Accumulation In Bivalves Research Articles

Studies on the characteristics of polycyclic aromatic hydrocarbons accumulation in lipids and the disturbance of lipid metabolism of Ruditapes philippinarum

Polycyclic aromatic hydrocarbons (PAHs) constitute a class of persistent organic pollutants with strong lipophilicity, which readily accumulate within organisms and have the effect to induce disorders in lipid metabolism. The present study aimed to investigate the accumulation localization and pattern of PAHs in Ruditapes philippinarum, and to reveal the association between PAHs and lipids metabolism. The 21-day exposure experiment was conducted using a mixture of phenanthrene, chrysene, and benzo[a]pyrene (the proportion is 1:1:1) at concentrations of 0.4 μg/L, 2 μg/L, and 10 μg/L. The tissue distribution of PAHs indicated that the digestive gland was the primary site of PAHs accumulation. Meanwhile, fluorescence colocalization suggested that PAHs primarily accumulated within the lipid droplets of digestive gland cells. This study further determined the transcriptomic and lipidomic profiles of the digestive gland to analyze the key genes involved in disrupted lipid metabolism and the major lipids affected. Lipidomic analysis identified the key differential metabolites as triglycerides (TGs). Furthermore, TGs were upregulated in the digestive gland had a total carbon atom number of 50–64 and a total number of 3–9 double bonds in the acyl side chains. Biochemical analysis experiments and oil red O stained frozen sections confirmed that the content of TGs steadily increased in various tissues during the experiment, leading to an elevated digestive gland index. Changes of lipid metabolism associated genes expression level also indicated that the synthesis of lipid in digestive gland were up-regulated while the decomposition was down-regulated. This study is the first to demonstrate the cellular localization of PAHs accumulation in bivalves and confirms the pattern of variation in TGs, providing new insights into the mechanisms of PAHs bioaccumulation and lipid metabolism disruption.

Microplastic accumulation in bivalves collected from different coastal areas of Vietnam and an assessment of potential risks.

Microplastic (MP) pollution is an emerging problem in many areas around the world and in coastal areas of Vietnam, requiring more studies dedicated to the accumulation of this pollutant in the food chain as well as its potential risk to human health. This study investigated MP levels in tissues of five common bivalve species collected from aquaculture areas along the coast of Vietnam. MPs were found in all bivalve samples, with average values of 10.84 ± 2.61 items/individual or 2.40 ± 1.34 items/g wet weight. Impacts of feeding habits of bivalves showed influences on MP abundance in the samples. Fibers were the dominant shape of MPs recorded, most of which accumulated in the gills and digestive glands of all bivalve samples, with the majority falling within the size range of 300-2000µm. MPs found in all studied species had relatively similar chemical compositions, mainly composed of polypropylene (PP) and polyethylene (PE). In this study, a diverse diet consisting of different bivalve species and detailed data on the consumption rate of these species were used to assess the human health risk of MPs dedicated to the coastal communities of Vietnam. The results suggested a significant part of MP uptake by human could be via bivalve consumption, in which removing viscera and proper depuration should be applied prior to eating, thereby reducing the risk.

Sea temperature influences accumulation of tetrodotoxin in British bivalve shellfish

Tetrodotoxin (TTX), a potent neurotoxin mostly associated with pufferfish poisoning, is also found in bivalve shellfish. Recent studies into this emerging food safety threat reported TTX in a few, mainly estuarine, shellfish production areas in some European countries, including the United Kingdom. A pattern in occurrences has started to emerge, however the role of temperature on TTX has not been investigated in detail. Therefore, we conducted a large systematic TTX screening study, encompassing over 3500 bivalve samples collected throughout 2016 from 155 shellfish monitoring sites along the coast of Great Britain. Overall, we found that only 1.1 % of tested samples contained TTX above the reporting limit of 2 μg/kg whole shellfish flesh and these samples all originated from ten shellfish production sites in southern England. Subsequent continuous monitoring of selected areas over a five-year period showed a potential seasonal TTX accumulation in bivalves, starting in June when water temperatures reached around 15 °C. For the first time, satellite-derived data were also applied to investigate temperature differences between sites with and without confirmed presence of TTX in 2016. Although average annual temperatures were similar in both groups, daily mean values were higher in summer and lower in winter at sites where TTX was found. Here, temperature also increased significantly faster during late spring and early summer, the critical period for TTX. Our study supports the hypothesis that temperature is one of the key triggers of events leading to TTX accumulation in European bivalves. However, other factors are also likely to play an important role, including the presence or absence of a de novo biological source, which remains elusive.

