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The University of Montana
Living Large in Antarctica
Scientists study polar gigantism
Andes to Amazon Adventure
UM offers remote South American
CO2 Sea Change
Researcher studies ocean impacts
on global warming
Growing UM center tests limits of
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Living Large in Antarctica
Scientists study polar gigantism
Friendly had become a problem.
Every time University of Montana researcher Art Woods and his colleagues dove under the Antarctic ice at one of their main collecting sites, Friendly was there. The 1,000-pound Weddell seal shadowed them like a finned blimp as they hunted nudibranchs — strangely beautiful sea slugs — as well as egg masses and other specimens.
Sometimes Friendly would shoot off into the gloom for 10 minutes or more, but he never strayed far. He would return with eerie vocalizations that sounded to Woods like a movie flying saucer coming in for a landing. A few times Friendly surfaced in their dive hut placed atop an access hole drilled through a dozen feet of sea ice. The seal would float like a cork, take a nap, fill the hut with his fishy breath and then inhale deeply before swimming on.
The divers enjoyed Friendly at first. He added magic to Antarctica’s 28-degree water world of fish, worms, jellies and centuries-old sponges — all roofed in frozen white. And despite their size, Weddell seals are docile and rarely hostile to humans.
Of course they can still cause problems. Near the end of one dive, the researchers returned to their access hole to find tail flippers hanging down and Friendly’s vast cylinder of blubber plugging their only escape route to the surface.
The divers were cold after being submerged for 35 minutes. What to do? People working at the U.S. science base on McMurdo Sound aren’t supposed to bother local wildlife, but Friendly seemed in no hurry to move.
After several long minutes giving one another “Now what?” looks, the divers tried sending air bubbles up the access hole to rouse Friendly. Weddell seals are supposedly skittish, but Friendly didn’t budge. Finally, growing worried, they tugged a tail fin.
“Instead of scattering, he just came down the hole and floated up right under the ice to watch us,” Woods says. “It was like he said, ‘OK, you can go now.’ Whew!”
That was one of many I’m-not-in-Montana-anymore moments Woods experienced while working in Antarctica supported by National Science Foundation funding. He went to the bottom of the world during October and November (the Antarctic spring) 2006 and again in 2007. He did 25 dives in 2006 and 35 last year. A primary goal: learn how water temperature affects animal metabolic systems.
Woods, an assistant professor in UM’s Division of Biological Sciences, chose nudibranchs to study because they are diverse, occurring in thousands of fantastic varieties around the globe. They also are simple creatures that use reproductive structures called egg masses — basically slug snot embedded with embryos.
Between trips to Antarctica, Woods also studied nudibranchs off the coast of Washington at the Friday Harbor Laboratories.
“We were interested in this latitudinal comparison of how their physiology works,” he says. “The idea of going all the way to the end of the Earth is that animals often do really extreme things in extreme environments.”
In the case of Antarctic nudibranchs, they get really big. It’s a phenomenon called polar gigantism. Woods says cold water contains more oxygen and, more importantly, it depresses metabolic rates, so animals consume oxygen less quickly. This means they actually live more slowly. The same holds true for their egg masses.
“Off the coast of Washington and Oregon, nudibranchs might be babies in the egg mass for two weeks,” Woods says, “but in Antarctica they can be inside the egg mass for a year and half. In addition, the babies they produce are 20 to 30 times as large as those off the West Coast. The egg masses are bigger, and the embryos within them are gigantic.”
Why? Woods and colleagues are testing the idea that Antarctic species have a much easier time getting oxygen to all their tissues.
“So if you are living really fast and you are really hot, it might be good to be small, because then you can still get oxygen to your middle tissues easily,” he says. “If you are living slowly and there is plenty of oxygen around, then you can afford to get really big without suffering from oxygen constraints.”
Slow-living nudibranchs move at glacial speeds. Woods says if your collecting bag gets full, you can set one on an interesting landmark and come back during the next day’s dive. It will still be there.
Woods’ research is complicated by the fact none of his study species occurs in both Washington and McMurdo Sound. So he compares different varieties and then takes into account how closely related they are to one another. This has led to creation of a nudibranch phylogeny — a family tree that describes the evolutionary relationships among sea slug species.
Woods’ main research partner is Amy Moran of Clemson University. One of her graduate students, Chris Shields, has made the phylogenetic tree his research focus, trying to determine how Antarctic nudibranchs are related to those in the rest of the world. If Antarctica is an isolated sea slug outback, then they should be most closely related to their neighbors. However, the genetic work has shown that most Antarctic sea slugs are more closely related to nudibranchs in other oceans. This suggests the southernmost continent has been invaded by nudibranchs many times in the past and that it’s not that difficult for them to migrate there.
Woods says his group’s genetic research has doubled the number of described nudibranch species in McMurdo Sound to about 16.
“It wasn’t our main goal to find new species,” he says, “but it’s amazing to me that you can go somewhere in the world and — with not much effort — double the number of known species. It’s remote there, but you would think in this day and age the fauna would have been sampled pretty well.”
Another species the researchers became interested in are pycnogonids, or sea spiders. They are relatively small on the West Coast, but once again they become gigantic in Antarctica, growing to a foot wide or more. Woods says on many under-ice dives, he could spot 30 at once.
“They weren’t skittering around,” he says of the slow-moving creatures that use a proboscis to eat sea anemones and other immobile bottom dwellers. “You aren’t going to get mobbed by sea spiders.”
To study whether big sea spiders are more affected by oxygen constraints than smaller ones, Woods’ team set up an experiment in the NSF’s state-of-the-art lab aquariums at McMurdo Station. This involved an “aerobic workout” in which the spiders were turned on their backs. Most animals hate to be exposed on their backs, and the team measured how often the pycnogonids could right themselves in an hour. The exercise was done in normal McMurdo seawater and then water with reduced oxygen content.
Some big ones could only right themselves twice an hour, while a few smaller super-athletes could un-flip themselves 200 times.
“The idea was the big ones evolved because they were released from oxygen constraints,” Woods says. “If so, low levels of oxygen imposed experimentally should impact the big ones more than the smaller ones.
But we found they all suffered equally. That’s how it goes. Maybe our workouts weren’t realistic. Or maybe it’s easier for spiders — with their extended, elongate bodies — to get oxygen to all of their tissues regardless of their size.”
Woods also studies what would happen if Antarctic seas grow warmer from climate change. When environmental change strikes an area, many species often choose to migrate. But Antarctic sea creatures trying to stay cool would be stuck, he says, because they have a continent in the way to colder climes in the south. Water a few degrees warmer also could speed up metabolic rates.
“You could get a decoupling of life cycles from the seasonal pulses of light and algae that happen (each summer) down there,” he says. “Many species might go extinct or be forced to evolve to survive.”
After studying moderate ocean off Washington and cold Antarctic waters, the next phase of Woods’ research could take him to some of the warmest seawater in the world — the Solomon Islands in the South Pacific.
“The water there is the heart of nudibranch diversity,” he says. “What happens when you heat water up a lot? Do you see really small nudibranch egg masses? We plan to write a grant to take us there.”
— By Cary Shimek
UM’s Art Woods waits for Friendly the Weddell seal to vacate a dive access hole in Antarctic sea ice. (Upper right) A common nudibranch in McMurdo Sound. (Bottom right) A large sea spider placed on the head of researcher Amy Moran. (Photos by Chris Shields, Jon Sprague and Bruce Miller.)
|Art Woods on the ice (Photo by Amy Moran)