October 5, 2009--Marine biologist Serena Fonda Umani approaches a blob of dead and living organic matter, called a mucilage, in the Adriatic Sea, an arm of the Mediterranean, in 1991 (Adriatic Sea map).

Umani, of Italy's University of Trieste, remembers diving about 50 feet (15 meters) down when she got the sensation of a ghost floating over her--"sort of an alien experience."

Enormous sheets of such "mucus" occur naturally throughout the Mediterranean, especially in the Adriatic. But in recent years, as sea temperatures have risen, these sea congregations are exploding in number and size--sometimes stretching over hundreds of kilometers, generally near coastlines, according to a study published in September 2009 in the journal PLoS One.