How does bivalve size influence microplastics accumulation?

Microplastics (wasted plastic particles < 5 mm in diameter) are ubiquitously distributed in the marine environment. Filter-feeding and low trophic level bivalves are vulnerable to microplastics accumulation from the surrounding depositional environment, thereby threatening both ecological health and human food safety. Microplastics had been detected in lots of coastal Bivalvia species. However, the influence of biological morphology on the mechanism of microplastics accumulation is not clear. There is also a knowledge gap of which species are preferred for commercial consumption, which creates loopholes in risk identification for food safety. A survey on a commercial popular eaten but under-researched hard clam (Meretrix meretrix; Linnaeus, 1758) from a famous fishery port city in southern China was carried out to comprehensively analyze shell size influence on microplastics accumulation in bivalves and consequently, human intake risk via bivalve consumption. Detected microplastics count in per individual (MCI) was 24.64 ± 19.11 items · individual−1, and microplastics count per gram (MCG; wet weight with shell) was 0.66 ± 0.54 items · g−1. When the shell width grew by 1 mm, MCI increased by 1.01 times, but MCG decreased by 0.97 times. Dominant microplastics characteristics found in this study was fiber and fragment. Sizes ranged from 25 to 150 μm, and dark colors (black, red, and blue) were found. The mostly common polymers were polyethene (PE, 40%), polyethylene terephthalate (PET, 23%), and polypropylene (PP, 18%). Estimated annual intake (EAI) risk of microplastics via hard clam consumption by residents was 6652.26 ± 5327.28 items · year −1 · person −1. The microplastics in bivalves and EAI was relatively high. When shell width grew by 1 mm, EAI decreased by 0.97 times. Therefore, eating a fixed amount of larger hard clams with a relatively low amount of microplastics can reduce EAI risk for consumers. A systematic investigation of emission sources along main coast, where bivalve production is prominent will be useful for food safety control in this region.

Mitigation of harmful algal blooms caused by Alexandrium catenella and reduction in saxitoxin accumulation in bivalves using cultivable seaweeds

Alexandrium catenella is a harmful algal bloom (HAB)-forming dinoflagellate that causes significant damage to the cultivation and harvest of shellfish due to its synthesis of paralytic shellfish toxins. To evaluate the potential for macroalgae aquaculture to mitigate A. catenella blooms, we determined the effects of three cultivable macroalgae - Saccharina latissima (sugar kelp), Chondrus crispus (Irish moss), and Ulva spp. - on A. catenella in culture- and field-based experiments. Co-culture growth assays of A. catenella exposed to environmentally realistic concentrations of each macroalgae showed that all species except low levels of C. crispus caused cell lysis and significant reductions in A. catenella densities relative to control treatments of 17–74% in 2–3 days and 42–96% in ~one week (p<0.05 for all assays). In a toxin accumulation experiment, S. latissima significantly lessened (p<0.05) saxitoxin (STX) accumulation in blue mussels (Mytilus edulis), keeping levels (71.80±1.98 µg STX 100 g−1) below US closure limits (80 µg STX 100 g−1) compared to the untreated control (93.47±8.11 µg STX 100 g−1). Bottle incubations of field-collected, bloom populations of A. catenella experienced significant reductions in cell densities of up to 95% when exposed to aquaculture concentrations of all three macroalgae (p<0.005 for all). The stocking of aquacultured S. latissima within mesocosms containing a bloom population of A. catenella (initial density: 3.2 × 104 cells L−1) reduced the population of A. catenella by 73% over 48 h (p<0.005) while Ulva addition caused a 54% reduction in A. catenella over 96 h (p<0.01). Among the three seaweeds, their ordered ability to inhibit A. catenella was S. latissima > Ulva spp. > C. crispus. Seaweeds’ primary anti-A. catenella activity were allelopathic, while nutrient competition, pH elevation, and macroalgae-attached bacteria may have played a contributory role in some experiments. Collectively, these results suggest that the integration of macroalgae with shellfish-centric aquaculture establishments should be considered as a non-invasive, environmentally friendly, and potentially profit-generating measure to mitigate A. catenella-caused damage to the shellfish aquaculture industry.

