Physiology Of Bivalves Research Articles

Filtration and respiration responses of mussels (Mytilus edulis) to trematode parasite infections (Renicola roscovita) and transient heat exposure.

The mussel Mytilus edulis, a host to various trematode species, experiences performance decrements due to these infections. Yet, the impact magnitude and potential interactions with environmental stressors remain largely unexplored. This study scrutinizes the effect of Renicola roscovita infections on mussel filtration and respiration. We first assessed performance in both uninfected and lab-infected mussels at a mild temperature (16°C), following an acute heat ramp to 30.5°C and subsequent cooling. The experiment revealed neither a significant direct impact of the infection on the mussels' performance, nor any significant interplay between the infection and temperature variations. To account for possible infection effects obscured by low sample sizes or mussel size disparities, we conducted a reassessment at 16°C using both small and large mussels. Infection notably hampered filtration in large mussels, with a marginal impact on smaller ones. A positive correlation was found between infection intensity and mussel filtration capacity, though the infection had no discernible impact on respiration. Our consistent finding of an 11-12 % infection effect size across all experiments indicates a slight reduction in mussel filtration due to trematode infections. While the exacerbating effect of transient heat stress on the infection's impact on filtration was not statistically significant, future investigations should explore potential interactions with prolonged heat stress. Our findings underscore the nuanced ways in which parasitic infections can influence marine bivalve physiology, emphasizing the need for more comprehensive studies that incorporate environmental stressors, such as heat stress, to fully elucidate the impact of parasitism on marine ecosystem health and resilience.

Transcriptome and Network Analyses Reveal the Gene Set Involved in PST Accumulation and Responses to Toxic Alexandrium minutum Exposure in the Gills of Chlamys farreri.

Bivalve molluscs are filter-feeding organisms that can accumulate paralytic shellfish toxins (PST) through ingesting toxic marine dinoflagellates. While the effects of PST accumulation upon the physiology of bivalves have been documented, the underlying molecular mechanism remains poorly understood. In this study, transcriptomic analysis was performed in the gills of Zhikong scallop (Chlamys farreri) after 1, 3, 5, 10, and 15 day(s) exposure of PST-producing dinoflagellate Alexandrium minutum. Higher numbers of differentially expressed genes (DEGs) were detected at day 1 (1538) and day 15 (989) than that at day 3 (77), day 5 (82), and day 10 (80) after exposure, and most of the DEGs were only regulated at day 1 or day 15, highlighting different response mechanisms of scallop to PST-producing dinoflagellate at different stages of exposure. Functional enrichment results suggested that PST exposure induced the alterations of nervous system development processes and the activation of xenobiotic metabolism and substance transport processes at the acute and chronic stages of exposure, respectively, while the immune functions were inhibited by PST and might ultimately cause the activation of apoptosis. Furthermore, a weighted gene co-expression network was constructed, and ten responsive modules for toxic algae exposure were identified, among which the yellow module was found to be significantly correlated with PST content. Most of the hub genes in the yellow module were annotated as solute carriers (SLCs) with eight being OCTN1s, implying their dominant roles in regulating PST accumulation in scallop gills. Overall, our results reveal the gene set responding to and involved in PST accumulation in scallop gills, which will deepen our understanding of the molecular mechanism of bivalve resistance to PST.

Cardiac function of the deep-sea bivalve, Calyptogena okutanii, observed at atmospheric pressure via magnetic resonance imaging

