Ashmore Reef and Cartier Island and surrounding Commonwealth waters

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 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

Ashmore Reef is the largest of only three emergent oceanic reefs in the north-eastern Indian Ocean and is the only oceanic reef in the region with vegetated islands. Emergent reefs are areas of enhanced primary productivity in an otherwise oligotrophic environment (Stambler 2011). Localised upwelling and turbulent mixing in the Commonwealth waters around the reef systems provide nutrients to the system and therefore support the reef structure and ecology (DEWHA 2008b).

Ashmore Reef and Cartier Island and the surrounding Commonwealth waters are regarded as biodiversity hotspots as they support a diverse array of pelagic and benthic marine species. Ashmore Reef supports the highest number of coral species of any reef off the Western Australian coast (Veron 1993) and provide varied habitat that attracts a diverse range of primary and secondary consumers, including a particularly diverse fish fauna. Toothed whales, dolphins and whale sharks are found in the Commonwealth waters around these reefs, as is a genetically distinct dugong population at Ashmore Reef (Whiting 1999).

The marine habitats among the reefs are nationally and internationally significant supporting diverse and abundant marine reptile populations (Limpus 2008). Both Ashmore and Cartier reefs support an unusually high diversity of sea snakes, for which these reefs are internationally significant. The sea snake population at Ashmore Reef has suffered significant decline in recent years for reasons that are yet to be understood. Ashmore Reef and Cartier Island also support a genetically distinct breeding population of green turtles and provide foraging grounds for this species as well as for loggerhead and hawksbill turtles (Limpus 2008). The reef system is an important staging post for seabirds and migratory shorebirds and the area is home to some of the most important seabird colonies in the North-west Marine Region (Milton 2005). The importance of Ashmore Reef for seabirds and shorebirds is reflected in its listing as a Ramsar Wetland of International Importance in 2003.

National and/or regional importance

Ashmore Reef and Cartier Island and surrounding Commonwealth waters are defined as a key ecological feature for their high productivity, biodiversity and aggregations of marine life, which apply to both the benthic and pelagic habitats within the feature.

Location

Ashmore Reef and Cartier Island are situated on the shallow upper slope of the Sahul Shelf, north of Scott and Seringapatam reefs. They form part of a series of submerged reef platforms along the outer edge of the continental slope of the North-west Marine Region.

Ashmore contains a large reef shelf, two large lagoons, several channelled carbonate sand flats, shifting sand cays, an extensive reef flat, three vegetated islands—East, Middle and West islands—and surrounding waters. Rising from a depth of more than 100 m, the reef platform is at the edge of the North West Shelf and covers an area of 239 km². Ashmore Reef Commonwealth Marine Reserve encloses an area of about 583 km² of seabed (EA 2002).

Cartier Island Commonwealth Marine Reserve (Cartier) is located in the West Sahul region of the Indian Ocean. The island is about 350 km off Australia’s Kimberley coast, 115 km south of the Indonesian island of Roti and 45 km south-east of Ashmore Reef Commonwealth Marine Reserve. Cartier Island Commonwealth Marine Reserve covers 167 km² and contains one unvegetated sand cay and mature reef flat with two shallow pools to the north-east of the cay (EA 2002).

The spatial boundary of this KEF, as defined in the Conservation Values Atlas, includes all of the existing Ashmore Reef Commonwealth Marine Reserve and Cartier Island Commonwealth Marine Reserve and waters between them plus the surrounding areas of reef, apron/fan and canyon as defined in the Geoscience Australia geomorphic features dataset.

Description

Species at Ashmore and Cartier include more than 225 reef-building corals, 433 molluscs, 286 crustaceans, 192 echinoderms, and the most diverse variety of fish of any region in Western Australia with 709 species (EA 2002). Thirteen species of sea snakes occur in high numbers at Ashmore and Cartier reefs but are believed to have experienced recent declines, the cause of which is not known. Ashmore and Cartier also attract feeding and breeding aggregations of marine and other fauna. An estimated 11 000 green and hawksbill turtles feed over seagrass beds present on reef flats throughout the year (M Guinea, pers. comm., 2009). Sandy beaches provide important habitat for nesting green and hawksbill turtles throughout the year. Seagrass present at Ashmore Reef provides critical breeding (April–May) and foraging (throughout the year) habitat for a genetically distinct population of dugong with their range probably extending to other submerged shoals within the area (Brown & Skewes 2005; Whiting 1999).

The emergent habitat at Ashmore also provides important nesting sites for seabirds, many of which are migratory. Ashmore’s islands are regarded as supporting some of the most important seabird rookeries on the North West Shelf seasonally supporting up to 50 000 seabirds (26 species) and up to 2000 waders (30 species, representing almost 70 % of wader species that regularly migrate to Australia) (Milton 2005). Large colonies of sooty terns, crested terns, bridled terns and common noddies breed on the east and middle islands. Smaller breeding colonies of little egrets, eastern reef egrets, black noddies and possibly lesser noddies also occur. Migratory wading birds include eastern curlews, ruddy turnstones, whimbrels, bar-tailed godwits, common sandpipers, Mongolian plovers, red-necked stints and tattlers, during October–November and March–April as part of the migration between Australia and the Northern Hemisphere (Milton 2005).

