Pinnacles of the Bonaparte Basin

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 North-west and North Marine Bioregional Plans. 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

National and/or regional importance

The Pinnacles of the Bonaparte Basin are defined as a key ecological feature as they are a unique seafloor feature with ecological properties of regional significance.

Location

The limestone pinnacles are located in the Joseph Bonaparte gulf. They represent 61 % of the limestone pinnacles in the North-west Marine Region, 40 % of all pinnacles that exist in the North Marine Region and 8 % of limestone pinnacles in the Australian exclusive economic zone (Baker et al. 2008).

The largest concentration of pinnacles along the entire Australian margin occurs in the Northwest Shelf Transition provincial bioregion where more than 110 pinnacles are found, covering a total area of more than 520 km² (Heap & Harris 2008).

The spatial boundary of this KEF, as defined in the Conservation Values Atlas, includes all pinnacles that are located within the basin feature of the Joseph Bonaparte gulf, as defined in the Geoscience Australia geomorphic features dataset.

Description

The limestone pinnacles of the Bonaparte Basin lie on the mid-outer shelf in the western Joseph Bonaparte Gulf. The surrounding area is relatively featureless soft sediments (Brewer et al. 2007). The pinnacles can be up to 50 metres high and 50–100 kilometres long (Baker et al. 2008) and are thought to be remnants of calcareous shelf and coastal features from previous low sea-level stands (Baker et al. 2008, Heyward et al. 1997).

The oceanographic influence of the Indonesian Throughflow brings warm, low-salinity water into the region which is oligotrophic for much of the year. Primary productivity is largely from phytoplankton and zooxanthellae within the hard corals located on the limestone pinnacles and through sporadic upwelling across the Sahul Shelf (Brewer et al. 2007). The pinnacles are subject to frequent disturbances from tropical cyclones and tidal currents driven by the large tidal fluctuations of the region. This mobilises mud sediments which creates high levels of turbidity in the water column (NERP MBH 2014).

Surveys undertaken in 2012 suggest the area supports a wide range of high-order pelagic animals with 32 species observed, including 11 shark species, black marlin, barracuda, olive ridley turtle, sea snakes and orcas. Demersal fish communities were found to occur in larger and more diverse populations on the shallower, less turbid banks and pinnacles (Nichol et al. 2013). Marine turtles including flatback, loggerhead and olive ridley are known to forage around the pinnacles (Donovan et al. 2008; Whiting et al. 2007), and flatback turtles feed on squid eggs laid on the hard substrate of the pinnacles (M Guinea, pers. comm., 2009). The pinnacles are considered a general use area for sawfishes (green and freshwater), although the functioning of the pinnacles ecosystem is not thought to depend on these species (Donovan et al. 2008).

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 30 KEFs, including the Pinnacles of the Bonaparte basin. 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 the Pinnacles of the Bonaparte Basin.

Pressures assessed as of potential concern are changes in sea temperature and ocean acidification as a result of climate change; and extraction of living resources. 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). KEFs 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.

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). 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.

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, only 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 this KEF following the removal of sharks is unknown. 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.