A new study published in the journal Global Change Biology studied the effects of diminishing sea ice on the Emperor penguin population in Terre Adelie, a region in East Antarctic. The study was led by researchers from the Woods Hole Oceanographic Institution (WHOI). Emperor penguins are Antarctica’s largest sea bird, normally standing at almost 4 feet tall. A disappearance in this population as already been observed in other areas of the Antarctic. The Dion Islets penguin colony, located in the West Antarctic Peninsula, decreased from 150 breeding pairs in 1948 and 1970, to 20 pairs in 1999, and finally vanished completely in 2009.
Stephanie Jenouvrier, the lead author and biologist on the study, thinks that declines in these penguin populations are connected to decline in Antarctic sea ice caused by warming temperatures. Emperor penguins breed and raise their offspring on the sea ice. Increasing temperatures causes the sea ice to break up and disappear, which may be causing breeding failures on a large scale. “As it is, there’s a huge mortality rate just at the breeding stages, because only 50 percent of chicks survive to the end of the breeding season, and then only half of those fledglings survive until the next year,” says Jenouvrier.
Not only do the penguins rely on sea ice for breeding, their food source stems from the ice as well. Fish, squid and krill make up the majority of the Emperor penguins diet. These species feed on zooplankton and phytoplankton that grow on the bottom of sea ice. Melting sea ice causes a chain reaction in food supply that reaches the Emperor penguins.
Jenouvrier’s team is attempting to project the fate of future populations of the species. By combining climate models, sea ice forecasts, and a demographic model of the Emperor penguin population in Terre Adelie, the team was able to determine how changes in the temperature and sea ice may effect the future population of Emperor penguins in Terre Adelie.
Hal Caswell, a senior mathematical biologist at WHOI says that “if you want to study the effects of climate on a particular species, there are three pieces that you have to put together.” He continues to say that “the first is a description of the entire life cycle of the organism, and how individuals move through that life cycle. The second piece is how the cycle is affected by climate variables. And the crucial third piece is a prediction of what those variables may look like in the future, which involves collaboration with climate scientists.”
Jenouvrier and her team determined that if greenhouse gas emissions continue to rise at the same or similar rates as today, the Emperor penguin population will slowly diminish in Terre Adelie. By 2040, the rate of population decline would increase dramatically as the sea ice coverage drops below a usable threshold.
“Our best projections show roughly 500 to 600 breeding pairs remaining by the year 2100. Today, the population size is around 3000 breeding pairs,” says Jenouvrier.
Melting sea ice not only effects the penguin population, but many other species as well, including humans. “We rely on the functioning of those ecosystems. We eat fish that come from the Antarctic. We rely on nutrient cycles that involve species in the oceans all over the world,” says Caswell. “Understanding the effects of climate change on predators at the top of marine food chains — like Emperor penguins — is in our best interest, because it helps us understand ecosystems that provide important services to us.”