Pressures on the coast
Since 1988, state of the environment reports identified similar coastal pressures and impacts for SA, with some changes in intensity and location. The 2016 Australia State of the Environment Report identified the following pressures relevant to South Australia:
- severe localised impacts on the coast from Port Pirie refinery
- high recreational fishing pressure near population centres
- gaps in investment in Indigenous land and sea management
- high impacts from bottom trawling on benthic communities in the Spencer Gulf
- localised pressures and impacts from large and growing aquaculture production.
The EPA aquatic ecosystem condition assessments evaluates the pressures specific to various parts of the SA coast. The program reflects the biological and geomorphological diversity of the coast and breaks the coastline down into smaller spatial units based on collated biological data and inferred ecosystem patterns. Typical pressures include:
- wastewater treatment plant discharges
- agricultural runoff
- urban stormwater
- septic tank leakage
- highly modified, impacted and regulated rivers
In 2017, the SA Government published a series of baseline reports for marine parks that identified the following coastal pressures.
Along developed parts of SA’s coast, seagrass and reef ecosystems are at risk from nutrients, pollutants, sediment loads and turbidity associated with freshwater inputs from stormwater, treated sewage, seepage and agricultural runoff or industrial discharges.
Coastal habitats are also at risk from nutrients generated by offshore aquaculture operations, and from pollution from shipping and offshore mining including accidental petrochemical spills.
Through concerted effort by the SA Government based on evidence from the Adelaide Coastal Waters Study, there has been a persistent decline in nitrogen and phosphorus emissions from land-based point sources such as major wastewater plants and other facilities along the Adelaide coast.
Consistent with a growing industry, emissions from offshore aquaculture have showed an increasing trend since 2012–13. These trends in nutrient load are estimated based on feed inputs for the aquaculture industry.
The most significant decline in nitrogen emissions followed the ceasing of production by Penrice Soda in 2014 and the associated decline in discharges into the Port River.
Phosphorus emissions have also declined slightly. Emissions for both nitrogen and phosphorus were higher in 2016–17 because higher than average rainfall resulted in higher volumes of flow into the wastewater treatment plants and a decrease in the demand for recycled water from the plants.
Increased concentrations of nutrients (mainly nitrogen) in the marine environment causes fast-growing algae to grow on seagrass leaves and across rocky reef habitats. This reduces the amount of light available for photosynthesis and over time, this can result in seagrass loss and smother rocky reef habitats.
The following graphs [Figures 53(a) and (b)] show the trends in total emissions of nitrogen from 2 key land-based sources (wastewater treatment plants and major industries) and the estimated emissions from offshore aquaculture.
In addition to nutrients, plastics and other debris are also a threat to coast and marine species and ecosystems. Plastics and other debris find their way into the marine environment in increasing volumes via pollution from ships, fishing vessels, littering, stormwater and wastewater.
Reducing plastic pollution
It is estimated that around 70% of all litter in the sea is plastic. Plastics can either float on the ocean surface or sink to the sea floor if they are made of polymers denser than sea water. Over time, buoyant plastics can drift ashore or drift out into the open ocean. The main sources of plastics in the ocean include marine vessels, fishing gear, waste- and stormwater outlets and litter. Plastic pollution affects marine fauna and flora through ingestion, entanglement, transport and bio-accumulation of harmful chemicals, and the transport of invasive species.
An Australian Government parliamentary inquiry into the threat from marine plastic pollution described the concerns about plastic in the marine environment as its vast distribution, its persistence and the fact that it breaks down in ever smaller pieces, rather than decomposing. The inquiry made 23 recommendations, many aimed at preventing plastics from entering the sea, such as through the banning of single-use plastic bags and phasing out of plastic microbeads in products.
In 2016, Australian environment ministers endorsed a voluntary industry phase out of microbeads by 1 July 2018. An Australian Government commissioned assessment in early 2018 found that, out of approximately 4,400 relevant supermarket and pharmacy products inspected, only 6% still contained microbeads.
In the past, the main causes of overfishing were identified as inadequate controls and poor data. Both these areas improved over time and, today, exploitation of fish stocks is no longer a major concern in South Australia, mainly due to improved controls.
According to the 2018 Fisheries Trend and Condition Report, natural variations in recruitment, environmental conditions and fishing pressure all impact on the status of fish stocks. Improvements in technology are increasing the catch potential for recreational and commercial fishers. Other pressures include climate change, coastal development and pollution. These pressures can directly impact habitats like mangroves and seagrass that support fish stocks.
- quota evasion
- illegal and undersized take
- disease or pest incursion
- fishing in closed seasons or closed areas
- illegal sales or gear
- inaccurate reporting
- loss of ecosystems and breeding areas.
