Krill blame for the dramatic penguin loss?

New data show strong declines in krill densities, discouraged sea-ice hypothesis

Chinstrap Penguin © Jerzy Strzelecki / CC-by-sa 3.0
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What is to blame for the dramatic decline in penguin populations in West Antarctica? So far, the sea ice melt has been the most likely cause, but now American researchers have a completely different factor suspected: the Antarctic krill. As reported in the Proceedings of the National Academy of Science (PNAS), the density of small crustaceans in the Arctic Ocean has fallen by up to 80 percent since 1979. The penguins could therefore simply suffer from lack of food.

In the last 50 years, the populations of Adélie and chinstrap penguins in the West Antarctic Peninsula have fallen sharply. By up to 50 percent, the stocks reduced - but why? According to the popular "sea-ice hypothesis", the shrinking of the winter ice surface is directly involved in the decline of ice-loving species such as the Adélie penguin. This avoids larger water surfaces and prefers areas with dense pack ice.

Penguin decline: Is the sea ice melt to blame?

In contrast, the chinstrap penguins, who favor free water with a maximum of 30 percent ice cover. They hypothesized that they should benefit from the ice melt. A research group led by Wayne Z. Trivelpiece of the National Oceanic and Atmospheric Administration (NOAA) in the USA has now re-analyzed field data from the last 30 years on the penguin populations and refuted this assumption: During the investigation period, the population numbers of both penguin species decreased significantly, an advantage for the "eismeidenden" chinstrap penguins was not to be recognized.

Krill density has dropped 80 percent since the 1970s

According to Trivelpiece and his colleagues, another factor could be responsible for this wastage of penguins in West Antarctica: the Antarctic krill. These small crustaceans living in the plankton of the sea experienced in the 1930s to 1970s due to favorable climatic conditions and only a few predators a flower, which also drove the penguin populations in the air. Increasing competition - by penguins, but also by large marine mammals - and rising sea temperatures have the krill density, however, thereafter reduced by up to 80 percent, according to the results of the evaluations.

Since chinstrap penguins feed mainly on krill, and adelie penguins on small fish, which in turn eat krill, according to the researchers, today's shrinkage of both species may be due to the decline in krill. The decline in sea ice, on the other hand, may be an additional factor, but does not appear to be the only one. Should krill fisheries be expanded in the future, this could further hinder the critical situation of many penguin species, the scientists warn. (PNAS, 2011; DOI: 10.1073 / pnas.1016560108) Display

(PNAS, 12.04.2011 - NPO)