MONITORING MARINE ECOLOGICAL CHANGES ON THE EAST-COAST OF BAHRAIN WITH LANDSAT TM

The main aim of this study was to assess the potential of Landsat TM f or detecting and quantifying marine habitat changes on the Fasht Al-Ad ham reef complex of the east coast of Bahrain. The raw data comprized several digital TM images acquired between 1985 and 1992 during differ ent tidal conditions. Following pre-processing and registration to a d igitized UTM marine chart, the image processing proceeded in two parts . In the first part, visual interpretation was employed using a combin ation of principal component and false color composites (FCCs) of the multi-temporal images to identify the changed areas. Then, and in conj unction with extensive field data, the changed areas between the two d ates were identified. In the second part, post-classification comparis on was employed in combination with digital elevation data to quantify the magnitude of habitat change in the identified areas. The spectral similarity between some of the submerged habitats and, in particular, between seagrass and deep water, and between seagrass, corals, and al gae caused confusion in classification. However, it was found that the problems can be significantly reduced by subdividing the images aroun d the change areas and then classifying each subscene independently af ter appropriate masking of deep water areas. The results indicated tha t between 1985 and 1992, an estimated total of 38,700 m2 of dense cora ls, 1.8 x 10(5) m2 of lower density corals, and 10.2 x 10(6) m2 of sea grass areas were lost. On the other hand, an increase of 4.3 x 10(5) m 2 of algae (Sargassum) was detected in the study area near a large ind ustrial outfall.