REPRODUCTION OF THE ARCTIC COPEPOD CALANUS-HYPERBOREUS IN THE GREENLAND SEA-FIELD AND LABORATORY OBSERVATIONS

The seasonal vertical migration of adult Calanus hyperboreus Kroyer an d their female reproductive biology have been studied in the central G reenland Sea, based on 7-month coverage during one annual cycle. Femal es dwelled in surface waters only between April and July. Gonad matura tion began after the summer descent into deeper waters between Septemb er and October in the absence of food. Breeding was assessed from gona d development and egg production experiments. It started around the be ginning of November and was mostly completed by March/April, before th e spring ascent. The overwintering depth of females ranged from close to the surface to 3000 m, and mature females had a preference for shal lower depths. Males were mostly found during the breeding period, wher e they inhabited the 500- to 1000-m layer. Female dry weight was highe st in August and November and lowest in February. Field observations w ere supplemented by observations on gonad development and egg producti on of females, which were collected in June and August and kept in the laboratory for up to 6 months. Clutch size, spawning interval and fec undity were determined at 0 degrees C. Females collected in June were mature earlier. Due to their low dry weight, they developed only small gonads and very few of them spawned. Females from August were much fa tter and produced up to 1000 eggs in several clutches deposited at reg ular intervals.