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Jaws II Sharks are next in the supper line. Spiny dogfish, in particular, are already abundant off the coast of South America, poised for invasion as soon as the water gets a tad warmer, says Wilga. The cold poses a different set of challenges for sharks, she explained. For one thing, sharks need to keep swimming to stay afloat, which requires a lot of energy. Very cold water slows them down to the point where it's hard to keep swim muscles moving. Shark bodies are also infused with a chemical called triethylamine oxide (TMAO), which counters the toxic effects of urea that builds up in shark tissues. The colder or deeper the waters, the more TMAO sharks need to offset the urea, Wilga explained. Sharks appear to reach a TMAO limit before they can reach Antarctic waters. But if there's any shark that can eke out a living first in the warming waters, Wilga is putting her money on the diminutive and virtually global spiny dogfish. While this is more bad news for the Antarctic sea lilies and brittle stars, there will be a sliver of a silver lining to the sharks' return, said Wilga: "Sharks also eat crabs." A Moving Feast Some other marginally good news is that the seafloor invasion may have little effect on the better known animals of Antarctica -- penguins, fish and whales. These live on what is essentially a separate, krill-based, shallow-water food web, explains Antarctic marine biologist Robert Pitman of National Oceanic and Atmospheric Administration's Southwest Fisheries Science Center in La Jolla, Calif. The top predator in the shallow water ecological realm is the orca, or killer whale, Pitman said. There are, in fact, more killer whales in Antarctica than anywhere on Earth. And if anything, dogfish will be welcome aperitifs for them, he explained. Global warming might fill orcas' bellies in other ways as well, Pitman told Discovery News. Penguins, seals and Minke whales need lots of ice to hide from the fierce and intelligent marine mammal. The less ice, the easier the hunt. "The best protection seals and penguins have from killer whales is on the ice," Pitman said. "Even offshore, the Minke whales migrate to pack ice for protection from killer whales." So as the waters warm and the ice melts, Antarctica's existing predators may enjoy some feast days of their own. Thwarting the Invasion The predator invasion of Antarctica may be unavoidable, say the researchers, but it could be moderated if something is done immediately to reduce emissions of global warming greenhouse gases into the atmosphere. "As global warming proceeds, the deeper water (around Antarctica) will only get warmer," said Aronson. The momentum of global warming is, indeed, huge and can not be stopped, he said, but it can be slowed. "If we're going to do something about the planet we have to do it now." Aronson said. "The window is closing."
Satellites Track Antarctica's Penguins |
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