Extracted from:

Donald F. Boesch, Donald A. Anderson, Rita A. Horner, Sandra E. Shumway,Patricia A. Tester and Terry E. Whitledge. 1997. Harmful Algal Blooms in Coastal Waters: Options for Prevention, Control and Mitigation. NOAA Coastal Ocean Program, Decision Analysis Series No. 10, Special Joint Report with the National Fish and Wildlife Foundation, February 1997.

Site developer's note: genus and species names of algae are indicated in red, rather than standard underlining (not a webpage option unless a link...) or italics, in order to make the names easier to find and read.

Amnesic Shellfish Poisoning

Domoic acid has been detected in finfish and shellfish resources on both the east and west coasts.. This neurotoxin, produced by diatoms in the genus Pseudo-nitzschia, may cause permanent short-term memory loss in victims, hence the name amnesic shellfish poisoning (ASP). Another term often used for this syndrome is domoic acid poisoning (DAP) because amnesia is not always present and there have been no confirmed cases of ASP in humans in the U.S.

Toxic Pseudo-nitzschia species are present in the northeast and Gulf of Mexico and low levels of domoic acid have been detected in shellfish on the east coast, but not at levels that necessitate quarantine. On the west coast, however, domoic acid poisoning has been a serious problem affecting razor clams and Dungeness crabs in California, Oregon, and Washington.

The west coast has two different environments to consider in terms of harmful algal bloom development. The Pacific Ocean coast is associated with the upwelling events in late summer and fall. On the other hand, inland waters of Puget Sound and fjords and inlets of Alaska are enclosed areas with restricted water exchange.

Domoic acid production has been confirmed for three species of Pseudo-nitzschia on the west coast: P. australis, P. multiseries, and P. pungens. Domoic acid poisoning first became a noticeable problem in 1991 when pelicans and cormorants in Monterey Bay (California) died or suffered from unusual neurological symptoms similar to ASP. Many tons of anchovy catches were recalled or diverted following this episode. That same year, domoic acid was identified in razor clams and Dungeness crabs on the Oregon and Washington coasts. Since 1991, Pseudo-nitzschia spp. and domoic acid have recurred in Monterey Bay, but relatively low cell numbers and concentrations. Blooms are common in late summer and fall when the upwelling season has ended, sea surface temperatures are warmer, thermal stratification is evident, and concentrations of inorganic nutrients are low. On the Washington coast razor clams on some beaches continue to contain low levels of domoic acid, but the source in not known. Meanwhile a bloom of mixed Pseudo-nitzschia species occurred in Hood Canal (an arm of Puget Sound) in November-December 1994, resulting in toxin levels of about 10 ug/g in mussels and 14 ug/g in phytoplankton (Horner et al. 1996). Closure limits are 20 ug/g.

In western Washington, the economic impact for the 1991 domoic acid event was estimated to be between $15 and 20 million based on lost tourist visits (at $25 per digger trip); lost or delayed retail sales and lower prices of oysters that were never toxic but were avoided by confused consumers (halo effect), lost employment, bankruptcies of local businesses, potential adverse health effects (there were no confirmed illnesses due to domoic acid), and costs to the state health department for increased testing.

UNIVERSITY OF MARYLAND College of Ag & Natural Resources Department of Veterinary Medicine Aquatic Pathobiology Center