Early reproduction and development of dominant calanoid copepods in the sea ice zone of the Barents Sea—need for a change of paradigms?
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Reproduction and growth of the dominant copepods Calanus finmarchicus, C. glacialis, C. hyperboreus and Pseudocalanus minutus were studied on transects across the sea ice zone of the northern Barents Sea in May and June 1997. C. glacialis and C. finmarchicus were numerically dominant and also the largest component of the biomass. C. hyperboreus was rather rare. Moderate levels of phytoplankton and eventually high concentrations of ice algae supported maximum egg production rates of 53.6 and 48.5 eggs female−1 day−1 of C. glacialis in May and June, respectively. Results of incubation experiments were supported by a tremendous abundance of C. glacialis eggs in the water column ranging from 7×103 to 4.4×104 m−2 in May and from 9.8×103 to a maximum of 9.7×104 m−2 in June. In contrast, C. finmarchicus spawned only in the vicinity of the ice edge, at a maximum rate of 30 eggs female−1 day−1. Egg sacs of P. minutus were often observed in the preserved samples, but contained only few eggs, which may be due to loss during sampling. The presence of considerable concentrations of young stages in May and June indicated successful recruitment of C. glacialis and P. minutus. Back calculation using published stage duration estimates indicates March/April as the begin of the reproductive and growth period for these species under the first-year ice of the Barents Sea. Hence, secondary production in the study area starts at the same time as in open water regions and polynyas in the northern North Atlantic. Although the role of ice algae in the nutrition of copepods was not clarified here, the significant relationship between phytoplankton chlorophyll and egg production of C. glacialis suggests that high reproductive activity has already been achieved at moderate food concentrations.