Seringapatam Reef and Commonwealth waters in the Scott Reef complex

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

Seringapatam Reef and Commonwealth waters in the Scott Reef complex are regionally important in supporting the diverse aggregations of marine life, high primary productivity and high species richness associated with the reefs themselves. As two of the few offshore reefs in the north-west, they provide an important biophysical environment in the region.

The coral communities at Scott and Seringapatam reefs play a key role in maintaining the species richness and subsequent aggregations of marine life. Scott Reef is a particularly biologically diverse system and includes more than 300 species of reef-building corals, approximately 400 mollusc species, 118 crustacean species, 117 echinoderm species and around 720 fish species (Woodside 2009).

Scott and Seringapatam reefs and the waters surrounding them attract aggregations of marine life including humpback whales and other cetacean species, whale sharks and several species of sea snake (Donovan et al. 2008; Jenner et al. 2008; Woodside 2009). Two species of marine turtle nest during the summer months on Sandy Islet, located on South Scott Reef. These species also internest and forage in the surrounding waters (Guinea 2006). This key ecological feature also provides foraging areas for seabird species such as the lesser frigatebird, wedge-tailed shearwater, brown booby and roseate tern (Donovan et al. 2008).

National and/or regional importance

Seringapatam Reef and Commonwealth waters in the Scott Reef complex are defined as a key ecological feature as they support diverse aggregations of marine life, have high primary productivity relative to other parts of the region, are relatively pristine and have high species richness, which apply to both the benthic and pelagic habitats within the feature.

Location

Scott and Seringapatam reefs are part of a series of submerged reef platforms that rise steeply from the sea floor between the 300–700 m contours on the north-west continental slope and lie in the Timor Province (Falkner et al. 2009). Scott and Seringapatam reefs provide an important biophysical environment in the region as one of few offshore reefs in the north-west.

Scott Reef consists of two separate reef formations, North Reef and South Reef. The key ecological feature encompasses the waters beyond the 3 nm limit at South Scott Reef and the reefs and surrounding waters at North Scott and Seringapatam reefs. The total area of the key ecological feature is approximately 2418 km².

The spatial boundary of this KEF, as defined in the Conservation Values Atlas, includes both reefs plus the adjacent apron/fan features, and the canyon approximately 10 km to the west of Scott Reef (based on the Geoscience Australia geomorphic features dataset). The southern edge of the KEF is defined by the state water boundary around Scott Reef.

Description

Scott and Seringapatam reefs and the waters surrounding them attract aggregations of marine life including humpback whales on their northerly migration, Bryde’s whales, pygmy blue whales, Antarctic minke whales, dwarf minke whales, minke whales, dwarf sperm whales and spinner dolphins (Jenner et al. 2008; Woodside 2009). Whale sharks and several species of sea snakes have also been recorded in this area (Donovan et al. 2008). Green and hawksbill turtles nest during the summer months on Sandy Islet on South Scott Reef. These species also internest and forage in the surrounding waters (Guinea 2006).

Corals and fish at Scott Reef have higher species diversity than the Rowley Shoals, (Done et al. 1994). Recent studies suggest that the capacity for coral dispersal between Scott Reef and other offshore reefs in the region may be limited (Underwood et al. 2009). Genetic studies of two coral species at Scott Reef indicate that the majority of coral larvae are retained close to their spawning site. Consequently, coral communities at Scott Reef are largely self-seeded and rely on the reproductive output of Scott Reef resident corals to maintain populations and facilitate recovery (Underwood et al. 2009). Reef fish populations at Scott Reef and adjacent reef systems may be more connected as fish larvae remain in the water column longer before settling onto reefs (Woodside 2009). Research on the coral trout species Plectropomus leopardus suggests that populations at Scott Reef contribute approximately 50 % of larval recruits to the population of this species at the Houtman Abrolhos Islands, 2500 km away (van Herwerden 2009).

Aggregations of marine life, high primary productivity and species richness on the reefs and in the surrounding Commonwealth waters are likely due to the steep rise of the reef from the seabed. This causes nutrient-rich waters from below the thermocline (about 100 m) to mix with the warmer, relatively nutrient-poor tropical surface waters via the action of internal waves and from mixing and higher productivity in the lee of emergent reefs (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 winds of the south-east monsoon (approximately April–September) facilitate the 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 Seringapatam Reef and Commonwealth waters in the Scott Reef complex. 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.

