CALANUS AND ENVIRONMENT IN THE EASTERN NORTH-ATLANTIC .2. INFLUENCE OF THE NORTH-ATLANTIC OSCILLATION ON C-FINMARCHICUS AND C-HELGOLANDICUS

The influence of the North Atlantic Oscillation (NAG) on 2 major zoopl ankton species of the eastern North Atlantic and the North Sea, Calanu s finmarchicus and C. helgolandicus (Copepoda, Calanoida), was investi gated. Our results confirm that from December to April, west wind stre ss (WWS) intensity and temperature are strongly related to the NAG. If these results were expected, more striking were the close relationshi ps between NAO and Calanus species abundance. Fluctuations in abundanc e of C. finmarchicus mainly result from the combination of 2 factors, both driven by the NAG: WWS effects on spring primary production and t emperature. The case of C. helgolandicus is more complicated, as the l inks between this species and the NAO result from the combination of s everal factors. Two of these factors, spatial heterogeneity of WWS str ength over the area and temperature, are directly driven by the NAG. T he third one, competition between the 2 Calanus species, is indirectly influenced by the NAG. Biogeographical boundaries of the 2 copepods a re also modified by the NAG. Thus, in a comparable way to the El Nino Southern Oscillation in the Pacific, the NAO impacts the pelagic ecosy stem of the eastern Atlantic and the North Sea.