ANTARCTIC NERITIC KRILL EUPHAUSIA-CRYSTALLOROPHIAS - SPATIOTEMPORAL DISTRIBUTION, GROWTH AND GRAZING RATES

Dynamics of distribution, growth, life span and feeding were studied i n the endemic Antarctic euphausiid Euphausia crystallorophias in the c entral part of the Indian sector of the Southern Ocean during the aust ral summer, from 1977 to 1990, and in the Lazarev Sea during the summe r 1990/91. Both larvae and adult E. crystallorophias were found in abu ndance in shelf waters of 100-500 m depth. Maximum abundances of larva e (up to 23,969 ind. 1000 m(-3)) and adults (up to 12,670 ind. 1000 m( -3)) were found in the Prydz Bay region. Size frequency analysis indic ated that the generation time was approximate to 3 years in the Indian sector of the Southern Ocean. Total life span of E. crystallorophias may reach 5 years in the Prydz Bay region and 4 years in the Cosmonaut Sea. Analysis of size distribution by sex suggests that male E. cryst allorophias may have a shorter life span than females. Growth for only 180 days per year is assumed, mean growth rates ranged from 0.070-0.0 75 to 0.019-0.022 mm per day during the first and the fourth year, res pectively. Von Bertalanffy growth curves calculated for different area s were similar to those obtained in the Antarctic Peninsula region. In the Prydz Bay and the Cosmonaut Sea, spawning of E. crystallorophias appears to peak from the end of November to early December and may ext end to the beginning of January. Most larvae were in the stage of meta nauplius/calyptopis I at the beginning of January and calyptopis III/f urcilia I during February. The year-1 cohort was identified in January -February and exhibited a mean length in the range 10.8-15.8 mm. In si tu feeding rates were estimated in the Lazarev Sea using the gut fluor escence method. Ingestion rates during austral summer 1990/91 ranged f rom 52 to 471 ng (pigm) ind(-1) h(-1) in adults and from 2.5 to 25.2 n g (pigm) ind(-1) h(-1) in calyptopis III larvae. Total population impa ct on the phytoplankton stock varied between 160-2860 and 215-652 mu g (C) m(-1) day(-1) for adults and larvae, respectively. This is equiva lent to 0.06-1.12% and 0.02-0.07% of total daily production. In areas with dense E. crystallorophias swarms, however, daily consumption rate s may attain levels as high as 13.6-96.5% of daily primary production. The long-term monitoring of different populations of E. crystalloroph ias allowed the identification of similar patterns between its abundan ce and spawning success and the formation of coastal polynyas, especia lly in the Prydz Bay region.