Organisms Abound Below Sea Ice

The occasional skua swooping around McMurdo Station scavenging for food, or the odd seal lounging next to a crack in the sea ice, is generally the only reminder for many here that there is life in the Antarctic aside from human beings.

But below the swath of seemingly impenetrable ice that separates the station and the Royal Society Range, about 65 kilometers away, a riotous and colorful marine community thrives in McMurdo Sound.

“It’s one of the cool things about diving down here: it’s so stark on the surface, and then you get underneath and it’s lush under there. There’s tons of critters,” said Rob Robbins, dive supervisor for Raytheon Polar Services Co., the National Science Foundation contractor charged with logistical support of the U.S. Antarctic Program.

Robbins knows better than most about the plethora of life in McMurdo Sound, having spent more than two decades diving here. There are few critters he can’t identify, and scientists rely on his expertise to choose a dive site depending on what organism they’re studying.

For example, scientists Amy Moran and Art Woods are making their first dives in McMurdo Sound, so they’re taking Robbins’ advice to explore the Intake Jetty dive site near McMurdo Station as one study location. It’s an area rich with nudibranchs, or sea mollusks with no shell.

Moran, the principal investigator (PI), and Woods, the co-PI, are studying how the egg masses of nudibranchs respond to cold and oxygen. They believe that the higher oxygen content of cold waters may allow the embryo masses to reach much greater size than they would in lower latitudes. Oxygen levels are double compared to those closer to the equator, they say.

There are about 3,000 species of nudibranchs worldwide, though only perhaps a half-dozen or so are represented in McMurdo Sound.

On the other hand, Sam Bowser has his hands full with the plethora of foraminifera around Explorers Cove across the sound from McMurdo Station. These single-celled organisms, referred to as forams for short, are an ancient and prolific life form that he says are not very well understood. But he knows of nowhere else in the world where he can find such a great diversity of the early evolving forams, whose evolutionary birth date may go back 650 million years.

Moran and Bowser are the only PIs leading groups under the sea ice this year to study the many kinds of critters in McMurdo Sound. While few other coastline areas of Antarctica have been as thoroughly explored, the larger view of the ecosystem is still a little fuzzy.

So, what is down there?

Of course, there are far more species of animals in McMurdo Sound than just forams and nudibranchs. Bowser says he sees Antarctic scallops and sea spiders everywhere on the silty sand bottom of Explorers Cove. Sea stars and sea urchins dominate where Moran and Woods have been diving on the other side of the sound. Fish, sponges, anemones and other soft corals also abound in the shallow depths where divers blow bubbles.

While the animals that live both above and below the sea ice, like AdÈlie penguins or Weddell seals, are probably the most emblematic of the sound, they are in the minority of life forms.

“Life here is way dominated by the invertebrates,” Robbins noted. “You see some fish but not many of them. On a coral reef, you see lots of fish.” For the armchair marine scientist or the Antarctic researcher needing to identify an animal, there is at least one online resource devoted specifically to this region. The Underwater Field Guide to Ross Island and McMurdo Sound features dozens of close-up, color photos of everything from forams to featherduster worms to krill and other crustaceans.

Peter Brueggeman, library director at the Scripps Institution of Oceanography, maintains the Web site (http://siolibrary.ucsd.edu/nsf/fguide/). The project was one of the original goals that brought famed underwater photographer Norbert Wu to the Antarctic beginning in 1997, according to Brueggeman. Wu’s photographs provided the core collection of pictures.

“It’s pretty extensive, and it’s a huge help for the researchers down here,” Robbins said of the online field guide.

Brueggeman, who accompanied Wu to McMurdo Sound in 1997 and 1999, has devoted “hundreds of hours” to creating and maintaining the Web site. During a phone interview, Brueggeman said he still receives photos from McMurdo divers, crediting Robbins as a key contributor.

“He knows where to find the uncommonly seen animals,” Brueggeman said.

