Zooplankton of Massachusetts Bay, USA, 19922003: relationships between the copepod Calanus finmarchicus and the North Atlantic Oscillation

Zooplankton community analyses were performed on 102 µm mesh net samples from 1992 to 2003 from 2 stations, in Massachusetts Bay, USA, approximately 15 km offshore from Boston Harbor.There was significant (p < 0.05) negative correlation, with no temporal lag, between the boreal winter North Atlantic Oscillation (NAO) index and winter abundance of Calanus finmarchicus adults plus copepodites (CI to CV) at both stations.The negative correlation between the NAO Index and C. finmarchicus is the opposite of the positive relation emerging from other long-term studies in the Gulf of Maine (GOM) region, but is similar to the negative correlation in many areas of the NE Atlantic.Our data reflect primarily abundance of younger copepodites, which dominated our C. finmarchicus data.These younger copepodites had probably been produced during the first winter cohorts of C. finmarchicus each year, and were only weeks to months old upon capture.Previous positive correlations between C. finmarchicus abundance and the NAO index reported in the literature, with temporal lags of 2 to 4 yr, reflected data for larger CV and adult C. finmarchicus, which had probably been produced the previous year and had overwintered in deep basins in the Gulf of Maine.These older individuals would probably have been more subject to longer-term effects of NAO variability on large-scale interannual circulation patterns than the younger copepodites in our samples, which appeared to be more related to short-term climatic variability.Significant negative correlation between wind speed and abundance of C. finmarchicus supported this conclusion.