Natural diets of zooplankton off southern California

Abstract

Plant and animal carotenoid pigments were isolated from the guts of the copepods Calanus pacificus and Clausocalanus sp, and the cladocerans Evadne spp. by high performance Liquid chromatography. Measured carotenoid concentrations were converted to eshmates of class-specific phytoplankton biomass and total microzooplankton biomass In the zooplankton diets. Different pigments were present in the guts at dfferent times of day and night and the tllnmg of peak gut fullness var~ed between species. In C. pacificus, pigment concentrat~ons were highest during the period from evening twilight to midnight. Evadne spp. exhibited a midnight peak In gut pigmentation. Clausocalanus sp. contained elevated levels of pigments between midnight and noon. The gut contents of C. pacificus and Evadne spp. were dominated by animal carbon when phytoplankton biomass and productivity were relatively low, and by algal carbon when phytoplankton biomass and productivity were high. Clausocalanus sp. did not follow this pattern. Our observations are consistent with the hypothesis that carnivory may represent an important mode of feeding among small zooplankton and, further, that the diets of some species of zooplankton vary in response to quantitative and qualitative attributes of the food environment.