PATTERNS OF ABUNDANCE FOR CALANUS AND SMALLER COPEPODS IN THE NORTH-SEA - TIME-SERIES DECOMPOSITION OF 2 CPR DATA SETS

We present a time series analysis of 34 yr of continuous plankton reco rder (CPR) data for 2 taxa: 'total small copepods' and Calanus copepod ite stages 5 and 6 in the North Sea. Each was resolved into spatial av erages over areas which correspond to the hydrographic regimes of the North Sea as defined by ICES. An iterative method which enables reliab le determination of the long-term trends, mean annual cycles and confi dence bounds for the monthly means is presented. We find that a purely time-dependent (i.e, trend plus seasonality) model can explain in exc ess of 70% of the variance in the (log-transformed) data. Nonetheless, the correlation structure in the residuals is indicative of the addit ional influence of past abundances upon subsequent dynamics. The resid uals of many of the adjacent regions within the North Sea exhibit sign ificant cross correlations at lag zero. This suggests that stochastic events can influence zooplankton dynamics over very large areas. We fo und no evidence that the zooplankton dynamics in up-current regions dr ive the dynamics of their downstream neighbours. In contrast, hydrogra phically similar regions tend to share a common seasonal dynamic even when they are not adjacent.