Isotopic shift for defining habitat exploitation by the Antarctic limpet Nacella concinna from rocky coastal habitats (Marian Cove, King George Island)

Abstract

δ 13C and δ 15N of the Antarctic limpet Nacella concinna tissues and their potential food sources were used to determine their dietary origins and their movements between diverse habitats of intertidal and subtidal rocky shores and tide pools of Marian Cove, King George Island, Antarctica in the austral summer. δ 13C and δ 15N of the organic matter sources of epilithic microalgae, macroalgae and suspended particulate organic matter (SPOM) were readily distinguishable to discern their relative contribution to the limpet diets, with the most depleted values being found in SPOM and the most enriched in macroalgae. The limpets exhibited a spatial trend in distribution due to their seasonal migration, with smaller individuals in the subtidal zone compared with larger ones on the intertidal sites. The limpet isotopes had relatively broad ranges of δ 13C and δ 15N (−26.6 to −12.8‰ and 2.6–7.1‰, respectively), suggesting a dietary shift between habitats as well as size classes. The stable isotope ratios for each habitat seem likely to reflect the differing availabilities of the three potential food sources. Isotope mixing model results indicate a spatial shift in dietary mixture between habitats as well as limpet size classes. Epilithic microalgae and phytoplankton made great contributions to the diet of the subtidal limpets. Together with epilithic microalgae, macroalgae were significant contributors to the intertidal limpets where macroalgae were abundant. A higher contribution of macroalgae to the limpet diets was found in the tide pools. In contrast, while phytoplankton was an important food source for the limpet spat, a great dietary dependence on epilithic microalgae was found in the small-size limpets from the lower intertidal zone. Our results suggest that limpet grazing can determine microalgal and/or macroalgal abundance and coverage on the Antarctic rocky-shore ecosystem, and trophic structure of benthic food web can change along environmental gradients even at spatial scales of tens or hundreds of metres in the Antarctic.