Canyons linking the Argo Abyssal Plain and Scott Plateau

Legal description

The Commonwealth marine area is a matter of national environmental significance under the Environment Protection and Biodiversity Conservation Act 1999(EPBC Act). As such, actions that have, will have, or are likely to have, a significant impact on it require approval.

In February 2014, the National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA) became the sole designated assessor of petroleum and greenhouse gas activities in Commonwealth waters in accordance with the Minister for the Environment’s endorsement of NOPSEMA’s environmental authorisation process under Part 10, section 146 of the EPBC Act. Under the streamlined arrangements, impacts on the Commonwealth marine area by petroleum and greenhouse gas activities will be assessed solely through NOPSEMA.

Key ecological features (KEFs) are not matters of national environmental significance and have no legal status in their own right. However, they may be considered as components of the Commonwealth marine area.

This KEF was identified in the North-west Marine Bioregional Plan. Under section 176 of the EPBC Act, once a bioregional plan has been made the minister responsible for the environment must have regard to it when making any decision under the Act to which the plan is relevant.

Values

National and/or regional importance

The Canyons linking the Argo Abyssal Plain with the Scott Plateau are defined as a key ecological feature for their high productivity and aggregations of marine life. These values apply to both the benthic and pelagic habitats within the feature.

Location

The Bowers and Oates canyons are the largest canyons connecting the Scott Plateau with the Argo Abyssal Plain. They are situated in the Timor Province, west of Scott reef.

The spatial boundary of this KEF, as defined in the Conservation Values Atlas, includes the three canyons, as defined in the Geoscience Australia geomorphic feature dataset, adjacent to the south-west corner of Scott Plateau.

Description

The canyons cut deeply into the south-west margin of the Scott Plateau at an approximate depth of 2000–3000 metres, and act as conduits for transport of sediments to depths of more than 5500 metres on the Argo Abyssal Plain (Stagg 1978, cited in Falkner et al. 2009). The water masses at these depths are deep Indian Ocean water on the Scott Plateau and Antarctic bottom water on the Argo Abyssal Plain. Both water masses are cold, dense and nutrient-rich (Lyne et al. 2006).

Whaling records from the 19th century (Bannister et al. 2007) indicate that sperm whales occurred on Scott Plateau; however, the reasons for these historical aggregations of marine life remains unclear (DEWHA 2008).

Pressure

During the development of marine bioregional plans, a regional pressure analysis was conducted to assess present and emerging pressures affecting conservation values in the Marine Regions and the effectiveness of mitigation and management arrangements that are currently in place to address these pressures. The analysis enabled pressures to be categorised in terms of their relative importance or concern and has informed the identification of regional conservation priorities. For the purpose of the plans, pressures are defined broadly as human-driven processes and events that do or can detrimentally affect the region's conservation values.

No pressures were assessed as of concern for the Canyons linking the Argo Abyssal Plain with the Scott Plateau.

Only one pressure is assessed as of potential concern - ocean acidification as a result of climate change. This pressure is described in more detail below.

Ocean acidification (climate change)
Driven by increasing levels of atmospheric CO₂ and subsequent chemical changes in the ocean, acidification is already underway and detectible. Since pre-industrial times, acidification has lowered ocean pH by 0.1 units (Howard et al. 2009). Furthermore, climate models predict this trend will continue with a further 0.2–0.3 unit decline by 2100 (Howard et al. 2009).

Ocean acidification will compromise carbon accretion and, together with increasing ocean temperatures, may result in loss of ecosystems based on geologic features formed from coral or coralline algae (Hoegh-Guldberg 2011; Hoegh-Guldberg et al. 2007; Kleypas & Yates 2009; Kuffner et al. 2008). Increasing acidity impairs the ability of species with calcareous shells, such as echinoderms, crustaceans and molluscs, to maintain shell integrity resulting in reductions of the overall abundance and biodiversity of these species (see review by Kleypas & Yates 2009). A decrease in the abundance of fauna with carbonate-based skeletons and coral and coralline algal abundance, and the complex structural habitats they create, could lead to changes in ecosystem structures, processes, and connectivity between the reef complex and the adjacent deeper waters.