* portions of this chapter will be reprinted in the forthcoming Esri Press book, Undersea With GIS, due out in the fall of 2001.
Currently there are thirteen sites in the U.S. National Marine Sanctuary System that protect over 18,000 square miles of American coastal waters. Coral reefs are a particular concern at several of these sites, as reefs are now recognized as being among the most diverse and valuable ecosystems on earth, as well as the most endangered. The smallest, remotest, and least explored site is the Fagatele Bay National Marine Sanctuary (FBNMS) in American Samoa, the only true tropical coral reef in the sanctuary system. It is still largely unexplored below depths of ~30 m, with no comprehensive documentation of the plants, animals, and submarine topography. Indeed, virtually nothing is known of shelf- edge (50-120 m deep) coral reef habitats throughout the world, and no inventory of benthic-associated species exists. This chapter presents the results of: (1) recent surveys at the FBNMS in April-May, 2001, to obtain complete topographic coverage of the deepest parts of the bay with multibeam bathymetric mapping, as well as digital video and still photography of physical features and biological habitats; and (2) efforts to integrate these baseline data into a GIS to facilitate key management and research decisions within the sanctuary, and to establish future survey, sampling, monitoring, and management protocols.
Figure 1. Location of twelve of the sites (black dots) comprising the National Marine Sanctuary System (excluding the most recent addition to the system at Thunder Bay in the Great Lakes region). Red squares indicate sites recently explored by the Sustainable Seas Expeditions. Map courtesy of the National Geographic Society,
http://www.nationalgeographic.com/seasCoral reefs are a particular concern at several of the sanctuaries as they are now recognized as being among the most diverse and valuable ecosystems on earth. Reef systems are storehouses of immense biological wealth and provide economic and ecosystem services to millions of people as shoreline protection, areas of natural beauty and recreation, and sources of food, pharmaceuticals, jobs, and revenues (Jones et al., 1999; Wolanski, 2001). Unfortunately, coral reefs are also recognized as being among the most threatened marine ecosystems on the planet, having been seriously degraded by human over-exploitation of resources, destructive fishing practices, coastal development, and runoff from improper land-use practices (Bryant et al., 1998; Wolanski, 2001).
A major initiative, administered by NOAA, has recently been launched to explore, document, and provide critical scientific data for the sanctuaries, with the goal of developing a strategy for the restoration and conservation of the nation's marine resources (Bunce et al., 1994; Wilson, 1998). One of the major catalysts behind this effort is the 5-year Sustainable Seas Expeditions (SSE; http://sustainableseas.noaa.gov), led by marine biologist and National Geographic Explorer-in-Residence Dr. Sylvia Earle and former National Marine Sanctuary program director Francesca Cava. SSE has been using the 1-personed submersible, DeepWorker, to pioneer the first explorations of the sanctuaries. Its mission plan for as many of the National Marine Sanctuaries as possible includes three phases: (1) to provide the first photo documentation of sanctuary plants, animals, and habitats at depths up to ~610 m; (2) expand on the characterization of habitats, focusing on larger animals such as whales, sharks, rays, and turtles, and compare habitat requirements among sanctuaries (Wilson, 1998); and (3) the all-important analysis and interpretation of the masses of data collected, as well as public outreach and education.
