Coastal and marine environment

Fowlers Bay is the last large area of seagrass before the Western Australian border. This bioregion represents 15% of the total area of seagrass recorded in South Australia, covering an area of 86 160 hectares in Streaky Bay and Smoky Bay alone (DEH 2007a). Anecdotal evidence suggests that loss of seagrass beds in Smoky Bay is likely to be due to high levels of nutrient inflow.

The large number of sheltered, sandy embayments in the Eyre bioregion—including Baird, Venus, Waterloo, Sceale, Coffin, Proper, Boston, Louth and Peake bays off Eyre Peninsula, and D’Estrees Bay at Kangaroo Island—boast extensive areas of seagrass meadows, which are estimated to cover an area of 56 956 hectares. The lee side of some islands in the bioregion, such as the Sir Joseph Banks and Investigator groups, provides sheltered conditions and supports dense seagrasses in excellent condition. The seagrasses of the Investigator Group region are expansive and diverse. Almost all known South Australian species have been documented across the region, including six species of Posidonia, two species of Amphibolis, two species of Heterozostera, and Halophila australis (Bryars and Wear 2008). The seagrass meadows in the Investigator Group region are all considered healthy.

Within Boston Bay, sea-cage aquaculture, stormwater run-off from Port Lincoln, the Billy Lights Point wastewater treatment plant and fish-processing discharges all contribute nutrients into the sheltered bays. This is likely to contribute to the eutrophic condition of both Boston and Louth bays and subsequent seagrass losses. The remaining seagrass in these bays was in moderate to poor condition, with dense epiphytic algal growth indicating widespread nutrient enrichment in these areas. The seagrasses in other areas of the Eyre region were largely in good condition and the overall condition of the bioregion was considered good. Many of the seagrass meadows in these bays provide habitat and nursery areas for prawns and various fishes of commercial and recreational importance. D’Estrees Bay supports the only seagrass bed on the south coast of Kangaroo Island; this bed is considered to be in very good condition (KI NRM Board 2009).

Although seagrasses are not widespread in this bioregion, they occur in the more sheltered areas, such as Franklin Harbour in the west, Hardwicke Bay in the east, Port Victoria and areas around the Wardang Island group, and other areas along the mid-east coast (including Balgowan). Highly productive seagrass meadows are also a feature of the Tiparra Reef area, which is exposed to strong currents. There were small stands of seagrass (often interspersed with reef patches or sand) in the south-east of Spencer Gulf, such as off Port Minlacowie and the southern part of Hardwicke Bay. The Environment Protection Authority assessed the ecological condition between Arno Bay and Franklin Harbour as good, while on the eastern side of the gulf, around Moonta and Wallaroo, the ecological condition was classified as excellent with seagrass meadows of Posidonia spp. and Amphibolis spp. Throughout Spencer Gulf there are signs of nutrient enrichment reflected in dense growths of epiphytic algae on the seagrasses, indicating that the habitats are under stress (Gaylard et al. 2013).

North Spencer Gulf bioregion’s warm, shallow waters support seagrass beds over 53% of the sea floor, mostly in the central and northern reaches. At 4215 square kilometres (50% of the state’s total seagrass coverage), this is the largest area of seagrass meadows recorded in South Australia, and one of the largest areas of temperate seagrass meadows in Australia. The area has limited water movement and low wave energy, so it is vulnerable to land-based sources of pollution that are not readily dissipated. There has been a loss of Amphibolis antarctica due to exposure to heat and ultraviolet light (Seddon 2000). This trend is expected to continue and might increase with climate change, as temperatures in the gulf rise.

