1. Monterey Bay Aquarium Research Institute, 770 Sandholdt Rd, Moss Landing, California 95039, USA
2. The Marine Mammal Center, Marin Headlands, Sausalito, California 94965, USA
3. Marine Biotoxins Program, NOAA/National Ocean Service, 219 Fort Johnson Rd, Charleston, South Carolina 29412, USA
4. Moss Landing Marine Laboratories, PO Box 450, Moss Landing, California 95039, USA
5. National Marine Fisheries Service, 501 West Ocean Blvd., Suite 4,200, Long Beach, California 90802, USA
6. National Marine Mammal Laboratory, 7,600 Sandpoint Way NE, Seattle, Washington 98115, USA
7. Monterey Bay National Marine Sanctuary, 299 Foam St., Monterey, California 93940, USA
8. Institute of Marine Science, University of California at Santa Cruz, Santa Cruz, California 95064, USA
9. Armed Forces Institute of Pathology, Veterinary Pathology, Washington, District of Columbia 20306, USA
10. California Department of Health Services Food and Drug Branch, PO Box 942732 MS 357, Sacramento, California 94234-7320, USA
11. Department of Pathology, Microbiology and Immunology, University of California at Davis, Davis, California 95616, USA
12. Biological Sciences, University of North Carolina at Willmington, 601 S. College Rd., Willmington, North Carolina 28403, USA
13. National Marine Fisheries Service, 1315 East West Highway, Silver Spring, Maryland 20910, USA
14. College of Veterinary Medicine, Colorado State University, Fort Collins, Colorado 80523, USA
15. NOAA/NMFS/ECD, 2,725 Montlake Blvd., Seattle, Washington 98112, USA

Correspondence to: Correspondence and requests for materials should be addressed to C.S. (e-mail: Email: scholin@mbari.org).

Abstract

Over 400 California sea lions (Zalophus californianus) died and many others displayed signs of neurological dysfunction along the central California coast during May and June 1998. A bloom of Pseudo-nitzschia australis (diatom) was observed in the Monterey Bay region during the same period. This bloom was associated with production of domoic acid (DA), a neurotoxin¹ that was also detected in planktivorous fish, including the northern anchovy (Engraulis mordax), and in sea lion body fluids. These and other concurrent observations demonstrate the trophic transfer of DA resulting in marine mammal mortality. In contrast to fish, blue mussels (Mytilus edulus) collected during the DA outbreak contained no DA or only trace amounts. Such findings reveal that monitoring of mussel toxicity alone does not necessarily provide adequate warning of DA entering the food web at levels sufficient to harm marine wildlife and perhaps humans.