The smallest, most remote, and least explored of the sanctuaries is the Fagatele Bay National Marine Sanctuary (FBNMS) in American Samoa, the only true tropical coral reef in the sanctuary system (Figure 1). This site was largely unexplored below depths of ~30 m, with no comprehensive documentation of the plants, animals, and submarine topography. Indeed, virtually nothing is known of shelf-edge (50-120 m deep) coral reef habitats throughout the world, and no inventory of benthic-associated species exists (e.g., Koenig et al., in press). FBMNS is also unique in that it is the only site with a submerged national park in the near vicinity. The National Park of American Samoa is also unexplored beyond the shallow coral reefs 0.5 km offshore. It will be extremely difficult to meet the sanctuary's and the park's mission of protecting the coral reef terrace and broader marine ecosystem without adequate knowledge of the deeper environment. Unlike the larger sanctuaries off the coast of the continental U.S. and Hawaii, the FBNMS will not be visited by the DeepWorker submersible in the near future on an SSE mission, nor is the DeepWorker an adequate tool for surveying large regional areas. DeepWorker has been appropriate for the other sanctuaries because there already existed baseline surveys and maps from which to draw upon, so that the submersible could focus on specific regions to photograph and sample. Because FBNMS is so remote, there has been a critical need there for regional-scale, high- resolution, fully processed, interpreted and accessible baseline data, in order to properly characterize the geological and biological environment. This chapter presents the results of: (1) recent surveys at the FBNMS in April-May, 2001, to obtain complete topographic coverage of the deepest parts of the bay with multibeam bathymetric mapping, as well as digital video and still photography of physical features and biological habitats (in particular for visual estimation of the distribution and relative abundance of echinoderms, fish assemblages); and (2) efforts to integrate these baseline data into a GIS to facilitate key management and research decisions within the sanctuary, and to establish future survey, sampling, monitoring, and management protocols.
American Samoa (as opposed to the independent nation of Samoa directly to the west) is the only U.S. territory south of the equator (Figure 2) and is composed of five volcanic islands (from west to east: Tutuila, Anunu, Ofu, Olosega, and Ta'u), as well as two small coral atolls, Rose and Swain (Figure 3). Tectonically, the entire Samoan archipelago lies just east and 100 km north of the subduction of the Pacific Plate beneath the northeastern corner of the Australian Plate at the Tonga Trench (Figure 4). The estimated westward convergence rate of the Pacific Plate at the Tonga Trench is approximately 15 cm/yr (Lonsdale, 1986). However, recent GPS measurements indicate an instantaneous convergence of 24 cm/yr across the northern Tonga Trench, which is the fastest plate velocity yet recorded on the planet (Bevis et al., 1995). It has long been hypothesized that the islands of the Samoan archipelago were formed as a result of the tearing of the Pacific Plate as it bends abruptly to the west (aka "the Samoa corner") along the Tonga Trench (e.g., Isacks et al., 1969; Billington, 1990). The Samoan chain is also unusual in that the islands are largest at the western end (Savai'i, Samoa), deeply eroded in the middle (Tutuila, American Samoa), and the easternmost feature (Rose Atoll, American Samoa) is a coral atoll that breaches the surface of the ocean, instead of an active underwater seamount (Hawkins and Natland, 1975). In the Hawaiian archipelago, for instance, far to the north but oriented along a similar azimuth, these characteristics are completely reversed. However, the recent discovery of the underwater volcano Vailulu'u (formerly named Fa'afafine) to the east of the Samoan chain by Hart et al. (1999) provides strong evidence for a hotspot (as opposed to a "plate tearing") origin for the islands, and one that is consistent with the westward plate movement of the Pacific.
Figure 2. Regional map showing the location of the Samoan archipelago within the greater southwest Pacific Ocean (courtesy of the National Park of American Samoa,
http://www.nps.gov/npsa/location.htm).
Figure 3. Regional map showing the islands of the independent nation of Samoa (formerly Western Samoa) to the west and American Samoa to the east (courtesy of the National Park of American Samoa,
http://www.nps.gov/npsa/location.htm).
Figure 4. Plate tectonic map showing the major submarine tectonic features in the region (after Wright et al., 2000): the Samoan archipelago is marked by star, the Tonga Trench by a solid line with barbs on the overriding plate, the Fiji Fracture Zone and Vitiaz Trench Lineament by dashed lines, and the Louisville Ridge by a dotted line.
