Honing in on Deep-water Corals: Ground-truthing AUV Data in the Straits of Florida

Although deep-water corals account for two-thirds of the world’s identified coral species, they are relatively unexplored. In the Straits of Florida (SoF) a comprehensive description of entire mound fields was accomplished using an Autonomous Underwater Vehicle (AUV) with a variety of sensors that collectively captured the anatomy and distribution of the mounds in five areas. Subsequent submersible dives to prominent mounds in each survey area collected samples, photographs, and abundant video footage of these deep-water coral reefs that help relate the sedimentary facies and coral coverage to the geophysical data by the exact positioning of the submersible video footage on the backscatter and the side-scan sonar (SSS) maps. The submersible video footage at time stamps of every 4 seconds on each of the ten dive tracks was classified as one of seven facies, describing sea floor substrate type and standing coral presence. Using these data as ground-truthing of the geophysical data reveals that the backscatter and SSS intensity vary according to the facies and density of coral coverage. Denser coral is often found in darker regions of the backscatter and SSS maps, while softer substrates such as mud and floatstone are seen in lighter areas on the maps. In addition, the maps consistently characterize the structures of the sea floor. Ten dives in various mound fields in the Straits of Florida were studied. No two dive sites are identical, but every dive had both live and dead corals present. The three sites on the eastern side of the SoF (Great Bahama Bank sites) have larger, denser standing coral than the western side of the SoF (Miami Terrace sites) that had sparser standing corals and often more coral rubble. Combining AUV and submersible data is a powerful methodology to provide square kilometers of high-resolution maps that have the ability to illustrate different facies from the substrate across entire mound fields. Studying the coral habitat in this comprehensive way will lead to a better understanding of what enables deep-water corals to thrive where they do.