Domoic acid production near California coastal upwelling zones, June 1998

Abstract

Sea lion mortalities in central California during May and June 1998 were traced to their ingestion of sardines and anchovies that had accumulated the neurotoxin domoic acid. The detection of toxin in urine, feces, and stomach contents of several sea lions represents the first proven occurrence of domoic acid transfer through the food chain to a marine mammal. The pennate diatoms, Pseudo-nitzschia multiseries and P. australis, were the dominant, toxinproducing phytoplankton constituting algal blooms near Monterey Bay, Half Moon Bay, and Oceano Dunes, areas where sea lions with neurological symptoms stranded. Toxic Pseudo-nitzschia were also found near Morro Bay, Point Conception, Point Arguello, and Santa Barbara, demonstrating that these species were widespread along the central California coast in June 1998. Measurements of domoic acid during three cruises in early June showed the highest cellular toxin levels in P. multiseries near Point Año Nuevo at 6 pg cell Ϫ1 and in P. australis from Morro Bay at 78 pg cell Ϫ1 . Maximum cellular domoic acid levels were observed within 20 km of the coast between 0 and 5 m depth, although toxin was also measured to depths of 40 m. Hydrographic data indicated that the highest toxin levels and greatest numbers of toxic cells were positioned in water masses associated with upwelling zones near coastal headlands. Nutrient levels at these sites were less than those typically measured during periods of active upwelling, due to the 1998 El Niño event. The flow of cells and/or nutrients from coastal headlands into embayments where cells can multiply in a stratified environment is a possible mechanism of bloom development along the central California coast. This coupling of toxic Pseudo-nitzschia growth near upwelling zones with physical processes involved in cell transport will be understood only when long-term measurements are made at several key coastal locations, aiding in our capability to predict domoic-acid producing algal blooms.In May and June 1998, at least 70 California sea lions (Zalophus californianus) and one northern fur seal (Callorhinus ursinus) were found stranded along the central California coast. This stranding event occurred between 15 May 1 Corresponding author (Vera.L.Trainer@noaa.gov). AcknowledgmentsWe thank the captain and the crew of the RV Ballena, RV Shana Rae, and PB Bluefin for their help during these cruises, at times under strenuous conditions. We acknowledge the following people for their help in providing useful information that directed the locations of the cruises:

Pseudo-nitzschia Peragallo (Bacillariophyceae) diversity and domoic acid accumulation in tuberculate cockles and sweet clams in M’diq Bay, Morocco

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Field applications of the second‐generation Environmental Sample Processor (ESP) for remote detection of harmful algae: 2006‐2007

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