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Ecological Responses to Climate Change on the Antarctic Peninsula

The peninsula is an icy world that's warming faster than anywhere else on Earth, threatening a rich but delicate biological community

James McClintock, Hugh Ducklow, William Fraser

A Paleozoic Community

The geological history of Antarctica has presented some obvious adaptational challenges to the inhabitants of the land and the surrounding seas. Some 200 million years ago, when Antarctica was part of the southern supercontinent Gondwana, the climate was temperate and the biota included land plants, insects, reptiles and many kinds of fish. As the continent migrated toward the pole, most of these organisms perished, but a few adapted to the harsh conditions and flourished.

Studies of invertebrate fossils from Seymour Island, along the eastern peninsula, have given us a glimpse of the region's marine fauna 45 million years ago, in the mid-Eocene. Of particular note are thick-shelled gastropods and bivalve mollusks, whose heavy armor indicates an abundance of durophagous predators: organisms that get at their prey by crushing. Such predators include fish with well-developed jaws and large-clawed crabs.

Later in the Eocene, water temperature in the Southern Ocean abruptly fell by 14 degrees Celsius. Among the victims of this rapid cooling were essentially all the durophagous marine predators. These animals must exert strong forces to crack open shells and often move rapidly as well; both of these activities are inhibited by low temperature. In the absence of duro­phagous predators, the invertebrate community on the peninsular continental shelf has lost the defensive shell architectures commonly found in warmer waters. Except for chemical defenses, the invertebrates are poorly equipped to withstand predator attacks.

The benthic community today looks rather like an assemblage of organisms from the Paleozoic Era, before durophagous predators were widespread. Snails, clams and brachiopods have unusually thin, delicate, shells. A preponderance of animals are filter feeders; among them are soft corals, crinoids, bryozoans, tunicates, brachiopods and sponges. Many of the species are endemic—found here and nowhere else. There is a tendency to gigantism among sponges, sea spiders, isopods and ribbon worms (Nemertea). The only common fishes are notothenioids—members of a family whose secret to survival in a sub-freezing environment is a natural antifreeze molecule, a glycoprotein, or sugar-coated protein. The antifreeze probably evolved in a single Antarctic notothenioid species, but a subsequent adaptive radiation has given rise to some 250 species today.

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