Aequipecten Opercularis Research Articles

THE GENERA GLYCYMERIS, AEQUIPECTEN AND ARCTICA , AND ASSOCIATED MOLLUSK FAUNA OF THE LOWER PLEISTOCENE ARDA RIVER SECTION (NORTHERN ITALY)

The Lower Pleistocene marine succession of the Arda River, cropping out at Castell'Arquato (Northern Italy), is well exposed, continue and richly fossiliferous. Itconsists of sandstones, siltstones and claystones and it is topped by continental conglomerates which indicate a major sea level drop. In the present paper Glycymeris glycymeris, Glycymeris inflata, Glycymeris insubrica, Aequipecten scabrella, Aequipecten opercularis and Arctica islandica are described and revised. In addition, the associated fauna is illustrated, and its biostratigraphic and palaeoclimatic significance is analyzed. This study points out that: 1) the fauna has a high biodiversity, comprising 159 taxa; bivalves are dominant, followed by gastropods, corals, serpulids, brachiopods, echinoids, arthropods (e.g. barnacles), bryozoans and scaphopods; 2) The last occurrences of the bivalves Aequipecten scabrella , Glycymeris inflata and Chama placentina , the first occurrence of Arctica islandica and the last occurrences of the gastropods Turritella tricarinata pliorecens and Nassarius prysmaticus suggest a late Gelasian-Calabrian age (Early Pleistocene) for the investigated marine succession; 3) the occurrence of boreal guests, such as Arctica islandica, Pseudamussium peslutrae and possibly Mytilus edulis, testify to a climatic change with a shift from warm to cold seawater temperatures.

Effects of ecosystem protection on scallop populations within a community-led temperate marine reserve

This study investigated the effects of a newly established, fully protected marine reserve on benthic habitats and two commercially valuable species of scallop in Lamlash Bay, Isle of Arran, United Kingdom. Annual dive surveys from 2010 to 2013 showed the abundance of juvenile scallops to be significantly greater within the marine reserve than outside. Generalised linear models revealed this trend to be significantly related to the greater presence of macroalgae and hydroids growing within the boundaries of the reserve. These results suggest that structurally complex habitats growing within the reserve have substantially increased spat settlement and/or survival. The density of adult king scallops declined threefold with increasing distance from the boundaries of the reserve, indicating possible evidence of spillover or reduced fishing effort directly outside and around the marine reserve. However, there was no difference in the mean density of adult scallops between the reserve and outside. Finally, the mean age, size, and reproductive and exploitable biomass of king scallops were all significantly greater within the reserve. In contrast to king scallops, the population dynamics of queen scallops (Aequipecten opercularis) fluctuated randomly over the survey period and showed little difference between the reserve and outside. Overall, this study is consistent with the hypothesis that marine reserves can encourage the recovery of seafloor habitats, which, in turn, can benefit populations of commercially exploited species, emphasising the importance of marine reserves in the ecosystem-based management of fisheries.

Habitat Characteristics Predicting Distribution and Abundance Patterns of Scallops in D’Entrecasteaux Channel, Tasmania

Habitat characteristics greatly influence the patterns of distribution and abundance in scallops, providing structure for the settlement of spat and influencing predation risk and rates of survival. Establishing scallop-habitat relationships is relevant to understanding the ecological processes that regulate scallop populations and to managing critical habitats. This information is particularly relevant for the D’Entrecasteaux Channel, south-eastern Tasmania (147.335 W, 43.220 S), a region that has supported significant but highly variable scallop production over many years, including protracted periods of stock collapse. Three species of scallops are present in the region; the commercial scallop Pecten fumatus, the queen scallop Equichlamys bifrons, and the doughboy scallop Mimachlamys asperrima. We used dive surveys and Generalized Additive Modelling to examine the relationship between the distribution and abundance patterns of each species and associated habitat characteristics. The aggregated distribution of each species could be predicted as a function of sediment type and species-specific habitat structural components. While P. fumatus was strongly associated with finer sediments and E. bifrons with coarse grain sediments, M. asperrima had a less selective association, possibly related to its ability to attach on a wide range of substrates. Other habitat characteristics explaining P. fumatus abundance were depth, Asterias amurensis abundance, shell and macroalgae cover. Equichlamys bifrons was strongly associated with macroalgae and seagrass cover, whereas M. asperrima abundance was greatly explained by sponge cover. The models define a set of relationships from which plausible hypotheses can be developed. We propose that these relationships are mediated by predation pressure as well as the specific behavioural characteristics of each species. The findings also highlight the specific habitat characteristics that are relevant for spatial management and habitat restoration plans.

