TURNOVER OF CARBON AND NITROGEN DURING GROWTH OF LARVAL KRILL, EUPHAUSIA-SUPERBA DANA - A STABLE-ISOTOPE APPROACH

Using natural abundances of stable isotopes (delta(13)C and delta(15)N ) as tracers, carbon and nitrogen turnover rates were determined for l arval krill, Euphausia super ba Dana, maintained in the laboratory. Ex perimental populations of larvae were reared at +1.5 degrees C and -1. 5 degrees C on foods of known isotopic composition and subsampled week ly (8-10 weeks) for a determination of wet weight and isotopic composi tion. Metabolic turnover of carbon and nitrogen, manifested as tempora l shifts in delta(13)C and delta(15)N, was tied closely to temperature . Larval krill reared at +1.5 degrees C had replaced 22-29% of their o riginal body carbon at the conclusion of the experiment, but only 13-2 2% of their original body nitrogen. Larvae reared at -1.5 degrees C ex hibited little evidence of carbon turnover and replaced less than 6% o f their original body nitrogen. These are the first simultaneous, coup led measurements of long-term carbon and nitrogen turnover for any mar ine animal, and provide an essential calibration for the interpretatio n of stable isotope ratios in animals collected from the field. In add ition to the feeding experiments, animals were starved for 2 months at +1.5 degrees C and -1.5 degrees C. Starved krill exhibited little iso topic change. This finding suggests that starvation cannot account for large temporal variations observed in the isotopic composition of lar val krill collected from the field. (C) 1997 Elsevier Science B.V.