Toxicity and histopathological effects of toxic dinoflagellate, alexandrium catenella exudates on larvae of blue mussel, mytilus galloprovincialis, and pacific oyster, crassostrea gigas

Abstract

Blooms of the toxic dinoflagellate Alexandrium catenella have affected shellfish industries globally due to their capacity to produce paralytic shellfish toxins (PST). This study aimed to investigate the toxicity effect of exudate A. catenella on larvae of blue mussel Mytilus galloprovincialis and Pacific oyster Crassostrea gigas and filtration methods to reduce the toxic effect. Blue mussel and Pacific oyster larvae were assessed their survival and histopathological changes after exposure to extracellular exudates of A. catenella ranging from 100 to 1,000 cells ml-1. The results showed that exposure to exudate A. catenella caused significantly higher larval mortality (39 to 52%) than exposure to an equivalent biovolume of the non-toxic species, Tisochrysis lutea (33%) or unfed controls (17%). Filter-sterilization (0.22 µm) of exudates and activated carbon filtration decreased the mortality of Pacific oyster larvae to a level similar to controls (unfed), with the exception of the highest concentrations (600 and 1,000 cells ml-1) and mortality of blue mussel larvae mortality by 32% respectively. Blue mussel larvae exposed to exudate A. catenella showed pathological changes mainly in the stomach (digestive gland and style sac) as early as three hours after onset of exposure. The findings of this study suggest that early detection of blooms in the vicinity of mussel and Pacific oyster hatcheries and taking steps to mitigate their effects, is important to reduce the effects of A. catenella blooms on shellfish larval rearing.