The first closure of shellfish harvesting resulting from elevated levels of domoic acid in Puget Sound, Washington, USA

Brian D. Bill¹, Frank H. Cox², Jerry A. Borchert², Rita A. Horner³ and Vera L. Trainer¹

¹NOAA Fisheries, Marine Biotoxin Program, Northwest Fisheries Science Center, 2725 Montlake Blvd East, Seattle, WA 98112 USA (brian.d.bill@noaa.gov, vera.l.trainer@noaa.gov)
²Washington State Department of Health, Food Safety and Shellfish Programs, 7171 Cleanwater Lane, Olympia, WA 98504 USA (frank.cox@doh.wa.gov, jerry.borchert@doh.wa.gov)
³University of Washington, School of Oceanography, Box 357940 Seattle, WA 98195 (rita@ocean.washington.edu)

The first domoic acid (DA) related closure of shellfish harvesting in Puget Sound, Washington, USA, occurred in September 2003. DA reached 29 ppm in blue mussel samples taken on September 2 from Kilisut Harbor, a northward-facing embayment at the entrance to Puget Sound. Subsequent beach and shipboard sampling in the area revealed a near monospecific bloom of Pseudo-nitzschia australis. DA was detected in shellfish across an area over 80 km2 from September 2 through October 22. Cell concentrations reached 2.5 million cells per liter and particulate DA up to 15.5 nM was measured. DA was detected in numerous shellfish species, including blue mussel, littleneck clam, geoduck clam, manila clam, and Pacific oyster. Since the early 1990s, Pseudo-nitzschia have usually been present as multiple species populations and low toxicity levels have been detected in shellfish. While these historical data do not reflect comprehensive sampling in all parts of Puget Sound, highly toxigenic, near monospecific blooms have not been observed previously. Although it is not known why this highly toxic strain of P. australis occurred in Puget Sound at this time, we speculate that perhaps a more toxic "oceanic" strain may have been advected recently from the Pacific Ocean or that local environmental conditions became more conducive to toxin production than observed previously.