic differentiation with oceanographic transport time (isolation by oceanographic distance (IBD) set by marine currents). Genetic differentiation was detected between Banyuls and Murcia and between Murcia and Mallorca. However, no genetic break was detected between the Balearic populations and the mainland. Migration rates together with numerical Lagrangian simulations showed that (i) the Ebro Delta is a larval source for the Balearic populations (ii) Alicante is a sink population, accumulating allelic diversity from nearby populations. The inferred connectivity can be applied in the development of MPA networks in the Western Mediterranean.
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... P. nobilis has previously been the subject of various scientific studies [4,6,[20][21][22][23], however no updated data exist about the morphology and functionality of its haemocytes. Consequently, in this study, we investigated the haemocytes of P. nobilis, using both morphological and functional methods. ...
Article
The fan mussel Pinna nobilis (Linnaeus, 1758) is one of the biggest bivalves worldwide. Currently, no updated information is available in the literature concerning the morpho-functional aspects of haemocytes from this bivalve species. Consequently, in this study, we characterised P. nobilis haemocytes from both a morphological and functional point of view. The mean number of haemocytes was about 5 (×105) cells mL haemolymph−1, and the cell viability was about 92–100%. Two haemocyte types were distinguished under the light microscope: granulocytes (51.6%), with evident cytoplasmic granules, and hyalinocytes (48.4%), with a few granules. The granules of the granulocytes were mainly lysosomes, as indicated by the in vivo staining with Neutral Red. Haemocytes were further distinguished in basophils (83.75%), acidophils (14.75%) and neutrophils (1.5%). After adhesion to slides and fixation, the cell diameter was approximately 10 μm for granulocytes and 7 μm for hyalinocytes. The granulocytes and hyalinocytes were both positive to the Periodic Acid-Schiff reaction for carbohydrates. Only granulocytes were able to phagocytise yeast cells. The phagocytic index (6%) increased significantly up to twofold after preincubation of yeast in cell-free haemolymph, suggesting that haemolymph has opsonising properties. In addition, haemocytes produce superoxide anion and acid and alkaline phosphatases. Summarising, this preliminary study indicates that both the granulocytes and hyalinocytes circulate in the haemolymph of P. nobilis and that they are active immunocytes.
... People have known and used it since ancient times, primarily for food, but also for the production of jewelry (pearls, mother-of-pearl from shells) and for making special fabrics from byssus threads. It mainly inhabits sedimentary bottoms, often in seagrass meadows [1][2][3][4][5], and it was recorded at depths of 0.5 m to 60 m, in a temperature range of 7 to 28 • C, and salinity range of 34-40 PSU [5,6]. In the Adriatic Sea, in Croatia, it was generally widespread, to the point of being exceptionally numerous at depths between 2 and 20 m in some places since 2005 to the onset of mass mortality (Petricioli D. and Bakran-Petricioli T., personal observation). ...
Article
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In the last few years, the endemic Mediterranean bivalve Pinna nobilis has been exposed to dramatic mortality in its entire area, which could lead to the extinction of the species. Throughout the Mediterranean, a lot of effort is being put into finding ways of preserving it. One of the methods used to monitor recruitment and juveniles’ survival is the installation of collectors for bivalve larvae. We installed collectors at two locations: in Brijuni National Park (North Adriatic) and Luka Cove (central Adriatic). Our aim was to compare the fouling community on the collectors in two consecutive years (2019 and 2020), especially because the installation of collectors in 2020 coincided with mass mortality events of P. nobilis in the area. The number and size of juvenile P. nobilis and the qualitative and quantitative composition of the fouling communities were determined. The results show a reduction in the number and size of juvenile P. nobilis and an explosion of the invasive bivalve Anadara transversa population on collectors in the second year. In Luka Cove, another invasive species—the ascidian Styela plicata—also seriously affected other organisms on the collectors to the point of preventing analysis of the fouling community.
... However, hydrodynamics may be one of the key parameters re sponsible for the structuring of fan mussel distribution. Several studies (García-March et al. 2007b, 2016, 2020a, Hendriks et al. 2011, Prado et al. 2021 pointed out that high hydrodynamics may be a limiting factor for the settlement and the development of fan mussels. For example, García-March et al. (2007a) demonstrated that drag forces, generated by waves, increase mortality in shallow open-sea populations by breaking or dislodging shells. ...
Article
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In 2019, the status of the Mediterranean fan mussel Pinna nobilis was elevated to ‘Critically Endangered’ on the IUCN Red List, in response to the pandemic caused by the parasite Haplosporidium pinnae . Identifying refuge habitats, free from parasites, is critical to the survival of the mussel. The distribution of P. nobilis was investigated along the Occitan coast (Northwest Mediterranean Sea) because of the presence of a unique lagoonal system that may provide potential refuges. Interviews with users and managers were conducted to identify target zones where the species was sighted. In situ surveys were carried out to define the main aggregations of fan mussels and characterize the habitat. Line transects were deployed to count and measure individuals to estimate density, abundance, and size distribution. Population densities were variable, ranging from 0.6 ± 0.2 (SE) to 70.8 ± 7.6 ind. 100 m ⁻² , representing one of the highest densities reported in the Mediterranean Sea. The total abundance of individuals across the coast was extrapolated to 163000, with 87% located in Thau and Salses-Leucate, highlighting these lagoons as essential for the survival of the species. This study also revealed the diversity of habitats colonized by P. nobilis . In the context of the pandemic, only the lagoon populations remain unaffected and provide natural refuges that have disappeared from all open-water coastal areas. However, the conditions in these lagoons could become unfavorable, leading to the collapse of the last P. nobilis populations. We therefore propose that Thau and Salses-Leucate lagoons, which harbor the largest remaining populations of P. nobilis, should be declared as conservation priorities.
... For instance, evidence shows that populations of A. maura, A. oldroydii, A. pectinata and A. tuberculosa, P. bicolor, P. nobilis and P. rugosa have been declining over the past decades. 13,21,22,[35][36][37][38] Some of those populations are so seriously threatened that collecting specimens for research would be more harmful than beneficial, as in the case of P. nobilis 39 and Pinna rudis. 40 This points to the need to implement strategies for restoring pen shell populations in many regions of the world. ...
Article
Pen shells hold some potential for cultivation, but information on aquaculture activities is fragmentary, and no sustained or commercial production of any such species is currently in place. We reviewed information available worldwide on reproductive cycles, wild juvenile collection, spat production in hatcheries and cultivation systems for 45 pen shell species. We found information on the topics of interest for 15 species, Atrina maura and Atrina pectinata being the most studied. Reproductive cycles have been described for ten species, but size at first maturity has been reported only for A. maura and Pinna rugosa. Onion mesh bags and mosquito nets are the materials used for wild juvenile collection of most species. Nevertheless, seed collection has decreased for some species because of overexploitation, diseases or trawling that has severely impacted populations, so spat production in hatcheries is a fundamental aspect. Yet, hatcheries face challenges due to the high mortality of umbo larvae and during metamorphosis, and larvae produced by broodstock with overmature gonads. Market size individuals can be produced using culture methods currently available, but hatchery protocols and culture devices must be tailored specifically for pen shells. Reduced availability of wild spat and limited spat production in hatcheries are major constraints for developing and sustaining cultures. Studies on reproduction and spat production are necessary, as well as the implementation of protection measures and development of restoration plans for pen shell populations. Apparently, there is insufficient information available to foster the development of aquaculture, with tensions between preserving species and aquaculture programmes.
... The endemic sea bivalve species Pinna nobilis (Linnaeus, 1758) is one of the largest bivalve species in Mediterranean marine ecosystems, reaching up to 120 cm shell length and inhabiting coastal areas with Posidonia oceanica (Delile, 1813) or Cymodocea nodosa (Ucria) (Ascherson, 1870) meadows at depths of 0.5-60 m [1,2]. P. nobilis is characterized by its fast growth rate alongside other pinnids, with a recorded lifespan of about 20 years [3]. ...
Article
Full-text available
Due to the rapid decrease of Pinna nobilis populations during the previous decades, this bivalve species, endemic in the Mediterranean Sea, is characterized as ‘critically endangered’. In addition to human pressures, various pathogen infections have resulted in extended reduction, even population extinction. While Haplosporidium pinnae is characterized as one of the major causative agents, mass mortalities have also been attributed to Mycobacterium sp. and Vibrio spp. Due to limited knowledge concerning the physiological response of infected P. nobilis specimens against various pathogens, this study’s aim was to investigate to pathophysiological response of P. nobilis individuals, originating from mortality events in the Thermaikos Gulf and Lesvos and Limnos islands (Greece), and their correlation to different potential pathogens detected in the diseased animals. In isolated tissues, several cellular stress indicators of the heat shock and immune response, apoptosis and autophagy, were examined. Despite the complexity and limitations in the study of P. nobilis mortality events, the present investigation demonstrates the cumulative negative effect of co-infection additionally with H. pinnae in comparison to the non-presence of haplosporidian parasite. In addition, impacts of global climate change affecting physiological performance and immune responses result in more vulnerable populations in infectious diseases, a phenomenon which may intensify in the future.
... In Maltese waters, no comprehensive studies concerning the distribution of these two species and the occurrence of the MME within local P. nobilis populations have been published to date. Moreover, these species are usually found in very low densities (García-March et al., 2007;Basso et al., 2015), making it easy to underestimate their real distribution and abundance. For this reason, in this study, two different monitoring techniques were deployed: systematic SCUBA diving visual census surveys as well as a citizen science questionnaire. ...