The 2018 Fisheries Trend and Condition Report notes that, of the 49 SA commercial fishery stocks classified, 37 (76%) are classified as 'sustainable', one as 'recovering', 7 as 'depleting', 3 as 'overfished' and one as 'environmentally limited', as shown in Figure 54.
Previous state of the environment reports describe the rapid growth of the aquaculture industry amid concern about the lack of information about its impacts. Since then, policies, standards, assessment, monitoring and management practices have improved. The environmental impacts of a still-growing industry are now better understood and managed.
About 40 possible risk events are considered as part of the process of assessing aquaculture operations including:
- nutrient discharge
- chemical use
- water quality
- disease management
- water flow
- interaction with migratory species.
Species farmed in SA marine waters include tuna, oysters, abalone, finfish, mussels, microalgae and trout.
Aquaculture operations (zones, leases and licences) extend from Denial Bay west of Ceduna to Lacepede Bay in the South East. Bivalve aquaculture can decrease plankton levels in surrounding waters, reducing food availability for native filter feeders. Chemicals and other waste, such as nutrients and organic matter from aquaculture, pose risks to the environment if not well-managed.
Aquaculture zones policies (Figure 55) provide an overview of the environment and establish areas in which aquaculture is deemed ecologically sustainable. Specific controls based on the farmed species are applied through leases, licences and the Aquaculture Regulations 2016.
These aim to minimise impacts during the construction phase and ongoing operations, such as feed and chemical use, escape of stock, disease incidents, marine debris, waste disposal (for example oyster baskets) and interactions with the benthic environment (for example disturbance by infrastructure and shading of seagrass). The main impacts from the tuna and finfish sectors are dissolved nutrients and chemicals from fish metabolism and solid wastes from faeces and excess feed.
The largely unspoiled Great Australian Bight is an area of interest for oil and gas exploration. It is also an area of global conservation significance for rare and endangered marine mammals. Offshore petroleum projects are assessed by the National Offshore Petroleum Safety and Environmental Management Authority.
Previous reports identified coastal sprawl, stormwater runoff, marinas and associated residential development, and a growing coastal population as major pressures. While progress has been made to better manage stormwater and environmental impacts of coastal development, coast and marine habitats are still impacted by various activities, such as:
- prawn trawling
- recreation including offroad vehicle use
- climate change impacts including sea-level rise, ocean acidification, increased ocean temperature, and changes to storm frequency and strength
- invasive pest species
- vessel moorings
- land reclamation
- placement of coastal structures, such as breakwaters, oyster racks, fish cages, jetties and marinas.
Pest species and disease
Weeds can have a negative impact on coastal dunes. Weed species can be introduced or spread by wind, water, animals and humans – accident or deliberately. Weeds readily invade and cause a local loss of native plants, reducing the amount of habitat, food and shelter available for native animals and insects.
Port handling, shipping traffic, biofouling from ship or boat hulls, fishing equipment and ballast water are also increasing the risk of incursion by pest species. The number of cargo ships visiting SA ports over the last 5 years has increased from 1,135 in 2009–10 to 1,831 in 2014–15, with about 15% from overseas and 85% arriving from other Australian ports (Figure 56).
The Australia ballast water management requirements provide guidance on how vessel operators should manage ballast water when operating within Australian seas in order to comply with the Biosecurity Act 2015. The requirements align to the International Convention for the Control and Management of Ships’ Ballast Water and Sediments 2004 (the Ballast Water Management Convention), which enters into force internationally on 8 September 2017.
Perkinsus olseni, a native parasite found in both wild and farmed abalone, clams, mussels and pearl oysters has been recorded in SA waters. Abalone are more susceptible to Perkinsus at higher temperatures, and outbreaks may be exacerbated by climate change.
Abalone viral ganglioneuritis is a disease that may cause mass mortalities of abalone and has been recorded within 40 km of the SA border. Possible vectors for the spread include unregulated translocation of stock, discharge from fish processing or aquaculture facilities, launch and retrieval of anchors or pots, abalone fishing and the use of abalone as berley or bait.
A herpes virus was thought responsible for both the 1995 and 1998 mass mortalities of sardines in SA and believed to have been caused by an exotic pathogen. Potential vectors for the pathogen include ballast water, seabirds and imported baitfish used in aquaculture. Translocation of oyster spat and abalone has the potential to spread diseases, parasites and viruses, which can impact shellfish.
Pacific Oyster Mortality Syndrome (POMS) is a virus that causes rapid and high mortality in farmed oysters. The virus was first detected in NSW in 2010, and subsequently in Tasmania. To reduce the risk of the disease entering SA, the government has restricted the importing of oysters and banned the movement of live Pacific Oysters, oyster spat and farming equipment from Tasmania into SA.