Preliminary video-spatial analysis of cold seep bivalve beds at the base of the continental slope of Israel (Palmahim Disturbance)

Seafloor video surveys were carried out with the ROV Max Rover in the Palmahim Disturbance (PD) area, offshore Israel, in September 2016 during the EUROFLEETS2 SEMSEEP cruise on board the R/V AEGAEO. Preliminary observations of distribution and frequencies of bivalve accumulations show that they are mostly composed by Lucinoma kazani shells. Valves are distributed mainly along the base of authigenic carbonate crusts, in association with bacterial mats and inside inactive chimney-like structures, sometimes associated with crabs and living tubeworms. However, no living molluscs were observed.The relation between distribution of bivalve beds and seepage activity is not straightforward in the PD area. However, the presence of these accumulations and the size of L. kazani, suggest that seepages may have lasted for at least one decade, before its reduction/cessation that induced L. kazani mortality. The presence of few articulated valves of this species indicates that they were alive up to one year before the ROV observations and their different preservation state may imply different seepage phases. This research shows that chemosymbiotic benthic communities may be used as a proxy for better understanding the past dynamics of fluid emissions at the seafloor. However, further quantitative studies are needed to confirm these observations.

Corbicula fluminea rapidly accumulate pharmaceuticals from an effluent dependent urban stream

Freshwater bivalve populations are stressed by watershed development at the global scale. Though pharmaceuticals released from wastewater treatment plant effluent discharges are increasingly reported to bioaccumulate in fish, an understanding of bioaccumulation in bivalves is less defined. In the present study, we examined accumulation of 12 target pharmaceuticals in C. fluminea during a 42 day in situ study in Pecan Creek, an effluent dependent wadeable stream in north central Texas, USA. Caged clams were placed at increasing distances (5 m, 643 m, 1762 m) downstream from a municipal effluent discharge and then subsampled on study days 7, 14, 28 and 42. Acetaminophen, caffeine, carbamazepine, diltiazem, diphenhydramine, fluoxetine, norfluoxetine, sertraline, desmethylsertraline, and methylphenidate were identified in C. fluminea whole body tissue homogenates via isotope dilution liquid chromatography-tandem mass spectrometry. Tissue concentrations ranged from low μg/kg (methylphenidate) to 341 μg/kg (sertraline). By study day 7, rapid and apparent pseudo-steady state accumulation of study compounds was observed in clams; this observation continued throughout the 42 d study. Notably, elevated bioaccumulation factors (L/kg) for sertraline were observed between 3361 and 6845, which highlights the importance of developing predictive bioaccumulation models for ionizable contaminants with bivalves. Future research is also necessary to understand different routes of exposure and elimination kinetics for pharmaceutical accumulation in bivalves.

