Mermaid Reef and Commonwealth waters surrounding Rowley Shoals

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

Mermaid Reef and Commonwealth waters surrounding Rowley Shoals are regionally important in supporting high species richness, higher productivity and aggregations of marine life associated with the adjoining reefs themselves (Done et al. 1994). The Rowley Shoals contain 214 coral species and approximately 530 species of fishes (Gilmour et al. 2007), 264 species of molluscs and 82 species of echinoderms (Done et al. 1994; Gilmour et al. 2007). The reefs provide a distinctive biophysical environment in the region as there are few offshore reefs in the north-west. They have steep and distinct reef slopes and associated fish communities. In evolutionary terms, the reefs may play a role in supplying coral and fish larvae to reefs further south via the southward flowing Indonesian Throughflow. Both coral communities and fish assemblages differ from similar habitats in eastern Australia (Done et al. 1994).

National and/or regional importance

Mermaid Reef and Commonwealth waters surrounding Rowley Shoals is defined as a key ecological feature for its enhanced productivity and high species richness, that apply to both the benthic and pelagic habitats within the feature.

Location

The Rowley Shoals are a collection of three atoll reefs, Clerke, Imperieuse and Mermaid, which are located about 300 km north-west of Broome. The key ecological feature encompasses Mermaid Reef Commonwealth Marine Reserve as well as waters from 3 nm out to 6 nm surrounding Clerke and Imperieuse reefs.

Mermaid Reef lies 29 km north of Clerke and Imperieuse reefs and is totally submerged at high tide. Mermaid Reef falls under Commonwealth jurisdiction. Clerke and Imperieuse reefs constitute the Rowley Shoals Marine Park, which falls under Western Australian Government jurisdiction (EA 2000).

The spatial boundary of this KEF, as defined in the Conservation Values Atlas, includes all existing State and Commonwealth marine reserves plus adjacent apron/fan features, as defined in the Geoscience Australia geomorphic features dataset, within a 6 nm buffer of the reef features, as defined in the Geoscience Australia geomorphic features dataset.

Description

Rowley Shoals’ reefs are different from other reefs in the chain of reefs on the outer shelf of the North-west Marine Region, both in structure (Done et al. 1994) and genetic diversity (Underwood et al. 2009). There is little connectivity between Rowley Shoals and other outer-shelf reefs (Hooper & Ekins 2004; Underwood 2009; Underwood et al. 2009). An additional difference is that sea snakes do not occur there (Done et al. 1994).

Enhanced productivity is thought to be facilitated by the breaking of internal waves in the waters surrounding the reefs, causing mixing and resuspension of nutrients from water depths of 500–700 m into the photic zone. The steep changes in slope around the reef also attract a range of migratory pelagic species including dolphins, tuna, billfish and sharks.

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 Mermaid Reef and Commonwealth waters surrounding Rowley Shoals. 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 Mermaid Reef and Commonwealth waters surrounding Rowley Shoals.

Pressures assessed as of potential concern are sea level rise, changes in sea temperature and ocean acidification as a result of climate change; physical habitat modification; 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 corals reef 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). In 2005, elevated sea surface temperatures resulted in a minor bleaching event at the Rowley Shoals, which impacted a large proportion of benthic organisms, including corals, clams and anemones (Gilmour et al. 2007).

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).

Increases in ocean water temperature may also affect deeper water fish species, such as those within the demersal slope fish key ecological feature. Climate change modelling predicts that by 2070 ocean water temperatures at a depth of 500 m will warm by 0.5–1 °C, which could adversely impact larval fish development and survival (Hobday et al. 2006). Benthic and demersal fish species may shift south and some populations may decline where ranges are bounded to the south (Hobday et al. 2006). Structurally complex epifauna (i.e. sponges, algae and coralline algae) may also suffer mortality from elevated water temperatures (Lawrence et al. 2007).

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.

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.

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 o 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.