A review and new analysis of trophic interactions between Prorocentrum minimum and clams, scallops, and oysters

There has been no consensus on whether Prorocentrum minimum is “toxic,” despite sporadic reports suggesting possible shellfish toxicity and laboratory studies showing harmful effects of this dinoflagellate on molluscan shellfish. Shellfish toxicity outbreaks associated with natural blooms of P. minimum have been confounded by co-occurrence of other toxic phytoplankton. Laboratory studies have demonstrated unequivocally that some P. minimum isolates can produce toxins that kill mice on injection, but the bioactive compound or compounds remain unidentified, and accumulation of toxin in grazing mollusks has not been demonstrated. Laboratory experiments testing the responses of grazing mollusks to P. minimum cultures have yielded variable results, ranging from mortality in scallops and oysters to normal growth of oysters. Effects observed in the laboratory include rejection as pseudofeces by clams, poor larval development in oysters, tissue pathologies (sometimes transient) in oysters and scallops, and systemic immune responses in oysters and scallops. Several recent studies have provided evidence that variation in toxicity of P. minimum is dependent on environmental conditions and their effects on the physiology of this dinoflagellate. Accordingly, seemingly conflicting observations from field and laboratory studies may be explained by transient toxin expression in P. minimum.