DISTRIBUTION AND BIOACCUMULATION OF HEAVY METALS Pb AND Cd ON BIVALVES Anadara nodifera, Meretrix lyrata, AND Solen lamarckii IN COASTAL WATERS OF THE WEST MADURA STRAIT

Madura strait receives waste disposal from various activites in the mainland, making it vulnerable to contamination of harmful pollutants. Some of the harmful pollutants are heavy metal Pb and Cd. The high concentration Cd and Pb give negative impacts to the biota including bivalves. This study was conducted to assess the distribution of heavy metals Pb and Cd in the waters and their accumulation in bivalves Anadara nodifera, Meretrix lyrata, and Solen lamarckii in coastal waters of the West Madura Strait. Heavy metal analysis refer to APHA 2012 using AAS. The results showed that concentration of Cd and Pb in water were below the quality standards, while in sediment were above the standard (Cd of 7.20 mg/kg and Pb of 62.06 mg/kg). The concentration of Cd in bivalve were different among the species tested A. nodifera of 6.10 mg/kg, M. lyrata of 3.65 mg/kg, and S. lamarckii of 2.74 mg/kg, as well as Pb concentration A. nodifera of 60.10 mg/kg, M. lyrata of 51.48 mg/kg, and S. lamarckii of 45.29 mg/kg). These results indicated that the three shells have exceeded the maximum limit of heavy metal contamination in food (Cd of 1.0 mg/kg and Pb of 1.5 mg/kg). Keywords: bivalve, heavy metal, Madura Strait

Taphonomy and evolution of Lower Jurassic lithiotid bivalve accumulations in the Apennine Carbonate Platform (southern Italy)

Lower Jurassic Tethyan and Panthalassan marine shallow-water successions are characterized by aberrant lithiotid bivalves belonging to the Lithiotis Fauna. Their widespread occurrence, often in rock-forming abundance, represents a global biofacies, mostly restricted to the Pliensbachian–early Toarcian. Despite their wide occurrence and their prominent role as carbonate producers in shallow-water platforms, the biogeographic and stratigraphic distribution of this group of bivalves and their evolutionary history are obscure, mostly because they commonly have not been identified at the generic or specific level. In particular, their evolution and demise in relation to important global palaeoenvironmental perturbations, such as the Pliensbachian-Toarcian boundary event and the early Toarcian oceanic anoxic event are not yet known in detail.In the Apennine Carbonate Platform of southern Italy, the Lithiotis Member, in the upper part of the Lower Jurassic Palaeodasycladus Limestones Formation, is characterized by the abundant occurrence of lithiotid bivalves. They disappear abruptly in the lowermost beds of the overlying Oolitic-oncolitic Limestones Formation, at the onset of the early Toarcian Oceanic Anoxic Event. More than 60 lithiotid bivalve concentrations occur in a nearly 120m-thick succession spectacularly exposed on freshly cut walls in a quarry west of Mercato San Severino (Salerno). Field observations on the taxonomic composition and fabric of the shell beds (packing, maximum shell size, degree of shell articulation and fragmentation) allowed to distinguish four taphofacies (A–D). Taphofacies A records the appearance and spreading of the lithiotids, with accumulations characterized mainly by small-sized and loosely packed shells. Taphofacies B records the acme of lithiotid bivalves, with densely packed accumulations of large shells. These two taphofacies yield prevailing articulated individuals, commonly in life position. Taphofacies C records a decrease of the shell packing and frequency of articulated shells. However, it is not clear whether this represents the beginning of a prolonged crisis or just the local response to less favourable environmental conditions around a sequence boundary. Taphofacies D consists of three shell beds, one in the uppermost part of the Lithiotis Member and two within the lowermost part of the Oolitic-oncolitic Limestones Formation, in the stratigraphic interval characterized by the negative carbon isotope excursion of the early Toarcian OAE. The bivalve shells of these two beds consist exclusively of disarticulated and fragmented shells, possibly reworked from underlying levels. The demise of the lithiotids carbonate factory in the Apennine Carbonate Platform and the extinction of the largest aberrant bivalves of the Lithiotis Fauna at the onset of the early Toarcian anoxic event were probably due to the physiological stress imposed by ocean acidification and increased nutrient input.

