Research Communications

Life Under Ice 

Biologist Lisa Crockett explores how the unusual icefish survives the frigid climate of Antarctica

Nov. 2, 2010

As a child, Lisa Crockett was regaled with tales of an icy wonderland. In her mind’s eye, she saw the frozen plains, the looming ice formations, the gleaming snow. She heard the barking of sled dogs as they raced across the barren landscape. She pictured the fur-clad driver poised behind the dogs, like a gladiator guiding a chariot of horses into battle. She sensed the man’s spirit of adventure, his wild excitement.

The character in Crockett’s childhood stories was her father. A dog handler for the first team of Americans—the Byrd Antarctic expedition (1928-1930)—to explore the Antarctic wilderness, he helped to conduct geological surveys and to discover places that had never before been seen by human eyes.

“He was my hero,” she says. “I loved listening to his stories.”

Lisa Crockett's father
Lisa Crockett became fascinated by Antarctica after hearing stories from her father, above, a dog handler for the first team of Americans to explore the wild, cold continent.

When her father died in 1978, Crockett, who now is an associate professor of biological sciences at Ohio University, vowed to visit the continent that he had loved. “I knew then that I would do just about anything to get myself to Antarctica,” she says.

As it happens, she had only to work as an assistant for a biological researcher to realize her dream. She made her first trip to the icy continent in 1980. “It was the most beautiful place I could imagine,” she says. “It had the same magical quality that captivated me as a child.”

In her travels, Crockett encountered majestic emperor penguins, massive humpback whales, and meat-eating leopard seals. But it was another animal—a much more bizarre animal—that would become the focus of her research.

In the frigid waters of the Southern Ocean there lives an extraordinary group of fishes with blood as white as snow. Known as the icefishes, the group lacks hemoglobin, the iron-containing protein that transports oxygen throughout the bodies of red-blooded animals and gives their blood its ruddy color.

“The icefishes are an exceptional group of animals,” she says. “They are the only vertebrates in the world that lack hemoglobin as adults. My goal is to find out whether the lack of hemoglobin provides some benefit to the animals.”

Lacking hemoglobin, the icefish have unusual white blood
Photo Credit: Dr. Jody Beers. Lacking hemoglobin, the icefish have unusual white blood.

According to Crockett, scientists previously assumed that there must be an energy advantage associated with the loss of hemoglobin in the icefishes. Perhaps without hemoglobin, the blood is less viscous and, therefore, easier to pump? they wondered. But research eventually revealed that to compensate for the lack of hemoglobin, the icefishes evolved a number of traits, including a massive heart with which to pump large volumes of blood to their tissues.

“The icefishes actually expend twice as much energy as red-blooded fishes of the same size to circulate blood throughout their bodies,” Crockett says. “It turns out that the loss of hemoglobin likely was a fluke caused by a sub-lethal mutation in the DNA that never righted itself.”

Despite the apparent lack of a benefit to their unusual physiology, the icefishes persist in the Antarctic alongside their red- blooded brethren. According to Bruce Sidell, a professor of marine sciences at the University of Maine and one of Crockett’s collaborators, the icefishes require very cold temperatures in order to survive. Cold temperatures reduce the animals’ metabolic rates, reducing their demand for oxygen, he says.

Although the icefishes thrive in cold water, Crockett and her colleagues have shown that the creatures are less capable of dealing with warmer temperatures than their red-blooded relatives. “This finding suggests to us that the icefishes may be in trouble as global warming causes ocean temperatures to rise,” Crockett says.

In April 2009, Crockett boarded a plane to Punta Arenas, Chile, the southernmost city in the Americas. Upon landing, she visited a warehouse stocked by the National Science Foundation, where she picked up a red parka, some extra-thick gloves, and a woolen hat. Supplies in hand, she climbed aboard the Laurence M. Gould (named for the second-in-command of the first Byrd Antarctic expedition and a favorite colleague of Crockett’s father) and looked southward toward her destination: Antarctica. There, she and her colleagues Sidell and Kristin O’Brien, associate professor of biology and wildlife at the University of Alaska, planned to investigate the physiological and biochemical underpinnings of warm-water sensitivity in the icefishes.

Having previously made the journey to Antarctica nine times, Crockett knew what lay ahead. The Drake Passage contains some of the roughest seas in the world, with swells that can reach 70 feet. “Most of us get sick at some point,” she says.

This time, however, the team was lucky. The four-day voyage turned out to be fairly uneventful. When they arrived at the research station, the scientists checked into their dormitory-style rooms and settled in for the long haul. It would be two months before they would return to their homes.