However, in February 2018, the virus was detected in feral Pacific Oysters in the Port River. At this time, POMS has not been detected in SA oyster farming areas, and the SA Government has implemented a ban on the removal of all bivalve organisms (oyster, mussels and cockles) from the Port River. Other strategies to mitigate the spread of the virus have also been implemented.
Introduced animals, such as foxes, cats and rodents cause vegetation degradation, compete for habitat and food sources and prey on native species, including shorebirds. Foxes are opportunistic predators and present a significant threat to the breeding success and recruitment of shorebirds. Feral cats and rodents also prey on chicks, adults and eggs and reduce populations of seabirds and shorebirds.
Weeds tolerant of salt and aridity can invade saltmarsh, cliffs and dune environments and compete with native vegetation. A number of coastal weed species have been observed along the SA coast, including Beach Daisy, Pyp Grass, Sea Wheat-grass, Polygala, Sea Spurge, Sea Lavender, Common Ice Plant, African Boxthorn, Pimpernel, Marguerite Daisy, Western Coastal Wattle, Ward's Weed, Wild Turnip and Red Brome.
- habitat and species loss
- inundation of fringing coastal habitats
- changes in salinity of freshwater systems, estuarine systems and groundwater
- changes to distribution of plants and animals
- changes to ecosystems and ecological communities
- damage to private and public assets.
- an increase in sea surface temperature (which could benefit some marine species)
- a change in sea surface salinity (with species-specific impacts)
- an increase in ocean acidity (which may affect plate and shell forming in phytoplankton and molluscs)
- sea-level rise (which poses a threat to habitat for seagrass, mangroves, saltmarshes, dunes and the fauna that rely on these habitats)
- a weakening of the Leeuwin Current (with an impact on recruitment of species reliant on currents)
- increased upwelling (with positive impacts for lobster and prawn)
- increased extreme weather events (where low tides with extreme hot air temperatures and strong northerly winds could lead to large-scale seagrass diebacks, as happened in the Spencer Gulf between 1987 and 1994.
Extreme weather also brings increased erosion threatening human infrastructure, ecological communities and habitat for threatened species. It can also destabilise dunes and cliffs.
Many SA coastal areas are subject to erosion and flooding hazards exacerbated by rising sea levels, which results in a rise in mean sea level, alteration of the elevation of tides and sea-water inundation of coastal habitats, including mangroves, saltmarshes, beaches and rocky intertidal reefs. The impact of extreme weather events on elevated sea levels will also produce greater coastal erosion due to more intense storm-wave action. South Australia has experienced increases in sea level of between 2 and 7 mm per year since the early 1990s.
In 2011, the Australian Government estimated that between 31,000 and 48,000 residential buildings in SA may be at risk of inundation from a sea-level rise of 1.1 m. The analysis, which does not take account of existing coastal protection, such as seawalls, estimated that a 1.1 m sea-level rise will also put about 6,700 km of roads, 200 km of railways, and 1,100 light industrial and 1,500 commercial buildings at risk in SA.
Estimates of the replacement value of at-risk homes was around $5–8 billion, commercial buildings was $22–27 billion, light-industrial buildings was $0.6–1.2 billion, roads was $7 billion and rail was from $0.6–1.3 billion. While development policies aim to respond to these risks, a large number of coastal settlements already exist in areas of active coastal erosion and will require significant additional investment in infrastructure.
There are currently 11 tide gauges in SA operated by Flinders Ports and one operated by the Bureau of Meteorology. Of these, only 5 (Port Lincoln, Port Pirie, Outer Harbor, Inner Harbor and Victor Harbor) operating since 1966 or earlier, are suitable for estimating relative sea-level rise. Long-term sea-level records are required to assist with both tidal predictions and detecting and monitoring changes in sea level.
Two more accurate gauges were established in the early 1990s at Port Stanvac and Thevenard. These were able to determine vertical land motion, which contributes to the estimate of absolute sea-level rise. Observations at Port Stanvac were discontinued in 2010 following the closure of the refinery and may be reinstated at a nearby location.
To visualise the potential sea-level rise, the Australian Government has produced a series of maps. The predicted increase in sea level and storm surge are likely to amplify sand loss and coastal erosion. South Australia has an ongoing program for managing sand along Adelaide’s beaches. This includes beach replenishment, construction of breakwaters and sand slurry pumping. The extent to which the program will be able to stem the tide of loss of dune volume and beach width from sea-level rise and increase in storm surge will be a significant ongoing challenge.
There are major risks for marine-based ecosystems from a changing climate. In a research article published in early 2018, it is argued that climate stressors, such as warming and ocean acidification, can drastically alter the structure and function of marine food webs through altered trophic flows and cyanobacterial proliferation.