Fast ice determines breeding success of emperor penguins | Polarjournal
Emperor penguins rely on fast ice – sea ice that is firmly attached to land, islands, or ice shelves and not pushed around by tides and currents – to breed and raise their young. The seasonal change in the extent of the fast ice is of crucial importance for the survival of the penguin chicks. Climate change is playing an increasingly important role in the formation and melting processes of the fast ice, and is thus one of the factors determining the breeding success of the emperor penguins. Foto: Heiner Kubny

So far, scientists have paid a lot of attention to the development of sea ice extent in Antarctica in the wake of climate change and its impact on Antarctic animals at the top of the food chain. However, little was known about the fast ice – apex predator connection. Therefore, an international team of researchers took a closer look at the relationship between the variability of the fast ice and local weather conditions and the breeding success of emperor penguins in East Antarctica.

In the current study, scientists from France, the USA and Australia investigated the relationship between fast ice and breeding success of the Emperor penguin colony at Point Géologie in East Antarctica using long-term data sets. They evaluated satellite imagery, weather reports and records of emperor penguin breeding success covering a 39-year period.

The colony at Point Géologie is located not far from the French station Dumont-d’Urville in East Antarctica and is one of the best investigated emperor penguin colonies. Map: Wikipedia/Alexrk2

One finding of the study, published in the journal Biology Letters, is that icebergs have a major impact on the behavior of fast ice. An iceberg that broke off from the ice shelf in the 1980s and collided with a glacier near the colony in 2010 caused an ice jam, turning the distance from the colony to the ice edge too far for the penguins to adequately feed their chicks. This was followed by a jump in chick mortality between 2012 and 2014, with some decline in subsequent years. Overall, the number of breeding pairs at Point Géologie has declined from 6,075 in the early 1970s to about 3,500 today.
The results of the study illustrate how strongly penguin populations can be affected by small changes in their environment. As warming increases, these become more unpredictable.

The researchers also found that ice conditions are optimal for emperor penguin breeding success only within a narrow range, according to a normal distribution. If there is too little fast ice or if it melts too early, the chicks with their downy feathers run the risk of falling into the water and freezing to death. If the distance to the edge of the ice and thus to the food source is too far, the parents cannot bring enough food for the chicks.
The ice is so sensitive to environmental changes and the penguins in turn are sensitive to changing ice conditions, so climate change will determine the fate of the emperor penguins.

Emperor penguins are so perfectly adapted to this harsh, icy habitat that the slightest environmental change can be their undoing. Photo: Dr. Michael Wenger

Overall, however, fast ice is still little investigated, although it plays an essential role in the survival of emperor penguins. The reasons for this lie in its variability and the influence of various factors such as storms, icebergs or the breaking strength of the ice itself. All of this complicates modeling and making accurate predictions. Even at the colony at Point Géologie, which is one of the best-documented colonies, scientists have long assumed that the ice under the feet of the emperor penguins would melt away with increasing warming. However, the opposite is true. Over the past decade, the extent of fast ice has increased. As Alexander Fraser, a glaciologist at the University of Tasmania and co-author of the study, tells the National Audubon Society, icebergs are largely responsible.

Due to global warming, climate scientists say more icebergs will break off in the future. And these have the potential to alter environmental conditions in ways that could have devastating effects on penguin colonies. So the outlook for emperor penguins, the least numerous of all true Antarctic penguin species with an estimated 595,000 individuals, is anything but rosy.

Julia Hager, PolarJournal

Link to the study: Labrousse Sara, Fraser Alexander D., Sumner Michael, Le Manach Frédéric, Sauser Christophe, Horstmann Isabella, Devane Eileen, Delord Karine, Jenouvrier Stéphanie and Barbraud Christophe, 2021. Landfast ice: a major driver of reproductive success in a polar seabird. Biol. Lett.172021009720210097

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