Zooplankton of Massachusetts Bay, USA, 1992–2003: relationships between the copepod Calanus finmarchicus and the North Atlantic Oscillation

Abstract

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.

Springtime transport and retention of Calanus finmarchicus in Massachusetts and Cape Cod Bays, USA, and implications for right whale foraging

“…A stronger coastal transport, on the other hand, would imply a shorter residence time of water parcels in western MB and possibly a smaller locally-produced younger generation of C. finmarchicus. This is consistent with the negative correlation between the C. finmarchicus abundance in western MB and wind speed at NOAA 44013 (Turner et al 2006), since higher wind speed would generally imply stronger coastal current.…”

“…The coastal current becomes weaker and it is likely that the retention zone in CCB also shifts northward, which may partly explain why right whales normally leave CCB in late April and early May. Another possible reason for the departure of right whales may be the seasonal decline of Calanus finmarchicus abundance, which normally starts in late April or May in MB-CCB (Turner et al 2006).…”

“…Concentrations of total zooplankton were calculated based on the number of animals counted, divided by the volume of water filtered by the net, and multiplied by the aliquot concentration factor. A more detailed sampling and analysis description can be found in Turner et al (2006). In this study, we only used the total abundance of C. finmarchicus of all copepodite and adult stages for the month of April from 1997 to 2004 to understand the correlation of this copepod with right whale feeding activity.…”

“…Zooplankton abundances. Zooplankton abundances in MB-CCB have been measured since 1992 as part of an MB monitoring program (Turner et al 2006). Among the monitoring stations, 4 stations in CCB and 2 stations in the North Passage were occupied 6 times per year (February, April, June, August, October and December) (Fig.…”

“…Hydrology, nutrients and phytoplankton in the GOM are also subject to largescale influences (Petrie & Drinkwater 1993, Barton et al 2003, Thomas et al 2003. As a shallow embayment connected to the GOM through the intruding branch of the WMCC, MB-CCB likely is affected by climate variability indirectly through changes in the boundary conditions (Jiang et al 2007b) and directly through changes in surface forcing, such as the sea surface temperature (SST) (Keller et al 2001) and surface winds (Turner et al 2006). However, the problem becomes more complicated because signals of largescale variability propagating into coastal regions can be amplified or weakened.…”