MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps14726

ABSTRACT: The reconstruction of the predator-prey interactions in a biological community provides a better understanding of the species ecological roles and helps predict how change in one component will affect the others. Doris kerguelenensis is an Antarctic heterobranch mollusc reported to feed on sponges according to gut content analysis. Stable isotopes of carbon and nitrogen and fatty acids (FA) were used to assess the relative contribution to its diet of several species of demosponges (Axinella crinita, Dendrilla antarctica, Hemigellius pilosus, Kirkpatrickia variolosa, Mycale acerata, Sphaerotylus antarcticus, and Haliclona sp.). Particulate organic matter (POM) and two macroalgae species were also analyzed to better characterize the diversity of sources fueling the food web. The δ¹⁵N values of all sponges suggested a trophic position of 2-3 for A. crinita, D. antarctica, M. acerata and Haliclona sp., and 3-4 for H. pilosus and S. antarcticus. Mixing models failed to resolve the nudibranch diet because either the sponges were too enriched in ¹³C or the diet-to-tissue discrimination factor (DTDF) values available in the literature for gastropods are unsuitable for this nudibranch species. The high abundance of bacterial FA markers in H. pilosus, S. antarcticus and K. variolosa, and their high δ¹⁵N values, rule them out as major prey of D. kerguelenensis. The overall evidence suggests that A. crinita, D. antarctica, M. acerata, and Haliclona sp. are consumed regularly by D. kerguelenensis, but do not represent its only dietary sources. Hence, the analysis of biomarkers refutes the previously stablished role of D. kerguelenensis as a specialized spongivore.