Adelaide Metropolitan coastline

Seagrass beds along the metropolitan coastline have been characterised by the loss of more than 5000 hectares of both Amphibolis spp. and Posidonia spp. in the nearshore waters and in several locations adjacent to wastewater discharges, as indicated in the Adelaide Coastal Water Quality Improvement Plan (EPA 2013). The remaining seagrasses are fragmented, leaving them vulnerable to further degradation. The numerous discharges of nutrients and sediment into the coastal waters, and the high residence time of discharges in the nearshore waters, due to lack of mixing with deeper waters are likely to continue to cause further loss of seagrass along this section of coastline. The EPA assessed the shallow waters throughout this part of the coast and determined that the condition was fair, with some areas of intact seagrasses particularly around Semaphore, while the area between Grange and Glenelg was degraded (Gaylard et al. 2013). Although losses have been reported for the deeper waters offshore, recent investigations by the EPA determined the ecological condition to be very good because the meadows surveyed were typically dense with low epiphyte loads in clear water. Further south, the ecological condition of the waters less than 15 metres deep is considered to be poor because the seagrasses are patchy, and there are indications of nutrient enrichment throughout the region. Testing of rehabilitation methods by Irving et al. (2010) found that sand-filled hessian bags provided a viable and cost-effective option for mitigating losses; however, successful long-term recovery will rely on improvements in water quality, as outlined in the draft Adelaide Coastal Water Quality Improvement Plan (EPA 2013).

Yankalilla Bay and Light River

Levels of epiphyte cover observed in Yankalilla Bay are low. Seagrass off the Light River delta is in very good condition and not affected by discharges from the Light River.

Northern Gulf St Vincent (Clinton bio-unit)

Seagrass meadows dominate the shallow, low-energy environment at the top of Gulf St Vincent and are subjected to large tides and limited water exchange. Overall, the sites were dominated by dense seagrass habitats consisting mainly of Posidonia spp. and Amphibolis spp., and the region was considered to be in very good condition. However, there are emerging signs of nutrient enrichment, which might lead to seagrass loss in the future (Gaylard et al. 2013).

Yorke Peninsula (Orontes bio-unit)

The low–wave energy environment of western Gulf St Vincent sustains large seagrass meadows between Ardrossan and Troubridge Island. Recent investigations by the EPA classified the ecological condition of the region as very good, but large parts of the region were under significant stress because of nutrient enrichment, particularly near small coastal developments such as Black Point and Wool Bay (Nelson et al. 2013).

Kangaroo Island (Nepean bio-unit)

The northern coast of Kangaroo Island is dominated by seagrass-filled embayments punctuated by rocky headlands. In some of these bays, there is evidence that seagrass meadows are degraded and seagrass habitat has been lost (Western Cove), probably as a result of eutrophication (Bryars et al. 2003, Gaylard 2005). The region was assessed as generally in good condition, but in some areas the seagrass was significantly impacted (such as Western Cove) while in others (such as Bay of Shoals) it was in good condition. Throughout the region there were heavy epiphyte loads on seagrasses, indicating that the area is under stress from excess nutrients (Gaylard et al. 2013).

Seagrass beds are scarce along most of the coast because of high wave energy and active sand movement. In the more sheltered waters of Lacepede Bay, there is a dense and extensive seagrass meadow (25 062 hectares). This meadow is vulnerable to the impacts of high-nutrient water flowing from agricultural drains and coastal development. There is little seagrass north of the Granites because of higher wave power; some patches of seagrass are interspersed between reefs and sandy areas in the western part of the bioregion. The nearshore seagrass has regressed approximately 100 metres offshore in front of the township of Kingston.

Seagrasses are a minor feature of the Otway bioregion. The most easterly bed of Posidonia is found at Port MacDonnell, and other small patches occur near Beachport and Boatswain Point. Seagrass meadows in the Otway bioregion are dominated by strapweed (Posidonia australis), wire grass (Amphibolus antartica) and eelgrass (Heterozostera tasmanica). Historical seagrass loss documented in Rivoli Bay has been attributed to the impacts of drain discharges (Seddon et al. 2003). The remaining seagrass in the bay is vulnerable to high wave energy and seabed instability resulting from the previous losses (Wear et al. 2006).

Of the habitats that have been mapped in the Murat bioregion, 17.2% are subtidal reef. Reefs in the bioregion, including rocky parts of bays, headlands and around islands, support a diverse cover of brown canopy macroalgae (including various species of Cystophora and Sargassum), and many species of red algae. Nuyts Reef, Fowlers Bay and Point Bell are characterised by a diversity of red algae. The diverse assemblages of algae provide an important food source for herbivores and habitat for other animals.