Article
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The genus Pinna includes two species in the Mediterranean Sea: Pinna nobilis and Pinna rudis. Both these species are under threat from multiple stressors. Pinna nobilis, in particular, has been exhibiting mass mortality events (MMEs) since 2016. The population and distribution of these species have never been comprehensively explored in the Maltese archipelago, and in this work, we collate information collected between 2006 and 2019 through a number of SCUBA underwater visual census monitoring programs. The logistical barriers surrounding SCUBA-based sampling techniques and the low-density distribution of these species constitute significant obstacles to an extensive conventional population assessment. Citizen science was thus also deployed in this study to supplement the data collected through SCUBA surveys: recreational SCUBA divers worked as citizen scientists, providing data on the distribution of these two endangered species from areas never explored before. This information can be used for assessing the conservation status of P. nobilis and P. rudis in Maltese waters, whilst contributing to the next generation of ocean-literate citizens.
... The two layers perform different functions. The thick (1-5 μm) periprismatic organic membranes make the outer prismatic layer particularly flexible [12]. When the two valves abut, tight sealing [13][14][15] is achieved by flexible deformation of the wide prismatic margins. ...
Article
The reinforcement function of shell ribs depends not only on their vaulted morphology but also on their microstructure. They are part of the outer layer which, in the case of the Pinna nobilis bivalve, is built from almost monocrystalline calcitic prisms, always oriented perpendicular to the growth surfaces. Originally, prisms and their c-axes follow the radii of rib curvature, becoming oblique to the shell thickness direction. Later, prisms bend to reach the nacre layer perpendicularly, but their c-axes retain the initial orientation. Calcite grains form nonrandom boundaries. Most often, three twin disorientations arise, with two of them observed for the first time. Nano-indentation and impact tests demonstrate that the oblique orientation of c-axes significantly improves the hardness and fracture toughness of prisms. Moreover, compression tests reveal that the rib area achieves a unique strength of 700 MPa. The detection of the specific microstructure formed to toughen the shell is novel.
... Sabella spallanzani), ascidians (e.g. Halocynthia papillosa, Phallusia mammillata, P. fumigata), gastropods and bivalves (such as the fan mussel Pinna nobilis) [75][76][77][78][79]. Pinna nobilis (box 5) density was estimated along 20 transects 10-m long and 1-m wide. ...
... A gradual size shift of specimens cannot be excluded. At least one case of an adult specimen performing slow autonomous movement into the Lake Faro has been reported (Bottari et al., 2017); the hypothesis that after settlement in shallower waters juveniles might move to deeper zones (Zavodnik, 1967;Moreteau and Vicente, 1980;Vicente and Moreteau, 1991) was questioned by García-March et al. (2007a), yet supported by the study of Katsanevakis (2007). ...
Article
The largest bivalve in the Mediterranean Sea, the fan mussel Pinna nobilis, is at risk of extinction due to mass mortality events (MMEs) caused by the spread of pathogens, Haplosporidium pinnae in particularly. In spite of being a protected area, Lake Faro (northeast Sicily, Italy) suffers from high anthropogenic pressures that affect the P. nobilis population that inhabits the lake and the two canals that connect it to the sea. In the present study, the population's long-term changes have been monitored in three distinct periods: before the MME (2010), at the beginning of the epidemic spread along the Italian coasts (2018), and after the MME (2020). The survey, carried out by visual census, showed that, relative to 2010, the population of P. nobilis halved in 2018 and disappeared from the canals in 2020; while in the lake, living specimens were only 27.69 % of the total at this time, without recruits. The disappearance of P. nobilis, allowed rapid colonization by the congeneric Pinna rudis and the invasive oyster Pinctada imbricata radiata, which had never been recorded in the Lake Faro system before 2020.
... The two layers perform different functions. The thick (1-5 µm) periprismatic organic membranes make the outer prismatic layer particularly flexible 11 . When the two valves abut, tight sealing [12][13][14] is achieved by flexible deformation of the wide prismatic margins. ...
Preprint
Full-text available
The reinforcement function of shell ribs depends not only on their vaulted morphology but also on their microstructure. They are part of the outer layer which, in the case of the Pinna nobilis bivalve, is built from almost monocrystalline calcitic prisms, always oriented perpendicular to the growth surfaces. Originally, prisms and their c-axes follow the radii of rib curvature, becoming oblique to the shell thickness direction. Later, prisms bend to reach the nacre layer perpendicularly, but their c-axes retain the initial orientation. Calcite grains form nonrandom boundaries. Most often, three twin disorientations arise, with two of them observed for the first time. Nano-indentation and impact tests demonstrate that the oblique orientation of c-axes significantly improves the hardness and fracture toughness of prisms. Moreover, compression tests reveal that the rib area achieves a unique strength of 700 MPa. The detection of the specific microstructure formed to toughen the shell is novel.
... Remarkably, this species hosts the crustaceans Pontonia pinnophylax and Nepinnotheres pinnotheres (Rabaoui et al., 2008). Pinna nobilis also plays a pivotal role in the trophic web, being a prey of other species, such as Octopus vulgaris (García-March et al., 2006). As all of the representatives of its family, P. nobilis is a filterfeeder species, whose populations may filter water in the amount of 6 liter/min (Zavodnik et al., 1991;Schultz and Huber, 2013). ...
Article
Full-text available
Pinna nobilis is the largest bivalve of the Mediterranean Sea, where it represents a flagship species. As a possible consequence of several human disturbing activities, at the beginning of the ‘80s, populations of fan mussel started a severe demographic decline. To reverse this trend, P. nobilis was included in a regime of full protection which led to a significant recovery of the species at the start of the millennium. Unfortunately, P. nobilis is presently facing a dramatic epidemic, which is bringing this species to the brink of extinction. This phenomenon started in early autumn 2016, from the Mediterranean coasts of Spain. Since then, the mass mortality of fan mussels spread quickly eastward reaching almost all Mediterranean areas. First epidemiological surveys ascribed this phenomenon to the infection of the protozoan Haplosporidium pinnae, but recent studies indicated some species of bacteria belonging to the genera Mycobacterium and Vibrio as further or alternative etiological agents. Presently, a multifactorial disease, mediated by the combined action of several pathogens, seems to be the most probable responsible factor which is favouring the mass mortality of P. nobilis. Despite its conservational prominence, a low number of studies investigated the genetic structure of P. nobilis before its mass mortality and all were consistent in evidencing a very good health for populations throughout the whole Mediterranean, pointing out high levels of genetic variability and good genetic connectivity among areas. Now it would be useful to provide an extended post-epidemic molecular survey.
... The two layers perform different functions. The thick periprismatic organic membranes make the outer prismatic layer particularly flexible [8]. When the two valves abut, shell closing is achieved by flexible deformation of the wide prismatic margins, providing a tight sealing ( [9][10]). ...
Preprint
Full-text available
The shell structure of the Pinna nobilis species constitutes a model for others formed by bivalves of the Ostreida order. The outer part is built of monocrystalline columns whose axes remain parallel to the calcite c-axis. The present work reveals a new microstructure induced by mantle damage in the early stage of growth. The calcite c-axes, oriented perpendicularly to the strongly rough outer surface, deviate significantly from the shell thickness direction. The inclination angle is maintained up to the nacre layer. The transfer is made by the monocrystalline prisms which initially run along the c-axis and then deflect taking the thickness direction. They form coherent systems with low-energy twin boundaries. The uncovered twin relationships significantly improve the mechanical properties, as demonstrated using the nano-indentation and impact tests. Moreover, compression tests were performed, which confirms that the untypical structure exhibits a unique combination of high fracture toughness and strength.
... Indeed, P. nobilis is considered a key species (habitat former) because it provides a hard substrate in areas with soft bottoms, increasing habitat complexity by providing a surface for other benthic species (algae, sponges, bivalves, polychaetes, etc.) [38,39]. In addition, the fan mussel is a host for symbionts such as the crustaceans Pontonia pinnophylax and Nepinnotheres pinnotheres [40], and it is also predated by other species (e.g., the cephalopod Octopus vulgaris), playing a key role in the trophic web [41]. This study sheds further light on the intricate patterns that are involved in the mass mortality of P. nobilis in the Western Mediterranean. ...
Article
Full-text available
I.A.); picossu@uniss.it (P.C.); gsesposito@uniss.it (G.E.); eantuofermo@uniss.it (E.A.); marcasu@uniss.it (M.C.) Abstract: The fan mussel, Pinna nobilis, represents the largest bivalve endemic to the Mediterranean Sea. Since 2016, dramatic mass mortality of this species has been observed in several areas. The first surveys suggested that Haplosporidium pinnae (currently considered species-specific) was the main etiological agent, but recent studies have indicated that a multifactorial disease may be responsible for this phenomenon. In this study, we performed molecular diagnostic analyses on P. nobilis, P. rudis, and bivalve heterologous host species from the island of Sardinia to shed further light on the pathogens involved in the mass mortality. The results support the occurrence of a multifactorial disease and that Mycobacterium spp. and H. pinnae are not necessarily associated with the illness. Indeed, our analyses revealed that H. pinnae is not species-specific for P. nobilis, as it was present in other bivalves at least three years before the mass mortality began, and species of Mycobacterium were also found in healthy individuals of P. nobilis and P. rudis. We also detected the species Rhodococcus erythropolis, representing the first report in fan mussels of a bacterium other than Mycobacterium spp. and Vibrio spp. These results depict a complicated scenario, further demonstrating how the P. nobilis mass mortality event is far from being fully understood.
