Where
Submarine canyons within the southwest marine region.
Who
Johnathan Kool, Zhi Huang, Scott Nichol
When
2015
Why
There are 205 identified submarine canyons in the southwest marine region, spanning almost 3000 kilometres along Australia’s continental margin. These canyons host a diversity of marine life, including deep-water corals, crustaceans, fish, whales and seabirds, and support important commercial fisheries such as the southern Bluefin tuna and western rock lobster. However many of the biota found in any given canyon may not have originated there, but instead may have been transported there as larvae via ocean currents from any number of source locations. Understanding source areas and the different pathways marine larvae travel to end up at a particular location is critical for species conservation and fisheries management, as well as in the design and implementation of networks of marine reserves.
How
Larval dispersal was simulated within and above submarine canyons of the southwest region using a 4-dimensional (3D x time) connectivity model. The model uses oceanography, bathymetry, habitat and larval species data to predict where larvae will disperse depending on where and when they are released into the water column. This study focused on ophiuroid (brittlestar) larvae, which are common on the seafloor in this region, and play an important ecological role as detritivores and as prey for larger fish. Dispersal patterns were analysed using a variety of spatial and statistical techniques to identify key source and sink areas, and compared to information on the location and characteristics (e.g. size, shape, depth) of submarine canyons. Canyon information was obtained from previous research by Huang et al. (2014).
What did we learn?
Larval dispersal in the southwest marine region is strongly influenced by the Leeuwin Current, which transports larvae from the area of the Carnarvon Canyon and Abrolhos Australian Marine Parks southwards before rounding Cape Leeuwin and continuing east across the Great Australian Bight. Due to the influence of the Leeuwin Current, offshore canyons occurring at more upstream (northern) locations are more likely to act as sources of larvae to canyons further downstream. This result supports the management of canyons in the region as a network of interconnected systems.
Although the Leeuwin Current was overall the most dominant influence on transport, and enabled larvae to be transported over hundreds of kilometres, approximately 50 percent of larval dispersal was found to occur over distances of just 10–20 kilometres. Given an average distance between canyons of 550 kilometres, this indicates that canyons demonstrate a strong capacity to retain their larvae. This was particularly true of larvae released within the canyon walls as compared to those released above, and of canyons that are large, wide and deep, which were found to act as relative larval sinks.
What next?
Given the potential for canyons located at the upstream end of the Leeuwin Current to contribute larvae over time to canyons off southern Australia, a key next step is to quantify this contribution and to monitor select canyon environments across the southwest region. This will be important for biodiversity conservation and fisheries management in this region into the future.
Related data and publications
Kool, J.T., Huang, Z. & Nichol, S. (2015) Simulated larval connectivity among Australia’s southwest submarine canyons. Marine Ecology Progress Series 539, 77-91. DOI 10.3354/meps11477
For more information please contact marinescience@environment.gov.au.