Late Quaternary fluvial channel deposits are notoriously difficult to date. In the midwestern United States, shells of aquatic mollusks can be found within many fluvial channel sediments and therefore can be radiocarbon (14C) dated to determine the age of the deposits. However, carbonate platform rocks are abundant in this region, potentially causing freshwater 14C reservoir effects (FRE) in mollusk shells. We 14C dated 11 aquatic gastropod and bivalve shell samples from specimens collected live from a stream in southwestern Ohio during three different years to assess the modern 14C reservoir effect. Modern samples yielded an average 14C FREmodern of 518 ± 65 14C yrs for 2020 (n=5), 640 ± 34 14C yrs for 2021 (n=2), and 707 ± 76 14C yrs for 2022 (n=4). We also 14C dated matched pairs of organic wood or charcoal and aquatic mollusk shells from late Pleistocene and Holocene deposits in the Four Mile Creek floodplain to determine the FREfossil. These samples, free of any potential influence from nuclear bomb testing, yielded an overall weighted mean FREfossil of 1029 ± 345 14C yrs. We then assess the advantages and limitations of both the FREmodern and FREfossil methods for determining freshwater reservoir effects. Finally, we apply the FREfossil correction to a series of shell ages from fluvial terrace deposits as a case study. The results indicate that although there is a 14C FRE in streams from the midwestern United States, aquatic shells can provide robust age control on fluvial channel deposits. More research is needed to understand the spatial and temporal variability of FREs, as well as any species effects, among various watersheds across the midwestern United States.

Over the past decade, there have been increasing recognition and concern of the toxicological impacts of microplastics (MPs) in the environment, which have been widely found in various marine environments from estuary to deep oceans. Numerous toxicological studies have been conducted on the impacts of MPs on various marine organisms, especially phytoplankton, zooplankton, bivalves, and fish of different trophic levels. These studies mainly focused on the measurements of MPs bioaccumulation and their resulting biological impacts at molecular, metabolic, biochemical, physiological, and organismic levels. This review examines the various studies conducted over the recent years on the toxicology of MPs in different marine organisms, particularly on the bioaccumulation and toxicity of MPs. The impacts of MPs on marine organisms are diverse, and the complexity of organism physiology as well as MPs physical and chemical properties need to be considered. Future studies should consider the environmental relevance of toxicological research and the development of quantitative tools to model the transport, bioaccumulation, and toxicity of MPs. These are important for the real environmental risk assessments of MPs in the marine environments.

Tsunamis are huge disasters that can significantly damage benthic organisms and the sea-bottom environment in coastal areas. It is of great ecological importance to understand how benthic ecosystems respond to such destructive forces and how individual species are affected. Investigating the effect of such disasters on animals that are seldom caught alive is particularly difficult. Bivalve mollusks are especially suitable for investigating how a tsunami affects coastal benthic species because they preserve an environmental record in their shells that can be extended back in time by crossdating the records of multiple individuals. Here we studied dead shells of Mercenaria stimpsoni, a long-lived clam, and precisely determined the time of death by using nuclear bomb–induced radiocarbon (bomb-14C) and by counting annual growth increments. First, a quasi-continuous, regional bomb-14C record was created by analyzing the shells of 6 live-caught M. stimpsoni individuals. Then 27 dead shells collected from the seafloor of Funakoshi Bay were 14C-dated and analyzed. The results showed that the huge tsunami that struck northeastern Japan on 11 March 2011 caused mass mortality of this bivalve in Funakoshi Bay. Nine of the 27 clams died during the March 2011 tsunami, probably by starvation after burial by tsunami deposits or exposure above the seafloor as a result of sediment liquefaction during the earthquake. The dating method used in this study can help us understand how long-lived marine organisms with low population density are affected by huge natural disasters such as a tsunami.

