Jim McMahon/Mapman®

Deep-sea explorers made a surprising discovery while mapping a section of the Pacific Ocean last fall. Off the coast of the island of Tahiti, divers found a healthy coral reef.

Based on the reef’s size, experts believe it has been around for at least 25 years. It’s deeper than most reefs—from about 100 to 230 feet below the ocean’s surface. 

Scientists say the reef’s location not only kept it hidden but also kept it safe. Reefs closer to the surface, where the water is warmer, are in danger because of rising ocean temperatures.

The corals in the reef near Tahiti are shaped like roses. Though they look like plants, all corals are tiny animals. Their hard outer skeletons form reefs. Corals get their nutrients, and color, from tiny plantlike organisms called algae. When the ocean gets too warm, corals release the algae and turn white. This process, called coral bleaching, can kill reefs.

Coral reefs are important ecosystems. Though they cover less than 1 percent of the ocean floor, reefs are home to about 25 percent of all marine species. Scientists say finding a healthy new reef is good news.