Biodiversity and taphonomy of bivalve assemblages of the Pliocene of Algeria (Bas Chelif Basin)

Similar to the Miocene, the Pliocene of the outcrops of Bas Chelif Basin delivered abundant and much diversified fossiliferous levels of malacofauna (bivalvia). The paleontological study of two typical Pliocene series, in the center (Sidi Brahim) and at the northwestern margin of the Bas Chelif Basin (Sassel Beach), permit the identification of 4 orders, 8 families, 15 genera, and 20 species among the bivalvia. The simultaneous study of autoecological and taphonomic features of the fauna contained in the Sidi Brahim geological section allowed distinguishing at once four fauna associations, in which each one characterizes a particular ecozone which is attributed to an environment: (1) the muddy deep environment association (Cristatopecten cristatum, Pelecyroa brochii, and Tellina donacina); (2) the muddy instable and frankly deep environment association (Anadara diluvii, C. cristatum, P. brochii, and T. donacina); (3) the association of the infralittoral environments, rich in sandy supplies; and (4) the association of the upper infralittoral sandy environment and three shell assemblages—the “3D census assemblage,” “3D multihabitat time-averaged assemblage,” and “3D allochthon assemblage”—where their spatiotemporal enchainment allowed making obvious four phases of transgressive–regressive oscillation in the general transgressive tendency of Sidi Brahim section, during the lower and average Pliocene. With a reduced thickness, the Sassel Beach section is characterized, on one hand, by the setup of two fauna associations of the infralittoral sandy environments (Pecten benedictus and Ostrea lamellosa) and infralittoral muddy environments (Aequipecten opercularis, Aequipecten seniensis, and P. benedictus), and of other parts by the piling up of three types of assemblages (3D allochthonous assemblage, 3D census assemblage, and 3D multihabitat time-averaged assemblage), defining three phases, comparatively less pronounced of the transgressive cycle of the Pliocene.

Oyster (Ostrea edulis) extirpation and ecosystem transformation in the Firth of Forth, Scotland

Marine inshore communities, including biogenic habitats have undergone dramatic changes as a result of exploitation, pollution, land-use changes and introduced species. The Firth of Forth on the east coast of Scotland was once home to the most important oyster (Ostrea edulis Linnaeus, 1758) beds in Scotland. 19th and early 20th century fisheries scientists documented the degradation and loss of these beds, yet transformation of the wider benthic community has been little studied. We undertook archival searches, ecological surveys and shell community analysis using radioisotope dated sediment cores to investigate the history of decline of Forth oyster beds over the last 200 years and the changes to its wider biological communities. Quadrat analysis of the present day benthos reveal that soft-sediment communities dominate the Firth of Forth, with little remaining evidence of past oyster beds in places where abundant shell remains were picked up by a survey undertaken in 1895. Queen scallops (Aequipecten opercularis Linnaeus, 1758) and horse mussels (Modiolus modiolus Linnaeus, 1758) were once common within the Forth but have also markedly decreased compared to the earlier survey. Ouranalyses of shell remains suggest that overall mollusc biomass and species richness declined throughout the 19th century and early 20th century, suggesting broader-scale community change as human impacts increased and as habitats degraded. Inshore communities in the Firth of Forth today are less productive and less diverse compared to past states, with evidence suggesting that most of the damage was done by early bottom trawling and dredging activities. Given the pervasive nature of intensive trawling over the past 150 years, the kind of degradation we document for the Firth of Forth is likely to be commonplace within UK inshore communities.

