An Ecotoxicological Perspective on Bivalve Safety Frameworks: Linking HAB Management and Microbiological Limits to Physiological Responses in Shellfish

Abstract

Harmful algal blooms (HABs) pose a growing ecotoxicological threat to bivalve molluscs and their consumers. Current regulatory frameworks governing shellfish safety, however, rely on acute human toxicity limits that poorly capture the biological complexity of bivalve–HAB interactions. This narrative review synthesises the published literature on the effects of HAB toxins on bivalves. It assesses their physiology, immune function, and stress resilience, comparing these findings against the limits set by the EU, the United States (US) and Australia/New Zealand. Sublethal responses from immunosuppression and impaired reproduction to oxidative stress and altered valve activity frequently occur at concentrations below current action levels. Environmental variables such as marine heatwaves, salinity fluctuations and hypoxia shift toxin bioaccumulation and depuration in ways that existing safety limits fail to capture. The main toxin groups, their mechanisms of action and species-specific accumulation and elimination kinetics are examined alongside current monitoring and management strategies. The review concludes that bridging the gap between shellfish-safety regulation and bivalve ecotoxicology requires integrating physiological stress indicators into regulatory frameworks. Such integration must draw on advanced monitoring technologies and adaptive management capable of responding to a rapidly changing ocean.