Contribution of ciliated Microprotozoans and Dinoflagellates to the diet of three Copepod species in the Bay of Biscay

Predation of three calanoid copepods (Calanus helgolandicus, Temora longicornis and Centropages chierchiae) on phytoplankton, dinoflagellates and ciliates was estimated in the Gironde estuarine plume (Bay of Biscay) during winter by means of in situ incubations. Both phytoplankton and ciliates were part of the diet of those three species, while only Centropages chierchiae also included a significant portion of dinoflagellates in its diet. The clearance rates of Calanus helgolandicus for ciliates and phytoplankton reached 2.8 and 4.0 ml copepod(-1) h(-1), respectively, those of Temora longicornis were 3.2 and 1.8 ml copepod(-1) h(-1), and those of Centropages chierchiae were 4.3 and 0.8 ml copepod(-1) h(-1). Neither Calanus helgolandicus nor Temora longicornis selected dinoflagellates, given the low clearance rates measured for this prey category (0.05 and 0.03 ml copepod(-1) h(-1), respectively). By contrast, Centropages chierchiae included dinoflagellates in its diet, with a clearance rate of 4.9 ml copepod(-1) h(-1). Within a given prey category (ciliates or dinoflagellates), all three copepods selected larger prey types (> 40 mum) over smaller ones (less than or equal to 40 mum). This implies a better detection and capture of larger motile prey compared to small ones. The results are discussed with regard to the omnivorous feeding behavior of these copepods observed here, during a late winter phytoplankton bloom.