Penguins in western Antarctica have undergone significant population declines, largely due to a reduction in the availability of their main food source, krill.
As the dominant prey for nearly all vertebrates in the Antarctic region, Antarctic krill (Euphausia superba) is one of the most important species in the Antarctic ecosystem.
However, in the past 40 years, the population of krill in the Southern Ocean surrounding Antarctica has fallen by around 80%.
Climate-driven changes, such as warming waters and less sea ice cover, as well as increasing whale and seal numbers, have been cited as some of the reasons behind the krill decline.
The Antarctic region is among the fastest warming areas on the planet, with increases of 5 to 6 ºC in mean winter air temperatures, and associated decreases in winter sea ice cover. Krill are dependent on sea ice during their larval stages, and the shrinking sea ice has contributed directly to a decline in breeding success.
Dr Wayne Trivelpiece, lead author of a new paper published in the Proceedings of the National Academy of Sciences, warns that “as warming continues, the loss of krill will have a profound effect throughout the Antarctic ecosystem.”
According to the study, the reduction in krill abundance has caused numbers of both the chinstrap penguin (Pygoscelis antarcticus) and the Adelie penguin (Pygoscelis adeliae) to fall steadily since 1986.
The team found that linking trends in penguin abundance with trends in krill biomass explains why populations of Adelie and chinstrap penguins increased after competitors, such as fur seals and baleen whales, declined due to hunting by humans in the 19th to mid-20th Centuries, as well as why they are currently decreasing in response to climate change.
The new findings challenge the current leading theory behind penguin declines in Antarctica, known as the ‘sea ice hypothesis’.
The sea ice hypothesis proposes that reductions in winter sea ice leads directly to declines in species which depend on sea ice for breeding and other activities by decreasing their winter habitat, while populations of species which do not depend on sea ice will increase.
However, the new findings show that populations have declined in the Adelie penguin, which depends on sea ice, and the chinstrap penguin which does not. Populations in both species have fallen by up to 50% since the mid-1980s, suggesting that the declines were instead linked to the abundance of their main food source.
Over the past 10 years, chinstrap penguin populations have fallen by 4.3% annually, while Adelie penguin populations have fallen by 2.9% annually over the last decade.
The researchers, a team from the National Oceanic and Atmospheric Administration (NOAA) and the Scripps Institution of Oceanography in the US, concluded that penguin numbers and krill abundance are both likely to fall further if the unprecedented warming trend in the Antarctic region continues.
Read the paper in the Proceedings of the National Academy of Sciences.
Find out more about Antarctic species on ARKive.
Explore other species affected by climate change on ARKive’s climate change pages.
Helen Roddis, ARKive Species Text Author