1 Why is it important?
South Australia’s marine environment spans more than 60 000 square kilometres of waters and more than 5000 kilometres of coastline (Geoscience Australia 2010). The coast, estuaries and adjacent marine waters are a unique part of the South Australian environment. It is a distinct, complex and interconnected natural system, with finite resources that are vulnerable to overuse and degradation when not well managed.
1.1 Unique features and species endemism
Australia’s long period of geologic isolation from the rest of the world (more than 65 million years), the state’s extensive continental shelf, the long east–west ice-free extent of the southern coastline, and the characteristic low nutrient condition of coastal waters have all contributed to the biological richness and endemism of South Australia’s temperate marine environments (Edyvane 1999). South Australia has a wide range of coastal landforms and marine habitats, and also a variety of oceanographic conditions, including a high degree of variability in sea temperatures.
Of particular significance are the two large, sheltered tidal gulf ecosystems of Gulf St Vincent and Spencer Gulf, which provide habitat for some of the largest areas of temperate mangrove, seagrass and tidal saltmarsh communities in Australia. In addition, the marine fauna and flora of South Australia include both the typical cold temperate biota of Tasmania, Victoria and southern New South Wales and the transitional warm to cool temperate biota of southern Western Australia. A range of habitats is evident, from warm salty waters in the gulfs to cool-water kelp forests in the south-east, and from the low-productivity waters of the Great Australian Bight to the nutrient-rich upwellings of the south-east. These factors have combined to produce a rich diversity of organisms and communities along the South Australian coast, which is unparalleled in Australia and the world (Edyvane 1999). South Australian waters support more than 6000 invertebrate species, 350 fish species, 16 breeding seabird species, 33 mammal species, 1200 algae species and 12 seagrass species. In the Southern Ocean, 75% of the red algae species, 85% of the fish species and 95% of the seagrass species are found nowhere else in the world, giving them local, national and international significance (Government of South Australia 2004).
The largest breeding colonies of Australian sea lion, and more than 80% of the total population, are found in our state. South Australia also has 32 species of whales and dolphins and more than 70 species of seabirds, including little penguin, osprey and the white-bellied sea eagle. We are still to discover some of the many species of invertebrates. South Australia has 24 coastal wetlands that support populations of migratory birds of conservation significance.
Within the Flindersian Province, a biogeographic region that extends across the southern coast of Australia, approximately 1155 species of macroalgae, 22 species of seagrass, 600 species of fish, 110 species of echinoderms and 189 species of ascidians have been recorded (Lewis et al. 1998). Of these, approximately 85% of fish species, 95% of molluscs and 90% of echinoderms are endemic. In contrast, approximately 13% of fish, 10% of molluscs and 13% of echinoderms are endemic in the tropical regions of Australia. Similarly, marine macrofloral diversity and endemism in the temperate regions of Australia are among the highest in the world. The richness of the temperate macroalgal flora (i.e. 1155 species) is 50–80% greater than for comparable regions around the world, with approximately 800 species and more than 75% endemism recorded in red algae alone. The level of temperate species biodiversity in macroalgae is approximately three times the level recorded in the tropical regions of Australia, where approximately 200–400 species of macroalgae have been described (Edyvane 1999).
South Australia has many fish species of conservation significance, including two types of seadragons, and several species of seahorses and pipefish, as well as the world’s largest known breeding aggregation of Australian giant cuttlefish (Steer et al. 2013). Our waters are feeding grounds for endangered blue whales, bottlenose dolphins, and sperm and pilot whales, and attract increasing numbers of southern right whales to breed and calve each year. At the other end of the spectrum, our waters are also home to the world’s smallest live-bearing starfish, known locally as ‘Little Patty’, which is found in only one location on the west coast of Eyre Peninsula.
Ninety metre–high limestone cliffs extend from the Western Australian border to Cape Adieu, and Spencer Gulf has some of the largest mangrove forests in southern Australia. South Australia has the second largest (after Western Australia) area of temperate-water seagrass meadows. The Coorong, as well as being a wetland of international importance, also has the largest high-energy beaches in the Southern Hemisphere. Colourful sponge gardens can be found in the shallow waters of Pelican Lagoon and Bay of Shoals off Kangaroo Island. The deep trenches at Backstairs Passage have sponges that are more than one metre in diameter, and gorgonian corals. Underwater forest communities of giant kelp reaching up to 30 metres tall can be found in the south-east, along with the smaller intertidal and subtidal bull kelp.
1.2 Ecosystem services
Seagrasses dominate the South Australian sheltered nearshore habitats and provide important spawning and nursery areas for a wide variety of fish and invertebrates. Seagrass performs many functions, including nutrient cycling, carbon storage, reducing coastal erosion (by stabilising sand and attenuating wave action) and filtering out suspended solids in the water column.
Rocky reefs and their macroalgae create complex habitats and support some of the most productive and biologically diverse ecosystems. These systems have been shown to be important spawning and nursery areas for a wide variety of fish and invertebrates, and contribute to biodiversity and ecosystem services. They are also easily accessible to humans.
South Australia’s coastal, estuarine and marine ecosystems provide a large number of ecosystem services that have yet to be quantified. Provisioning, regulating, cultural and supporting services include food supply, bioprospecting, flood and storm protection, education, research and nutrient cycling.
1.3 Economic and social benefits
More than 90% of South Australians live within 50 kilometres of the coast (ABS 2002), and many rely on the coast and adjacent marine waters for their livelihood. Social and economic benefits from the coast and marine environment include benefits from recreation, tourism, urban development, commercial fisheries and aquaculture, shipping and transportation, coastal agriculture, mining, manufacturing, science and education.
Fishing (both commercial and recreational) and aquaculture (tuna, oysters, mussels, abalone, freshwater and marine finfish, marron, yabbies and others) have become increasingly economically important to South Australia; the total value of seafood production in 2010–11 was almost $426 million (EconSearch 2012). South Australia’s total seafood production in 2009–10 was approximately 68 000 tonnes, of which aquaculture contributed approximately 49%. Tuna is the largest single sector in the state’s aquaculture industry, accounting for approximately 53% of the state’s gross value of aquaculture production in 2009–10. The other two main sectors are oysters (18%) and marine finfish (14%) (EconSearch 2011). The industry is expected to contribute $306 million to gross state product in 2010–11 (EconSearch 2012).