Researchers find the future belongs to penguins that can adapt their diet

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: A gentoo penguin leaps off an ice flow into Mikkelsen Harbor
A gentoo penguin leaps off an ice flow into Mikkelsen Harbor, Antarctic Peninsula.
Photo: Kelton McMahon.

KINGSTON, R.I., – December 2, 2019 – Over the past 100 years, Antarctic penguins have experienced dramatic human impacts including the whaling industry’s rise and fall and recent climate change. New research published in the Proceedings of the National Academy of Sciences finds that depending on their diet, some species are able to thrive in this rapidly changing ecosystem while others are facing decline.

URI Graduate School of Oceanography assistant professor Kelton McMahon and his co-authors from Louisiana State University, University of Oxford, University of California Santa Cruz and the University of Saskatchewan chose penguins for their study because the charismatic creatures serve as sentinel species for environmental change, and they occupy a central node in the Southern Ocean food web.

“Antarctica is often thought of as one of the last untouched frontiers, but humans have had an impact on its ecosystem since the early 1800s,” said McMahon, a co-lead author of the new study. “By the early 20th century, seals and whales were hunted to near extinction. These marine mammals are making a comeback thanks to international regulations, but the Antarctic Peninsula is one of the fastest warming areas on Earth. Coupled with a growing commercial fishing industry, there is tremendous pressure on the environment and the organisms that call the continent home.”

The research team’s goal was to understand how human interference in Antarctic ecosystems during the past century led to booms and busts in the availability of a key food source for penguins: Antarctic krill.

“Antarctic krill is a shrimp-like crustacean that is a key food source for penguins, seals, and whales,” said Michael Polito, assistant professor at Louisiana State University and co-lead author of the study. “When seal and whale populations dwindled due to historic over-harvesting, it is thought to have led to a surplus of krill during the early to mid-1900s. In more recent times, the combined effects of commercial krill fishing, anthropogenic climate change, and the recovery of seal and whale populations are thought to have drastically decreased the abundance of krill.”

The team focused their research on the diets of chinstrap and gentoo penguins because chinstrap penguins have had severe population declines and gentoo penguin populations have increased in the Antarctic Peninsula over the past half century.

“Given that gentoo penguins are commonly thought of as climate change winners and chinstrap penguins as climate change losers we wanted to investigate how differences in their diets may have allowed one species to cope with a changing food supply while the other could not.” said Tom Hart, co-author and penguinologist at the Department of Zoology at the University of Oxford.

The research team analyzed the nitrogen stable isotope values of amino acids in feathers and eggshells collected over the past century—by historic Antarctic explorers as well as the authors themselves during recent expeditions.

“We’ve all heard the adage, ‘you are what you eat,’” said McMahon. “All living things record a chemical ‘isotopic’ signal of the food they eat in their tissues. Over the last decade, my collaborators and I have pioneered powerful new techniques to examine the isotope ratio of individual compounds within an organism. This allows us to reconstruct critical components of food web structure supporting penguins back through time in a way that was simply not feasible with traditional ecological approaches.”

The authors found that both species of penguins primarily fed on krill during krill surpluses in the early to mid-1900s caused by the historic harvesting of krill-eating marine mammals like whales and seals. However, during the latter half of the past century as krill abundance decreased, gentoo penguins adapted by shifting from strictly eating krill to including fish and squid in their diets. In turn, their populations increased. Chinstrap penguins, on the other hand, continued to feed exclusively on the dwindling amount of krill and experienced severe population declines in the Antarctic peninsula.

The findings suggest that species with specialized diets are more sensitive to human-induced environmental change than generalist foragers. According to McMahon, researchers can now hypothesize about how krill predators in the Antarctic and Southern Ocean will respond to climate change and other human impacts in the future by knowing how they responded to past shifts in krill availability.

“By understanding how past ecosystems respond to environmental change, we can better predict future responses and improve the management of human-environment interactions in Antarctica,” said McMahon.

The National Science Foundation Office of Polar Programs and the Antarctic Science Bursary provided funding for this research.

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