Now, we're diving the best of the Great Barrier Reef, a far-flung ledge called Osprey Reef. The first things you notice when diving Osprey Reef are the sharks, dozens of them, white-tipped and prowling just a few meters below your feet. They swim along the huge coral ledge, which starts at 10 feet and disappears into the dark blue depths of the Coral Sea. In such a remote place, so far out at sea, I expected to find perfectly healthy reef. Instead, I was shocked to find several bright white patches on the coral.
White coral is bad news.
It means it's dead, dying, or diseased. The animal part of coral is a close relative of the jellyfish. It gives coral their brilliant color. Corals filter what they can from the water, but they get about 95 percent of their food from this algae that lives in their tissues. Disease and predators kill corals and their zooxanthellae.