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Bloom of toxic dinoflagellate, Alexandrium fundyense has inflicted significant economic loss of both wild fisheries and aquaculture farming. This toxic dinoflagellate is capable of producing extracellular (exudates) and intracellular toxic compound (lysates), causing mass mortality of shellfish in hatchery operation. Despite its significant impacts, there is lack of study to understand the toxicity mechanism and cellular effect of A. fundyense lysates on shellfish larvae. This study aimed to investigate pathological changes of digestive tissues in blue mussel (Mytilus galloprovincialis) larvae exposed to A. fundyense lysates. Blue mussel larvae were exposed to A. fundyense lysates at a bloom concentration of 1 500 cells · ml-1 and sampled for histological assessment at every 0 h, 3 h, 15 h, 24 h, and 48 h after exposure. This study found that pathological changes in digestive tissues occurred as early as 3 h after exposure. Pathological changes included cell vacuolation, necrosis, and cilial exfoliation of style sac. Of these changes, only the prevalence and intensity of cell necrosis increases with increasing exposure duration (from low at 3 h to 15 h to intermediate at 24 h to 48 h). The finding of this study suggests that early detection and appropriate mitigation of A. fundyense bloom is needed to minimize its impact on shellfish hatchery. [ABSTRACT FROM AUTHOR]