SEAFLOOR HABITAT MAPPING AND OCEANOGRAPHIC STUDIES IN THE KONA COAST NATIONAL PARKS

A cooperative study between the U.S. Geological Survey and the National Park Service is focused on mapping and understanding the seafloor geology, benthic habitats, and water quality and circulation adjacent to three National Parks along the Kona coast of Hawaii. Using a combination of aerial photography, bathymetric lidar, ship-towed underwater video, and SCUBA, benthic habitat maps are being developed to document the geological and biological framework. Although the bottom substrate in all three parks is volcanic in origin, different morphologies and coral cover make each offshore environment unique. For example, spur and groove morphology, supporting a diverse assemblage of coral species, is found within Kawaihae Bay, off the northernmost park of Pu'ukohola Heiau (PUHE).  In contrast, multiple volcanic flows that coalesce within Kaloko-Honokohau National Historic Park (KAHO) on the central part of the Kona coast, have created a complex offshore morphology that includes flat to gently rolling pahoehoe flows, shear ledges, pinnacles and ridges, and steep flow fronts. Each morphology provides a distinct habitat for coral species ranging from isolated heads of Porites lobata and Pocillopora meandrina to dense thickets of Porites compressa. Near the southernmost park, Pu'uhonua O Honaunau National Historic Park (PUHO), some of the highest coral cover observed in the Hawaiian Islands is found in nearby embayments.

Oceanographic measurements within the parks include comprehensive spatial surveys with profiling CTD (conductivity, temperature, salinity) and OBS (optical backscatter) sensors and high-resolution time series measurements of waves, currents, temperature, salinity and turbidity. Preliminary results from the CTD/OBS surveys show complex patterns of freshwater and subterranean ground water discharge across the reef at KAHO and PUHO. These data are being correlated with analyses of Ra isotope activity, nutrient concentration, and DIC to explore cross-shore gradients in ground water and associated flux of nutrient into the coastal waters and across the reef. The time series measurements will provide information on processes controlling the distribution and transport of sediment, coral larvae, groundwater effluence, nutrients, and contaminants within the park's boundaries.