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2008 Red tide
Outcome and conclusions

The red tide was clearly visible from the air off Sainte-Flavie.

DFO  M. Starr

From August 5 to 21, 2008, people living along the St. Lawrence estuary witnessed an unusual and worrisome incident. Massive mortalities of marine animals, including mammals, were reported along several kilometres of the St. Lawrence estuary. Suspicion quickly fell on Alexandrium tamarense, a microalgae well known in the estuary for its ability to produce paralyzing toxins. Mortalities associated with the 2008 red tide stand as follows: thousands of seabirds, some one hundred seals, eleven belugas and numerous fish of various species.

The spread of A. tamarense is a recurrent phenomenon in the St. Lawrence estuary. The Lower Laurentian strain is recognized as being one of the most toxic in the world. Bloom is generally localized and has limited consequences. However, massive bloom can result when certain conditions occur simultaneously. These conditions include such things as lower salinity and the presence of humic substances (dissolved matter derived from decomposing soils) carried into the gulf by river water. In fact, these were the prevailing conditions in 2008 when heavy rains in late July were followed by some ten days of fine, sunny weather in early August.

The 2008 A. tamarense outbreak was the most devastating one in terms of marine animal mortality since the Maurice Lamontagne Institute (MLI) was established in 1987. The most recent massive mortalities were recorded in 1996 and 1998 and at the time, affected primarily birds and fish.

This exceptional occurrence has allowed researchers – for the first time – to see the direct connection between A. tamarense and marine mammal mortality. For the beluga, a threatened species in the St. Lawrence, the presence of A. tamarense adds a new hazard that must be taken into account as a factor affecting mortality within the population.

At present, there are no effective techniques for eradicating toxic algae bloom. However, toxic algae monitoring as it is done at MLI allows researchers to detect and follow its evolution. The analyses conducted during the 2008 outbreak were an opportunity to learn more about the effects of paralyzing toxins on the organisms involved. The development of models could also serve to predict bloom and issue alerts to concerned stakeholders and the industry (fishing, aquaculture) early enough so that people can take the appropriate measures to prevent or mitigate the socio-economic impacts of toxic algae bloom.


Michael Scarratt, Sonia Michaud and Michel Starr