From warm to cold waters: new insights into the habitat and trophic ecology of Southern Ocean squids throughout their life cycle.

Cephalopods play a major role in marine ecosystems, yet very little is known about the dynamics of their habitat use and trophic ecology across the stages of their life cycle, particularly in the Southern Ocean. Here, we used stable isotope analyses of δ13C (a proxy for foraging habitat) and δ15N (a proxy for trophic position) to investigate the habitat use and trophic ecology of 10 squid species, collected from the diet of Antipodean (Diomedea antipodensis antipodensis) and Gibson’s (D. a. gibsoni) albatrosses breeding at Antipodes and Adams Island (South Pacific), respectively. We analyzed isotopes in 2 sections of squid lower beaks, representing 2 stages of the life cycle: the tip of the rostrum (juvenile stage) and the wing (adult stage). Higher δ13C values in early life stages (-20.8 ± 1.7‰) than in adult life stages (-21.6 ± 1.9‰) suggest that Southern Ocean squids tend to move southwards as they grow, with oceanic fronts being an important habitat for these species. Our results also suggest that adults may move southwards with climate change, possibly impacting top predators living on northern islands. Overall, δ15N values revealed an increase in trophic position from early (6.7 ± 2.7‰) to adult life stages (9.0 ± 2.5‰) in all species. Nevertheless, significant differences between δ15N values of the 10 species, in both beak sections, suggest different feeding strategies between species and life stages.

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