In order to assess the cardiovascular physiology of bivalves living in deep-sea hydrothermal vents and seeps, the Calyptogena okutanii was collected at depths of around 860 m at the Off Hatsushima seep site. The anatomical structure and function of the heart of the clams were studied by T1-weighted magnetic resonance imaging (T1w-MRI) at atmospheric pressure in seawater without sulfide supply at 10 °C. In the 58 MRI sessions employing 5 clams at 2–3 days after sampling, the average heart rate was 6.5 ± 2.0 beats·min−1, which was lower than the average of 5 individual Bathymodiolus platifrons (10.3 beats·min−1). A regular rhythm was observed in 50% of the sessions, and arrhythmia (including cardiac arrest) appeared in the remaining sessions. The arrhythmia appeared more frequently than the regular heartbeat during sessions with foot motion. Indeed, a short cardiac arrest was often observed during extension of the foot, and the heartbeats restarted when the foot was withdrawn into the shell. The ejection fraction of the ventricle of C. okutanii (75%) was higher than those shown by the Mytilus and human. In a separate experiment, the heart rate of 2 clams was measured for 7 days after sampling. Foot motion was hardly observed after the 6th day, and the faster and slower components of the heart rates decreased and increased from the 5th day after sampling, respectively. Judging from these results, the pattern of the heart rate frequency distribution might be useful to assess the vital condition of C. okutanii.

A novel peptide identified from visceral ganglia induces oocyte maturation, spermatozoa active motility, and spawning in the pen shell Atrinapectinata

The identification of novel peptides that regulate reproduction is essential for studying reproductive physiology in bivalves. Therefore, we aimed to identify peptides that affect the reproductive physiology of bivalves. We identified an oocyte maturation-, sperm motility-, and spawning-inducing peptide from the visceral ganglia of the pen shell, Atrina pectinata. The peptide consisted of 26 amino acid residues (GFDSINFPGTIDGFKDYSSNKKERLL). This peptide induced oocyte maturation and sperm motility activation at less than 1 nM upon the treatment of gonad fragments and induced spawning at 1 nmol when injected into mature individuals. Mature eggs and sperms artificially spawned by peptide administration were fertilized, and we confirmed that the development proceeded normally to veliger (D-shape) larvae. These results indicated that GFDSINFPGTIDGFKDYSSNKKERLL stimulated the gonads of pen shells and induced oocyte maturation, sperm motility activation, and spawning.

Nitrogen Isotope Sclerochronology—Insights Into Coastal Environmental Conditions and Pinna nobilis Ecology

Pinna nobilis is a large bivalve endemic to the Mediterranean Sea that lives in shallow coastal areas. Due to its size and relatively fast shell growth rates, it is an interesting taxon for high-resolution study of nitrogen isotopes of carbonate bound organic matter (δ15NCBOM). In this study we tested if P. nobilis shells can be used as an indicator of the nitrogen isotope baseline of the system, if it can provide high-resolution data on environmental δ15N variability, and if the chemical properties of the shell and biomineralization process change in response to mass mortality events spreading in the Mediterranean. Shells were opportunistically collected during 2019 and 2020 by skin diving, as a part of a project on mortality monitoring, from four shallow coastal localities in the eastern Adriatic. Shell powder for δ15NCBOM analysis was collected by milling sample swaths from the internal (low-resolution) and external (high resolution) shell surface. Significant differences in δ15NCBOM, obtained from the internal shell surface, were observed between sampling localities with different anthropogenic influences, with lowest values (∼3–4‰) recorded for shells obtained from Pag Bay, and highest (∼6–8‰) for shells sampled in Lim and Kaštela Bays. High-resolution samples from the external shell surface of Pinna nobilis showed spatial and temporal variations in δ15NCBOM values, with temporal resolution of 1–3 weeks. High-resolution δ15NCBOM data obtained from the shell Kas1 corresponded to a time interval from spring 2018 to summer 2019 and had a pronounced increase of δ15NCBOM values closest to the shell margin coupled with a decrease in δ13Cshell values, indicating that this animal was experiencing stressful conditions several months prior to its death. According to our findings, δ15NCBOM values from P. nobilis shells can serve as an indicator of the isotopic baseline of the ecosystem potentially as a powerful tool to study bivalve physiology.

