Benthic Bivalves Research Articles

Molecular characterization of a novel sulfide:quinone oxidoreductase from the razor clam Sinonovacula constricta and its expression response to sulfide stress.

The razor clam Sinonovacula constricta is a commercial benthic bivalve, and burrows the deeper cave than the other buried benthic bivalves. Due to the little exchange of seawater and to anoxic conditions, S. constricta is exposed to considerable amounts of sulfide during low tide, but exhibits strong sulfide tolerance. Mitochondrial sulfide oxidation is a particular defense strategy against sulfide toxicity of sulfide-tolerant organisms, for which sulfide:quinone oxidoreductase (SQR) is the first key enzyme. In order to investigate the mechanism of sulfide tolerance in S. constricta, its SQR (designated as ScSQR), was cloned and characterized. The full-length cDNA of ScSQR was 3698 bp and encoded 443 amino acids. The deduced ScSQR protein contained conserved FAD-binding domains, two cysteine residues, two histidines, and one glutamic acid, which are the essential elements for the catalytic mechanism of SQR. Subcellular localization analysis by the TargetP 1.1 prediction and the Western blot confirmed that ScSQR was only located in the mitochondria. The response of ScSQR in the gill and liver of S. constricta were investigated during sulfide exposure (50, 150, and 300 μM sulfide) for 0, 3, 6, 12, 24, 48, 72, and 96 h by qRT-PCR. Moreover, the time-course expressions of ScSQR protein in the S. constricta gill were detected when exposed to 150 μM sulfide by Western blot. The expression level of ScSQR increased significantly and showed a time-dependent pattern. In addition, under sulfide stress, the expression level of the gill was higher than that of liver. Together, our results suggest that ScSQR may perform important roles in protecting cells from sulfide stress by participating in mitochondrial sulfide detoxification and providing high sulfide tolerance to S. constricta.

Heavy metal concentrations in commercial marine organisms from Xiangshan Bay, China, and the potential health risks

Commercial marine organisms were collected from the coast of Xiangshan Bay to investigate the concentrations of eight heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) and evaluate the potential health risks. The results indicated considerable variations in the heavy metal concentrations among six species groups, of them mollusks (seasnail, benthic bivalve, and oyster) generally contained relative high levels of most metals, followed by crustaceans (crab and shrimp), by contrast, fish had low concentrations of all metals, except Hg. Three heavy metal groups were identified to interpret the accumulative characteristics in the marine organisms. Spatial distributions illustrated the geographical variations of heavy metal concentrations in the sampling areas. Moreover, maricultured organisms demonstrated lower heavy metal concentrations than did the wild. Health risks of most heavy metals exposed from marine organism consumption were safe, except for As which is associated with the high target cancer risk values.

First insights towards the population genetic structure and the phylogeographic status of the horse mussel (Modiolus barbatus) from the eastern Mediterranean

AbstractThe horse musselModiolus barbatusis a marine benthic bivalve, distributed mainly in the Mediterranean basin, that constitutes a fishery product of high economic importance and a promising candidate for aquaculture. The current study provides the first insights regarding the genetic profile ofM. barbatuspopulations from the eastern Mediterranean, by analysis of a partial segment of the mitochondrialCOIgene in individuals collected from five sampling localities within the Aegean Sea. To the best of our knowledge, the derived haplotypes represent the first DNA barcodes ofM. barbatusfrom the entire Mediterranean region. Maximum likelihood phylogenetic analysis revealed thatM. barbatusfrom the North Sea andM. barbatusfrom the eastern Mediterranean may not belong to the same species and as a consequence, there might be three species of the genusModiolusin Europe. On the other hand, eastern MediterraneanM. barbatushaplotypes were found to be more closely related to the Asian-PacificModiolusspecies. All geographic populations analysed displayed high levels of genetic diversity, in terms of haplotype and nucleotide diversity and a considerable number of unique alleles. Divergence among populations was found at generally low levels, corresponding with the majority of pairwiseFstvalues not being significant. These findings suggest no population structure and high levels of gene flow, a common feature observed in marine bivalves with long pelagic larval phases.

Comparison and combination of selective grazing on natural seston by benthic bivalves (Hyriopsis cumingii) and pelagic fish (Hypophthalmichthys molitrix).

