Landsat thematic mapper: Detection of shifts in community composition of coral reefs

We assembled a time series of 20 Landsat thematic mapper images from 1982 t o 1996 for Key Largo, Florida, to ascertain whether satellite imagery can d etect temporal changes in coral reef communities, Selected reef and control areas were examined for changes in brightness, spectral reflectance, band ratios, spatial texture and temporal texture (Pixel-to-pixel change over ti me). We compared the data to known changes in the reef ecosystem of Carysfo rt Reef and terrestrial sample sites. Changes in image brightness and spect ral-band ratios were suggestive of shifts from coral-to algal-dominated com munity structure, but the trends were not statistically significant. The sp atial heterogeneity of the reef community decreased in the early 1980s at s cales consistent with known ecological changes to the coral community on Ca rysfort Reef. An analysis of pixel-scale variation through time, termed tem poral texture, revealed that the shallow reef areas are the most variable i n regions of the reef that have experienced significant ecological decline. Thus, the process of reef degradation, which alters both the spatial patte rning and variability of pixel brightness, can be identified in unclassifie d thematic mapper images.