USING STABLE ISOTOPE AND SR/CA RATIOS TO ASSESS THE PALEOECOLOGY AND EXTINCTION SELECTIVITY OF MIO-PLIOCENE FREE-LIVING CORALS

There are twenty-six shallow water free-living flabello-meandorid corals known from the Neogene of the Caribbean and western Atlantic. Nearly all of these species went extinct (with the exception of Manicina areolata and Meandrina brasiliensis) around the Pliocene/Pleistocene boundary in association with the closure of the Central American Seaway. In order to investigate the temperatures and symbiotic associations of these corals, we measured Sr/Ca ratios and the δ¹³C and δ ¹⁸O ratios for 6 extinct free-living coral species from the Cibao Basin in the northern Dominican Republic. These data were then compared to known zooxanthellate and azooxanthelate corals from the modern.

The two extant free-living coral species are zooxanthellate and typically live in very shallow water (2-3 meters). Based on taxonomic associations, most of the extinct species are presumed to be zooxanthellate. However, as a result of strong positive correlation between δ¹³C and δ¹⁸O ratios we determined that despite taxonomic associations with other zooxanthellate corals, many of the sampled corals were probably not zooxanthellate. In addition, elevated Sr/Ca ratios compared to nearby reef coral assemblages suggests that these free-living corals were probably living in significantly cooler and deeper forereef environments. This suggests that while the Mio-Pliocene free-living corals were likely able to live in a wider range of environments, their elevated extinction could be due to a poor symbiotic relationship.