Penguin numbers suffering with krill decline due to global warming

A new study of declining penguin populations shows a strong correlation between penguin numbers and krill availability. Krill availability is affected by reduced sea ice conditions in Antarctica due to global warming and climate change.

"For penguins and other species, krill is the linchpin in the food web. Regardless of their environmental preferences, we see a connection between climate change and penguin populations through the loss of habitat for their main food source," said Dr. Wayne Trivelpiece, lead author and seabird researcher of the National Oceanic and Atmospheric Administration's Antarctic Ecosystem Research Division. "As warming continues, the loss of krill will have a profound effect throughout the Antarctic ecosystem."

Related: On the brink: Penguins face an uncertain climate future (Oct 2010)

The study - Penguins in peril: variability in krill biomass links harvesting and climate warming to penguin population changes in Antarctica - was published in the Proceedings of the National Academy of Sciences on April 11, 2011. The study used extensive data from the last 30 years to track fluctuations in Adelie (ice-loving) and chinstrap (ice-avoiding) penguins. Populations of both species in the West Antarctic Peninsula and Scotia Sea have declined by respective averages of 2.9 and 4.3 percent per year for at least the last 10 years, with some colonies in the South Shetland Islands have decreased by more than 50 percent. Other studies have shown declines of up to 75 percent in nearby regions during this time.

The scientists also assessed krill abundance, air temperature changes and sea-ice levels in the region during the same time period to explore the relationship between these factors and penguin abundance. Since the 1970s climatic warming, a commercial krill fishery and recovering whale and fur seal populations, as well as penguins,have depressed krill abundance by almost 80 percent in the Southern Ocean.

Around Antarctica reduction in sea ice, ocean warming and ocean acidification is reducing one of the main penguin food sources - the small crustaceans known as krill. The Marine Stewardship Council in early 2010 approved the continuation of krill harvesting as sustainable to manufacture feed for fish farming and nutritional supplements for humans and came under criticism by marine conservationists.

Krill are at the bottom of the food chain and are dependent on sea ice conditions for feeding on ice algae. Larger mammals such as whales, penguins and seals are dependant upon the large swarms of krill either directly or indirectly through the food chain. In winters with shorter and smaller sea-ice coverage, krill reproduction is markedly reduced. The Southern Ocean is also a major sink for atmospheric carbon dioxide which is progressively turning the water more acidic impacting on the ability of krill to form their shells.

Chinstrap penguins were thought to be less vulnerable to climate change and the reduction in sea ice, but their breeding restriction to the Scotia Sea region and their reliance on krill as their primary food source may make them more vulnerable to the environmental changes brought on by global warming. "Once thought to benefit from diminished sea-ice, chinstrap penguins may instead be among the most vulnerable to climatic warming. Given their limited range, the authors suggest that chinstrap penguins be evaluated by the International Union for the Conservation of Nature for a higher status within their Red List, which describes the vulnerability of a species or population to extinction." the study says.

The study warns that:

Antarctic ecosystems face profound changes due to rapid climatic warming and expanding fishing efforts. Previous studies have implicated changes in sea-ice cover due to climate change as a major driver of population shifts in predators, such as penguins, because some species prefer extensive ice cover while others do not. Yet, penguin populations are also likely to be influenced by the availability of their primary prey, krill, whose abundance has been altered by climatic warming. Fishing for krill and increased competition among other krill predators may also have made krill less available to penguins.

"Penguins are excellent indicators of changes to the biological and environmental health of the broader ecosystem because they are easily accessible while breeding on land, yet they depend entirely on food resources from the sea. In addition, unlike many other krill-eating top predators in the Antarctic, such as whales and fur seals, they were not hunted by humans," said Dr. Trivelpiece. "When we see steep declines in populations, as we have been documenting with both chinstrap and Adelie penguins, we know there's a much larger ecological problem."

In October 2010 I reported that Penguins face an uncertain climate future which examined in detail the decline of the African Penguin. This latest study confirms that penguins face an uncertain future.