Coastal ecosystems and habitats

Coastal ecosystems and habitats are the physical and biotic environments in which many coastal species reside. They include strictly terrestrial or aquatic habitats, as well as those in the tidal zone, which experiences both sets of conditions.

Species that provide habitat for other species are sometimes called ‘habitat-forming’ species. Due to their vital and broad ecological roles, the health of habitat-forming species is important for both their own and other species’ survival, and their condition is a proxy for that of coastal biodiversity more generally. Habitat-forming species can be either invertebrates or plants.

Habitat-forming invertebrates include shellfish and corals. Although shellfish reefs have been long forgotten due to their historical extirpation from many locations, they were once dominant habitats on the Australian coast, and remnant shellfish reefs and beds remain ecologically important in estuaries around the country. While knowledge of these ecosystems has been poor in the past, there has recently been a significant increase in their study and management (Gillies et al. 2018). Coral reefs are discussed in the Marine chapter (see the Marine chapter).

Habitat-forming plants in the tidal zone include mangroves, saltmarshes and seagrasses, each distributed according to tidal inundation and elevation. These are supplemented by salt pan and mudflat habitats, which are often vegetated with nonvascular plants such as algae. Other major vegetation types that can be inundated by tides, especially in south-eastern Australia, include paperbark (Melaleuca) and she-oak (Casuarina) woodlands.

A major event impacting all these vegetation types was the 2019–20 megafires that devastated coastal ecosystems and habitats in south-eastern Australia (Figure 10; see the Extreme events chapter). Between July 2019 and February 2020, an estimated 97,000 square kilometres (km2) of vegetation was burned, representing habitat for 832 native vertebrate species (Ward et al. 2020). This included habitat for 378 birds, 254 reptiles, 102 frogs, 83 mammals and 15 freshwater fish. Seventy native taxa lost more than 30% of their habitat; 21 of the 70 were already listed as threatened with extinction (Ward et al. 2020).

Figure 10 Percentage burned area by bioregion (Interim Biogeographic Regionalisation for Australia), showing the impact of the 2019–20 megafires in south-eastern Australia

Assessment The condition of coastal ecosystems and habitats
2021
2021 Assessment graphic showing the environment is in poor condition, resulting in diminished environmental values, and the situation is deteriorating.
Somewhat adequate confidence
Indigenous assessment
2021 Assessment graphic for an assessment conducted by Indigenous community members, showing the environment is in good condition, resulting in stable environmental values, and the situation is stable.

With the exception of seagrasses, most coastal habitat types are considered to be in poor and declining condition. Saltmarshes, mangroves and dune vegetation are all recovering from historical losses and face current threats. Even so, their condition is considered to be deteriorating nationally, although this is regionally variable. Islands are particularly vulnerable to invasive species and climate-related pressures.
The Indigenous assessments for the state of coastal ecosystems and habitats for all assets are good; the trend is stable for 3 assets and unclear for 2.
Local government assessments (see Approach) indicate that mangroves and saltmarshes are considered to be in poor condition in the south of Australia and in better condition to the north. This likely reflects impacts of urbanisation and coastal development in the south, but does not capture the mangrove dieback that occurred in remote areas in the north.
Related to United Nations Sustainable Development Goal targets 14.2, 15.5

Assessment Mangroves
2021
2021 Assessment graphic showing the environment is in poor condition, resulting in diminished environmental values, and the situation is deteriorating.
Somewhat adequate confidence
2016
Assessment graphic from 2011 or 2016 showing the environment was in poor condition, resulting in diminished environmental values, and the situation was deteriorating.

Mangroves are threatened by a range of human activities, including extreme weather events that have resulted in mass dieback in northern Australia.
The Indigenous assessment for some regional areas was good, with a stable trend.

Assessment Saltmarshes
2021
2021 Assessment graphic showing the environment is in poor condition, resulting in diminished environmental values, and the situation is deteriorating.
Limited confidence
2016
Assessment graphic from 2011 or 2016 showing the environment was in poor condition, resulting in diminished environmental values, and the situation was deteriorating.

Recent surveys show saltmarsh decline is continuing.
The Indigenous assessment for some local areas was good, with a stable trend.

