Canyons on the eastern continental slope

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 Temperate East 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

Canyon systems have a marked influence on diversity and abundance of species through their combined effects of topography, geology and localised currents, all of which act to funnel nutrients and sediments into the canyon (Kloser & Keith 2010). As such, these features are valued for their enhanced productivity and biological diversity properties. Canyons contribute to habitat diversity by providing a hard surface that offers anchoring points and vertical relief for filter feeder benthic species (Bax & Williams 2001). Hard substrata support different species assemblages; particularly favouring large filter feeder–dominated benthic species (e.g. attached sponges and crinoids) that thrive in abundance in the enhanced current flow conditions (Brewer et al. 2007). Large benthic animals such as sponges and feather stars are abundant, with particularly high diversity found in the upper slope regions (150–700 m) (Kloser & Keith 2010).

A range of higher trophic level species, including crustaceans, echinoderms, bivalves, cephalopods and fish are then attracted to these regions. Canyons are therefore significant contributors to overall biodiversity, particularly in terms of benthic organisms. Due to isolation, restricted dispersal and connectivity, it is also expected this diversity encompasses a high degree of endemism, further contributing to the social and biological values of these communities (Brewer et al. 2007; Stocks & Boehlert 2003).

National and/or regional importance

The canyons on the eastern continental slope provide habitat (through changes in topography and productivity) that supports a diverse range of benthic, demersal and pelagic species.

The Canyons on the eastern continental slope are defined as a key ecological feature as they are a unique seafloor feature with enhanced ecological functioning and integrity, and biodiversity, which apply to both its benthic and pelagic habitats.

Location

Submarine canyons are widespread features around the Australian continent and island margins (Heap & Harris 2008, in Kloser & Keith 2010) and the eastern continental slope features a large number of canyons (Brewer et al. 2007).

The spatial boundary of this KEF, as defined on the Conservation Values Atlas, is a combination of partial datasets - shelf incising canyon head perimeters (CSIRO 2010) and Geomorphic features of the EEZ (Geoscience Australia 2004).

Description

Canyons also affect the water column, interrupting the flow of water across the sea floor and creating turbulent conditions in the water column. This turbulence transports bottom waters to the surface, creating localised upwellings of cold, nutrient-rich waters, which result in regions of enhanced biological productivity relative to surroundings waters (Prince 2001). The enhanced food availability acts to aggregate higher trophic level species, from pelagic tunicates and coelenterates to apex species such as tuna and seabirds, creating regions of high biodiversity (Brewer et al. 2007). During winter, a decrease in water temperature can change water-mass densities, creating regions of downwelling. Although generally associated with low nutrient regimes, in this context these events are thought to play an important role in breaking down shelf-edge fronts, displacing deeper oceanic slope water and consequently pushing relatively nutrient-rich water towards the photic zone (Prince 2001).

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 on the eastern continental slope.

Pressures assessed as of potential concern are changes in sea temperature and change in oceanography as a result of climate change; chemical pollution; marine debris; physical habitat modification; extraction of living resources; bycatch; and oil pollution. 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 a further 1 °C warmer by 2030 (Lough 2009). Expected impacts include changes to food web dynamics (Hoegh-Guldberg & Bruno 2010), potentially increasing the frequency or severity of coral bleaching events, and a southerly shift in the distribution of pelagic fish species (Hobday et al. 2006). For features located in the deeper waters of the region, the impacts of rising sea temperatures are more complex. Rising temperatures drive changes such as thermal expansion (Hoegh-Gulberg & Bruno 2010), resulting in greater stratification in the water column, reducing mixing in some parts of the ocean, and consequently affecting nutrient availability and primary production at depth (Hoegh-Gulberg & Bruno 2010).

Changes in oceanography (climate change)
Changes in oceanography include consideration of circulation patterns; current intensities; wind strength and direction; the location and strength of eddy and upwelling events; and climatic oscillations such as the El Niño–Southern Oscillation. In the region, changes in oceanography will be primarily influenced by the East Australian Current, which is one of the key drivers of the region’s biological productivity, species distribution and abundance (Dambacher et al. 2011). The East Australian Current has been strengthening, pushing warmer, saltier water further southward along the east coast for up to 350 km (Ridgway & Hill 2009). Changes in the strength and extent of the current are likely to impact on productivity, shifting trophic webs, and changing migration patterns and reef and shelf habitats, all of which have implications for marine species (Chin et al. 2010). Offshore, the current is partly responsible for the unique mix of warm and cold water species associated with Elizabeth and Middleton reefs and the Tasmantid and Lord Howe seamount chains (Dambacher et al. 2011).

