Long-term changes in habitat and trophic level of Southern Ocean squid in relation to environmental conditions

Abstract

Long-term studies of pelagic nekton in the Southern Ocean and their responses to ongoing environmental change are rare. Using stable isotope ratios measured in squid beaks recovered from diet samples of wandering albatrosses Diomedea exulans, we assessed decadal variation (from 1976 to 2016) in the habitat (δ13C) and trophic level (δ15N) of five important Southern Ocean squid species in relation to indices of environmental conditions—Southern Oscillation Index (SOI) and Southern Annular Mode (SAM). Based on δ13C values, corrected for the Suess effect, habitat had changed over the last 50 years for Taonius sp. B (Voss), Gonatus antarcticus, Galiteuthis glacialis and Histioteuthis atlantica but not Moroteuthopsis longimana. By comparison, mean δ15N values were similar across decades for all five species, suggesting minimal changes in trophic levels. Both SAM and SOI have increased in strength and frequency over the study period but, of the five species, only in Taonius sp. B (Voss) did these indices correlate with, δ13C and δ15N values, indicating direct relationships between environmental conditions, habitat and trophic level. The five cephalopod species therefore changed their habitats with changing environmental conditions over the last 50 years but maintained similar trophic levels. Hence, cephalopods are likely to remain important prey for top predators in Southern Ocean food webs, despite ongoing climate change.

Global Connectivity of Southern Ocean Ecosystems

“…Changes in small and largescale ocean dynamics will affect cross-frontal exchange and the dispersal of plankton. Such changes in the rates of mixing between polar, sub-polar and subtropical waters may also potentially disrupt the life cycles of fish and cephalopod species that cross oceanic fronts during development, thus affecting their role in Southern Ocean food webs (Murphy et al, 2007;McMahon et al, 2019;Saunders et al, 2019;Abreu et al, 2020). The APF is not expected to undergo major changes in location in the coming century (Meijers et al, 2019b), potentially limiting the southward extension of the distributions in the Southern Ocean of pelagic fish species from farther north (Boyce et al, 2008).…”

Productivity and Change in Fish and Squid in the Southern Ocean

“…Antarctic squid are likely to be influenced by climate change, including by changes in mesoscale oceanography, position of the oceanic fronts (and associated productivity), sea ice extent, and ocean acidification (Rodhouse, 2013;Xavier et al, 2018). A recent long-term study showed that the habitat of Taonius notalia, Gonatus antarcticus, G. glacialis, and Histioteuthis atlantica had changed over the last 50 years despite their trophic levels remaining similar (Abreu et al, 2020).…”

Trophic ecology of northern gannets Morus bassanus highlights the extent of isotopic niche overlap with other apex predators within the Bay of Biscay

“…The study of apex predators' trophic ecology can reveal a great deal of information due to the importance of predator-prey relationships and their dynamics on the evolution and structure of animal communities (Forero et al 2004). Apex predators such as cetaceans, seabirds and large predatory fish constitute an ideal model for studying trophic relationships, as they tend to integrate long-term and large-scale ecosystem signals due to their high position in food webs (Einoder 2009;Abreu et al 2020). Each component (i.e.…”