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The eastern oyster (Crassostrea virginica) and northern quahog (= hard clam, Mercenaria mercenaria) are two species of economic and ecological significance in east coast waters of the United States and the Gulf of Mexico. Commercial industries for these species, especially within the state of Florida, are significant. The current study was undertaken to build upon the already established body of knowledge surrounding effects of the toxic dinoflagellate Karenia brevis on shellfish, to provide an understanding of the kinetics of brevetoxins within shellfish tissues, and to provide an estimate of brevetoxin retention times in these shellfish after a bloom event. Individual clams and oysters were exposed to the toxic dinoflagellate, K. brevis at a bloom concentration of 5 × 10(5) cells·L(-1) for eight days and then transferred to filtered water for depuration. Individuals were sampled periodically to determine depuration rates. Concentrations of brevetoxins (and/or their metabolites measured as PbTx-3 equivalent) in tissues were determined using an Enzyme Linked Immunosorbent Assay (ELISA). After five days of exposure, brevetoxin levels in tissues of both species reached concentrations well above the regulatory limit of 800 ng g(-1) (Pb-TX3 equivalent). Averaged concentration of brevetoxins in clams was 1000 ng g(-1), while the oysters averaged 1986 ng g(-1). After two weeks of depuration, tissue concentrations in both species were below regulatory levels with clams averaging ~204 ng g(-1) and oysters averaging ~437 ng g(-1). Toxins (or their metabolities) remained detectable in both clams (139 days) and oysters (82 days) for the duration of the experiment., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

The culture of oysters, clams, scallops, and other molluscs is collectively one of the fastest growing sectors of the domestic aquaculture industry. An inherent issue with shellfish culture methods, particularly for off-bottom culture (i.e., floating trays, racks, long lines, strings, rafts), is biofouling. Controlling and mitigating biofouling can result in significant costs for commercial shellfish culture operations. A survey of existing commercial shellfish culture operations was conducted among growers in seven US regions. A total of 1375 surveys were distributed. An overall response rate of 37% was achieved. The survey solicited information on business descriptors, perceptions of biofouling as a problematic issue, and costs associated with control. Respondents indicated that efforts to control biofouling accounted for an average of 14.7% of total annual operating costs. Survey findings suggest that the total costs associated with biofouling control by shellfish growers in the regions studied exceed $21 million. Over 40% of respondents indicated that biofouling affected the marketability of their product. The survey findings reveal significant variation in responses by region. [ABSTRACT FROM AUTHOR]

Abstract: A series of experiments was conducted to examine effects of four strains of the estuarine dinoflagellate, Pfiesteria shumwayae, on the behavior and survival of larval and adult shellfish (bay scallop, Argopecten irradians; eastern oyster, Crassostrea virginica; northern quahogs, Mercenaria mercenaria; green mussels, Perna viridis [adults only]). In separate trials with larvae of A. irradians, C. virginica, and M. mercenaria, an aggressive predatory response of three strains of algal- and fish-fed P. shumwayae was observed (exception, algal-fed strain 1024C). Larval mortality resulted primarily from damage inflicted by physical attack of the flagellated cells, and secondarily from Pfiesteria toxin, as demonstrated in larval C. virginica exposed to P. shumwayae with versus without direct physical contact. Survival of adult shellfish and grazing activity depended upon the species and the cell density, strain, and nutritional history of P. shumwayae. No mortality of the four shellfish species was noted after 24h of exposure to algal- or fish-fed P. shumwayae (strains 1024C, 1048C, and CCMP2089) in separate trials at ≤5×103 cellsml−1, whereas higher densities of fish-fed, but not algal-fed, populations (>7–8×103 cellsml−1) induced low (≤15%) but significant mortality. Adults of all four shellfish species sustained >90% mortality when exposed to fish-fed strain 270A1 (8×103 cellsml−1). In contrast, adult M. mercenaria and P. viridis exposed to a similar density of fish-fed strain 2172C sustained <15% mortality, and there was no mortality of A. irradians and C. virginica exposed to that strain. In mouse bioassays with tissue homogenates (adductor muscle, mantle, and whole animals) of A. irradians and M. mercenaria that had been exposed to P. shumwayae (three strains, separate trials), mice experienced several minutes of disorientation followed by recovery. Mice injected with tissue extracts from control animals fed cryptomonads showed no response. Grazing rates of adult shellfish on P. shumwayae (mean cell length ±1 standard error [S.E.], 9±1μm) generally were significantly lower when fed fish-fed (toxic) populations than when fed populations that previously had been maintained on algal prey, and grazing rates were highest with the nontoxic cryptomonad, Storeatula major (cell length 7±1μm). Abundant cysts of P. shumwayae were found in fecal strands of all shellfish species tested, and ≤45% of the feces produced viable flagellated cells when placed into favorable culture conditions. These findings were supported by a field study wherein fecal strands collected from field-collected adult shellfish (C. virginica, M. mercenaria, and ribbed mussels, Geukensia demissa) were confirmed to contain cysts of P. shumwayae, and these cysts produced fish-killing flagellated populations in standardized fish bioassays. Thus, predatory feeding by flagellated cells of P. shumwayae can adversely affect survival of larval bivalve molluscs, and grazing can be depressed when adult shellfish are fed P. shumwayae. The data suggest that P. shumwayae could affect recruitment of larval shellfish in estuaries and aquaculture facilities; shellfish can be adversely affected via reduced filtration rates; and adult shellfish may be vectors of toxic P. shumwayae when shellfish are transported from one geographic location to another. [Copyright &y& Elsevier]

