In recent years, coral in the seas around Okinawa Prefecture has been turning black and dying off due to a particular variety of coral-killing sponge called Terpios hoshinota.

“It's otherwise known as the 'Black Devil.' The way the damage is spreading poses a new threat to coral,” says Hideyuki Yamashiro, a professor at the University of the Ryukyus' Tropical Biosphere Research Center. "I want to develop research and stop the damage."

The sponge is like a sheet of paper of about 1 millimeter thick and attaches itself to coral’s calcareous skeleton. It expands by 1 to 2 millimeters every day, covering the coral in black material.