Assessment Seagrasses
2021
2021 Assessment graphic showing the environment is in good condition, resulting in stable environmental values, and the situation is stable.
Limited confidence
2016
Assessment graphic from 2011 or 2016 showing the environment was in poor condition, resulting in diminished environmental values, and the situation was deteriorating.

Limited monitoring data and anecdotal accounts suggest seagrass in unpopulated areas is largely healthy, but areas with coastal development have ongoing losses.
The Indigenous assessment for some regional areas was good, with a stable trend.

Assessment Dune vegetation
2021
2021 Assessment graphic showing the environment is in poor condition, resulting in diminished environmental values, and the situation is deteriorating.
Somewhat adequate confidence

While land clearing is less prominent than in previous years, it is still an issue with continued and profound cumulative impacts. Previously stable areas, away from urban development, have seen marked increases in environment-related degradation (climate change and large-scale bushfires), with little marked improvement at the macroscale in dune vegetation condition attributable to restoration.
The Indigenous assessment for some regional areas was good, with an unclear trend.

Assessment Islands
2021
2021 Assessment graphic showing the environment is in poor condition, resulting in diminished environmental values, but the trend is unclear.
Somewhat adequate confidence

The current condition of islands varies, but trends are unclear without a national perspective. Pressures include invasive species, climate-induced changes, and over-exploitation from people and industry.
The Indigenous assessment for some regional areas was good, with an unclear trend.

Mangroves

Mangroves are the dominant vegetation type in Australia’s tidal wetland zone, often found alongside tidal saltmarsh and salt pan microphytes (microscopic algae). Mangroves are found on temperate, subtropical and tropical coastlines, but are absent from Tasmania. The number of mangrove species and their size, biomass and cover, relative to saltmarsh and salt pan, all tend to be highest in areas of high rainfall and run-off. There is a great floristic diversity of mangroves in Australia and a strong latitudinal distribution in species richness. Mangroves are more species rich in the north and saltmarshes richer in the south (Specht & Specht 1999).

Mangrove ecosystems provide immense benefits and value. They provide productive marine fisheries habitat, habitat for coastal terrestrial fauna, a key source of coastal primary production, carbon sequestration, a valuable sink for organic carbon, stability of soft sediment shorelines, a vital filter and purifier of coastal and estuarine waters, and protection of coastal land from erosion and storm-driven damage (Gedan et al. 2011).

Risks to mangroves

Mangroves have occupied Australian shorelines for more than 50 million years (Woodroffe & Grindrod 1991, Duke 2017) and are clearly well adapted to past conditions. However, their future productivity and distribution are threatened by climate change (e.g. harsher and more frequent heatwaves) and human factors (Lovelock et al. 2015, Schuerch et al. 2018), which are disrupting their natural functioning, establishment, recovery and survival. Mangroves are highly sensitive to environmental factors, such as sediment type and tidal inundation (Duke 2006), and to climate, including temperature and rainfall (Duke et al. 2019).

Influences of global climate change can be clearly seen in mangrove shoreline and estuarine ecosystems (Harris et al. 2018, Bergstrom et al. 2021). For example, we saw a dramatic climate-related mass dieback of mangroves in northern Australia in 2015 (Duke 2017) (Figure 11), and dieback in Western Australia in 2003 and 2015–16 (Lovelock et al. 2017). However, mangroves are increasing in areas of southern Australia where pressures are less severe, and show a long-term trend of expansion with sea level rise (Lymburner et al. 2020), often at the expense of saltmarsh (Whitt et al. 2020). There is an urgent need to systematically monitor and evaluate changes in mangroves so that more informed remedial strategies can be devised and implemented. The capacity to monitor change is growing, for example, through the development of a national mangrove monitoring system (Lymburner et al. 2020) (see case study: A national mangrove monitoring system in support of sustainable management), as well as national (Kelleway et al. 2020) and state efforts (e.g. the Blue Carbon Strategy in South Australia and the Land Restoration Fund in Queensland) in mangrove restoration for blue carbon and other ecosystem services (Creighton et al. 2015, Clarke et al. 2021a, Waltham et al. 2021).