Brueggeman’s detailed and annotated text accompanies individual photos. For example, he writes that “Antarctic and subantarctic sea spiders comprise 251 species, representing 21.5 [percent] of worldwide species, with 101 species en demic to Antarctica and 60 endemic to subantarctic areas.”

Brueggeman is always on the lookout for more photos of animals and specific behaviors. One item on the wish list includes a sponge called Asbestopluma lycopodina. He is after a macro photograph showing the carnivorous sponge, which somewhat resembles a pipe cleaner, capturing tiny crustaceans such as krill on Velcro-like protrusions called spicules.

While there are still blanks to fill, Brueggeman said he believes the online field guide is a fairly unique resource that has proven valuable for marine ecologists and others.

“It’s given a lingua franca for the scientists and students to talk among themselves,” he said.

A different kind of resource also grew out of Wu’s visits to McMurdo Sound. The book “Under Antarctic Ice: The Photographs of Norbert Wu” features pictures of the marine environment, accompanied by text from Jim Mastro. A professional writer and photographer, Mastro worked in Antarctica on and off for 23 years as a scientist, diver and science laboratory supervisor.

Mastro said via e-mail that the book synthesizes “40 years of research into a natural history of the sound. It’s the only place that’s been done, to my knowledge.”

For science divers, there is an “Antarctic Scientific Diving Manual” that describes 20 established dives sites around the sound in detail. Information includes common fauna and the benthic geography a diver may find. Always questions to answer

Much of the early coastal and benthic, or seafloor, ecology of the sound was conducted by Scripps researcher Paul Dayton and a few others in the 1970s. Dayton spent more than 50 months in McMurdo Sound, performing research during more than 500 dives under the ice. Other scientists followed in the 1980s and 1990s for some additional broad ecology research, but a full-scale study of the ecosystem has never come forward.

“Now people are looking at specific questions. A lot of microbiology,” Robbins said.

Moran noted that bathymetric studies of the McMurdo Sound seafloor, unrelated to her own fieldwork, showed deep troughs or gouges where icebergs have pushed through the region. “It’s one of the most disturbed ecosystems in the world,” she said. “It’s different from other ecosystems in that it’s structured by ice.”

That statement has been particularly true over the last decade due to heavy ice cover in McMurdo Sound. At some dive sites, the divers must bore down about six meters to reach the nearly freezing salt water.

Robbins said he hasn’t noticed any changes in the region’s ecology due to the long-term ice cover. The thick ice does make for some claustrophobic diving, however.

“It’s dark,” he said. “Normally you go out there and it’s light. You dive under the ice and there’s this big glowing light. Before this started happening, you just didn’t need [flashlights].”

While individual investigators will continue to study the specialized components of the McMurdo Sound ecosystem, a broad scale ecosystem investigation, such as the Long Term Ecologic Research programs at Palmer and the McMurdo Dry Valleys, has not been initiated.

“It’s interesting that in an area that’s been so intensively studied, [McMurdo Sound] has not been documented very well,” Bowser noted. “We really need some fundamental information.”

Some basic information that would be helpful includes bathymetry and other physical measurements, such as water temperatures and currents.

“There are no comprehensive studies, and so much remains unknown,” Mastro said, echoing Bowser’s sentiments. The list of questions is long, according to Mastro.

“What about all those amazing critters from the deepest parts of the sound that sometimes show up in fish traps? What about the mid-water ecology?” he asked. “What about all the unknown interactions between benthic invertebrates? Why do the sea urchins tend to move up into the anchor ice at about the same time they spawn?

“Lots of questions, no answers.”

NSF-funded research in this story: Sam Bowser, New York State Department of Health Division of Molecular Medicine, www.bowserlab.org; Amy Moran, Department of Biological Sciences at Clemson University, http://www.clemson.edu/biosci/faculty/moran/lab/Antarctic_research/Index.html; Art Woods, Division of Biological Sciences at University of Montana; and Norbert Wu, U.S. Antarctic Artists and Writers Program, www.norbert wu.com.