Phytoplankton‐zooplankton relationships in narragansett bay. iv. the seasonal importance of grazing1

Abstract: Grazing experiments with freshly caught plankton from Narragansett Bay were performed at weekly or biweekly intervals through most of a seasonal cycle. The laboratory rates (obtained under simulated natural conditions) were multiplied by the zooplankton concentration in the natural environment and the effects of grazing on the phytoplankton community were assessed. Grazing was most extensive in spring and early summer; phytoplankton production was believed to be high and a large standing crop of Skeletonema costatum persisted. The grazing population was severely reduced during summer, but the phytoplankton standing crop did not increase markedly and some other factor must have been limiting primary production at this time. During fall, decreasing light allowed little phytoplankton growth and mild grazing kept the standing crop at a minimum. This grazing ceased in December and with the release in grazing pressure the winter-spring diatom flowering began. Skeletonema costatum, the dominant bay diatom, was selectively grazed and its longer chains were preferentially removed.