Relationship between zooplankton distribution and physicals structures during two different seasons in the Gulf of Lion.

Abstract

International audienceDuring three cruises (2 to 17 October 2009, 26 April to 7 May 2010, 23 January to 4 February 2011), the whole French continental shelf of the Gulf of Lion was sampled to obtain an overview on the zooplankton community size structure. 6 transects from the coast to the open ocean were conducted for a total of 160 stations. A laser optical plankton counter (LOPC) was used to estimate abundance, biovolume, and general characteristics of size spectra. The vertical distribution of, the LOPC counts, the chla concentration and the hydrological parameters was investigated in order to highlight their interactions and the main structures. Different patterns of particle distributions occur following the water column structure and the bathymetry. A PCA was done on physicals and biological parameters to interpret the links between the different parameters. A clustering test allowed us to define 3 spatial areas corresponding potentially to different type of habitat: the Rhône plume, the coastal area and the continental shelf area. The zooplankton size distribution was investigated within the three areas using the normalized biomass size spectrum (NBSS). The coastal area was characterized by the highest NBSS slopes and highest chla concentration, the upwelling and the formation of deep water participated to keep the water mixed. The Rhône plume showed the lowest NBSS slopes associated with strong water stratification. These waters were rich in nutrient promoted high chlorophyll a concentrations in the surface water layer and carried on the continental shelf a lot of organic matter. The continental shelf showed the lowest abundances and was hit by the Liguro-Provençal current depending on the season. The NBSS slopes were higher during winter, meaning the proportions of large organisms were more important during the post bloom period (May and October)