Describing the coast
The coast includes all water between the low-water line on the coast and 3 nautical miles (or 5.5 km) seaward. It includes all of Gulf St Vincent and Spencer Gulf. It also includes estuaries, wetlands, rocky shores, sand dunes, beaches, mudflats and mangroves stretching inland from the low-water line.
The marine area of the SA coast consists of 8 bioregions, each with its own distinct oceanographic and ecological characteristics. Just over 44% of SA’s coastal waters are included in a network of 19 marine parks. A total of 9 of these marine parks are in Eyre, the largest bioregion. The coast is also divided into 7 natural resources management (NRM) regions.
More than 90% of South Australians live within 50 km of the coast with approximately 75% living in Greater Adelaide. The health of our coast is determined by both land- and marine-based human activities and a changing climate.
Key features of the coast include:
- Only 15 out of a total of 783 estuarine systems classified in Australia are found in SA. This reflects SA’s arid climate.
- Gulf St Vincent and Spencer Gulf represent the largest temperate inverse1 estuaries in Australia.
- Estuaries provide essential habitat for marine organisms and are important areas for some of SA’s commercial and recreational fisheries.
- Estuaries can be affected by pollution, habitat disturbance, recreational activities, surface water diversion, upstream water extraction, climate change and human-made infrastructure, such as weirs and fish passages.
- Often linked to estuarine systems, SA’s coastal and marine wetlands are of national importance, with those in the Coorong and South East also of international significance.
1 Often more saline at the top of the gulf than at the mouth of the gulf/estuary due to high evaporation and low freshwater input.
- These islands make up almost a quarter (1,251 km out of 5,067 km) of SA’s coastline, with Kangaroo Island accounting for nearly half.
- The islands are largely free of foxes, cats and rabbits introduced to the mainland.
- As a result of the low numbers of feral animals, some have retained species extinct on the mainland, such as the Stick-nest Rat.
- They are safe places for seals and seabirds to rest and breed.
- Parts of Gulf St Vincent and Spencer Gulf together represent the largest sheltered coastal marine wetland ecosystem in temperate Australia.
- The extensive low-gradient coastal zone provides habitat for some of the largest areas of temperate seagrass, mangrove and saltmarsh communities in Australia.
- The waters of Spencer Gulf are some of the most commercially productive in SA, supporting key commercial fisheries, including marine scale fish species, Blue Swimmer Crab, and Western King Prawn. These waters also support important aquaculture activities such as farming of Southern Bluefin Tuna, Yellowtail Kingfish, Blue Mussels and Pacific Oyster.
- As the flora and fauna found in Upper Spencer Gulf have some tropical and subtropical influences, the area has been assigned as a distinctive biogeographical region.
- Large areas of the shallow nearshore waters are subject to nutrient enrichment. This is not restricted to the areas close to large industrial discharges but also adjacent some small coastal towns or river discharges. In many circumstances the effects of nutrient enrichment can be exacerbated by low current speeds and poorer flushing.
- Lasting changes to seagrass and reef condition are resulting in habitat loss, which impacts on the provision of ecosystem services. This includes decline in commercial and recreational fisheries production, reduction in the ability of the environment to treat wastes through nutrient assimilation and help to regulate our climate through carbon sequestration, and potential changes to beach erosion.
- Reef habitats occur on a large portion of SA’s coasts except in the upper gulf areas where sand and seagrass are dominant.
- Subtidal reefs in SA comprise mainly low-profile Pleistocene limestone reefs, and on the wave exposed southern areas, steeply sloping Precambrian rocks and reefs.
- Canopy forming macroalgae cover is an important indicator of subtidal reef condition in SA.
- Reef habitats are important for a number of species caught by commercial and recreational fishers, including snapper, abalone and the Southern Rock Lobster.
- Margaret Brock Reef, west of Cape Jaffa on the boundary between the Coorong and Otway bioregions, is considered a biodiversity hotspot.
Sandy and soft-sediment habitats
- Sandy habitats dominate SA’s coastline, occupying about 59% of the coastline and are prevalent in all 8 bioregions.
- These habitats are particularly common in the high-wave energy dominated regions, such as the South East. These areas are exposed to the Southern Ocean and experience some of the highest wave energies in Australia.
- Sandy and soft-sediment habitats are characterised by grain size, depth and chemistry. These have a major influence on the types of organisms populating these areas.
In SA, coastal plant communities are generally characterised as dune, clifftop, mangrove and saltmarsh. Each is made up of a diverse variety of plant species that have adapted to the hot, dry and saline coastal environment. These communities form important habitats for a variety of native fauna, including birds and reptiles. They also play a very important role in stabilising and trapping marine sediments and forming protective buffers.
- The Grey Mangrove Avicenna marina is the only species of mangrove in SA.
- Mangroves are generally found along low-energy, fine-sediment shorelines and there are significant stands near Ceduna on the West Coast, Franklin Harbour near Cowell, the northern ends of the 2 gulfs near Port Pirie, and between Port Adelaide and the Light River delta.
- Mangroves are highly productive nurseries, feeding and breeding areas for fish and crustaceans, habitat for seabirds and waterbirds, and form part of the coastal food chains.
