Distribution of Potentially Harmful Phytoplankton Species in the Northern Strait of Georgia, British Columbia

Spatial and temporal distributions of Chaetoceros convolutum (including C. concavicorne), Heterosigma akashiwo, Protogonyaulax (= Alexandrium) catenella, and Dinophysis are presented for the northern Strait of Georgia from March to September, 1986. In spring C. convolutum was found on the slightly stratified eastern side in concentrations just below those leading to kills of caged salmon (4-5000 cells∙L−1). The northern Strait became thermally stratified in summer. At this time the population centre of C. convolutum shifted to mid-Strait near the edge of the Discovery Passage tidal jet where it was maintained near the pycnocline (10–15 m) in concentrations up to 35,000 cells∙L−1. Heterosigma akashiwo, another fish killer, was the pbotosynthetic dominant in June and reached 200 000 cells∙L−1 in the northwest at 5 m. Protogonyaulax catenella, a source of paralytic shellfish poison (PSP), was also most abundant in the north and west, where dangerous levels of PSP often occur, particularly near Comox. Collectively, Dinophysis species exceeded the critical concentration for diarrheic shellfish poisoning (200 cells∙L−) on the western side during summer. All the potentially harmful flagellated species seem to be introduced from the northern passageways. Sheltered bays to the north are possible seed beds for cyst-forming species whereas C. convolutum remains in the Strait year-round.