Biomanipulation of filter-feeding bivalves or fish can serve as complementary measures to zooplankton manipulation approach in lakes dominated by large-sized algae. A laboratory grazing experiment was conducted to compare the selective grazing of benthic bivalves (Hyriopsis cumingii) and planktivorous fish (silver carp) on particle size and algae species. Their combination grazing effects were also detected. The results showed that the clearance rates of silver carp were higher than that of H. cumingii, and that silver carp preferred particles in the 30-50 and 50-100μm size fraction whereas H. cumingii did not show a significant selective grazing on seston size. Furthermore, the differences between the selective grazing of H. cumingii and silver carp on algae species were detected. Some algae species, which had not been digested well by silver carp, were not detected in H. cumingii's pseudofeces. Similarly, some algal species in the pseudofeces of bivalves were not detected in the feces of fish. Moreover, the combined clearance rates of H. cumingii and silver carp (ranging from 12.14 to 95.99mLgDW-1h-1) were higher than that of single filter feeder (0.47 to 10.18mLgDW-1h-1). We suggest therefore that when using biomanipulation measures to control large-sized algal overgrowth, a combination of different filter feeders may be a better way considering their collaborative grazing in both particle size and algae species selectivity.

Ion microprobe–measured stable isotope evidence for ammonite habitat and life mode during early ontogeny

AbstractAmmonites have disparate adult morphologies indicative of diverse ecological niches, but ammonite hatchlings are small (~1 mm diameter), which raises questions about the similarity of egg incubation and hatchling life mode in ammonites. ModernNautilusis sometimes used as a model organism for understanding ammonites, but despite their outward similarities, the groups are only distantly related. Trends in ammonite diversity and extinction vulnerability in the fossil record contrast starkly with those of nautilids, and embryonic shells from Late Cretaceous ammonites are two orders of magnitude smaller than nautilid embryonic shells. To investigate possible environmental changes experienced by ammonite hatchlings, we used secondary ion mass spectrometry to analyze the oxygen and carbon isotope composition of the embryonic shells and early postembryonic whorls of five juveniles ofHoploscaphites comprimusobtained from a single concretion in the Fox Hills Formation of South Dakota. Co-occurring bivalves and diagenetic calcite were also analyzed to provide a benthic baseline for comparison. The oxygen isotope ratios of embryonic shells are more like those of benthic bivalves, suggesting that ammonite eggs were laid on the bottom. Ammonite shell immediately after hatching has more negative δ18O, suggesting movement to more shallow water that is potentially warmer and/or fresher. After approximately one whorl of postembryonic growth, the values of δ18O become more positive in three of the five individuals, suggesting that these animals transitioned to a more demersal mode of life. Two other individuals transition to even lower δ18O values that could suggest movement to nearshore brackish water. These data suggest that ammonites, like many modern coleoids, may have spawned at different times of the year. Because scaphites were one of the short-term Cretaceous–Paleogene extinction survivors, it is possible that this characteristic allowed them to develop a broader geographic range and, consequently, a greater resistance to extinction.

High benthic methane flux in low sulfate oceans: Evidence from carbon isotopes in Late Cretaceous Antarctic bivalves

The shell material of marine benthic bivalves provides a sensitive archive of water chemistry immediately above the sediment–water interface, which in turn is affected by sedimentary geochemistry and redox reactions. Sulfate has a major controlling effect on sedimentary carbon cycling, particularly the processes of methane production and oxidation, with lower concentrations of sulfate likely resulting in an increase in sedimentary methane production. Whilst it is accepted that ocean sulfate varied markedly across the Phanerozoic, evidence of changes in methane production in sediments has so far been lacking. There is potential for the oxidation products of sedimentary methane to be preserved and detected in marine fossils. Here we present the results of high resolution carbonate isotope records from two taxa of well-preserved shallow-infaunal bivalve (Lahillia and Cucullaea) collected from the marine shelf succession across the Cretaceous–Paleogene (K–Pg) boundary in Seymour Island, Antarctica. The succession has pre-existing subtle indications of more abundant methane, and the time period is characterized by much lower marine sulfate concentrations than modern.These shell carbonate–carbon isotope records vary widely: at one extreme, shells have typical average values and small ranges compatible with a contemporaneous marine dissolved inorganic carbon (DIC) source and modern-style sedimentary carbon cycling. At the other, the shells have large-amplitude annual cycles of carbon isotopic variability of up to 23.8‰ within a single year of growth and shell carbonate δ13C compositions as negative as −34‰. Shells with these increased ranges and unusually negative values are found at discrete intervals and across both bivalve taxa. The contribution of methane required to explain the most negative carbonate–carbon isotopic values in the bivalve shells is extremely high (between 30 to 85% of bottom-water DIC based on mass balance calculations). Records of organic-carbon isotopes from the same succession remained between −26.1 and −21.7‰ throughout, suggesting that methane influence was restricted to bottom-waters. A lack of authigenic carbonate in the section indicates that methane oxidation progressed aerobically and may have provided a significant driver for transient bottom water de-oxygenation.Where methane addition is indicated, the seasonal sensitivity precludes control by methane hydrates. We argue that these data represent the increased importance and sensitivity of methanogenesis in the sediments, enabled by lower ocean sulfate concentrations during the Late Cretaceous. The tendency towards a more dynamic role for marine methane production and oxidation is likely to apply to other times of low marine sulfate in Earth's history.

