Some Factors Affecting the Feeding of Marine Copepods of the Genus Calanus1

The grazing rates of 4 species of Calanus were measured on several species of marine phytoplankton, both singly and in mixtures. Grazing rates varied inversely with phytoplankton concentration, the duration of the experiment, and the age of the phytoplankton cultures used. Calanus spp. generally removed large cells at higher rates than small when feeding on a mixture of two species of phytoplankton. Because of this selectivity and the difference in volume between large and small cells, the large cells contributed by far the greater fraction of the total volume of food ingested by the copepods, even when considerably less abundant than the smaller cells. Comparison of the grazing rates of the copepodite stage V and adult female animals of C. finmarchicus, C. glacialis, and C. hgperboreus on a mixture of 7 species of diatoms demonstrated further the importance of large cells. Marked quantitative differences in rate of food intake were found between the different developmental stages of each species and between the different species of copepods, and some qualitative differences in selective feeding were also indicated.