FOOD TYPE INDUCES DIFFERENT REPRODUCTIVE RESPONSES IN THE COPEPOD CENTROPAGES TYPICUS

Egg production and hatching success were determined for individual Cen tropages typicus fed two diatoms (Thalassiosira rotula and Phaeodactyl um tricornutum) and two dinoflagellates (Prorocentrum minimum and Gony aulax polyedra). Both reproductive responses were strongly affected by food type. Females incubated without males produced eggs with all die ts, but fecundity was twice as high with the larger T. rotula and G. p olyedra cells. In contrast, hatching success was 2-3 times higher with the dinoflagellate diets. The presence of males did not enhance egg p roduction rates. Males also did not improve hatching success when the diet consisted of the diatom T. rotula. However, egg viability was hig her for couples fed the dinoflagellate G. polyedra, indicating that eg g viability was possibly being controlled by both remating and food ty pe. Egg viability was artificially lowered by exposing newly spawned e ggs to high concentrations (10(4)-10(9) pg C) of extracts from T. rotu la, whereas the development of eggs proceeded normally at all concentr ations of extracts from P. minimum. Blockage of egg development was no t due to anoxia, but to the presence of intracellular, deleterious che mical compounds in diatoms, suggesting that bottom-up prey control mec hanisms underlie seasonal fluctuations in C. typicus populations at se a.