NCCOS produced georeferenced, digital benthic habitat maps for the shallow-water (< 30m) coral ecosystem habitats around the Northwestern Hawaiian Islands, to provide baseline information for research, management, and conservation of critical resources found in the region.
Why We Care
Coral reef ecosystems are enormously valuable culturally, ecologically, and economically, but they are declining globally primarily because of human influences. The ecosystem off the Northwestern Hawaiian Islands (NWHI) hosts a distinctive array of marine mammals, fish, sea turtles, birds, and invertebrates, including species that are endemic, rare, threatened, and endangered. Our ability to better understand, protect, and improve their condition relies on ongoing assessments, and mapping is an important component of those efforts. Maps depict the extent of coral reefs, are used to monitor reef health over time, help identify which areas need further protection, and which need improved management measures.
What We Did
Staff and contractors from NCCOS and the University of Hawaii’s Hawaii Institute of Marine Biology produced comprehensive, detailed maps for 2,361sq km of the shallow-water benthic habitats of the Northwestern Hawaiian Islands (NWHI) The NWHI is now part of the Papahanaumokuakea Marine National Monument. These benthic habitat maps represent the first comprehensive assessment of benthic habitats of the shallow water environments (less than 30 meters or 99 feet water depth) in the NWHI.
The NWHI chain extends across 2,200 km of open ocean, and the total area of the atolls down to 150 Meters water depth is estimated to encompasses nearly 12,725 square km. Due to the remoteness and large spatial extent of these reefs, high-resolution satellite imagery was the primary source of data for this map. Field data, in the form of underwater still photography and associated seafloor characterizations, collected during a NOAA/NOS NWHI cruise in August-September, 2001 were essential to map production. Commercially-available IKONOS high-resolution, color satellite imagery from Space Imaging (now GeoEye) was collected between 2000 and 2002 and used to characterize NWHI seafloor habitats. As a cost-saving measure, moderate resolution Landsat 7 Enhanced Thematic Mapper Plus (ETM+) imagery was used to identify shallow depth bank areas in the NWHI.
Products include maps, data, and satellite imagery depicting the location and distribution of shallow-water coral ecosystem habitats of the NWHI. Map products include georeferenced, true color images derived from IKONOS satellite data, estimated bathymetry (in meters) derived from the imagery, benthic habitat cover, and detailed benthic habitat classes. Maps, GIS data and imagery are included in the Data Collections page linked below, along with documents on the process of map development and a description of the classification scheme.
What We Found
Thirty-four distinct benthic habitat types (e.g., patch reef, unconsolidated sediment, etc.) within eleven unique ecological zones (e.g., lagoon, reef crest, etc.) were mapped directly into a GIS using a combination of semi-automated computerized and visual interpretation of satellite images. For the total habitat area that was classified for NWHI, the most common seafloor habitat was “unconsolidated with 10% or less macroalgae or seagrass” (1,150 sq km or 48.7% of the total habitat area classified), followed by “hardbottom with indeterminate cover “ (823 sq km or 34.9%). Habitat types with known coral covered relatively small areas: “hardbottom with >10% live coral (109 sq km or 4.6%), and “hardbottom with >10% crustose coralline algae” (7.3 sq km or 0.3%).
Benefits of Our Work
The seafloor habitat maps are routinely used to develop, plan for, and catalog underwater habitat characterization surveys conducted by NOAA and the University of Hawaii. The maps also are used routinely to catalog areas where new bathymetry data of the NWHI are needed.