Changing mangrove distributions in the Pioneer estuary (Queensland, Australia): evaluating a technique for monitoring mangrove health

The net area of mangroves in the Pioneer estuary (Queensland, Australia) has declined by 22% (137 ha) since 1948 due to clearing, development, hydrological manipulations, and climate variation. Within the past decade, a severe species-specific dieback has additionally affected over 50% of remnant mangrove cover within the system. We predict this recent, rapid mangrove loss has increased erosion of estuarine sediments and pollutants to nearshore waters. Quantifying historical mangrove changes in the Pioneer Estuary is the key for understanding potential threats to nearshore water quality. While manual digitization from aerial photography is suitable for mapping broadscale changes in mangrove distribution, this technique underestimates the total loss due to dieback. Regions of mangrove dieback can be mapped more effectively and efficiently by applying the Normalized Difference Vegetation Index (NDVI) to Landsat satellite data. In change detection analyses from 1990 to 2000, 44 ha had “lower NDVI” (i.e. reduced canopy density) and 56 ha had “higher NDVI” (i.e. increased canopy density). This study illustrates use of change detection analysis as an important monitoring tool for mangrove habitats in regions of heavy anthropogenic influence; its advantages include rapid processing time (hours), low data costs, and high accuracy