Plateaux and saddle north-west of the Wellesley Islands

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 (KFEs) 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 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

Abundance and species density are high in the plateaux and saddle as a result of increased biological productivity associated with habitats rather than currents. Submerged reefs support corals that are typical of northern Australia, including corals that have bleach-resistant zooxanthellae.

The species found in the plateaux and saddle north-west of the Wellesley Islands differ from those found in other areas of the Gulf of Carpentaria. Reef fish species found in this key ecological feature in particular, differ from those found elsewhere in the Gulf (S Blaber, pers. comm., May 2011). Higher trophic species present in the area include hawksbill, olive ridley, green and flatback turtles (Robbins et al. 2002). Fish such as snapper, cod and emperor occur around reefs (DEEDI 2009), and Spanish mackerel is concentrated to the north and west of the Wellesley Islands. Seabird species known to occur in the area include frigates, boobies and shearwaters that most likely rely on the area’s predictable food sources for feeding offspring (C Limpus, pers. comm., 8 November 2009). Corals present in the area are likely to include typical northern Australian coral reef fauna such as octocorals, sponges, ascidians and gorgonians.

National and/or regional importance

Plateaux and saddle north-west of the Wellesley Islands are defined as a key ecological feature for the areas high aggregations of marine life, biodiversity and endemism.

Location

The plateaux and saddle north-west of the Wellesley Islands are located in the southern end of the Gulf of Carpentaria and are characterised by two hard substrate plateaux separated by a narrow saddle.

The spatial boundary of this KEF, as defined in the Conservation Values Atlas, including the canyon is based on the Geoscience Australia geomorphic features dataset.

Description

Isolated living patch reefs occur on the broad, flat-topped plateaux which extend north-east from Mornington Island at depths of 15–30 metres (P Rothlisberg, pers. comm., May 2011). Strong tidal influences occur in this area (S Condie, pers. comm., May 2011). Abundance and species diversity is higher in the sandy sediments of the east and south-east of the Gulf of Carpentaria (Long & Poiner 1994) and in coastal waters that receive nutrients from river flows (NOO 2003). However, biological activity around the plateaux and saddle is believed to be associated more with habitat type than with productivity or oceanic processes (P Rothlisberg, pers. comm., May 2011).

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 the plateaux and saddle north-west of the Wellesley Islands. 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.

Marine debris is a pressure assessed as of concern for the Plateaux and saddle north-west of the Wellesley Islands.

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.

Marine Debris
Marine debris such as derelict fishing nets are an increasing global threat to marine life (MacFadyen et al. 2009). In northern Australia, debris have entangled sharks, cetaceans, large piscivorous fishes and turtles (Kiessling 2003). Much of the marine debris found along the northern Australian coastline, including derelict fishing nets, is believed to be of foreign origin (Roeger et al. 2005). Northern Australia is especially vulnerable to marine debris given the proximity of intensive legal and illegal fishing operations, difficulties in surveillance and enforcement of existing management arrangements, and ocean circulation patterns that are likely to concentrate floating debris before dumping it on coastlines and beaches (Kiessling 2003).

Reports suggest a high number of marine species are being harmed and killed by debris while at sea, or as a result of injuries onshore (Chatto 1995 in Kiessling 2003). For example, turtle mortality associated with ghost nets in the Gulf of Carpentaria is unquantified, but is likely to amount to many hundreds of turtles per year (Limpus 2009). Marine debris may disrupt the breeding cycles of individual animals and compromise foraging habitats. Monofilament is highly persistent in the marine environment and has been documented as a major source of coral mortality in heavily fished localities (Smith et al. 2006). Marine species such as seabirds are also vulnerable to injury and mortality from marine debris through ingestion of lost or discarded plastics and other rubbish. In addition, marine debris such as derelict fishing gear can impact the Gulf of Carpentaria basin and coastal zone, and the plateaux and saddle north-west of the Wellesley Islands, through physically scouring or damaging the sea floor. A threat abatement plan was prepared in 2009 (DEWHA 2009).

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). This projected temperature change is expected to exceed the threshold for inducing coral bleaching on an annual basis (Hoegh-Guldberg 1999, 2005 cited in Hobday et al. 2006).

Increases in sea temperature is expected to impact on the key ecological features of the North Marine Region, particularly through changes to the distribution, abundance, physiology, morphology and behaviour of zooplankton and pelagic, benthic and demersal fishes (Hobday et al. 2006). Extended periods of elevated temperature in shallow estuarine and coastal waters within the Gulf of Carpentaria coastal zone are likely to impact the distribution of fish and prawn nursery habitats, such as estuarine and coastal seagrasses and mangroves (Hobday et al. 2008). Coastal fringing coral reef communities are expected to be affected (Hoegh-Guldberg 2011); however, any likely impacts on corals within the submerged reefs of the Gulf of Carpentaria, and the plateaux and saddle north-west of the Wellesley Islands are unknown.

Coral reefs and their associated fauna are especially vulnerable to impacts connected to changes in sea temperature through coral bleaching and mortality. Any decreases in coral abundance could lead to changes in ecosystem structure, processes and connectivity between coral reefs and adjacent waters. Nutrients and organic matter sourced from dynamic reef complexes and ontogenetic (lifecycle) movements of fish and crustaceans may be disrupted (Haywood & Kenyon 2009). Epifauna such as sponges, algae and coralline algae may also be impacted by elevated seawater temperatures (Brooke et al. 2009).

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 is of particular concern for those key ecological features of the North Marine Region that have coral formations. Acidification of corals is likely to alter the distribution and abundance of corals generally (Hobday et al. 2006), and atmospheric CO₂ levels above 500 parts per million will severely compromise coral viability (Hobday et al. 2006). The acidification of the ocean will impair the ability of species with calcareous shells such as echinoderms, crustaceans and molluscs to maintain shell integrity, resulting in reductions in the abundance and biodiversity of these species (Lawrence et al. 2007).

For the plateaux and saddle north-west of the Wellesley Islands and the submerged coral reefs of the Gulf of Carpentaria, a decrease in coral abundance could lead to changes in ecosystem structure, processes and connectivity between the plateaux and reef waters. Nutrients and organic matter sourced from dynamic reef complexes could also be disrupted.

Extraction of living resources (IUU fishing)
In recent years, foreign illegal, unregulated and unreported (IUU) fishing has been a considerable issue across northern Australian waters for the threat it poses to target and bycatch species, border security, quarantine concerns and conservation of the marine environment more generally (Vince 2007). For example, in 2005, 13 018 illegal foreign fishing vessels were observed in Australian waters, and of those, only 600 were apprehended by Australian officials (Vince 2007). The number of foreign IUU fishing vessels sighted in northern Australian waters has declined significantly since 2005, but there is some concern that fewer numbers of more powerful and sophisticated IUU fishing vessels may now be targeting Australian stocks (Lack & Sant 2008).

IUU fishing has the potential to adversely affect widespread populations of multiple species, possibly with long-term, permanent impacts. Illegal foreign fishers have tended to target sharks for the valuable fin market, although the full extent of IUU fishing for shark in northern Australia is largely unquantified. Selected shark stocks targeted by foreign IUU fishers have declined or are overfished (Heupel & McAuley 2007). IUU catch of sharks is estimated to be twice that of reported legal catch (Heupel & McAuley 2007).