Effects of elevated levels of suspended particulate matter and burial on juvenile king scallops Pecten maximus

The effects of exposure to elevated levels of suspended particulate matter (SPM) and burial on juvenile king scallops Pecten maximus L. were assessed in 2 separate experiments. Shell gape activity was monitored during exposure to no SPM and 'low' (50 to 100 mg l �1 ) and 'high' (200 to 700 mg l �1 ) levels of SPM for 18 d. The frequency of shell 'claps' (a complete shell closure) and shell movements (of ≥10°) differed significantly among treatments. Shell 'claps' and move- ments were significantly greater under high SPM than under low or control conditions. Scallops under low and high levels of SPM showed significantly lower growth rates compared to scallops under control conditions. The response to burial was assessed under varying burial duration (1 to 8 d), depth (0 to 5 cm) and size-fraction of sediment (fine: 0.1 to 0.3 mm, medium fine: 0.4 to 0.8 mm and coarse: 1.2 to 2.0 mm diameter). All 3 conditions had a significant influence on the ability of scallops to emerge from burial, as well as on mortality while buried. Emergence was higher at shallower depths and in coarse to medium grain sizes. Mortality rates while buried under coarse and medium grain sizes were low and appeared unrelated to depth, while within fine sediment, mortality increased with depth of burial. Survival decreased across all 3 sediment types with increasing burial duration. Comparison with earlier studies indicates that P. maximus appears more tolerant of burial and elevated levels of SPM than the queen scallop Aequipecten opercu- laris. Elevated SPM did not have any short-term effects on survival; however, the reduction in growth rate observed has implications for the management of scallop fishing grounds.

Repeatability of escape response performance in the queen scallop (Aequipecten opercularis)

In order for natural selection to operate, physiological and behavioural traits must exhibit both inter-individual variability and intra-individual consistency (i.e. repeatability) in performance. In this study, we describe individual variation and temporal repeatability in the escape responses of the queen scallop, Aequipecten opercularis, and determine whether individuals exhibited consistently high or low rankings in different aspects of the escape response. Five measures of individual performance were recorded on four occasions (days 0, 2, 7 and 28), providing proxies for sensory acuity (response latency), immediate and sustained swimming performance (burst and average clap rates), and swimming endurance (total number of claps and total time spent clapping). All components of the escape response exhibited significant inter-individual variability (all P<0.0001). Escape response latency, burst clap rate, total number of claps and total duration spent clapping maintained significant repeatability over 28 days (all P<0.016). Average clap rate was repeatable in the short term (2 days, P<0.0001) but repeatability declined by 28 days (P=0.097). Concordance analysis indicated that individuals maintained the same performance rankings over time for each component of the escape response (all P<0.001). In addition, some individuals ranked as consistently high or low performers across response latency, burst and average clap rate, and total number of claps. An individual's ability to evade predators through the provision of an escape response of an appropriate magnitude, subject to physiological, behavioural and organismal constraints, will have clear fitness-related consequences.

Patterns and impacts of fish bycatch in a scallop dredge fishery

ABSTRACT Dredging for marine bivalves can cause considerable damage to benthic invertebrates and habitats. However, it is largely unknown how dredging affects fish communities. In this study patterns and impacts of fish bycatch in scallop dredges around the Isle of Man, in the north Irish Sea, were investigated by analysing data from fisheries‐independent surveys conducted between 1992 and 2005. Almost all (97.6%) tows of the survey gear generated fish bycatch, with a total of approximately 50 species recorded. Cuckoo ray (Leucoraja naevus) and monkfish (Lophius piscatorius) dominated the bycatch, accounting for 46.82% of the total. Three other species of particular commercial or ecological interest; lemon sole (Microstomus kitt), plaice (Pleuronectes platessa) and lesser spotted dogfish (Scyliorhinus caniculus), were also abundant. Most of the cuckoo ray, monkfish and plaice captured were juveniles, whereas lesser spotted dogfish and lemon sole were a mixture of juveniles and adults. In general, rates of fish bycatch appeared low, but this may be at least partly because background fish densities around the Isle of Man were also low. There was considerable spatial, temporal, and species‐specific variation in fish bycatch, and the finer meshed dredges traditionally used to catch queen scallops (Aequipecten opercularis), caught significantly more fish than the great scallop (Pecten maximus) dredges. The density of lesser spotted dogfish bycatch increased significantly over the 14 years of the study whereas the density of monkfish decreased significantly. These patterns appear to reflect differences in the susceptibility of the two species to capture and damage by scallop dredging, and/or have been caused by regional trends in stock levels. An assessment of the impact of the local great scallop dredge fishery indicated that it may be catching substantial numbers of monkfish. Given the recent expansion of scallop dredging around the UK, such effects should be factored into ecosystem‐based management plans.Copyright © 2012 John Wiley &amp; Sons, Ltd.

