Temporal and spatial distribution of the ichthyotoxic dinoflagellate Gyrodinium aureolum Hulburt in the St Lawrence, Canada

The occurrence of the potentially ichthyotoxic dinoflagellateGyrodinium aureolum Hulburt is reported for the first time inthe Lower Estuary and Gulf of St Lawrence. Taxonomic identificationusing an iramunochemical tagging method suggests a close taxonomicproximity between the species found in the St Lawrence and G.aureolumpresent in European waters. In 1993, G.aureolum was observedalong the entire coast of Quebec and in offshore waters of theGulf of St Lawrence. At the coastal stations, G.aureolum showedlarge week-to-week variations, but higher densities were observedduring late August and early September. Bloom concentrations(10⁶ cells 1^–1) were only observed in the GaspéCurrent at Mont-Louis, on the north coast of the Gaspd peninsula.In the central part of the Gulf, G.aureolum was concentratedin the upper 5 m of the stations directly influenced by thefreshwater run-off of the St Lawrence Estuary. Results fromprincipal component analysis indicate that G.aureolum favorsenvironments with high nitrogen recycling activity.