Nitrogen-rich runoff from sewers and farms is fueling a rise in invasive seaweed that, when consumed by the reptiles, may trigger an otherwise dormant herpes virus. This virus in turn causes the often fatal growths.

The cauliflower-like tumors—which can sprout on a turtle's eyes, mouth, joints, and internal organs—have contributed to declines in the 4-foot-long (1.2-meter-long) turtles. Listed as endangered by the International Union for Conservation of Nature, green sea turtles are found in the world's tropical and subtropical waters. (See sea turtle pictures.)

In some parts of Hawaii, where green sea turtle strandings occur regularly, as many as 90 percent of stranded dead or dying turtles discovered have been