Zooplankton community during the transition from spring bloom to oligotrophy in the open NW Mediterranean and effects of wind events. 2. Vertical distributions and migrations

Vertical distribution of zooplankton was investigated over a 3-week period at a fixed station in the open NW Mediterranean during the DYNAPROC cruise (May 1995). The observational period coincided with the transition from spring bloom to oligotrophy in this area. Vertical distribution and migration in the 0-1000 m water column are described in detail for the main species of copepods (>500 mum). Ontogenetic migration is reported for Neocalanus gracilis, Euchaeta acuta and Pleuromamma abdominalis. This study also documented the downwards seasonal migration of Calanus helgolandicus. Short-term changes in the vertical distribution of the small-sized organisms (>50 mum) in the upper 100 m are discussed in relation to the two major wind events that occurred during the cruise. The naupliar stages of copepods and euphausiids appeared unable to counter the upwards vertical advection and the wind-induced mixing, while no marked changes were observed for Oithona spp. and Microsetella spp.