Reproductive cycles of dominant calanoid copepods in the North Sea

Abstract

The seasonal cycles of reproduction of the dominant copepods Acartia clausi, Temora longicornis, Centropages hamatus, C. typicus and Pseudocalanus spp. were studied at Helgoland Roads, southern North Sea. Egg production rate, clutch size, number of spawning females and pro- some length were compared with temperature and phytoplankton concentration. Female A. clausi, T. longicornis and Pseudocalanus spp. were present all year round. T. longicornis and Pseudocalanus spp. bred continuously throughout the year, although egg production rates and the proportion of spawning females were low in winter. A. clausi did not spawn between the end of September and the end of January. Female C. hamatus were absent from the water column from November to May, and C. typicus from February to August. As the latter 3 species spawn year round in warmer regions, low temperature inhibition of reproduction is suggested for Helgoland, where winter temperatures are below 0°C. Maximum egg production was observed in all species, except the late-arriving C. typicus, in April/May, when females were largest. Significant correlations were only obtained between clutch size or egg production rate and prosome length, which in turn was correlated with temperature. It is therefore concluded that for Helgoland waters temperature controlled egg production by its effect on prosome length, and that food conditions were not limiting.