EGG-PRODUCTION IN 3 SPECIES OF ANTARCTIC CALANOID COPEPODS DURING AN AUSTRAL SUMMER

Egg production in three species of calanoid copepods Rhincalanus gigas , Calanoides acutus and Calanus simillimus was investigated via incuba tions of females and recovery of eggs from net hauls made around South Georgia during January 1993. Average daily egg production was highest for the sub-Antarctic C. simillimus, (15.5 eggs female(-1) d(-1)). Th is species normally spawns in the spring in the central part of its ge ographical range but was apparently delayed by the colder waters found around South Georgia. For R. gigas and C. acutus egg production avera ged 8.9 and 6.0 eggs female(-1) d(-1), respectively. The former specie s appeared to be undergoing protracted recruitment while the populatio n of the latter was preparing to overwinter. Considerable inter-statio n variability existed, although no relationships were apparent between surface chlorophyll concentrations and either egg production in exper iments or in the numbers of eggs recovered by the nets. Clutch size (e ggs produced spawning female(-1) d(-1)) did not differ significantly b etween the three species although the maximum clutch size recorded for R. gigas (94 eggs) was almost twice that of C. simillimus. Samples ta ken from the Bellingshausen Sea during the latter part of 1992 indicat ed that recruitment of R. gigas and C. acutus commenced in early Decem ber in this region when adult females were concentrated in the surface 250 m and a diatom bloom was developing. Egg numbers were highest in the surface 50 m (up to 350 m(-3)) al both the Bellingshausen and Sout h Georgia stations. At the latter site females migrated into these sur face layers at night; thus it would appear that spawning is largely no cturnal and linked to diurnal migratory behaviour.