Even a species that has benefited from temperature increases in the past may be hurt by excessive warming.
Adélie penguins (Phygoscelis adeliae) have lived in Antarctica for millions of years. They are one of only two penguin species found exclusively on the continent, the other being Emperor penguins (Aptenodytes forsteri). Unlike Emperor penguins, which trek for miles to breeding colonies located in ice-covered regions of Antarctica, Adélie penguins breed solely in ice-free areas along the coast, building nests out of rocks to keep their eggs and chicks dry. Thus, rising temperatures have historically benefited Adélie penguin populations, while glacial expansion has caused the penguins to abandon breeding colonies. However, there is a limit to how much warming benefits the species.
A new study headed by Megan Cimino of the University of Delaware indicates that temperatures in Antarctica may soon become too high even for Adélie penguins, as excessive warming brought on by climate change will soon make their habitats unfit for breeding. According to Cimino, “It is only in recent decades that we know Adélie penguins population declines are associated with warming, which suggests that many regions of Antarctica have warmed too much and that further warming is no longer positive for the species.”
The most recent census of Adélie penguins shows that there are 3.79 million breeding pairs in Antarctica. For the most part, these numbers have been stable or increasing. However, Cimino’s study found that Adélie penguin populations in many breeding colonies along the West Antarctic Peninsula (WAP) have been declining over the last few decades, even though some colonies are almost 6,000 years old. These population declines are likely due to sea surface temperatures and sea ice concentrations that are outside the range of average historical conditions, a phenomenon known as novel climate. Palmer Station, an American research center in Antarctica, experienced the most years of novel climate of all areas analyzed in the study, and penguin colonies there experienced an 80% decline since the 1970s. Colonies with increasing or stable populations, on the other hand, have generally experienced stable climate conditions over the last 30 years.
Areas outside of the WAP may soon experience novel climates as well, resulting in diminished penguin populations throughout Antarctica. In the study, Cimino and her researchers analyzed Adélie penguin population trends from 1981-2010 using satellite imagery and field survey data. They also looked at global climate model projections from 2011-2099 to determine how the populations would be affected in the future. Their findings reveal that if current climate trends continue, Adélie penguins across the continent could see a mean population decrease of 36% by 2060 and a decrease of 58% by 2099.
Climate change will primarily affect the penguins’ nesting and food sources. For example, one major component of the penguins’ diets, Antarctic silverfish (Pleuragramma antarcticum), has experienced declines in the WAP coinciding with several years of novel climate. Populations of Antarctic krill (Euphausia superba), another staple in penguin diets, may soon be diminished as well if temperatures become too high.
Furthermore, novel climates can cause an increase in precipitation, and large puddles formed by melting snow or ice can drown penguin chicks. Cimino told Natural Geographic, “Rain and puddles are bad because eggs can’t survive when they’re lying in a pool of water. Chicks that don’t have waterproof feathers can become wet and die from hypothermia.”
Fortunately, the researchers found several refugia, or safe havens, for Adélie penguins after 2099. If current projections hold true, penguin populations will likely decline at northerly latitudes by the end of the century, but the species could still breed in the Amundsen and Ross Seas, as these areas maintain generally stable climate conditions. In fact, the oldest known Adélie penguin colony is located in the Ross Sea and was first used for breeding 45,000 years ago.
Still, Cimino stresses the importance of protecting penguins from climate change. As she explained to Phys.org, "Studies like this are important because they focus our attention on areas where a species is most vulnerable to change. The results can be used for management; they can have implications for other species that live in the area and for other ecosystem processes."