SPECIES DISTRIBUTION, CORAL GROWTH AND SEDIMENTATION IN A MID-HOLOCENE CORAL REEF: CAÑADA HONDA, WESTERN DOMINICAN REPUBLIC

Concerns about the decline of modern coral reefs have led many scientists to look into the fossil record in an effort to understand coral-reef development prior to the onset of anthropogenically-induced disturbance. The Mid-Holocene Cañada Honda fossil reef, located in the southwestern Dominican Republic represents a unique opportunity to examine a coral reef that thrived in a high-sedimentation environment before any major human settlement on Hispaniola. The excellent preservation of the fossil reef allows detailed examination of its community structure over an extended time period. Quantitative assessments of coral abundance, species richness and sediment distribution were obtained throughout most of the reef outcrop using quadrats along vertical transects. Measurements of coral-growth rates, and sediment size/composition were also conducted to characterize their variability within the reef.

The reef sediment is characterized by less than 10% non-carbonate material. XRD analyses reveal the mineralogical composition of the reef sediment. Neogene limestones located north of the study site are believed to be the source of most of the incoming carbonate sediment on the reef. Measured growth rates in the corals Siderastrea siderea (0.2-0.4 cm/yr) and Montastraea faveolata (0.13-0.45 cm/yr) are relatively low compared with growth rates in corals from other sites, and are indicative of high sediment conditions. Also, coral growth rates in Montastraea faveolata show more variability compared with Siderastrea siderea. Twenty-four coral species were identified in the outcrop. Sediment-tolerant species such as Siderastrea siderea and Montastraea faveolata were the predominant corals of the community. Despite high sedimentation, the coral assemblage is very rich and with a zonation pattern similar to many undisturbed modern Caribbean coral reefs.

The Cañada Honda fossil reef presents the persistence of a rich coral community over an extended period of time within high-sediment conditions. Few modern coral reefs are known to endure in such conditions. Yet, it is possible that even though sedimentation was high, this occurred sporadically allowing time for the reef corals to respond and grow back, in such a way that they were able to “keep-up” with sedimentation.