Occurrence and variation of lipophilic shellfish toxins in phytoplankton, shellfish and seawater samples from the aquaculture zone in the Yellow Sea, China

Lipophilic shellfish toxins (LSTs) produced by diverse microalgae have become a potential threat to the marine aquaculture industry in coastal regions throughout the world. In this study, phytoplankton, scallop, and seawater samples were collected and monitored in the aquaculture zone of Liuqing Bay located in the coast of Qingdao, Yellow Sea, in 2014 and 2015. Dissolved LSTs in seawater were adsorbed by solid phase adsorption toxin tracking (SPATT) bags and solid phase extraction (SPE) cartridges, respectively. PTX2 was found to be the predominant LSTs, while OA and DTX1 were detected at trace levels in the three species of Dinophysis and Phalacroma genera picked from the investigation zone. The highest quota of PTX2 occurred in D. fortii (0.28 pg cell−1), followed by D. acuminata complex (0.08 pg cell−1) and P. rotundatum (=D. rotundata) (0.02 pg cell−1). PTX2 (nd∼5.7 μg kg−1), OA (nd∼2.8 μg kg−1) and DTX1 (nd∼1.6 μg kg−1) were also observed in cultivated scallops, but in addition to the former, PTX2sa, 7-epi-PTX2sa and an isobaric form of DTX1 suspected as DTX1b were also found in the SPATT bags. The isobaric compound of DTX1 only appeared in the SPATT bags deployed in field samples of seawater. A significant higher quantity of OA was adsorbed by SPATT bags compared to DTX1, although similar concentrations of both toxins were adsorbed by SPE cartridges from the aquaculture zone. AZA2 was also found in the concentrated phytoplankton cells, which demonstrated that AZA-producing microalgae were present in this investigated area. The variation in concentrations of PTX2 adsorbed by SPATT bags could reflect the change of Dinophysis density in seawater, but there was a time lag behind the peaks of Dinophysis density. Comparative results did not support the SPATT technology as a useful warning tool for toxic algal blooms and toxin accumulation in bivalves. The data suggest that the contamination of LSTs was prevalent in the coast of Qingdao and the environmental behavior of LSTs should be explored further.

Comparative transcriptomics reveals genes involved in metabolic and immune pathways in the digestive gland of scallop Chlamys farreri following cadmium exposure

Chlamys farreri is an economically important mollusk that can accumulate excessive amounts of cadmium (Cd). Studying the molecular mechanism of Cd accumulation in bivalves is difficult because of the lack of genome background. Transcriptomic analysis based on high-throughput RNA sequencing has been shown to be an efficient and powerful method for the discovery of relevant genes in non-model and genome reference-free organisms. Here, we constructed two cDNA libraries (control and Cd exposure groups) from the digestive gland of C. farreri and compared the transcriptomic data between them. A total of 227 673 transcripts were assembled into 105 071 unigenes, most of which shared high similarity with sequences in the NCBI non-redundant protein database. For functional classification, 24 493 unigenes were assigned to Gene Ontology terms. Additionally, EuKaryotic Ortholog Groups and Kyoto Encyclopedia of Genes and Genomes analyses assigned 12 028 unigenes to 26 categories and 7 849 unigenes to five pathways, respectively. Comparative transcriptomics analysis identified 3 800 unigenes that were differentially expressed in the Cd-treated group compared with the control group. Among them, genes associated with heavy metal accumulation were screened, including metallothionein, divalent metal transporter, and metal tolerance protein. The functional genes and predicted pathways identified in our study will contribute to a better understanding of the metabolic and immune system in the digestive gland of C. farreri. In addition, the transcriptomic data will provide a comprehensive resource that may contribute to the understanding of molecular mechanisms that respond to marine pollutants in bivalves.

