Stomach content characterisation of the marine range-shifting Octopus tetricus using DNA metabarcoding

The common Sydney octopus Octopus tetricus has undergone range extension along the east coast of Australia, associated with regional warming and the strengthening and southward extension of the East Australian Current (EAC). Its historical range of distribution is from southern Queensland to southern New South Wales, but it is now also found off north-east Tasmania, where it may affect local ecosystem dynamics due to changes in trophic interactions. This study aims to identify the prey and trophic level of O. tetricus from specimens collected off Tasmania to anticipate potential ecological, economic, and conservation effects in the range-extended area. The stomach contents of 18 O. tetricus individuals captured off north-east Tasmania in 2011 were characterised using DNA metabarcoding. Sixteen families of prey were identified; crustaceans (Alpheidae, Calcinidae, Diogenidae, and Galatheidae) were the most frequently detected prey, followed by fishes and bivalves. Prey species of commercial importance included blue-throated wrasse Notolabrus tetricus and the scallop Pecten fumatus. O. tetricus was found to have an intermediate trophic level of 3.66, participating in the transfer of energy from lower to upper trophic levels. Predation by O. tetricus could present competition to local fishers for resources and additional pressure on local fishery stocks, and may alter estimates of natural mortality used by fisheries management. The present study may be useful to scientists, fishery managers, and conservationists because it provides a preliminary assessment of the diet of O. tetricus, with potential ecological, economic, and conservation implications in the range-extended area.