FOOD TYPE INDUCES DIFFERENT REPRODUCTIVE RESPONSES IN THE COPEPOD CENTROPAGES TYPICUS

Egg production and hatching success were determined for individual Centropages typicus fed two diatoms (Thalassiosira rotula and Phaeodactylum tricornutum) and two dinoflagellates (Prorocentrum minimum and Gonyaulax polyedra). Both reproductive responses were strongly affected by food type. Females incubated without males produced eggs with all diets, but fecundity was twice as high with the larger T. rotula and G. polyedra cells. In contrast, hatching success was 2-3 times higher with the dinoflagellate diets. The presence of males did not enhance egg production rates. Males also did not improve hatching success when the diet consisted of the diatom T. rotula. However, egg viability was higher for couples fed the dinoflagellate G. polyedra, indicating that egg viability was possibly being controlled by both remating and food type. Egg viability was artificially lowered by exposing newly spawned eggs to high concentrations (10(4)-10(9) pg C) of extracts from T. rotula, whereas the development of eggs proceeded normally at all concentrations of extracts from P. minimum. Blockage of egg development was not due to anoxia, but to the presence of intracellular, deleterious chemical compounds in diatoms, suggesting that bottom-up prey control mechanisms underlie seasonal fluctuations in C. typicus populations at sea.