... The population of Pinna nobilis has been greatly reduced in most Mediterranean areas in the past few decades due to anthropogenic pressure (García-March et al. 2007, Katsanevakis 2007, Katsanevakis & Thessalou-Legaki 2009, Rabaoui et al. 2011). However, from 1983, when the first observation of P. nobilis in the lagoon was made (Rodríguez Babio & Navarro Tárre ga 1983), to 2014, the Mar Menor has witnessed colonization and stabilization of the fan mussel, with a total of 7385 ha of potential habitat. ...
Article
Populations of the Mediterranean fan mussel Pinna nobilis have progressively decreased over the last decades as a result of anthropogenic activities. The rate of decline has strongly increased since 2016, when a mass mortality event triggered by the parasite Haplosporidium pinnae occurred, and evidence exists that Mycobacterium species may also have played a major role in the event. Indeed, the epidemic has spread throughout the Mediterranean, although coastal lagoons seem to offer a degree of ‘resistance’ against the parasite. In the early 1980s, P. nobilis appeared in the Mar Menor lagoon and rapidly became an important component of the benthos. However, colonization of the lagoon by the fan mussel was cut short in 2016 when a massive mortality event occurred, possibly as a consequence of the environmental collapse that occurred in the lagoon, parallel to the mortality that the species suffered in the Mediterranean that same year. In this study, we estimated the spatial distribution of P. nobilis in the Mar Menor for 3 periods: 2003-2004, 2013 and 2016. The first 2 periods use published data, and the last period uses data collected in a new campaign. The probability of occurrence for the 3 periods was estimated using random forest and random forest regression-kriging models. The main environmental variables that determined the dispersion and colonization of the bivalve in the lagoon before 2016 are also identified.
... The pen shell, Pinna nobilis Linnaeus, 1758, is one of the most imposing endemic bivalves in the Mediterranean (MacDonald and Barrett, 2008). It reaches up to 120 cm in size (García-March et al., 2007) with a suggested age of up to 45 years (Rouanet et al., 2015) and can be found in coastal areas at depths of 0.5 -60 m (Templado et al., 2004). The pen shell lives in sediment bottom areas (Katsanevakis, 2005) and seagrass meadows (Prado et al., 2014), partially buried in the sediment and held tightly by its byssus (SoHelFI, 2007). ...
Article
We identified areas with high individual densities of the pen shell, Pinna nobilis, in two areas along the Croatian Adriatic coast. The surveys carried out in 2018 and 2019 showed population densities of approximately 9 to 13 individuals/100 m². However, in 2019 a mass mortality event (MME) causing 36% to 100% mortality of this bivalve species was observed in the surveyed Croatian bays. The parasite Haplosporidium pinnae was identified by histological and molecular methods in all affected sampled individuals, while Mycobacterium sp. and Gram negative bacilli were detected in some affected and live bivalves. This finding constitutes the first record of these pathogens affecting P. nobilis in the middle Adriatic, confirming the continuous spread of the disease. Previously, the Adriatic water body was considered to be a natural shelter against the MME caused by pathogens in pen shell populations because of its distinct ecological features. The Adriatic Sea is a semi-closed water body with the largest continental shelf in the Mediterranean Sea, and due to its geomorphology and bathymetry, it is a sea with distinct characteristics. Monitoring plans and further studies in the Adriatic bays are now a priority for mitigating the high risk of extinction and working toward the conservation of this protected species.
... The presence of fan mussel juveniles in collectors and the fish farm indicates that at least they can survive for a few months in open waters. However, if fan mussel juveniles could survive for up to two years, like those of O. edulis infected by B. ostreae, at least some of the spat that settled in summer 2016, the size of which should be approximately 20 cm by summer 2018 (García-March et al., 2007;García-March et al., 2011;Kersting and García-March, 2017), should have been spotted already. Data gathered to date, however, show that the affected areas are not being repopulated naturally by P. nobilis. ...
Article
Anthropogenic drivers and global warming are altering the occurrence of infectious marine diseases, some of which produce mass mortalities with considerable ecosystemic and economic costs. The Mediterranean Sea is considered a laboratory to examine global processes, and the fan mussel Pinna nobilis a sentinel species within it. Since September 2016, fan mussels suffer a die-off, very likely provoked by the protozoan Haplosporidium pinnae. Population dynamic surveys, rescue programmes, larvae collector installation and protection of infected adults from predators, have increased knowledge about the factors conditioning the spread of the die-off; previous model simulations indicate that water temperature and salinity seem to be related to the manifestation of the disease, which at the end are strongly influenced by climate change and anthropogenic actions. The absence of natural recruitment implies that fan mussel populations are not recovering, but the survival of populations living in paralic environments provides an opportunity to study the disease and its conditioning factors. The fan mussel disease outbreak provides a case example for how climate change may mediate host-protozoan dynamics and poses several questions: are we witnessing the potential extinction of a sentinel species? Can we avoid it by applying active measures? If so, which measures will be more effective? How many other more overlooked species might experience a massive and unnoticed die-off before it is too late to implement any preservation action? This is especially relevant because the loss of keystone species can drive to community effects that influence marine ecosystem processes.
... When fan mussels sustain damage they may be more vulnerable to predators, thereby increasing mortality from predation. For instance, García-March, García-Carrascosa, Cantero, and Wang (2007) reported that when specimens became detached for a long period, predators such as ...
Article
Pinna nobilis is a sensitive and vulnerable species and is hence considered a good indicator of anthropogenic pressures on marine ecosystems. This study provides novel data on the density and distribution of endangered P. nobilis on the Turkish coasts. Threats to the status of P. nobilis, including by‐catch and illegal collection, were assessed, as was the general awareness of people about the endangered status of fan mussels. The data sources consisted of direct observations from diving surveys and the local ecological knowledge (LEK) of fishers and scuba‐divers. Results demonstrated that the density of P. nobilis significantly changed with environmental parameters, such as depth, and among different sampling areas. The number of damaged individuals was lowest in the areas that were distant from human influences such as ports and tourist beaches. The density estimations of P. nobilis across a wide geographic area around the Turkish coasts revealed that the density of fan mussels was highest around western coasts in comparison with southern coasts. Fishers and divers indicated that the population of this species has decreased during the last decade. The main causes of this decline were suggested to be the impacts of fishing gear, poaching, pollution, and boat anchoring. The highest volume of by‐catch was estimated to be taken by trawls. In general, the knowledge and local awareness of the conservation importance and status of fan mussels was poor. The study has identified those areas where fan mussels occur at a high density, and hence may indicate areas for possible conservation protection status. Second, areas exposed to the illegal harvesting of fan mussels were highlighted. Societal concern would benefit from educational activities to raise awareness of the ecological importance and conservation needs for fan mussels in Turkey.
... This represents an advantage of oceanica and Cymodocea nodosa or in open sandy areas (Katsanevakis, 2006(Katsanevakis, , 2007. P. nobilis buries a part of the shell into sandy or muddy bottoms leaving its wider posterior end exposed and uses its byssus to secure the shell to the sea bottom (García-March et al., 2007a). Usually, fan mussels have a patchy distribution (Richardson et al., 2004;Katsanevakis, 2006) that depends on optimal habitat availability, recruitment success and pollution (García-March et al., 2007a,b;Katsanevakis and Thessalou-Legaki, 2009;Rabaoui et al., 2010). ...
... The pen shell is a sessile organism commonly inhabiting coastal and estuarine environments at depth ranging from 0.5 to 60 m, with the apex of the shell anchored by byssus threads in the substrate, mostly sand and muddy-sand bottoms preferentially overgrown by seagrass meadows of Posidonia oceanica or Cymodocea nodosa ( Zavodnik et al. 1991;Richardson et al. 1999;Vazquez-Luis et al. 2014). The presence of pen shell populations in the Mediterranean Sea was documented in various areas with discrepancies in physico-chemical features, including the western Mediterranean along Mallorca Island and in the Cabrera Archipelago National Park ( Natalotto et al. 2015), along the eastern Spanish coastlines in the Moraira Bay ( García-March et al. 2006), in the southeastern France in the Embiez archipelago ( Trigos et al. 2015), in the northeast Tunisia in the hyper-eutrophic Ghar El Melh Lagoon ( Zakhama-Sraieb et al. 2011), along the northern and eastern Tunisian coastlines in Bizerta Lagoon, Gulf of Tunis and in the Monastir Bay ( Rabaoui et al. 2008Rabaoui et al. , 2009, in the eastern Mediterranean in Greece in the marine Lake Vouliagmeni (Katsanevakis 2007) and in the North Aegean Sea in the Thermaikos Gulf ( Galinou-Mitsoudi et al. 2006), and in the central Mediterranean in the Croatian Adriatic Sea ( Richardson et al. 2004), in Italy in the Gulf of Oristano ( Addis et al. 2009), in the Ionian Sea in the Gulf of Taranto ( Centoducati et al. 2007), in the Strait of Messina ( Matozzo et al. 2016), and in the meromictic Faro Lake in Sicily ( Bottari et al. 2017). However, over the last few decades, populations of P. nobilis have greatly declined due to habitat degradation resulting in reduction and loss of seagrass meadows, and increased anthropogenic activities such as reckless fishing, illegal trawling, and boat anchoring ( Basso et al. 2015;Natalotto et al. 2015;Vazquez-Luis et al. 2017). ...
