Time-series analysis of copepod diversity and species richness in the southern Bay of Biscay off Santander, Spain, in relation to environmental conditions

Abstract

Changes in the copepod species composition and their relative abundances at two stations on a cross-shelf section off Santander (Spain) in the southern Bay of Biscay are described by means of species richness, Shannon-Weaver diversity, and similarity coefficients. The seasonal and inter-annual variability in these indices is compared with changes observed in thermal stratification indices from monthly collected data over 5 years (June 1991 to June 1996). Copepods represent the main taxonomic group in the zooplankton assemblage in terms of abundance and persistence. Ordination of the samples by their similarity coefficients has a clear temporal meaning, and the clusters formed are linked to seasonal characteristics of the water column. Autocorrelation and spectral analysis of species richness and diversity show a 12-month periodic cycle throughout the time series, with a less important peak every 30 months. The long-term trends between these indices and the standard deviation of water column temperature (as an index of thermal stratification) are of opposite sign. The significant negative correlation between the pairs suggests a strong relationship between the maintenance of copepod diversity and environmental conditions.