Two-Compartment Kinetic Modeling of Radiocesium Accumulation in Marine Bivalves under Hypothetical Exposure Regimes.

Interpreting the variable concentrations of (137)Cs in the field biological samples requires mechanistic understanding of both environmental and biological behavior of (137)Cs. In this study, we used a two-compartment model to estimate and compare the (137)Cs biokinetics in three species of subtropical marine bivalves. Significant interspecific difference of (137)Cs biokinetics was observed among oysters, mussels, and scallops. There was considerable (137)Cs assimilation from phytoplankton in the bivalves, but the calculated trophic transfer factors were generally between 0.04 and 0.4. We demonstrated a major efflux of radiocesium in the scallops (with a rate constant of 0.207 d(-1)), whereas the efflux was comparable between oysters and mussels (0.035-0.038 d(-1)). A two-compartment kinetic model was developed to simulate the (137)Cs accumulation in the three bivalves under four hypothetical exposure regimes. We showed that the bivalves respond differently to the exposure regimes in terms of time to reach equilibrium, equilibrium concentration, and maximum concentration. Bivalves suffering more frequent intermittent exposure may have higher maximum concentrations than those receiving less frequent exposure. The interspecific difference of (137)Cs accumulation in bivalves has important implications for biomonitoring and implementing management techniques. This study represents one of the first attempts to combine both dissolved and dietary pathways to give a realistic simulation of (137)Cs accumulation in marine bivalves under dynamic exposure regimes.

Harvesting molluscs in the Eneolithic: a study of freshwater bivalve accumulations from the tell settlements of Borduşani-Popină and Hârşova (Romania, 5th millennium BC)

Freshwater bivalve shells are frequently identified in faunal assemblages from Neo-Eneolithic tell settlements along the Danube River valley in South-East Romania (5th millennium BC). Up until now, significant accumulations of freshwater bivalve shells have been identified only in household refuse areas of the settlements, where they form consistent shell layers. The origin and formation of such shell accumulations and, more generally, the role of bivalves in the animal economy of the prehistoric populations that inhabited the settlements, are poorly understood. Two freshwater bivalve shell accumulations were studied in household refuse areas of Eneolithic tell settlements, one at Borduşani-Popină and the other at Hârşova tell. The occurrence of similar accumulations in the two settlements indicates generalized practices between the two communities. This first study of such accumulations addresses the relationship between bivalves and other animal species used in alimentation by the two Eneolithic communities, as well as the relationships between these communities, their environment, and the evolution of the settlements. Bivalves were harvested in the close vicinity of the settlements and large quantities were obtained only towards the end of the summer season. During this season there is an inverse relationship between high water levels in the river and the availability of bivalves for harvesting. Bivalves played an important role in the alimentation of the prehistoric populations – at Hârşova tell their contribution to alimentation in terms of energetic yield surpasses that of fish, at least for the short period of time represented by the stratigraphic sequence analysed. Bivalve shells were used, along with other types of household refuse, in construction techniques aimed at limiting soil humidity in the settlements and inside the dwellings.

Behaviour of Au-citrate nanoparticles in seawater and accumulation in bivalves at environmentally relevant concentrations

The degree of aggregation and/or coalescence of Au-citrate nanoparticles (AuNPs, mean size 21.5 ± 2.9 nm), after delivery in simulated seawater, are shown to be concentration-dependent. At low concentrations no coalescence and only limited aggregation of primary particles were found. Experiments were performed in which the marine bivalve (Ruditapes philippinarum) was exposed to AuNPs or dissolved Au and subsequently, bivalve tissues were studied by Scanning and Transmission Electron Microscopy and chemical analyses. We show that the bivalve accumulates gold in both cases within either the digestive gland or gill tissues, in different concentrations (including values of predicted environmental relevance). After 28 days of exposure, electron-dense deposits (corresponding to AuNPs, as proven by X-ray microanalysis) were observed in the heterolysosomes of the digestive gland cells. Although non-measurable solubility of AuNPs in seawater was found, evidence is presented of the toxicity produced by Au3+ dissolved species (chloroauric acid solutions) and its relevance is discussed.

