Mortality of sea lions along the central California coast linked to a toxic diatom bloom

Over 400 California sea lions (Zalophus californianus) died and many others displayed signs of neurological dysfunction along the central California c oast during May and June 1998. A bloom of Pseudo-nitzschia australis (diato m) was observed in the Monterey Bay region during the same period. This blo om was associated with production of domoic acid (DA), a neurotoxin(1) that was also detected in planktivorous fish, including the northern anchovy (E ngraulis mordax), and in sea lion body fluids. These and other concurrent o bservations demonstrate the trophic transfer of DA resulting in marine mamm al 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 provi de adequate warning of DA entering the food web at levels sufficient to har m marine wildlife and perhaps humans.