Temperature and Salinity Tolerance of Modern and Holocene Acropora Cervicornis from Barbados and the Dominican Republic

A significant Caribbean reef-builder throughout the Pleistocene and Holocene, Acropora cervicornis (staghorn coral) has recently been recognized as a threatened species. Global warming, disease, fishing pressure, storm activity, and other stresses have been cited as causes for recent collapse of the species. In order to better understand conditions favorable or detrimental to Acropora cervicornis growth, modern and Holocene specimens were analyzed for geochemical composition to constrain environmental tolerance of the species.

Modern Acropora cervicornis specimens were collected offshore of Barbados in summer 2007 at depths from 25 to 72 feet bsl. Stable isotope data from these specimens were compared to similar data from Holocene (~9-5 ka) Acropora cervicornis specimens from the Enriquillo Valley, Dominican Republic. Preliminary results indicate that stable isotope data from modern Barbados specimens correlate best with Dominican samples that existed closest to the Holocene Thermal Maximum (HTM) ~6 ka. This is not surprising as the δ¹⁸O of corals is temperature dependant and temperatures today closely resemble tropical HTM temperatures.

However, much of the δ¹⁸O signal recorded in these Barbados and Dominican corals is likely controlled by the variable influx of isotopically light freshwater to both systems, indicating that environmental conditions at these locations may be remarkably similar despite many obvious differences. The Barbados corals were collected in an open marine, fringing reef setting while the Dominican corals thrived in a semi-restricted embayment. The δ¹³C and δ¹⁸O data from the fossil Acropora cervicornis specimens show evidence of dramatic precipitation anomalies during a shift from cooler/dryer to warmer/wetter climate. Salinity measurements during collection of modern samples indicate that Barbados corals are currently growing in water significantly fresher than normal marine for at least part of the year. The freshwater signal may be a result of seasonal influx of water from the Orinoco River.