The trophic interactions of Octopus insularis in the food web of a pristine tropical atoll: a baseline for management and monitoring under environmental changes

In the present study, we evaluated the trophic role of Octopus insularis Leite and Haimovici 2008 in the food web of Rocas Atoll, a preserved insular territory in the Southwest Atlantic. Using stable isotope analysis of C and N, we showed that the local trophic web comprises at least four trophic levels, where the octopus occupies a trophic position (TP) between the second and third trophic levels (mean +/- SD TPadditive = 3.08 +/- 0.36; TPBayesian = 3.12 +/- 0.17). Among other benthic/reef-associated consumers, this cephalopod stood out for its much wider isotopic niche, pointing to a diet diversified in carbon sources, but focussed on prey in lower TPs. This finding was in accordance with the time-minimizing feeding strategy described for the species, which seemed almost permanent throughout the life cycle of the octopus, given the great niche overlap between octopuses in different maturity stages and their very similar trophic positions. Also, as a prey, octopuses composed up to almost 23% of the diet of some benthic/demersal predators. Overall, O. insularis represented an important mesopredator for the local food web, principally for bottom-associated organisms, while also serving as a substantial energy input to the next trophic levels.

Automated summary

This study evaluated the trophic role of Octopus insularis in a preserved insular territory, showing that it occupies a high trophic position in the local food web as an important mesopredator. The octopus was found to have a diet diversified in carbon sources but focused on prey in lower trophic positions, contributing significantly to energy input in the ecosystem.