The zooplankton

Abstract

The Mediterranean Sea bears one of the longest traditions in the study of zooplankton. Pioneer work focused more on taxonomy to suit the high diversity of zooplankton that inhabits the Mediterranean, and indeed very few ecosystems have such a deep and broad knowledge on zooplankton like the one gathered in the Mediterranean. Further research into ecological aspects encompassed more descriptive studies on distribution and seasonality patterns, to lead in current times to more functional and modelling approaches. In this chapter we present an overview of the seasonality and distribution patterns of zooplankton in the Mediterranean, with special emphasis on the driving mechanisms behind. We will focus essentially on the western basin, and provide an overview on the outcome of the studies conducted by the different schools of marine biologists and oceanographers established in the geographical areas surrounding the Catalan/Balearic Sea, the Ligurian Sea and the Thyrrenian Sea. The latitudinal gradient, the marked seasonality, and the particular productivity patterns in the Mediterranean provide a frame for a zooplankton community in which the succession of species and assemblages occurs with not drastic changes in the whole standing stocks. As in other seas, examples of diel, ontogenetic and seasonal vertical migration can be found in the Mediterranean; however, the presence of a deep chlorophyll maximum during the stratified period drives a distinct vertical distribution of epipelagic zooplankton. Mesoscale singularities such as density fronts and eddies, the presence of submarine canyons which modify the general circulation, and other local phenomena like riverine runoff are responsible for the enhancement of production and favours the aggregation of zooplankton, either by local increase phenomena or by passive accumulation. Finally, current challenges in zooplankton research in the Mediterranean, such as the long-term changes in relation to large-scale atmospheric forcing, the occurrence of gelatinous zooplankton proliferations and the changes in species distribution and presence of non-indigenous ones will be also discussed.