Effects of the toxic dinoflagellate Alexandrium catenella on the behaviour and physiology of the blue mussel Mytilus edulis

The effects of harmful algae on bivalve physiology are complex and involve both physiological and behavioural responses. Studying those responses is essential to better describe and predict their impact on shellfish aquaculture and health risk for humans. In this study we recorded for two months the physiological response of the blue mussel Mytilus edulis from Eastern Canada to a one-week exposure to a paralytic shellfish poisoning producing dinoflagellate strain of Alexandrium catenella, isolated from the St Lawrence estuary, Canada. Mussels in a ‘control’ treatment were fed continuously with a non-toxic diet, while mussels in a ‘starvation’ treatment were fed the same non-toxic diet the first week and subsequently starved for seven weeks. Mussels in a ‘toxic’ treatment received A. catenella for one week before being starved until the end of the experiment. Over a two-month experiment we monitored shell and tissue growth, filtration capacity, respiration rate, byssal attachment strength, valve opening behaviour, and toxin content in tissues. Mussels fed normally on the toxic dinoflagellate and accumulated an average of 51.6 µg STXeq 100 g–1 after one week of exposure. After seven weeks of depuration, about half of the specimen showed levels around 18 µg STXeq 100 g–1. The condition index of exposed mussels (‘toxic’ treatment) decreased rapidly from the start as compared to mussels that received a one-week non-toxic diet (‘starvation’ treatment). Oxygen consumption rates increased in the ‘toxic’ treatment before leveling out with that of mussels from the ‘starvation’ treatment. Valve opening amplitude was lower in the ‘toxic’ treatment during and following the exposure. Average valve closure duration was higher right after the exposure, during the peak of mussel tissue intoxication. No significant change in byssal thread strength was observed through time in each treatment but less force was required to detach mussels from the ‘toxic’ and ‘starvation’ treatments. The number of byssus threads produced by mussels exposed to the toxic dinoflagellate was also lower than in the control group. These results represent advancements in our understanding of the impacts of harmful algae on bivalves and contribute to the development of mitigation measures necessary to both the safety of consumers and the sustainability of aquaculture operations.

EAT BREATHE EXCRETE REPEAT: Physiological Responses of the Mussel Mytilus galloprovincialis to Diclofenac and Ocean Acidification

Combined effects of the nonsteroidal anti-inflammatory drug diclofenac and lowered seawater pH were assessed on the physiological responses of the mussel Mytilus galloprovincialis. Bivalves were exposed for 1 week to natural pH (8.1) and two reduced pH values (pH −0.4 units and pH −0.7 units), as predicted under a climate change scenario. After the first week, exposure continued for additional 2 weeks, both in the absence and in the presence of environmentally relevant concentrations of diclofenac (0.05 and 0.5 µg/L). Clearance rate, respiration rate, and excretion rate were measured after 7 days of exposure to pH only and after 14 (T1) and 21 (T2) days of exposure to the various pH*diclofenac combinations. At all sampling times, pH significantly affected all the biological parameters considered, whereas diclofenac generally exhibited a significant influence only at T2. Overall, results demonstrated that the physiological performance of M. galloprovincialis was strongly influenced by the experimental conditions tested, in particular by the interaction between the two stressors after 21 days of exposure. Further studies are needed to assess the combined effects of climate changes and emerging contaminants on bivalve physiology during different life stages, especially reproduction.

Effects of high stocking density on the galectin gene expression in noble scallop Chalmys nobilis under bacterial infection

High stocking densities have been shown to have adverse effects on the physiology of bivalves. The noble scallop Chlamys nobilis is one of the most important cultured shellfish in Southern China. However, the effects of scallop stocking density on its immunity is not well understood. In this context, this study was conducted to assess the effect of high stocking density on the galectin (an important protein in innate immunity) gene expression of C. nobilis during bacterial infection. A full-length galectin (CnGal) gene was cloned. The ORF of the CnGal cDNA encodes a predicted protein containing 549 aa with four CRDs and no signal peptide. Our results reveal that high stocking density in the scallop not only led to high mortality and slow growth, but also changed tissue distribution of the CnGal expression. The individuals from the high stocking density group exhibited more differences among tissues than those from the control group, but the highest expression were both recorded in hemolymph. After the Vibrio parahaeomlyticus challenge, the gene's expression levels were all significantly up-regulated in the hemolymph and gill, but the time up to peak was different between the two tissues. The findings of this study could fill a gap in knowledge about how high stocking density affect scallop immunity at the molecular level.

