Brok en-down calcareous green algae are a source of carbonate sand for sandy bottoms and beaches. In addition to the corals, many other animals feed, hide, and rest in the complex reef habitat. Sponges in brilliant colors grow as both encrusting patches and as freestanding shapes, including vase and basket sponges. Some mollusks live on the reef, b ut many more live in the sandy areas and grass beds around the reef. Arthropods such as crabs, shrimp, and spiny lobsters hide in the many nooks and crannies of the reef.
Fish are the most prominent animals of the reef.
They exhibit glorious colors and fascinating ways of living. These specializations provide efficient means of feeding, schooling, and protection for a variety of fish, and enable large numbers of different types of fish to use all the areas of the reef as feeding, resting, or hiding places during the day and night. The rock-hard skeletons of corals do not protect them from all of the fish that inhabit the reef. These teeth are fused together into upper and lower plates. This allows these fish to graze on algae which grows on dead coral, as well as zooxanthellae in live coral, by crunching pieces of the hard surface with the attached vegetable matter.