Seasonal and Spatial Variations of Macro Benthos in the Intertidal Mudflat of Southern Yellow River Delta, China in 2007/2008

In order to examine the seasonal and spatial distributions of benthic animals in the intertidal mudflat of the southern Yellow River Delta, field investigations were carried out in 2007 and 2008 and multiple methods were applied. Results showed that, the biomass of macro benthos ranged at 0.75-1151.00 g wet m−2 and averaged at 156.31 g wet m−2, in which Mactra veneriformis accounted for 75.6%-93.4% of the total macro benthic biomass. More than 90% of macro benthos inhabited in the middle and low tide lines, and higher biomass occurred in early summer and lower in winter. Statistical analysis showed that: 1) M. veneriformis growth was primarily favored at higher temperature and lower salinity; 2) after long time interaction, benthic bivalve grazers led to patching distributions of Chlorophyll a (Chl a); 3) macro benthic biomass positively related with Chl a when the concentration of Chl a was low, but they were negatively related when Chl a concentration was high; and 4) furthermore, the biomass of benthic bivalves peaked in the sediment with median grain size about 0.55 mm, but decreased gradually in coarse or fine sediments. The secondary productivity ranged at 0.37-283.68 g m−2yr−1 and averaged at 47.88 g m−2 yr−1, in which 69.7% was contributed by M. veneriformis It was estimated that primary production was transformed to secondary production at a rate of 6.87% approximately, which implies that there is a local sustainability of high bivalve production.

Oceanographic variation influences spatial genomic structure in the sea scallop, Placopecten magellanicus.

Environmental factors can influence diversity and population structure in marine species and accurate understanding of this influence can both improve fisheries management and help predict responses to environmental change. We used 7163 SNPs derived from restriction site‐associated DNA sequencing genotyped in 245 individuals of the economically important sea scallop, Placopecten magellanicus, to evaluate the correlations between oceanographic variation and a previously identified latitudinal genomic cline. Sea scallops span a broad latitudinal area (>10 degrees), and we hypothesized that climatic variation significantly drives clinal trends in allele frequency. Using a large environmental dataset, including temperature, salinity, chlorophyll a, and nutrient concentrations, we identified a suite of SNPs (285–621, depending on analysis and environmental dataset) potentially under selection through correlations with environmental variation. Principal components analysis of different outlier SNPs and environmental datasets revealed similar northern and southern clusters, with significant associations between the first axes of each (R 2 adj = .66–.79). Multivariate redundancy analysis of outlier SNPs and the environmental principal components indicated that environmental factors explained more than 32% of the variance. Similarly, multiple linear regressions and random‐forest analysis identified winter average and minimum ocean temperatures as significant parameters in the link between genetic and environmental variation. This work indicates that oceanographic variation is associated with the observed genomic cline in this species and that seasonal periods of extreme cold may restrict gene flow along a latitudinal gradient in this marine benthic bivalve. Incorporating this finding into management may improve accuracy of management strategies and future predictions.

Trace metals in oysters: molecular and cellular mechanisms and ecotoxicological impacts.

