A Qualitative Study of Zooplankton Grazing in an Oligo-Mesotrophic Lake Using Phytoplanktonic Pigments as Organic Markers

The impact of grazing by various zooplankton fractions (calanoid copepods, cyclopid copepods, cladocerans, and small-sized zooplankton: 80-315μ m) on various phytoplankton groups was measured in Lake Pavin (Central Massif, France) by means of phytoplankton pigments separated by HPLC as natural organic markers. The impact of grazing was determined from April to November in the depth-sampling layers (0-7 and 7-20 m) in which most zooplankton organisms were concentrated. Selective grazing by consumers created spatial (vertical) and temporal variation in mortality exerted on the various phytoplankton groups. For example, the avoidance of dinoflagellates (characterized by peridinin) by most of the zooplankton organisms studied led to low grazing impacts$(