The coral reefs of Dry Tortugas National Park harbor a rich and colorful variety of marine life such as fish, sponges, sea stars, and anemones. Clear waters with excellent visibility attract snorkelers and SCUBA divers to the park, which offers some of the best underwater viewing opportunities in the United States.
The park is home to about 30 species of coral. Corals are marine organisms that typically live in colonies consisting of many individual soft-bodied organisms called polyps, each only a few millimeters in diameter. After a polyp attaches itself to a hard substrate on the sea floor, it divides itself into thousands of clones. The polyps cement themselves to each other by secreting a skeleton of calcium carbonate, thereby creating a colony that acts as a single organism. Over the course of hundreds to thousands of years, the colonies join together to form reefs.