Oysters are important benthic bivalves in coastal and estuarine environments. They are widely farmed due to their rapid growth and taste; they are also widely applied in environmental monitoring of coastal pollution due to their accumulation of contaminants. Most importantly, oysters are among the few marine organisms that are considered to be hyper-accumulators of many toxic metals, such as cadmium, copper and zinc. As such, there is a tremendous call to study the interactions between metals and oysters, especially due to the increasing metal pollution in many coastal and estuarine waters. Over the past decades, many studies have focused on metal accumulation in oysters as well as the ecotoxicological effects of metals on oysters. In this review, we summarize the recent progress in our understanding of the molecular and cellular mechanisms of metal accumulation, sequestration and toxicity in oysters. Applications of modern technologies such as omics and nanoscale imaging have added significantly to our knowledge of metal biology in oysters. Variations between different metals also demonstrate the diversity of the interactions between oysters and metals. Despite this recent progress, however, there is a need for further study of the molecular mechanisms of metal uptake and toxicity as well as the joint effects of metal mixtures on oyster populations. Oysters have higher numbers of stress responsive genes than most animals, which may have been induced by gene duplication during the evolution of their intertidal environmental adaptations. The divergent expression of stress responsive genes may explain the different tolerances for metals among different species. These fundamental studies may eventually provide promising solutions for reducing toxic metal concentrations in oysters for safe consumption by humans. To conclude, the complexity of life history and metal chemistry of oysters coupled with emerging pollution and application of modern techniques represents an important and exciting research area in modern ecotoxicology.

Immunotoxicity of nanoparticle nTiO2 to a commercial marine bivalve species, Tegillarca granosa

The increasing production and extensive application of nanoparticles (NPs) inevitably leads to increased release of NPs into the marine environment and therefore poses a potential threat to marine organisms, especially the sessile benthic bivalves. However, the impacts of NPs on the immunity of commercial and ecological important bivalve species, Tegillarca granosa, still remain unknown to date. In addition, the molecular mechanism of the immunotoxicity of NPs still remains unclear in marine invertebrates. Therefore, the immunotoxicity of nTiO2 exposure to T. granosa at environmental realistic concentrations was investigated in the present study. Results obtained showed that the total number, phagocytic activity, and red granulocytes ratio of the haemocytes were significantly reduced after 30 days nTiO2 exposures at the concentrations of 10 and 100 μg/L. Furthermore, the expressions of genes encoding Pattern Recognition Receptors (PPRs) and downstream immune-related molecules were significantly down-regulated by nTiO2 exposures, indicating a reduced sensitivity to pathogen challenges. In conclusion, evident immunotoxicity of nTiO2 to T. granosa at environmental realistic concentrations was detected by the present study. In addition, the gene expression analysis suggests that the PRRs (both TLRs and RIG1 investigated) may be the molecules for NPs recognition in marine invertebrates.

Passive transport of a benthic bivalve (Corbicula fluminea) in large lakes: implications for deepwater establishment of invasive species

Once introduced into a new ecosystem, the benthic bivalve Corbicula fluminea (Asian clam) will spread rapidly through both active and passive transport. In Lake Tahoe, CA-NV, where C. fluminea was introduced in 2002, populations have been found to thrive at shallow depths, where individuals are reproductive, but also at deeper depths where the only possible mechanism of population growth is downslope recruitment. This study used a variety of field and laboratory measurements to parameterize a hydrodynamic drag force model to predict passive clam transport under varying flow conditions. Laboratory results for clam shells ranging from 5 to 20 mm in length under flow conditions from 10 to 25 cm s−1 were used to solve for drag and lift coefficients. Field results are presented during weak stratification (September 2010–March 2011) when cooler water temperatures acted as a potential stressor for buried individuals to rise to the surface and be subjected to flows from which they would otherwise be isolated. During episodic wind events throughout this time period, peak horizontal water velocities of 25 cm s−1 and peak vertical (downwards) water velocities of 4 cm s−1 were measured in which all size classes of adult C. fluminea were potentially transported. Using a fundamental hydrodynamic drag force model approach to predict passive transport, the results of this study can be extended to other bivalve species for a wide array of flow conditions.