Article
Full-text available
The pen shell Pinna nobilis (Linnaeus, 1758) is the largest endemic bivalve mollusc of the Mediterranean Sea, listed as an endangered species in the European Union. Because no information is available about the adaptation of pen shells to different habitats, herein the fundamental conditions of adaptation of P. nobilis to peculiar natural environments, such as the Strait of Messina (SM) and the meromictic Faro Lake (FL; Sicily, Italy), were explored by assessing the morphology, mucous production, osmoregulation and neurotransmission of their gills. Although gills of the pen shells from both sites exhibited a regular morphology, a higher presence of acid mucous cells was detected in P. nobilis from FL than SM, as well as higher levels of osmolytes but without interfering the osmoregulatory processes. About the functioning of gills, the cholinergic (i.e. acetylcholine and AChE) neuronal system was unaltered between individuals from the two sites, whereas the GABAergic neurotransmission (i.e. 4-aminobutyrate or GABA) was significantly augmented in gills of P. nobilis from FL than SM. This may be an adaptive response to hypoxic conditions in FL, as supported by the increased hypoxia-inducible factor (HIF-1α) in gills of pen shells from FL than SM. Noteworthy, this study reports for the first time the presence of the GABA neurotransmitter within the metabolite profile, obtained by application of a protonic Nuclear Magnetic Resonance (¹H NMR)-based metabolomics approach, of a marine bivalve. Therefore, GABA may be suggested as a metabolite biomarker in pen shells. Overall, findings from this study provide new insights on the behavioural and adaptive responses of the pen shell Pinna nobilis settled in different peculiar environments.
... Even if now and then there are sightings of healthy and maybe resistant individuals, they are extremely scattered, reducing the probability of reproduction among them (as male and female gametes are released to the water column and fertilization is external 21 ), so relatively dense populations might be needed to assure successful fertilization. In the case of overcoming this reproductive handicap, if the scattered resistant individuals were able to produce some recruits, their natural mortality would be very high, because the species is extremely vulnerable to predators when young 6,14 . Furthermore, the pen shell's slow growth-rate and dynamics (e.g., only individuals larger than 37 cm of shell length -at least 4 years old-released gametes in experimental conditions 65 ) turn this species highly vulnerable to catastrophic events and predict a very slow recovery of the species even if recruits manage to establish in infected areas. ...
Article
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A mass mortality event is devastating the populations of the endemic bivalve Pinna nobilis in the Mediterranean Sea from early autumn 2016. A newly described Haplosporidian endoparasite (Haplosporidium pinnae) is the most probable cause of this ecological catastrophe placing one of the largest bivalves of the world on the brink of extinction. As a pivotal step towards Pinna nobilis conservation, this contribution combines scientists and citizens’ data to address the fast- and vast-dispersion and prevalence outbreaks of the pathogen. Therefore, the potential role of currents on parasite expansion was addressed by means of drift simulations of virtual particles in a high-resolution regional currents model. A generalized additive model was implemented to test if environmental factors could modulate the infection of Pinna nobilis populations. The results strongly suggest that the parasite has probably dispersed regionally by surface currents, and that the disease expression seems to be closely related to temperatures above 13.5 °C and to a salinity range between 36.5–39.7 psu. The most likely spread of the disease along the Mediterranean basin associated with scattered survival spots and very few survivors (potentially resistant individuals), point to a challenging scenario for conservation of the emblematic Pinna nobilis, which will require fast and strategic management measures and should make use of the essential role citizen science projects can play.
... Clams in the Pinnidae family, collectively known as pen shells or fan clams, are large, habitat-forming bivalves that occur within seagrass meadows and adjacent sand flats in many of the world's oceans and estuaries. In some regions, such as Baja California in Mexico, they occur in extremely high densities and constitute a critical and profitable fishery [33][34][35]. However, little scientific knowledge exists regarding the ecological role pen clams may play in marine systems. ...
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Invertebrate diversity can be a key driver of ecosystem functioning, yet understanding what factors influence local biodiversity remains uncertain. In many marine and terrestrial systems, facilitation cascades where primary foundation and/or autogenic ecosystem engineering species promote the settlement and survival of a secondary foundation/engineering species have been shown to enhance local biodiversity and ecosystem functioning. We experimentally tested if a facilitation cascade occurs among eelgrass (Zostera marina), pen clams (Atrina rigida), and community diversity in temperate seagrass beds in North Carolina, U.S.A., and if this sequence of direct positive interactions created feedbacks that affected various metrics of seagrass ecosystem function and structure. Using a combination of surveys and transplant experiments, we found that pen clam density and survivorship was significantly greater in seagrass beds, indicating that eelgrass facilitates pen clams. Pen clams in turn enhanced local diversity and increased both the abundance and species richness of organisms (specifically, macroalgae and fouling invertebrate fauna)—the effect of which scaled with increasing clam density. However, we failed to detect an impact of pen clams on other seagrass functions and hypothesize that functioning may more likely be enhanced in scenarios where secondary foundation species specifically increase the diversity of key functional groups such as epiphyte grazers and/or when bivalves are infaunal rather than epifaunal. Our findings add to the growing amount of literature that demonstrates that secondary foundation species are important drivers of local biodiversity in marine ecosystems. Further experimentation is needed that directly examines (i) the role of functional versus overall diversity on seagrass functions and (ii) the relative importance of life-history strategy in determining when and where engineering bivalves increase biodiversity and/or functioning of seagrass beds.
... Los estudios de demografía de las poblaciones necesitan un periodo de tiempo de estudio más largo, necesario para conocer la dinámica de las poblaciones de la especie objeto de estudio, y son muy útiles a la hora de evaluar la estabilidad de las poblaciones y su evolución en el tiempo (Garcia-March et al, 2007). En el caso de la nacra el estudio de la demografía presenta ...
... For each parameter (i through ix), at each site (1 through 6), a mark was assigned, based on [3,5] and field observations: 0 = abnormal, 1 = intermediate and 2 = normal. A few parameters were correlated with the anchoring pressure (i, v and vii), while most of them were not clearly correlated (Table 1). ...
... Platyceramus platinus Bivalvia Campanian 3 m [162] Cenozoic Pinna nobilis Bivalvia Recent 571 mm [163] ...
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Gigantism-very large body size-is an ecologically important trait associated with competitive superiority. Although it has been studied in particular cases, the general conditions for the evolution and maintenance of gigantism remain obscure. I compiled sizes and dates for the largest species in 3 terrestrial and 7 marine trophic and habitat categories of animals from throughout the Phanerozoic. The largest species (global giants) in all categories are of post-Paleozoic age. Gigantism at this level appeared tens to hundreds of millions of years after mass extinctions and long after the origins of clades in which it evolved. Marine gigantism correlates with high planktic or seafloor productivity, but on land the correspondence between productivity and gigantism is weak at best. All global giants are aerobically active animals, not gentle giants with low metabolic demands. Oxygen concentration in the atmosphere correlates with gigantism in the Paleozoic but not thereafter, likely because of the elaboration of efficient gas-exchange systems in clades containing giants. Although temperature and habitat size are important in the evolution of very large size in some cases, the most important (and rare) enabling circumstance is a highly developed ecological infrastructure in which essential resources are abundant and effectively recycled and reused, permitting activity levels to increase and setting the stage for gigantic animals to evolve. Gigantism as a hallmark of competitive superiority appears to have lost its luster on land after the Mesozoic in favor of alternative means of achieving dominance, especially including social organization and coordinated food-gathering.
... This species is protected by the Mediterranean Specially Protected Areas protocol (95/96 SPA ANNEX II) and under European legislation (92/43 EEC). Although there is intensive research regarding the population ecology and the species distribution around Mediterranean (Zavodnik 1967, Zavodnik et al. 1991, de Gaulejac & Vicente 1990, Butler et al. 1993, Garc ıa-March & Ferrer 1995, Richardson et al. 1999, Siletic & Peharda 2003, Galinou-Mitsoudi et al. 2006, Centoducati et al. 2007, Garc ıa-March et al. 2002, Garc ıa-March & Vicente 2006, Garc ıa-March et al. 2007a, b, Rabaoui et al. 2008, Katsares et al. 2008, Katsanevakis & Thessalou-Legaki 2009, Coppa et al. 2010, Vafidis et al. 2014, there is limited knowledge about zootechnical aspects of the animal such as feeding behavior (Cabanellas-Reboredo et al. 2009a, Davenport et al. 2011, Najdek et al. 2013, Trigos et al. 2014), reproduction (de Gaulejac et al. 1995a, b, Richardson et al. 2004, and the recruitment (Peharda & Vilibic 2008, Cabanellas-Reboredo et al. 2009b, Acarli et al. 2011a, Soria et al. 2014. ...
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The fan mussel Pinna nobilis (Linnaeus, 1758) is an endangered bivalve species and is endemic to the Mediterranean Sea. Juvenile animals have been found growing on mussels Mytilus galloprovincialis (Lamarck, 1819) long line aquaculture bounces and ropes within the Maliakos Gulf (Aegean Sea). Animals were sampled from the harvested mussel lines. The results show twelve juvenile P. nobilis per ton of harvested M. galloprovincialis
... Pinna nobilis is the largest endemic bivalve in the Mediterranean Sea, reaching a size of up to 120 cm and appearing in coastal areas at a depth of 0.5e60 m, particularly in areas where soft sediments abound and there are Posidonia oceanica and Cymodocea nodosa meadows (Zavodnik et al., 1991;García-March et al., 2007). Over the past decades the P. nobilis population has suffered a significant reduction as a consequence of the destruction of their habitats, recreational and commercial fishing, and accidental killing when anchoring. ...
