Graduate Thesis Or Dissertation
 

The development and application of benthic classifications for coral reef ecosystems below 30 m depth using multibeam bathymetry : Tutuila, American Samoa

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/hm50tx417

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  • Coral reef ecosystems are the most diverse on earth, and their subsistence is being threatened by natural and adverse anthropogenic patterns and processes. In an effort to understand and protect these marine environments, several programs have outlined strategies and initiatives. For example, the United States Coral Reef Task Force’s Mapping and Information Working Group has outlined a specific goal to map all coral reefs below 30 m depth by 2009. This study contributes to achieving that goal for three sites around the island of Tutuila, American Samoa, lying in the heart of the South Pacific. American Samoa, a U.S. territory, is home to the Fagatele Bay National Marine Sanctuary, the smallest and most remote in the United States, and to the National Park of American Samoa. Extensive modern scientific surveys were implemented around the territory in 2001 and have since continued and increased. The presence of protected areas and the existence of scientific data collected with state of the art technology have made the site a priority for the Coral Reef Task Force. In this study, methods for classifying surficial seafloor characteristics as bathymetric position index (BPI) zones and structures were developed and applied to the study sites. BPI zones and structures were classified by using algorithms that combine high-resolution (1 m) multibeam bathymetry and its derivatives: bathymetric position index at multiple scales and slope. The development of algorithms and the classification scheme involved the use of historical and current classification studies and three-dimensional visualization. In addition, the BPI zones and structures were compared to limited biological, geological, and physical attributes recorded during accuracy assessment surveys (photos) and towed diver surveys (video). A rugosity (surface ratio) analysis was added to the study to give a picture of the seafloor roughness. The BPI zone and structure classifications overlap and extend existing classifications from Ikonos satellite imagery for water depths shallower than 30 m. Methods, data and classifications developed and applied in this study will be available to the public as a benthic habitat mapping tool (ArcGIS extension), in an online GIS data archive, and on a compact disc attached to this thesis. They contribute to a broader understanding of the marine and coastal environment and will serve as a baseline of information for benthic habitat mapping and future biological, ecological, and geological surveys. The baseline gives a good indication of characteristics that may indicate areas of high biodiversity. The final maps presented here are especially useful to managers, researchers and scientists that seek to establish and monitor a wider and more effective network of marine and coastal protection.
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