Benthic habitats of the moderate-depth marine environment in and around the Virgin Islands Coral Reef National Monument were mapped using a combination of semi-automated classification and visual interpretation of acoustic imagery. The objective of this effort, conducted by NOAA's Center for Coastal Monitoring and Assessment - Biogeography Branch in partnership with the U.S. National Park Service (NPS), was to provide spatially-explicit information on the habitat types, biological cover and live coral cover of the moderate-depth area south of St. John.
This product provides a fine-scale assessment of the status, abundance, and distribution of moderate-depth marine habitats south of St. John. The NOAA effort provides the U.S. National Park Service with increased technical capacity for ocean exploration, management, and stewardship. Direct implications to management measures include evaluation of management efficacy, a spatial framework for improved monitoring sampling design, improved assessment of human-use impacts, and marine spatial planning to support alternative marine protected area boundary alternatives.
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A comprehensive assessment was conducted to evaluate the thematic accuracy of the St. John moderate-depth benthic habitat map. Thematic accuracy was characterized for major and detailed geomorphological structure, major and detailed biological cover, and percent coral cover. An independent accuracy assessment revealed overall map accuracies to be over 95% for major structure and cover classes, and over 88% and 74% for detailed structure and cover classes, respectively. The 88.7% accuracy achieved for detailed structure in NOAA's moderate-depth benthic habitat map is similar to the accuracies of recent NOAA shallow-water benthic habitat map for St. John (85.7%), as well as for the Florida Keys (86.2%), Palau (90.0%), and the Main Eight Hawaiian Islands (90.0%).
Acoustic imagery was acquired for the southern VICRNM boundaries on two separate missions onboard the NOAA ship, Nancy Foster. The first mission took place from 2/18 to 3/5/2004, and the second mission took place from 2/1 to 2/12/2005. On both missions, seafloor depths between 14 to 55 m were mapped using a RESON SeaBat 8101 ER (240 kHz) MBES sensor (Figure 2.5). This pole-mounted system measured water depths across a 150 degree swath consisting of 101 individual 1.5 degree x 1.5 degree beams. The vessel survey speed was between 5 and 8 knots. In 2004, the ship's location was determined by a Trimble DSM 132 DGPS system, which provided a RTCM differential data stream from the U.S. Coast Guard Continually Operating Reference Station (CORS) at Port Isabel, Puerto Rico. Gyro, heave, pitch and roll correctors were acquired using an Ixsea Octans gyrocompass. In 2005, the ship's positioning and orientation were determined by the Applanix POS/MV 320 V4, which is a GPS aided Inertial Motion Unit (IMU) providing measurements of roll, pitch and heading. The POS/ MV obtained its positions from two dual frequency Trimble Zephyr GPS antennae. An auxiliary Trimble DSM 132 DGPS system provided a RTCM differential data stream from the U.S. Coast Guard CORS at Port Isabel, Puerto Rico. For both years, CTD (conductivity, temperature and depth) measurements were taken approximately every 4 hours using a Seabird Electronics SBE-19 to correct for changing sound velocities in the water column. GIS topologic quality was established by executing ArcGIS extension routines that check for: overlapping polygons, multipart polygons, sliver polygons and void polygons. Additionally checks for adjacent polygons with the same habitat attributes were completed. All errors were identified and corrected. This file is believed to be logically consistent.
Delineation of all habitat boundaries was conducted using edge-detection algorithms. The minimum mapping unit (MMU) for identifying habitats or features was 1,000 square meters.
Please see the following document for more information on positional accuracy: Battista, T. A., and Lazar, J.V. (2005). MBES data acquisition & processing report: Project NF-05-05-USVI, NOAA Data Acquisition & Processing Report, NOS NCCOS CCMA (On-line). On-line: http://ccma.nos.noaa.gov/products/biogeography/usvi_nps/pdf/NF-05-05_DAPR.pdf
This section of the report describes the habitat classification scheme used to classifiy habitat features. The St. John habitat classification scheme defines benthic communities on the basis of four primary coral reef ecosystem attributes: 1) broad geographic zone, 2) geomorphological structure type, 3) dominant biological cover, and 4) degree of live coral cover.