Figure 11 Shoreline mangroves comparing damaged and undamaged sections of the coastline east of the mouth of the Limmen Bight estuary (Northern Territory), June 2016

Consistent with findings of recent national and global assessments (Goldberg et al. 2020, Lymburner et al. 2020), 2 recent regional assessments of the condition of mangroves and shorelines across northern Australia (including around 1,000 km of the north-eastern shoreline of Cape York Peninsula (Duke & Mackenzie 2018) and 2,000 km of the Gulf of Carpentaria (Duke et al. 2021c)) found that threats ranged in scale from regional to local, and stemmed from both human and ‘natural’ pressures (Figure 12). While natural pressures understandably dominated in the areas surveyed – due to the remoteness of northern Australia – it was clear that the main pressures were related to global climate change. These included rising sea levels and the prevalence of more severe tropical cyclones. Natural pressures were also exacerbated by local, nonclimate-related factors, such as damage by feral pigs, scorching by uncontrolled scrub fires and smothering by invasive weeds (Duke & Mackenzie 2018, Duke et al. 2021b, Duke et al. 2021c).

While the 2015 mass dieback of shoreline mangroves was a marked feature throughout the Gulf of Carpentaria, it was notably absent from the eastern coast of Australia. Those investigating the event suggested this was partly due to higher rainfall levels further east. Furthermore, the influences of climate were reasonably consistent across the entire Gulf area, although the influences of sea level rise (as indicated by bank erosion, salt pan scouring and terrestrial retreat) increased towards the north of Cape York, into Torres Strait, and further west across the Gulf. Across the region, there were notable detrimental influences were notably caused by wallowing feral pigs, smothering exotic weeds and scorching brush fires – all hampering upland mangrove colonisation (Duke et al. 2021a).

Different risks are faced by mangroves in southern Australia, where threatening processes are predominantly related to coastal development and local human activities (Boon et al. 2015, Rogers et al. 2016b). Southward shifts of mangrove species beyond their current southern latitudinal limits are anticipated as temperatures rise with global climate change (Saintilan et al. 2014, Boon 2017, Whitt et al. 2020). No species have been observed to shift south, but this may be due to lack of monitoring rather than an absence of range shifts.

Figure 12 Dominant threats and issues affecting estuarine and shoreline tidal wetlands of 8 regional areas, 2017

Case Study A national mangrove monitoring system in support of sustainable management

Much knowledge of the changing landscapes of Australia has come from multitemporal Earth observations over at least the past 50 years. However, interpreting and consistently quantifying the extent of land covers and ecosystems across Australia from Earth observation data has proved a significant challenge that has required major investment in research and development and capacity for ground data collection (Jackson & Rankin 2017). Australia’s Terrestrial Environment Research Network (TERN) has played a large role in data integration, building cross-institutional collaborations, facilitating the sharing of infrastructure and providing open access to data.

TERN has focused on developing information systems that give access to data and knowledge, thereby ensuring a better understanding of ecosystems and environments. The TERN Mangrove Portal (Lymburner et al. 2020) shows how disparate environmental data can be collected and collated to support the development of mangrove monitoring (Figure 13).

Through a joint effort by Geoscience Australia and TERN, 25-metre-spatial-resolution maps of mangrove extent by canopy cover type (open woodland, open and closed) have been generated annually (1986–2016), Australia-wide, using dense timeseries of satellite data held within the Digital Earth Australia platform (Lymburner et al. 2020) (Figure 14). These maps show the annual dynamics of mangroves across Australia and provide better information on impacts of change (e.g. dieback) due to environmental and anthropic pressures, including those related to climate (e.g. sea level rise and changes in storm positions, frequencies and intensities), and ultimately better inform options for mangrove management. The timeseries shows that Australia’s mangroves expanded between 1992 and 2010 and contracted thereafter.