High primary productivity, species richness and subsequent aggregations of marine life on the reefs and in the surrounding Commonwealth waters are primarily due to the mixing of nutrient-rich waters from below the thermocline (about 100 m) with the warmer, relatively nutrient-poor tropical surface waters of the Indonesian Throughflow. This mixing is due to interactions between internal waves and sea-floor structures (Brewer et al. 2007). Seasonal weather patterns also influence the delivery of nutrients from deepwater to shallow water. Cyclones and north-westerly winds during the north-west monsoon (approximately November–March) and the strong offshore (south-easterly) winds of the south-east monsoon (approximately April–September) facilitate upwelling and mixing of nutrients from deepwater to shallow water environments (Brewer et al. 2007).

Model information

The department and CSIRO conducted collaborative research on KEFs to identify indicators for monitoring marine ecosystem health in the Commonwealth Marine Area. As part of this process, qualitative models were developed for 27 KEFs, including Ashmore Reef and Cartier Island and surrounding Commonwealth waters. Further information can be found at https://publications.csiro.au/publications/publication/PIcsiro:EP132926.

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 Ashmore Reef and Cartier Island and surrounding Commonwealth waters.

Pressures assessed as of potential concern are sea level rise, changes in sea temperature and ocean acidification as a result of climate change; marine debris; physical habitat modification; extraction of living resources; oil pollution and invasive species. These pressures are described in more detail below.

Sea level rise (climate change)
Sea level has been rising at approximately 7.1 mm per year in the North-west Marine Region since the 1990s, the largest increase in Australia (NTC 2010). Global sea levels have risen by 20 cm between 1870 and 2004 and predictions estimate a further rise of 5–15 cm by 2030, relative to 1990 levels (Church et al. 2009). Longer term predictions estimate increases of 0.5 m to 1.0 m by 2100, relative to 2000 levels (Climate Commission 2011).

Sea level rise is of potential concern for key ecological features with shallow reefs. Under pre-climate change conditions, reefs could be expected to grow upward to match sea level rise. However, the cumulative effects of coral bleaching (sea temperature) and decline in calcification in corals (ocean acidification) may render corals incapable of recovery to match sea level rise (Hoegh-Guldberg 2011). Sediment production, erosion and sediment transport will depend on water depth and wave-generated forces, and the microtopography of reef crests will change and effect the habitat of biota (Sheppard et al. 2002). Critically, the growth of reefs more than 30–40 m deep will most likely not match sea level rise regardless of calcification rates. During the Holocene transgression, sea levels rose at 10–20 mm per year and coral reefs growing at depths below the critical 30–40 m failed to flourish (Grigg & Epp 1989).

Changes in sea temperature (climate change)
Sea temperatures have warmed by 0.7 ºC between 1910–1929 and 1989–2008, and current projections estimate ocean temperatures will be 1 ºC warmer by 2030 (Lough 2009). Key ecological features supporting coral reef communities are vulnerable to bleaching and mortality from elevated sea temperatures. Projected temperature changes in Australian seas exceed the threshold for inducing bleaching events on an annual basis (Hobday et al. 2006). A decrease in coral abundance would lead to changes in ecosystem structure, processes, and connectivity between reefs and adjacent waters. Nutrients and organic matter sourced from dynamic reef complexes may be disrupted.

In 1998, high sea temperature led to widespread bleaching of corals at Ashmore and Cartier reefs, the Rowley Shoals, and Scott and Seringapatam reefs (Gilmour et al. 2007; Pittock 2003). At Scott and Seringapatam reefs, corals bleached at depths up to 30 m and hard coral cover decreased from 41 % before the event to 15 % (Pittock 2003).

While the effects of increased sea temperatures are likely to vary greatly across communities and ecosystems, there is a high level of agreement from different datasets that warming is affecting distributional ranges and larval phase of tropical marine fishes (Munday et al. 2009). Changes in sea temperature may also result in changes to phytoplankton and zooplankton communities, with implications for trophic dynamics (Richardson et al. 2009) and fish larval supply and survival (Lo-Yat et al. 2011).

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.

Marine debris
Injury and fatality to vertebrate marine life caused by ingestion of, or entanglement in, harmful marine debris was listed in 2003 as a key threatening process under the EPBC Act (DEWHA 2009t). Debris harmful to marine wildlife includes plastics washed or blown from land into the sea, recreational and commercial fishing gear (known as ghost nets), and solid floating materials (such as plastics) from ships at sea. Large amounts of fishing net are discarded or lost from the fisheries of the Arafura Sea (Limpus 2009). However, the characteristics and impacts of debris disposed of or lost overboard in the Arafura Sea are largely unknown (Kiessling 2003) and it is not known what proportion of such debris enters the North-west Marine Region.

