Role of squid in the Southern Ocean pelagic ecosystem and the possible consequences of climate change
Southern Ocean squid are important predators and prey and are a potential fishery resource. Their future under climate change is analysed from predictions of change by 2100 and assessments of the effects on squid biology. There are ∼18 Antarctic species of squid. Young feed primarily on crustaceans and switch later to fishes. They are preyed on by odontocetes, seals and seabirds – which together consume ∼34×106 t yr−1 – and fish. As predators, squid are second to fish as biomass producers but recent evidence suggests predator consumption of squid needs to be reassessed. Fatty acid composition and stable nitrogen isotope ratios indicate some predators consume less squid in their diet than gut contents data suggest. Southern Ocean oceanography is unique in having circumpolar circulation and frontal systems and at high latitudes it is heavily influenced by sea ice. The Antarctic Peninsula is among the fastest warming regions worldwide but elsewhere the Southern Ocean is warming more slowly and the Ross Sea is probably cooling. Sea ice is receding in the Peninsula region and increasing elsewhere. Modelled predictions for 2100 suggest although the Southern Ocean will warm less than other oceans and sea ice will reduce. The Antarctic Circumpolar Current may shift slightly southwards with intensification of westerly winds but resolution of the models is insufficient to predict mesoscale change. Globally, pH of seawater has decreased by 0.1 units since the mid-1900s and is predicted to decrease by another 0.5 units by 2100. Impact on calcifying organisms will be high in the cold Southern Ocean where solubility of calcium carbonate is high. Predicted temperature increases are unlikely to have major effects on squid other than changes in distribution near the limits of their range; acidification may have greater impact. Small changes in large scale circulation are unlikely to affect squid but changes in mesoscale oceanography may have high impact. Change in sea ice extent may not have a direct effect but consequent ecosystem changes could have a major impact. Cephalopods are ecological opportunists adapted to exploit favourable environmental conditions. Given their potential to evolve fast, change in the Southern Ocean pelagic ecosystem might act in their favour.