LONG-TERM CHANGES IN ZOOPLANKTON AND THE CLIMATE OF THE NORTH-ATLANTIC

Long-term variations in zooplankton abundance in the north-east Atlant ic, the North Sea, and in freshwater UK lakes are investigated bq mean s of the Continuous Plankton Recorder survey and the Windermere and Es thwaite lakes data. Inter-annual variability of plankton abundance in these data sets shows strong correlation with two modes of climatic va riability in the North Atlantic: the latitudinal shifts of the north w all of the Gulf Stream and the North Atlantic Oscillation. Detailed an alyses reveal that the connection between environmental forcing and pl ankton response depends on various mechanisms, i.e., timing and intens ity of the spring phytoplankton bloom resulting from changes in strati fication levels, changes in temperature, and. in the case of the copep od Calanus finmarchicus, advection of the population into the North Se a at the end of the winter season. Future attempts to predict changes in marine ecosystems on the basis of climate scenarios will require fo cusing major effort on biological-physical modelling and large-scale p lankton population ecology. The maintenance of long-term monitoring pr ogrammes is also essential to determine whether the climate-plankton c onnections observed during several decades will persist in the future or will be overruled by other mechanisms and principally human-induced perturbations. (C) 1998 International Council for the Exploration of the Sea.