Copepod egg production, moulting and growth rates, and secondary production, in the Skagerrak in August 1988

Abstract

Measurements of hydrography, chlorophyll, moulting rates of juvenile copepods and egg production rates of adult female copepods were made at eight stations along a transect across the Skagerrak. The goals of the study were to determine (i) if there were correlations between spatial variations in hydrography, phytoplankton and copepod production rates, (ii) if copepod egg production rates were correlated with juvenile growth rates, and (iii) if there was evidence of food-niche separation among co-occumng female copepods The 200 km wide Skagerrak had a stratified water column in the center and a mixed water column along the margins. Such spatial variations should lead to a dominance of small phytoplankton cells in the center and large cells along the margins; however, during our study blooms of Gyrodinium aureolum and Ceratium (three species) masked any locally driven differences in cell size: 50% of chla was >11 μm, 5% in the 11–50 μm fraction and 45% <50 μm. averaged for all stations. Chlorophyll ranged from 0.2 to 2.5 μg l −1 at most depths and stations. Specific growth rates of copepods averaged 0.10 day −1 for adult females and 0.27 day −1 for juveniles The latter is similar to maximum rates known from laboratory studies, thus were probably not food-limited. Egg production rates were food-limited with the degree of limitation varying among species: 75% of maximum for Centropages typicus , 50% for Calanus finmarchicus , 30% for Paracalanus parvus and 15% for Acartia longiremis and Temora longicornis . The degree of limitation was unrelated to female body size suggesting food-niche separation among adults. Copepod production, summed over all species, ranged from 3 to 8 mg carbon m −3 day −1 and averaged 4.6 mg carbon m −1 day −1 . Egg production accounted for 25% of the total.