Direct and indirect effects of microplastics on bivalves, with a focus on edible species: A mini-review

Bivalves play important roles in the ecosystem. However, bivalve populations have suffered a global decline in recent decades. This decline has caused public concern, because bivalves provide ecosystem services and are important sources of protein and ornaments (such as pearls) that support the fishing industry in coastal zones worldwide. Microplastics are an emerging global threat for bivalves and have been commonly detected in commercial edible bivalves, including mussels, oysters and clams. To comprehensively understand impacts of microplastics on bivalves, the potential exposure pathways by which microplastics affect bivalves are reviewed. The existing scientific evidence indicates that microplastics not only directly affect the physiology of bivalves, but also indirectly affect them by changing the structure of their sedimentary habitats, impairing their food resources and delivering persistent organic pollutants. In addition, the consumption of contaminated bivalves is a main pathway of exposure to microplastics by humans, which raises potential human health concerns. An evaluation of the hazards associated with the consumption of bivalves that contain microplastics and associated toxic chemicals is urgently needed. More studies related to the effects of microplastic fibers on bivalves should be conducted, because microplastic fibers comprise the largest proportion of microplastics in the environment and bivalves.

Bioreactivity and Microbiome of Biodeposits from Filter-Feeding Bivalves.

Bivalves serve an important ecosystem function in delivering organic matter from pelagic to benthic zones and are important in mediating eutrophication. However, the fate of this organic matter (i.e., biodeposits) is an important consideration when assessing the ecological roles of these organisms in coastal ecosystems. In addition to environmental conditions, the processing of biodeposits is dependent on its composition and the metabolic capacity of the associated microbial community. The objectives of this study were to compare the biological reactivity, potential denitrification rates, and microbial communities of biodeposits sourced from different bivalve species: hard clam (Mercenaria mercenaria), eastern oyster (Crassostrea virginica), and ribbed mussel (Geukensia demissa). To our knowledge, this is the first study to investigate and compare the microbiome of bivalve biodeposits using high-throughput sequencing and provide important insight into the mechanisms by which bivalves may alter sediment microbial communities and benthic biogeochemical cycles. We show that clam biodeposits had significantly higher bioreactivity compared to mussel and oyster biodeposits, as reflected in higher dissolved inorganic carbon and ammonium production rates in controlled incubations. Potential denitrification rates were also significantly higher for clam biodeposits compared to oyster and mussel biodeposits. The microbial communities associated with the biodeposits were significantly different across bivalve species, with significantly greater abundances of Alteromonadales, Chitinophagales, Rhodobacterales, and Thiotrichales associated with the clam biodeposits. These bioreactivity and microbial differences across bivalve species are likely due to differences in bivalve physiology and feeding behavior and should be considered when evaluating the effects of bivalves on water quality and ecosystem function.

The dinoflagellate Alexandrium minutum affects development of the oyster Crassostrea gigas, through parental or direct exposure

