We developed benthic habitat maps for shallow areas (< 30 m) around St. John and moderate-depth areas (30–60 m) south of St. John in the U.S. Virgin Islands. These maps are helping local managers develop place-based strategies to address and remedy specific threats to coral reefs inside Virgin Islands National Park and the Virgin Islands Coral Reef National Monument.
Why We Care
Shallow-water (< 30 m) and moderate-depth (30–60 m) coral reef ecosystems in the surrounding waters of St. John are unique natural resources that must be preserved. The mosaic of habitats, including hard and soft corals, is home to a diversity of marine organisms that provide important ecosystem services to the community of St. John, including fishing, tourism, and shoreline protection. However, coral reef ecosystems throughout the U.S. Caribbean are under increasing pressure from environmental and anthropogenic stressors. Mitigating these threats requires that resource managers first understand the spatial distribution of these resources, making benthic habitat mapping an integral component of ecosystem-based approaches to management.
What We Did and Are Doing
We mapped 53.4 km2 of shallow-water habitats around St. John and 90.2 km2 of moderate-depth habitats south of St. John for the National Park Service’s Inventory and Monitoring Program. This work replaces previous NOAA maps generated by Kendall et al. (2001) for the waters around St. John. We mapped 32 distinct benthic habitat types using a combination of visual interpretation of aerial and satellite imagery and semi-automated classification of acoustic imagery. Through this effort we mapped approximately 93 percent of the Virgin Islands Coral Reef National Monument and 92 percent of the Virgin Islands National Park.
Sand and pavement dominated the shallow-water habitats around St. John, covering 43 percent and 16 percent of the mapped area, respectively. Rhodoliths (encrusting marine red algae that resemble coral) and sand were the most common found habitats in the moderate depth region south of St. John. Turf, fleshy, coralline, or filamentous algae were pervasive in both the shallow and moderate depth areas, accounting for 74 percent and 92.8 percent of these mapped areas, respectively. Only 17 percent of the shallow area and four percent of the moderate depth area had live hard and soft coral covers greater than 10 percent. We assessed the thematic accuracy of these two maps using independent data sets. The maps were also reviewed and edited by local experts, including the National Park Service, before being finalized. The final deliverables for this project included the benthic habitat maps, source imagery, and georeferenced underwater videos and photos.