Featured Science Paper
Potential Climate Change Effects on the Habitat of Antarctic Krill in the Weddell Quadrant of the Southern Ocean
The current generation of climate models suggest that the Southern Ocean will get warmer during the 21st Century unless mankind substantially reduces greenhouse gas emissions. How is this warming likely to affect the cold water species that live in the Southern Ocean? The response of living things to temperature change results from complex interactions between many different processes. This study simplified the problem by focusing on the growth of Antarctic krill, a single biological process that is both sensitive to temperature and ecologically important. The growth of Antarctic krill has the potential to produce more than 300 million tonnes of new biomass per year, which supports the wide range of Antarctic predators that feed on krill. The study considered krill growth in the Weddell Quadrant, the part of the Southern Ocean between the Greenwich Meridian and 90°W, which includes important predator feeding and industrial fishing areas in the Scotia Sea and southern Drake Passage.
The growth rate of adult krill changes in response to sea temperature and food availability. The study used a statistical model of this relationship to assess how krill growth rates might change in response to future warming. It used spatially-resolved temperature projections from sixteen climate models based on three of the Representative Control Pathways (RCPs) developed to investigate the consequences of different levels of greenhouse gas accumulation. Projected average warming under RCP2.6, which represents substantial future cuts in greenhouse gas emissions, was 0.27°C whereas that under RCP8.5, which represents continued growth in greenhouse gas emissions, was 1.08°C. Inevitably, the projected impact on krill growth was more severe when projected warming was more intense.
Projected changes in krill growth rate were different for different parts of the ocean. Krill growth rates did not change substantially in the Weddell Sea but they declined in the northern part of the modelled area. The projections suggest that, by the end of the century, some parts of the Southern Ocean will not support any krill growth. Under RCP8.5 this reduced the total area of krill growth habitat by 20%. South Georgia, which is an important breeding site for large populations of krill predators, including about 95% of the global population of Antarctic fur seals, is located in this area of projected habitat loss. The study suggests that, under RCP8.5, krill could be extirpated from almost half of the habitat accessible to Antarctic fur seals rearing offspring at South Georgia.
The study uses available knowledge to produce a best estimate of potential outcomes. Nonetheless, it is impossible to predict the future with certainty. This study follows others which suggest that human-induced acidification and sea-ice loss could also affect Antarctic krill populations. This mounting evidence suggests that the Southern Ocean ecosystem is likely to be severely affected by climate change. This type of spatially-resolved information is important for informing management measures which seek to mitigate or manage the effects of climate change on Southern Ocean biodiversity and fisheries.
Simeon L. Hill, Tony Phillips, Angus Atkinson