Title: Mesozooplankton distribution, and feeding and reproduction of Calanus finmarchicus in the western Norwegian Sea in relation to hydrography and chlorophyll a in spring

Species composition, mesozooplankton distribution, and feeding and reproduction of Calanus finmarchicus were investigated in the western Norwegian Sea in May 2003. Copepods were the most numerous group (~85-96% of all the animals caught). Calanus finmarchicus (mainly stage CV and females) was the dominant species among the copepods (~42-92%). Among the copepods Oithona similis was the second most numerous species (~5-58%). Maximum abundance of C. finmarchicus was observed in the southeastern part of the studing area, whereas the lowest abundance of C. finmarchicus was observed on the northwest, where cold water from the East Icelandic Current enters the Norwegian Sea. Gut content of Calanus finmarchicus females varied from 0.78 to 10.73 Chl a equiv. ng female-1. The proportion of mature females (GS4) varied between 41 and 98%. The highest proportion of mature females was observed in the Atlantic water in the northeast. On average about ~43% of the females were spawning. Daily rates of egg production varied from low (1 egg female-1 d-1) to high (101 eggs female-1 d-1). Mean egg production was 16 eggs female-1 d-1. No statistically significant relationship was found between egg production of C. finmarchicus and temperature, chlorophyll a concentration, females gut content, prosome length and weight. In cold Arctic water feeding and reproduction activity of C. finmarchicus population was higher, whereas abundance of zooplankton was higher in warmer Atlantic water.