The nearshore advection of a toxigenic Pseudo-nitzschia bloom and subsequent domoic acid contamination of intertidal bivalves

Along the coast of Washington State, USA, periods of downwelling-favourable winds increase in frequency in late summer and may advect domoic acid (DA)-producing Pseudo-nitzschia to the coast where they toxify coastal razor clams Siliqua patula. During the late summer and early autumn of 2002, measurements of Pseudonitzschia species, particulate DA (pDA) and salinity were made in nearshore waters and at Kalaloch Beach. A shift in the relative abundance of Pseudo-nitzschia species was observed following a storm during 8-10 September. After a second storm during 16-18 September, Pseudo-nitzschia cell numbers and levels of pDA increased in nearshore waters. Salinity measured with moored sensors showed the presence of relatively fresh Columbia River plume water on the inner shelf for several weeks, beginning on 8 September and persisting for approximately eight days after the second storm. During that time, DA in intertidal razor clams accumulated to levels that exceeded the regulatory action limit. This study helps to clarify the complex role of the Columbia River plume in the advection of Pseudo-nitzschia populations to the Washington coast.