As the Earth warms from the buildup of carbon dioxide in its atmosphere, the oceans that cover 70 percent of its surface are warming too. This warming will likely benefit some marine species at the expense of others.

A study in the May 20 issue of the journal Nature confirmed that there has been a warming trend in the world's oceans since 1993, as the waters have absorbed much of the excess energy in the planet's atmosphere.

The warming that has already occurred, and is expected to continue in the coming decades, will likely spell bad news for many ocean species, such as corals and species that dwell in the cold waters of the planet's poles. But some creatures beneath the ocean surface might actually have an advantage in the newly warmed waters.

A 2008 study, for example, revealed that a warming of just a few degrees Fahrenheit in Antarctic waters could make them hospitable to sharks, which haven't lived in the area for about 40 million years. It's easier for sharks to maintain their high metabolism in warmer waters. If sharks do migrate into the area, they could wreak havoc on the existing ecosystems of the oceans around Antarctica.

A study of starfish found these iconic ocean dwellers grew faster in water at warmer temperatures and higher carbon dioxide levels (another result of all the extra greenhouse gas in the atmosphere) than at normal conditions which is bad news for the clams, mussels and other bivalves they prey on.

Work by Jeremy Jackson, a professor of oceanography at Scripps Institution of Oceanography at the University of California at San Diego, suggests that ocean warming along with other threats such as overfishing and habitat destruction could convert once complex ocean ecosystems into ones that favor simpler species, such as microbes, toxic algal blooms and jellyfish.