Harmful algal blooms are a threat to aquatic organisms and coastal ecosystems. Among harmful species, the widespread distributed genus Alexandrium is of global importance. This genus is well-known for the synthesis of paralytic shellfish toxins which are toxic for humans through the consumption of contaminated shellfish. While the effects of Alexandrium species upon the physiology of bivalves are now well documented, consequences on reproduction remain poorly studied. In France, Alexandrium minutum blooms have been recurrent for the last decades, generally appearing during the reproduction season of most bivalves including the oyster Crassostrea gigas. These blooms could not only affect gametogenesis but also spawning, larval development or juvenile recruitment. This study assesses the effect of toxic A. minutum blooms on C. gigas reproduction. Adult oysters were experimentally exposed to A. minutum, at environmentally realistic concentrations (102 to 103 cells mL−1) for two months during their gametogenesis and a control group, not exposed to A. minutum was fed with a non-toxic dinoflagellate. To determine both consequences to next generation and direct effects of A. minutum exposure on larvae, the embryo-larval development of subsequent offspring was conducted with and without A. minutum exposure at 102 cells mL−1. Effects at each stage of the reproduction were investigated on ecophysiological parameters, cellular responses, and offspring development. Broodstock exposed to A. minutum produced spermatozoa with decreased motility and larvae of smaller size which showed higher mortalities during settlement. Embryo-larval exposure to A. minutum significantly reduced growth and settlement of larvae compared to non-exposed offspring. This detrimental consequence on larval growth was stronger in larvae derived from control parents compared to offspring from exposed parents. This study provides evidence that A. minutum blooms, whether they occur during gametogenesis, spawning or larval development, can either affect gamete quality and/or larval development of C. gigas, thus potentially impacting oyster recruitment.

Alga diet formulation – An attempt to reduce oxidative stress during broodstock conditioning of Pacific oysters

The Pacific oyster Crassostrea gigas is among the most frequently cultured aquaculture species worldwide. In bivalve aquaculture, some environmental factors may induce the production of Reactive Species of Oxygen (ROS) that besides causing injuries to several vital cellular components, may lead to inflammatory processes. Usually, antioxidant enzymes of bivalves defense systems have an important role in the diminution of harmful effects of ROS. However sometimes it is not enough to restore the oxidative balance, being required an additional action of external antioxidant compounds.Knowing that biochemical composition of the diets may influence the physiology of bivalves, the aim of this study was to evaluate the effects of different ratios of microalgae and macroalgae on the oxidative stress responses during broodstock conditioning of C. gigas.Seven hundred and twenty oysters were divided in four dietary groups (3 tanks/diet; 60 oysters/tank). Each group was fed with one of the following diets: 100% macroalgae (Ulva rigida) (Diet 1); 50% macroalgae +50% live microalgae blend (Diet 2); 25% macroalgae +75% microalgae blend (Diet 3); or 100% microalgae blend (Diet 4). The microalgae blend comprised 33% Tisochrysis lutea and 66% diatoms (75% Skeletonema costatum + 25% Chaetoceros calcitrans). To assess diets effectiveness in the reduction of oysters oxidative stress, antioxidant capacity of the diets and the oxidative stress responses of the oysters were determined. The ABTS+, DPPH, ORAC, O2− and −NO assays were performed on diets to characterize their antioxidant capacity; Moreover, a possible anti-inflammatory effect of diets was assessed via human red blood cell (HRBC) membrane stabilization by heat induced assay. Catalase, lipid peroxidation, glutathione S-transferase and total and oxidized glutathione were quantified in the oysters to evaluate the dietary effects on the oxidative stress responses. Flesh weight of oysters fed Diet 3 and 4 was significantly higher than oysters fed with diets 1 and 2 (P ≤ .001). Results revealed that a 25% macroalgae and 75% microalgae blend (Diet 3) was the most effective dietary formulation in decreasing the oxidative stress, in terms of TG levels during the broodstock conditioning of the Pacific oysters, and in terms of NO and O2−; also exhibiting a potential anti-inflammatory effect. An additional advantage in supplementing 25% of Ulva rigida is the reduction of microalgae production costs during the broodstock conditioning of Pacific oysters.

Microbial Ecology of the Bivalvia, with an Emphasis on the Family Ostreidae

Rapid improvements in the technology used to assess microbial communities have led to an expansion of the breadth and scope of microbial ecology research over the past 20 y. The rapid increase in microbiome research, spurred by nextgeneration amplicon sequencing, has allowed researchers to characterize the microbial communities of organisms and environments which were previously poorly understood. Research on marine invertebrates is still developing, with the mechanisms that determine interactions between the host and their associated microbes largely unknown. Bivalves are of particular interest because of their crucial ecological and economic roles. With the anticipation of shifting environmental conditions, defining the natural variation and role of bivalve-associated microbes is vital to more complex research questions. The current knowledge of the spatial and temporal distributions of bivalve-associated microbes, microbial functional and genetic diversity, host-specific and tissue-specific interactions, and core microbial community composition is summarized here, as well as the beginning stages of understanding the role of microbiome in bivalve physiology and disease susceptibility.

