Naturaliste 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 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 South-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

The Naturaliste Plateau is Australia’s deepest temperate marginal plateau. Although very little is known about the marine life of this plateau, the combination of its structural complexity, mixed-water dynamics and relative isolation indicate that it supports deepwater communities with high species diversity and endemism (DEWHA 2008a). The plateau acts as an underwater ‘biogeographical island’ on the edge of the abyssal plain, providing habitat for fauna unique to these depths (Richardson et al. 2005). The plateau is also within a deep eddy field that is thought to be associated with high productivity and aggregations of marine life (Pattiaratchi 2007). Proximity to the nearby subtropical convergence front is thought to have a significant influence on the biodiversity of the plateau (DEWHA 2008a).

National and/or regional importance

The Naturaliste Plateau is recognised as a key ecological feature for its biodiversity values, including a unique seafloor feature with ecological properties of regional significance, which apply to its benthic and demersal habitats.

Location

The Naturaliste Plateau lies west of Cape Leeuwin and Cape Naturaliste, and is Australia’s deepest temperate marginal plateau. It extends approximately 400 km east-west and 250 km north-south, covering approximately 90 000 km² of deepwater habitat (depths of 2000–5000 m). It is relatively flat with a slight northward dip, and has steep southern and western sides and a more gently sloping northern side. Submarine canyons incise the northern parts of the slope and parts of the Naturaliste Plateau. The Plateau features cliffs up to 1000 m high.

It is bordered by the South Australian Abyssal Plain in the south and the Perth Abyssal Plain in the west and north, and is separated from continental Australia by the Naturaliste Trough to the east. A terrace feature is present on the steep southern side of the plateau between 4500–5000 m, before the margin grades into the abyssal plain (Borissova 2002; Harris et al. 2005). The plateau marks the boundary between Australia’s western and southern continental margin (Borissova 2002).

The spatial boundary of this KEF, as defined on the Conservation Values Atlas, is based on the area identified in the Geoscience Australia geomorphic features dataset.

Description

The Naturaliste Plateau is a complex and isolated seafloor feature that occurs in an area where numerous water bodies and currents converge. It is also the only seafloor feature in the region that interacts with the subtropical convergence front.

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 Naturaliste Plateau.

Pressures assessed as of potential concern are changes in sea temperature, change in oceanography and ocean acidification as a result of climate change. These pressures are described in more detail below.

Changes in sea temperature (climate change)
Sea temperatures have warmed by 0.7 °C between 1910–1929 and 1989–2008, and current projections estimate ocean temperatures will be 1 °C warmer by 2030 (Lough 2009). The implications of changes to the region’s sea temperatures and oceanography for deeper ocean environments are uncertain, although sea-water warming at depth is expected to have significant implications for benthic and demersal fish.

Change in oceanography (climate change)
The strength of the Leeuwin Current has decreased slightly since the 1970s. This weakening is expected to continue, although this prediction currently has low confidence (Feng et al. 2009). The Leeuwin Current is the basis of much of the region’s biological productivity, and its strength and seasonal/climatic variability are a primary driver for the intensity, timing and locations of productivity events in the region, from the waters off Geraldton to the Great Australian Bight (Pattiaratchi 2007). Numerous water bodies and currents converge at the Naturaliste Plateau, including the subtropical convergence front. These complex water dynamics are likely to experience considerable changes if there are significant changes to ocean circulation in the region, with flow-on effects for the entire ecosystem.

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). Projected changes in Australian waters by 2070 include a decline in pH of 0.2 units (Lawrence et al. 2007). There is a high level of uncertainty about the effects of ocean acidification on marine life. While some organisms might be able to adapt (Orr et al. 2009), anticipated changes to phytoplankton and zooplankton have the potential to detrimentally affect ecosystem processes and the structure of ecological communities. Research on the impact of ocean acidification on Antarctic krill has found that increased levels of CO₂ kill their embryos (Kawaguchi et al. 2011). Krill are an important part of the food chain because they feed on phytoplankton and zooplankton, and are a key food source for many species that occur in Australian waters. Consequently, acidification impacts have the potential to affect species further up the food chain. The potential effects of increased acidity on the region’s biodiversity also include changes to growth and population dynamics of some shell-forming organisms, impacts on the reproductive and metabolic functions of a number of fish and invertebrate species, and sensitivity of some early-life stages to acidification (Orr et al. 2009).