Divergent realized ecological niches of sister species of the Antarctic amphipod genusCharcotia

Abstract

Climate change and resource exploitation in the Southern Ocean are important Anthropogenic pressure on Antarctic food webs. Understanding the eco-functional roles of Antarctic communities is essential for ecosystem management and conservation. Amphipods are among the most dominant and ecologically important benthic taxa in the Southern Ocean. The amphipod genusCharcotiais part of the scavenger guild playing a dominant role in nutrient recycling. To study the trophic habits of two sister species,C. amundseniandC. obesa, stable isotope ratios of carbon and nitrogen were investigated along geographical and bathymetrical gradients.Charcotia obesabelongs to the fourth andC. amundsenito the fifth trophic level, based on significant differences in δ15N. Benthic primary producers dominate the diet in both species as derived from their δ13C values.Charcotia obesa, the species with the narrowest depth range, did not show a depth-related pattern in isotopic ratios. An increasing geographic gradient of both δ15N and δ13C values was observed forC. obesa, ranging from the northern most tip of the Western Antarctic Peninsula to the southwestern most part of the Bellingshausen Sea. This might be linked to nutrient rich glacial meltwater in the latter part of the Southern Ocean. Nitrogen stable isotope ratios ofC. amundsenishowed a significant difference between Crown Bay and the other locations; this might be explained by the close location of the Filchner Area to nutrient rich upwelling in the Weddell Sea Gyre. Our study provides evidence for niche differentiation between two closely related amphipod species. Incorporation of additional samples from other locations and depth ranges in combination with isotope analysis and DNA-based prey identification might clarify the trophic position of benthic amphipods.