The Effect of Depth on the Reproductive and Reserve Storage Cycles of the PectinidsAequipecten opercularis(L., 1758) andChlamys varia(L., 1758) in Galicia, Northwest Spain

Spat of 2 pectinid species of commercial interest were grown in suspension to study the growth of the gonad, digestive gland, and adductor muscle at 3 different depths (2.5 m, 7.5 m, and 12.5 m). For the experiments, we used spat immediately after they were detached from the collectors (Aequipecten opercularis) or 3–4 mo later (Chlamys varia). The first sexual maturation of each species was recorded. The variations observed in the gonad development pattern were clearly a result of the effect of depth on the gonad growth of the 2 species. Both species showed faster gonad development at 2.5 m. Reproduction of C. varia was more intense in deeper water. This was also the case for A. opercularis in the first reproduction period, from the end of winter to early summer. After a resting period in summer, there was a first peak of gonad growth at 2.5 m in October that did not occur at 7.5 m and 12.5 m. There was a peak in January at all depths. The reserve storage organs of both A. opercularis and C. varia showed a regular pattern of evolution. In general, the variations in the reserve organs followed the same pattern at all depths with 2 exceptions: the digestive gland in C. varia in spring at 2.5 m, which showed a faster growth rate related to higher temperatures; and the digestive gland and muscle in A. opercularis, which showed a large growth peak in late spring and early summer at 12.5 m that did not occur at other depths and that was related to lower temperatures and greater food availability. The growth of the reserve organs was more conservative despite the variations in the environmental conditions that occurred during the experimental period. Gonad growth was affected more by environmental changes, and was more versatile.

Refinement of AOAC Official MethodSM 2005.06 Liquid Chromatography-Fluorescence Detection Method to Improve Performance Characteristics for the Determination of Paralytic Shellfish Toxins in King and Queen Scallops

AOAC Official Method 2005.06 LC-fluorescence detection (FLD) method is an official alternative to the mouse bioassay for the determination of paralytic shellfish poisoning (PSP) toxins in bivalve shellfish. To validate the method for species of relevance to the UK official control monitoring program, the method performance characteristics were tested for whole king and queen scallops. Validation showed that, while the performance was generally acceptable for the quantitation of non-N-hydroxylated toxins, poor toxin recovery and sensitivity was evident for the analysis of N-hydroxylated toxins following periodate oxidation. These effects occurred in a range of scallop samples with variable temporal and spatial sources. The effects were also noted in other laboratories following a small interlaboratory study. As a result, the method was refined to improve the recovery and sensitivity of analysis following the periodate oxidation step in the PSP method for scallops. Performance improved through alterations to the preparation of the periodate oxidant, use of higher volumes for C18 cleanup, and injection volumes in combination with the use of a king scallop matrix modifier for oxidation of N-hydroxylated toxin calibration standards. A single-laboratory validation of the refined method showed that the selectivity, linearity, sensitivity, recovery, and precision were acceptable and similar to values reported previously for AOAC Official Method 2005.06 in other bivalve species. Results showed the method to be rugged for all parameters investigated, including small changes to the composition of the new periodate reagent utilized in the refined method. The refined scallops LC method was subsequently compared with the European reference method. PSP-positive scallops showed an excellent agreement between the methods for queen and Atlantic scallops, with a small level of positive bias in the LC results for whole king scallops. These differences were related solely to the use of the highest toxicity equivalence factors for toxin epimeric pairs, with gonyautoxin (GTX)1,4 and GTX2,3 in particular present at high concentrations in the king scallops. Overall, the refined LC-FLD method improved the performance characteristics of AOAC Official Method 2005.06 for the determination of PSP toxins in whole king and queen scallops, and showed a good overall agreement between the official methodologies. It is, therefore, recommended as a more appropriate option for the routine monitoring of PSP toxins in these species.

