Contribution of heterotrophic material to diet and energy budget of Antarctic krill, Euphausia superba

A novel approach was used to estimate the heterotrophic carbon component in the diet of the Antarctic krill Euphausia superba. Over 200 specimens from seven samples collected in the Lazarev Sea (January 1993 and 1995), at the Antarctic Polar Front (January 1993), and around South Georgia (February/M arch 1994) were dissected, and the total carbon content of their stomachs w as estimated with a CHN-analyser. Gut-pigment contents were also measured b y the gut-fluorescence technique in specimens collected at the same time, a nd the equivalent amount of their gut carbon was then subtracted from the t otal organic carbon content of guts from the same samples. The remaining ca rbon was assumed to originate entirely from heterotrophic food sources. Thi s heterotrophic component accounted for a substantial proportion of the tot al food consumed by Antarctic krill, ranging from 17.4 to 98.9% of the mass of the gut contents (mean = 78.8% +/- 21.2 SD). The results make an import ant contribution to the elucidation of the energy budget of krill and its d aily carbon ration. With a few exceptions, previous estimates were largely calculated from a solely autotrophic carbon source, and were unable to acco unt for the metabolic requirements of E. superba. Krill plays an important role in Antarctic food webs, as it often constitutes similar or equal to 50 % of the total biomass of the zoo-plankton, and produces fast-sinking, dens e faecal pellets which are important in the vertical transport of organic c arbon from the euphotic layer to the deep ocean. High consumption rates of smaller heterotrophic organisms by krill suggest that this large microphage may be more important than previously believed in re-packaging micro- and mesozooplankton into a longer-lasting and more easily sequestered carbon po ol.