Treasure under the sea
Great Barrier Reef teems with life off Australian coast
Unfortunately for Capt. James Cook, the man who mapped the Pacific Ocean and claimed most of it for the British Empire, the Great Barrier Reef lies underwater -- where it has snared many ships since grounding Cook's Endeavour in 1770.
The world's longest-spanning natural wonder (not including auroras) is ironically the most fragile. The 2,000-kilometer (1,242-mile) reef, which sweeps along the northeast coast of Australia, is made up of the skeletons of generations of marine polyps that lived and died just under the surface of the crystal clear sea.
Pollution, climate change and human intrusion are some of the factors endangering the delicate lime-based coral that covers some 344,000 square kilometers (137,600 square miles), often as close as 50 kilometers (31 miles) from shore.
The reef -- home to the current generations of polyps -- is also inhabited by many colorful and exotic species of marine life. Nearly microscopic fish co-exist with much larger whale sharks, countless shellfish and other fanciful creatures.