Coral reef habitat mapping: A combination of object-based image analysis and ecological modelling

Abstract Despite being one of the most important and well-studied coral reefsin the world, the full extent of coralhabitat of the Great Barrier Reef(GBR) is not well mapped and there is no current and comprehensive map of the GBR's geomorphic zonation or benthic composition. This paper demonstrates an approach that integrates ecological coralhabitat mapping with empirical modelling to map the geomorphic zonation and benthic composition of the “shallow offshore reefs” of the GBR, using the Capricorn BunkerGroup (CBG) as a case study. The approach combined environmental datasets and geo-ecological rule sets to identify geomorphic zones. The benthic composition of individual geomorphic zones was mapped for: shallow reefflat zones, using object-based image analysis with context driven rules based on coral reefecology; and reefslope zones, using levels of wave exposure to predict the distribution of coraltypes. The environmental datasets used were field-based benthic composition data, Landsat 8 OLI satellite image-derivedbottom reflectance, water depth and slope (15 m × 15 m pixel size) data, reefimpact data, and modelled wave exposure. The study showed that the combination of geomorphic-ecological rules and models with remote sensing imagery provided robust mapping results over a large (~2500 km 2 ) reefsystem, of which 245 km 2 was mapped as shallow coral reefsand 88 km 2 of that was mapped as areas containing coral. Most importantly, the method produced defined the geomorphic zones and benthic composition of a study area that is significantly larger than the majority of coral reefremote sensing mapping projectspreviously published. With some modifications, the methods presented have the potential to be applied to the full extent of the shallow offshore reefsof the GBR, or any large reefglobally. Monitoring and management of coral reefsfor conservation and other purposes, at regional to global scales will benefit from the ability to produce and use this type of essential information on a regular basis.