EVIDENCE OF CORAL REEF ACCRETION UNDER UNIQUE ENVIRONMENTAL CONDITIONS: THE MID-HOLOCENE FOSSIL REEFS IN THE ENRIQUILLO VALLEY OF THE SOUTHWESTERN DOMINICAN REPUBLIC

The fossil record provides very useful information that can shed light on how coral reefs varied and responded to natural changes prior to anthropogenically induced disturbances. The Mid-Holocene reefs of the Enriquillo Basin in the southwestern Dominican Republic thrived under environmental conditions generally considered to discourage reef development in modern counterparts. The excellent exposure of a reef that thrived under the influence of periodic high sedimentation provides useful information about resilience and the capacity of reef corals to adapt to varying degrees of extreme natural disturbance. The fossil coral reefs of the Enriquillo Basin not only adapted to high terrigenous sediment inputs but also to extreme fluctuations in salinity having been developed within an enclosed embayment in a semi-arid climate. No such conditions have been described in the Greater Caribbean today, which makes these Holocene fossil reefs unique. One particular fossil reef, in the Cañada Honda locality, is characterized by an overwhelming abundance of the massive corals Siderastrea siderea. Modern Caribbean coral reefs characterized by high sedimentation do not have the almost monospecific S. siderea community structure found in Cañada Honda. This coral species is known to its tolerance to high sedimentation but also to high salinity fluctuations which could explain their high abundance in Enriquillo. In addition, reef sediment is characterized by more than 85% carbonate material. A significant portion of the carbonate is allochtonous and was derived from nearby Neogene limestones. The fossil reef was able to survive under high-sedimentation conditions because the high carbonate content of incoming terrestrial sediment would have allowed better light penetration and probable sporadic storms that would have provided intervening low-sedimentation periods during which reef corals could respond and grow back, keeping-up with sedimentation.