Modelling the distribution, sustainability and diapause emergence timing of the copepod Calanus finmarchicus in the Labrador Sea

It is now recognized that Calanus finmarchicus, the dominant copepod zooplankter of the North Atlantic, has most of its biomass in the open ocean. While the Labrador Sea does contain a large population of Calanus finmarchicus, the importance of possible connections with the rest of the North Atlantic are not understood. Although there are few wintertime observations, sufficient data exist to model the role of the circulation, temperature and food supply on population dynamics. This study couples a biological model of Calanus finmarchicus with a physical oceanographie model of the Labrador Sea, using chlorophyll data derived from observations by the satellite-borne SeaWiFS (Sea-viewing Wide Field-of-view Sensor) as a proxy food supply for the numerical copepods. We produce a large-scale, comprehensive picture of the spatial distribution of Calanus finmarchicus in the Labrador Sea, along with an exploration of the timing of diapause and an examination of population sustainability. We are able to simulate reasonably well the temporal and spatial patterns of Calanus finmarchicus in the Labrador Sea. During a year long model run, the population has a single generation over most of the Labrador Sea, with a final diapausing population about 50% the size of the initial for the parameters used in these simulations. A latitudinally dependent diapause emergence scheme with early emergence to the south of Newfoundland provides the best fit to data. A change of 0.5°C in the temperature field can cause significant changes in the population abundance in a single year, due to changes in Calanus finmarchicus growth rates.