Research Document - 2013/124
Phycotoxin analyses in St. Lawrence Estuary beluga
By Michael Scarratt, Sonia Michaud, Lena Measures, Michel Starr
The St. Lawrence Estuary is frequently subjected to harmful blooms (colloquially termed “red tides”) of the toxic dinoflagellate Alexandrium tamarense which can cause outbreaks of Paralytic Shellfish Poisoning (PSP), with consequent health risks for marine organisms and humans. PSP toxins can be transferred throughout the food web, and have been observed in a wide variety of organisms other than shellfish, both in the St. Lawrence Estuary and elsewhere. PSP and other algal toxins have been implicated in the mortalities of various marine mammal species around the world, and their potential effects on the endangered population of St. Lawrence Estuary beluga is a matter of concern, particularly in light of an intense bloom of A. tamarense in 2008 which coincided with an unusually high number of beluga mortalities in a short period. Between 1995 and 2012, 66 beluga carcasses stranded in the Estuary were tested for the presence of PSP toxins using High Performance Liquid Chromatography (HPLC) and Enzyme-Linked ImmunoSorbent Assay (ELISA) techniques. Overall, 18 of the 66 animals tested positive for the presence of saxitoxins in one or more tissues, 6 of these during the 2008 red tide. A total of 7 animals showed positive results in more than one tissue. All positive results occurred in years when A. tamarense was relatively abundant, and there is a positive relationship between the normalized anomalies in the number of mortalities and cumulative A. tamarense abundance. The simultaneous occurrence of PSP toxins in prey species and beluga digestive tracts indicates that beluga were ingesting toxic prey, while the absence of other evident illnesses or lesions (determined by necropsy) in at least one of these animals suggests that intoxication may have been the ultimate cause of death. We conclude that algal toxins should be considered as potential factors in any unexplained marine mammal mortalities. The potential effects of both major toxic algal blooms and chronic low-level exposure to toxins on vulnerable marine mammal populations should be of concern, especially in the context of climate change and the apparently increasing frequency of toxic algal blooms worldwide.
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