Patterns of Diversity
The pattern of diversity at family level is mostly a matter of distant geological history as seen in the fossil record. That is, it reflects a time in the distant geological past when the presence of the Tethys Sea and the Central American Seaway led to a uniform circum-global fauna. At this taxonomic level, there is no well-defined Indo-Pacific centre of diversity and the Caribbean is almost as diverse as the Indo-Pacific.
The pattern of diversity at generic level is primarily created by the many taxa that evolved in the Tethys Sea and which now survive only in the Indo-Pacific, together with genera that evolved in, and remained in, the Indo-Pacific. At this taxonomic level there is a well-defined Indo-Pacific centre of diversity and the Caribbean has a substantially lower diversity than the Indo-Pacific. From the central Indo-Pacific there is little attenuation of diversity west across the Indian Ocean, but a regular attenuation occurs east across the Pacific.
The pattern of diversity at species level is primarily the outcome of ocean circulation patterns and resulting geographic and evolutionary changes from the Plio-Pleistocene to present time. There is a well-defined Indo-Pacific centre of diversity, the so-called ‘Coral Triangle’ (see here). This centre attenuates progressively in the north along the Ryukyu Island chain of Japan and in the east across the Pacific. Within the tropical Indian Ocean, species diversity remains approximately uniform. The diversity of the Caribbean is no more than that of a depauperate outlying location of the Indo-Pacific.