Bivalve pavements from shallow-water black-shales in the Early Jurassic of northern Italy: A record of salinity- and oxygen-depleted environmental dynamics

Thin shelled-bivalve pavements which constitute the Eomiodon horizon occur in a distinctive black-shale unit in the lowermost part of a Lower Jurassic carbonate platform sedimentary system, of the Southern Alps, Italy. The Eomiodon horizon is characterised by laminated mudstone and fissile, dark grey and black organic-rich marlstone and claystone, yielding abundant bivalve pavements with monotypic to paucispecific assemblages dominated by Eomiodon, an opportunistic, brackish, shallow-infaunal veneroid bivalve. Litho- and biofacies indicate environmental conditions ranging from nearshore euhaline waters to oxygen-depleted brackish lagoon, with a high input of terrestrial organic matter, culminating in marsh and terrestrial conditions. These pavements were analysed, using a microstratigraphic approach, while considering their taxonomic composition, the geometry of the beds, their biofabric criteria (size-sorting, abundance, fragmentation, orientation, and disarticulation), origin and time-averaging. These characteristics led to reconstruction of the following palaeoenvironmental dynamics:(1)the event concentrations, represented by mass mortality of stunted and juvenile individuals caused by anoxia, are indicative of deeper and predominantly stagnant parts of the lagoon;(2)an increase in shell sizes, higher growth rate and a decrease in size sorting and winnowing illustrate higher and more continuous bottom oxygenation and enhanced life in oxygen-fluctuated environmental conditions;(3)poorly sorted, highly fragmented and bioturbated bivalve accumulations indicate the Eomiodon habitat. Here, large-sized Eomiodon specimens record a decrease in water depth and sedimentation rate and almost constantly oxygenated bottom conditions;(4)the appearance of byssally attached bivalves (Lithioperna) marks the transition from the muddy–soupy substrate of the Eomiodon habitat to firm/hard bottom conditions. This new substrate allowed the settlement of Lithioperna, a byssate isognomonid, which records a shallower and landward marsh setting.The Eomiodon horizon testifies to a short-term warm–humid climatic phase and yielded Lithioperna, the first genus of the Lower Jurassic Lithiotis fauna to appear in Southern Alps. This fauna is composed of large and aberrant bivalves which are spread throughout the Lower Jurassic Tethyan and tropical Panthalassian carbonate platforms. As a result, the Eomiodon horizon and its salinity- and oxygen-depleted environmental setting represent a possible progenitor incubator for the Lithiotis fauna.

Accumulation of Paralytic Shellfish Poison (PSP) and Biotransformation of Its Components in Oysters Crassostrea gigas Fed with the Toxic Dinoflagellate Alexandrium tamarense

As a part of our studies on the mechanism of uptake of paralytic shellfish poison (PSP) and the kinetics of its accumulation in bivalves, oysters Crassostrea gigas were experimentally contaminated with PSP by being fed with the toxic dinoflagellate Alexandrium tamarense for 2, 4, 6, 8 and 10 days. Temporal variations in the PSP contents and their profiles in oysters during the feeding experiment were monitored by high-performance liquid chromatography (HPLC) and the toxin profile of the oysters was compared with that of A. tamarense. Toxins excreted from the infested oysters into the seawater for 2 and 10 days were recovered and analyzed by HPLC. PSP toxicity rapidly appeared in the tissues of oysters and their toxicity levels reached 0.6 (0.3), 2.2 (1.1), 1.0 (0.5), 3.4 (1.6) and 1.1 (0.5) MU/g (nmol/g) shucked meat at 2, 4, 6, 8 and 10 days, respectively. The accumulation rates of toxin, calculated from the total amount (nmol) of toxins expressed by the total cell number fed during the exposure period and the toxicity of the oysters, were 14.1, 18.7, 5.1, 14.9 and 3.2% for 2, 4, 6, 8 and 10 days. During feeding experiments, the toxin profile of oysters changed substantially, showing marked differences from the proportions found in the toxigenic dinoflagellate used as food. The toxin components in this strain existed almost exclusively as beta-epimers, which accounted for 66.3 mol% of the total. This contrasts with the case of the oysters, where the beta-epimers represented 24.8, 29.8, 25.1, 27.3 and 25.2 mol% of the total at 2, 4, 6, 8 and 10 days, respectively. The amount of gonyautoxin-1 (GTX1) accumulated in oysters increased linearly and slowly for 8 days and the maximum content of GTX1 reached 51.3 mol%. The composition of GTX group compounds recovered from the seawater in which the oysters had been reared was a little different from that within the oyster tissues.