Bioaccumulation of heavy metals and health risk assessment in three benthic bivalves along the coast of Laizhou Bay, China

This study investigated the tissue- and species-specific bioaccumulation of heavy metals (Cr, Cu, Hg, Zn, As, Cd, and Pb) in three benthic bivalves (the ark shell, Scapharca subcrenata; the surf clam, Mactra veneriformis; and the Manila clam, Ruditapes philippinarum) collected from the coast of Laizhou Bay in the Bohai Sea. The results demonstrated that the visceral masses of the bivalves tended to accumulate heavy metals more efficiently than their muscles. The capacities of the bivalves to bioaccumulate metals followed a similar order: Cd>Hg>Zn=As>Cu>Cr=Pb. The conditions of metal contamination in the bivalves tended to be worse along the eastern coast than in other regions. Overall, the Manila clam was more severely contaminated by heavy metals than the surf clam and ark shell. Judging by the hazard quotients (HQ) of the metals in the muscles of the bivalves, the greatest hazard risk to human health comes primarily from As.

Potential human health risk from consumption of metallic elements-contaminated benthic mollusks from Don Hoi Lot sandbar, Thailand

Environmental pollutants have raised more concerns for human health risk, especially via consumption of contaminated food. Terrestrial as well as aquatic animals are capable of bioaccumulation a variety of toxic substances including metallic elements. With increasing anthropogenic activities along the coastal areas, living organisms have more chances to be exposed to released contaminants. In this study, seven metallic elements (Cd, Cu, Fe, Mn, Ni, Pb and Zn) were determined in sediments and water from Don Hoi Lot sandbar, Samutsongkharm province, Thailand. Potential human health risks via the consumption of two benthic bivalves Solen corneus (Larmarck, 1818) and Meretrix meretrix (Linnaeus, 1758) were also estimated using the target hazard quotients (THQs). The variations of metallic element concentrations were apparent between wet and dry season. Fe was the predominate metallic element in the sediment and the remaining were Mn>Pb>Zn>Ni>Cu>Cd. Whereas metallic element concentrations in water were Pb>Ni>Fe>Zn>Cu>Mn>Cd. PCA analysis confirmed that the contaminations of these metallic elements were from Mae Klong river surface water. Most Pb THQ values in both S. corneus and M. meretrix were >1 indicating that human health risk is of concern. However, the sum of THQs of an individual metallic element should also be considered since multiple metallic elements exposure is so common.

Permian endemic bivalves of the “Irati anoxic event”, Paraná Basin, Brazil: Taphonomical, paleogeographical and evolutionary implications

Anoxic to dysoxic conditions must have existed in the Paraná Basin during the deposition of the Permian oil-bearing shales of the Irati Formation, reflecting the marine isolation of the basin from the Panthalassic Ocean. In this environment, benthic invertebrates are extremely rare, in contrast to the overlying Serra Alta and Teresina formations, which were deposited in dysoxic/oxic waters, respectively. Hence, the abundant shallow-burrowing, endemic bivalves recorded in the shales of the basal portion of the Irati Formation are one of the most distinctive features of this stratigraphic interval. Their preservation in offshore deposits is, however, a product of storm flows in shallow waters that swept the shells to distal settings. Subsequently, these were sorted by long-lasting shelf currents that produced dense (2–5shells/20cm2) pavements in which shells in a hydrodynamically stable posture (convex-up) predominate, forming thin, complex shell concentrations despite their simple internal stratigraphy. The new data presented here have important paleoecologic, paleogeographic and evolutionary implications and indicate that (a) during the deposition of the oil-rich shales of the Irati Formation, numerous benthic bivalves thrived in the contemporary shallow-water bottoms of the Paraná Basin; (b) the mono- to paucispecific nature of the studied shell-rich pavements is, in part, due to hydrologic shell transport; and (c) restricted connections to open ocean waters (Panthalassa) existed during Irati times. Therefore, the origin of the endemic Passa Dois molluscan fauna occurred somewhere between the interval represented by the underlying Palermo Formation and the basal portion of the Irati Formation. Finally, these endemic bivalves appeared at least ~10millionyears earlier than previously thought.

