Ahermatypic Coral Banks: Living and Fossil Counterparts

Reef-like structures referred to as banks are produced by framework-building ahermatypic scleractinians in cool water at various depths, usually below those of hermatypic shallow-water reef corals. The distribution of Holocene banks is closely related to the ecological requirements of the ahermatypic corals. Fifteen major regions of bank development are known today in the Atlantic and Pacific and these banks vary widely in composition and ecological structure. Newly discovered living banks come from the Subantarctic South Pacific and off the coast of Chile. Emphasis is given to the high fauna! content but low coral species diver.sity as well as the potentially high predation pressures which can exist on these banks. Only eight widely scattered fossil examples are known. These range from Triassic to Tertiary in age and, Uke living examples, each varies in composition and structure. It is suggested that the earUest scleractinian corals of the Triassic were ahermatypic and that the development of extensive shallow-water coral reefs in post-Triassic time was related to the acquisition of symbiotic algae (zooxanthellae). Caution is urged in the interpretation of all ancient reef-like coral accumulations since deep-water banks can superficially resemble shallow-water reefs. Increasing amounts of new information of Holocene examples can yield considerable insight into recognition of ancient counterparts.