Pseudo-nitzschia blooms and physical oceanography off Washington State, USA

Blooms of harmful algal species occur along the Washington coast. usually a s a fraction of the total phytoplankton population. Although more than 20 p otentially harmful species have been identified along that coast. the most deleterious effects on public health and the economy are from Pseudo-nitzsc hia spp. and Alexandrium catenella. During three surveys conducted in early summer 1996, 1997 and 1998. high concentrations of Pseudo-nitzschia spp, ( values of up to 10(6) cells-l(-1), but generally < 10(5) cells-l(-1)) were present. P. pungens was dominant in 1996, whereas P. pseudodelicatissima wa s most abundant in 1997 and 1998. A. catenella was rare and in low concentr ations (usually < 10 cells-l(-1)). Patterns of phytoplankton distributions during each survey appear to be closely related to upwelling and downwellin g conditions prior to the survey.