Diamantina Fracture Zone

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 Diamantina Fracture Zone is a rugged, deep-water environment composed of seamounts and numerous closely spaced troughs and ridges covering more than 100 000 km². Ridges can rise up to 4000 m from the seafloor; together with seamounts, these can affect water dynamics and flow, enhancing productivity. They may act as ‘stepping stones’ for species dispersal and migration across the region and the wider abyssal plain (Wilson & Kaufman 1987, in Richardson et al. 2005). While research on the Diamantina Fracture Zone is limited, its size, physical complexity and isolation indicate that it is likely to support deepwater communities characterised by high species diversity and endemism.

National and/or regional importance

The Diamantina Fracture Zone is defined as a key ecological feature because it is a unique seafloor feature with ecological properties of regional significance which apply to its benthic and demersal habitats.

Location

The Diamantina Fracture Zone is a structurally complex area of extremely rugged topography south of the Naturaliste Plateau. It is a deepwater environment (> 3000 m depth) composed of numerous closely spaced troughs and ridges, with a characteristic east–west orientation (Stow 2006). Covering more than 100 000 km², the zone extends from Broken Ridge 95° E in the Indian Ocean to 120–125° E (Richardson et al. 2005). The ridges, troughs and seamounts forming the fracture zone can have a relief of up to 4000 m. Such complex topography results in highly variable environmental conditions, such as depth, temperature, trophic conditions and ocean current systems (Heinz et al. 2004 in Richardson et al. 2005).

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 range of environmental conditions found in the fracture zone may create distinctive community structures, and has the potential to support a variety of unique habitat types. High habitat heterogeneity is thought to be linked to increased biodiversity, although the study of this relationship is still in its infancy (Levin et al. 2010). Seamounts and ridges can create obstacles to current flow, causing eddies and circular currents, turbulent mixing and localised upwelling and downwelling. These physical processes may result in increased local primary and secondary productivity and the trapping of particles, nutrients or organisms (Richardson et al. 2005). Such an accumulation of particles and nutrients may promote phytoplankton growth, which in turn encourages a variety of marine life, such as whales and dolphins, fish species and benthic biota; a paradigm in seamount ecology that was confirmed as plausible by the review of Rowden et al. (2010).

The area is expected to sustain habitats similar to those occurring at similar depths on and around the Tasmanian Seamounts in the South-east Marine Region (Richardson et al. 2005). The Diamantina Fracture Zone encompasses the deepest known points in Australia’s exclusive economic zone, reaching depths of more than 6000 metres.

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 Diamantina Fracture Zone.

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).