Past, Present, and Future: Performance of Two Bivalve Species Under Changing Environmental Conditions

Globally, the production of marine bivalves has been steadily increasing over the past several decades. As the effects of human population growth are magnified, bivalves help provide food security as a source of inexpensive protein. However, as climate change alters sea surface temperatures (SST), the physiology, and thus the survival, growth, and distribution of bivalves are being altered. Challenges with managing bivalves may become more pronounced, as the uncertainty associated with climate change makes it difficult to predict future production levels. Modelling techniques, applied to both climate change and bivalve bioenergetics, can be used to predict and explore the impacts of changing ocean temperatures on bivalve physiology, and concomitantly on aquaculture production. This study coupled a previously established high resolution climate model and two dynamic energy budget models to explore the future growth and distribution of two economically and ecologically important species, the eastern oyster (Crassotrea virginica), and the blue mussel (Mytilus edulis) along the Atlantic coast of Canada. SST was extracted from the climate model and used as a forcing variable in the bioenergetic models. This approach was applied across three discreet time periods: the past (1986-1990), the present (2016-2020), and the future (2046-2050), thus permitting a comparison of bivalve performance under different temporal scenarios. Results show that the future growth is variable both spatially and interspecifically. Modelling outcomes suggest that warming ocean temperatures will cause an increase in growth rates of both species as a result of their ectothermic nature. However, as the thermal tolerance of C. virginica is higher than M. edulis, oysters will generally outperform mussels. The predicted effects of temperature on bivalve physiology also provided insight into vulnerabilities (e.g. mortality) under future SST scenarios. Such information is useful for adapting future management strategies for both farmed and wild shellfish. Although this study focused on a geographically specific area, the approach of coupling bioenergetic and climate models is valid for species and environments across the globe.

Feeding behavior of eastern oysters Crassostrea virginica and hard clams Mercenaria mercenaria in shallow estuaries

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 567:125-137 (2017) - DOI: https://doi.org/10.3354/meps12050 Feeding behavior of eastern oysters Crassostrea virginica and hard clams Mercenaria mercenaria in shallow estuaries E. Galimany*, J. Lunt, C. J. Freeman, S. Reed, I. Segura-García, V. J. Paul Smithsonian Marine Station, 701 Seaway Dr., Fort Pierce, FL 34982, USA *Corresponding author: galimany@icm.csic.es ABSTRACT: Eastern oysters Crassostrea virginica and hard clams Mercenaria mercenaria are key organisms for both the ecosystem services they provide and for their commercial value, but their populations have declined greatly worldwide. In an attempt to understand the interaction between bivalve physiology and environmental conditions, filter-feeding assays were carried out in a shallow estuary, the Indian River Lagoon (IRL; Florida, USA). The feeding behavior of the bivalves was studied using in situ filter-feeding devices and the biodeposition method in the 3 basins of the IRL during March and August 2015. Water characteristics (temperature, salinity, dissolved oxygen, chl a, and total, organic, and inorganic particulates) were related to possible changes in the feeding physiology of the bivalves. Oysters had higher clearance rates, filtration rates, and rejection than clams. The high rejection of inorganic matter allowed oysters to increase the organic matter ingested, leading to high absorption efficiencies. In contrast, because clam rejection was low regardless of elevated levels of inorganic matter, their absorption efficiency only increased with higher organic matter content. Both species preferred higher salinities, and the amount of organic matter in the water had a negative relationship with some feeding parameters (filtration rate for both species, and rejection for oysters). Acute environmental change brought about by a brown tide (caused by the alga Aureoumbra lagunensis) also affected these 2 bivalve species differently, supporting the hypothesis that oysters and clams have different physiological capabilities that drive their ability to survive in dynamic estuarine ecosystems. KEY WORDS: Indian River Lagoon · Brown tide · Aureoumbra lagunensis · Seston · Clearance rate · Bivalves Full text in pdf format Supplementary material PreviousNextCite this article as: Galimany E, Lunt J, Freeman CJ, Reed S, Segura-García I, Paul VJ (2017) Feeding behavior of eastern oysters Crassostrea virginica and hard clams Mercenaria mercenaria in shallow estuaries. Mar Ecol Prog Ser 567:125-137. https://doi.org/10.3354/meps12050 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 567. Online publication date: March 13, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