The mangrove portal was developed primarily because the 2015–16 dieback event across the northern coastline showed the need for a mangrove monitoring system. Dieback resulted in the death of more than 7,000 hectares (ha) of mangroves (Duke 2017) over several months. Such an event was unexpected given that previous remote-sensing observations had reported a steady landward and seaward expansion of mangroves along sections of this coastline since 1985 (Asbridge et al. 2016). Due to the area’s remoteness, the dieback was first discovered by fishermen and scientists conducting unrelated fieldwork. The discovery and reporting of the event, which included uncertainties around the real area lost to dieback (initial estimations cited over 10,000 ha), exposed the need for ongoing monitoring to establish the extent and distribution of changes in ecosystem condition, support prioritisation of interventions, and monitor trends (e.g. recovery, ongoing degradation, stable conditions).

A major benefit of the TERN Mangrove Portal is that it provides multiple openly available datasets relevant to mangroves (including those affected by the dieback event), which assist not only with the development of a monitoring system, but also support scientific research, the conservation, management and sustainable use of mangroves, policy development, and evaluation management actions (Lucas et al. 2017, Metternicht et al. 2018).

The mangrove portal shows the potential of data integration (satellite, drones, airborne, historical aerial photographs, field data) to advance understanding and identify knowledge gaps. It also highlights that datasets and products need to be open access and easily discoverable to inform policy and enable coordinated scientific research. A wide and diverse range of datasets are available through the portal, and capacity exists for continual upload of new and existing datasets.

Figure 13 Conceptual framework of a mangrove monitoring system responding to policy and monitoring needs

Note: © 2018 IEEE. Reprinted, with permission, from Metternicht G, Lucas R, Bunting P, Held A, Lymburner L & Ticehurst C (2018). Addressing mangrove protection in Australia: the contribution of earth observation technologies. In: IGARSS 2018 – 2018 IEEE International Geoscience and Remote Sensing Symposium, Valencia, Spain, IEEE, 6548–6551.

Source: Metternicht et al. (2018)

Figure 14 Extent of mangroves in Australia in 2017, using data integration from satellite, airborne and field observations

ha = hectare; km = kilometre

Source: Lymburner et al. (2020)

Saltmarshes

Australian saltmarshes consist of around 130 species of grasses, herbs, rushes, sedges and shrubs growing in the upper intertidal environment, characteristically between mean sea level and the inundation limits of the highest tides. Saltmarsh plants support estuarine fisheries (Raoult et al. 2018, Jinks et al. 2020), and the marshes and associated tidal pools form an important habitat for migratory shorebirds and a preferred feeding habitat for microbats and macropods (Kelleway et al. 2020). Saltmarshes are a particularly efficient carbon sink, storing over 200 million tonnes of organic carbon in Australia (Macreadie et al. 2017).

There have been widespread declines in saltmarsh extent since photographic records in the mid-20th century. The imposition of flood control measures in eastern Australian estuaries from the 1950s to the 1970s isolated mangroves and saltmarshes from tidal waters, leading to their replacement by freshwater wetland and terrestrial grasses in some areas. In New South Wales, some 65,000 ha of prime fish habitat, including saltmarshes, were lost this way, (Rogers et al. 2016a, Wegscheidl et al. 2017) and 35,000 ha of saltmarsh were lost this way in Queensland(Rogers et al. 2016a, Wegscheidl et al. 2017).

In more recent decades, an important driver of saltmarsh loss has been competition with mangroves, which have proliferated in some parts of Australia with changes to climate and sea level (Saintilan et al. 2014). Whitt et al. demonstrated an ongoing decline in saltmarsh extent due to mangrove encroachment in Western Port (Victoria) to 2017 (Whitt et al. 2020). Further loss of saltmarsh is expected as the rate of sea level rise accelerates.

Monitoring and management of saltmarshes

Remote sensing (through the USGS/NASA Landsat program) of saltmarsh grass extent of the Rocky Dam Creek/Cape Palmerston National Park region in central Queensland over 2004–17 revealed a 3.6% decrease (a loss of 1,551 ha), possibly the result of recent cyclone activity, sea level variability and prolonged inundation (Chamberlain et al. 2020a). Landsat was used to document statewide changes in saltmarsh extent in South Australia, showing an increase in habitat extent between 1987 and 1995, which then plateaued to 2015. While there are some discrepancies between results derived from satellite sensors and aerial photography (up to 25%), recent technical advances in monitoring are making assessment of broadscale saltmarsh extent and condition viable (Alam & Hossain 2020, Meng et al. 2021).