Chemical pollution
Chemical pollution/contaminants is of potential concern for KEFs with values that make them particularly vulnerable to the impacts of a chemical spill, such as important aggregations of marine life at or near the sea surface. As is the case with oil spills, chemical spills are unpredictable events and their likelihood is low in the context of the international and domestic regulatory mitigation measures that apply in Australia. The effects of a major chemical spill can be similar to those of oil spills (GBRMPA 2009), particularly in areas and at times of biological significance for important or threatened species. The impacts vary depending on the toxicity of chemicals, how the materials are packaged and transported, the quantity spilled, the site and ecological sensitivity.

Marine debris
Marine debris is defined as any persistent, manufactured or processed solid material that has been disposed of, or abandoned, in the marine and coastal environment (UNEP 2005). This includes a range of materials from plastics (e.g. bags, bottles, ropes, fibreglass and insulation) to derelict fishing gear, and ship-sourced, solid, non-biodegradable floating materials (DEWHA 2009). Although region-specific marine debris data is limited, key sources for the introduction and spread of debris, such as shipping, commercial fishing and major current systems, are present across the region. This suggests that all KEFs will experience a high degree of overlap with this pressure (Katsanevakis 2008). Marine debris has been listed as a key threatening process under the EPBC Act, in recognition of its negative impacts on substantial numbers of Australia’s marine wildlife, including protected species of birds, turtles and marine mammals. Therefore, this pressure has implications for values such as biodiversity and aggregations of marine life. The Australian Government has developed a threat abatement plan that provides a coordinated national approach to prevent and mitigate the effects of harmful marine debris on marine life (DEWHA 2009).

Physical habitat modification (fishing gear)
Physical habitat modification due to fishing gear can result in loss or significant degradation of KEFs that are subject to bottom trawl activities or are inherently vulnerable to habitat modification, including the shelf rocky reefs and canyons on the eastern continental slope. Both of these features are characterised by complex communities of benthic species that are highly vulnerable to the impacts of demersal trawl fishing, which removes, modifies or disturbs seabed flora and fauna (Furlani et al. 2007). These communities, particularly the deepwater coral species, are highly fragile, long lived and therefore susceptible to disturbance (Williams et al. 2010). Potential impacts include declines in the richness, diversity and density of benthic species and the range of invertebrates and fish that depend on these habitats for prey opportunities and shelter (Althaus et al. 2009).

Extraction of living resources (commercial fishing)
The ecosystem effects of fishing are not well understood. The rating of potential concern is primarily driven by the impact of the targeted take of commercial fisheries on top-order predators, which are considered to be a key functional species group within these features. The extraction of top predators by fishing activities has implications for ecological communities as it influences the abundance, recruitment, species composition, diversity and behaviour of prey species. Removal of top predators can have a ‘cascading’ effect on all the components of a food web (Baum & Worm 2009; Ceccarelli & Ayling 2010). Reef sharks, cod and groupers are important for coral reef communities, while tuna and billfish are important for pelagic systems (Ceccarelli & Ayling 2010). In the context of active fisheries management and the steady move towards ecosystem‑based management of fisheries by all jurisdictions in Australia, the of potential concern rating is considered a conservative assessment. This rating highlights the limited understanding of both the ecosystem effects of individual fisheries and the cumulative effects of a number of fisheries on protected species, marine communities, habitats and ecosystems.

Bycatch (commercial fishing—domestic)
Commercial fishing operations are a key activity in the region and overlap with this feature (e.g. Eastern Tuna and Billfish Fishery, Southern and Eastern Scalefish and Shark Fishery). In the context of active fisheries management and the steady move towards ecosystem-based management of fisheries by all jurisdictions in Australia, the of potential concern rating is considered a conservative assessment. For example, a recent review of all Commonwealth fisheries found that the current numbers of independent observers are not sufficient to allow a cumulative assessment of the catch of non-target species (Phillips et al. 2010). The review stated that such assessment is important to understand the environmental performance of fisheries more broadly and to underpin a holistic approach to the management of ecosystem impacts (Phillips et al. 2010). Generally, there is also a need to increase our understanding of the effectiveness of bycatch mitigation measures (Bensley et al. 2010).

Oil Pollution
Oil pollution is of potential concern for KEFs with values that make them particularly vulnerable to the impacts of an oil spill, such as important aggregations of marine life at or near the sea surface.

Australia has a strong system for regulating industry activity that is the potential source of oil spills and this system has been strengthened further in response to the Montara oil spill. While oil spills are unpredictable events and their likelihood is low based on past experience, their consequences, especially for threatened species at important areas can be severe. The level of impact that actually occurs depends on a number of factors including the concentration of oil; chemical and physical properties of the oil (or oil and dispersant mixture).

Also influencing the impact of an oil spill event are the timing of breeding cycles and seasonal migrations of species, the amount of contact, the susceptibility of particular species; and the health, age and reproductive status of the individuals (AMSA 2011).

Both the intensity and distribution of activities that might lead to oil spills, such as transport, are expected to increase in the region.