Characteristics of zooplankton standing stock and communities in the Western Mediterranean Sea: Relations to hydrology
Gisèle Champalbert

The standing stock and specific composition of zooplankton from neritic and oceanic waters were analyzed in different areas of the western Mediterranean. Comparisons with data from the eastern basin show that zooplankton biomass is situated in the same range in both basins. Local variations in the standing stocks are marked. They are strongly related to topography and complex hydrological events which control nutrients and productivity. Biomasses are usually higher in neritic than in oceanic waters. Seasonal fluctuations are particularly important in both basins. Frontal zones or areas of upwelled waters, particularly rich in nutrients, are highly productive (biomasses >20 mg m-3). Total production is particularly intense in the Alboran Sea, and the Almeria-Oran front. Conversely, the Tyrrhenian Sea is not very productive: minima are around 0.2 mg m-3. The uniformity of zooplankton composition clearly appears in the western and the eastern Mediterranean Sea. Specific diversity is lower inshore, especially when the continental shelf is narrower than offshore. The neritic community consists of a few species with > 50% copepods. Specific assemblages with low diversity inhabit brackish or eutrophic areas. The oceanic community encompasses neritic and oceanic species in low densities; its diversity is high. In the western basin, specific diversity tend to decrease eastward from the strait of Gibraltar and the Alboran Sea, which is rich and influenced by water of Atlantic origin. In the eastern basin, the diversity is maximum in the easternmost Levantine waters. The deep water fauna, mainly composed of mesopelagic species is fairly uniform all over the Mediterranean and poorer than the Atlantic deep fauna. Besides variations related to hydrology and biotic factors, important changes of zooplankton biomass and specific composition are induced by diel vertical migrations which favour active transfer of organic matter as well as passive horizontal transport.

Keywords: Zooplankton, biomass, specific composition, hydrology, Mediterranean Sea
Contents of this volume Sci. Mar. 60(Suppl.2) : 97-113 Back PDF
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