International audienceAlthough cephalopods play a critical role in marine food webs both as predators andprey, there is a limited knowledge of several basic aspects of their ecology, including their habitatand trophic level, in the Southern Ocean. We examined the ecological role of several SouthernOcean cephalopod species by analyzing δ13C and δ15N values in lower cephalopod beaks obtainedfrom diet samples of wandering albatross Diomedea exulans from South Georgia (AtlanticOcean), and from Crozet and Kerguelen Islands (Indian Ocean). Beak δ13C values ranged from−25.7 to −17.9‰, and were used to assign different cephalopod species to the subtropical, sub-Antarctic or Antarctic Zones. Beak δ15N values were more variable among species, ranging from2.4 to 13.3‰, a difference of ~11‰ that represents approx. 3 trophic levels. Differences amongislands in isotope ratios in the same cephalopod species (higher δ15N and lower δ13C values inSouth Georgia) were attributed to regional oceanographic processes. Antarctic cephalopodsoccupy niches similar to those found in some pelagic fish, seabirds and marine mammals. Ascephalopods are key components in Southern Ocean food webs, these results greatly advance ourunderstanding of the structure, energy and carbon flows in this polar ecosystem

Climate change is expected to have major negative effects on marine life across phylogenetic groups. Cephalopods, however, have life history characteristics that suggest they may benefit from certain climate change scenarios. Of all cephalopods, squids reach the greatest biomasses; as a result, they are of substantial importance for human and predator consumption. To test the hypothesis that the effects of climate change are beneficial for commercial squid, we used species distribution models on climate scenarios for the period between 2000 and 2014, as well as the years 2050 and 2100 (RCP [representative concentration pathway] 2.6, 4.5, 6.0, and 8.5; CMIP5). Our results suggest that consequences of climate change scenarios are species specific. In the North Pacific and Northwest Atlantic, squid’s habitat suitability may increase (from + 0.83% [Doryteuthis pealeii] to + 8.77% increase [Illex illecebrosus]), while it is predicted to decrease in other regions (from − 1.03% [Doryteuthis opalescens] to − 15.04% decrease [Loligo reynaudii]). Increases in habitat suitability occurred mostly at higher latitudes (north of 50° N), while suitable habitat decrease was predicted for the tropical regions. These shifts in future habitat suitability were stronger under harsher emission scenarios. Starting in 2050 (with RCP scenarios 4.6, 6.0 and 8.5), as a result of warming of the Arctic, squid habitat may increase along both coasts of North America. In the Southern Hemisphere, squids may lose habitat with no poleward habitat alternatives to move into. Contrary to our hypothesis, these commercial squid do not stand to benefit from climate change. Since these squid are an important food source for marine megafauna and humans, it is imperative that climate change biogeographic impacts are considered for a sustainable management of this important group of molluscs.