Stable isotope composition (δ13C and δ15N) of larval krill, Euphausia superba, and two of its potential food sources in winter

Abstract

A h c t . Natural abundances of I3C (6I3C) and IsN (6IsN) were measured in larval krill (Euphnusio supcrba), suspended particulate organic matter (POM) and ice-associated POM during early and late winter along the west coast of the Antarctic Peninsula. Larval krill were enriched in I3C (8°C 2 n%D) relative to both larvae and adults sampled during summer months ( 6 ' T generally S 27%). Elevated 6'3C values were also recorded in suspended POM (6°C 2 21%) during early winter.'Ihese data imply that (i) seasonal shifts in the isotopic composition of larval krill need not result from changes in diet and (ii) mechanisms other than (2% limitation in the ice can account for 'T enrichments in ice-associated POM. Stable carbon isotopes could not be used, in this study, to discern between suspended POM and ice-associated POM as alternative food sources for larval krill. During one early winter sampling period, larval krill were markedly depleted in I5N (615N < I%), suggesting that they are primarily herbivorous prior to exploiting ice-associated food resources Mechanisms are proposed to explain variation in the isotopic composition of POM and larval krill, and will be of particular interest to those investigating f d web dynamio, and biogeochemical processes in the region.