Abstract

Hydrographers Passage lies on the shelf edge of the central Great Barrier Reef in northeastern Australia. The survey location is approximately 800km(2) in area and ranges in depth from 14 to 300 m. The mapped geomorphic features (>1 km) include a broader-scale slope, terrace, and platform, with smaller reefs and dune features. Sediment grabs from two cross-shelf transects show a generally similar composition of poorly-sorted, muddy sand, and iron stained carbonate gravel. In contrast, dune sediments are a well-sorted sand with no iron staining. Images from two autonomous underwater vehicle (AUV) transects provide the data for a hierarchical clustering of substrate types into five substrate groups: sand, gravel, rubble, sediment-covered limestone, and reef. The AUV imagery reveals a clear distinction between the benthos associated with hard substrate, and soft substrate habitats at a finer-scale than can be shown within the broader-scale geomorphic features. Maximum entropy modeling is used to generate a habitat preference map for azooxanthellate, filter-feeding octocorals.