Article
Several biomarkers were determined to evaluate the effects of the Don Pedro spillage on the digestive gland of the fan mussel Pinna nobilis (Linnaeus, 1758). Two areas in the southeast of Ibiza Island (Western Mediterranean) were selected; one affected by the oil spill (Talamanca) and one did not affected (Espardell). Mussels were sampled one, six and twelve months after the accident. PAH levels were elevated in P. nobilis from the affected area one month after the accident and, although they were decreasing gradually, they were always higher than in the control area. An increase in enzyme activities, reduced glutathione and lipid peroxidation were evidenced one month after the spillage, with no changes in acetylcholinesterase. All biomarkers progressively returned to basal levels one year after the oil spill. In conclusion, the Don Pedro oil spill induced an acute situation of oxidative stress on P. nobilis that were recovered twelve months later. Copyright © 2015 Elsevier Ltd. All rights reserved.
Thesis
Les systèmes marins côtiers sont généralement discontinus et constitués d’une mosaïque de paysages sous-marins différents, créant ainsi des distributions parfois très fragmentées chez les espèces qui les colonisent. Les espèces marines côtières sont donc structurées en réseaux de populations connectées entre elles via la dispersion larvaire. Comprendre le fonctionnement et la connectivité entre les populations d’une espèce est indispensable pour adapter les stratégies de conservation. La grande nacre, Pinna nobilis, est une espèce endémique de la mer Méditerranée qui fait aujourd’hui face à une crise majeure qui menace sa survie. Depuis Octobre 2016, des mortalités de masse sont signalées sur ses populations, à travers toutes la mer Méditerranée, causées par un protozoaire parasite, Haplosporidium pinnae. Il s’agit d’un évènement sans précédent, que ce soit par le taux de mortalité (près de 100 %) ou la vitesse de propagation, et qui pourrait conduire à l’extinction de l’espèce. En se focalisant sur le littoral Occitan, cette thèse apporte des connaissances sur la biologie et l’écologie de l’espèce mais aussi sur son fonctionnement et les processus qui permettent le maintien de ses populations afin de proposer des priorités de conservation. Ainsi, nous avons mis en évidence la diversité d’habitats colonisés par l’espèce ainsi que l’importance des lagunes car elles abritent près de 90 % des grandes nacres, sur le littoral Occitan, et semblent servir d’habitat refuge à l’espèce en limitant l’infestation par le parasite. A l’aide de marqueurs microsatellites nouvellement développés, nous avons montré une structure génétique très homogène sur toute la côte, ce qui implique un certain niveau de connectivité et laisse penser qu’une grande partie de la diversité génétique de l’espèce reste préservée dans les lagunes. En se focalisant sur la population de la baie de Peyrefite, dans la Réserve Naturelle Marine de Cerbère-Banyuls, et grâce à une analyse de parenté, nous avons apporté des connaissances sur la dynamique démographique et les processus de repeuplement de l’espèce. L’ensemble de cette thèse permet de définir des recommandations qui seront utiles à la mise en place de mesures de conservation adaptées, indispensables pour la survie de l’espèce.
Article
An emergent disease has relegated populations of the Mediterranean pen shell, Pinna nobilis L. critically endangered to sanctuaries featuring salinities outside the 36.5 to 39 range. Point pattern analysis was used in three areas of the Alfacs Bay (Ebro Delta) still hosting pen shells to assess the possible undergoing of disease spread by comparing the spatial distribution of live individuals vs. empty shells across spatial scales. We also evaluated the importance of other ecological aspects of conservation relevance such as the size distribution of individuals, and the possible association to seagrass habitats. The population assessment showed no recent mortality and a clear dominance of large adults among empty shells (97.3%) pointing to no disease spread during the study period. At the low spatial scale Nearest Neighbor (NN) analyses evidenced significant clustering (NN Ratios of 0.4-0.8), but in one of the zones NN distances were closer in empty shells than in live individuals, suggesting a former localized outbreak. At the larger spatial scale, MDSCA confirmed clustering patterns up to distances of 115 to 190 m, with higher aggregation of empty shells at the same study zone. The bay also featured low juvenile availability (3.2%), which risks the continuity of the population. No evidence for habitat or conspecific selection could be observed from abundance patterns and variation in NN across study regions. Our research provides a tool for assessing population condition in paralic environments, where salinity conditions tend to slow down disease spread, thus allowing a time gap for undertaking conservation decisions.
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The endemic fan mussel (Pinna nobilis) in the Mediterranean Sea is at high risk of disappearance due to massive mortality events. The aim of the study was to evaluate the antioxidant response of P. nobilis collected in the Balearic Islands (Western Mediterranean) before and after the mass mortality event. Individuals collected before (between 2011 and 2012) and after (between 2016 and 2017) the event were analyzed by histological, molecular, and biochemical methods to compare pathogenic loads and biochemical responses. All the individuals collected during 2016-2017 presented symptoms of the disease and were positive for Haplosporidium pinnae, while acid-fast bacteria or/and Gram-negative bacteria were detected in some individuals of both sampling periods. The activities of the antioxidant enzymes catalase and superoxide dismutase in the gills were significantly lower in P. nobilis affected with the parasite compared to those in the asymptomatic ones, while levels of malondialdehyde, as an indicator of lipid peroxidation, were higher in infected individuals. When analyzing the differential effects of H. pinnae and Mycobacterium sp. on P. nobilis, it was observed that significant effects on biomarkers were only observed in the presence of H. pinnae. Co-infection of P. nobilis by H. pinnae with other pathogens such as Mycobacterium sp. constitutes a serious problem due to its high mortality rate in the Balearic Island waters. This concerning situation for P. nobilis is favored by a reduction in antioxidant defenses related to H. pinnae infection that induces oxidative stress and cell damage.
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The Stirone riverbanks (Northern Italy) host a famous Pliocene-Pleistocene marine succession, interpreted as a mosaic of shallow marine palaeoenvironments. One of the most remarkable occurrences is fossil Pinnidae in life position, here identified as Pinna nobilis Linnaeus, 1758. It is an endemic Mediterranean bivalve, commonly reported from within Posidonia or Cymodocea meadows, or more rarely from other unvegetated shallow sedimentary bottoms, and even under hypoxic conditions. Few reports are found in the fossil record because of the low preservation potential of this large, semi-infaunal, fragile nacreous bivalve. Although already mentioned in the literature, no detailed palaeoecological investigation has been conducted on the mollusc association of the Pinnidae biofacies outcropping at the Stirone River. Four replicas of bulk sediment (2 l each) have been collected from the Pinnidae biofacies, in order to conduct a palaeontological and palaeoecological analysis, aimed at defining the composition and structure of the mollusc fossil assemblage, for the reconstruction of the associated palaeoenvironmental setting. The associated sediment, rich in tiny plant frustules, is a poorly sorted fine to very fine sand, with a bimodal distribution of sand and mud together with a coarse bioclastic fraction. The mollusc fossil assemblage is formed by a mixing of species which are related to both infralittoral vegetated and unvegetated bottoms, together with species with an affinity for both mud and coarse detritic sediments. One of the most common and abundant species is Corbula gibba, a bivalve considered of high ecological importance due to its opportunistic nature and reported as tolerant to elevated organic mud input, bottom hypoxia and unstable sedimentation rate. The fossil assemblage and the associated sediment point to a likely colonisation by Cymodocea, although the occurrence of mosaic facies of unvegetated and vegetated bottoms, with both Cymodocea and sparse Posidonia, cannot be ruled out. The bottom was strictly infralittoral (shallower than 15 m of water depth), with pulses of mud by fluvial transport, supporting the mixing of infralittoral and mud-loving deeper species, and the ubiquitous occurrence of C. gibba.
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1. Vegetated marine and freshwater habitats are being increasingly lost around the world. Habitat restoration is a critical step for conserving these valuable habitats, but new approaches are needed to increase restoration success and ensure their survival. 2. We investigated interactions between plants and bivalves through a review and analysis of 491 studies, determined the effects, mechanisms, and key environmental variables involved in and driving positive and negative interactions, and produced guidelines for integrating positive interactions into restoration efforts in different habitats. 3. 50% of all interactions (both correlative and experimental studies) were positive. These were predominant between epifaunal bivalves and plants in all habitats, and between infaunal bivalves and plants in subtidal habitats. Plants primarily promoted bivalve survival and abundance by providing substrate and shelter, while bivalves promoted plant growth and survival by stabilising and fertilising the sediment, and reducing water turbidity. The prevalence of positive interactions increased with water temperature in subtidal habitats, but decreased with water temperature in intertidal habitats. The subset of studies conducted in a restoration context also showed mostly positive interactions. 4. 25% of all interactions were negative, and these were predominant between plants and infaunal bivalves in intertidal habitats, except sulphide‐metabolising bivalves, which facilitated plant survival. Interactions involving non‐native species were also mostly negative. 5. Synthesis and applications. Promoting facilitative interactions through plant‐bivalve co‐restoration can increase restoration success. The prevalence of positive interactions depends on habitat and environmental conditions such as temperature, and were especially important in subtidal habitats (involving both infaunal and epifaunal bivalves) and in intertidal habitats (involving only epifaunal bivalves). Thus sites and species for co‐restoration must be carefully chosen to maximise the chances of success. If done properly, co‐restoration could increase initial survival, persistence, and resilience of foundation species, and promote the recovery of associated biodiversity and ecosystem services.
