diverse underwater ecosystems held together by calcium carbonate structures secreted by corals. Coral reefs are built by colonies of tiny animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps belong to a group of animals known as Cnidaria, which also includes sea anemones and jellyfish.
Florida Keys National Marine Sanctuary visitor Daryl Duda spotted this balloonfish at Pickles Reef. At night, balloonfish hunt the reef for mollusks and crustaceans. When threatened, a balloonfish can inflate its body by taking in water, making its spikes stand out defensively!