Zooplankton community during the transition from spring bloom to oligotrophy in the open NW Mediterranean and effects of wind events. 1. Abundance and specific composition

Short-term changes in the zooplankton community were investigated at a time-series station in the open NW Mediterranean during the DYNAPROC cruise programme (May 1995). Based on the samples obtained with three devices (12 l bottle, 200 mum and 500 mum mesh nets), the abundance and specific composition are presented for mesozooplankton (copepods mainly), macroplankton and micronekton. Over the 3 week sampling period, overall density of the copepod community decreased and changes in the specific composition occurred. The decline was also observed in nauplii and was more marked in small-sized copepod species than in larger ones; one species, Centropages typicus, even disappeared. An increase in the proportion of carnivorous organisms appeared in both copepods (Euchaeta acuta, Heterorhabdus spp.) and euphausiids (Nematoscelis megalops, Stylocheiron longicorne). These changes are discussed in relation to environmental features and in the context of seasonal variability, the observational period coinciding with the transition from spring bloom to oligotrophy in this area. Effects of a major wind event that appeared to have induced long-lasting changes are also explored.