From the late Pliocene to now, blooms of toxic algae are associated with mortalities of marine birds. Given the long historical presence of harmful algal blooms (HABs) worldwide and the numbers of seabirds that feed on filter-feeding fish and shellfish, it is surprising that relatively few incidents of seabird deaths as a result of toxic algae have been reported. The limited information available tends to come from major events, whereas the rare events are missed and hence not reported. Much is anecdotal and still more probably is not published. We suspect that factors working in concert may lead to deaths and wrecks that might not occur as a result of anyone factor working independently, e.g. starvation tends to render birds more vulnerable to stress.“Seabird wrecks”, very much larger than usual concentration of seabird corpses washed ashore over a short period of time, often provide evidence of deleterious conditions in offshore populations, e.g. weather, food, pollution, fishing activities, and parasites. It is noted in the literature that wrecks caused by natural toxins such as botulism and algal toxins are apparently less common; however, this perception may be due to a combination of factors including the bird species involved, size of populations, location, and chance of discovery. Wrecks involving near-shore species probably provide a more accurate estimate of total mortality for any given event than offshore species.A survey of available data on the impacts of toxic algae on seabirds revealed an array of responses ranging from reduced feeding activity, inability to lay eggs, and loss of motor coordination to death. Severe impacts on recruitment have been noted in some populations. There are few experimental studies; however, evidence has been provided for the ability of some species to ‘learn’ to avoid toxic food sources. We present a summary of available data on seabird/toxic algal interactions and suggestions of how impacts on seabirds during future blooms of harmful algae be recorded. [Copyright &y& Elsevier]

Microplastics (MP) have repeatedly been found in commercially cultured species of bivalves. There are concerns regarding the amount of MP released into the environment by aquaculture activities, and questions regarding possible higher MP loads in farm-grown shellfish compared to levels in shellfish collected from recreational beds. To explore this concept, seawater, aquaculture gear, and eastern oysters (Crassostrea virginica) were sampled from an aquaculture site in Niantic Bay, CT, USA, and a 2-week transplantation experiment was performed in which oysters were transplanted between the aquaculture site and a plastic-free cage off the dock at the University of Connecticut-Avery Point campus. The digestive gland-stomach complex (gut) was dissected from the oysters and MP were extracted from the adjacent seawater and oyster gut samples using previously validated extraction methods. Extensive quality assurance and control measures were taken to reduce MP contamination. Particles in all samples were isolated, imaged under a stereomicroscope, and characterized (size, shape, polymer) using ImageJ software and micro-Fourier transform infrared spectroscopy. Water samples contained 0–0.3 MP/L and oyster gut samples contained 0–1.3 MP/g wet weight indicating very low concentrations of MP at the farm (0–2 MP/individual) or away from the farm (0–3 MP/individual). Aquaculture gear in this area is not contributing to MP ingestion in farmed oysters or elevated MP levels in the surrounding water. • Microplastic concentrations were explored on an oyster aquaculture farm. • Oysters were transplant to or away from the aquaculture farm. • Microplastics in oyster-gut and seawater samples were compared to aquaculture gear. • Microplastic concentrations are low at and away from the farm in Long Island Sound. • Aquaculture gear did not contribute to microplastic ingestion in farmed oysters. [ABSTRACT FROM AUTHOR]