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Based on the fact that the Mediterranean sea is an existing place to the bi-valves fan mussels of Pinna nobilis, the aim of this introductory study is to focus on understanding the nature of P.nobilis population density and its structure with an ongoing purpose to encourage future investigation of the subject matter to successfully uncover more ecological models; in order to reach the latter, a fieldwork took place from 2015 to 2018 in the Algerian west coasts on multiple sites with an end goal of better understanding the dynamics of the species, as well as assessing the effectiveness of protective measures of P.nobilis on the Algerian Western coastlines. The density, population structure and the growth of individuals noted on P.nobilis were examined through scuba diving along with multiple transects on the west coast of Algeria and measurements were executed on different spatial scales in populations occupying different sites; one of, is that of the protected naval area of "Habibas Island" in addition to other unprotected ones.. The results varied and they are as follows: the density of P. nobilis ranged from 0.28 in /m-2 on the transect to 0.08 in /m-2. The measured individuals were certainly a representative of their environment. The size of the P.nobilis did not prove itself to be prominent disturbance in the structure of the associated biota; the latter however showed that it was influenced by different areas. The outcomes of the study state that the recovery of the P. nobilis population on the west coast of Algeria was highlighted; stating the urgent need for setting security and protection of these species located on the Algerian West Coasts
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The pen shell, Pinna nobilis L., is a critically endangered bivalve threatened by mass mortality events throughout the Mediterranean, but the Alfacs Bay (Ebro Delta) still hosts many healthy individuals. Herein, we study the main factors controlling recruitment patterns in this locality, including gonadal development and abundance of critical life-stages, as well as the effect of environmental factors. Growth records from empty shells suggested a single major peak of recruitment during a period of 11 years, although many juveniles were found in two very shallow sand bars possibly acting as a barrier for water circulation and as a trap for larvae. Collectors deployed outside these sand bar areas showed zero settlers, and the availability of planktonic larvae was very low. Gonadal examination evidenced breeding throughout the summer period with successive hermaphroditism, but 20% of individuals were simultaneous hermaphrodites, a condition that has been associated with environmental stress and that could lead to in-breeding depression and potentially reduced fertility. Yet, given the large size of the population and the wide breeding period observed, planktonic processes causing larval mortality such as freshwater discharges from rice locally important rice agriculture are also proposed as possible impacts accounting for patterns of low larval availability.
Article
Highlights • High variability is observed in growth models of 12 Pinna nobilis populations. • Three general growth models are proposed for distinct environments. • The models could be used to plan conservation strategies for P. nobilis. • Populations surviving the die-off in paralic environments show low longevity. • Oldest fan mussels were observed in marine protected areas. Abstract The present work, which is the first comparative study of the growth of the fan mussel Pinna nobilis in the western Mediterranean, encompasses 12 populations of this species living in different environments in France and Spain. Two hundred nine shells were processed and used to obtain growth records from the posterior adductor muscle scar. Size-at-age data were fitted to the Von Bertalanffy growth model. Considerable variability in growth parameters and age was detected among the populations. The results show that the only two fan mussel populations remaining in Spain, which live in an estuary and a coastal lagoon, occupy habitats that are optimal for fast growth, but individuals show low longevity, complicating the long-term conservation of the species. Multivariate analyses groups the populations into three groups (SO, EO and LG), and a general model is proposed for each group; the model can be used as an approximation to calculate the ages of individuals living in similar environments.
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The ecology of the family Pinnidae was studied by sampling three pinnid species from 36 sampling sites across four different microhabitats in the Gulf of Thailand. The species spatial distributions were mostly uniform, with some populations having random distributions. Species abundances differed between sandy and coral habitats according to non-metric multi-dimension scaling analyses. Although the Gulf of Thailand is a relatively small geographic area, habitats are varied enough to provide variable shell densities. Small islands are important distribution areas, and coral reefs provide both direct and indirect shelter which support high abundances, densities and increased shell size. The highest density was recorded in sand beds within coral reefs. Low density and small shell size in sand beaches might be related to high mortality in shallow water or to adaptations for survival in shallow waters. A clear correlation between sediment composition and species abundance was found in Pinna atropurpurea; abundance increased with the sand content of the sediment. For P. deltodes, abundance increased as the rock fraction of the sediment increased. These results suggest that adaptations in Pinnidae, such as shell size, shell morphology, and the exposure of the shell above the sediment-water interface, are responses for survival in different habitats.
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Transplantation of the protected Mediterranean fan mussel Pinna nobilis is assessed as a potential conservation action. A pilot study in the marine Lake Vouliagmeni (Greece) showed variable success of transplantation, due to spatial variation in mortality rates: in a shallow (4 m) and easily accessible area, mortality of 20 transplanted individuals of various size classes was 100% in 72 d, mainly because of poaching, while in a deeper (12 m), less-accessible area, mortality was only 20%, unrelated to poaching and affecting mainly small individuals (all transplants of the first size class were found dead in both shallow and deep areas). In a subsequent transplantation experiment of 45 large fan mussels, transplanted from a depth of 4 m to a depth of 12 m, growth and mortality rates were monitored for 5 yr. Survival after 5 yr was very high (95.6%), and growth rates did not differ to those of non-transplanted individuals at the same depth (control). A metapopulation, time-invariant, stage-classified matrix model was used to assess the effect on the population of possible massive transplantation of fan mussels from the shallow waters of the lake (suffering from poaching) to the deeper protected areas. Several scenarios about transplantation effort were analysed. Massive transplantation would result in a substantial increase of the average life expectancy, expected lifetime offspring production, population growth rates, and abundance, at a reasonable estimated cost. Hence, in areas where fan mussels suffer from high mortality, transplantation of individuals older than the 1st age class appears to be an effective action to protect local populations.
Article
A new bivalve species of the genus Pinna Linnaeus, 1758, is described from shallow water off the coast of Easter Island, southeastern Pacific Ocean. Pinna rapanui sp. n. has a small, broad, slightly angulated shell with a sculpture of commarginal growth lines and prominent radial ribs decorated by almost tubular, perpendicularly erect spines. This species is the 249th marine molluscan species found in Easter Island waters, and it is, by far, the largest bivalve species living around the island. A Polynesian origin of this species is suggested; however, its definite affinities with Indo-Pacific or South American fauna are still unknown.
Conference Paper
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La nacra Pinna nobilis (Linnaeus, 1759) es una especie endémica del mar Mediterráneo, principalmente asociada a praderas de las fanerógamas marinas Posidonia oceanica y Cymodocea nodosa y sustratos blandos aledaños, en un rango de entre 0,5 y 60 m de profundidad. Desde 1999 está Incluida en el Catálogo Español de Especies Amenazadas con la categoría de “vulnerable” y figura también en el Anexo II de los convenios de Barcelona y Berna. En las costas españolas existen muy pocos datos acerca de las poblaciones de este gran bivalvo. En el presente estudio se presentan datos de la distribución y abundancia de Pinna nobilis en los fondos del refugio Nacional de Caza de las Islas Chafarinas, un pequeño archipiélago de soberanía española situado junto a las costas magrebíes (38º 11’ N, 2º 25 W). Los fondos del archipiélago albergan las praderas de Posidonia oceanica más occidentales conocidas en las costas africanas. Se trata de praderas bien desarrolladas y en buen estado de conservación. En conjunto presentan una superficie total estimada en torno a 18,2 ha en un rango batimétrico de entre 1 y 15 m. Dichas praderas albergan una población de Pinna nobilis que posiblemente represente también la más occidental de la especie en las costas del norte de África. Por todo ello se ha considerado de interés aportar datos acerca de esta población. En el presente estudio se han realizado censos de ejemplares en 10 estaciones de muestreo distribuidas en el interior de praderas de Posidonia oceanica del archipiélago, entre 7,4 y 11,2 metros de profundidad. Los censos consistieron en el recuento de ejemplares y la toma de algunos datos biométricos de los hallados en una zona circular de 5,65 m de radio, correspondiente a un área aproximada de 100 m². Dado que los ejemplares viven semienterrados y no se puede medir su talla total sin extraerlos del sedimento, se analizaron conchas muertas de ejemplares para establecer una relación entre distintos parámetros biométricos y la longitud total de la concha. Las densidades de Pinna nobilis observadas presentan un rango de entre 1 y 6 ejs/ 100 m², con un promedio de 2,9 ejs./100m². Los grupos de talla más abundantes fueron los de 40-50 cm y 50-60 cm de longitud total estimada de la concha (LTE). La LTE del ejemplar vivo de mayor tamaño fue de 75,8 cm. Asimismo, durante los censos se detectaron 2 ejemplares juveniles de talla inferior a 10 cm LTE. Estos resultados muestran para el archipiélago una población bien estructurada por grupos de talla/edad, si bien con una abundancia de ejemplares moderada en comparación con otras áreas del Mediterráneo. A lo largo de los censos también se han observado y se han tomado datos biométricos de ejemplares de otra especie del género de procedencia africana, Pinna rudis. En conjunto, la densidad de ejemplares de P. rudis en el rango batimétrico estudiado es menor que la de P. nobilis. La densidad media de P. rudis es de 0,7 ejs./100 m², lo que representa una proporción P. nobilis vs. P. rudis de 4,1 : 1. Las poblaciones del archipiélago presentan de momento buenas perspectivas de conservación, dado que las dos principales causas de regresión, su recolección por buceadores o la regresión de las praderas en que habita, no parecen tener lugar en su entorno. Se discuten sin embargo otras amenazas que pudieran tener lugar en el futuro.
Technical Report
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I relitti sommersi possono rappresentare un habitat e rifugio per specie “sensibili”, una delle quali è certamente la nacchera (Pinna nobilis L.). Scopo del presente progetto consiste nel valutare le potenzialità di rifugio per Pinna nobilis date dall’ambiente peculiare creato dai relitti, avviando uno studio pilota sui relitti prospicienti la costa della provincia di Trapani e comunemente visitati dai subacquei afferenti ai diving della stessa provincia.
