Bioactive extracellular compounds produced by the dinoflagellate Alexandrium minutum are highly detrimental for oysters

Behavioral and physiological responses of the Pacific oyster Crassostrea gigas were monitored after exposure to three strains of Alexandrium minutum over four days.

• Oysters exposed to a strain producing only bioactive extracellular compounds (BECs) showed significant changes in valve activity and increased hemocyte mobilization in the gills.
• A strain that produces paralytic shellfish toxins (PSTs) caused inflammation in the digestive gland and disrupted the oysters' daily valve activity rhythm.
• BECs may have harmful effects on the gills, which are the first organs to encounter the substances released into the water.
• PSTs primarily affect the digestive gland, where they accumulate after the degradation of algal cells during the bivalve digestion process.
• The findings suggest that BECs play a significant role in the overall toxicity of Alexandrium minutum to oysters.

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