TIME-SERIES ANALYSIS OF COPEPOD DIVERSITY AND SPECIES RICHNESS IN THESOUTHERN BAY OF BISCAY OFF SANTANDER, SPAIN, IN RELATION TO ENVIRONMENTAL-CONDITIONS

Changes in the copepod species composition and their relative abundanc es at two stations on a cross-shelf section off Santander (Spain) in t he southern Bay of Biscay are described by means of species richness, Shannon-Weaver diversity, and similarity coefficients. The seasonal an d inter-annual variability in these indices is compared with changes o bserved in thermal stratification indices from monthly collected data over 5 years (June 1991 to June 1996). Copepods represent the main tax onomic group in the zooplankton assemblage in terms of abundance and p ersistence. Ordination of the samples by their similarity coefficients has a clear temporal meaning, and the clusters formed are linked to s easonal characteristics of the water column. Autocorrelation and spect ral analysis of species richness and diversity show a 12-month periodi c cycle throughout the time series, with a less important peak every 3 0 months. The long-term trends between these indices and the standard deviation of water column temperature (as an index of thermal stratifi cation) are of opposite sign. The significant negative correlation bet ween the pairs suggests a strong relationship between the maintenance of copepod diversity and environmental conditions. (C) 1998 Internatio nal Council for the Exploration of the Sea.