REPRODUCTION AND DEVELOPMENT OF CALANUS-FINMARCHICUS, CALANUS-GLACIALIS AND CALANUS-HYPERBOREUS IN THE BARENTS SEA

The aim of this study is to examine the reproduction and development o f Calanus finmarchicus, C. glacialis and C. hyperboreus in relation to the timing and progress of the phytoplankton spring bloom in differen t water masses of the Barents Sea. From 1986 to 1988, 8 cruises were c onducted, covering Atlantic water in central parts of the Barents Sea and the Polar front region in the north. During the cruises hydrograph y, nutrients, chlorophyll and abundances of eggs, nauplii and copepodi tes 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 earl ier than in Atlantic water. A close relationship was found between phy toplankton 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 dev elopment of the overwintered stock. Mis-match between egg production a nd the phytoplankton bloom due to late development may be the main fac tor making C, finmarchicus an expatriate in the Arctic. In Atlantic wa ter masses stabilisation oi the water column was probably caused by fo rmation of a thermocline due to atmospheric warming, and development o f the phytoplankton spring bloom was closely related to this process. A strong correlation between rate of egg production and water column c hlorophyll content and a high fraction of adult females in the populat ions before spawning of both C. finmarchicus and C, glacialis indicate d a functional relationship between egg production and food supply. C. finmarchicus had a predominantly 1 yr life cycle within the study are a. From copepodite stage distribution the population of C. glacialis w as 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 pop ulation having a Life cycle shorter than 2 yr was highest in Atlantic water masses. C. hyperboreus started reproducing before February, show ing a pre-bloom spawning strategy. Nauplii older than NIII, which may be the first feeding stage, did not occur in the samples until the foo d concentrations increased during the spring bloom. A secondary egg pr oduction during the bloom was probably important, and part of the popu lation seemed to have a reproductive strategy similar to that of C. fi nmarchicus and C. glacialis.