The FBNMS is located at the southwest corner of the island of Tutuila (Figure 5). The bay is an ancient flooded volcano, with a thriving coral and calcareous algal reef community that is rapidly recovering from an infestation of crown-of-thorns starfish that devastated the corals in the late 1970s (
http://www.fbnms.nos.noaa.gov
Figure 5. Map of Tutuila, American Samoa showing the location of the FBNMS (purple arrow at southwest corner of island) and part of the national park (purple arrows at north side of island). Inset photograph at lower left is an aerial shot of the FBNMS. Total area of FBNMS is 0.65 sq km, total area of submerged national park offshore Tutuila is ~5 sq. km. Map courtesy of National Park of American Samoa,
http://www.nps.gov/npsa/maproom.htm), and photo courtesy of the FBNMS (http://www.fbnms.nos.noaa.gov/).
Prior to the April-May 2001 mission, no scientific survey had been conducted in the deepest parts of Fagatele Bay. Two previous surveys reached depths of ~43 m, but were both were only brief, localized "snapshots": an algal reconnaissance in 1996 (N. Daschbach, unpublished data, 1996), and a rapid assessment survey for fish and coral in 1998 (Green et al., 1999). Therefore, two primary surveying objectives during the 2001 mission were to obtain: (1) complete topographic coverage of the ocean floor via a portable multibeam bathymetric mapping system; and (2) digital video and still photography of the biological habitats and physical features below 30 m via SCUBA and rebreather technology. In contrast to SCUBA, where the entire breath of a diver is expelled into the surrounding water when s/he exhales (open circuit), a rebreather apparatus is able to "reuse" the oxygen left unused in each exhaled breath (closed or semi- closed circuit), resulting in greatly extended dive times that are relatively quiet (little or no bubbles produced) and with much smaller tanks (Elliot, 2000). This chapter focuses primarily on the bathymetric mapping survey. Specific research questions that guided both surveys included:
Shallow-water, multibeam depth soundings were gathered by the Kongsberg-Simrad EM-3000 system, contracted from the University of South Florida College of Marine Studies, and operated from a boat owned by the America Samoa Government (ASG), Dept. of Marine & Wildlife Resources (DMWR; Figure 6). The Kongsberg- Simrad EM-3000 is a 300 kHz system that fans out up to 121 beams at a 130 degree angle, yielding swaths that are up to 4 times the water depth (Figure 7). The system can capture depths in the 3-150 m range at survey speeds of 3-12 knots. With differential GPS (not available in real-time during our surveys), the system is capable of centimeter resolution with an accuracy of 10-15 cm. Grid size spacing may be 30 cm to 15 m for depths in the 3-150 m range. The beams are automatically adjusted to be equidistant horizontally. A sound velocity profile for calculating accurate depths of soundings were obtained with a sound velocimeter ,deployed before the start of a survey. Depth soundings were merged with 24-hour, P-code Global Positioning System (GPS) navigation. GPS fixes from two receivers aboard the survey boat were collected with a POS/MV Model 320 (Position & Orientation System/Marine Vessels).
Figure 6. 30-foot survey boat of the America Samoa DMWR used for bathymetric surveys.
Figure 7. Kongsberg-Simrad EM-3000 transducer for collecting depth soundings. The transducer was mounted at the end of a metal pole secured to the port side pontoon of the survey boat.
Processing steps included the "cleaning" of depth soundings with a 2nd standard deviation filter to flag outliers (i.e., points beyond the 2nd standard deviation in Simrad bin stat post processing software were flagged or removed). Depth soundings have an accuracy of ~24 m (i.e., points fall within a circle of radius 24 m). Then tidal corrections were applied using NOAA, non- verified downloaded tide data available for the study area. Preliminary pressure water level (N1) data used for the corrections were in meters above MLLW datum from reference station 1770000, Pago Pago, American Samoa. Data have not yet been corrected with differential GPS.
