Reproduction and development of Calanius finmarchicus, C. glacialis and C. hyperboreus in the Barents Sea

The aim of this study is to examine the reproduction and development of Calanus finmarchicus, C. glacialis and C. hyperboreus in relation to the timing and progress of the phytoplankton spring bloom in different water masses of the Barents Sea. From 1986 to 1988, 8 cruises were conducted, covering Atlantic water in central parts of the Barents Sea and the Polar front region in the north. During the cruises hydrography, nutrients, chlorophyll and abundances of eggs, nauplii and copepodites were mapped. In the Polar front region stabilisation of the water column was caused by ice melting and a surface layer of melting ater. The phytoplankton bloom was initiated in April, more than a month earlier than in Atlantic water. A close relationship was found between phytoplankton spring bloom development and egg production of C. glacialis. Egg production of C, finmarchicus did not match the spring bloom and peaked here during the decline of the bloom, probably due to late development of the overwintered stock. Mis-match between egg production and the phytoplankton bloom due to late development may be the main factor making C, finmarchicus an expatriate in the Arctic. In Atlantic water masses stabilisation of the water column was probably caused by formation of a thermocline due to atmospheric warming, and development of the phytoplankton spring bloom was closely related to this process. A strong correlation between rate of egg production and water column chlorophyll content and a high fraction of adult females in the populations before spawning of both C. finmarchicus and C, glacialis indicated a functional relationship between egg production and food supply. C. finmarchicus had a predominantly 1 yr life cycle within the study area. From copepodite stage distribution the population of C. glacialis was judged to contain individuals having both 1 yr and 2 yr Life cycles, and CIV to be a resting stage during winter. The fraction of the population having a Life cycle shorter than 2 yr was highest in Atlantic water masses. C. hyperboreus started reproducing before February, showing a pre-bloom spawning strategy. Nauplii older than NIII, which may be the first feeding stage, did not occur in the samples until the food concentrations increased during the spring bloom. A secondary egg production during the bloom was probably important, and part of the population seemed to have a reproductive strategy similar to that of C. finmarchicus and C. glacialis.