Tasmania is the only Australian state in which saltmarshes grow in the absence of mangroves. Recent monitoring supported by local communities has identified a range of human impacts on Tasmanian saltmarshes. A citizen science program in the Tamar estuary has demonstrated ongoing evidence of degradation, including mowing or slashing of saltmarsh, weed invasions, off-road vehicle damage, and conversion of saltmarsh into agricultural land by the imposition of levees and drains (Dykman & Prahalad 2018). Diffuse effects, including increased wind strength and sea level rise, may also be driving local retreat of saltmarshes (Prahalad et al. 2020).

Most Australian states and territories have policies in place to protect coastal saltmarsh from development, and south of 23°S latitude, saltmarshes are protected as a Threatened Ecological Community under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act). However, these policy instruments do not protect saltmarshes from the impacts of climate change, and retreat pathways and landholder incentives will be needed to help saltmarsh adjust to sea level rise (Rogers et al. 2016a). One promising opportunity is the potential for greenhouse gas abatement from the facilitated retreat of saltmarsh. In particular, in areas where tidal flow is (re)introduced, an estimated 6–8 tonnes of carbon per hectare may be sequestered each year (Kelleway et al. 2020).

Other management options include the restoration of tidal inundation behind flood control works, creating the tidal conditions needed by saltmarsh and mangroves. This has the dual benefit of restoring the carbon sequestration services of mangroves and saltmarshes, while also introducing seawater microbes capable of decreasing methane emissions (Negandhi et al. 2019). Successful tidal reinstatement and saltmarsh restoration projects in Australia have been demonstrated (Creighton et al. 2019), as has the efficacy of control structures (e.g. tide gates) to create suitable inundation regimes (Sadat-Noori et al. 2021).

Seagrasses

Seagrasses are flowering plants that form meadows on intertidal and subtidal sediments around Australia. Approximately 40% of the world’s seagrass species occur in Australia, including several species only found here (endemic), and Australia has some of the world’s largest seagrass meadows (Larkum et al. 2018). The Wooramel seagrass bank in Shark Bay (Western Australia) occupies 1,030 km2 and is the largest seagrass bank in the world. Seagrasses provide vital ecological functions that benefit humans (Barbier et al. 2011). They form the base of the food web, stabilise sediments, and have a critical role as nursery habitat for important commercial, cultural and recreational fisheries (Unsworth & Cullen-Unsworth 2014). They are also a globally significant reservoir of carbon (Serrano et al. 2019).

Seagrasses are highly sensitive to changing water quality. They are particularly threatened by nutrient inputs and associated algal blooms, sediment inputs and resuspension due to dredging or flooding, boating (anchoring and mooring), habitat loss to coastal development, contaminants, and disease. They also face emerging challenges from climate change, including increasing temperatures, more frequent extreme weather events (e.g. Strydom et al. (2020)) and the immigration of tropical species whose impacts are unpredictable (Hyndes et al. 2017, Orth & Heck 2021).

Historical seagrass losses are extensive (Waycott et al. 2009) and ongoing in some areas. Pressures on seagrass are set to continue, particularly near centres of coastal development (Waycott et al. 2009). The impacts of climate change, primarily local heatwave effects, are likely to interact with local disturbances such as catchment development and aquaculture-related nutrient enrichment. The long-term outlook is uncertain and will depend on how species can respond to changes in water temperature, sea level, storm activity, freshwater inputs, water quality and erosion.

Regional condition of seagrasses

The health of seagrasses and seagrass meadows varies across Australia:

