Recent changes in the pelagic ecosystem of the Iberian Atlantic in the context of multidecadal variability

Trends in ecosystem variables of the Eastern North Atlantic shelf near the Iberian Peninsula were analysed in relation to regional climate and oceanographic variability. In addition, detailed changes in oceanographic properties (surface temperature, upwelling and poleward current activity) and biological components (plankton and pelagic consumers) in the period 1989-2005 were compared with the main trends and multidecadal periods observed in time series dating back to 1950. In contrast to previous studies, the North Atlantic Oscillation did not appear as the main influence in the climate of the North Iberian region, while East-West and subtropical gradients were the dominant modes. Climatic oscillations at decadal scales were paralleled by similar oscillations in oceanographic and biological variables, but the latter appeared weakly related to climate. Time- lags of up to 5 years in the biological response may partly explain these relationships. The main planktivorous fish species (sardine and anchovy) alternate in periods of 10-15 years of relative dominance, in synchrony with equivalent species around the world. In contrast, plankton cycles appear greatly modified after 1990 in coincidence with shifts in climatic and oceanographic variables. Subregional variability indicated divergent trends in biological variables, particularly the zooplankton increase off A Coruña and the decrease in the Bay of Biscay since 1990. Such divergences are related to direct and indirect effects of global changes in this transitional upwelling region