The coast of the Eyre bioregion alternates between intermittent, island and reef exposures. There is a highly diverse range of subtidal reef habitats, including ledges, boulders, caves, crevasses, overhangs, cobble reefs, wave-exposed granite outcrops and reef platforms. In some parts of the Eyre bioregion, reefs extend from intertidal wave-cut shore platforms to at least 50 metres deep. Reefs at the bottom of Yorke Peninsula and Eyre Peninsula support different assemblages, despite their geographic proximity. These reefs generally have a large diversity and abundance of invertebrates (sponges, ascidians, bryozoans and hydroids), including some rare and uncommon species. The condition of two reefs within the Eyre bioregion, located around the toe of Yorke Peninsula, has been described as typical through Reef Health surveys (DEH 2008).

Parts of the west and south coast of Kangaroo Island also support a dense cover of macroalgae, including regionally unusual assemblages. Intertidal reefs (rocky shores) are a common feature of the coastline of Kangaroo Island and have high invertebrate and algal diversity. Two sites in this area—Browns Beach and Hanson Bay—are identified as having higher species richness than other Australian temperate coastlines (KI NRM Board 2009).

The Spencer Gulf shoreline includes a wide variety of bedrock platforms and intertidal reefs. Although a large portion of the inshore benthic habitats have been mapped, the condition of ecological communities is still largely unknown.

The only intertidal reef in the North Spencer Gulf bioregion is found around Black Point and Point Lowly. It consists of a platform of plate-like fragments, which extends out beyond the intertidal zone and gradually becomes low-relief subtidal rocky reef out to 70–130 metres offshore. The subtidal reef around Point Lowly is recognised as an important area for spawning aggregations of the Australian giant cuttlefish Sepia apama. The area also provides habitat for the many species and abundant numbers of echinoderms, including sea urchins, molluscs and ascidians (sea squirts). The overall condition of these reefs is not known. A decline in numbers of cuttlefish in 2011 has prompted an extension of the protection area and an investigation by the South Australian Government (PIRSA 2012ab).

Intertidal reefs in the Gulf St Vincent bioregion are typically calcareous or limestone rock platforms. Intertidal limestone reefs occur at Aldinga Reef Aquatic Reserve and Lady Bay. Harder reefs of granite, basalt and volcanic conglomerates occur at Second Valley and Hallett Cove. Around the tip of Fleurieu Peninsula, the intertidal zone occurs as a narrow band adjacent to sheer coastal cliffs, and is little studied. The intertidal communities vary according to wave exposure and type of substrate. Red and brown leafy algae dominate lower intertidal zones on cliffs of hard crystalline rock around the high-energy tips of Yorke and Fleurieu peninsulas and some nearshore islands. Above the algae, layers of polychaete worms, green algae, barnacles and limpets can be observed, while little blue snails appear in crevices.

In 2006–07, results of surveys of 15 intertidal reefs around Fleurieu Peninsula suggested that, in general, these reefs were in good health, with diverse invertebrate communities at most sites and no introduced species. The lowest invertebrate biodiversity was recorded within the Noarlunga Reef and Aldinga aquatic reserves, where there was heavy recreational traffic. Lady Bay on Fleurieu Peninsula appeared to have a higher intertidal species richness (AMLR NRM Board 2008). The remote boulder fields found at Myponga and Kings Beach, near Victor Harbor, indicated high invertebrate biodiversity, probably due to the lack of disturbance. Relatively low diversity recorded within boulder field areas at Aldinga Aquatic Reserve appeared to be due to unusually abundant populations of the predatory crab Ozius truncatus. The unusually high densities of scavenging and predatory crustaceans within these aquatic reserves might indicate disruptions to the normal ecological balance (AMLR NRM Board 2008). Research is required to determine the role of predatory crabs in marine systems.

