Ontogenetic changes in habitat and trophic ecology of the giant Antarctic octopus Megaleledone setebos inferred from stable isotope analyses in beaks

The giant Antarctic Octopus Megaleledone setebos is the largest Southern Ocean octopod whose ecology is poorly known. Here, we study ontogenetic shifts of habitat and trophic ecology of M. setebos throughout its life cycle by stable isotopic analysis of δ13C and δ15N on its beaks collected from the diet of Antarctic toothfish in Amundsen and Ross Seas (Antarctica). Values of δ13C (from − 24.3 to − 19.4‰) differed between beaks of individuals from different capture locations, thus reflecting the ability of M. setebos living in different habitats. Despite sequential sampling along beaks showed a small (< 2.3‰), but significant variation in lower beak’s δ13C values, a relation with δ15N values suggests that such differences are related to changes in the diet with M. setebos inhabiting the same area its entire life. Values of δ15N differed between beaks of individuals from different capture locations, suggesting that different habitats of M. setebos are associated with different diets. Serial sampling along the beaks (from + 4.2 to + 10.7‰) suggests an ontogenetic change of, at least, one trophic level from juvenile to adult. We also report a capture of two large intact specimens from Dumont D’Urville Sea (Antarctica): a male with 1150 mm of total length and 18,300 g of mass and a female with 1030 mm of total length and 10,061 g of mass. The beaks of these both specimens, confirmed to be of M. setebos through genetic analysis, were also used to confirm the identification of M. setebos collected from Antarctic toothfish stomachs.

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