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

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Abstract
Natural abundances of 13C (δ13C) and 15N (δ15N) 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 13C (δ13C ≥ 27‰) relative to both larvae and adults sampled during summer months (δ13C ≥ 27‰). Elevated δ13C values were also recorded in suspended POM (δ13C ≥ 21‰) during early winter. These 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 (CO2 limitation in the ice can account for 13C 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 15N (δ15N < 1‰), 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.

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