Seasonal and spatial variability in egg production and biomass of Calanus finmarchicus around Iceland

Abstract

A summary of data on the reproductive biology of Calan us finmarchicus from winter to summer is presented for the years 1996 to 2002. Egg production rates, clutch size, gonad development stage, female body size and female abundance were measured in conjunction with food availability in the different oceanographic domains around the island. The egg production rates varied both seasonally and spatially. SW of Iceland, spawning of C. finmarchicus started earlier on the shelf (April) than in the open sea (May). In this area, the period of appreciable reproductive activity also lasted longer onshore (similar to3 mo, April to June) than offshore (similar to2 mo, May to June). On the SW shelves, monthly means of egg production rates were highest in June (similar to45 eggs female(-1) d(-1)), whereas in offshore areas the highest rates were observed in May (similar to35 eggs female(-1) d(-1)). The best spatial coverage is provided by the May data, when average egg production rates were higher north and east of Iceland (similar to35 eggs female(-1) d(-1)) than off the south and west coasts (similar to26 eggs female(-1) d(-1)). In contrast, the average biomass of C. finmarchicus was lower off the north (similar to360 mg C m(-2)) and east coasts (similar to810 mkg C m(-2)), as compared to off the south and west coasts (similar to1660 mg C m(-2)), suggesting that factors such as predation or advection were important in dictating the distribution of biomass in these areas. Multiple regression analysis showed that over the large spatial and temporal scales of the present study, the egg production rates were positively related to food conditions (chlorophyll a) and female size, but not to temperature. Specific egg production rates were used to estimate secondary production and potential grazing impact of C. finmarchicus in the different oceanographic domains around Iceland. The results show marked differences in secondary production and potential grazing impact of C. finmarchicus, both between seasons and oceanographic domains.