Parasitic castration of bivalves by trematodes is common, and may significantly reduce the reproductive capacity of ecologically important species. Understanding the intensity of infection is desirable, as it can indicate the time that has passed since infection, and influence the host's physiological and reproductive response. In addition, it is useful to know the developmental stage of the trematode, to understand trematode population trends and reproductive success. However, most existing methods (e.g. visually estimating the degree of infection) to assess intensity are approximate only and not reproducible. Here, we present a method to accurately quantify the percentage of bivalve gonad filled with digenean trematode tissue, based on small squashes of gonad tissue rapidly photographed under light microscopy. A maximum of 15 photographs is required to determine the percentage of the whole gonad occupied by trematodes with a minimum of 90% confidence, with smaller mussels requiring fewer. In addition, the stage of trematode infection can be assessed because full sporocysts, spent sporocysts and free cercariae are clearly distinguishable. Although variation exists in the distribution of trematodes in gonad tissue, and thus in the estimate of percentage of the gonad filled with trematodes, this method represents a marked improvement on current coarse assessments of infection which typically focus on binary presence/absence measures. This technique can be used to facilitate a more sophisticated understanding of host–parasite interactions in bivalves, and can inform the conservation and reproductive biology of environmentally crucial species.

This study combines radiocarbon (14C) analysis and sclerochronology research, an approach that to the best of our knowledge, has not yet been applied using bivalves from the Mediterranean Sea. We analyzed shells from the North Adriatic Sea: live- and dead-collected specimens of the infaunal bivalve Glycymeris pilosa and two dead-collected specimens of Glycymeris sp. According to crossdating results, growth increment time series obtained from acetate peels of the dead-collected G. pilosa (S3FP11) indicate the potential for creating longer chronologies from live and dead-collected specimens. The greatest longevity was seen in the dead-collected Glycymeris sp. specimen S3F3, estimated to be ~130 years (started growing AD 1678–1742 and died AD 1826–1860), indicating the potential to extend Glycymeris growth increment chronologies to past centuries. The highest ∆14C values obtained corresponded to the calendar year 1974. The 14C record obtained from G. pilosa correlates well with the modeled surface ocean (mixed-layer) bomb pulse curve (Reimer et al. 2009). Based on the results obtained from the shell growth increment assigned to AD 1950, the reservoir age and reservoir correction (ΔR) are 264±23 years and –6±32 years, respectively.

Multivariate analyses applied to Pleistocene bivalve assemblages from the Oga Peninsula (northern Japan) discriminate three distinct assemblages. The assemblages and their taphonomy were used to recognize environmental settings and changes. The Astarte–Cyclocardia–Glycymeris assemblage indicates shelf environment (below the storm wave base) where gravels and shells are transported from shallower settings. Supply of the exotic coarse sediment probably enabled epifaunal bivalves to inhabit the sea floor. The Glycymeris assemblage is characterized by dominance of G. yessoensis and represents current-swept shoreface environment (above the storm wave base). The Moerella assemblage is characterized by bivalves inhabiting bay to open-marine conditions and diverse deposit-feeders, indicating a moderately land-locked environment, such as an open bay or a bay mouth. Fine-grained substrata rich in organic matters in the bay were probably suitable for the deposit-feeders. Ordination also shows the assemblages along two environmental gradients, a bathymetrical one and the other related to open-marine and bay conditions. The environmental changes are explained mainly by glacio-eustatic sea-level changes and alternation of coastal geomorphology caused by local crustal movements. This study also suggests that fossil assemblages can be a powerful tool to reconstruct environments and depositional dynamics even in intensely bioturbated sedimentary facies.

The grooved carpet shell Venerupis decussata (=Ruditapes decussatus) (Linnaeus, 1758) is a Mediterranean autochthonous species that in Tunisia is heavily harvested from natural populations. It represents one of the important economic issues, especially in terms of employment and the trade balances of the country via its exportation. Despite its economic value, no studies have been carried out about the spread of this mollusc. Thus the status of this species is still poorly known and there is a knowledge gap about its stocks assessment. This study aimed to investigate the distribution, abundance and population structure of the carpet shell clam in Sfax coastal areas. In terms of geographic occupation, maps of the population distribution were drawn. The results showed a scattered distribution pattern of the species according to location ranging between 0 and 152 ind m−2. The consequence was a remarkable biomass which represented 891 tonnes of total fresh weight and high abundance levels reaching over 261.7 ± 84.2 million individuals estimated in the area of 4182 hectares. The distribution of the species has also been investigated in consideration with the size which varied markedly according to location, the shell length ranged between 2 and 41 mm. The overall sex ratio (F:M) was 1:1.17, which was significantly different from parity (1:1). The size at which 50% of the population reached maturity was 24.08 and 24.76 mm shell length for males and females, respectively. Findings of the current study suggest that V. decussata proliferates along southern Tunisian coasts.