- Mangroves provide an important sink for nutrients, blue carbon and physical protection against storms.
- The extent of mangrove vegetation is increasing and is estimated as 16,960 ha, with 7,870 ha in Northern and Yorke, 5,820 ha on Eyre Peninsula, and 3,270 ha in Adelaide and Mount Lofty Ranges region.
- Saltmarshes are recognised as one of the most efficient natural systems for capturing and storing carbon.
- In contrast to mangroves, the species richness of tidal saltmarshes increases with latitude. Where saltmarsh and mangrove distribution overlap, they usually form adjacent, connected communities in the intertidal zone.
- Spencer Gulf and Gulf St Vincent contain some of the largest and most diverse areas of temperate saltmarshes in Australia.
- These highly productive tidal environments provide key habitat for resident and migratory shorebirds, feeding and refuge areas for fish, and rare or endangered plants species such as Centrolepis, Wilsonia and Tecticornia.
- Intertidal and supratidal saltmarshes are an essential hydrological buffer between seaward mangroves and terrestrial ecosystems, regulating salinity and water velocity, and decreasing the suspended sediment load and nutrients entering the marine environment.
- The extent of coastal saltmarsh was estimated as 21,120 ha with almost half (10,790 ha) in the Northern and Yorke region, and 6,270 ha on Eyre Peninsula.
- There are 12 recorded species of seagrasses in SA coastal waters.
- The most extensive seagrass meadows occur in the upper reaches of Spencer Gulf and Lacepede Bay.
- Seagrasses provide essential habitat for marine organisms and support some of SA’s commercial and recreational fisheries such as the Marine Scalefish, Blue Swimmer Crab, and Western King Prawn fisheries. They function as nursery, breeding and feeding areas for fish, crustaceans and other marine animals.
- They stabilise nearshore sediments, improve coastal water clarity, assimilate nutrients, and reduce wave energy.
- The historic extent of seagrass in many of the regions is largely unknown and seagrass cover within sampling sites was estimated at 45%.
- The greatest macroalgae diversity is found on nearshore reefs in areas of high-wave exposure and cold-water oceanic upwelling (South East, southern Eyre Peninsula and southwestern Yorke Peninsula).
- The majority of the 1,200 recorded species of macroalgae in SA are endemic and their diversity is amongst the highest in the world. This is largely due to the length of the southerly-facing rocky coastline (the longest east–west, temperate coastline in the world) and the long period of geological isolation.
- South Australian waters have the richest collection of ascidians or ‘sea squirts’ recorded in the world, with over 200 described species.
- Crustaceans (lobsters, prawns and crabs) provide a significant commercial resource.
- Molluscs such as abalone, pipi and vongole are also economically important, as are calamari and octopus.
- More than 370 marine fish species have been recorded in SA, of which 77 are harvested for commercial, recreational and cultural purposes.
- Wild-catch species include the iconic King George Whiting, Southern Garfish, Snapper and Southern Bluefin Tuna.
- South Australia is one of the key sites in the world for scientific research of the White Shark.
- Non-endemic species such as the Black Marlin and Lizardfish occasionally visit, probably as a result of the easterly flowing Leeuwin Current.
- 3 species of turtles have been recorded visiting SA marine waters from more tropical and subtropical waters, probably as a result of the easterly flowing Leeuwin Current – the Loggerhead, Green Turtle and Leathery Turtle.
- A great diversity of seabirds, resident and migratory shorebirds, coastal bush birds and coastal raptors can be found in SA.
- The majority of seabirds breed on islands off the coast, the most common being the Short-tailed Shearwater and White-faced Storm Petrel.
- Other common breeding species include the Little Penguin, terns (Crested, Caspian and Fairy), gulls (Silver and Pacific) and cormorants (Pied and Black-faced).
- Other bird species include the Cape Barren Goose, White-bellied Sea-Eagle and Osprey.
- SA waters, particularly the Great Australian Bight, are recognised as an area of global conservation significance for rare and endangered marine mammals, that is, the Southern Right Whale and 3 species of seals or pinniped, Australian Sea Lion, Australian Fur Seal, and Long-nosed Fur Seal.
- The world population of the endangered Southern Right Whale is estimated at between 1,500 and 3,000, with an Australian population of about 400–600.
- Other cetaceans recorded in SA include Blue Whale, Sperm Whale, Minke Whale, Humpbacks and Killer Whale.
- 3 species of dolphin are common in SA coastal waters – offshore Bottlenose Dolphin, inshore Bottelnose Dolphin, and Common Dolphin.
- The Australian Sea Lion is one of the rarest and most endangered pinnipeds in the world and is endemic to Australia. Of the estimated 10,000 to 12,000 world population, 7,500 are found in SA and 3,100 in Western Australia.
- There are 49 Australian Sea Lion breeding sites in South Australia, with an estimated annual pup production of about 3,100.
- There are about 100,000 Long-nosed Fur Seals in SA, which is more than 80% of the Australian population.
- Populations of Long-nosed Fur Seal have been expanding over recent decades, resulting in increased interaction with fishing.
- There are 35 breeding sites for the Long-nosed Fur Seal in SA, with an estimated pup production of 20,400.