Isotopic niche partitioning of co-occurring large marine vertebrates around an Indian ocean tropical oceanic island

Tropical oceans host a high diversity of species, including large marine consumers. In these oligotrophic eco-systems, oceanic islands often favour the aggregation of species and biomass as they provide feeding opportu-nities related to the mechanisms of island mass effect. As such, the waters surrounding La Reunion (Southwest Indian Ocean) host seabirds, large pelagic teleosts, elasmobranchs, delphinids and sea turtles. Isotopic niche partitioning and comparison of trophic levels among these species (n = 21) were investigated using stable carbon (delta 13C) and nitrogen (delta 15N) isotope analysis. Overall, delta 13C values were highly variable among taxa, indicating that the species exploit multiple foraging habitats along a coast-open ocean gradient. Overlap in delta 15N values was limited, except for teleost species, the two species of sea turtles and two species of delphinids, the Indo-pacific bottlenose dolphin (Tursiops aduncus) and the Spinner dolphin (Stellena longirostris). Stable isotope analyses of samples collected over a 9-years period on different tissues with different integration times provide a consistent picture of the structure of the community of large marine vertebrates species around La Reunion and highlight the underlying mechanisms to limit the competition between species. The wide range of isotopic values confirms that large marine vertebrates have different trophic roles in coastal marine food webs around this oceanic island, which limits their potential of competitive interactions for resources.

Automated summary

Tropical oceans with oligotrophic eco-systems often have oceanic islands that favor the aggregation of species and biomass. The waters surrounding La Reunion in the Southwest Indian Ocean host a diverse range of marine species, including seabirds, pelagic teleosts, elasmobranchs, delphinids, and sea turtles. Stable isotope analysis reveals that these species have different trophic roles and utilize multiple foraging habitats. The findings highlight the mechanisms that limit competition and the importance of understanding the structure of marine vertebrate communities.