GIS Use in Mapping Coral Reefs

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1 GIS Use in Mapping Coral Reefs Coral reefs rank among the most biologically productive and diverse of natural ecosystems and are undoubtedly one of the major biodiversity hot spots on the planet. Coral reefs occur mainly between the Tropics of Cancer and Capricorn, and further north and south within warm currents. Corals are slow growing and sensitive to their environment, making it more of a challenge for reefs to restore themselves after impact. With a general worldwide trend towards coral reef degradation, the management of these valuable ecosystems has become more important than ever. Habitat mapping is a prerequisite for condition and resources assessment of any ecosystem which leads to the implementation of management practices. There are many causes for the degradation of coral reef systems, including urbanization of coastal areas (Lewis 2002), hurricanes and tropical storms (Gardner et al. 2005). Degradation has more than one form. Symptoms of coral decline may include skeleton breakage and lose of live coral cover, changes in community composition and loss of species diversity, reduction in reproductive output and recruitment, disease, death and coral bleaching (Lewis 2002). Specifically, coral bleaching is the expulsion of symbiotic pigmented zooxanthellae from the coral body (Andréfouët 2002). Regardless of the type of degradation, it can be monitored using GIS and remote sensing. One method of mapping coral reefs is through oceanographic methods such as sidescan sonar. For mapping with side-scan sonar, overlapping transects of the reef area are run producing a georeferenced mosaic (Franklin et al. 2003). This mosaic can be used a base layer in GIS, and be digitized to show areas, boundaries and specific locations (points, lines, and polygons), creating a map. In their study of the Tortugas region of Florida, Franklin et al. interpreted five categories of deeper reef habitats based on image contrast and density that reflected the apparent relief and complexity of benthic features from a side-scan sonar mosaic (2003). Using GIS, they digitized polygons of the categories, and displayed them accordingly in a map (Franklin et al. 2003). Another method of mapping coral reefs is analyzing aerial photographs. Aerial photograph analysis is also a good way of monitoring change in reefs over long periods of time, since there are many archived aerial photos going back decades that can be used for comparison to current photos. With aerial photography analysis, reefs are described according to their geomorphology rather than explicit ecological properties (Lewis 2002). Using GIS analysis of aerial photography from 1950 and 1991, Lewis was able to show structural loss of fringing coral reefs at the island of Barbados (2002).

2 He did this by digitizing polygons of the borders of the reefs and calculating the areas in GIS, then overlaying the layers to see the changes (Lewis 2002). Despite the many advancing in other remote sensing techniques, aerial photography often remains as the preferred technology (Dahdouh-Guebas 2002), especially in shallow reefs close to the ocean surface. The use of satellite imagery is also common in the mapping of coral reefs. Satellite imagery has the advantages of increased spectral resolution, more frequent temporal resolution (though not as far in the past as aerial photography), and a large range of spatial resolution (Dahdouh-Guebas 2002). For a temporal study of mapping coral bleaching, satellite imagery is the preferred technology, as bleached corals have a distinct increase in reflectance, though a very fine resolution is required (~10cm) to best see the full extent of the bleaching event (Andréfouët 2002). Turner and Klaus used Landsat ETM imagery, processed with ERDAS, in their study of the coral reefs of the Mascarenes (2005). Scuba and snorkel surveys collected data which was then linked to the Landsat imagery and compared with aerial photography in GIS to create a map showing reef classifications (Turner and Klaus 2005). The authors acknowledged the usefulness of GIS in integrating data of many different types into a single database (Turner and Klaus 2005), which can be queried and mapped accordingly. Bello-Pineda et al. took GIS mapping of coral reefs to a new level with the incorporation of Landsat TM imagery, aerial photography, and aerial video mosaics (2006). This fusion of imagery technology created a complex thematic map, which was used to create map units in the Automated Land Evaluation System (ALES) software (Bello- Pineda et al. 2006). The ALES data was exported to the GIS as an attributes database and linked to the thematic map (Bello-Pineda et al. 2006). The combined data was used to create suitability maps of utilizing different resource types of the reef, for example a lobster fishery and snorkeling (Bello-Pineda et al. 2006). There are many different ways of mapping coral reef systems, and the method selected seems to depend on what question you are asking. To demonstrate the temporal change in area of a reef system, a simple area calculation from an aerial photo is sufficient. However, if the sustenance of an area is dependent on the reef resources, the method described by Bello-Pineda et al. for creating a suitability map for different resources for proper management would probably be a better analysis to conduct. However, the more complex the analysis, the more it will cost to perform said analysis, and cost is often an issue. Despite this, as the need to better manage the world s coral

3 reefs the best we possibly can increases each year, I would like to see more suitability assessment analyses conducted to better manage what resources remain. In the future, it is likely that coral reef mapping will also start including larger analyses of artificial reefs. Artificial reefs are deployed for various reasons to increase reef fish production with new habitat (Rubec 1999), and to provide additional hard substrate to increase the settling of coral polyps in attempts to restore reefs. The artificial reefs are usually deployed close to natural reefs (Tseng et al. 2001). Over time, it is assumed that polyp settlement will occur, and will build up over the years, possibly creating new reef systems, as the more the corals build, the more reef dependent species will settle in as well, creating new ecosystems. Artificial reef deployment will by no means create new reefs overnight, but in the future, they have the potential to become more ecologically important as natural reefs continue to decline. Florida is ahead of the game and has already mapped many of its artificial reefs in GIS and made the data available to the general public (Rubec 1999), and I should like to see more areas follow suit. Satellite imagery has the potential to replace aerial photography, as the technology is progressing quickly. The availability of hyper-spectral imagery will have an impact, as more minute data will be able to be obtained from images at incredible resolution. Satellite imagery is there, if you have the money and know the site location. Aerial photography is not always easily obtainable, readily available, or cost effective, if the reef is in a remote location. In addition, each year more satellites are deployed with the newest technology, so there are many options in getting the imagery you need of the target reef to complete a GIS analysis. In the future, I think hyper-spectral imagery will take GIS mapping to a level that will be amazing. Literature Cited Andréfouët, S., et al Choosing the appropriate spatial resolution for monitoring coral bleaching events using remote sensing. Coral Reefs 21: Gardner, Toby A., et al Hurricanes and Caribbean coral reefs: impacts, recovery patterns, and role in long-term decline. Ecology 86(1): Tseng, Chen-Te, et al GIS-assisted site selection for artificial reefs. Fisheries Science 67:

