Distribution and Ecology of Mesozooplankton in the Northern and Central Adriatic Sea

Abstract

Within the framework of the Prisma 2 Project, four oceanographic cruises were carried out in the central and northern Adriatic Sea from June 1996 to March 1997. Samples were collected both by BIONESS electronic multinet (204 samples from 54 sites) and by WP2 (101 samples from 19 sites) along inshore-offshore sections. The spatial-temporal distribution of the zooplankton community was analysed in relation to the variability of physico-chemical and biological parameters. The seasonal succession of the zooplankton community was characterized by an inversion of the dominance ratio between copepods and cladocerans. In early June, copepods and cladocerans represent on average 52 and 20% of the zooplankton community, respectively, while in late summer they represent 17 and 66%. During late spring-summer, the cladoceran population was clearly dominated by Penilia avirotris, which in some coastal sites constituted more than 90% of the zooplankton. In the coastal zone, the copepod population was characterized by low species diversity and greater dominance of A. clausi, P. parvus and T. stylifera (73% of the population). In the offshore zone of the neritic system, there was instead a more homogeneous copepod species composition. Because of their spatial distribution patterns, P. elongatus and T. longicornis, typical of estuarine environments,can be considered as hydrological indicator species of different water masses of the Adriatic neritic system. In winter, the zooplankton community was characterized by strong dominance of copepods (31 species identified), on average constituting 75% of the zooplankton, followed by invertebrate larvae, appendicularians, cladocerans, siphonophores and chaetognaths. From our analysis of the spatial distribution of the zooplankton community, we have formulated a preliminary trophic model concerning the association of ecologically similar species in the water masses of the Adriatic neritic system.