Grazing by protozoa in marine coastal and oceanic ecosystems off New Zealand

Abstract

Uptake rates for ciliates and flagellates grazing on bacteria and picophytoplankton were measured in different water masses around South Island, New Zealand, in April 1992. Fluorescent particles were used to established uptake rates for major ciliate taxa, phytoflagellates, and hetero-trophic flagellates. Protozoan grazing had little impact on the bacterial population, removing < 5% of the population per day. Heterotrophic flagellates and ciliates selected picophytoplankton in preference to bacterial-sized particles, both groups removing 6–32% of the picophytoplankton population per day. Highest removal rates for picophytoplankton were found in coastal waters and for bacterial populations in subantarctic waters. This difference was attributed to differences in community composition and taxa-specific clearance rates. © 1996, Copyright Taylor & Francis Group, LLC.