Biodiversity surveys were undertaken at the Port Stanvac intertidal reef in 1988, in 1998 and at the end of 2007. According to Dutton and Benkendorff (2008), the Port Stanvac area appears to have biological importance for intertidal diversity along the Adelaide metropolitan coast and Fleurieu Peninsula. The surveys identified Port Stanvac as an important reef in the region for molluscs, echinoderms and red algae, because it supports rare species that have not been recorded to date on other intertidal reefs in South Australia. Over the past 20 years, there appeared to be an overall increase in the number of taxa found.

The subtidal rocky reefs in the Gulf St Vincent bioregion were dominated by large macroalgae and abundant invertebrate life, such as sponges, bryozoans, ascidians, hydroids, echinoderms, molluscs and crustaceans. The reefs also provided abundant habitat for several species of fish, including the western blue groper, the western blue devil, the harlequin and several species of wrasse. Based on the health indices developed during the Reef Health surveys, many of the reefs along the metropolitan coastline have a health status index of caution (Turner et al. 2007). Reefs that were considered good were predominantly in the south and nonmetropolitan areas. There is a general trend for the condition of Adelaide metropolitan reefs to improve in condition from north (worst condition) to south (best condition) (Westphalen 2011).

A preliminary baseline investigation of the sedimentation on 12 metropolitan reefs was conducted over winter, summer and autumn from 2007 to 2008. Spatial variation in reef sedimentation was found along the metropolitan coast. The highest amount of sedimentation was found between Hallett Cove and Southport near the mouth of the Onkaparinga River (fluvial origin), and in autumn (Turner et al. 2007). The ecological condition for waters less than 15 metres deep in the area between Marino and Sellicks was considered to be fair.

Based on the presence of larger brown algae and the number and diversity of fish as a measure of coastal reef health (Turner et al. 2007), the subtidal reefs on Kangaroo Island could be considered to be in good condition, since they are covered in a dense canopy of macroalgae and have a high fish diversity and abundance (Brock and Kinloch 2007).

Most of the reef habitat within the Coorong bioregion is subtidal; there is only a small portion of intertidal reef. Limited research has been conducted on the intertidal reefs in this region, and little is known about their condition.

Subtidal reefs include low platform reefs, offshore calcareous reefs to the south, and fringing granite reefs in Encounter Bay. Much of the sea-floor habitat for this region is unmapped. Low platform reefs, approximately 4.5 kilometres offshore, run parallel along much of the Coorong coast. Many of these reefs are covered in sand as a result of the high turbulence in the region, and few plants and animals are found on them. In the western part of the bioregion, near Port Elliot, there is a series of reef structures, which are complex as a result of the presence of ledges, crevices and cracks. They are ideal habitat for adult and juvenile rock lobsters. In the shallow high-energy areas, reef systems are mostly dominated by kelps and other tough, brown, branching algae, with a diverse understorey of green and red foliose algae, and crustose coralline algae. The latter is a known habitat for juvenile abalone. The reefs at the southern end of Lacepede Bay are dominated by a different mix of algae, with an abundance of bryozoans in waters deeper than 20 metres.

In the southern part of the Coorong bioregion, mixed patch reef and sand habitat is dominated by coarse sediments, bryozoans and mixed red macroalgae to a depth of at least 35 metres. Surveys have also revealed the presence of offshore reefs dominated by invertebrates and immobile filter feeders, rather than algal species. In deeper water (more than 25 metres), the flat calcareous platform reefs contain many holes and crevices and are a major habitat for rock lobster, sponges and other benthic invertebrates. The parallel calcareous reefs in this area stretch from the Coorong to Cape Jaffa, on the Lacepede Shelf, from a depth of around 11 metres to 60 metres.

Margaret Brock Reef, west of Cape Jaffa and at the southerly extent of the Coorong bioregion, is located in the transition between two biogeographical regions. Giant kelp, which typically dominates the high-energy reefs of the neighbouring Otway bioregion and other cold-water areas of south-eastern Australia, is found on the outer, more exposed parts of the reef. This is of special interest because Cape Jaffa represents the most westerly extent of this cold-water plant.

