SOUTH AUSTRALIA Dry All Year
Mangroves in South Australia are confined to sheltered shores in the Gulf of Saint Vincent and Spencer Gulf, and protected bays on the Eyre Peninsula. Low rainfall in this driest of all Australian states creates a scarcity of estuaries, with small amounts of freshwater, nutrients and sediments entering the sea. Coastal waters are therefore oligotrophic, except for seasonal upwelling events off the Eyre Peninsula and the south-east. The Gulfs are further considered inverse estuaries,as salinity is higher inshore and temperature fluctuations larger at the top of the Gulfs than towards the ocean. Mangroves can be found generally seaward of saltmarshes and often interspersed with seagrass beds and mudflats. They range from extensive and dense forests to sparse and isolated stunted trees at more extreme settings. The total area of mangroves in South Australia is around 156 km2, and there is only one species, Avicennia marina. Trees of A. marina around Adelaide aregenetically intermediate between two varieties, var. marina and var. australasica. Populations in Spencer Gulf and along the west coast of Eyre Peninsula might be more closely related to var. marina, while those to the east are perhaps more like var. australasica.
Large temperate mangrove forests
Some of the largest temperate mangrove stands in Australia. Trees of Avicennia marina grow to around 8 m. These contrast with other mangrove stands with stunted growth where extreme environmental conditions prevail, as in upper reaches of the Gulfs. photo: Sabine Dittmann
Mangroves and saltmarshes
South Australia has extensive supratidal areas of samphire saltmarsh, generally with a succession from saltmarsh to the lower-lying mangroves in the intertidal zone. Major plant species in the saltmarsh zone are Sclerostegia, Sarcocornia and Halosarcia. photo: Sabine Dittmann
Mangroves and seagrass beds
Mangroves and seagrass beds Low turbidity in most coastal waters allows the close proximity of seagrasses and mangroves. Almost all large and small mangrove creek estuaries have dense beds of the seagrasses Heterozostera and Zostera towards their seaward margins. photo: Sabine Dittmann
Avicennia marina var. australasica - CC,FG,MC
var. marina - CC, FG
- Avicennia marina
- photo: Sabine Dittmann
- photo: Sabine Dittmann
Excess nutrients and eutrophication affecting mangrove growth and survival.
Pollution of mangroves from oil spills and heavy metal contamination.
Mangroves occur naturally along sheltered sections of the South Australian coast mostly within deep gulfs and inlets (Ozestuaries 2006, SA DEH 2006), influenced by cool, mostly arid conditions, micro tides and severe waves. Three regions are based on the types of mangrove habitat determined by varying geological and physiographic settings.
Ceduna Coast (CC) - Arid Exposed Coast
Nullarbor to the western side of Eyre Peninsula – a coastal area of numerous intermittent flow, dry channels. This coast is exposed with moderate to severe wave energy from the Great Australian Bight. Mangroves occur in sheltered intertidal bays near Ceduna between Tourville Bay and Smoky Bay, with additional isolated patches in Streaky and Anxious Bay. The region has one mangrove species with a total mangrove area of ~26 km2.
Flinders’ Gulfs (FG) - Cool and Moist Inverse Estuaries
Coffin Bay on Eyre Peninsula to Spencer Gulf, to Gulf Saint Vincent and Fleurieu Peninsula – 9 local catchment areas. The two large gulfs are inverse estuaries with low to moderate wave energy comprising extensive inter- and supratidal areas characterised by micro- to mesotidal ranges at taheir respective heads. Mangroves occur chiefly along the top ends of these gulfs, from Cowell to Port Broughton in Spencer Gulf, and from Price River near Port Clinton to Sandy Point south of Port Wakefield in Gulf St. Vincent. The most extensive mangroves in Spencer Gulf are in Franklin Harbour, Tumby Bay, and around Port Augusta, with Chinaman Creek having the largest
Murray Coorong (MC) - Exposed Southeast and Kangaroo Island
The River Murray to the Millicent Coast, including Kangaroo Island – 3 local catchment areas. This exposed southeast coast is affected by high wave and low tidal energy. The region has no naturally-occurring mangroves. Some isolated mangroves were planted near the River Murray mouth about 40 years ago. These introduced mangroves (marked with * on the map) were apparently sourced locally.
