A COMPARATIVE-STUDY OF THE INHIBITORY EFFECT OF DIATOMS ON THE REPRODUCTIVE-BIOLOGY OF THE COPEPOD TEMORA-STYLIFERA

Egg production and viability in the copepod Temora stylifera (collecte d in the Bay of Naples, Italy in 1992) were strongly dependent on food type. A flagellate (Isochrysis galbana) diet induced the production o f good quality eggs that developed to hatching. By contrast, two diato ms (Chaetoceros curvisetum, Phaeodactylum tricornutum) resulted in poo r egg quality, with hatching success as low as 20% of total egg produc tion. With the third diatom tested, Skeletonema costatum, females prod uced eggs for only 3 to 4 d, after which time they either became steri le or died. These results are discussed in relation to previous findin gs regarding the impact of the dinoflagellate Prorocentrum minimum and the diatom Thalassiosira rotula on the hatching success of T. stylife ra eggs. Low egg viability was possibly not due to an absence of remat ing or a deficiency of some specific essential nutrient required for e gg development but to the presence of inhibitory compounds blocking ce ll division during early copepod embryogenesis. This questions the tra ditional view that diatoms are an important food item regulating copep od secondary production.