Researchers are surprised to find much happier Antarctic penguins with less sea ice

Adelie Penguins Lutzow Holm Bay

Adelie penguins in Lützow-Holm Bay, Antarctica, enjoy easy access to food and increase body weight and reproductive success in an ice-free summer. Credit: Yuuki Watanabe (National Polar Research Institute, Japan)

Researchers have been surprised to discover that Adelie penguins in Antarctica prefer reduced sea-ice conditions, not just a little, but a lot. As climate models project a rapid reduction in the continent’s sea ice for the rest of the century, this iconic polar predator could be a rare winner of global warming. Their research findings are published today (June 24, 2020) in Scientific advances.

Adelie Penguins Ice Free Summer

Credit: Yuuki Watanabe (National Polar Research Institute, Japan)

In recent decades, Antarctica has seen a steady increase in the extent of its sea ice, frozen seawater, even as its polar twin, the Arctic, has suffered a marked decline. But this is not expected to last much longer as the climate changes, as Antarctica will also project a decrease in its sea ice, with all the consequences of such changes in the marine habitat for organisms living there.

But such consequences are not always negative.

Polar biologists have known for some time that Adelie penguins, the most common penguin species in Antarctica, tend to see population increases during years of low sea ice and suffer massive reproductive failures during those years with the highest ice growth. Marine.

Penguin equipped with video camera

A penguin equipped with a video camera on the back and an accelerometer on the head. Credit: Yuuki Watanabe, National Polar Research Institute

But until now, researchers really didn’t know why this happened. The few studies that mentioned the relationship between population growth and sea ice have only established a correlation, not a cause.

Krill sampled from penguin stomachs

Krill sampled from penguin stomachs. Krill (Euphausia superba, left; E. crystallorophias, right) were sampled from a penguin in January 2017 during an ice-free season and in January 2011 during an ice-covered season, respectively. The krill sampled on the left is much larger than those sampled on the right. The service is 24 centimeters in diameter. Credit: Yuuki Watanabe, National Polar Research Institute

That missing information has now been found. Researchers from the Japan National Polar Research Institute electronically tagged 175 penguins with GPS devices, accelerometers, and video cameras at four stations with different sea ice conditions, allowing them to track penguins on their travels, classify walking behavior, swim and rest, and estimate the amount of prey captured during dives.

Adelie Penguins

Credit: Yuuki Watanabe (National Polar Research Institute, Japan)

“It turns out that these penguins are happier with less sea ice,” said lead researcher Yuuki Watanabe of the National Polar Research Institute. “This may seem counterintuitive, but the underlying mechanism is really quite simple.”

He explained that in ice-free conditions, penguins can travel more swimming than walking.

“For penguins, swimming is four times faster than walking. They can be elegant in the water, but they are quite slow on land, “he added.

In seasons with heavy sea ice, penguins have to walk (and sometimes slide) a long way to find cracks in the ice to access the waters where they hunt, sometimes taking quite long breaks along the way.

Adelie Penguins Lutzow Holm Bay Antarctica

Credit: Yuuki Watanabe (National Polar Research Institute, Japan)

But when there is less sea ice, penguins can dive anywhere they want, often simply by entering the water right next to their nests. This is more energy and time efficient and extends your power range. Most importantly, this probably reduces competition with other penguins for the prey and allows them to catch more krill, the penguin’s main prey. Less sea ice also means more sunlight enters the water, leading to larger blooms of the plankton that krill feeds on.

However, all of this only happens for penguins that live in the main, “continental” part of Antarctica. The opposite is true for penguins that live on the thin Antarctic peninsula that juts out from the mainland or live on its islands.

Adelie Penguins Antarctica

Credit: Yuuki Watanabe (National Polar Research Institute, Japan)

The researchers have some hypotheses as to why this might be the case, so the next chapter in this story will be to test those ideas as well.

Reference: “Foraging behavior links sea ice to reproductive success in Antarctic penguins,” by YY Watanabe; N. Kokubun; A. Takahashi at the National Polar Research Institute in Tokyo, Japan; YY Watanabe; K. Ito; N. Kokubun; A. Takahashi, June 24, 2020, Scientific advances.
DOI: 10.1126 / sciadv.aba4828