Spawning and development of Calanus spp. in the Barents Sea
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From 1986 to 1988 eight cruises were conducted in the Barents Sea, covering Atlantic water in central parts of the Sea and meltwater and Arctic water in the Polar front region. During the cruises hydrography, nutrients, phytoplankton biomass and abundances of life stages of the three Calanus species; C. finmarchicus, C. glacialis and C. hyperboreus, were mapped. From this, development and spawning of the copepods in different water masses were related to the timing and progress of the phytoplankton spring bloom. In central parts of the Atlantic water stabilization was caused by formation of a thermocline due to atmospheric warming and the process was time dependent. Phytoplankton spring bloom development was closely related to water column stability. Rates of egg production of the female populations of C. finmarchicus and C. glacialis showed strong correlations with chlorophyll content, indicating a functional relationship between spawning and food supply. In the meltwater region water column stabilization was caused by ice melting, which is not purely a time dependent process. However, also in this region a close relationship between phytoplankton spring bloom development and spawning of C. glacialis was found. Spawning of C. finmarchicus was out of phase with the spring bloom and peaked during the post-bloom period. This was explained by a retarded development of the overwintered stock of C. finmarchicus in the meltwater region. In Arctic water development seemed to be slower for both species. Thus, mis-match between the phytoplankton bloom and spawning of C. finmarchicus due to retarded development is suggested as the main factor making this species an expatriate of the northern Barents Sea. In C. glacialis a two-year life cycle in the warmer parts of the Barents Sea, may result in a too long life span relative to the mortality rate of this area, and the species may be expatriated in the southern Barents Sea. C. hyperboreus was found to spawn in January and February, or earlier, well before the spring bloom. The nauplii, however, did not develop beyond stage NIII which is the first feeding stage until the food concentrations increased during the spring bloom.