Recruitment, development and mortality of Calanus finmarchicus in the Georges Bank Region

Li, X.1, D.J. McGillicuddy1, and E.G. Durbin2
1Woods Hole Oceanographic Institution, Woods Hole, MA 02543
2Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02282

An adjoint data assimilation approach was used to quantify the time-space-stage specified physical and biological controls on Calanus finmarchicus N3 and C6 stages over Georges Bank and its surrounding regions. Large seasonal and spatial variabilities are present in the inferred supply sources, mortality rates, computed molting fluxes and physical transports. Partially recovered off-bank initial conditions show that the deep basins of the Gulf of Maine, and the Scotian Shelf are major offbank source regions of early stage nauplii, C5 and C6, in January. In the growing season from January to April, inferred sources of young nauplii N3 are mainly confined on Georges Bank, especially on the Northeast Peak. These on-bank sources of young nauplii N3 are able to populate the bank with nauplii in late winter, becoming copepodites in spring. Large mortality rates of stages N4 - C2 between January - February are the main regulators to limit the population increase rates. In the meantime, advection and mixing processes transport this species from source regions on Georges Bank to surrounding waters in the Gulf of Maine, the continental slope and South Atlantic Bight. Between April - May, the populations dynamics on the bank are driven by molting from lower to higher stages. Between May - June, abundances of copepodites drop sharply on Georges Bank, especially on the Crest. Large mortality rates are mainly responsible for the population decline. In addition, down-stream transport of advection and down-gradient transport of turbulent mixing enforce the June decline. Mortality rates of N4 to C2 are large between January - March and May - June. Mortality rates of C5 and C6 are large between April - June. Calanus finmarchicus are most vulnerable to death at stages N6 and C1, but most unlikely to die at stages C3 and C4. When they mature to adults, their mortality rates are large in the warm water of early summer.

Click here for a PDF image of the poster.