Geomorphic and habitat mapping of submarine canyons of the Australian continental margin

Submarine canyons influence oceanographic processes, sediment transport, productivity and benthic biodiversity from the continental shelf to the slope and beyond. The relative influence of an individual canyon on these processes will, in part, be determined by its form, shape and position on the continental margin. Based on the latest bathymetry data for the Australian margin, we have mapped 753 submarine canyons and derived a large number of geomorphic metrics based on canyon form, shape and position. In this presentation we highlight key results, which show that these canyon metrics describe a wide variety of canyon form and physical complexity that is consistent with the geological evolution of the Australian margin and the local influence of geological and geomorphological processes. Thus, Australian submarine canyons cluster in the east, southeast, west and southwest where the margin is steepest and continental shelf is narrow. Subsequently, we used 22 environmental variables (including many of the geomorphic metrics) as surrogates to derive estimates of habitat potential for these submarine canyons. Our analysis shows that the high geomorphic and oceanographic diversity of Australian submarine canyons creates a multitude of potential habitat types, notably for benthic infaunal and epifaunal communities. Canyons with particularly high benthic habitat potential are located mainly offshore of the Great Barrier Reef and the New South Wales coast, on the eastern margin of Tasmania and Bass Strait, and on the southern Australian margin. Many of these canyons have complex bottom topography, are likely to have high primary and secondary production, and have less potential for sediment disturbance due to bottom current. Canyons that incise the shelf tend to score higher in habitat potential than those confined to the slope. This habitat potential is exemplified by Perth Canyon, a large shelf-incising canyon on the southwest Australian margin, which we present in this talk as a case study. High-resolution (20m) multibeam sonar data for the canyon reveals the geomorphic complexity characterised by escarpments, transverse ridges, large-scale mass movements and active bedform fields. This geodiversity and the interaction of the Perth Canyon with regional oceanographic currents (the Leeuwin Current and Undercurrent) provide highly diverse habitats for benthic fauna such as deep-sea corals and sponges and a variety of pelagic fauna including cetaceans (e.g., Australian pygmy blue whales, minke whales, sharks and tunas). Abstract submitted to/presented at the 2018 International Network for Submarine Canyon Investigation and Scientific Exchange (INCISE) Symposium (https://www.incisenet.org/)