Diel variations of the bathymetric distribution of zooplankton groups and biomass in Cap-Ferret Canyon, France

The bathymetric distribution, abundance and diel vertical migrations (DVM) of zooplankton were investigated along the axis of the Cap-Ferret Canyon (B ay of Biscay, French Atlantic coast) by a consecutive series of synchronous net hauls that sampled the whole water column (0-2000 m in depth) during a diel cycle. The distribution of appendicularians (maximum 189 individuals m(-3)), cladocerans (maximum 287 individuals m(-3)), copepods (copepods < 4 mm, maximum 773 individuals m(-3), copepods > 4 mm, maximum 13 individuals m(-3)), ostracods (maximum 8 individuals m(-3)), siphonophores (maximum > 2 individuals m(-3)) and peracarids (maximum > 600 individuals 1000 m(-3)) were analysed and represented by isoline diagrams. The biomass of total zoo plankton (maximum 18419 mu g C m(-3), 3780 mu g N m(-3)) and large copepods ( > 4 mm maximum 2256 mu g C m(-3), 425 mu g N m(-3)) also were determined . Vertical migration was absent or affected only the epipelagic zone for ap pendicularians, cladocerans, small copepods and siphonophores. Average ampl itude of vertical migration was about 400-500 m for ostracods, some hyperii ds and mysids, and large copepods, which were often present in the epipelag ic, mesopelagic, and bathypelagic zones. Large copepods can constitute more than 80% of the biomass corresponding to total zooplankton. They may play an important role in the active vertical transfer of carbon and nitrogen. ( C) 1999 Elsevier Science Ltd. All rights reserved.