Gonad maturation as an indication of seasonal cycles for several species of small copepods in the Barents Sea

Abstract

In a remote oceanic area like the Barents Sea, it is often difficult to follow the seasonal development of copepod populations in detail. Information on the gonad maturation stage of older juveniles and adults of a species will reveal the immediate state of reproduction and the expected development of juveniles into reproductively active adults. Winter “resting stages” in juveniles can also be recognised. Zooplankton were caught during Pro Mare cruises in early March, May, July/August, mid-September and mid-October. Abundance and composition of developmental stages of small copepods were determined for several stations from each cruise. Samples consisting of Stages CIV to CV1 of Pseudocalanus acuspes (Giesbrecht 1881), P. minutus (Kröyer), Microcalanuspusillus (Sars), and M. pygmaeus Sars were stained with carmine and analysed with respect to gonad maturation stage, length, width, and area of the prosome and the area of the gonad and the oil sac. Image analyses were performed from photographs or drawings of copepods using a digitising pad. With additional information on abundance and stage composition, and by comparing the present data set with information on Pseudocalanus spp. from Balsfjorden, northern Norway, seasonal cycles for the species could be inferred.