Commonwealth marine environment within and adjacent to Geographe Bay

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.

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 South-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

Geographe Bay is a large, sheltered embayment with extensive beds of tropical and temperate seagrass that account for about 80 per cent of benthic primary production in the area. The seagrass beds are noted for their high species biodiversity and endemism. Similar to the lagoons to the north, Geographe Bay provides important habitat for a range of species, including nursery habitat for a number of commercially and economically valuable fish species. Geographe Bay is also an important migratory habitat for humpback whales.

National and/or regional importance

The Commonwealth marine environment within and adjacent to Geographe Bay is defined as a key ecological feature for its high productivity and aggregations of marine life, and high levels of biodiversity and endemism. These values apply to both the benthic and pelagic habitats within the feature.

Location

Geographe Bay is a large, shallow (< 30 m deep), sheltered bay that encompasses a wide curve of the Western Australian coastline extending from Cape Naturaliste to Bunbury.

The spatial boundary of this KEF, as defined on the Conservation Values Atlas, is largely based on information available on the extent of seagrass in Geographe Bay. The seaward boundary extends from commonwealth waters north of Cape Naturaliste in about 40m depth, easterly to the 30m depth contour, then northeasterly along the 30m contour before following a line towards the coastal water limit off Point Casuarina (the northern extent of Geographe Bay).

Description

Geographe Bay is an area of high productivity supported by extensive and diverse seagrass meadows that cover approximately 60 per cent of the bay (McMahon et al. 1997). The tropical and temperate seagrass beds account for approximately 80 per cent of benthic primary production in the area (DEH 2006). The conditions of the bay, and the south-flowing warm waters of the Leeuwin Current, make this an area of high biodiversity and endemism, with a mix of tropical and temperate species. The Leeuwin Current exerts a strong influence on the bay, and brings warm and oligotrophic waters and tropical species along the temperate south coast of Western Australia (Dambacher et al. 2009).

Similar to the inshore lagoons to the north, Geographe Bay provides important nursery habitat for many shelf species. For example, juvenile dusky whaler sharks use the shallow seagrass habitat as nursery grounds for several years, before ranging out to adult feeding grounds along the shelf break. The seagrass also provides valuable habitat for fish and invertebrates (Carruthers et al. 2007). Geographe Bay is also recognised as an important resting area for migrating humpback whales during the late winter–spring months (McCauley et al. 2000). The whales, sharks and fish species highlight the value of this feature for aggregations of marine life.

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 Commonwealth marine environment within and adjacent to Geographe Bay. 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.

Pressures assessed as of concern for the Commonwealth marine environment within and adjacent to Geographe Bay are changes in sea temperature and change in oceanography as a result of climate change.

Pressures assessed as of potential concern are sea level rise and ocean acidification as a result of climate change; changes to water quality due to chemical and nutrient pollution or changes in turbidity; noise pollution; 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)
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 m by 2100, relative to 2000 levels (Climate Commission 2011). One of the anticipated effects of sea level rise is the increase in coastal erosion processes, which might be accompanied by an increase in sediment loads in the water column, particularly in inshore environments, and a possible loss of seagrass beds (Hobday et al. 2006).

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). The south-west of Western Australia in particular is one of three hotspots in the Indian Ocean where rising temperature trends exceed the Indian Ocean basin average (Feng et al. 2009). All key ecological features considered important for the region’s primary productivity and biological production are at risk from climate change. Changes in sea temperature and oceanographic processes have been implicated in the region in shifts in distribution of marine species, changes to prey variability (including positive changes for some species, such as bridled tern) and effects on reproductive time and success (Dunlop 2009; Gaughan et al. 2002; Surman & Nicholson 2009). The overall implications for ecosystem processes in the region are not known.

Change in oceanography (climate change)
The strength of the Leeuwin Current has decreased slightly since the 1970s. This weakening is expected to continue, although this prediction currently has low confidence (Feng et al. 2009). The Leeuwin Current is the basis of much of the region’s biological productivity, and its strength and seasonal/climatic variability are a primary driver for the intensity, timing and locations of productivity events in the region, from the waters off Geraldton to the Great Australian Bight (Pattiaratchi 2007). The long-term implications for the region’s ecosystems and its key ecological features are uncertain. This pressure is considered of concern for those key ecological features important for the region’s productivity and for which the Leeuwin Current is considered a primary ecological driver.

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). Projected changes in Australian waters by 2070 include a decline in pH of 0.2 units (Lawrence et al. 2007). There is a high level of uncertainty about the effects of ocean acidification on marine life. While some organisms might be able to adapt (Orr et al. 2009), anticipated changes to phytoplankton and zooplankton have the potential to detrimentally affect ecosystem processes and the structure of ecological communities. Research on the impact of ocean acidification on Antarctic krill has found that increased levels of CO₂ kill their embryos (Kawaguchi et al. 2011). Krill are an important part of the food chain because they feed on phytoplankton and zooplankton, and are a key food source for many species that occur in Australian waters. Consequently, acidification impacts have the potential to affect species further up the food chain. The potential effects of increased acidity on the region’s biodiversity also include changes to growth and population dynamics of some shell-forming organisms, impacts on the reproductive and metabolic functions of a number of fish and invertebrate species, and sensitivity of some early-life stages to acidification (Orr et al. 2009).

Chemical pollution/ contaminants
Introduction of chemical pollution into the marine environment is usually localised and associated with shipping and ports operations, particularly dredging; industrial development in the coastal zone; and proximity to urban centres and estuaries in areas with intense industrial and agricultural development. This pressure is of potential concern for key ecological features that are close to coastal areas experiencing industrial developments, intense land use and/or large ports.

