Submarine canyons, often rich and productive, have been identified in the Australian Government’s marine bioregional plans as areas of relatively high productivity and marine life aggregation. But few canyons around Australia have had their bathymetry mapped in detail or been biologically sampled.

A national classification of canyons being developed by the NERP Marine Biodiversity Hub will provide an analysis of physical and biological variation among canyons, which will be important for conserving biodiversity and sustainable use of resources. The work will show how unique a particular canyon is – in a local, regional and national context – and how likely it is to support a higher level of biodiversity than surrounding areas.

The classification will draw on the national bathymetry grid compiled by Geoscience Australia (GA) at a spatial resolution of 250 metres and incorporate finer resolution data collected by CSIRO and GA for many years from the Marine National Facility Research Vessel Southern Surveyor.

It will derive a range of metrics that describe canyon form (location and exposure to large-scale ocean currents), and which may influence biodiversity through processes such as upwelling. These physical parameters will be tested against available biodiversity data from the seafloor to large charismatic megafauna.

Some of the data to be used for this analysis are being collected in a Marine Hub survey of Flinders Commonwealth Marine Reserve off north-eastern Tasmania. The survey, from the Research Vessel Challenger, includes several canyons that extend onto the continental shelf that have now been mapped at fine resolution (see Flinders Reserve story in this newsletter).

The classification builds on earlier research by Dr Peter Harris of GA. While working with the CERF Marine Biodiversity Hub, Dr Harris and co-author Tanya Whiteway published an inventory of 5849 large submarine canyons in the world ocean that extended over at least 1000 metres in depth. They found that large river-associated or shelf-incising canyons of this size were absent from the Australian and Antarctic coastlines and rare for NE Asia and islands. River-associated or shelf-incising canyons tend to hold greater benthic biomass and biodiversity than non-shelf-incising canyons, and Dr Harris and Ms Whiteway concluded that the need to conserve canyon ecosystems in Australia, NE Asia and islands would be greater than elsewhere.

The canyon classification being undertaken by the Marine Hub will extend the global analysis of large submarine canyons to smaller canyons around Australia. This extension is only possible because Hub scientists are able to use ship-collected swath bathymetry data to provide higher resolution maps of the seafloor than was available in the global analysis of canyons.

The swath mapper on RV Southern Surveyor was funded by the National Oceans Office (now part of the SEWPaC), GA and CSIRO, and has been used routinely on most research voyages since 2004.  Directing the vessel to maximise the topographic information collected during transit legs and translating these data into maps and other management tools, however, has relied on the interest and dedication of individual scientists.

The enhanced capabilities and capacity of Australia’s new RV Investigator, scheduled for duty in 2013, will provide an opportunity to re-consider how the national research capability can support the Australian Government’s commitment to marine bioregional plans.

Map:

• Location of canyons from this study using the ETOPO1 one mile (1.85 km) grid, projected onto an extract of a seafloor geomorphology map of the Australian continental margin compiled by Heap and Harris (2008) based on a 250 m bathymetry grid. Canyon locations are similar but not exact. (Fig. 3, Harris and Whiteway, p77)

Further reading:

• Harris P. T., Whiteway T. (2011). Global distribution of large submarine canyons: Geomorphic differences between active and passive continental margins. Marine Geology 285, 69-86.

Contact:
Dr Scott Nichol, Geoscience Australia