Abstract
Five bottle incubation experiments were done to investigate the grazing and food selection by the copepod Calanus finmarchicus (Gunnerus) during a phytoplankton bloom in aN and P fertilized mesocosm. The phytoplankton biomass was dominated by diatoms and lager dinoflagellates (< 35 µm), while the haptophyte Emiliania huxleyi (Lohmann) Hay et Mohler dominated numerically (up to 10 · 103 ml−1). The concentration of dinoflagellates (35 µm) was always low (≤39 ml−1). The ciliate abundance in the mesocosm was within the lower end of previous recordings at the start of the period (3.8 ml−1), and decreased throughout the bloom. The copepod C. finmarchicus preferentially fed upon ciliates and dinoflagellates (> 35 µm), and selective copepod predation may have controled the development of these protists in the mesocosm. However, diatoms made up the largest part of the copepod carbon ingestion due to their dominance in the plankton. The haptophytes E. huxleyi and Phaeocystis cf. pouchetii were not prefeITed food types, and never made up a significant part of the copepod diet. However, there was a significant grazing on small single cells, presumably swarming Phaeocystis, at the end of the bloom.
