Squid are pelagic and feed on a range of prey, including fish, cephalopods, and crustaceans, with their diet shifting over their lives. They play a key role in the Southern Ocean ecosystem, serving as prey for numerous predators, including whales, seals, seabirds, and fish, with around 34 million tonnes of squid being consumed annually in this region. Considering their importance in the Southern Ocean ecosystem, this study analyses the long-term ecological dynamics of five key squid species over the last five decades. The study focuses on how these squid species have adapted to changing environmental conditions, particularly the Southern Oscillation Index (SOI) and the Southern Annular Mode (SAM), by analysing stable isotope ratios (δ13C and δ15N) in squid beaks found in the diet of wandering albatrosses.
The study found significant changes in the habitat of four out of the five squid species, as indicated by shifts in δ13C values. This suggests that these species have changed their geographical distributions over time, likely in response to environmental changes. Taonius sp. B, Gonatus antarcticus, Galiteuthis glacialis, and Histioteuthis atlantica all showed changes in habitat, moving towards more northerly regions over the decades. Moroteuthopsis longimana (Figure 1) was the only species that maintained consistent habitat use, indicating a potentially greater tolerance to environmental changes.
Despite changes in habitat, the trophic levels of all five squid species, as concluded from δ15N values, remained relatively stable over the study period. This suggests that their roles within the food web have not shifted significantly, maintaining their importance as prey for top predators.
Of the five species, only Taonius sp. B showed a significant correlation between its isotope ratios and the environmental indices (SOI and SAM), indicating that these climatic factors directly influenced its trophic level and habitat.
In conclusion, the study suggests that while Southern Ocean squid have altered their habitat in response to changing environmental conditions, their trophic roles have remained stable. This adaptability could ensure their continued importance in the Southern Ocean ecosystem, even as climate change progresses. The findings highlight the potential resilience of these species to environmental variability and their critical role in the marine food web. This research provides valuable insights into the ecological responses of key nekton species in the Southern Ocean, which could be crucial for predicting future changes in the ecosystem under ongoing climate change.
Source: Abreu J, Phillips RA, Ceia FR, Ireland L, Paiva VH, Xavier JC (2020) Long-term changes in habitat and trophic level of Southern Ocean squid in relation to environmental conditions. Sci Rep
DOI: 10.1038/s41598-020-72103-6
Author: Sara Santos
