Toxic dinoflagellates (Alexandrium fundyense and A. catenella) have minimal apparent effects on oyster hemocytes

Abstract

The possible effect of Alexandrium spp. containing paralytic shellfish poisoning (PSP) toxins on the hemocyte parameters of oysters was tested experimentally. In separate experiments, eastern oysters, Crassostrea virginica, were exposed to bloom concentrations of the sympatric dinoflagellate, Alexandrium fundyense, alone and in a mixture with a non-toxic diatom, Thalassiosira weissflogii, and Pacific oysters, Crassostrea gigas, were exposed to a mixed suspension of the sympatric, toxic species Alexandrium catenella, with T. weissflogii. Measurements of numbers of oyster hemocytes, percentages of different cell types, and functions (phagocytosis, reactive oxygen species-ROS-production, and mortality) were made using flow-cytometric methods. During and after exposure, no significant effect of Alexandrium upon hemocyte numbers, morphology, or functions were detected, despite observations of adductor-muscle paralysis in eastern oysters and measured toxin accumulation in C. gigas. Significant effects of physical displacement of oysters into the experimental conditions and of temperature (repeated at 12 and 18°C) upon immune status were detected in Pacific oysters. Correlations between hemocyte numbers and function were consistent with previous studies and were representative of normal, unstressed oysters. The finding of no effect of toxic Alexandrium spp. upon oyster hemocytes is consistent with the knowledge that PSP toxins interfere specifically with sodium-channel function in neural tissues and supports the expectation that sodium-channel physiology has no importance in hemocyte functions in oysters. Finally, we found no evidence of bioactive compounds, other than PST, in the two species of Alexandrium studied.

Combined effects of a parasite, QPX, and the harmful-alga, Prorocentrum minimum on northern quahogs, Mercenaria mercenaria

“…These results are consistent with the findings of Hégaret et al (2007b), who demonstrated combined effects of P. olseni and the harmful-alga Karenia selliformis on concentration of circulating hemocytes and hemocyte phagocytic activity in Manila clams. Indeed, when quahogs were subjected to both stressors, combined infection with QPX and exposure to the HAB, hemocyte size decreased, indicating an increase in impact when both stressors were combined.…”

Effects of toxic Alexandrium tamarense on behavior, hemocyte responses and development of brown ring disease in Manila clams

“…Similarly, no effects of in vivo exposure to toxic Alexandrium spp. on hemocytes were found in oysters Crassostrea virginica and C. gigas, although they attained only low toxicities (<130 µg STXeq 100 g -1 ) (Hégaret et al 2007b). In the present study, in which R. philippinarum attained much higher toxicities, a significant, deleterious effect of A. tamarense on hemocyte function was found only for percent phagocytosis (15% reduction, p ≤ 0.05) and phagocytic capacity (11% reduction, p ≤ 0.01).…”

In vitro interactions between several species of harmful algae and haemocytes of bivalve molluscs

“…cells or both. These in vitro exposures also revealed an intermediate reaction of haemocytes to K. mikimotoi, compared to K. selliformis, which was previously observed in vivo (Hégaret et al 2007a). Jenkinson and Arzul (2000) also showed intermediate haemolytic properties in K. mikimotoi, compared to K. selliformis, in exposures of horse red blood cells.…”