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During 1996 the Museo Nacional de Ciencias Naturales (Madrid) co-ordinated a national project to make an inventory of Habitats Directive (HD) invertebrate species (Directive 92/43/EEC). The work was promoted by the Ministry for the Environment (MMA) and received financial support thanks to an agreement between the General Directorate for Nature Conservation (of the ME) and the Spanish Research Council (CSIC). Its objectives were 1) to review and map the species distribution area with special emphasis on the species from Annexe II, 2) to review the status of the populations and the biology of the species, and 3) to identify real or potential threats in order to propose measures to protect species habitats or to control commercial exploitation for Annexe II and V species, respectively. Ten of the study species were molluscs, representing 77% of total molluscs listed in the HD Annexes (13 species), which is a reflection of species biodiversity in Spain. The species we studied were: Elona quimperiana (Férussac, 1821), Geomalacus maculosus Allman, 1843, Vertigo moulinsiana (Dupuy, 1849), Margaritifera auricularia (Spengler, 1793), Margaritifera margaritifera (Linnaeus, 1758), Unio elongatulus (Pfeiffer, 1825), Unio crassus Philipsson, 1788, Patella ferruginea Gmelin, 1791, Pinna nobilis Linnaeus, 1758, Lithophaga lithophaga (Linnaeus, 1758). We indicate herein the need for more thorough studies on some species, and summarise the most relevant information obtained as the first step towards implementing the HD with this group of species in Spain.
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Although previous studies have noted the presence of the bivalve Pinna nobilis Linnaeus, 1758 in Mljet National Park, there is a lack of basic knowledge of this endangered species. The present study was initiated as part of a long-term investigation of P. nobilis density and growth with the aim of gaining a better understanding of this species' population dynamics, as well as evaluating the efficiency of protection measures of P. nobilis in Mljet National Park. Density, population structure, growth of tagged individuals and epibionts on P. nobilis were studied using SCUBA diving in 1998 and 2000 along four transects in Mljet inlets, Adriatic Sea. The density of P. nobilis ranged from 0.20 ind/m2 on transect MLJ-9 in Malo Jezero in 1998 to 0.02 ind/m2 on transect MLJ-5 in Veliko Jezero in 2000. Individuals measured in 1998 were significantly smaller than those measured in 2000. Growth curves were constructed from data collected by tagging and re-measuring 47 individuals. A decrease in density along some of the transects and the disappearance of 24 tagged individuals in 2000 is suggestive of poaching. The results of the present study indicate recovery of the P. nobilis population in Mljet lakes, but also provide evidence for the illegal removal of this protected species.
Article
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Pinna nobilis L., 1958 is the largest bivalve inthe Mediterranean. Due to the fact that P. nobilis lives partly buried in sediment, it becomes impossible to measure its total length in the field. To date several equations have been proposed to calculate the length of their valves. In this paper, we demonstrate the error in data obtained using the lastest equation published by De Gaulejac and Vicente (1990), and we propose a new equation that has been verified with data from individuals from two different populations of Pinna nobilis.
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Although previous studies have noted the presence of the bivalve Pinna nobilis Linnaeus, 1758 in Mljet National Park, there is a lack of basic knowledge of this endangered species. The present study was initiated as part of a long-term investigation of P. nobilis density and growth with the aim of gaining a better understanding of this species' population dynamics, as well as evaluating the efficiency of protection measures of P. nobilis in Mljet National Park. Density, population structure, growth of tagged individuals and epibionts on P. nobilis were studied using SCUBA diving in 1998 and 2000 along four transects in Mljet inlets, Adriatic Sea. The density of P. nobilis ranged from 0.20 ind/m 2 on transect MLJ-9 in Malo Jezero in 1998 to 0.02 ind/m 2 on transect MLJ-5 in Veliko Jezero in 2000. Individuals measured in 1998 were significantly smaller than those measured in 2000. Growth curves were constructed from data collected by tagging and re-measuring 47 individuals. A decrease in density along some of the transects and the disappearance of 24 tagged individuals in 2000 is suggestive of poaching. The results of the present study indicate recovery of the P. nobilis population in Mljet lakes, but also provide evidence for the illegal removal of this protected species.
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Blue mussels, Mytilus edulis, were exposed to the water‐borne scent of predators, either to the starfish Asterias rubens, or the shore crab Carcinus maenas, in laboratory experiments. Predator‐exposed mussels developed a stronger byssal attachment compared to that of unexposed mussels, which was significant after about, 24 h, and twice as strong after four days. The byssal attachment response was variable. In the short term (<10h), predator scents could inhibit byssus production in those experimental batches where unexposed mussels had a high rate of byssus production. Predator‐exposed mussels also formed larger aggregates, migrated less, and sought structural refuges more often. Experiments showed that these traits gave significant protection against predation from both crabs and starfish.
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A substantial population of the endangered Mediterranean bivalve Pinna nobilis exists in the marine Lake Vouliagmeni (Korinthiakos Gulf, Greece). The population density of P. nobilis was estimated in the lake with line transect sampling. Individuals of the youngest age class (small) had peak densities in the 1 to 3 m bathymetric zone and their densities were higher in poorly sorted sediments. Older (large) individuals (belonging to all age classes except the first one, 9 to 11 mo) had peak densities in the 11 to 13 m bathymetric zone. No P. nobilis was found deeper than 22 m. The absence of large individuals in shallow waters may partly be explained by illegal fishing. There are several hypotheses proposed to explain the lack of small individuals in deeper areas, but no definitive explanation is offered. In Lake Vouliagmeni, P. nobilis densities were high, although marine seagrass was completely absent. Thus, P. nobilis does not actually require seagrass meadows, as stated by many authors, and it may exist in large numbers in bare soft-sediment areas as well. P. nobilis grew fast, mostly during the first 3 yr of life, and may live beyond 15 yr. By recording the exact location of each P. nobilis individual within 800 m2 transects, as a pair of coordinates, the exact spatial distribution was defined and aggregation indices were calculated. P. nobilis had an aggregated dispersion, but no evidence for preferential settlement near adults or previously-settled individuals was found. The aggregated dispersion of P. nobilis probably relates to the patchiness of the local environment. The size of P. nobilis population in Lake Vouliagmeni was estimated to be 8501 ± 4395 (mean ± 1 SD) individuals, of which 4355 ± 3460 belonged to the first age class and 4146 ± 1405 belonged to all other age classes.
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Stable oxygen isotope analyses of U-shaped spines removed at intervals along profiles of the outer shell surface of Pinna nobilis (L) were used to reconstruct sea surface temperature (SST) and validate the periodicity of adductor muscle scar rings on the inner shell surface. Elemental ratios (Mg:Ca and Sr:Ca) of spines, determined using Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES), were compared with the SST estimated from the stable oxygen isotopic composition of the shell deposited at the same time. The elemental ratios and the stable oxygen isotopic composition recorded in the shell were significantly correlated: Mg:Ca ratio=0.0002 (seawater temperature)+0.0095 (r2=0.445), Sr:Ca ratio=0.00005 (seawater temperature)+0.0014 (r2=0.887). The ratios in the spines were highest when the SST was warmest during July and August and were lowest between January and February when the SST was minimal.The positions of the first and second adductor muscle scar rings, unlike the later rings, are often difficult to discern, and in large shells they are obscured by nacre. Seasonal patterns in the elemental ratios were used to characterise the age in regions of the outer shell surface corresponding to the first two years of shell growth. A combination of both elemental ratios and muscle scar rings were used to estimate the age and hence the growth rate of P. nobilis from three locations in the Croatian Adriatic. Annual cycles of shell growth, inferred from the seasonal pattern in the element ratios, were used to determine the season of recruitment of fan mussels at several localities along the Croatian coastline. Pinnids generally settled during late autumn and winter although one shell from Mali Ston Bay settled during the summer. P. nobilis from Mali Ston Bay exhibited the fastest growth reaching a length of ∼60 cm and an age of 9 years, whereas those from Malo jezero grew the slowest attaining a length of ∼50 cm at 12 years of age.
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Experiments on the movement and behaviour of a freshwater mussel Limnoperna fortunei (Dunker) were conducted m the laboratory. Small mussels of 5–12 mm shell lengths moved over 100 cm during a day within plastic containers, with a maximum distance of 300 cm. However, their movement was concentrated during the first five hours of the experiments. The distance moved decreased with increasing shell length, and mussels larger than 27 mm moved less than 20 cm. Both small (< 15 mm) and large (>15 mm) mussels showed negative photo-taxis and positive geotaxis under the light, but positive geotaxis of small mussels tended to be weak in darkness or under the shade Small mussels had strong thigmotaxis with a preference for settling in the angled crevices between the vertical walls and the flat bottoms of the containers Small mussels tended to aggregate, after movement, and the presence of large mussels facilitated secretion of byssal threads by the small mussels. The possible adaptive significance of these behaviours and movement are discussed in relation to response to predation and dislodgement by waves or water current
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This article develops a method for analysis of growth data with multiple recaptures when the initial ages for all individuals are unknown. The existing approaches either impute the initial ages or model them as random effects. Assumptions about the initial age are not verifiable because all the initial ages are unknown. We present an alternative approach that treats all the lengths including the length at first capture as correlated repeated measures for each individual. Optimal estimating equations are developed using the generalized estimating equations approach that only requires the first two moment assumptions. Explicit expressions for estimation of both mean growth parameters and variance components are given to minimize the computational complexity. Simulation studies indicate that the proposed method works well. Two real data sets are analyzed for illustration, one from whelks (Dicathais aegaota) and the other from southern rock lobster (Jasus edwardsii) in South Australia.
