CENOZOIC REEF-CORAL DIVERSITY DURING THE OLIGOCENE/MIOCENE TRANSITION

Previous syntheses of the stratigraphic distribution of Caribbean zooxanthellate corals suggested the existence of five major Cenozoic faunas corresponding with broad stratigraphic intervals. These include the (1) Middle to Late Eocene, (2) Oligocene to earliest Miocene, (3) Early to Middle Miocene, (4) Late Miocene to Pliocene, and (5) Plio/Pleistocene to Recent faunas. Two of these faunas (Oligocene to earliest Miocene and Plio/Pleistocene to Recent) lived on extensive fringing and barrier reef tracts in an ocean characterized by low planktonic productivity. In contrast, regional planktonic productivity was relatively high and the Caribbean lacked extensive reef buildups during the Miocene and Pliocene. How did reef- coral diversity respond to the large-scale environmental changes associated with the Oligocene/Miocene and Plio/Pleistocene transitions? This question was addressed using new large collections from Late Oligocene and Early Miocene reef units in Antigua, Jamaica, and Puerto Rico, that were combined with existing museum collections to create a specimen-based compilation of regional reef-coral distributions. Cumulative sampling curves suggest that we have a good idea of how Late Oligocene coral communities were assembled, but significant undiscovered diversity remains in the Early and Middle Miocene units. This suggests that the presence of a distinct Early to Middle Miocene fauna is likely an artifact of inadequate sampling. However, Late Miocene and Pliocene regional (gamma) diversity is nearly twice as high as Oligocene and extant diversity. This high Pliocene diversity is a function of a combination of high local (alpha) diversity and geographical or environmental heterogeneity. Contrary to expectations of high reef-coral diversity on coral reefs in oligotrophic seas, this paradoxical result suggests that both local and regional zooxanthellate coral diversity is actually higher during periods of high planktonic productivity but only weak reef development.