THE PRODUCTION OF OITHONA-SIMILIS (COPEPODA, CYCLOPOIDA) IN THE SOUTHERN-OCEAN

Seasonal variation in abundance and biomass of different instars of Oi thona similis was studied for stations in the Weddell Sea and the Anta rctic Circumpolar Current south of 60 degrees S sampled in different y ears. Egg production was more spread over the seasons than in most cal anoid copepod species and the mean stage was more constant, indicating a mixing of age classes and overlap of generations. Juvenile stages i ncrease in abundance between October and January, but the main develop ment of copepodids was between January and May. A minimum estimate of daily growth rate of 1.5% body weight corresponds with a development f rom Nauplius 1 to Copepodite 5 between 1 November and 30 May and leads to an annual Production/Biomass (P/B) ratio of 3.3. The mean populati on biomass in the southern waters was 150 mgC m(-2) in the epipelagic zone and the minimum estimate of annual production 0.5 gC m(-2) Becaus e the contribution of the species to zooplankton biomass in the Southe rn Ocean may be higher than elsewhere and the annual P/B is generally much higher than in the larger calanoid species, the production of Oit hona similis may be the highest of all zooplankton species in the Anta rctic region. (C) 1995 International Council for the Exploration of th e Sea