  • Seagrasses in the Torres Strait are in good condition, but large losses were reported from some reefs in 2019, possibly due to overgrazing or shifts in sediment (Carter et al. 2020). In the Gulf of Carpentaria, seagrasses in the north, near Weipa, are in good condition (McKenna & Rasheed 2019a, McKenna & Rasheed 2019b), but some regions in the south-west and west, particularly near Karumba, have suffered seagrass loss due to flooding-related sediment deposition (Shepherd et al. 2020), cyclones and propeller scarring.
  • In the Great Barrier Reef, monitoring of more than 40 inshore seagrass sites and at meadows in ports indicates seagrass is in good-to-poor condition based on abundance (McKenzie et al. 2021). Meadows have generally stabilised or increased following several years of decline due to widespread extreme weather and flood-related disturbances up to 2011, but remain well below historically high levels (in the 1990s to early 2000s) in some habitat types and regions (McKenzie et al. 2020). Overall, inshore seagrass condition was rated as poor when abundance was combined with other indicators (sexual reproduction and nutrient content) (McKenzie et al. 2020). Declines in condition have occurred in the Southern Wet Tropics (south of Cairns) and Mourilyan Harbour; the Burdekin region, where cover and biomass have declined but extent is stable; the Mackay–Whitsundays region, where the percentage of seagrass cover is poor overall for the region, but good in some habitats (McKenzie et al. 2020, Van de Wetering et al. 2020); and Hervey Bay, where the overall condition is rated as poor.
  • In south-east Queensland, seagrass is showing recovery in some degraded areas of Moreton Bay and is otherwise stable (Maxwell et al. 2019).
  • In New South Wales, some populations of the seagrass Posidonia australis continue to be recognised under the EPBC Act as Threatened Ecological Communities. Overall in New South Wales, the extent appears to be stable, although in many estuaries this is the net result of increases in the lower estuarine reaches compensating for losses in the upper reaches (Evans et al. 2018); there are ongoing declines of P. australis in 4 New South Wales estuaries (NSW MEMA 2017). The losses are driven mainly by shading through coastal structure development and moorings (Glasby & West 2018).
  • The condition of seagrass in Victoria is good overall. There have been historical losses in Western Port Bay due to warming and eutrophication (excess nutrients); there are signs of significant recovery but extent is still well below pre-impact levels (Commissioner for Environment & Sustainability Victoria 2016).
  • In South Australia, seagrass is in good condition on the south-eastern and western coasts, with the exception of a few embayments, but has continued to decline at Kangaroo Island and is in poor condition over extensive areas of northern and south-eastern Spencer Gulf due to eutrophication (EPA SA 2021). Off Adelaide, there are signs of significant recovery of seagrass that was lost in the 1980s (Clarke et al. 2021b).
  • In Western Australia, the relatively unmodified north-western coast is likely to support large areas of pristine seagrass habitat. In the south of the state, seagrass is generally in good condition with the exception of some areas adjacent to development, such as Cockburn Sound, Leschenault Inlet and Oyster Harbour, though recovery is occurring in these systems (Vidyan 2018, Bennett et al. 2021). Over 1,300 km2 of seagrass was lost in Shark Bay World Heritage Area due to a heatwave and sediment-loading effects in 2011, but recent mapping has shown recovery of approximately 125 km2 of meadow (Strydom et al. 2020).
  • Relatively little is known about seagrass populations in the Northern Territory, but most of the region experiences little pressure and seagrasses are likely to be in good to very good condition, with the exception of parts of the Gulf of Carpentaria.

Dune vegetation

Dune vegetation is one of the key factors in managing dune erosion. As highlighted in the 2016 state of the environment (SoE) report, less than 25% of pre-European native coastal vegetation remains across the south-eastern and south-western coastal regions of Australia. This is a result of pressures from land clearing for urban and infrastructure development, coastal erosion, disturbance from trampling (i.e. informal pedestrian beach access), and damage from off-road vehicles. Invasive plants and animals increase the pressure on the environment, and often initiate and exacerbate ecosystem decline in dune vegetation.

The 2016 SoE report identified the need for ‘active ecological restoration’ of coastal dune vegetation, but despite growing community and government support, the impact of such activities is unlikely to reverse the continued loss and decline in ecological condition in the short term. Large-scale recovery of dune communities has not yet been achieved (Figure 15), but there are instances where remediation works accompanied by revegetation have successfully reinstated dune profiles at local scales. For example, net gains in dune vegetation have been achieved along the Illawarra coast (New South Wales) since the late 1980s through mechanical remediation (e.g. moving sand to re-profile dunes) followed by revegetation. Similarly, high-quality restoration of ecological values has been achieved in sections of the Quindalup Dune ecosystems in Western Australia (see case study: Restoration of coastal dune ecosystems).

