Domoic acid depuration by intertidal bivalves fed on toxin-producing .

Domoic acid (DA), a neurotoxin produced by certain species within the diatom genus , has caused numerous persistent harvest closures for razor clam along the outer coast of Washington State (USA) over the last three decades. In comparison, bivalve harvest closures for DA have only occurred three times in Washington's largest inland estuary, Puget Sound, which has a variety of bivalve species excluding razor clam. While differing bloom dynamics in the two locations are responsible for much of the disparity in shellfish harvest closures, species-specific differences in DA depuration may affect the duration of harvest closures in the two regions. Toxin-producing were fed to four species of bivalves, followed by measurement of tissue DA content over time to estimate depuration rate. Experimental species include razor clam and three species of intertidal Puget Sound bivalves: soft-shell clam , purple varnish clam and Manila clam . Using an exponential decay model, DA depuration rates were estimated as: 0.02·day ±0.08 for razor clam, 0.10·day ±0.07 for purple varnish clam, 0.37·day ±0.03 for soft-shell clam, and 0.44·day ±0.02 for Manila clam. Puget Sound species depurated DA between five and 22 times as fast as outer coast razor clam. Within Puget Sound species, slow DA depuration rates in purple varnish clam indicate that it may be a good sentinel organism for assessing beach-wide maximum DA concentrations in Puget Sound bivalves.