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

Biweekly zooplankton sampling was carried out from 1984 to 1990 in surface waters (0-50 m) at a coastal station (MC) in the Gulf of Naples (western Mediterranean Sea). Despite variability in environmental parameters, the zooplankton community showed recurrent patterns throughout the years, both in total abundance and community structure. Total zooplankton 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 cladocerans and appendicularians. A total of 125 copepod species was recorded at St. MC, most of which showed the same seasonal pattern throughout the years. Ten copepod species always accounted for 39-52% of total zooplankton, with only minor differences among years in the rank order. Paracalanus parvus, Acartia clausi, Centropages typicus, and Temora stylifera, among the most abundant species in Mediterranean coastal waters, showed some quantitative variations between years. However, they represented a very stable fraction of the zooplankton, always ranking among the first four dominant species. A peculiar element of regularity in the structure of the copepod assemblages was represented by the temporal succession of species within the genera Oithona and Clausocalanus, suggesting ecological differentiation among congeners. The present 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) 1995 International Council for the Exploration of the Sea.