Florida's coral reefs have been in hot water the past two summers.
Scientists hope to find out if global warming's behind it.
Home to an undersea wilderness, the reefs also protect the low-lying islands of the Keys from storms that would otherwise erode the land and wash away beaches. The Acquarius submerged lab lets scientists monitor the health of the Conch coral reef, an ecosystem as complex as a tropical rainforest. But the reefs are in trouble. The warmer water can bleach the colorful algae from the corals, leaving a white skeleton instead of the pastel robes that normally cloak the reef. If the event is not too serious they can recover, but sometimes they die.