Seagrass detritus covering and smothering pneumatophores of Avicennia marina. Photo: Sabine DittmannSouth Australian mangroves are exposed to various extreme conditions by: a dry climate, high salinities in coastal waters, and broad coastal areas exposed to large waves. Various natural factors are indicative of changes taking place. In the case of sea level rise, levee banks and salt ponds may prevent the landward retreat of mangroves in some areas. Seagrass detritus washed into mangroves areas will smother pneumatophores and juvenile plants. Coastal erosion, saltation and dune encroachment have lead to the some loss of mangroves.
The close proximity of human settlement with mangroves often creates problems that result in further loss of mangrove area. Photo: Sabine Dittmann Most tidal wetlands in the northern ends of the Gulfs, and Barker Inlet in Port Adelaide, are severely altered by coastal development. Over 90% of the population live near the coast with the majority in the Adelaide region where mangroves occur. Increased sedimentation associated with coastal strip development may explain the mangrove expansion at around five hectares per year in Barker Inlet. There has been contamination of marine sediments by heavy metals from the lead smelter in Port Pirie and the Whyalla steelworks, with further contamination from salt and chemical works near Adelaide and northern Spencer Gulf. Eutrophication has resulted from urban stormwater runoff and sewage discharges, especially around Adelaide and northern Spencer Gulf, causing the proliferation of nuisance macroalgae (Ulva) that smothers mangrove roots and seedlings. Around 250 ha of mangroves have died near the outfall of Adelaide’s Bolivar sewage treatment plant, and since 1954, 25% of mangroves were lost in Gulf St. Vincent. Oil spills, notably that in 1992 near Port Bonython in northern Spencer Gulf, have affected nearly 100 ha of mangroves and 23 ha have died. Uncontrolled public access to mangrove areas has resulted in severe stem damage from trampling of roots and this will take several decades to recover, if at all.
Community conservation & education
There is strong community interest in mangroves. Groups like the Port Adelaide Resident’s Environment Group are active in protecting mangroves in the Port River estuary while the Arno Bay Estuary Group and Franklin Landcare Group in Spencer Gulf are both active in mangrove restoration and community awareness through boardwalk construction. There is a growing awareness, particularly by people interested in fishing and coastal activities, that mangroves are a valued part of coastal habitat. Boardwalks are located at St. Kilda, north of Adelaide, which includes an information centre, and at Cowell, Arno Bay and Tumby Bay on the Eyre Peninsula. Further public access is possible in most other mangrove sites and all intertidal areas in the state are intensively used by recreational fishermen. Research on South Australia’s mangroves has been concentrated on their value for fisheries and trophic interactions. This work was mainly carried out by the SARDI (South Australian Research and Development Institute) Aquatic Sciences.
South Australian mangroves are protected and managed under a number of Government initiatives. They are covered under the Fisheries Act 1982 and the Harbours Act 1936-1981, as well as under the Native Vegetation Act 1991. Furthermore, 28% of South Australia’s mangroves are lying within protected areas. Policy direction, to protect and manage the marine environment, is set out in the Living Coast Strategy for South Australia DEH (Department for Environment & Heritage, 2004). The State is committed further to the establishment of a Representative System of Marine Protected Areas, and 19 Marine Protected Areas will be progressively dedicated by 2010. Protection through the planning system under local government Development Plans is provided under the Planning Strategy for Regional South Australia and more recently promoted under both the Draft Planning Strategies for Metropolitan and Outer Metropolitan Adelaide. These Strategies require planning authorities to consider the protection and management of mangrove habitats and the minimisation of impacts on mangroves with the administration of strategic and statutory planning. Additional protection for mangroves is provided under the Marine Planning Framework, the Estuaries Policy and Action Plan, and the Adelaide Dolphin Sanctuary in Port River and Barker Inlet. Several mangrove stands in northern Spencer Gulf and north of Adelaide in Gulf St. Vincent are included in the Directory of Important Wetlands in Australia as areas of high conservation value. Several sites, like Franklin Harbour, Clinton and Port Gawler/St. Kilda are conservation parks or aquatic reserves. State regulatory agencies responsible for managing mangrove habitat, include: DEH sections - CMB (Coast & Marine Branch) and NPW (National Parks & Wildlife), plus DWLBC (Department of Water, Land & Biodiversity Conservation), EPA (Environmental Protection Agency), PIRSA Fisheries (Primary Industries & Resources) and SARDI.