Trophic relationships among Southern Ocean copepods and krill: Some uses and limitations of a stable isotope approach

• Main Authors: Katrin Schmidt, Angus Atkinson, Dorothea Stübing, James W. McClelland, Joseph P. Montoya, Maren Voss
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2003
• Subjects: Antarctic; Lazarev; Lazarev Sea; Marguerite; Marguerite Bay; Southern Ocean; Antarc*; Euphausia superba; Mesozooplankton; Copepods
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.117.4745; http://www.aslo.org/lo/toc/vol_48/issue_1/0277.pdf

The use of stable isotopes to study food webs has increased rapidly, but there are still some uncertainties in their application. We examined the �15N and �13C values of Antarctic euphausiids and copepods from the Polar Front, Lazarev Sea, and Marguerite Bay against their foodweb baseline of particulate organic matter (POM). Interpretations of trophic level were helped by comparison with other approaches and by calibration experiments with Euphausia superba fed known diets. Results for well-known mesozooplankters (e.g., Calanoides acutus and Metridia gerlachei) were internally consistent and corresponded to those derived from independent methods. This gave confidence in the isotope approach for copepods and probably larval euphausiids. Among the dominant yet poorly known species, it suggested mainly herbivory for Rhincalanus gigas but omnivory for Calanus simillimus and furcilia larvae of Thysanoessa spp. and Euphausia frigida. The �15N values of adult copepods were up to 3 ‰ higher than those of early copepodites, pointing to ontogenetic shifts in diet. In the Lazarev Sea in autumn, the isotopic signals of E. superba larvae suggested pelagic, mainly herbivorous, feeding rather than feeding within the ice. In contrast to the mesozooplankton, some anomalous results for postlarval krill species indicated problems with this method for micronekton. The experiments showed that postlarval E. superba did not equilibriate with a new diet within 30 d. We suggest that the slower turnover of these larger species, partly in combination with their ability to migrate, has