Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 6 3 2009 10.5194/bg-6-431-2009 http://www.biogeosciences.net/6/431/2009/ http://www.biogeosciences.net/6/431/2009/bg-6-431-2009.html http://www.biogeosciences.net/6/431/2009/bg-6-431-2009.pdf 431 438 2009-03-18 Similar patterns of patterns of community organization characterize distinct groups of different trophic levels in the plankton of the NW Mediterranean Sea V. Raybaud A. Tunin-Ley M. E. Ritchie J. R. Dolan dolan@obs-vlfr.fr UPMC Univ Paris 6, UMR 7093, Laboratoire d'Océanographie de Villefranche, Observatoire Océanologique de Villefranche-sur-Mer, Station Zoologique, B.P. 28, 06230 Villefranche-Sur-Mer, France CNRS, UMR 7093, Laboratoire d'Océanographie de Villefranche, Observatoire Océanologique de Villefranche-sur-Mer, Station Zoologique, B.P. 28, 06230 Villefranche-Sur-Mer, France CNRS, UMR 7093, Laboratoire d'Océanographie de Villefranche, Microbial Ecology and Biogeochemistry, Observatoire Océanologique de Villefranche-sur-Mer, Station Zoologique, B.P. 28, 06230 Villefranche-Sur-Mer, France Biology Department, Syracuse University, Syracuse, NY, USA Planktonic populations were sampled over a 4 week period in the NW Mediterranean, at a site subject to little vertical advection during the Dynaproc 2 cruise in 2004. The characteristics of the phytoplankton, the tintinnid community and the zooplankton have recently been described in detail. Based on these studies, we compared the characteristics of 3 well-circumscribed assemblages of different trophic levels: <i>Ceratium</i> of the phytoplankton, herbivorous tintinnids of the microzooplankton, and large (&gt;500 &mu;m) omnivorous and carnivorous copepods of the metazoan zooplankton. In all three groups, diversity as H' or species richness, was less variable than concentration of organisms. Plotting time against species accumulation, the curves approached plateau values for <i>Ceratium</i> spp, tintinnids and large copepods but only a small number of species were consistently present (core species) and these accounted for most of the populations. 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