Accumulation of docosapolyenoic fatty acids in developing oocytes of the winged pearl oyster Pteria sterna

Ensuring supplies of pearl oyster spat for commercial grafting operations in Mexico is an ongoing problem. This has refocused research toward improving hatchery propagation protocols. Since gender plays an important role in the physiology of bivalves, we studied the use of fatty acids in the gonad and digestive gland of male and female winged pearl oyster (Pteria sterna) over its natural breeding season. Sampling included two peaks of ripening (February and April 2009), a pre-reproductive period (November 2008), and a post-reproductive period (June 2009). We found a significant increase in storage of docosapolyenoic fatty acids during development and ripe stages only in the female gonad, which indicates that these fatty acids could be a limiting factor for successful development of high quality eggs. The content of total monounsaturated fatty acids in male gonads, especially the fatty acid 16:1 n7, was significantly higher than in female gonads at the development and ripe stages. We also found differences between males and females in the use of some fatty acids in the digestive gland, especially at the spawned stage. Our results have future application in developing protocols for rearing of this pearl oyster in hatcheries. Incorporating dietary supplements containing docosapolyenoic fatty acids into diets of pearl oyster broodstock could be a practical way to improve their performance, which is crucial for enhancing the viability of larvae and spat.

Exploring the potentialities of comprehensive two-dimensional gas chromatography coupled to time of flight mass spectrometry to distinguish bivalve species: Comparison of two clam species (Venerupis decussata and Venerupis philippinarum)

Metabolomics represents an emerging topic that can be valuable in the knowledge of organism responses to different stimuli. Metabolomic studies of bivalves may reveal the constraints they are subjected to, and may help clarifying the functions most affected and the tolerance mechanisms triggered. In response to this approach, two-dimensional gas chromatography–time of flight mass spectrometry (GC×GC–ToFMS) combined with headspace solid phase microextraction (HS-SPME) was applied, for the first time to our knowledge, to the untargeted and comprehensive study of the volatile composition of clam species. Firstly, experimental parameters that influence the SPME extraction efficiency were evaluated: sample preparation mode, sample volume and SPME fiber coating. Taking into account the results from the optimization step, the metabolomic profiles were performed using 1ml of clam soft tissues homogenized with N2 and diluted in deionised water (1:2, w/v), using the PDMS/DVB fiber coating. From a total of more than 200 compounds detected per sample, 63 were tentatively identified and distributed over the chemical families of hydrocarbons, ketones, aldehydes, alcohols, and terpenoids, which seems to arise from clams own metabolism, and/or from their activity as filter-feeders. The potential of this methodology to discriminate close related species was explored by comparing the volatile profiles of Venerupis philippinarum and Venerupis decussata from Ria de Aveiro, two clams belonging to the same genus. Both species experience different environment conditions, and physiological and biochemical characteristics, which may explain the observed differentiation between their metabolic profiles. To our knowledge, this is the most detailed information available so far about clam volatile composition, which represents a valuable data for future advanced studies in the ecology, toxicology and physiology of bivalves based on clams fingerprinting.

