Bacterial mats are common the seafloor where oxygen is low. Mangroves of South Florida are threatened coastal development. Mangroves roots serve as critical habitat for many species and nutrient filters. Gravel-cobble bottom off Maine coast is favored scallop ground. Penguins explore snow-dunes in Antarctica 120.
Sponges are as important as corals for reef structure.
Florida Keys 1972 May 122. Reef fish use the reef for cover and food. Corals on the reef vary from large stony heads to whispy branches. Tiny coral animals build massive reef structures. Staghorn corals have declined at Caribbean reefs in the past 20 years.