COMPARATIVE-STUDY OF THE REPRODUCTION OF CALANUS-HELGOLANDICUS IN WELL-MIXED AND SEASONALLY STRATIFIED COASTAL WATERS OF THE WESTERN ENGLISH-CHANNEL

Field estimates of the production and viability of eggs of the copepod Calanus helgolandicus were conducted weekly during 1993 and 1994 at t wo fixed stations in the western English Channel. The stations were lo cated in the coastal zone off Roscoff (NW France) and Plymouth (SW Eng land). These areas are characterized by homogeneous and seasonally str atified waters, respectively. In these two different environments, the egg production rate varied seasonally and was significantly correlate d with chlorophyll a concentration, but not with surface temperature. Significant correlations between fecundity and particulate carbon and nitrogen were found only off Plymouth. The seasonal pattern of fecundi ty differed between the two sites. Off Plymouth, spawning occurred ear lier, lasted longer and was significantly higher than in Roscoff water s. In both localities, fecundity was generally below the maximum speci fic egg production rate (similar to 60 eggs female(-1) day(-1)), imply ing that adult females were permanently under, or close to, limiting f ood conditions. Egg viability showed seasonal variations in both local ities, ranging between 20 and 100%. However, in 1994, the amplitude of egg viability variation was lower in stratified waters. The results s how that the potential fecundity of C.helgolandicus was different betw een mixed and stratified waters of the western English Channel. Food q uality as well as quantity appear to be important for the reproductive success of this copepod species.