Circulation patterns in the North Atlantic and possible impact on population dynamics ofCalanus finmarchicus

Abstract

Due to advective impact few consistent time-series describing the population development of the copepod C.finmarchicus exist. Quantitatively, the spring generation seems to be the most important, and especially in the northern areas one generation per year seems to prevail. A fecundity of 102-103 eggs female^-1 and a sex ratio 1:1 then give a maximal reproductive rate of 3.9-6.2 year-1. This low rate seems to be compensated by low mortality due to effective predator avoidance in terms of diurnal and seasonal vertical migrations. We have calculated that the advective renewal of the habitats of C.finmarchicus in the subpolar gyre and in the Nordic Seas are 0.13 and 0.29 year^-1 respectively, while the birth and death rates of C.finmarchicus typically are above 3.9 year^-1.This means that the biological rates are likely to dominate over the advective rates in the two ocean areas, and that the C.finmarchicus development is facilitated by local production in both areas. Rough calculations for the Nordic Seas indicate that out of a total annual production of 74 mill, tonnes, 3.6 mill, tonnes are lost to adjacent seas by advection. Due to the flow of deep and cold waters southward and the seasonal migration of C.finmarchicus it is likely that the loss of individuals from the Nordic Seas southward to the North Atlantic is dominated by copepodite V, and that a higher proportion of younger life stages are carried in the south-north (Barents Sea) and west-east (Norwegian coast and the North Sea) directions with the warmer Atlantic Water