Trophodynamics of Southern Ocean pteropods on the southern Kerguelen Plateau.

Pteropods are a group of small marine gastropods that are highly sensitive to multiple stressors associated with climate change. Their trophic ecology is not well studied, with most research having focused primarily on the effects of ocean acidification on their fragile, aragonite shells. Stable isotopes analysis coupled with isotope-based Bayesian niche metrics is useful for characterizing the trophic structure of biological assemblages. These approaches have not been implemented for pteropod assemblages. We used isotope-based Bayesian niche metrics to investigate the trophic relationships of three co-occurring pteropod species, with distinct feeding behaviors, sampled from the Southern Kerguelen Plateau area in the Indian Sector of the Southern Ocean-a biologically and economically important but poorly studied region. Two of these species were gymnosomes (shell-less pteropods), which are traditionally regarded as specialist predators on other pteropods, and the third species was a thecosome (shelled pteropod), which are typically generalist omnivores. For each species, we aimed to understand (a) variability and overlap among isotopic niches; and (b) whether there was a relationship between body size and trophic position. Observed isotopic niche areas were broadest for gymnosomes, especially