Processed depth soundings from the Kongsberg-Simrad EM- 3000 system were available as ASCII xyz files. These were initially gridded using MB-System, a public-domain suite of software tools for processing and display of swath sonar data (Caress et al., 1996;
http://www.ldeo.columbia.edu/MB- System/html/mbsystem_home.html). Gridding was based on a Gaussian weighted average scheme, because in the absence of artifacts, it does the best job of representing a gridded field bathymetry. Also, the scheme is heavily biased towards those data points closest to the grid point and minimizes anomalous values from outliers (Keeton et al., 1997). Each data point’s contribution to a Gaussian weighted average for each nearby grid cell was calculated as the point was read and added to the grid cell sums (Caress and Chayes, 1995).Grids were then converted to ArcInfo format with ArcGMT, a public-domain suite of tools for converting from grids outputted from MbSystem and Generic Mapping Tools (GMT;
http://imina.soest.hawaii.edu/gmt/) to Arc format (Wright et al., 1998; http://dusk.geo.orst.edu/arcgmt ). Final spacings for most grids were 1-m, with coordinates in latitude/longitude decimal degrees, WGS84 datum. FGDC-compliant metadata records were prepared for all grids, as well as for additional GIS data obtained from the National Park of America Samoa, the USGS, and the Digital Chart of the World, using the NOAA Coastal Services Center metadata collector tool, version 2 (Figures 8 and 9).
Figure 8. Screen dump of the new FBNMS GIS including all multibeam bathymetry grids, as well as compilation of GIS data layers obtained originally from the National Park Service, the USGS, the Digital Chart of the World, and other sources. The top view shows a 10-m USGS DEM for the main island of Tutuila.
Figure 9. FGDC- compliant metadata records were written for all grids, coverages, and shapefiles.
Maps created with data from the Kongsberg-Simrad multibeam system are of excellent quality in terms of both the geological and manmade features that are detailed in them. The data will be suitable as base layers for the purposes of visual overlay and comparison with other data sets in the FBNMS GIS, and subsequent spatial analyses. They also helped to guide the location of a deep-diving mission to FBNMS in May 2001 immediately after the bathymetric surveys. Divers used rebreather technology to stay on the ocean floor for periods of time longer than traditional SCUBA and took numerous digital photographs and video of coral reef biota (see
http://www2.bishopmuseum.org/PBS/samoatz01 ). Even though the diving mission was cut short by poor weather, several new species of fish were discovered in the deepest, previously unsurveyed and unexplored portions of the FBNMS. Gridding and interpretation of the multibeam data are still ongoing, but Figures 10-12 show preliminary results.
Figure 10. 1-m bathymetric grid of the FBNMS with color shading and sun illumination. Cartography by Brian Donahue, University of South Florida. Map projection is Mercator.
Figure 11. 1-m bathymetric grid of the Pago Pago Harbor with color shading and sun illumination. Circle shows the location of a major shipwreck. Cartography by Brian Donahue, University of South Florida. Map projection is Mercator.
Figure 12. 1-m bathymetric grid of the wreck of the USS Chehalis in Pago Pago Harbor. The USS Chehalis (inset photo courtesy of
http://www.nara.gov/publications/sl/navyships/auxil. html) was a World War II oil and gas tanker that exploded and sank in the harbor in 1949. It is thought to be still be a source of pollution in the harbor. Cartography by Brian Donahue, University of South Florida. Map projection is Mercator.A web clearinghouse of data from the mission is now available at
http://dusk.geo.orst.edu/djl/samoa (Figure 13). The site provides GIS data from the recent shallow-water multibeam bathymetric surveys, as well as a compilation of GIS data layers obtained originally from the National Park Service, the USGS, the Digital Chart of the World, and other sources, as well as GMT grids, maps, and various photographic images and graphics. All GIS data are provided as ArcInfo export interchange files (i.e., *.e00 files), which may be imported into ArcInfo, ArcView, or ArcExplorer.