The environmental impacts of three different queen scallop ( Aequipecten opercularis) fishing gears

The negative impact of demersal fishing gears on the marine environment may be mitigated by utilizing less damaging fishing gears. Within this context three queen scallop fishing gears were tested for their catch efficiencies and their environmental impact on benthos: a traditional ‘Newhaven’ dredge, a new dredge design with a rubber lip instead of the traditional teeth as its main new design feature and an otter trawl. Both, the new dredge and the otter trawl showed high catches and relatively low by-catches. Catches made with the traditional dredge were lower and contained larger amounts of non–target species. Both dredges primarily caught invertebrate species, while by-catches of the otter trawl were dominated by demersal fish. The impact of these gears on the benthic biota demonstrated that while no effects were detected for the otter trawl both dredges showed similar negative effects. Clear negative effects were evident for the brittlestar Ophiura ophiura while positive trends for the common starfish Asterias rubens and the hermit crab Pagurus bernhardus indicated scavenging effects. Due to its higher catch efficiency the new dredge caused less damage per unit catch compared to the traditional dredge, yet compared to the otter trawl it appears less environmentally friendly. However, the new dredge may be an alternative to the otter trawls for fisheries where the by-catch of demersal fish has been identified as a significant problem.

Stable isotope variations in benthic filter feeders across a large depth gradient on the continental shelf

Spatial variations in carbon and nitrogen stable isotopes (δ 13C and δ 15N) of benthic filter feeders were investigated on an inshore-offshore gradient (0–250 km) along the continental shelf of the northern Bay of Biscay (NE Atlantic Ocean). δ 13C and δ 15N values were measured in muscle tissues of four filter-feeding mollusc species (epifaunal: Pecten maximus, Aequipecten opercularis; infaunal: Glycymeris glycymeris, Venus casina) and in benthic particulate organic matter along a corresponding water-depth gradient from 6 to 220 m. All four species showed a decreasing pattern of muscle δ 13C and δ 15N values with increasing depth. At the Ushant front (∼130 m water depth), where there is a decrease in both bottom water chlorophyll a and suspended particulate matter, muscle δ 13C and δ 15N values decreased in all species. Although δ 13C values of infaunal clams initially decreased at 30 m depth, δ 13C values of epifaunal scallops decreased around 120 m depth, far below the expected depth reduction in microphytobenthic production suggesting that carbon isotopes might not simply track microphytobenthic utilization. The difference between infaunal and epifaunal bivalve stable isotope values may reflect differences in feeding strategies. Muscle δ 15N values at the deepest stations (∼2‰) were lower than expected considering the typical trophic enrichment value of 3–4‰ between prey and consumers. These low δ 15N values may result from low metabolic rates and suggest the classic trophic enrichment may not hold true in species inhabiting deep waters. Stable isotopes in benthic filter feeders can reveal much information regarding their ecology and environment, but are not straightforward recorders of stable isotope baseline variations as is often assumed.

The long-term impacts of fisheries on epifaunal assemblage function and structure, in a Special Area of Conservation

Fisheries can have profound effects on epifaunal community function and structure. We analysed the results from five dive surveys (1975–1976, 1980, 1983, 2003 and 2007), taken in a Special Area of Conservation, Strangford Lough, Northern Ireland before and after a ten year period of increased trawling activity between 1985 and 1995. There were no detectable differences in the species richness or taxonomic distinctiveness before (1975–1983) and after (2003–2007) this period. However, there was a shift in the epifaunal assemblage between the surveys in 1975–1983 and 2003–2007. In general, the slow-moving, or sessile, erect, filter-feeders were replaced by highly mobile, swimming, scavengers and predators. There were declines in the frequency of the fished bivalve Aequipecten opercularis and the non-fished bivalves Modiolus modiolus and Chlamys varia and some erect sessile invertebrates between the surveys in 1975–1983 and 2003–2007. In contrast, there were increases in the frequency of the fished and reseeded bivalves Pecten maximus and Ostrea edulis, the fished crabs Cancer pagurus and Necora puber and the non-fished sea stars Asterias rubens, Crossaster papposus and Henricia oculata between the surveys in 1975–1983 and 2003–2007. We suggest that these shifts could be directly and indirectly attributed to the long-term impacts of trawl fishing gear, although increases in the supply of discarded bait and influxes of sediment may also have contributed to changes in the frequency of some taxa. These results suggest that despite their limitations, historical surveys and repeat sampling over long periods can help to elucidate the inferred patterns in the epifaunal community. The use of commercial fishing gear was banned from two areas in Strangford Lough in 2011, making it a model ecosystem for assessing the long-term recovery of the epifaunal community from the impacts of mobile and pot fishing gear.

