Phytoplankton blooms are known to induce diarrheic, neurotic, and paralytic shellfish poisoning in humans through the production of potent toxins by several dinoflagellate and flagellate species. Diatoms, another major component of the phytoplankton, have rarely been reported as toxic to marine organisms. But diatoms may be more insidious than is generally believed. High concentrations of domoic acid have been identified in Nitzschia pungens f. multiseries (Douglas and Bates, 1991), and recent studies indicate that several diatom species also contain antimitotic compounds inducing egg mortality in several invertebrates including crustaceans (several copepod species belonging to the genera Calanus, Centropages, Acartia, Eucyclops, Paracyclops,