Abstract

An unusually high number of marine mammals (including 10 beluga whales), birds, fish and invertebrates were reported dead or moribund on the shores of the St. Lawrence Estuary in August 2008 during an intense bloom of the toxic dinoflagellate Alexandrium tamarense which at one point covered some 600 square kilometers. Sub-sample analyses of the tissues using a Saxitoxin (STX)-ELISA kit and LC- fluorescence and mass spectrometry confirmed significant levels of STX and its derivatives in the liver and gastrointestinal contents of approximately half of the carcasses tested as well as in live fish, invertebrates and A. tamarense cells collected during the bloom. No other cause of mortality was identified in the majority of the necropsied animals which were generally in good body condition suggesting acute death. These results strongly support intoxication by STX. Anecdotal reports of marine fauna presenting neurological deficits during that episode were also supportive of exposure to this neurotoxin. This unusually intense and long lasting bloom was most likely a consequence of combined intense fresh-water runoff following heavy precipitation at the beginning of August which stimulated the initial proliferation of the dinoflagellates, and two weeks of calm wind conditions which prolonged the growth and retention of the bloom in the estuary. These unusual conditions led to exposure of marine fauna to levels of STX over the lethal threshold, thus demonstrating that STX-producing blooms should be considered potential threats to wildlife in this unique ecosystem and particularly to species at risk.