Vitellogenin’s putative role in Tegillarca granosa’s cadmium detoxification

The bloody clam, Tegillarca granosa, is a commercial benthic bivalve, having a strong accumulation ability and torrelence to cadmium. To investigate whether vitellogenin (Vg) is involved in cadmium (Cd) detoxification, the full-length cDNA of T. granosa Vg was cloned, and its expression pattern in response to cadmium exposure was studied compared with the reference metallothionein (MT) gene. The full T. granosa Vg sequence consisted of 8988 bp, including a 6930-bp open reading frame that encoded a 2309 amino acid polypeptide. The deduced Vg protein contained a Vg N-terminal domain, domain of unknown function (DUF1943), SbcC domain, and von Willebrand factor type D domain (VWD). Multiple metal-binding sites were predicted in the deduced T. granosa Vg protein, suggesting its potential in functioning as a metal-binding protein. In addition, Vg expression increased in the T. granosa digestive gland and hemolymph in time-dependent manner after exposure to 1, 3, 6 and 9 μg/L Cd for 28 days. MT expression was measured in parallel with Vg expression, and the latter was more sensitive to Cd induction than the former. Together, results of the present research suggested that Vg may play an important role in T. granosa metal detoxification.

潜砂制限がアサリの成長に及ぼす影響

In Hakodate Bay, Hokkaido, the short-necked clam Ruditapes philippinarum shows highly depressed growth rate above 30 mm in shell length. In this area, clams often burrow into the sediment at an angle, which seems to be caused by boulders in the sediment. For benthic bivalves, burrowing into sediment is an important behavior to escape severe environmental conditions and predation. To examine possible effects of boulders on burrowing behavior and growth of the clam, we compared burrowing depth of the clams in contact with boulders and those clear of boulders. The ratio of burrowing depth to shell length was higher in those clear of boulders than those touching boulders. To understand this depressed growth mechanism, we carried out a field growth experiment and a laboratory feeding experiment. In the field experiment, we compared the shell growth increments of clams with restricted burrowing into sediment and those of unrestricted burrowing for three months. Shell growth increments of the clams with restricted burrowing were smaller regardless of their initial shell sizes. In the laboratory experiment, we compared the clearance rates of clams under six different situations: predatory crabs were present or not and burrowing treatments were unrestricted (deep sediment), restricted (shallow sediment) or impossible (i.e., no sediment). Both the presence of predators and restriction of burrowing decreased the clearance rate of clams; however their interaction was not significant. These results suggest boulders in the sediment restrict burrowing, and then depress shell growth of the clams. Sediment features must be taken into account for fishery analysis and stock recovery potential in clams with burrowing behavior.

Longitudinal Plankton Dynamics in the Rivers Rhine and Elbe

We compared the longitudinal plankton development in the two large rivers Rhine and Elbe by means of four Lagrangian sampling campaigns performed within the time span 2009–2011. The campaigns revealed low chlorophyll concentrations in the Rhine along a long river stretch (Rhine-km 170 to 854) with maximum values below 5 µg L−1 in 2010. In contrast, the Elbe (Elbe-km 4 to 582) showed high and longitudinally increasing chlorophyll concentrations with maximal values of 174 µg L−1 in 2009 and 123 µg L−1 in 2011. Additional samples of the benthic bivalves along the river stretches revealed high densities of the filter feeders in the Rhine that could potentially explain losses of plankton production. Their densities in the Elbe were significantly lower, making important losses to benthic filter feeders unlikely. However, strong phytoplankton growth was observed during the sampling campaign in 2011 in the Rhine coinciding with a low discharge event. This resulted in an exceptionally high chlorophyll value of up to 244 µg L−1 in the lower river sections, a value that was not reached in the last two decades of continuous water quality monitoring in the Rhine. Even though we cannot fully explain this phenomenon, it shows that phytoplankton has a high growth potential in the Rhine but is usually controlled by other mechanisms. Tributaries represented an additional and important source of plankton biomass and suspended substances in the Rhine, whereas they primarily diluted the plankton concentrations in the Elbe. Copyright © 2015 John Wiley & Sons, Ltd.

