Comportement alimentaire de deux copepodes calanoides (Centropages typicus et Acartia clausi) en milieux nutritifs a une seule algue

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Abstract
Experiments were made with two pelagic copepods common in the Gulf of Marseilles, Centropages typicus and Acartia clausi. The experiments were carried out in 500 ml pyrex erlenmeyer flasks containing 300 ml of nutritive medium and about 15 copepods. The flasks were held in a temperature controlled tank and constantly agitated to prevent phytoplankton settling on the bottom. The plant cells used as food were diatoms (Skeletonema costatum, Phaeodactylum tricornutum, Lauderia borealis, Chaetoceros pseudocurvisetus) and flagellates (Amphidinium klebsii, Prorocentrum micans, Isochrysis galbana) of different shapes and dimensions. The results were based on two essential parameters: the filtration rate F (ml/copepod/24 h) and the ingestion rate I (cells ingested/ copepod/24 h). Two conclusions emerged from the experiments: a) The copepods were not automatic filterers. Their ingestion rate increased in a non-linear fashion with an increase in concentration, often rising swiftly from some concentrations which were lower for large cells than for small ones. In the former case consumption stabilized or tended towards a maximum at high densities, indicating an optimal ingestion. In other cases consumption increased, even at concentrations much higher than those found in the sea. Moreover, the filtration rate fell with an increase of the initial concentration. b) The copepods appear to regulate their intake over rather long periods of time. Thus, with experiments continued for several days, the curves constructed from ingestion rate estimated day by day were often irregular, whereas the plots established according to the average daily rate calculated on the 48 h or 72 h of experiments are in agreement with the observations mentioned above.

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