Egg and faecal pellet production of Calanus finmarchicus females from controlled mesocosms and in situ populations: influence of age and feeding history

Egg and faecal pellet production of Calanus finmarchicus females were inves tigated individually under superabundant food conditions at 5 and 10 degree s C. The females came from (1) in situ populations in the Raunefjord (south ern Norway) in March and May 1997 and (2) cohorts reared in 2 mesocosms, on e with high (H) and one with low (L) food concentrations. The egg productio n rates of newly moulted females coming from mesocosms increase from zero t o maximal rates over 10 to 15 d at 10 and 5 degrees C, respectively. The de lay in reaching maximal fecundity rates depends on time required for gonad maturation, which is related to the use of storage lipid and also to food s upply for ending the maturation. The faecal pellet production rates also in crease with time, suggesting that fecundity is governed by ingestion. Final ly, we suggest a conceptual model of different events between moulting and optimal spawning activity in newly moulted females in superabundant food co nditions. The fecundity, egestion and lipid metabolism of wild females (cau ght in March and May) were studied in the same way. The results are compare d to observations of young females from mesocosms and the influence of seas onal origin of females on the studied processes is assessed. Data from expe riments run with females from Mesocosms L and H permit us to discuss the ef fect of feeding history on fecundity and egestion. Although females from Me socosm L show shorter prosome lengths than those from Mesocosm H, fecundity is not significantly different. However, females from Mesocosm L have a mu ch higher production of faecal pellets than females from Mesocosm H, sugges ting that the previous food limitation during copepodite development in Mes ocosm L induces higher maximal ingestion rates of these females than the pr evious well-fed females (Mesocosm H). A few assumptions to explain these di fferent patterns are proposed.