Aloha Extinction: Earthwatch volunteers survey Maui's threatened reefs, led by Eric Brown of the Pacific Whale Foundation. Photo: Earthwatch

Pacific Ocean coral reefs are some of the world's healthiest overall; about 70 percent are rated in good-to-excellent condition. But 30 percent are rated fair-to-poor—many are dying, and human impacts are growing: The region's extremely diverse corals, mangroves, and seagrasses are pressured by deforestation, agriculture, construction, and pollution. Those in the best shape are off Australia's Great Barrier Reef, Papua New Guinea's atolls, New Zealand's Cook Islands, and the Micronesian nations of the Caroline Islands.

Many nations here still lack any protected coral areas, but the Pacific has recently become the focus of vigorous reef conservation work, and island governments across the region are acknowledging that their own existence is very much tied to the health of their coral reefs and the thousands of marine species that depend on them.