Knowledge of the population dynamics and productivity of exploited species is essential to achieve the sustainable development of fisheries, and to ensure sustainable, long-term use of these resources. The venerid clam Anomalocardia brasiliana is harvested as a fishery resource from the French West Indies to Brazil. Yet, the exploitation of this species is not backed by management or regulations based on scientific knowledge. This can result in reduced (or even depleted) A. brasiliana density and biomass. Here, we examined the population dynamics of A. brasiliana over the course of 1 year at Cidade Beach, a sheltered sandy beach located in south-eastern Brazil. Sampling was done monthly from March 2007 to February 2008. The sampled population was predominantly juvenile. Growth and recruitment were continuous, indicating no major fluctuation in limiting factors, such as temperature, salinity and food. Nevertheless, the abundance and the turnover rate (P/B ratio) of A. brasiliana at Cidade were much smaller than the values observed in other areas of occurrence. The mortality was more intense in young individuals, and the peak of individual production occurred in individuals with a 25 mm shell length, suggesting that individuals smaller than this size should not be exploited.

Shell aragonite δ180 values of unionid freshwater mussels are applied as a proxy for past river discharges in the rivers Rhine and Meuse, using a set of nine shells from selected climatic intervals during the late Holocene. A single Meuse shell derives from the Subboreal and its δ180 values are similar to modern values. The Rhine specimens represent the Subboreal, the Roman Warm Period and the Medieval Warm Period (MWP). These shells also show averages and ranges of aragonite δ180 values similar to modern specimens. This indicates that environmental conditions such as Rhine river dynamics, Alpine meltwater input and drought severity during these intervals were similar to the 20th century. These shells do not record subtle centennial to millennial climatic variation due to their relatively short lifespan and the large inter-annual and intra-seasonal variation in environmental conditions. However, they are very suitable for studying seasonal to decadal scale climate variability. The two shells with the longest lifespan appear to show decadal scale variability in reconstructed water δ180 values during the MWP, possibly forced by the North Atlantic Oscillation (NAO), which is the dominant mode of variability influencing precipitation regimes over Europe.

Changes in total lipids and fatty acid profiles (FAPs) of gonad, digestive gland, mantle and muscle of the tropical scallop Nodipecten nodosus were examined during coastal upwelling and upwelling relaxation periods. Total lipids were most abundant in digestive gland, and intermediate in female gonad. Multidimensional scaling analysis of similarities (MDS-ANOSIM) and similarity percentage analyses (SIMPER) revealed significant changes of FAPs of the four tissues during the upwelling and upwelling relaxation periods. During both periods, SIMPER analysis revealed an internal similarity index greater than 90% for FAP of each tissue. However, during upwelling the gonad-FAP showed a lower dissimilarity index with the digestive gland-FAP (10), than with muscle-FAP (11) or mantle-FAP (13). In general, during upwelling, the fatty acids 16:0, 18:0, 16:1 n-7, 20:5n-3, 22:6n-3 and total PUFAn-3 explained 42 to 63% of variance between tissues; during upwelling relaxation, these fatty acids together with 14:0 and 18:1 n-7, explained 46 to 64% of variance. During upwelling period, MDS-ANOSIM showed a close association between FAP of digestive gland and gonad, suggesting a rapid transfer of fatty acids between these tissues, and consequently, that N. nodosus follows an opportunistic strategy during this period. In contrast, during upwelling relaxation, the slow and continuous fall in total lipid contents of digestive gland (September to November) and the progressive reduction of MDS distances between FAPs of digestive gland and gonad (August until November), suggest a gradual transfer of lipids from digestive gland to gonad to support the gonad development observed during this period. This suggests that N. nodosus switches to a conservative strategy during the upwelling relaxation period.

