Domoic acid-producing diatoms: probable cause of neuroexcitotoxicity in California sea lions

The neurotoxin domoic acid (DA) was identified as the probable cause of death and neurological illness for approximately 70 California sea lions, Zalophus californianus, along the central California coast in May 1998. The apparent vector for sea lion intoxication was the filter-feeding northern anchovy, Engraulis mordax, via transfer of DA from the diatom, Pseudo-nitzschia australis, a natural source of this toxin. Both DA and siliceous frustules of P. australis were found in anchovy gut contents and in fecal material collected from sea lions exhibiting seizures. Anchovies contained 200.29±3.34 μg DA/g in viscera samples, 49.69±0.79 μg DA/g in whole body samples and 35.14±0.47 μg DA/g in body tissue samples. DA concentrations in sea lion fecal material ranged from 1.31 to 182.01 μg DA/g. This is the first documented case of DA toxicity in a marine mammal species