In the Otway bioregion, nearshore rocky platforms and rocky intertidal areas provide habitat for an abundance of plant and animal species. Apart from long stretches of high-energy beach, such as the Canunda area, much of the coastline from Cape Jaffa to Cape Northumberland is dominated by flat limestone reefs. The shallow calcareous platform reefs in the Robe area extend to a depth of about 20 metres. In the intertidal area, many rocky pools and crevices contain sea stars, gastropods and bivalve shells, anemones and other invertebrates. There is no condition baseline or benchmark for the general condition of most habitat types in the south-east, including intertidal reefs (SE NRM Board 2010).

Margaret Brock Reef, on the boundary between the Coorong and Otway bioregions, is considered to be a ‘hot spot’ of biodiversity. The limestone reefs around Robe and Nora Creina are also considered ecologically important because they provide habitat for various attached and mobile invertebrates, and have a high diversity of brown, green and red macroalgae.

Surf beaches and sheltered beaches are scattered within the Fowlers Bay area; they are less common in the Streaky Bay area because many of the embayments are dominated by mangrove and saltmarsh habitats (DEH 2007a, EP NRM Board 2009). Where reefs protect the coastline, the beach profiles tend to be shallow. This contrasts with exposed beaches on the western side of Murat, which are generally deeper and accumulate bigger sand-dune systems. Shallow, sandy bays, mudflats and tidal areas in mangrove forests provide key nursery habitat for fish and western king prawns. Many species of fish and birds, including migratory birds, visit these areas to feed. Subtidal soft sediments are not a dominant feature of the Murat bioregion, accounting for only 4% of its area.

There are many small sandy beaches that are open to high-energy wave action between the calcarenite cliffs, or at bases of cliffs, in the western area of this bioregion. The beaches along the lower Spencer Gulf are generally low-energy environments, either reflective or low-tide terraces. They are typically dominated by low-wind waves and are commonly fronted by seagrass meadows. The Eyre, Jussieu and Bolingbroke peninsula beaches are mostly sheltered from south-westerly swells, and this has helped to form a series of bays and estuaries, sandy beaches and rocky shores (DEH 2007b). Wader birds, which are protected by bilateral agreements between Australia and China, Japan and the Republic of Korea, use the tidal flats and beaches throughout the region (DEH 2007ac, DSEWPaC 2009a, EP NRM Board 2009).

Much less is known about the condition of intertidal soft-sediment habitats and communities in this bioregion than about their extent. The Kangaroo Island Natural Resources Management (NRM) Board (KI NRM Board 2008) reported that many of the island’s coastal and marine ecosystems were in good condition (as a result of the low level of coastal development), but recognised that data were patchy. Water quality in the nearshore environments on the Eyre Peninsula (Boston Bay, Coffin Bay, Venus Bay) was relatively good, with the lowest nutrient levels recorded of the Environment Protection Authority’s 65 ambient water-quality monitoring sites. Sandy bottom forms a large proportion of the region’s mapped benthic habitat. Soft-sediment communities are found in sheltered embayments; they support a large variety of invertebrates, particularly molluscs and worms, and provide habitat for various fishes and crustaceans.

The beaches of Spencer Gulf are generally low-energy environments and are dominated by low-wind waves, with greater tidal ranges in the upper reaches. The Eyre Peninsula beaches are mostly protected from the south-west swell, and waves generally develop from onshore winds. Most beaches have wide intertidal sand flats, backed by very low-energy to moderate-energy high-tide beaches, with extensive seagrass meadows at the front (EP NRM Board 2009). Much of the mid-eastern side of the gulf comprises long, sandy beaches with a single or narrow belt of dunes behind, interspersed with small rocky headlands, and shore platforms. Much less is known about the condition of intertidal soft-sediment habitats and communities in this bioregion than about their extent. Water quality in the nearshore environments at Port Hughes is relatively good. Subtidal soft sediments are a feature of the sheltered waters in the northern parts of the Spencer Gulf bioregion.

