Spatial distribution of digestive enzyme activities of Calanus finmarchicus and C.hyperboreus in Fram Strait/Greenland Sea

Abstract

Digestive enzymes of copepodite V (CV) Calanus finmarchicus and C.hyperboreus from two different depths were compared during MIZEX 1984 (June/July) at stations in the ice and open water. CV of both species from 500-200 m showed reduced enzyme activity, indicating that they were in a resting stage. In moulting experiments at the end of June using CV from 100-0 m moulting was delayed and began only after 3 weeks in C.finmarchicus and after 3 months in C.hyperboreus. These results suggest that the deep CV populations are the seed of the new overwintering stock. In surface CV C.finmarchicus and C.hyperboreus enzyme activities were generally much higher than in deep CV. In neither species were enzyme activities correlated with chlorophyll concentrations. Activities in C.finmarchicus reflected overall phytoplankton distribution and were highest in the marginal ice zone, whereas they decreased under the ice except for polynya stations on the East Greenland Shelf. In surface C.hyperboreus digestive enzymes were not correlated with those of C.finmarchicus, pointing to different diets or regulatory mechanisms. Enzyme activity was lowest in the marginal ice zone and increased under the ice. High activities were found at polynya stations and other close pack ice. The utilization of ice algae by C.hyperboreus could explain these discrepancies in digestive enzyme activities of both species. The two dominant copepod species in this region, Calanus finmarchicus and C.hyperboreus, have apparently chosen different life history strategies in coping with this variability: C.hyperboreus is at least biennial (Harding, 1966; Dawson, 1978), while C.finmarchicus has one generation per year in this area (Lie, 1965). Reproduction in C.finmarchicus is synchronized with the development of phytoplankton blooms by the dependency of egg production on food uptake (Marshall and Orr, 1955; Runge, 1984), while C.hyperboreus spawn in the absence of food, relying on fat reserves deposited in the previous year (Conover, 1967). Although C.finmarchicus is a boreal species inhabiting the North Atlantic (Marshall and Orr, 1955) and C.hyperboreus is an Arctic species (Grainger, 1963,1965), in the Fram Strait/Greenland Sea their distributions overlap (Smith, 1988). It is worthwhile to investigate the results of the two different life cycle strategies when they interact with the spatial and temporal pattern of food availability in the same habitat.