Physical habitat modification (storm events)
The intensity of storms is predicted to increase (Hyder Consulting 2008). Present indications are that modest to moderate (0–20 %) increases in average and maximum cyclone intensities are expected by the end of the century in some regions (Walsh & Ryan 2000). In conjunction with a more fragile coral matrix structure and a slower growth (recovery) rate due to ocean acidification, reefs may become extremely vulnerable to severe storm events, leading to severe flow-on effects for communities dependent on coral reef habitats.

Extraction of living resources (IUU fishing)
Illegal, unreported and unregulated (IUU) fishing has in the past been a significant issue in the North-west Marine Region and posed a major threat to target species and the conservation of the broader marine environment. In 2005, 13 018 illegal fishing vessels were sighted in Australian waters and of those, 600 were apprehended by Australian officials (Vince 2007). While the number of illegal vessels sighted per day has declined since 2005, there is concern that more powerful vessels with more sophisticated equipment may now be being used (Lack & Sant 2008). The Australian Government is also concerned with the issues of border security and quarantine that coincide with IUU fishing activities (Vince 2007).

IUU fishers predominantly target shark species for the valuable fin market. IUU catch of sharks is estimated to be twice that of reported legal catch (Heupel & McAuley 2007). The full extent of IUU shark fishing in northern Australia is largely unquantified; however, shark stocks targeted by IUU fishers have declined or are overfished (Heupel & McAuley 2007).

The effect on the marine environment of key ecological features following the removal of sharks is unknown. However, it is hypothesised that an increase in large reef fish species at Scott Reef is a result of the decline in abundance of shark species (Gilmour et al. 2009, cited in Woodside 2009). Due to the life history characteristics of sharks (long life, slow to mature and small numbers of offspring) it may take some time before the effects of overfishing of sharks in the region is reversed, despite drops in the level of IUU activity in the region.

Oil pollution (oil rigs)
Oil pollution is of potential concern for key ecological features with values vulnerable to the impacts of an oil spill, such as highly diverse coral communities that support an abundant array of marine species. The North-west Marine region is an area subject to significant petroleum exploration, development and production and this is likely to increase in the future (DEWHA 2008b). Shipping is likely to continue to expand in the region as a result of the growth of the resources sector. 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, could be severe. The level of impact that actually occurs depends on a number of factors including concentration of oil; chemical and physical properties of the oil (or oil and dispersant mixture); the timing of breeding cycles and seasonal migrations of species; the time of contact; susceptibility of particular species; and the health, age and reproductive status of the individuals (AMSA 2011a).

Coral reef communities are highly sensitive to both oil and oil/dispersant mixtures (Shafir et al. 2007). Oil spills are particularly significant for corals when spawning because broadcast coral gametes collect at the surface and may be exposed to petroleum products. Coral eggs and larvae are buoyant for the first few days after spawning and may suffer significant mortality if any oil or oil/dispersant mixture is encountered in significant concentrations. There is also evidence that metamorphosis (around 1–3 weeks following spawning) is particularly susceptible to oil (Negri & Heyward 2000). Scott and Seringapatam reefs and the Rowley Shoals are likely to be self-seeding over ecological timescales (Underwood 2009; Underwood et al. 2007, 2009). Therefore, recovery from damage by oil is likely to be far slower in such isolated reefs than in coastal settings and interconnected groups of reefs.

To manage oil spills, chemical dispersants (powerful detergents) may be applied to oil slicks on the surface to accelerate weathering processes and to disperse the oil into the water column to minimise the surface transport of oil to sensitive habitats, such as foreshores. These dispersants contain toxic elements that can be harmful to coral (Shafir et al. 2007). Certain dispersants combined with crude oil increase the toxicity of oil to some fish and invertebrates (Gulec & Holdway 2000, in Fandry et al. 2006). However, dispersants are only used when all environmental effects have been considered and are generally not used in close proximity to coral reefs (AMSA 2011b).

Invasive species
Invasive species have the potential to impact directly on benthic communities, coral and fish via competition for habitat and food resources. The two primary mechanisms for the inadvertent introduction and spread of invasive marine species are ballast water discharge and vessel biofouling. Key ecological features in areas of high international and domestic shipping traffic are at greater risk of an invasive species incursion. Offshore petroleum development also has the potential to introduce invasive species through the installation of rigs and subsea infrastructure. Ashmore Reef and Cartier Island are also visited by traditional Indonesian fishing vessels and illegal vessels. These foreign vessels have the potential to carry invasive species on their hulls, which could endanger the relatively pristine marine environments of these two offshore reef systems.