Perfect example of spur and groove reef formation at Niau Atoll, Tuamotus, French Polynesia, South Pacific, Pacific

Typical Spur and groove reef formation, Cayman Islands, Caribbean

Barrel sponge (Xestospongia muta), large barrel sponge in spur and groove reef, Little Cayman Island, Cayman Islands, Caribbean

Barrel sponge (Xestospongia muta), large barrel sponge in spur and groove reef, Little Cayman Island, Cayman Islands, Caribbean

Barrel sponge (Xestospongia muta), large barrel sponge in spur and groove reef, Little Cayman Island, Cayman Islands, Caribbean

Divers swimming over spur and groove reef, Grand Cayman Island, Cayman Islands, Caribbean

A close look at the detail of Brain coral (Platygyra sinensis) during the day with the its polyps closed, Yap, Federated States of Micronesia

Mouth detail of a colorful and healthy mushroom coral (Fungia fungites) that is growing on a tropical coral reef. Mushroom coral is unique in the coral world, in that it does not attach itself to the bottom, Philippines

Mouth detail of a colourful and healthy Mushroom coral, Fungia fungites, that is growing on a tropical coral reef in the Philippines. Mushroom coral is unique in the coral world, in that it does not attach itself to the bottom, Philippines