Previously unknown apicomplexan species infecting Iceland scallop, Chlamys islandica (Müller, 1776), queen scallop, Aequipecten opercularis L., and king scallop, Pecten maximus L.

Examination of three scallop species from three separate locations: Iceland scallop from Icelandic waters, king scallop from Scottish waters and queen scallop from Faroese and Scottish waters, revealed infections of a previously unknown apicomplexan parasite in all three scallop species. Developmental forms observed in the shells appeared to include both sexual and asexual stages of the parasite, i.e. merogony, gametogony and sporogony, which suggests a monoxenous life cycle. Meronts, gamonts, zygotes and mature oocysts were solely found in the muscular tissue. Zoites, which could be sporozoites and/or merozoites, were observed in great numbers, most frequently in muscles, both intracellular and free in the extracellular space. Zoites were also common inside haemocytes. Examination of the ultrastructure showed that the zoites contained all the major structures characterizing apicomplexans. This apicomplexan parasite is morphologically different from other apicomplexan species previously described from bivalves. Presently, its systematic position within the phylum Apicomplexa cannot be ascertained.

Margolisiellaislandica sp. nov. (Apicomplexa: Eimeridae) infecting Iceland scallop Chlamys islandica (Müller, 1776) in Icelandic waters

Wild Iceland scallops Chlamys islandica from an Icelandic bay were examined for parasites. Queen scallops Aequipecten opercularis from the Faroe Islands and king scallops Pecten maximus and queen scallops from Scottish waters were also examined. Observations revealed heavy infections of eimeriorine parasites in 95–100% of C. islandica but not the other scallop species. All life stages in the apicomplexan reproduction phases, i.e. merogony, gametogony and sporogony, were present. Trophozoites and meronts were common within endothelial cells of the heart’s auricle and two generations of free merozoites were frequently seen in great numbers in the haemolymph. Gamonts at various developmental stages were also abundant, most frequently free in the haemolymph. Macrogamonts were much more numerous than microgamonts. Oocysts were exclusively in the haemolymph; live mature oocysts contained numerous (>500) densely packed pairs of sporozoites forming sporocysts.Analysis of the 18S ribosomal DNA revealed that the parasite from C. islandica is most similar (97.7% identity) to an unidentified apicomplexan isolated from the haemolymph of the giant clam, Tridacna crocea, from Japan. Phylogenetic analyses showed that the novel sequence consistently grouped with the Tridacna sequence which formed a robust sister clade to the rhytidocystid group.We propose the name Margolisiella islandica sp. nov., referring to both type host and type locality.

Settlement of Queen ScallopAequipecten opercularison Artificial Substrates in Aldán, Ría De Pontevedra, Galicia, Northwest Spain

Artificial collectors deployed in May and early June obtained higher numbers of Aequipecten opercularis spat than when collectors were deployed in late June and July in both 2007 and 2008. Different recruitment patterns were found in the 2 y studied. Four successive cohorts settled in both 2007 and 2008; however, in 2007 the 4 cohorts settled over short periods of time, whereas in 2008 a single cohort settled for an extended period of time and produced most of the spat of the year. The effectiveness of collectors for spat settlement decreased after 2 mo. Spat showed a fast growth rate that was density dependent. In general, the survival rate was high, mainly because there were very few predators.

Mantle cavity water oxygen partial pressure (Po2) in marine molluscs aligns with lifestyle

Marine invertebrates with open circulatory system establish low and constant oxygen partial pressure (Po2) around their tissues. We hypothesized that as a first step towards maintenance of low haemolymph and tissue oxygenation, the Po2in molluscan mantle cavity water should be lowered against normoxic (21 kPa) seawater Po2, but balanced high enough to meet the energetic requirements in a given species. We recorded Po2in mantle cavity water of five molluscan species with different lifestyles, two pectinids ( Aequipecten opercularis , Pecten maximus ), two mud clams ( Arctica islandica , Mya arenaria ), and a limpet ( Patella vulgata ). All species maintain mantle cavity water oxygenation below normoxic Po2. Average mantle cavity water Po2correlates positively with standard metabolic rate (SMR): highest in scallops and lowest in mud clams. Scallops show typical Po2frequency distribution, with peaks between 3 and 10 kPa, whereas mud clams and limpets maintain mantle water Po2mostly &lt;5 kPa. Only A. islandica and P. vulgata display distinguishable temporal patterns in Po2time series. Adjustment of mantle cavity Po2to lower than ambient levels through controlled pumping prevents high oxygen gradients between bivalve tissues and surrounding fluid, limiting oxygen flux across the body surface. The patterns of Po2in mantle cavity water correspond to molluscan ecotypes.

