Twenty-First-Century Environmental Change Decreases Habitat Overlap of Antarctic Toothfish (Dissostichus mawsoni) and Its Prey.

Antarctic toothfish are a commercially exploited upper-level predator in the Southern Ocean. As many of its prey, the ectothermic, water-breathing Antarctic toothfish is specifically adapted to the temperature and oxygen conditions present in the high-latitude Southern Ocean. Additionally, the life cycle of Antarctic toothfish depends on sea-ice dynamics and the transport of individuals by currents between regions with different prey. To assess the impact of 21st-century climate change on potential interactions of Antarctic toothfish and its prey, we here employ the extended aerobic growth index (AGI), which quantifies the effect of ocean temperature and oxygen levels on the habitat viability of individual species. We quantify changes in predator-prey interactions by a change in viable habitat overlap as obtained with the AGI. As environmental data, we use future projections for four emission scenarios from the model FESOM-REcoM, which is specifically designed for applications on and near the Antarctic continental shelf. For the two highest-emission scenarios, we find that warming and deoxygenation in response to climate change cause a subsurface decline of up to 40% in viable habitat overlap of Antarctic toothfish with important prey species, such as Antarctic silverfish and icefish. Acknowledging regional differences, our results demonstrate that warming and deoxygenation alone can significantly perturb predator-prey habitat overlap in the Southern Ocean. Our findings highlight the need for a better quantitative understanding of climate change impacts on Antarctic species to better constrain future ecosystem impacts of climate change.