2016 SoE Marine Chapter - State and Trends - Canyons

Brief description

The Marine chapter of the 2016 State of the Environment (SoE) report incorporates multiple expert templates developed from streams of marine data. This metadata record describes the Expert Assessment "The state and trends of quality of habitats and communities – canyons". The full Expert Assessment, including figures and tables (where provided), is attached to this record. Where available, the Data Stream(s) used to generate this Expert Assessment are accessible through the "On-line Resources" section of this record. ---------------------------------------- DESCRIPTION OF ECOLOGICAL HABITAT/COMMUNITY FOR EXPERT ASSESSMENT Submarine canyons are a class of geomorphic seabed feature used as a physical surrogate for biodiversity distribution during Australia’s marine planning process and in designing the network of Commonwealth Marine Reserves. They are one of two ‘special’ feature types (together with seamounts) (Harris et al., 2008) believed to have potentially high influence on and value for marine biodiversity distribution and protection. It is these characteristics that have been used to define some canyons as Marine Key Ecological Features (Department of the Environment, 2012). Submarine canyons are located on all sides of the Australian continental margin. They form deeply incised networks of valleys and channels that extend from the continental shelf edge (<200 m water depth) to the foot of the continental slope (>4000 m water depth). Based on a recent compilation of all available bathymetric data for the Australian EEZ, a total of 713 submarine canyons are now mapped on the continental margin, with an additional 40 canyons that fringe islands within the external territories (Table 1; Huang et al., 2014). The majority (618) of the mapped canyons are classified as ‘blind canyons’, meaning that they are located only on the continental slope and terminate at their head in water depths of ~500 to 1000 m. The other 95 canyons are classified as ‘shelf-incising’ canyons that extend from the slope onto the continental shelf, with canyon heads that define an abrupt depth transition between the slope and shelf of up to 400 m. Between Marine Planning Regions canyons vary in number and spatial distribution. Thus, canyons are most abundant in the South-East (206 canyons) and South-West (204) Marine Regions, with the latter having the higher proportion (51) of shelf-incising canyons. The Temperate East has 124 canyons. In contrast, the North-West and North Marine Regions incorporate 90 and 6 canyons, respectively. Within canyons, the seabed is characteristically irregular with underlying substrate exposed along steep canyon walls, in places forming undersea cliffs hundreds of metres high. These localised areas of hard rock outcrop provide a stable surface for benthic biological communities, including sponges, corals and associated sessile flora and feeding grounds for demersal fishes (Schlacher et al., 2007; Fromont and Pisera, 2011; Currie and Sorokin, 2014; Kloser et al., 2014). Canyons also provide a pathway for the transport of sediments and nutrients, not only laterally from the shelf to the deep sea, but also vertically via upwelling of cold, nutrient-rich waters from the deep ocean toward the shelf (Kampf, 2010; Currie et al. 2012). This effect is now better understood through the modelling of larval dispersal, as driven by ocean currents. The modelling shows that more topographically complex canyons are potential settlement sites for marine larvae. For example, the canyons in the Albany Canyon Group which intersects the Leeuwin Current along the southwest margin are modelled as larval sinks, including the large Bremer Canyon and Wilson Canyon. DATA STREAM(S) USED IN EXPERT ASSESSMENT National Submarine Canyons of Australia [Geoscience Australia data product] ---------------------------------------- 2016 SOE ASSESSMENT SUMMARY [see attached Expert Assessment for full details] • 2016 • Assessment grade: Good but poor in the South-East Assessment trend: Unclear Confidence grade: Limited evidence and limited consensus Confidence trend: Limited evidence and limited consensus Comparability: Grade and trend are somewhat comparable to the 2011 assessment • 2011 • Assessment grade: Very good Assessment trend: Stable Confidence grade: Limited evidence or limited consensus Confidence trend: Limited evidence or limited consensus ---------------------------------------- CHANGES SINCE 2011 SOE ASSESSMENT Not clear how the 2011 assessment was undertaken.

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Statement: QUALITY OF DATA USED IN THE ASSESSMENT Very good

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Purpose
To describe the state and trends in submarine canyons for use in the Marine chapter of the 2016 State of the Environment report.