We developed predictive maps of the distribution of selected hard corals living in the mesophotic zone (30–150 meters deep) in and around the Au’au Channel, Hawai’i. This work is designed to support the management plan review process currently underway at the Humpback Whale National Marine Sanctuary, and provide baseline data for future management decisions. Prior to this project, very little information existed regarding the essential fish habitat provided by these deeper hard corals.
Why We Care
The Humpback Whale National Marine Sanctuary (HIHWNMS) is located off the main Hawaiian Islands, and was created by Congress in 1992 to protect humpback whales and their habitat in Hawai`i. The Sanctuary is one of the world’s most important humpback whale habitats, but also serves as a home to other marine life: whales, dolphins, sea turtles, marine birds, reef fish, invertebrates and mesophotic coral ecosystems (MCEs). MCEs are light-dependent coral communities that occur in the deeper part (30 – 150 m) of the photic zone in tropical and subtropical regions. Mesophotic corals play an important role in shaping the ecological communities in deeper waters because they provide habitat and refuge for many reef fish and invertebrate species. In order for the Sanctuary to shift from single species management (i.e., of humpback whales) to an ecosystem based approach, the Sanctuary needs more information about the status and functions of biotic ecosystem components, including MCEs.
What We Did
We developed a spatial model with a map of mesophotic hard coral presence from 30 to 150 meters in and around the Au’au Channel, Hawai’i using readily-available bathymetry (depth), PAR (photo-synthetically active radiation), water temperature, water currents and underwater videos describing MCE presence.
The MCE presence data used in this project was the result of work conducted by the Bishop Museum, Hawaii Division of Aquatic Resources, NOAA NMFS Pacific Island Fisheries Science Center and the University of Hawaii, which was funded under NCCOS’ Center for Sponsored Coastal Ocean Research’s Deep Coral Reef Ecosystem Studies Program. The predictor information (i.e., bathymetry, PAR, temperature and currents) were collected by the U.S. Geological Survey, University of Hawaii,and the National Aeronautics and Space Administration. The modeling portion of this project was funded by the HIHWNMS to support their management plan review process.
What We Found
The spatial predictions developed during this project had overall accuracies of 73.1 percent for all hard mesophotic corals, and (using absences only) were 86.1 percent for Montipora, 85.3 percent for Porites and 78.2 percent for Leptoseris. Several environmental variables were important to all four spatial predictions. These variables included depth, distance from shore, mean euphotic depth, and variance of euphotic depth. While it is likely that these variables are proxies for other variables, suitable environmental conditions for mesophotic corals were highest in a broad region in the south and eastern half of the Au‘au Channel.