Effects of diatom diets on the reproduction of the planktonic copepod Calanus finmarchicus

The potential for an adverse influence of diatom diets on the reproductive success of the planktonic copepod Calanus finmarchicus was investigated exp erimentally under laboratory conditions. A monospecific diet of the common diatom Thalassiosira nordenskioldii significantly reduced the viability of Calanus eggs, which either failed to hatch or hatched into deformed nauplii . The production of nonviable eggs increased with increasing Thalassiosira concentration and was proportional to the female ingestion rate. At a cell concentration of 10(4) ml(-1) (typical bloom concentration in the St. Lawre nce Estuary), the proportion of nonviable eggs was as high as 83 % of the t otal daily production. Nonviable egg production was also induced by a diato m of the genus Navicula, but not by two other diatoms, Skeletonema costatum and Chaetoceros debilis. Among non-diatom diets, maternal feeding on a din oflagellate (Protocentrum micans) and two flagellates (Isochrysis galbana, Pavlova lutheri) at food-saturated conditions resulted in the production of normal eggs, more than 70 % of which hatched into healthy nauplii. The hat ching success of eggs was independent of the daily egg production rate, as only three of the algal species (T. nordenskioldii, S costatum, and P. mica ns) supported maximum egg production at superabundant food concentrations. A failure of embryonic development also occurred when females were exposed to a diversified diet composed of Thalassiosira, Chaetoceros and Skeletonem a, even though T. nordenskioldii contributed less than 60 % of total ingest ed carbon. We conclude from these experiments that extended feeding on cert ain extremely common diatom species, by themselves and apparently also in m ixtures where they predominate, could have a negative impact on C. finmarch icus recruitment rates.