Effects of temperature and circulation on the population dynamics of Calanus finmarchicus in the Gulf of St. Lawrence and Scotian Shelf: Study with a coupled, three-dimensional hydrodynamic, stage-based life history model

Abstract

We developed a physical-biological model for the Gulf of St. Lawrence (GSL) and Scotian Shelf (SS) by coupling a stage-based life-history model of the planktonic copepod Calanus finmarchicus to a three-dimensional ocean circulation model. The life-history model consists of 13 morphologically distinct life stages of C. finmarchicus, with stage-specific and temperature-dependent molting rates. The model also includes stage-specific vertical distribution and seasonally varying diapause, egg production, and stage-specific mortality rates. The model domain covers the eastern Canadian shelf from 55degreesW to 72degreesW and from 39degreesN to 52degreesN, including the Gulf of St. Lawrence, Scotian Shelf, and Gulf of Maine. A comparison of a 1-year simulation with observations indicates that the physical-biological model reasonably describes the observed abundance and distribution of C. finmarchicus in this region. To determine the effects of ocean circulation in the C. finmarchicus population dynamics, we divided the GSL-SS region into eight sub-areas and compared the net fluxes of C. finmarchicus across lateral boundaries to the net production in each sub-area. We found that the annual cross-boundary exchange rates constitute from <1% to 39% of the local net production, indicating that the horizontal transport of C. finmarchicus by the ocean currents can play a very important role in the dynamics of local C. finmarchicus populations. The results provide insights into the mechanisms of exchange in the GSL-SS system, as put forward in recent hypotheses.