Seasonal dynamics of the hepatotoxic microcystins in various organs of four freshwater bivalves from the large eutrophic lake Taihu of subtropical China and the risk to human consumption

So far, little is known on the distribution of hepatotoxic microcystin (MC) in various organs of bivalves, and there is no study on MC accumulation in bivalves from Chinese waters. Distribution pattern and seasonal dynamics of MC-LR, -YR and -RR in various organs (hepatopancreas, intestine, visceral mass, gill, foot, and rest) of four edible freshwater mussels (Anodonta woodiana, Hyriopsis cumingii, Cristaria plicata, and Lamprotula leai) were studied monthly during Oct. 2003-Sep. 2004 in Lake Taihu with toxic cyanobacterial blooms in the summer. Qualitative and quantitative determinations of MCs in the organs were done by LC-MS and HPLC. The major toxins were present in the hepatopancreas (45.5-55.4%), followed by visceral mass with substantial amount of gonad (27.6-35.5%), whereas gill and foot were the least (1.8-5.1%). The maximum MC contents in the hepatopancreas, intestine, visceral mass, gill, foot, and rest were 38.48, 20.65, 1.70, 0.64, 0.58, and 0.61 microg/g DW, respectively. There were rather good positive correlation in MC contents between intestines and hepatopancreas of the four bivalves (r=0.75-0.97, p<0.05). There appeared to be positive correlations between the maximum MC content in the hepatopancreas and the delta13C (r=0.919) or delta15N (r=0.878) of the foot, indicating that the different MC content in the hepatopancreas might be due to different food ingestion. A glutathione (GSH) conjugate of MC-LR was also detected in the foot sample of C. plicata. Among the foot samples analyzed, 54% were above the provisional WHO tolerable daily intake (TDI) level, and the mean daily intakes from the four bivalves were 8-23.5 times the TDI value when the bivalves are eaten as a whole, suggesting the high risk of consuming bivalves in Lake Taihu.

Domoic acid accumulation in French shellfish in relation to toxic species of Pseudo-nitzschia multiseries and P. pseudodelicatissima

Within the French phytoplankton monitoring network (REPHY), domoic acid (DA), the toxin responsible for amnesic shellfish poisoning, was first detected in samples collected in 1998. Toxin analysis by the official method [liquid chromatography with diode array detection (LC/DAD)] was performed when Pseudo-nitzschia cell concentration was greater than 1.0×10 5 cells/l. LC/DAD results obtained in 1999 and 2000 showed increased DA accumulation in bivalves sampled at different sites along French coasts. The toxin maximum in 1999 was 3.2 μg DA/g of whole tissue, whereas the levels in 2000 (53 μg) were above the sanitary threshold (20 μg DA/g tissue). Phytoplankton samples collected during blooms were observed by both light and scanning electron microscopy (SEM). Identification of phytoplankton species by SEM analyses confirmed the presence of two known DA-producing species, P. pseudodelicatissima and P. multiseries. LC/DAD results for a mass culture of P. multiseries indicated that this species was involved in DA accumulation in French shellfish.