Community structure of mesopelagic copepods (>500 μm) in the Ligurian sea (western Mediterranean)

The distribution of mesopelagic copepods between 250 and 1000 m depth was studied along a transect off the coast of Villefranche-sur-Mer in June 1991 by means of a BIONESS multiple-net sampler. Among the most abundant species at all stations were Pleuromamma gracilis, Paraeuchaeta acuta and overwintering Calanus helgolandicus CV copepodites, each species inhabiting different depth layers with maximum abundances in the 250-350 m, 450-550 m and the 700-850 m layer, respectively. Cluster analysis of the vertical distribution of all species caught revealed three distinct strata ('TOP', 'INTERMEDIATE', 'BOTTOM') consisting of characteristic species that occurred in the same stratum at all stations. Differences in total abundances of the species assemblage occupying each layer are discussed with regard to predation pressure by mesopelagic macroplanktonic crustaceans and fish. We show that each stratum is characterized by distinct trophic interactions and life strategies, which play an important role in the structuring of mesopelagic zooplankton communities. (C) 1998 Elsevier Science B.V. All rights reserved.