4 Annotated Bibliography Bello-Pineda, J., R. Ponce-Hernandez, and M.A. Liceaga-Correa Incorporating GIS and MCE for suitability assessment modelling of coral reef resources. Environmental Monitoring and Assessment 114: This study focuses on the incorporation of GIS with multicriteria evaluation (MCE) for the development of suitability assessment models for coral reef resources at the Alacranes Reef National Park (ARNP), Yucatan, Mexico. Landsat TM imagery from February 1998 was georeferenced to 1:75,000 analog black and white aerial photos from January 1996 was used as the base layer for the GIS analyses. Aerial video transects were acquired and digitized to raster format and individual frames were pasted together to create video mosaics and then georeferenced. To create a thematic map of the ARNP, the video mosaics were overlaid on top of the aerial photographs, the composite Landsat TM image and an already existing bathymetric model in GIS. Using the spatial resolution of the video and field study data, conspicuous habitats at the reef were identified, and digitized in GIS, effectively mapping the reef system of the ARNP by classification. From this map, using MCE, and incorporating physical and biological data, a suitability map can be created for different resources and management strategies implemented. Dahdouh-Guebas, Farid The use of remote sensing and GIS in the sustainable management of tropical coastal ecosystems. Environment, Development and Sustainability 4: The author recognizes the importance of coastal ecosystems such as mangrove forests, seagrass beds, and coral reefs and the need to successfully develop and implement appropriate management practices. Remote sensing images provide a valuable look at the environment at different spatial, temporal, and spectral resolutions. GIS enables the researcher to view the different resolutions as different layers and displayed simultaneously. This paper s value is in the options presented for acquiring the imagery and which type of sensor is best for the ecosystem you want to study. The author stresses the ability to view temporal changes in GIS and its value in predicting the future status of coastal ecosystems. This is an important aspect of coral reef management. Franklin, Eric C., et al Benthic habitat mapping in the Tortugas region, Florida. Marine Geodesy 26: Franklin et al. recognize that the creation of no-take and marine protected areas (MPA) are a sure way to protect coral reefs and the associated fish species. Before new management practices can be implemented, the area must be thoroughly analyzed.

5 The authors created, integrated, and manipulated data with ArcInfo to produce a digital benthic habitat map of the Tortugas region of study. Data sets were collected for a period of roughly ten years using bathymetric soundings, thematic coverages generated from aerial photogrammetry, single-beam side-scan sonar, and in situ visual surveys. The combined data produced not only a bathymetric map of the areas reefs, but also a classification map. This data greatly contributed to the implementation of three no-take MPAs totaling approximately 675 km 2 in the Tortugas region. Lewis, J.B Evidence from aerial photography of structural loss of coral reefs at Barbados, West Indies. Coral Reefs 21: Lewis used aerial photography to show evidence of coral reef degradation around the island of Barbados in the West Indies. Archived aerial photos from 1950 (1:12,000) and 1991 (1:10,000) were scanned at 600 dpi. The 1:12,000 scale photos were enlarged and the scale corrected with reference to a 1:10,000 topographical map before scanning. Geospatial points of reference were added to the photos, and the coral reef borders were traced, the areas calculated, and the results overlaid using geographic information system analysis. Eight locations of detected reef degradation were selected for field verification. Lewis showed that Barbados reefs showed had lost up to 24% of their structure in the 41 year period. Rubec, P.J GIS as a tool for research, management and placement of artificial reef fisheries. Pages , In: Florida Artificial Reef Summit 98, Proceedings of a conference held in West Palm Beach, Florida. Florida Department of Environmental Protection, and Palm Beach County Department of Environmental Resources Management. In this paper, Rubec focuses on the mapping of benthic habitats for the deployment of artificial reefs and artificial reef systems using GIS. Artificial reefs are deployed to help restore coral reefs and coral reef fisheries. Just like natural coral reefs, artificial coral reefs must be appropriately managed and their status monitored over time. The monitoring of reef systems can facilitate immediate implementation of different management practices through database queries of potentially impacted areas (following hurricanes for example). The frequency with which GIS is now used allows researchers to easily provide the data sets to other agencies and the public. Turner, John and Rebecca Klaus Coral reefs of the Mascarenes, Western Indian Ocean. Philosophical Transactions of the Royal Society 363: In this study, Landsat imagery of the Mascarenes was processed using ERDAS image software and used as a base layer to develop relational database with GIS. In situ analysis was also conducted at reef locations, and all external data was linked to the database. The classified biotope map was converted to a polygon vector layer in GIS.

6 The reefs were classified into biotopes based on both physical and biological factors, such as age, vegetation, bathymetry, and density. This study is a good example of detailed classification mapping in GIS as a tool for management, specifically marine protected area planning.