Nutrient pollution
Waters in the South-west Marine Region are generally low in nutrients. Therefore, any significant increase in nutrient loads in the water column could detrimentally effect biodiversity. Increases in nutrients may arise from run-off from agricultural production (e.g. in Geographe Bay) and discharge of sewerage into the ocean.

Changes in turbidity
Changes in turbidity in the region can be associated primarily with increased coastal erosion (due to sea level rise). Increased run-off, which is the cause of turbidity changes in other parts of Australia, is not likely to be a significant source of pressure in the south-west due to the absence of large rivers and the anticipated dramatic decrease in rainfall predicted for the south-west corner of Australia (Hennessy et al. 2006). Key ecological features that are particularly vulnerable to increased turbidity are those that have extensive and important seagrass beds including Geographe Bay.

Noise pollution
All sources of man-made noise in the region are predicted to increase (Clifton et al. 2007). Sources include shipping, marine infrastructure construction and operation involving underwater blasting and pile driving, defence naval exercises and seismic surveys. Many marine organisms use sound for a number of biological functions, including navigation, social communication and location of prey. The effects of seismic activities on large whales have received the most attention in the region; however, there have also been experimental studies into the effects of seismic surveys on fish (Popper et al. 2002; McCauley et al. 2003). Although extrapolation from experimental studies to wild populations is problematic, the evidence available to date justifies a precautionary approach. The Royal Australian Navy’s Western Australia exercise area is located off Perth, and its operation involves noise-generating activities, including firing of live ammunition, shipping exercises and use of active sonar. Guidelines under the EPBC Act are in place to mitigate the effect of noise generated by seismic surveys on whales; similarly, the Royal Australian Navy implements operational procedures to minimise environmental impacts.

Physical habitat modification
Coastal, urban and industrial development and port activities can result in loss or significant degradation of areas of important habitat. Of potential concern are those features occurring on the west-coast continental shelf, where the rate of development is higher (Clifton et al. 2007). Inshore habitats, such as the seagrass beds and limestone reefs of the west coast and Geographe Bay, are important breeding and nursing areas for a range of fish and shark species and for western rock lobster. In the region, disturbance and physical changes to benthic habitats result from bottom trawling, although the extent of trawling varies broadly among the fisheries in the region. Sponges, bryozoans and sea squirts are particularly vulnerable to trawling impacts (Currie et al. 2009). Bottom trawling occurs on the west-coast shelf edge and slope, and loss or modification of the benthic community is likely (20 out of 48 habitat types occurring within the fishery area are at risk; Wayte et al. 2007). Other sources of benthic habitat loss or modification at more localised scales are dredging, construction of infrastructure, and laying of underwater pipelines and cables. The implications of benthic habitat loss on the region’s species and ecosystems are not adequately understood.

Extraction of living resources
Understanding of ecosystem effects of fishing is very limited. Evidence of reliance of species on targeted stocks include research on the feeding ecology of seabirds foraging around the Houtman Abrolhos Islands, which indicates that a number of species, including the threatened Australian lesser noddy, are reliant on the availability of specific species of small pelagic fish (Gaughan et al. 2002). Some seabird species that inhabit the region are also known to depend on large pelagic predators, such as tuna, for driving prey fish to the surface, and some species, such as sooty tern, are thought to be totally reliant on this method of feeding (Dunlop 2009; Jaquemet et al. 2007). There are also some concerns, underpinned by high levels of uncertainty, about competition for resources between Australian sea lion and fisheries (DEWHA 2010).

Based on the latest fisheries status reports from the Australian Government, Western Australia and South Australia (respectively, considering the 2009, 2008–09 and 2006 stock status reports), 10 stocks in the region are assessed as 'overfished.' 16 stocks have an uncertain status, including dhufish, for which substantial declines have been reported (Fletcher & Santoro 2009; Linnane et al. 2010, 2010a; Wilson et al. 2010). Recent management changes have been implemented to facilitate stock recovery for dhufish and other west coast demersal finfish (DoF 2011, 2011a). In light of limited understanding about the ecosystem effects of extraction of living resources for the key ecological features of the region, the pressure is considered of potential concern.

Oil pollution
A number of the key ecological features, including the Commonwealth marine environment within and adjacent to Geographe Bay, have characteristics that make their ecosystems and communities vulnerable to the effects of an oil spill, for example, features that include localised areas of high productivity, which attract large aggregations of marine life.

The intensity and distribution of activities implicated in oil spills, such as oil production and transport, are likely to increase in the region.

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.

Invasive species
Temperate southern Australian habitats are considered to be at great risk globally from introduced marine species because of their biogeographic isolation from other temperate marine habitats of the world. Species native to the east coast of Australia also present a risk, as they have evolved independently of those on the west coast and may become invasive if introduced in favourable conditions to the south-west marine environment. Marine pests can be introduced through ballast water exchange or via biofouling (the accumulation of microorganisms, algae and animals on objects in water). Vessels at high risk for introducing species include those that are slow moving, have spaces where marine species can settle, come in close contact with the sea bottom and remain in a single area for extended periods. Inshore areas, and particularly ports and sites where infrastructure development and maintenance take place, have the highest risk of marine pests becoming established. No marine pests have been recorded in the South-west Marine Region. Four marine pest species occur in the environment of four ports adjacent to the region (Fremantle, Bunbury, Albany and Port Adelaide). Pest species established in the neighbouring South-east Marine Region and capable of spreading into the deeper environments of the Commonwealth marine area include Northern Pacific seastar, New Zealand screw shell and Japanese kelp.