Figure 13. Screen dump of the new FBNMS GIS web site at
http://dusk.geo.orst.edu/djl/samoa, with free downloads of data, thumbnail graphics and FGDC-compliant metadata.In addition, details of the FBNMS surveys and a description of GIS and its utility for coral reef studies and sanctuary management will be featured in the SSE virtual teacher workshop "Conservation and The Coral Reef World: A Virtual Teacher Workshop" will be held on the web (
http://www. coexploration.org/sse), in July and August of 2001. Virtual teacher workshops take advantage of web-based and interactive television technology to reach large numbers of K-12 teachers nationwide, particularly teachers from non-coastal states and those from traditionally under-represented minority groups (Cava, 2001). The SSE has just begun to employ these as innovative ways to provide teachers with direct interaction with SSE scientists and collaborators, instruction on how to incorporate ocean studies into teaching practices, and important Internet skills such as effective use of online search tools, working with online images, and accessing and analyzing online data and maps (Cava, 2001).With the establishment of adequate baseline bathymetric and photo/video transect data, the next objective is the integration of data layers into the GIS for the creation of benthic habitat and species distribution maps on top of the bathymetry. It is also most desirable for these data and maps to be available not only to the FBNMS staff, but to collaborators throughout Oceania and the U.S. (including SSE scientists) via the web-based clearinghouse (Figure 13). The clearinghouse will facilitate the continued distribution and synthesis of information on the sanctuary so that there is less confusion about important data sets, increased contacts and opportunities for collaboration, and increased scientific understanding, particularly in key time series studies for habitat sustainability and coastal development policy-making. A further goal is collaboration with the NOAA Protected Areas GIS (PAGIS), the goal of which is to develop fully integrated GIS, spatial data management, and Internet capabilities within the National Marine Sanctuaries, as well as the National Estuarine Research Reserves (Killpack et al., in press).
Once a critical mass of data and information are available in a FBNMS GIS, steps must be taken to ensure that they are never scattered in various formats and among several agencies, research institutes or universities. Tracking down desired data and metadata will be daunting task for managers and scientists without a structured clearinghouse. For the general public the task will be even more difficult. Many data sets may be restricted to individual projects and then shelved, eliminating the potential for usefulness in a myriad of additional planning, management, and scientific projects. Managers, scientists, and the public may all express confusion over the complexity of identifying data at suitable scales, formats, and quality for designated management areas. Before the quantity of data at this site becomes somewhat overwhelming, the vision of long-term GIS coordination for the sanctuary includes: (1) timely documentation of data sources and contact information; (2) establishing an order of prioritization for data entry based both on availability and quality of the data; (3) integrating digital data into the GIS (ArcView and ArcInfo) using simple format filters and data input programs as necessary (e.g., Wright et al., 1998 and CD-ROM insert, this volume; Wong et al., 1999); (4) compilation of metadata compliant with the Federal Geographic Data Committee (FGDC) standard using the NOAA CSC metadata collector tool (CD-ROM insert, this volume); (5) uploading to a web-based clearinghouse where users can view and query data and metadata online; and (6) documentation of protocols and maintenance procedures for future acquisitions of data.
In terms of subsequent spatial analytical procedures, Bridgewater (1993) and Aspinall (1995) note that combining a landscape ecology approach (i.e., data analysis guided by purposeful ecological objectives) with a GIS is desirable because it allows for the study of structure, function and change within coral reef systems, while attempting to manage the many spatial and temporal scales. For the April- May 2001 survey, a primary long-term objective is analyze physical factors important to coral reef development in FBNMS, such as habitat classification, submarine aspect, submarine slope, and bottom substrate relief, along with several community descriptors, via GIS query, spatial correlation tests, and buffer analysis. Treml (1999) was successful with this approach in analyzing coral reef community ecology on St. John, U.S. Virgin Islands using factors such as current regime, substrate characteristics, coastal topography, bay geometry, watershed size, sedimentation, tropical storm impact, bathymetry, biodiversity, evenness biota distribution, and algae cover.
The "vision" for further post-mission analyses includes:
The author would like to acknowledge the support and contributions of Nancy Daschbach, coordinator of the Fagatele Bay National Marine Sanctuary, John McDonough of the NOAA-NOS Office of Special Programs, and Francesca Cava of the Sustainable Seas Expeditions. The portable multibeam system was provided by David Naar of the University of South Florida (USF), and the excellent assistance of USF research associate Brian Donahue in the collection and processing of the data is greatly appreciated. The author was supported by NSF grant OCE/EHR-0074635.
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