The first closure of shellfish harvesting due to domoic acid in Puget Sound, Washington, USA

The first domoic acid (DA)-related closure of shellfish harvesting in Puget Sound, Washington, USA, occurred in early September 2003 owing to a DA concentration of 29ppm measured in blue mussels Mytilus edulis from Fort Flagler, Kilisut Harbor. Subsequent beach and shipboard sampling in the area revealed a nearly monospecific bloom of the diatom Pseudo-nitzschia australis. DA was detected in several shellfish species over a 80km(2) area from 2 September through 22 October 2003. Concentrations of Pseudo-nitzschia up to 2.9 x 10(6) cells l(-1) and particulate DA up to 4.6 X 10(3)ng l(-1) were measured. Since the early 1990s, blooms containing multiple Pseudo-nitzschia species have been observed in Puget Sound and low levels of DA have been detected in shellfish, but highly toxic, nearly monospecific blooms had not been observed. We speculate that a more toxic 'oceanic' strain may recently have been advected from the Pacific Ocean or that local environmental conditions at the time of this bloom were more conducive to toxin production.