Overview of Buck Island Reef National Monument
Buck Island Reef National Monument (BIRNM or Monument) is located north of St. Croix in the U.S. Virgin Islands. This ecologically unique area was established in 1961 by Presidential Proclamation and is administered by the National Park Service (NPS). For the past two years, the NPS has been working with the National Centers for Coastal Ocean Science (NCCOS) to comprehensively map seafloor habitats within the Monument. BIRNM includes a mosaic of land and coral reef habitats that are home to a wide diversity of organisms, including the Brown Pelican, Hawksbill Turtle, and Elkhorn Coral, all of which are protected under the Endangered Species Act. In addition to providing habitat, the marine resources inside the Monument, such as coral and fish, provide valuable ecosystem services to the local community, including fisheries replenishment, recreation, and tourism. While the shallow-water habitats (< 30 meters in depth) had been mapped by NCCOS in 2001, the moderate to deep-water habitats (> 30 meters) have never been characterized prior to this project. Consequently, little was known about these deeper habitats inside the Monument. Given this information gap, the NPS asked NCCOS’ Center for Coastal Monitoring and Assessment (CCMA) (which has been partnering with the NPS since the early 2000’s) to help complete the first comprehensive habitat map of the BIRNM. This map will provide a baseline to local scientists and resource managers in support of ecosystem-based management of the Monument. The new assessment and related maps will help NPS resource managers structure their monitoring programs, site infrastructure, and identify areas within the Monument that need additional protection.
The Habitat Mapping and Characterization Process
In general, there are five main steps in the habitat mapping and characterization process. The first step in this process is to acquire source imagery; the images that are needed to make a map. For this project, six different types of source images were needed, from 0 to 1,830 meters in depth.
The second step is to draw lines around unknown, but visually distinct habitats. These lines are known as “polygons”. These lines were drawn both by hand and automatically using specialized software. The third step in the habitat mapping process is to collect underwater photos and videos, called ground validation data, to better understand what certain habitats look like in the source images. Since the Monument includes both shallow and deep-waters, different techniques were used to collect these videos and photos, including SCUBA divers, tethered underwater video cameras, and remotely operated vehicles. The fourth step in the mapping process is to use this ground validation (GV) data to classify each polygon and create a final habitat map. The final step in this process is to use additional underwater photos and video (collected independently of the GV data) to assess the accuracy of the habitat map. For more specific information about this benthic habitat mapping process, please look for past blog posts by my NCCOS/CCMA colleagues Tim Battista and Ken Buja.
For BIRNM, benthic habitat maps describing the geology and biology of the seafloor were generated for 98% of the Monument (about 74.3 km2) using a combination of manual and computer aided classification methods. The remaining 2% was not mapped due to lack of source imagery in the western part of the Monument. Three seamless habitat maps were developed for the Monument (instead of 1 single map) due to the wide range of spatial resolutions of the source images. A map for the shallow-water areas (0 ≤50 meters) was generated at the finest spatial scale because this area had the finest resolution source imagery. The moderate-depth (50 ≤1,000 meters) and deep-water maps (1,000 ≤ 1,830 meters) were developed at coarser spatial scales as these areas had source images with much coarser spatial resolutions. These different spatial scales require that care is taken when interpreting the maps together because some habitat characteristics are sensitive to the scale at which they are defined. Keeping this in mind, the three habitat maps showed that the Monument’s shallow-water area is dominated by sand, pavement, and aggregated patch reefs colonized by algae and seagrass, while the deeper areas are primarily made up of uncolonized sand, mud and rock/boulders. Such information is useful to managers because it provides a snapshot of the seafloor, which can be used to track changes in the benthic habitats overtime. While no accuracy assessment was conducted for areas deeper than 50 meters, the accuracy in waters shallower than 50 meters ranged from 81.4% to 94.4%. These thematic accuracies are similar to those reported for other NOAA benthic habitat mapping efforts, allowing these digital maps products to be used with confidence by scientists and resource managers for a multitude of applications.
Historical Use of Benthic Habitat Maps
In the past, scientific and management communities have used NOAA benthic habitat maps to structure monitoring programs, support management decisions (like siting infrastructure), as well as to establish and manage marine conservation areas. Additionally, several research and management applications may be possible using the bathymetry and benthic habitat maps developed during this project. These additional applications may include, but are not limited to:
- Updating the management plan of the BIRNM, including evaluating different zoning options for multiple use areas.
- Evaluating the efficacy of management actions taken by BIRNM.
- Mapping ecosystem services and estimating economic value of goods and services across the seascape.
- Understanding the seascape requirements for species and identifying the most productive and diverse seascape types.
- Predicting habitat suitability for priority species to help target monitoring and prioritize protection. For example, identifying the most highly suitable habitat for juvenile and adult spiny lobster can inform management actions and risk assessments.
For more information about these management applications, please look for future blog posts by the National Park Service.
Other Benthic Habitat Mapping Projects at NCCOS’ CCMA
To date, NOAA’s Biogeography Branch has mapped and characterized large portions of the U.S. Caribbean and continues to be engaged in mapping efforts beyond BIRNM in St. Croix. Future mapping efforts are focused on the following six locations within the next two to three years: (1) Guanica and Belvedere Bays in southwest Puerto Rico, (2) the Great Reserve off the northeast coast of Puerto Rico, (3) Lang Bank east of St. Croix, (4) the shallow-water (<25 m) area south of St. Thomas, (5) Virgin Passage between Isla de Culebra and St. Thomas, and (6) areas west of the east coast of Puerto Rico. The goal of each of these projects is to map and characterize seafloor habitats in support of ecosystem based management.
The Buck Isand Reef National Monument report can be found via the CCMA website, and more information on the project can be found on the CCMA project page for Benthic habitat mapping for the National Park Service, St. Croix, USVI.
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