Between 1966 and 1978 SCUBA investigations were carried out in French Polynesia, the Red Sea, and the Caribbean, at depths down to 70 m. Although there are fewer coral species in the Caribbean, the abundance of Scleractinia in deep-water associations below 20 m almost equals that in the Indian and Pacific Oceans. The assemblages of corals living there are described and defined as deep-water coral associations. They are characterized by large, flattened growth forms. Only 6 to 7 % of the species occur exclusively below 20 m. More than 90 % of the corals recorded in deep waters also live in shallow regions. Depth-related illumination is not responsible for depth differentiations of coral associations, but very likely, a complex of mechanical factors, such as hydrodynamic conditions, substrate conditions, sedimentation etc. However, light intensity determines the general distribution of hermatypic Scleractinia in their bathymetric range as well as the platelike shape of coral colonies characteristic for deep water associations. Depending on mechanical factors, Leptoseris, Montipora, Porites and Pachyseris dominate as characteristic genera in the Central Pacific Ocean, Podabacia, Leptoseris, Pachyseris and Coscinarea in the Red Sea, Agaricia and Leptoseris in the tropical western Atlantic Ocean.
Scleractinia (Hard Corals)