Impacts of electrofishing for razor clams (Ensis spp.) on benthic fauna

Dredge fisheries for benthic bivalves are among the most destructive in Europe. Other options such as electrofishing may be more sustainable, although this fishing method is currently illegal under EU law. Electrofishing trials conducted under an EU derogation in the dover sole and Crangon fisheries, have been shown to increase selectivity and reduce the detrimental effect of fishing on the viability of non-target benthic species. Illegal electrofishing for razor clams Ensis spp., has been reported in Scottish waters since 2004. Whilst the effects of this electrofishing on non-target species and the environment where razor clams live are poorly understood, it could present a potentially lower impact method of harvesting razor clams than conventional dredge fisheries. This study uses both tank experiments and direct observation in the field to assess the vulnerability of a range of vertebrate and invertebrate non-target species to electrofishing. The field properties of the AC electrical stimulus commonly used in the fishery are also recorded for the first time. Both tank experiments and sea trials indicated that behavioural changes induced by the electric field were temporary, lasting for a maximum of 8min (median=3min 37s) across all species tested. Tank trials involving Ensis and three other non-target species were unable to reveal a significant difference in survival when comparing control against electrically fished individuals. Physical impacts of the fishing gear on the seabed were minimal, presenting a lower impact on the environment than current fishing methods. Our results confirm that electrofishing is a low impact method of harvesting Ensis spp., however due to its high catch efficiency the regulation of fishing effort may be required to ensure a sustainable fishery.

Spatial changes in fatty acids signatures of the great scallop Pecten maximus across the Bay of Biscay continental shelf

The spatial variability of food resources along continental margins can strongly influence the physiology and ecology of benthic bivalves. We explored the variability of food sources of the great scallop Pecten maximus, by determining their fatty acid (FA) composition along an inshore–offshore gradient in the Bay of Biscay (from 15 to 190m depth). The FA composition of the digestive gland showed strong differences between shallow and deep-water habitats. This trend was mainly driven by their content in diatom-characteristic fatty acids, which are abundant near the coast. Scallops collected from the middle of the continental shelf were characterized by higher contents of flagellate markers than scallops from shallow habitats. This could be related to a permanent vertical stratification in the water column, which reduced vertical mixing of waters, thereby enhancing organic matter recycling through the microbial loop. In the deeper water station (190m), FA compositions were close to the compositions found in scallops from shallow areas, which suggest that scallops could have access to the same resources (i.e. diatoms). Muscle FA composition was more indicative of the physiological state of scallops over this depth range, revealing contrasting reproductive strategies among the two coastal sites and metabolic or physiological adaptation at greater depth (e.g. structural and functional adjustments of membrane composition). This study therefore revealed contrasted patterns between shallow and deeper habitats for both P. maximus muscle and digestive gland tissues. This emphasizes the variability in the diet of this species along its distribution range, and stresses the importance of analyzing different tissues for their FA composition in order to better understand their physiology and ecology.

Trophic Dynamics of Filter Feeding Bivalves in the Yangtze Estuarine Intertidal Marsh: Stable Isotope and Fatty Acid Analyses.

Benthic bivalves are important links between primary production and consumers, and are essential intermediates in the flow of energy through estuarine systems. However, information on the diet of filter feeding bivalves in estuarine ecosystems is uncertain, as estuarine waters contain particulate matter from a range of sources and as bivalves are opportunistic feeders. We surveyed bivalves at different distances from the creek mouth at the Yangtze estuarine marsh in winter and summer, and analyzed trophic dynamics using stable isotope (SI) and fatty acid (FA) techniques. Different bivalve species had different spatial distributions in the estuary. Glauconome chinensis mainly occurred in marshes near the creek mouth, while Sinonovacula constricta preferred the creek. Differences were found in the diets of different species. S. constricta consumed more diatoms and bacteria than G. chinensis, while G. chinensis assimilated more macrophyte material. FA markers showed that plants contributed the most (38.86 ± 4.25%) to particular organic matter (POM) in summer, while diatoms contributed the most (12.68 ± 1.17%) during winter. Diatoms made the largest contribution to the diet of S. constricta in both summer (24.73 ± 0.44%) and winter (25.51 ± 0.59%), and plants contributed no more than 4%. This inconsistency indicates seasonal changes in food availability and the active feeding habits of the bivalve. Similar FA profiles for S. constricta indicated that the bivalve had a similar diet composition at different sites, while different δ13C results suggested the diet was derived from different carbon sources (C4 plant Spartina alterniflora and C3 plant Phragmites australis and Scirpus mariqueter) at different sites. Species-specific and temporal and/or spatial variability in bivalve feeding may affect their ecological functions in intertidal marshes, which should be considered in the study of food webs and material flows in estuarine ecosystems.