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

Nauplii and adults of the copepod Eurytemora affinis Poppe collectedfrom the Multiscale Experimental Ecosystem Research Center (MEERC)mesocosms and from the Choptank River (a subestuary of ChesapeakeBay) reduced ciliate and dinoflagellate microplankton densitiessignificantly during grazing experiments. Protozoan microplanktongenerally were consumed in proportion to their availability,although both adult copepod and naupliar clearance rates werehigher for larger prey ({small tilde}40µm). Ingestionof ciliate microplankton was confirmed by examining copepodgut fluorescence after brief (1 h) incubations with ciliateslabeled with a fluorescent vital stain (5-chloromethylfluoresceindiacetate). In addition, both adults and nauplii of E.affiniscleared protozoan microplankton at considerably higher ratesthan chlorophyll a. Naupliar clearance rates were generallyan order of magnitude lower than adult rates, but given naupliarabundances in copepod assemblages, they should contribute substantiallyto total grazing on protozoan microplankton. Grazing by thetotal copepod assemblage in mesocosms and in the field may beunderestimated if juvenile stages are ignored.