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

Nicolaus G. Adams^1,2, Amoreena MacFadyen³, Barbara M. Hickey³, and Vera L. Trainer²

¹University of Washington, School of Aquatic and Fishery Sciences, Box 355020, Seattle, WA, 98195-5020, USA (Nicolaus.Adams@noaa.gov)
²NOAA Fisheries, Marine Biotoxin Program, Northwest Fisheries Science Center, 2725 Montlake Blvd. East Seattle, WA, 98112, USA (Vera.L.Trainer@noaa.gov)
³University of Washington, School of Oceanography, Box 357940, Seattle, WA, 98195, USA (amoreena@u.washington.edu, bhickey@u.washington.edu)

Along the coast of Washington State, USA, periods of storm winds intensify in late summer and may advect domoic acid-producing Pseudo-nitzschia to the coast where they impact the coastal razor clam fishery, rendering the clams toxic to humans. To test this hypothesis, during the late summer and early fall of 2002 repeated measurements of Pseudo-nitzschia species, particulate domoic acid, temperature, and salinity were made in nearshore waters and at Kalaloch beach on the central Washington coast. A shift in the composition of the Pseudo-nitzschia population to P. australis cells was observed following a storm event during 8-10 September. Following a second storm event that occurred 16-18 September, Pseudo-nitzschia cell numbers multiplied and a concurrent increase in levels of particulate domoic acid occurred in nearshore waters. Data from moored instruments show the presence of Columbia River plume water on the inner shelf for several weeks beginning on 8 September, persisting for approximately 8 days after the second storm and effectively inhibiting upwelling near the Washington coast. Domoic acid in intertidal razor clams accumulated to levels that exceeded the regulatory safety limit 18 days following the shift to P. australis cells. These data indicate that the strategic placement of a mooring in nearshore waters with appropriate sensors for the detection of cells, toxins and environmental data may provide coastal managers with an early warning of impending toxification of coastal shellfish.