DRONES IN TROPICAL SHALLOW-MARINE CARBONATE STUDIES: BENTHIC HABITAT AND FACIES MAPS, JAMAICA

Although being widely used in a broad range of disciplines over the last decade, the application of unmanned aerial vehicles (UAVs) or drones in sedimentology has been limited to siliciclastics. In this study, we test the hypothesis that the high-resolution (drone) orthophotography, when used in combination with the field (submarine) survey and subsequent laboratory analyses, can provide high-resolution habitat and facies maps in clear-water, shallow-marine settings, even in areas where field data is relatively sparse. In addition to the field data and orthophotographic imagery from a small (~600 ha) and low-energy Little Laughlands lagoon in Jamaica, the study utilizes laboratory analyses (granulometry, X-ray diffraction, and stable isotope analysis) of the collected carbonate sediment (n=39) to explore the relations between substrate types (both habitat and facies) and the water depth at which they occur in the study area. Sediment samples were collected along 11 shoreline-to-reef, ~150-m-apart transects; habitat type characteristics and depths were recorded while snorkeling along transects. Phantom 4 PRO was flown at 100 m altitude (31 minutes flying time) taking 503 images that were subsequently used to create a high-resolution photomosaic.

Seven lagoon-floor habitat types were revealed by the field survey. From lowest to highest energy, these include (depth and distance from the shoreline indicated in parentheses): (1) mangrove mud (depth 30-160 cm, 0-40 m ); (2) turfgrass sandy mud (0-80 cm, 0-30 m); (3) seagrass meadows (sand, depth 30-50 cm; 50-330 m); (4) sparse seagrasses with sand patches (30-80 cm, 0-260 m); (5) sandy shoal (60-210 cm, 20-210); (6) river wash (sandy gravel, 0-50 cm, 0-40); and (7) reef flat (40-185 cm, 60-400 m). All habitats exhibit distinct color hues in orthophotographs, which enabled the construction of a detail lagoon-floor habitat map. The relationship between water depth, habitats, and sedimentary facies is yet to be elucidated.