The Venice lagoon is the main Manila clam (Venerupis philippinarum) production site in Europe. Following the unsustainable exploitation of this site (free-access fishery) local authorities have been striving to regulate fishing activities and most clams are produced using mollusc culture techniques based on wild spat harvesting and on its seeding in appropriate, designated culture areas. Therefore, the quality and abundance of wild clam stocks are critical factors that could limit the full development of this activity. The present study aims at assessing Manila clam stocks (spat, adults per square meter) using ordinary kriging, in an area of the Venice lagoon located near the Porto Marghera industrial zone. Previous studies have identified this area as one of the most important natural clam settlement sites in the Venice lagoon. The study area was approximately 1085 ha; 46 sampling stations were examined. Stock assessment (animals were grouped by size and age group), biomass and correlation with sediment texture were evaluated. The results obtained and comparisons with studies from the literature enabled an estimation of clam recruitment potential and an analysis of the conservation status of clam stocks. Thereafter, in view of a full reclamation and an ecological restoration of the study area, different measures are proposed for the sustainable use of this area that include the establishment of a biological protection area and a shared and rational management of the nursery area; these measures could potentially increase the sustainability of clam culture in the Venice lagoon.

Sperm characteristics of scallops have not been well described in the scientificliterature. The effects of sperm release technique (thermal shock versus serotonininjection), of sperm collection technique (testis sampling versus serotonin injection), ofsperm sampling location along the genital tract, of in vitro sperm maturation, and of timepost activation on scallop sperm characteristics were assessed in the present work.Whatever sperm release technique used, no significant differences were observed regardingthe percentage of motile spermatozoa and the velocity of the average path (VAP). Comparedto testicular sperm, a higher percentage of motile spermatozoa, VAP and intracellularadenosine triphosphate (ATP) content were observed for sperm shed after serotonininjection. From the distal part of testes up to the gonopore, an increase of thepercentage of motile spermatozoa and VAP was assessed, suggesting a sperm ‘maturationprocess’ along the genital ducts. A higher increase in the percentage of motile sperm wasrecorded during a 5 min incubation of testicular sperm in seawater containing 2 mMserotonin and seawater containing 10 mM caffein compared to seawater (control). Inaddition, a higher VAP was assessed, incubating testicular sperm in caffein, compared tocontrol or serotonin. Then, the percentage of motile spermatozoa, VAP and intracellularATP content exhibited a progressive reduction during the 10 h swimming period. Mean valuesof the percentage of motile spermatozoa, VAP, sperm track linearity (LIN) andintracellular ATP content recorded at the beginning of the movement period for spermsamples collected after intragonadal serotonin injection, were 82 ± 7%,162 ± 15μm s-1, 0.33 ± 0.12 and 212 ± 133 nmol × 10-9 spermatozoa (n = 9 males), respectively. The presentstudy confirms the existence of a sperm “maturation process” along scallop genital ducts.In addition, the cessation of scallop sperm movement can be explained by the exhaustion ofATP content at the end of the movement phase.

The aim of this study was to apply indicators for monitoring the impacts of harvest in a recreational surf clam fishery. We investigated trends in abundance, biomass and size structure and proportion of sexual maturity for the pipi (Donax deltoides) in Venus Bay, Australia. The surf clam stock was sampled during the peak harvesting season in the Australian summer (November to February) at four sites exposed to varying degrees of recreational harvest. Sampling was based on three transects at each site; with 0.027 m3 (0.3 m × 0.3 m × 0.3 m) quadrats stratified within transects by tidal position. Restricted maximum likelihood mixed model analyses were used to examine fixed effect combinations after including a priori random effect for transect within site. Results demonstrated that relative abundance varied significantly (P = 0.0090) among sampling months but not among sites. Relative abundance declined across the peak summer harvest season. The proportion of maturity varied significantly (P = 0.00026) among sites whereas relative biomass varied significantly (P = 0.0043) among months by sites. Relative biomass and the proportion of maturity were considerably higher at the site exposed to minimal harvest compared to other sites. This study demonstrates that a suite of indictors including biomass, size–frequency and proportion of maturity are likely to provide a more accurate assessment of stock status in recreationally fished surf clam populations, than relative abundance. This highlights the need to develop methods to estimate relative biomass in surf clam populations that are not exploited commercially.

