Once similar to the U.S. Pacific Northwest, Antarctica now demands that life adapt to extreme cold—which explains, for instance, the existence of fish there that make their own antifreeze and lack red blood
December 8, 2014 | |Antarctica: Life on Ice.
“Damned improbable creatures” certainly captures the essence of the flora, fauna and microbiota of Antarctica described in this fascinating retrospective issue of Scientific American Classics.
The very first voyages to the far south—in the 18th century—sought to answer physical rather than biological problems. Through their journeys, early scientists tested navigating longitude by astronomical observation, measured Earth’s magnetic field and searched for the then hypothetical southern continent. Of these cruises, only Captain James Cook’s expeditions included skilled naturalists who contributed to our understanding of the unusual life at high southern latitudes. Antarctic biology remained largely descriptive and an opportunistic stepchild to the physical disciplines throughout the 19th century, occurring on the margins
So it is that we arrive at the 20th and 21st centuries, the true beginning of Antarctic exploration and science—and the starting point for this Scientific American collection. Biological investigations of the southernmost continent came of age after the International Geophysical Year (1957–1958), as numerous nations broadened their research portfolios, set up permanent bases around the continent, and sponsored wide-ranging field research and cruises to study life in situ.
As this issue reveals, currently most of Antarctica’s life inhabits primarily the marine environment. This was not always the case, however. George A. Doumani and William E. Long describe a very different ancient environment in their 1962 article featured here. Via the fossil record, they paint a picture of temperate Permian Antarctic rain forests, similar to the modern Northwest U.S., replete with trees and the traces of animals. Jurassic, Cretaceous and Tertiary flora were also lush, and recent fossil discoveries document the presence of terrestrial dinosaurs in Antarctica during the Jurassic and Cretaceous periods. The similarity of the Antarctic fossil record to those of South Africa, Australia and New Zealand reinforced the concept of the southern supercontinent of Gondwana, which remained in doubt even as Doumani and Long wrote their key article half a century ago.
How did Antarctica descend to its current status, where it boasts no terrestrial vertebrates, no trees, few insects and just three flowering plant species? This transition is poorly understood and the subject of current debate, with a major extinction event (perhaps global in size) hypothesized to have occurred two million to three million years ago. We now look to the hardiest of the terrestrial survivors—viable microbes frozen for hundreds of thousands of years in ice, microbial communities living in the porous rocks of the Antarctic Dry Valleys, rich bacterial communities recently discovered in subglacial Lake Whillans—for clues not just for the history of Antarctica but also for the existence and nature of possible extraterrestrial ecosystems.
When we turn to the marine environment of the Southern Ocean, we encounter a very different story. Though somewhat restricted, life is nonetheless abundant here. The Southern Ocean is home to the “improbable” penguins William J. L. Sladen describes in his 1957 article in this collection—as well as their archenemies, the skuas, which Carl R. Eklund investigates in his 1964 piece. The frigid waters can also teem with seals, capable of prodigious feats of diving, which William S. Bruce explores in his 1894 piece (more than a century ago!)—as does Warren M. Zapol later in the 20th century.
And over the years scientists have discovered surprising animals in the Antarctic depths, including strange fishes that can synthesize antifreeze, as elucidated by Joseph T. Eastman and Arthur L. DeVries in their 1986 article.
Ice fishes, in particular, provide remarkable insight into the power of an extreme environment to shape life. As the Southern Ocean cooled from temperate conditions to its chronically frigid state—the freezing point of seawater near Antarctica is –1.87 degrees Celsius—during the past 40 million years, most major fish groups there became locally extinct. Today the fish fauna around Antarctica is dominated by species (approximately 100) of a single suborder, the Notothenioidei. Having been isolated in a freezing ocean for so long, these fishes (as well as marine invertebrates) can now live only at cold temperatures; in fact, most die if temperatures rise as little as five degrees C. As Eastman and DeVries describe, two astounding adaptations enabled these fishes to exploit this underutilized habitat: (1) they evolved potent antifreeze molecules that prevent their body fluids from freezing (a constant hazard in icy waters), and (2) some species of this swimbladderless group evolved neutral or near-neutral buoyancy (weightlessness in water), which allowed them to feed throughout the food-rich water column, in contrast to their denser, bottom-living relatives.
The ice fish family (which includes 16 different species) provides us with further surprises. During a visit to South Georgia in 1929, a young Norwegian marine biologist, Johan T. Ruud, thought he was being made the butt of a joke when he was told by whalers that some of the local fishes had no blood (fish known as blodlaus-fisk). Sure enough, no red blood emerged from them, which was puzzling because red blood cells and hemoglobin are thought to be constants in vertebrate life. Ruud was not able to return to South Georgia until 1953 to investigate this mystery, which he describes in “The Ice Fish” from the November 1965 issue. One of Ruud’s important conclusions was that evolutionary loss of red cells and hemoglobin could occur only in very cold and oxygen-rich waters—precisely the conditions of the Southern Ocean.
The articles in this collection are a fascinating time capsule that illustrates a century of progress in understanding the “improbable” life of the Antarctic. Our knowledge, however, is still incomplete, and we face an uncertain biological future as climate change grips the region. Forbush recognized that the reproductive success of the Adélie penguins was intimately tied to their physical environment. Whether life in the Antarctic, including the cold-loving fishes and invertebrates, has the capacity to adapt to rapidly increasing air and water temperatures and ocean acidifi- cation is an important question to ponder as you read on.
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