Rising global temperatures, combined with other problems related to human activities like over-fishing, are putting pressure on Antarctic penguin populations and reducing the number of young penguins that survive to maturity. According to Wayne Z. Travelpiece of the National Marine Fisheries Service in California, warming in Antarctica is hurting populations of the invertebrates penguins and other marine birds and mammals feed on, cutting off the food supply which penguin chicks rely on to survive the first winter they spend on their own. Only one in ten chinstrap and Adélie penguins now survive their first winter, as compared to a 50% survival rate in the 1970s.
A decades-long study on penguin populations conducted by Travelpiece highlights the delicate balance between wildlife, planktonic organisms, and air and water temperatures in the southernmost region of the globe. It’s also a reminder that the northern Arctic, where much of the media’s coverage of global warming has been focused, isn’t the only part of the world affected by climate change. Ecosystems and wildlife all over the planet will be impacted by a changing climate, with the effects of rising temperatures stretching literally from pole to pole.
Around the Antarctic Peninsula where Travelpeice’s study focused, air temperatures have risen about ten degrees Fahrenheit since the middle of last century due to a buildup of carbon emissions in the atmosphere. This has meant less winter ice forms in the water in chinstrap and Adélie penguin habitat. Tiny algae called phytoplankton, which grow and thrive under ice flows, have declined as Antarctic ice recedes. That in turn leads to a reduction in krill, the small marine crustaceans that Adélie and chinstrap penguins feed on. Less krill means fewer young penguins are able to survive their first winter away from their parents, as recorded in Travelpeice’s study.
Yet that isn’t the end of the story, and a relatively simple explanation of penguin declines doesn’t do justice to the true complexity of Antarctic ecosystems. Though climate change is partly to blame for plummeting krill populations, another factor is the recovery of whale species hunted to near-extinction in the nineteenth and twentieth centuries. Like penguins, whales feed on krill—and as whales have recovered, the two groups of animals have had to compete over ever-dwindling krill populations.
In fact the decline of whales may have been what prompted Adélie penguins to take up eating krill in the first place, as analyses of penguin tissues from the early twentieth century show the species once fed mainly on fish. When whales largely disappeared from Antarctic waters, Adélies seem to have shifted to super-abundant krill as a food source and dropped their preference for fish. Yet that doesn’t mean the Adélies will automatically go back to eating fish now that krill are no longer plentiful. For one thing, over-fishing means many fish populations are themselves in a state of severe decline and can no longer support penguins the way they once did.
The chain of relationships between rising temperatures, fishing, whales and penguins, and the tiny plankton that make up the base of the ocean food web underscores the complexity of trying to predict how other species will respond to a changing climate. It also points to the grim reality that many species of wildlife won’t be able to survive major shifts in climate. As long as over-fishing and climate change continue, penguins and other ocean predators are likely going to suffer. Better management of ocean fisheries and policies that curb carbon emissions from major world economies will be needed if the Antarctic food web is ever to be wholly restored.
Photo credit: Chad Rosenthal