IS THE IVORY TREE CORAL, OCULINA VARICOSA, A RELIABLE PROXY FOR INTERMEDIATE/BOTTOM WATER VARIATION? EXAMPLES FROM THE OCULINA BANK, FLORIDA, USA

The Ivory Tree Coral Oculina varicosa is a scleractinian coral species with a known geographical range extending from Bermuda to the Caribbean Sea, and a known depth range between 3 and 100 m. It is considered a facultatively zooxanthellate, or apozooxanthellate, species due to its ability to convert between zooxanthellate and azooxanthellate life modes. Oculina varicosa branches intertwine to form dense colonies resembling thickets, with the branches of zooxanthellate shallow-water individuals being slightly more robust as compared to the azooxanthellate deeper-water individuals. The largest known colonies of O. varicosa form the Oculina Bank, which is situated on the shelf-margin of the east coast of central Florida. Because the Florida Current and upwelling from the Florida Straits regularly bathe this area with nutrients, it has been hypothesized that these water masses are largely responsible for supporting the reef and its associated biodiversity. Initial δ¹⁸O results of an O. varicosa specimen resolved annual isotopic fluctuations that could be representative of variations in the Florida Current and Florida Straits upwelling, indicating the isotopic composition of the species may be useful as a proxy for tracking the changes in these water masses over time. However, the species' environmental tolerance, which allows for a broader latitudinal and depth distribution than most scleractinians, demands a more thorough analysis of the isotopic systematics of the species to determine its capabilities and limitations as an environmental proxy. Using O. varicosa specimens collected from a variety of locations by the Smithsonian Institution and other specimen repositories, this study will begin to address what roles geography, depth, and life mode play in the isotopic composition of the species, and how they impact its proxy potential.