Authors: Beaman, R.J.
Publication: C. Field and J. Greenwood (Editors), Catchments to Coast, AMSA Annual Conference, 9-14 July 2006. Australian Marine Sciences Association, Cairns, Australia.
The northern end of the Great Barrier Reef is both remote and relatively unexplored. The area is the focus of questions regarding the role of modern oceanographic processes on sediment transport across the northeast Australian margin, from the high-discharge Fly River to the Gulf of Papua. A research cruise to this region investigated the relationship between sediment, geomorphology and biological communities. Knowledge of the deepwater benthic habitats is essential for effective environmental management and development of regional marine plans. The results from multibeam sonar and Chirp sub-bottom profiles display an unprecedented view of the true nature of the morphology of the seafloor and the variation in sediment texture.
The cruise discovered large relict reefs with karst-type erosion, deep submarine channels, and a vast inactive dune field. Large fluctuations in sea-level during the Pleistocene (last 2 Myr) have resulted in a diverse geomorphology due to both fluvial drainage of the Fly River and tidal scour during lower sea-levels. Extensive groundtruthing with grabs and underwater video established the strong relationships between surficial geology and associated biological assemblages. Diverse mixed gardens of soft corals and calcareous algae are established on the hard substrate relict reefs, with the soft unconsolidated substrate the habitat for mostly detritus- and deposit-feeding fauna. The events of the geological past have a profound influence on the present seabed, and an understanding of the long-term processes on a geological scale which have controlled the form of the seabed are very useful for interpreting benthic habitats.