Induction of reproductive failure in the planktonic copepod Calanus pacificus by diatoms

The inhibitory effect of diatoms upon egg viability was investigated by feeding the planktonic copepod Calanus pacificus (collected in coastal waters off Oregon. USA) 3 diatom species (Chaetoceros difficilis, Ditylurn brightweh, isolated from Oregon coastal waters, and Thalassiosira weissflogii, from culture collections at Oregon State University) ad libitum (2.6 to 3.9 mg C I-'). These diatoms induced the production of abnormal eggs which failed to hatch or hatched into deformed nauplii. In contrast, a dinoflagellate diet (Prorocentrum mlnirnurn, from the culture collections) resulted in the production of normal eggs, 96 6 , of which hatched into healthy nauplii. D~atom inhibitory effect disappeared quickly ( c2 to 3 d ) when females were transferred from diatom suspensions to dinoflagellate suspension. The inhibitory effect was also apparent when newly spawned eggs were exposed to dense diatom cell extracts, indicating that blocking of the embryonic development is chemically mediated. The production of unidentified anti-mitotic chemical compounds by diatoms may be ubiquitous. K E Y WORDS: Calanuspacificus Diatoms . Embryonic development . Inhibition