Limaria hians functions as a keystone species in construction of a highly diverse biogenic habitat. An investigation to quantify the biodiversity of two L. hians beds was carried out during the winter and summer seasons at two sites on the west coast of Scotland. Cores were taken semi-randomly through 100% L. hians nest material, organisms removed, identified and enumerated. Univariate and multivariate analyses of the data were used to establish temporal and locational differences. A total of 7275 individuals were found representing 282 species from 16 phyla. Univariate analysis revealed significant differences between the species richness of the two populations, whilst multivariate analysis illustrated differences in the assemblage compositions between sites and times. This study showed that in terms of richness and diversity these beds are among the most important biogenic habitats in the UK.

Juveniles of the mussel Mytilus chilensis were exposed to a dietcontaining paralytic shellfish poisoning (PSP) toxins produced by the dinoflagellateAlexandrium catenella (strain ACC02). The feeding behaviour and thedynamics of intoxication and detoxification were evaluated over an intoxication period ofnine days, followed by a detoxification period of eight days. A significant reduction inthe feeding activity was measured during the first days of exposure to the PSP toxins(days 0 and 2), followed by a period of recovery observed on days 5 and 9, when theclearance rate of the contaminated mussels significantly increased. During thedetoxification period, the contaminated bivalves showed a total recovery of clearancerate, and no significant differences were observed between contaminated and controlgroups. The intoxication dynamic was characterised by a rapid and sustained increase inthe amount of PSP toxins accumulated in the tissues of the bivalves. Due to this increase,the level of PSP toxins critical for human consumption was reached on the first day, andat the end of the intoxication period, the mussels had accumulated 1601μg STX eq. 100 g-1 tissue. During the detoxification period, adecrease of PSP toxins was observed, down to 319 μg STX eq. 100g-1 tissue. The lower clearance rates observed over the first days ofexposure would produce a decrease in the energy intake and could affect the rate of growthof juveniles. Despite this initial effect, the rapid intoxication capacity of M.chilensis corroborates that this species is a good indicator for the earlydetection of harmful algal blooms.

The dam reservoirs of the Upper Rhone were drained every three years until 2003, and the water level of the Villebois reservoir was lowered by 1.5 m. This resulted in considerable drying of its littoral habitats and the disappearance of the abundant macro-invertebrates that live in them. This study investigates the response to this drying disturbance of bivalve populations and especially of the life history traits of the two potamic species, Pisidium moitessierianum and Pisidium supinum. The low density of these bivalves observed during the months following the drying of May 2003 until spring 2004 shows that the contribution of drift in population recovery was very limited during this period. Due to the faster turnover of its cohorts and a higher increase in litter size in 2004, P. moitessierianum once again dominated bivalve communities from 2005 onwards. In the Villebois reservoir recovery of bivalve communities in terms of structure and density was total three years after the drying of 2003. Observations suggest an increase in litter size and continuous recruitment: the reproductive strategy adopted by these bivalves represent response to the fall in numbers on the one hand, and to considerable magnitudes of temperature and flow rates on the other hand, enabling the rapid adjustment of populations to drying disturbance and variations in environmental conditions. Taking into account the response of bivalve populations to this event, its effects are comparable to those of a supra-seasonal drought (Lake, 2003, Freshw. Biol., 48, 1161–1172).

