Spatial and temporal shifts in stable isotope values of the bottom-dwelling shrimp Nauticaris marionis at the sub-Antarctic archipelago

Spatial and temporal dynamics of carbon and nitrogen stable isotope signatures of the bottom-dwelling caridean shrimp Nauticaris marionis were measured during April and May between 1984 and 2000 in the vicinity of Marion Island (the Prince Edward Islands, Southern Ocean). There was one trophic-level enrichment in bulk δ15N and δ13C signatures between small (<20 mm long) and large (>20 mm) specimens of N. marionis, suggesting distinct trophic differentiation among major shrimp size groups. Both δ15N and δ13C values of N. marionis increased with the depth, reflecting changes in their diet. There were no clear temporal trends in bulk δ15N signatures of N. marionis. However, compound-specific δ15N measurements of amino acids indicated that N. marionis from the inter-island realm occupied the trophic level of second order carnivores, while similarly sized shrimps in the near-shore realm were at the trophic level of first order carnivores. Compound-specific measurements also identified a change in the source of inorganic nitrogen at the base of the food web between the inter-island and near-shore realms. In contrast to the bulk δ15N values, a significant shift in bulk δ13C values of N. marionis was observed between 1984 and more recent years. This temporal change appears to be linked to changes in the overall productivity of the Prince Edward Island interisland system, which could be linked to global climate change.