Sulu-Sulawesi Sea [huanqiu.com]

13. The Sulu-Sulawesi Sea, with neighboring Indonesian Seas and South China Sea, lies at the center of the world's tropical marine biodiversity. The coral ecosystems here are some of the most diverse on Earth, with more than 450 species of scleractinian, or stony, corals -- compared to 50 in the Caribbean and approximately 200 in the western Indian Ocean.

Encircled by three populous, developing nations, the Philippines, Indonesia and Malaysia, the Sea and its adjacent coastal and terrestrial ecosystems support about 33 million people, most with subsistence livelihoods heavily reliant on their renewable natural resources. But these resources are being impacted severely by rapid population growth and over-fishing.