Abstract: Little is known about interactions between shellfish and the toxic dinoflagellate Alexandrium monilatum. Toxic strains produce endotoxins with hemolytic and neurotoxic properties, and have been linked to fish and invertebrate kills. We experimentally assessed the survival, grazing and behavioral responses of three shellfish species to A. monilatum. Grazing studies were conducted with two size classes of Crassostrea virginica, Mercenaria mercenaria, and Perna viridis. These species inhabit areas where blooms of A. monilatum occur. Clearance rates of each species were depressed when exposed to toxic A. monilatum alone or with nontoxic Pavlova sp., in comparison to control animals fed only nontoxic algae. Exposure to toxic A. monilatum also caused shellfish to decrease shell valve gape. Intact cells of A. monilatum were found within shellfish feces, but the cells did not re-establish growing populations following gut passage. Survival of larval M. mercenaria and C. virginica was also tested when exposed to A. monilatum cells. Survival was significantly lower for larvae exposed to sonicated A. monilatum, in comparison to control larvae tested with nontoxic A. tamarense. Overall, the data indicate that blooms of A. monilatum can adversely affect some shellfish species by reducing valve gape and clearance rate, and by inducing larval mortality. [Copyright &y& Elsevier]

Abstract: Northern quahogs, Mercenaria mercenaria (L.), frequently are infected with the parasite Quahog Parasite Unknown (QPX, Labyrintohomorpha, Thraustochytriales), which can cause morbidity and mortality of the quahogs. Possible interactions between this parasitic disease and exposure to the harmful dinoflagellate Prorocentrum minimum in M. mercenaria were studied experimentally. Quahogs from Massachusetts with variable intensity of QPX infection were exposed, under controlled laboratory conditions, to cultured P. minimum added to the natural plankton at a cell density equivalent to a natural bloom. After 5days of exposure, individual clams were diagnosed histologically to assess prevalence and intensity of parasitic infection, as well as other pathological conditions. Further, cellular defense status of clams was evaluated by analyzing hemocyte parameters (morphological and functional) using flow-cytometry. Exposure of quahogs to P. minimum resulted in: a lower percentage of phagocytic hemocytes, higher production of reactive oxygen species (ROS), larger hemocyte size, more-numerous hemocytic aggregates, and increased numbers of hemocytes in gills accompanied by vacuolation and hyperplasia of the water-tubular epithelial cells of the gills. Quahogs had a low prevalence of QPX; by chance, the parasite was present only in quahogs exposed to P. minimum. Thus, the effect of QPX alone on the hemocyte parameters of quahogs could not be assessed in this experiment, but it was possible to assess different responses of infected versus non-infected quahogs to P. minimum. QPX-infected quahogs exposed to P. minimum had repressed percentage of phagocytic hemocytes, consistent with immuno-modulating effect of P. minimum upon several molluscan species, as well as smaller hemocytes and increased hemocyte infiltration throughout the soft tissues. This experiment demonstrates the importance of considering interactive effects of different factors on the immunology and histopathology of bivalve shellfish, and highlights the importance of considering the presence of parasites when bivalves are subjected to harmful-algal blooms. [Copyright &y& Elsevier]

Abstract: The dinoflagellate Prorocentrum minimum is increasingly recognized as a harmful algal bloom (HAB) species that affects filter-feeding shellfish. An experiment was done to investigate possible interactions between parasitic diseases and exposure to P. minimum in Manila clams, Ruditapes philippinarum. Manila clams, with variable levels of infection with Perkinsus olseni, were exposed for three or six days to the benign phytoplankton species Chaetoceros neogracile or a mixed diet of C. neogracile and P. minimum. After three or six days of exposure, clams were assessed individually for condition index, parasite status, and plasma and hemocyte parameters (morphological and functional) using flow-cytometry. Histological evaluation was also performed on individual clams to assess prevalence and intensity of parasitic infection, as well as other pathological conditions. Prorocentrum minimum caused several changes in Manila clams, especially after six days of exposure, such as decreased hemocyte phagocytosis and size and clam condition index. Pathological conditions observed in Manila clams exposed to P. minimum were hemocyte infiltration in the intestine and gonad follicles, myopathy, and necrosis of the intestine epithelial cells. The parasite P. olseni alone had no significant effect on Manila clams, nor did it modulate the hemocyte variables in clams exposed to P. minimum; however, the parasite did affect the pathological status of Manila clams exposed to the P. minimum culture, by causing atrophy and degeneration of residual ova in the gonadal follicles and hyaline degeneration of the muscle fibers, indicating synergistic effects of both stressors on the host over a short period of time. Additionally, an in vitro experiment also demonstrated detrimental effects of P. minimum and exudates upon P. olseni cells, thus suggesting HAB antagonistic suppression of transmission and proliferation of the parasite in the natural environment over a longer period of time. The results of this experiment demonstrate the complexity of interactions between host, parasite, and HAB. [Copyright &y& Elsevier]