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Book
Preface; 1. The purpose of the book; 2. Survey of contents; 3. How to use the book; 4. Notation, terminology and conventions; 5. Acknowledgements; Part I. Introduction: Part II. Descriptive Methods: 2.1. Introduction; 2.2. Data display; 2.3. Simple summary quantities; 2.4. Modifications for axial data; Part III. Models: 3.1. Introduction; 3.2. Notation; trigonometric moments; 3.3. Probability distributions on the circle; Part IV. Analysis of a Single Sample of Data: 4.1. Introduction; 4.2. Exploratory analysis; 4.3. Testing a sample of unit vectors for uniformity; 4.4. Nonparametric methods for unimodal data; 4.5. Statistical analysis of a random sample of unit vectors from a von Mises distribution; 4.6. Statistical analysis of a random sample of unit vectors from a multimodal distribution; 4.7. Other topics; Part V. Analysis of Two or More Samples, and of Other Experimental Layouts: 5.1. Introduction; 5.2. Exploratory analysis; 5.3. Nonparametric methods for analysing two or more samples of unimodal data; 5.4. Analysis of two or more samples from von Mises distributions; 5.5. Analysis of data from more complicated experimental designs; Part VI. Correlation and Regression: 6.1. Introduction; 6.2. Linear-circular association and circular-linear association; 6.3. Circular-circular association; 6.4. Regression models for a circular response variable; Part VII. Analysis of Data with Temporal or Spatial Structure: 7.1. Introduction; 7.2. Analysis of temporal data; 7.3. Spatial analysis; Part VIII. Some Modern Statistical Techniques for Testing and Estimation: 8.1. Introduction; 8.2. Bootstrap methods for confidence intervals and hypothesis tests: general description; 8.3. Bootstrap methods for circular data: confidence regions for the mean direction; 8.4. Bootstrap methods for circular data: hypothesis tests for mean directions; 8.5. Randomisation, or permutation, tests; Appendix A. Tables; Appendix B. Data sets; References; Index.
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A review is presented of the mechanism of byssus production in the genus Mytilus. The pedal glands which secrete the byssus material are described, followed by an account of the morphology, structure and chemistry of the byssus itself. Finally, the release or shedding of the byssus from the pedal tissues is discussed.
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Des comptages de densite des faisceaux de feuilles, effectues au sein des herbiers de Posidonia oceanica (L.) Delile de quatre regions de la Mediterranee fran se (Marseille, Toulon, Cannes et Calvi), ont permi de proposer un modele de classement de ces herbiers. Cinq stades ont ete defmis, depuis le stade qualifie d'herbiers tres denses (plus de 700 faisceaux/m2 ),jusqiTaux semi-herbiers 50 ä 150 faisceaux/m ), En dessous de 50 faisceaux/m2, nous parlons de tiges isolees plutöt que d'herbiers.
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This study investigated the effects of effluent of edible crab (Cancer pagurus) on byssus production by blue mussels (Mytilus edulis). Mussels held in the laboratory secreted more, shorter, and thicker byssus threads when placed in water in which an edible crab had been than in control seawater. The cumulative length of byssus produced by individual mussels was not affected by predatory crab effluent, but byssus volume increased by 72% in crab water compared with control seawater after a 6-h period. This difference in thread volume was still great (45%) but disappeared statistically after 22 h of exposure to crab effluent. By contrast, byssus number, length and diameter were not affected by maintaining mussels in water that had contained non-predatory, herbivorous common sea urchins (Echinus esculentus). Blue mussels can therefore alter byssus production selectively in the presence of potential predators.
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The shell of the Pinnidae consists of characteristic fan-shaped valves united for their entire length dorsally by some form of ligament. The posterior and postero-ventral extensions of the valves are formed exclusively by the outer lobe of the m antle edge and so consist of the outer calcareous (prismatic) layer only. In the Pinnidae this layer has an exceptionally high organic content and so is flexible. The inner (nacreous) calcareous layer is thin and confined to the region occupied by the body, i.e. between the two adductors. The ligament is composed of three layers (disregarding the outermost, but vestigial, periostracum ). Anteriorly it consists of inner and outer layers; posterior to this for a short distance of outer layer, and for the remaining, and greatest, length it represents a fusion layer. This also continues forward over the middle region and traces persist still farther forward. The inner ligament layer is secreted by the m antle isthmus, i.e. it corresponds to the inner calcareous layer of the valves; the outer ligament layer is secreted by the outer lobes of the m antle edge, i.e. it corresponds to the outer calcareous layer of the valves. The fusion layer represents the result of union posteriorly of the outer lobes of the m antle edge. T h at part of the ligament which is formed in the same way as the valves (all being constituents of the shell) is here termed the prim ary ligament, that part formed by fusion of the outer lobes of the m antle edge constituting the secondary ligament. The mantle epithelium is divisible into proximal and distal regions, both containing mucous glands. The former, continuous with the m antle isthmus, secretes the inner calcareous layer; the latter is pigmented. A part from the adductors, the m antle is attached only by the large anterior and posterior pallial retractors which subdivide within the m antle folds. Posterior elongation of the m antle involves corresponding extension of the eulamellibranchiate ctenidia. All connexions between the two ctenidia and between ctenidia and m antle are by ciliary junctions. The ctenidia are very m uscular; observations of Atkins on collection and sorting of particles are confirmed. The unique gutter-like waste canals, originally described by Stenta, ensure that pseudofaeces and other waste from the inhalant cham ber are continuously removed. A preoral, unpaired racemose gland opens into the inhalant chamber. Its most probable function is that of excretion; anything discharged from it will be removed by way of the waste canals. The pallia! organ in the exhalant chamber is composed of a stalk and a more swollen head. It can be greatly distended and probably serves to clear away shell fragments. The projecting valves are subject to frequent damage. The Pinnidae live vertically embedded in soft substrata into which they cannot withdraw. The animals burrow as they grow but only to the extent that the portion of the shell occupied by the body (i.e. as far as the position of the posterior adductor) is buried. The wide posterior region of the shell is always exposed. Water can thus be drawn in from well above the surface of the substratum. The waste canals in the inhalant chamber and the powerful exhalant current keep the cavity clear. The projecting valves can be rapidly repaired since they are composed exclusively of the outer calcareous layer. Such repair strengthens the valves. During repair new inner and outer ligament layers may be laid down beneath the previously formed primary ligament. In the Lamellibranchia change in form and proportions of the body on the one hand, and of the mantle and shell on the other, are best discussed by reference to the two major axes in the sagittal plane, i.e. the antero-posterior and median axes of the body and the hinge and normal axes of the mantle and shell. In their evolution the Pinnidae probably passed through a ‘Modiolus stage’ with the large posterior adductor close to the m argin of the shell and little secondary extension of the ligament. Subsequently posterior extension of the mantle and so of the shell doubled the length of the animal and was accompanied by secondary extension of the ligament. Such extensions of the mantle occur throughout the Anisomyaria (including the Pinnidae). They involve loss of the primitive pallial attachments apart from the adductors (the anterior of which is always reduced and often lost). The mantle becomes re-attached to the shell by secondary pallial retractors in the Pinnidae and also in Malleus , but along a new line peripherally in the Pectinacea and Ostreacea. Existing data on development in the Pinnidae show that, with the formation of the dissoconch, new shell, secreted by the outer lobe of the mantle edge, is added to the posterior margin of the almost equilateral prodissoconch. The adult form is probably quickly acquired by the post-larva, the proportions of the different regions then remaining constant although with continual reduction anteriorly. Success in the Pinnidae is due partly to characteristics shared with related families, partly to unique features. The former include great extension of mantle lobes without peripheral attachment, the latter include waste canals, pallial organ and pallial retractors. The rigid ligament only unites the valves; it has no opening thrust. The Pinnidae can survive loss of the anterior adductor or fusion of the ventral margins of the valves. It is only essential that the posterior adductor should be able when necessary to pull together the flexible posterior margins of the valves.
Article
A new exposure index is described which can be derived from wind velocity, direction, duration and the effective fetch. Effective fetch is calculated from actual fetch modified by shoreline and offshore extents of shaIlow water. The index is calculated from the sum of these components for each unobstructed 22.5 degree compass sector of the shoreline. Data are presented for tests of the index as a predictor for littoral zonation phenomena in Bermuda and the Bayof Fundy, Canada. For the zones in both locations the index satisfies the majority of variance in the data. The vertical distribution of species is weIl modeIled in many cases, but not for others. In many cases significantly better fits are obtained if the basic index is modified using a component for shore slope. The index is useful as a numerical index of exposure which can be derived from standard weather data and hydrographic charts. It is also useful in pointing out littoral species that either do not respond to exposure, or respond in a different way from the majority of species.
Article
Pinna nobilis Linnaeus 1758 is an endemic bivalve mollusc in the Mediterranean Sea, where it inhabits seagrass meadows, especially Posidonia oceanica (L.) Delile. It is the largest bivalve in the Mediterranean, reaching lengths up to 120 cm. In its natural habitat, P. nobilis lives with the anterior part of the valve buried in the seabed, attached to Posidonia rhizomes by byssus threads. This habit makes it impossible to measure its total length directly in situ. As the only way to determine the individual age is the relationship between age and total length, several equations have been proposed to estimate total length by relating it to the unburied parts of the shell. Such measurements are essential to ecological studies that consider age, growth, and population dynamics, and that evaluate the environmental factors that affect this species. Accurately estimating total length depends on the accuracy and precision of the method employed to measure the unburied shell parts. In this paper, we point out the lack of precision of the instruments and methods used until now; we also demonstrate the reason for this imprecision. A new device to measure unburied parts of Pinna nobilis with a precision comparable to that obtained when measuring extracted valves is described. This device is unaffected by su