The application of proxy data from high resolution marine archives to palaeoclimate models

Monitoring bioavailable contaminants and determining baseline conditions in aquatic environments has become an important aspect of ecology and ecotoxicology. Since the mid-1970s and the initiation of the Mussel Watch program, this has been successfully accomplished with bivalve mollusks. These (mostly) sessile organisms reliably and proportionately record changes of a range of organic and inorganic pollutants occurring in the water, food or sediment. The great majority of studies have measured the concentration of pollutants in soft tissues and, to a much lesser extent, in whole shells or fractions thereof. Both approaches come with several drawbacks. Neither soft tissues nor whole shells can resolve temporal changes of the pollution history, except through the analysis of multiple specimens collected at different times. Soft tissues and shell fractions provide time-averaged data spanning months or years, and whole shells time-averaged data over the entire lifespan of the animal. Even with regular sampling of multiple specimens over long intervals of time, the resulting chronology may not faithfully resolve short-term changes of water quality. Compounding the problem, whole shell averages tend to be non-arithmetic and non-linear, because shell growth rate varies through seasons and lifetime, and different shell layers often vary ultrastructurally and can thus be chemically different from each other. Mussel Watch could greatly benefit from the potential of bivalve shells in providing high-resolution, temporally aligned archives of environmental variability. So far, only circa a dozen studies have demonstrated that the sclerochronological approach – i.e., combined growth pattern and high-resolution chemical analyses – can provide sub-seasonally to annually resolved time-series documenting the history of pollution over centuries and even millennia. On the other hand, the sclerochronological community has failed to fully appreciate that the formation of the shell and its chemical composition is controlled by the soft parts and that a robust interpretation of the shell record requires a detailed understanding of bivalve physiology, behavior and ecology. This review attempts to bring together the Mussel Watch and sclerochronology communities and lay the foundation of a new subdiscipline of the Mussel Watch: retrospective environmental biomonitoring. For this purpose, we provide an overview of seminal work from both fields and outline potential future research directions.

Male germ cells of the Pacific oysterCrassostrea gigas: flow cytometry analysis, cell sorting and molecular expression

A technique was developed for dissection and isolation of male germ cells in the oyster Crassostrea gigas. This procedure can provide cells for the exploration of processes involved in the reproductive physiology of bivalves. Spermatogonia were chosen because of their essential role in spermatogenesis and the impact of gonia proliferation on reproductive effort. A non lethal method for determining sex and reproductive cycle stage was first validated in oysters. This first step was essential in order to constitute a homogeneous pool of oysters at the same stages of gametogenesis. Germ cell fractions were then obtained from a density gradient, and enrichment of each fraction was ratified by electron microscopy and by means of a 2-parameter flow cytometry procedure (DNA and mitochondrial staining). A significant enrichment in spermatogonia and spermatocytes was confirmed by the increased expression of markers of proliferative cells (proliferative cell nuclear antigen, PCNA) and early germ cells (oyster vasa-like gene). A preliminary cell sorting procedure is also reported, which was applied to fractions enriched in spermatogonia.

Cyclic AMP signaling in bivalve molluscs: an overview

The cyclic AMP (cAMP)-dependent signaling accounts for the control of cellular cascades involved in many physiological functions, and a wealth of information is available on the cAMP system that operates in mammalian cells. Nevertheless, cAMP has a central role also in nonmammalian vertebrates and invertebrates. The present review aims at examining the information available on bivalve molluscs, from the first studies carried out in the early 1980s to the last progresses made in the present days. The major focus is on the structural and operational characteristics of the main actors of the signaling pathway, i.e., adenylyl cyclase, G proteins, and protein kinase A, and on the role played by the cyclic nucleotide on smooth muscle, heart, gills, gonads, and metabolism regulation. Moreover, recent evidence regarding the cAMP system as a target of environmental stress factors are discussed. It will become clear that cAMP does play a wide and important role in bivalve physiology. Several issues have been sufficiently clarified, although investigated only in a few model species. However, further fundamental aspects remain unknown, mainly regarding molecular features and interactions with other signaling pathways, thus requiring further elucidation.