Trophic transfer of trace metals: Subcellular compartmentalisation in bivalve prey and comparative assimilation efficiencies of two invertebrate predators

We test the hypothesis that accumulated metal in prey that is trophically available to one predator is not necessarily equally trophically available to another predator feeding on the same prey, given the variability between invertebrate digestive systems. We provided two predators, the neogastropod mollusc Hinia reticulata and the palaemonid decapod crustacean Palaemonetes varians, with the digestive glands and adductor muscles of four bivalves radiolabelled with Zn, Cd or Ag. The bivalves (the mussel Mytilus edulis, the clam Ruditapes philippinarum, the scallop Aequipecten opercularis, the oyster Crassostrea gigas) have different metal accumulation patterns with differential dependence on soluble and insoluble detoxification, as confirmed by fractionation of the prey tissues. We found no consistent significant difference between the AE of the two predators for the three trace metals accumulated in the same prey tissues. There were no significant correlations for either predator between percentages of metal in soluble form (or soluble form with organelle-associated metal) and percentage AE for any of the three metals, allowing the conclusion that both predators are assimilating each metal from more than the soluble and organelle-associated metal fractions. For neither predator did an increased percentage of Zn in the form of metal rich granules (MRG) affect its Zn AE, but increases in the percentages of both Cd and Ag bound to MRG decreased the AE of the relevant metal in P. varians but not H. reticulata. Thus the Cd and Ag in some Cd-rich and Ag-rich granules in the bivalve tissues are not as trophically available to P. varians as they are to H. reticulata. This interspecific difference confirms that the neogastropod has the stronger digestive and assimilative powers involving Cd and Ag bound in prey than the palaemonid decapod.

Isolation and characterization of microsatellite markers in the queen scallopAequipecten opercularisand their application to a population genetic study

Microsatellites are one of the most popular markers in genetic studies but typically they need to be isolated and characterized de novo for each species. In this work, a genomic library enriched for a trinucleotide motif was con- structed to identify polymorphic microsatellite loci in Aequipecten opercularis, a scallop species commercially fished in Europe, and to examine the level of genetic variation and genetic differentiation in samples from Spain and Northern Ireland. Sequencing of 83 clones led to the identification of 30 microsatellite-containing sequences which showed often other repeated sequences. Five microsatellite loci were successfully amplified and found polymorphic. The number of alleles and the expected heterozygosity per locus ranged from 9 to 86 and 0.341 to 0.927, respectively, all localities showing similar levels of genetic variation (allelic richness, 13.164-15.487; expected heterozygosity, 0.527-0.638). Discrepancies in genotype proportions from Hardy-Weinberg equilibrium were observed in 11 out of 25 locality-locus combinations, a heterozygote deficiency occurring in all cases probably due to null alleles. Significant genetic dif- ferentiation was detected among A. opercularis from Northern Ireland, Fuengirola (southern Spain) and the homoge- neous samples from northwest Spain. Isolation by distance was the most likely hypothesis to explain the differentiation detected.

Cell turnover in tissues of the long-lived ocean quahog Arctica islandica and the short-lived scallop Aequipecten opercularis

Cell proliferation and apoptosis were investigated in tissues of two bivalve species, Arctica islandica from the German Bight (age of bivalves: 33–98 years) and Iceland (7–148 years) and Aequipecten opercularis from the English Channel (2–4 years). High proliferation rates (10% nuclei dividing) and apoptosis in tissues of A. opercularis were in line with high-energy throughput and reduced investment into antioxidant defence mechanisms in the scallop. In contrast, cell turnover was slow (<1% nuclei dividing) in A. islandica and similar in mantle, gill and adductor muscle between young and old individuals. In the heart, cell turnover rates decreased with age, which indicates less-efficient removal of damaged cells in ageing A. islandica. Cell turnover rates, mass specific respiration and antioxidant enzyme activities were similar in German Bight and Iceland ocean quahog. Variable maximum life expectancies in geographically separated A. islandica populations are determined by extrinsic factors rather than by fundamental physiological differences.