Ingestion of phytoplankton by the micro- and mesozooplankton communities in a productive subtropical estuary

Grazing on phytoplankton by the micro- and mesozooplankton communities was measured during four cruises in a shallow (1.5 m) productive (up to 6 g C m−2 day−1 estuary in the northern Gulf of Mexico. Grazing-induced mortality on phytoplankton was always high and >95% of the grazing was by the microzooplankton community The grazing contribution from the mesozooplankton community, comprised primarily of Acartia tonsa, is believed to be small because populations were kept low by predation and advective losses. A simple model is developed to describe phytoplankton-zooplankton interactions in this estuary. Attempts to understand the distribution and abundance of phytoplankton in estuaries must include estimates of grazer-induced mortality on the phytoplankton.