DECADAL CHANGE IN CORAL REEF HABITATS OF THE MIDDLE FLORIDA KEYS (USA) USING SATELLITE IMAGERY

摘要

Coral reef ecosystems worldwide are undergoing change due to a variety of anthropogenic impacts. The reefs in the Florida Keys have degraded significantly in the past 25 years. Recent studies detected a 15% decrease in live coral cover and an increase of bare substrate in the Middle Keys. However, the spatial extent of these changes has not been mapped. Coral reefs are traditionally sampled in situ, but remote sensing offers a cost-effective approach to mapping spatial and temporal change of coral reefs and associated habitats. To assess temporal change in coral reef substrates in the central Florida Keys, we acquired Landsat Thematic imagery from 1990 and 2000. The study area included reefs that demonstrated declining live coral cover since at least 1996. Landsat Thematic Mapper imagery was geo-rectified, an image-based water column attenuation correction performed, and an unsupervised classification used to identify coarse habitat types. We collected geo-coordinate data for substrate types (minimum 30 per substrate type) and used them to aggregate spectral classes into a habitat classification map. We also used the geo-coordinate data to determine the accuracy of the unsupervised classification. These results assess the feasibility of using Landsat TM to detect shifts in coral reef habitats (sand, seagrass, live coral, mixed hardbottom) over a 10-year time period.