SKELETAL GROWTH RATES OF CENOZOIC CARIBBEAN REEF-CORALS

The Oligocene to Recent history of Caribbean reef-corals is characterized by two episodes of apparently rapid biotic turnover during the Early Miocene and Plio/Pleistocene. These transitions were related to regional oceanographic changes associated with the emerging Central American Isthmus. Regional surface water productivity was higher during the Pliocene and Miocene than in the Quaternary. In Recent zooxanthellate corals, annual variation in the rate of skeletal extension is expressed as couplets of thin high-density and thicker low-density bands than can be seen in x-radiographs. Assuming that most couplets preserve an annual signal, couplet width can be used to estimate annual growth rates and explore the effects of regional oceanographic change on the health of individual colonies. Studies on Recent corals suggest that growth rates are inversely related to turbidity, temperature, and nutrient levels. Therefore, corals growing in the Miocene and Pliocene should have lower growth rates than Recent corals. To test this hypothesis, growth rates were estimated for the common faviid genera Agathiphyllia, Diploria, and Montastraea from Oligocene to Pliocene stratigraphic units in Antigua, Curacao, the Domincan Republic, Panama, and Puerto Rico. Fossil growth rates were compared with Recent estimates obtained from the literature. In general, growth rates from the fossil material are similar to rates reported from extant skeletons, and range from 6 to 10 mm/year. The fact that Neogene coral colonies were able to maintain rates of growth comparable to modern rates suggests that the corals were not adversely influenced by higher regional surface water productivity. Therefore, either the corals were living in habitats insulated from regional oceanographic changes or that coral species were adapted to higher levels of productivity in the past than they are today.