Differential grazing on protozoan microplankton by developmental stages of the calanoid copepod Eurytemora affinis Poppe

Abstract

Nauplii and adults of the copepod Eurytemora affinis Poppe collected from the Multiscale Experimental Ecosystem Research Center (MEERC) mesocosms and from the Choptank River (a subestuary of Chesapeake Bay) reduced ciliate and dinoflagellate microplankton densities significantly during grazing experiments. Protozoan microplankton generally were consumed in proportion to their availability, although both adult copepod and naupliar clearance rates were higher for larger prey (~40 μm). Ingestion of ciliate microplankton was confirmed by examining copepod gut fluorescence after brief (1 h) incubations with ciliates labeled with a fluorescent vital stain (5-chloromethylfluorescein diacetate). In addition, both adults and nauplii of E.affinis cleared protozoan microplankton at considerably higher rates than chlorophyll a. Naupliar clearance rates were generally an order of magnitude lower than adult rates, but given naupliar abundances in copepod assemblages, they should contribute substantially to total grazing on protozoan microplankton. Grazing by the total copepod assemblage in mesocosms and in the field may be underestimated if juvenile stages are ignored.