Surveys conducted in the south-western Dominican Republic showed that the penshell Pinna carnea is a consistent component of seagrass beds and is absent in adjacent sandflats. Population densities were low (0.012–0.076·m−2) and the size–structure skewed towards large individuals. Trials with different types of substrata in caged spat collectors, involving a combination of sand, seagrass blades and roots, and an artificial treatment by itself, indicated no settlement preference for any of the substrata tested. Comparison of additional spat collectors (caged and uncaged) indicated high predation losses (84%) for recently settled penshells. Experiments with penshells measuring 10–30, 50–70 and 90–110 mm (anterior to posterior dorsal tip) transplanted to plots in a seagrass bed and sandflat showed that predation losses decreased with increasing size and were much less in seagrass than in the sandflat. In 10-day trials, survival in the three size-groups was 27-fold greater in the seagrass bed than on the sandflat. During 3-day trials in the sandflat, survival increased from 6% for 50–100 mm penshells to 93% for 150–170 mm penshells. At the end of 100-day trials, during which the study area was subjected to Hurricane Dennis, the only surviving penshells were large individuals (90–110 mm) that had been transplanted to the seagrass bed. All individuals transplanted to the sandflat went missing. Growth measurements showed that small penshells grow rapidly (up to 2.2 mm·d−1), but the growth rate drops markedly at ~150 mm. Rapid juvenile growth may be a strategy for reducing the period of high vulnerability to predators. The high proportion of large individuals in the population likely represents the accumulation of successive recruitments as growth slows in older penshells. Pinna carnea is mainly restricted to seagrass beds because they provide more protection from predators than adjacent habitats. Moreover, the consolidation of sediments in seagrass beds by roots and algal rhizoids provides a degree of protection from physical disturbances such as hurricanes. The advantages provided by the seagrass habitat come at a cost because we detected a mortality factor in the seagrass bed (possibly related to the ~3-fold higher silt load) that was absent on the sandflat.

The proliferation of the voluntarily-introduced cupped oyster, Crassostrea gigas, has attained the proportions of species invasion in many intertidal habitats in Europe, presumably resulting from successful reproduction of farmed individuals. It is thus imperative to better understand the reproductive characteristics of farmed oysters, since they are directly under human control. We quantified the dry tissue mass (DTM), gametosomatic index (GSI), and reproductive cycle of farmed oysters at two sites in Bourgneuf Bay, France, in relation to environmental parameters using continuously-recording probes in 2005 and 2006. The GSI was developed for this study, based on the actual area occupied by gametes, rather than the area of the gonad previously used for quantitative histological estimation of reproductive effort. The two sites, intermediate – (IT) and high-turbidity (HT), differed markedly in the amount and quality of particulate suspended matter, and also in fine-scale temperature variations. Oysters at both sites presented two spawning periods in both 2005 and 2006; Bourgneuf Bay is thus near the northernmost European limit for a 2-spawning cycle in Crassostrea gigas. Gonad maturation was initiated when spring water temperature reached 8–10 °C, and gamete atresia occurred when water temperatures transiently dipped to 15–18 °C. Spawns, which occurred above 18 °C, were timed by fine-scale water temperature variations. Particulate organic matter quality peaks, coinciding with gonad maturation, were related to DTM variations before spawning periods, for the IT oysters in both years, and for the HT oysters in 2006. The reproductive effort (GSI) of oysters was similar at both sites; however, the fates of the gametes differed according to site. At the first spawning, the IT oyster gamete emissions were +1 month delayed, as were peak water temperatures greater than 18 °C, and more pronounced, compared to the HT site. Although the second spawning showed high proportions of atretic oocytes at both sites in both years, the IT oysters evacuated twice as many gametes as the HT oysters in 2005. The IT conditions therefore appear more suited to Crassostrea gigas gamete evacuation than the HT conditions.

The inter-relationship between the pea crab Pinnotheres sinensis and its bivalve host Septifer virgatus was studied from July 2002 to December 2004. The infested bivalve generally contained a single crab (72.4–94.7%), but multiple infestation was also observed in some cases (5.3–27.6%). Seasonal fluctuations in the prevalence rate, sex ratio and ovigerous rate were examined. The prevalence rate and sex ratio increased in autumn and decreased from spring to summer. By contrast, the rate of the ovigerous female increased in summer and decreased in autumn. The carapace width of females was larger than that of males, and seasonal fluctuation in the carapace width was observed in the female crabs. All the females had a soft carapace whereas most males had a hard carapace. No females were observed outside the host, though a small number of males were observed outside it. Mating probably took place inside the host where females remained stationary, with males visiting different bivalves as well as spending much time outside the bivalves.