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

The occurrence of the potentially ichthyotoxic dinoflagellate Gyrodinium aureolum Hulburt is reported for the first time in the Lower Estuary and Gulf of St Lawrence. Taxonomic identification using an immunochemical tagging method suggests a close taxonomic proximity between the species found in the St Lawrence and G. aureolum present in European waters In 1993, G. aureolum was observed along the entire coast of Quebec and in offshore waters of the Gulf of St Lawrence. At the coastal stations, G. aureolum showed large week-to-week variations, but higher densities were observed during late August and early September. Bloom concentrations (10(6) cells l(-1)) were only observed in the Gaspe Current at Mont-Louis, on the north coast of the Gaspe peninsula. In the central part of the Gulf, G. aureolum was concentrated in the upper 5 m of the stations directly influenced by the freshwater run-off of the St Lawrence Estuary. Results from principal component analysis indicate that G. aureolum favors environments with high nitrogen recycling activity.