Global warming could make Antarctic waters more inviting to crabs and sharks that would threaten the continent's unique ecosystem, biologists in the US have warned.

University of Rhode Island biology professor Cheryl Wilga said Antarctica's waters were too cold for crabs, sharks and other fish to survive in, but global warming had caused temperatures to increase by 1 to 2 degrees over the past 50 years.

Few predators capable of crushing shelled animals lived in Antarctic waters, Professor Wilga said.  "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," she said.  "Once they get there, it will completely change the ecology of the Antarctic benthic community."