This ArcGIS extension was used to digitize and attribute benthic zones, structure and biological cover of this map.
Used to identify and digitize benthic habitats of St. John, USVI.
1) Imagery Acquisition and Processing - The first step in this process was to acquire and process high-resolution acoustic imagery. Acoustic imagery was collected during two separate years, in order to map the full geographic extent of the VICRNM's southern boundaries. Several metrics were derived from the depth imagery, in order to describe the complexity of the seafloor in different ways. Principal components analysis was then used to reduce the redundancy of information contained in these metrics. Process_Date: 2005 and 2009
2) Habitat Boundary Delineation - A first draft benthic habitat map was generated using edge detection algorithms to delineate features on the seafloor with discrete acoustic signatures. During the creation of this first draft map, the cartographer placed discrete points on features in the map that had unknown acoustic signatures, warranting further field investigation. Points were also placed on features with known acoustic signatures (evenly distributed throughout the geographic extent of the map) to confirm that the habitats associated with these signatures remained consistent through the area of interest. These two types of points were labeled as "ground validation" sites and were visited in the field.
3) Ground Validation (GV) - NOAA scientists explored these ground validation locations using two different sampling techniques and two different pieces of equipment. Specifically, underwater video was collected along 13 transects using a remotely operated vehicle (ROV), and at 117 discrete points using a manually operated drop camera. The resulting GPS and video information was processed, analyzed and used to train the classification algorithm that was used to generate the second draft map. Process_Date: 2005 and 2009
4) Habitat Classification - A CART-like (Classification and Regression Tree) algorithm was used to classify each habitat feature delineated by the edge-detection algorithms described in step 2. To simplify this classification process, coral reef habitat features, and soft bottom and rhodolith habitat features were classified separately. The classification algorithm separated these two habitat feature types into different major and detailed structure, biological cover and lives coral classes. The two, resulting classifications were merged together and manually edited to create a final seamless habitat map.
5) Accuracy Assessment (AA) - AA sites were generated using a stratified random sampling design (based on detailed structure type) that allowed for a statistically rigorous assessment of map accuracy. Underwater video was collected at these 299 sites using a manually operated drop camera.
6) Final Products Creation - A final benthic habitat map for the VICRNM was generated by correcting inaccuracies identified by the accuracy assessment. Additionally, all associated datasets, including GIS files, field video and metadata were packaged and provided to project partners.
Internal feature number.
ESRI
Feature geometry.
A distinct identifier used to define each unique combination of habitat characteristics
NOAA
Calculated feature area (sq m)
Calculated feature perimeter (m)
Geographic Zone
Major Geomorphological Structure
Refer to Chapter 1: Benthic Habitat Classification Scheme of "Benthic Habitats of St. John, U.S. Virgin Islands" (Zitello et al. 2009)
Detailed Geomorphological Structure
Major Biological Cover
Percent Patchiness of Major Biological Cover
Percent Cover of Live Coral
Concatenation of Major Biological Cover and Percent Major Biological Cover. Used to describe the combination of major biological cover and its percent patchiness of the feature
Concatenation of Detailed Geomorphological Structure, Major and Percent Biological Cover and Percent Major Biological Cover, and Live Coral Cover
Specific details of the attributes and values therein can be found in Chapter 1: Benthic Habitat Classification Scheme of "Moderate-Depth Benthic Habitats of St. John, U.S. Virgin Islands" (Costa et al. 2009).
Costa, B.M., L.J. Bauer, T.A. Battista, P.W. Mueller and M.E. Monaco. 2009. Moderate-Depth Benthic Habitats of St. John, U.S. Virgin Islands. NOAA Technical Memorandum NOS NCCOS 105. Silver Spring, MD. 55 pp.
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The National Oceanic and Atmospheric Administration (NOAA) National Centers for Coastal Ocean Science (NCCOS) is publishing this data on their website. NCCOS Biogeography Branch does not guarantee the accuracy of the geographic features or attributes. Please see the written report and metadata records for each data set for complete information on the source, limitations, and proper use.
Contact NOAA for distribution options (see Distributor).
