Warming could bring sharks to Antarctica with devastating ecological consequences

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Warming could bring sharks to Antarctica with devastating ecological consequences
mongabay.com
February 15, 2008

Global warming could make the waters around Antarctica hospitable to sharks for the first time in 40 million years. Their return could have devastating ecological consequences report researchers from the University of Rhode Island.

Analyzing the physiological adaptations and metabolism of sharks and other predators, Cheryl Wilga and Brad Seibel found that an increase of just a few degrees Celsius could make Antarctic waters habitable for Benthic sharks, species that live on the seafloor and swim very little. Ocean-going sharks, which have a high metabolism rate because they must swim constantly to aerate their gills, would not survive in the cold waters around Antarctica.

Still Wilga and Seibel say that because "they cannot swim great distances and do not produce a larval stage capable of wide dispersal, it is unlikely [Benthic sharks] could easily get to Antarctica on their own."

Nevertheless, should sharks reach the Antarctic, they would likely have a significant ecological impact say the researchers.

Though it lives in cold waters, the leopard shark could not survive in the Antarctic. Unlike benthic sharks, the leopard shark must swim constantly to aerate their gills, requiring a high metabolism and large amounts of energy.

"There are few prey-crushing predators in Antarctic waters. As a result, the Antarctic seafloor has been dominated by relatively soft-bodied, slow-moving invertebrates, just as in ancient oceans prior to the evolution of shell-crushing predators." said Wilga. "The water only needs to remain above freezing year round for it to become habitable to some sharks, and at the rate we're going, that could happen this century. Once they get there, it will completely change the ecology of the Antarctic benthic community."

Wilga and Seibel that shrimp, ribbon worms and brittle stars will likely be the most vulnerable to population declines should sharks make it to the Antarctic.

"Ice fishes — the only bony fish that now lives in Antarctic waters, because it has antifreeze in its system — will face a new threat as well," Wilga added. "They are already preyed upon by seals and penguins. Adding sharks and other bony fishes to the mix will likely have a big affect on them."

Warming seas could also help crabs. Currently "cold Antarctic water reduces their ability to flush magnesium from their blood, leading to magnesium narcosis and death", according to a statement from the University of Rhode Island, but higher temperatures are enabling crabs to closer to the Antarctic.

The waters around the Antarctic Peninsula have warmed by 1 to 2 C in the last 50 years, a rate that is about double or triple the global average.

Wilga and Seibel's study, "None Like It Cold: Physiological Constraints on Predators in Antarctica," was presented today in Boston at the annual meeting of the American Association for the Advancement of Science.

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