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

Blooms of harmful algal species occur along the Washington coast. usually as a fraction of the total phytoplankton population. Although more than 20 potentially harmful species have been identified along that coast. the most deleterious effects on public health and the economy are from Pseudo-nitzschia 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 was most abundant in 1997 and 1998. A. catenella was rare and in low concentrations (usually < 10 cells-l(-1)). Patterns of phytoplankton distributions during each survey appear to be closely related to upwelling and downwelling conditions prior to the survey.