RECURRENT PATTERNS IN ZOOPLANKTON STRUCTURE AND SUCCESSION IN A VARIABLE COASTAL ENVIRONMENT

Biweekly zooplankton sampling was carried out from 1984 to 1990 in sur face waters (0-50 m) at a coastal station (MC) in the Gulf of Naples ( western Mediterranean Sea). Despite variability in environmental param eters, the zooplankton community showed recurrent patterns throughout the years, both in total abundance and community structure. Total zoop lankton abundance showed a clear seasonal pattern, with highest peaks and lowest values always in summer and winter, respectively. Copepods comprised from 70 to 80% of total zooplankton numbers, followed by cla docerans and appendicularians. A total of 125 copepod species was reco rded at St. MC, most of which showed the same seasonal pattern through out the years. Ten copepod species always accounted for 39-52% of tota l zooplankton, with only minor differences among years in the rank ord er. Paracalanus parvus, Acartia clausi, Centropages typicus, and Temor a stylifera, among the most abundant species in Mediterranean coastal waters, showed some quantitative variations between years. However, th ey represented a very stable fraction of the zooplankton, always ranki ng among the first four dominant species. A peculiar element of regula rity in the structure of the copepod assemblages was represented by th e temporal succession of species within the genera Oithona and Clausoc alanus, suggesting ecological differentiation among congeners. The pre sent data indicate the extreme flexibility of copepods in adapting to a fluctuating environment, with a strong tendency to maintain a stable standing stock even in the presence of variable food resources. (C) 1 995 International Council for the Exploration of the Sea.