Wiebe, P.H.1, M.F. Baumgartner1,
D. Mountain2, M.C. Benfield3,
C.H. Greene4, A.C. Lavery1,
N. Copley1, and G.L. Lawson1,
R. Converse4, and A. Aretxabaleta4
1Woods Hole Oceanographic Institution,
Woods Hole, MA 02543, USA
2
Northeast Fisheries Science Center, 166 Water St., Woods Hole, MA 02543
3
Louisiana State University, Baton Rouge, Louisiana 70803
4
Cornell University, Ithaca, NY 14853-1504
As part of the U.S. GLOBEC Georges Bank program, a series of cruises
were conducted in the fall 1997, 1998, and 1999 to survey diapausing
populations of Calanus finmarchicus and their predators in Wilkinson,
Jordan, and Georges Basins (Gulf of Maine). A 1-m2 MOCNESS was towed
obliquely from near-bottom to the surface at stations in each basin,
sampling eight depths intervals for biomass, taxonomic composition, and
species counts. In addition, the BIO-Optical Multi-frequency Acoustical
and Physical Environmental Recorder (BIOMAPER-II) was towyoed along
survey track-lines in each of the basins to collect acoustic data, video
images, and environmental data between the surface and bottom.
Following the precipitous drop in the NAO index that occurred in 1996,
colder and fresher water of Labrador Sea origin entered the Gulf of
Maine in 1998 after a lag of about two years. Coincidently, the autumn
diapausing C. finmarchicus abundance was much lower in 1998 than in 1997
or 1999. Despite the substantially lower Calanus abundance in 1998,
overall zooplankton biomass levels as revealed by net catches and
acoustic indices were comparable between the three years. Potential
competitors (other copepods, the pteropod Limacina retroversa), and
predators (euphausiids, decapods, medusae, and siphonophores) had
enhanced biomass and/or numbers. This comprehensive data set provides
insight into the relationship between far- and near-field effects on C.
finmarchicus, the former being principally NAO driven changes in the
hydrography and the latter being driven by competition and predation.
Click here for an attached image.