Coastal geomorphology north of Point Lowly consists of wide supratidal samphire and mudflats, intertidal mudflats, mangroves and sandflats. The supratidal zone comprises mainly of bare carbonate flats, which are occasionally inundated by high spring or storm tides. The diversity and productivity of the area are increased by the tidal currents of the northern gulf region. The majority of the beaches have wide intertidal sandflats, backed by very low-energy to moderate-energy high-tide beaches, with extensive seagrass meadows at the front. A distinctive feature of North Spencer Gulf is the unusual coastal sand barriers, which are absent from higher energy stretches of the lower gulf and form under the influence of storm surges or extreme tidal events. About 340 of these barriers are arranged in lines parallel to the shore along the sheltered shoreline, from Cowell to Port Augusta. They average 400 metres long, 10–50 metres wide, and rarely more than 1 metre high. Landward of the actively forming barrier islands are multiple lines of earlier stranded barriers, separated by supratidal flats that are active only when flooded by spring high tides and storm surges. Soft-sediment communities form a large proportion of the North Spencer Gulf bioregion.

This bioregion is home to a diverse group of soft-sediment communities, which were identified as six distinct assemblages by Shepherd and Sprigg (1976). More recent surveys (Tanner 2005) report declines or losses in all of these assemblages, both within the gulf and in Investigator Strait. The losses were linked predominantly to prawn trawling, but other impacts, such as dredging and wastewater discharges, also contributed.

Sandy to muddy tidal flats dominate the upper portion of Gulf St Vincent from Port Clinton to Port Adelaide (Womersley and Thomas 1976, AMLR NRM Board 2008). Mudflats on eastern Gulf St Vincent are associated with coastal mangroves, samphire habitats and seagrasses. Overall, beach biodiversity in gulf waters is relatively modest (AMLR NRM Board 2008). Dissipative beaches, which are around the eastern Fleurieu coast towards Goolwa, are rich in fauna (AMLR NRM Board 2008). Tidal mudflats and other habitats in Gulf St Vincent are nationally and internationally important for wading birds or shorebirds.

The Kangaroo Island NRM Board (2008) reported that many of the island’s coast and marine ecosystems were in good condition (as a result of the low level of coastal development), but recognised that data were patchy. A link has been found between nitrogen (particularly ammonia) in the nearshore regions of Nepean Bay and seagrass loss in the Kangaroo Island region (Bryars et al. 2006).

Monitoring indicated that water quality along the metropolitan coast was in poor condition for several indicators and continues to decline. Results from an ecological assessment in 2011 of Adelaide’s beach-nourishing program showed that 58 macroinvertebrate taxa and 558 individuals were found across the 15 metropolitan beaches studied. The most dominant taxa of invertebrates found were typically terrestrial species (mostly beetles). The total number of species found ranged between 77 at Semaphore South and 8 at Torrens Outlet.

The Coorong bioregion is a large, sandy ‘barrier coast’, dominated by large dunes, beach ridges and high-energy sandy beaches, including one of Australia’s longest continual sandy beaches (194 kilometres from the Murray mouth to Cape Jaffa). The lengthy ocean beach is an important feeding, breeding and nursery area for many marine species, including Australia’s largest single population of cockles. The region is also an important nesting site for the state’s listed vulnerable hooded plover and for migratory wading birds (SE NRM Board 2010). The condition and trends of the intertidal coastal environment in the south-east are unknown because of inconsistent and insufficient information (SE NRM Board 2010).

The region directly offshore from the Murray mouth is characterised by fine sediments. The high energy and constant sand movements in this area prevent immobile species from settling, but are also likely to provide habitat for bottom-dwelling and burrowing invertebrates. Animals associated with these sandy areas include flatfishes (e.g. flounder and flathead); rays and skates; worms; crustaceans, such as sand crabs; sea snails; and a variety of bivalve molluscs, including the well-known Goolwa cockle or pipi.

The intertidal and subtidal areas in the Otway bioregion are dominated by both flat and high-relief limestone reefs, patches of sand, and small areas of seagrass in some of the more sheltered bays. Where reefs are absent, sandy beaches and coastal dunes and barriers can be found. Subtidal soft-bottom habitats are not a dominant feature of the Otway bioregion, accounting for approximately 7% of its area. They are mostly found as patches of sand interspersed among the reefs.