Extraction of living resources by traditional Indonesian fishers were assessed as of concern for the Seringapatam Reef and Commonwealth waters in the Scott Reef complex.

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; oil pollution and invasive species. These pressures are described in more detail below.

Extraction of living resources (non-domestic commercial fishing)
In 1974, a Memorandum of Understanding (MoU) was signed between the Australian and Indonesian governments that recognised traditional fishing in the area, and permits traditional Indonesian fishers to fish in the MoU box, including on and around Scott and Seringapatam reefs. The MoU requires Indonesian fishers to use traditional sail-powered fishing vessels and non-motorised equipment, and prohibits them from taking protected species such as turtles, dugongs and clams. Fishers target a range of animals, including sea cucumbers (bêche-de-mer), trochus (topshell), reef fish and sharks. Indonesian fishing effort is high at Scott Reef. In 2008, approximately 80 Indonesian fishing vessels were observed at Scott Reef (Woodside 2009). Given the level of fishing pressure, it is predicted that many target species are overexploited (Meekan et al. 2006b; Skewes et al. 1999). Studies show that shark populations were severely depleted at Scott Reef compared to the Rowley Shoals, and that the most plausible reason was overfishing (Meekan et al. 2006b). Fishers are increasingly harvesting large reef fish species, such as the bumphead parrotfish and humphead wrasse. The bumphead parrotfish is a large, herbivorous species that is thought to be important in regulating the growth of coral and algae in reef communities, hence its removal could have implications for system functioning and reef resilience to other pressures (Bellwood et al. 2003).

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). At Scott and Seringapatam reefs, corals bleached at depths up to 30 m andhard 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).

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.

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.

Physical habitat modification (shipping anchorage)
Vessel anchorage may modify or damage benthic communities of Seringapatam Reef and Commonwealth waters in the Scott Reef complex. Each year, approximately 80 traditional Indonesian fishing vessels anchor in the waters of this key ecological feature, but there are currently no restrictions on where or how they can anchor. Petroleum industry and Australian surveillance vessels also use the area and, due to their size, must have appropriate anchoring systems in place and follow anchorage procedures to ensure the safety of crew and the surrounding environment (Australian Transport Commission 2010). The North West Slope Trawl Fishery operates in the area and targets deepwater species on muddy benthos. It is not known what impact the anchoring of these vessels is having on the values of this key ecological feature.

Physical habitat modification (offshore construction)
The installation of infrastructure may directly impact the benthic communities associated with Seringapatam Reef and Commonwealth waters in the Scott Reef complex. Construction, commissioning and operation of offshore gas facilities may also result in the release of marine discharges and effluents that could locally affect the quality of the receiving marine waters. Suspended solids generated from the disturbance to the seabed from the installation of infrastructure and from the discharge of drilling cuttings and muds may directly impact the physical and chemical properties of the receiving waters. In turn, this may indirectly affect flora and fauna in the area via physiological or toxicological impacts, and may also result in localised smothering of benthic communities and reduction in light availability (Woodside 2008).

It is unclear what effect, if any, the modification of benthic habitats could have on the broader functioning and integrity of this key ecological feature. However, the effects of construction and installation activities may have both direct and indirect impacts on the listed threatened species of marine mammals, turtles, birds and whale sharks that may occur in this area. These impacts may include avoidance behaviour, potential physiological effects and direct impact on foraging areas (Woodside 2008).

Physical habitat modification (fishing practices)
Habitat modification through physical damage can result from traditional Indonesian fishing practices. Traditional Indonesian fishers access Scott and Seringapatam reefs to fish for holothurians, trochus, molluscs and finfish, including shark. Some fishing involves walking the reef at low tide to hand collect species, such as holothurians, and involves turning over coral boulders. Corals are left upturned as 'markers' to indicate that the area has been searched. This practice may result in the death of other organisms left exposed, and may degrade and/or reduce habitat for other marine organisms. It is not known what effect this has on the coral ecosystem. However, since hundreds of traditional fishers walk the same reefs for extended periods, it is possible this fishing practice is placing pressure on the reef environment.

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. Seringapatam Reef, Commonwealth waters in the Scott Reef complex, 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.