First Evidence of Immunomodulation in Bivalves under Seawater Acidification and Increased Temperature

Water acidification, temperature increases and changes in seawater salinity are predicted to occur in the near future. In such a global climate change (GCC) scenario, there is growing concern for the health status of both wild and farmed organisms. Bivalve molluscs, an important component of coastal marine ecosystems, are at risk. At the immunological level, the ability of an organism to maintain its immunosurveillance unaltered under adverse environmental conditions may enhance its survival capability. To our knowledge, only a few studies have investigated the effects of changing environmental parameters (as predicted in a GCC scenario) on the immune responses of bivalves. In the present study, the effects of both decreased pH values and increased temperature on the important immune parameters of two bivalve species were evaluated for the first time. The clam Chamelea gallina and the mussel Mytilus galloprovincialis, widespread along the coast of the Northwestern Adriatic Sea, were chosen as model organisms. Bivalves were exposed for 7 days to three pH values (8.1, 7.7 and 7.4) at two temperatures (22 and 28°C). Three independent experiments were carried out at salinities of 28, 34 and 40 PSU. The total haemocyte count, Neutral Red uptake, haemolymph lysozyme activity and total protein levels were measured. The results obtained demonstrated that tested experimental conditions affected significantly most of the immune parameters measured in bivalves, even if the variation pattern of haemocyte responses was not always linear. Between the two species, C. gallina appeared more vulnerable to changing pH and temperature than M. galloprovincialis. Overall, this study demonstrated that climate changes can strongly affect haemocyte functionality in bivalves. However, further studies are needed to clarify better the mechanisms of action of changing environmental parameters, both individually and in combination, on bivalve haemocytes

Effects of Elevated Temperature and Carbon Dioxide on the Growth and Survival of Larvae and Juveniles of Three Species of Northwest Atlantic Bivalves

Rising CO2 concentrations and water temperatures this century are likely to have transformative effects on many coastal marine organisms. Here, we compared the responses of two life history stages (larval, juvenile) of three species of calcifying bivalves (Mercenaria mercenaria, Crassostrea virginica, and Argopecten irradians) to temperatures (24 and 28°C) and CO2 concentrations (∼250, 390, and 750 ppm) representative of past, present, and future summer conditions in temperate estuaries. Results demonstrated that increases in temperature and CO2 each significantly depressed survival, development, growth, and lipid synthesis of M. mercenaria and A. irradians larvae and that the effects were additive. Juvenile M. mercenaria and A. irradians were negatively impacted by higher temperatures while C. virginica juveniles were not. C. virginica and A. irradians juveniles were negatively affected by higher CO2 concentrations, while M. mercenaria was not. Larvae were substantially more vulnerable to elevated CO2 than juvenile stages. These findings suggest that current and future increases in temperature and CO2 are likely to have negative consequences for coastal bivalve populations

Toxin profile change in vegetative cells and pellicle cysts of Alexandrium fundyense after gut passage in the eastern oyster Crassostrea virginica

Abstract: Vegetative cells and pellicle cysts of the toxic dinoflagellate Alexandrium fundyense Balech were fed to the eastern oyster Crassostrea virginica Gmelin under controlled conditions. Para lytic shellfish toxins (PSTs) were measured in vegetative cells and pellicle cysts prior to feeding and directly after passage through the oyster alimentary canal and defecation as intact cells. Oysters fed with vegetative cells and those fed with pellicle cysts accumulated toxins. One experimental treatment tested for direct uptake of toxins from the water (oysters and A. fundyense cells were separated by a screen); PSTs were not accumulated from the water by the oysters. There were no significant changes in total, per-cell toxicity after passage through the oyster alimentary canal, suggesting limited transfer of toxins from intact cells to the oysters. However, there were statistically significant changes in the toxin composition of cells following gut passage. Vegetative cells and pellicle cysts from feces had increased amounts of saxitoxin (STX) and decreased amounts of gonyautoxin 4 (GTX4) per cell, compared to amounts prior to gut passage. Following gut passage, pellicle cysts showed better survival in the feces than vegetative cells, which is consistent with the view of pellicle-cyst formation as a successful survival strategy against adverse conditions