Current Control on Deep-Water Coral Mounds: Questioning an Emerging Paradigm

Eberli, Gregor P.¹, Mark Grasmueck¹, Miriam S. Andres¹, Thiago Correa¹ (1) University of Miami, Miami, FL

Factors controlling the initiation and maintenance of deep-water coral mounds are largely unknown and only explained by two hypotheses. The methane hypothesis predicts that coral mounds initiate above hydrocarbon seeps where microbial communities form the basis of the reef ecosystem. The current hypothesis argues that particulate material transported by currents is the main energy source for the corals. Drilling and subsequent analyses of Challenger Mound (IODP Expedition 307) did not detect evidence of methane. Consequently, the current hypothesis is now embraced and developing into a paradigm that relates current strength to mound health, morphology and height. A comprehensive data set collected with an Autonomous Underwater Vehicle (AUV) across five mound fields in the Straits of Florida at depths of 500-800 m and 8-12 °C cold water questions this emerging paradigm. The AUV brings multibeam, side scan sonar, subbottom profiler, current velocity profiler, thermometer, salinity- and methane sensor within 40 m of the seafloor. This collocated dataset reveals an unexpected alignment and diversity of mound morphologies that is not primarily controlled by current. While currents are rather uniform in strength coral mound coverage and height varies widely at the five sites. At the toe-of-slope of Great Bahama Bank large mounds (120m) follow low-relief ridges that trend perpendicular to the platform, while in the middle of the Straits mound coverage is high (70%) but mound height is small (5-10m); only coalesced mounds reach 40 m in relief. In all locations, neither current orientation nor strength is directly reflected in mound morphology and coverage.