PHYTOPLANKTON ECOLOGY OF SECHELT-INLET, A FJORD SYSTEM ON THE BRITISH-COLUMBIA COAST .2. POTENTIALLY HARMFUL SPECIES

Many temperate phytoplankton species considered harmful occur in the S echelt Inlet system, Britsh Columbia, Canada, Some of the harmful spec ies (Chaetoceros concavicornis, Nitzschia (Pseudonitzschia) pungens, a nd Dinophysis fortii) were predictable spatially and/or temporally on an annual basis. Other species (Alexandrium catenella and Heterosigma carterae) exhibited greater interannual variability and are probably i nfluenced by cyclical events (e.g. El Nino Southern Oscillation) longe r than the period of this study. The ecology of C. concavicornis sugge sted a physiological adaptation to low light, enabling this diatom to live along the pycnocline in stratified water away from turbulence. Fa ll blooms of C. concavicornis appear to be a function of lower tempera tures and decreasing light levels characteristic of the summer-autumn transition. N. pungens was found to occur regularly in summer and autu mn; populations during the latter period were chiefly composed of f. p ungens but f. multiseries, which has been linked to domoic acid produc tion, also occurred. One large bloom of A. catenella occurred in late September 1989, which appeared to originate from outside the inlet com plex. This PSP (paralytic shellfish poison)-producing dinoflagellate w as advected into the system where it found conditions favourable to fo rm an extensive bloom, with cell concentrations well in excess of thos e considered harmful (1000 cells l(-1)) down to 10 m throughout. This led to the highest toxicity ever recorded in British Columbia (31 000 mu g per 100 g shellfish). Dinophysis, which produces okadaic acid, fo rmed subsurface concentrations exceeding the reportedly harmful level of 200 cells l(-1). D. acuminata was the predominant Dinophysis specie s and was often abundant at 10 to 15 m in summer near the region of ti dal turbulence. In autumn there was a regular increase in the D. forti i population at 5 to 10 m in waters of the sheltered southern end. The fish killer H. carterae appeared as early as March in the relatively shallow waters of the southern end. The predominant pattern, however, was summer advection of H. carterae into the inlet complex from outsid e. Further stimulation of growth occurred at the confluence of 2 inlet s where nutrient flux from tidal jets was possibly augmented by the ch emical conditioning from waters overlying an anoxic bottom.