During their stay, they went on several fishing expeditions, each lasting three to four days. They worked in 12-hour shifts, dragging nets along the bottom of the sea to capture both icefishes, which are about 18 inches long, and red-blooded fishes. The traps yielded dozens of fantastical creatures: pale-pink sea stars, feathery crinoids, and fluted deep-sea corals. These the biologists threw back into the sea. The fishes, however, with their gaping mouths full of sharp teeth, the team wrangled into holding containers.

The creatures, about 18 inches in length, play an important role in the Antarctic ecosystem
Courtesy of Lisa Crockett.

Back at the research station, they placed the fishes into 500-gallon tanks. To determine how elevated temperatures would affect the animals, the team slowly increased the water temperature from the natural temperature of about 30 degrees Fahrenheit to about 55 degrees Fahrenheit. “At a certain temperature, the fishes lose their equilibrium,” Crockett says. “They begin to swim awkwardly; they go belly up; and, eventually, they would die.”

The team found that the icefishes are less tolerant of elevated temperatures than their red-blooded relatives. According to Crockett, at higher body temperatures, all animals experience greater oxygen demands because their metabolism revs up. The icefishes— because they don’t have the hemoglobin that the red-blooded species have—may not be able to meet that higher oxygen demand. “Our research has shown that at a certain elevated temperature, the icefishes die, while the red-blooded fishes survive,” she says. “Like canaries in a coal mine, the icefishes are sentinels for climate change.”

Crockett said that the western side of the Antarctic Peninsula, where the team conducted their fieldwork, has suffered from some of the greatest warming on the planet. In fact, during the 2009 trip—Crockett’s first visit to the continent in 20 years—she was shocked to see the tremendous changes that had taken place as a result of climate change. “I used to take a break from my research to explore this massive ice cave,” she said. “But in 2009, the cave was gone. Even the glacier behind the research station had retreated considerably.”

According to Crockett, so little is known about these animals that the impact of their potential loss in the ecosystem is unknown. “There are 16 species of icefishes,” she says. “Some eat krill; some eat small fish; some hang out at the bottom of the ocean; and some are pelagic. There is no doubt in my mind that they play important roles in the Antarctic ecosystem.”

Although Crockett and her teammates know that the icefishes are more sensitive to warm water than red-blooded fishes, they have yet to determine why. Is it because the icefishes lack hemoglobin or is some other factor to blame for their sensitivity? To find out, they are looking deep inside the animals’ cells.

Crockett explains that the icefishes have very high densities of mitochondria—energy- producing structures—in their cells, and that this proliferation of mitochondria may enable the animals to produce the energy they need to stay active in very cold water. However, in addition to producing energy, mitochondria also create molecules that are highly reactive. According to Sidell, these reactive molecules can threaten the integrity of biological membranes.

Crockett believes that as temperatures rise, the mitochondria in the cells of icefishes begin to work harder to produce energy, thus triggering the creation of more and more of the dangerous reactive molecules (such as oxygen radicals). “Eventually, the stress caused by these molecules may kill the fish,” she said. “But what’s really interesting is that the lack of hemoglobin—despite the fact that it prevents the icefishes from meeting the higher oxygen demand required to survive in warmer waters—may help the icefishes by protecting them from this stress.”

The creatures, about 18 inches in length, play an important role in the Antarctic ecosystem
Courtesy of Lisa Crockett. The creatures, about 18 inches in length, play an important role in the Antarctic ecosystem.

From her office in Athens, Ohio, Crockett already is planning her next research trip to the Antarctic, which is slated for spring 2011. There she will begin to investigate whether the loss of hemoglobin provides some protection against oxidative stress, and will explore other topics related to warm-water sensitivity in the icefishes.

She expects that her research on the icefishes will yield valuable information that can be applied to a variety of organisms. “Many animals, including the striped bass that is the focus of another of my studies, undergo biochemical and physiological changes at low temperatures,” she said. “My work on the icefishes is an important step toward understanding how animals, in general, respond to cold temperatures.”

As she makes her travel arrangements, Crockett thinks about her father and imagines what his reaction would be to the dramatic changes that have taken place in the icy continent. “I think my father would be as sad as I am to see the snow melting, the glaciers retreating, and the ice caves disappearing. After all, he was crazy about snow and ice. He taught me to ski and to build igloos, which was easy to do growing up in New England. It’s because of him that I love the cold. It’s also because of him that I found my work in Antarctica."

By Sara Lajeunesse

This article appears in the Autumn/Winter 2010 issue of Perspectives magazine.