ENERGETICS AND FEEDING DYNAMICS OF EUPHAUSIA-SUPERBA IN THE SOUTH GEORGIA REGION DURING THE SUMMER OF 1994

Measurements of adult Antarctic krill (Euphausia superba) gut contents , evacuation and egestion rates, as well as digestive efficiency, were carried out during February-March 1994 in the vicinity of South Georg ia to estimate in situ daily ration. These were combined with acoustic ally derived biomass data to calculate the grazing impact of Antarctic krill and its contribution to the carbon flux in the region. Individu al levels of gut pigment concentrations and evacuation rates ranged fr om 27 to 1831 ng chlorophyll a-eq. ind.(-1) and from 0.133 to 0.424 h( -1), respectively. Losses of pigment fluorescence during digestion wer e very high, ranging from 58 to 98% of the total pigment digested. Dai ly carbon consumption estimated using the gut fluorescence method vari ed from 0.234 to 0.931 mg C ind.(-1) day(-1) (or 0.4-1.7% of body carb on), compared to -2.73 mg C ind.(-1) day(-1) (or similar to 5% of body carbon) using the faecal pellet production data. The 3-fold higher da ily ration estimated using egestion rate data may be explained by pred ation on micro- and mesozooplankton. Maximum krill grazing impact rang ed from 0.4 to 1.9% of the total phytoplankton stock or from 10 to 59% of the total daily primary production. However, grazing impact on the microphytoplankton (>20 mu m) was substantially higher, at times exce eding 100% of the daily microphytoplankton production. It is suggested that to meet its energetic demands, krill must consume a substantial proportion of heterotrophic carbon.