A NEW PERSPECTIVE: THE UTILIZATION OF SUAS FOR CORAL REEF ASSESSMENTS

Coral reefs are in global decline. In order for us to effectively manage and conserve these ecologically and economically important coastal resources, we must understand coral reef dynamics over a range of spatial and temporal scales. Current in situ and remote sensing reef assessment techniques are time, money, and personnel-intensive, and consistent surveys of large reef areas are unfeasible, unavailable, or uninformative at the colony level. We present a new technique using small unmanned aerial systems (sUAS) that target an intermediate spatial scale to understand how coral communities reacted and recovered at the colony level during the 2015 bleaching event on patch reefs in Kaneohe Bay, Oahu. Overlapping images were collected at 4 reefs and processed using Structure-from-Motion techniques to produce georeferenced and spatially accurate orthomosaics of reef areas. Mosaics were analyzed manually to identify benthic substrate and coral health (bleached, paled, fully pigmented). We found that bleached and paled colonies had clumped distributions on patch reefs in Kaneohe Bay. Our work demonstrates that UAVs provide a low cost, efficient platform that can rapidly and repeatedly collect high-resolution imagery (1 cm) and map large areas of shallow reef ecosystems (5 hectares). We envision that similar low altitude aerial surveys would be incorporated as a standard component of shallow-water reef studies, especially on reefs too dangerous or remote for in situ surveys.