Changes in dune vegetation

The median change in coastal dune vegetation across Australia is a loss of 11% over 2014–19 (Figure 15): 66% of coastal dune vegetation areas lost more than 5% vegetation, 18% underwent minimal change, and 16% showed improvement. On a national scale, none of the areas with improved vegetation cover are near zones of urban development, or are attributable to ecosystem restoration efforts. Most of these areas of recovery are natural regeneration after fire events.

Figure 15 Change in coastal dune vegetation, 2014 to 2019

Note: To assess the change in coastal dune vegetation condition since SoE 2016, remotely sensed data of perennial vegetation cover curated by AusCover were used from 2014 and 2019. The 1M-scale geological map of Australia from 2012 was used to define the extent of coastal dunes. Note that 2014 data were used in the 2016 SoE report; while preparing SoE 2021, the most recently available perennial vegetation data were for 2019. Through analysis of satellite and weather records over 2014–19, the probable cause of vegetation loss greater than 25% has been assessed (Figure 16).

While the 2016 SoE report indicated that coastal vegetation in northern and north-western Australia was generally in good condition, there were significant zones of vegetation loss through large tracts of tropical Australia over 2014–19 (Figure 16).

The main cause of coastal dune vegetation loss in tropical Australia is the unseasonably dry wet season for 2019–20, with many areas receiving less than 60% of their average rainfall for the season. While coastal dunes in this region do show significant seasonal variations in vegetation cover between wet and dry seasons, the loss of vegetation in 2019 has left the coastal dunes exposed to erosion from cyclonic activity. Land clearing contributed to just 5% of the major vegetation loss over 2014–19 (Figure 16), but this was concentrated in a relatively small area of the tropical coast in Queensland, showing that urban development is having a disproportionately large impact on this area.

The historically unprecedented fire season for southern Australia in the summer of 2019–20 is the major cause of coastal dune vegetation decline for this region. As these fires occurred immediately before the data collection for the current SoE report, the effect may be overstated in some cases and these areas may recover. However, they are at exceptionally high risk of further degradation and erosion until recovery occurs.

Figure 16 Change in perennial coastal dune vegetation from 2014 to 2019, with causes of major vegetation loss annotated

Islands

Australia is custodian of incredibly diverse island landscapes: tropical atolls (e.g. Cocos-Keeling); coral cays; tropical, subtropical and temperate continental islands; sea stacks; the world’s largest sand island (K’gari/Fraser); sea mounts forming oceanic islands (e.g. Christmas, Lord Howe and Norfolk); and subantarctic islands (e.g. Heard and Macquarie). Some, including the Great Barrier Reef, have World Heritage status and are unique in the natural world. These islands provide innumerable ecosystem services that underpin the Australian lifestyle, economic development and traditional cultural ties. For some Traditional Custodians, their sea Country, sense of connection and identity are attached to the health of the land and sea of islands.

Many islands support critical populations of threatened flora and fauna, contain distinctive habitats, have many endemic species (e.g. James et al. (2019)), and support most of Australia’s breeding colonies of seabirds, marine turtles, seals and sea lions. For some species, they provide important refuge areas where threats occurring on the mainland are limited or not (yet) present (Legge et al. 2018).

Due largely to their geographical and environmental diversity, the current state of Australian islands varies enormously – from highly altered (e.g. some residential islands in south-east Queensland and north-eastern Australia) to largely unmodified (e.g. the Kimberley in north-western Australia) or almost pristine (e.g. subantarctic Heard Island) (Moro et al. 2018). However, all island ecosystems are threatened by invasive non-native species and the effects of climate change.

The resilience of islands against different pressures is largely dictated by their size and proximity to the Australian mainland. Some very small islands are already heavily affected by partial inundation driven by climate change (e.g. Raine Island, Queensland, the world’s largest green turtle rookery). Larger islands and islands with more elevation are more resistant to such inundation, but some of these have been heavily affected by recent bushfires (e.g. Kangaroo Island, South Australia), most likely exacerbated by climate change.

The current outlook for islands – and especially the maintenance of island biosecurity – is uncertain and awaits concerted national-level coordination and governance to reduce future risks to these national assets.

Island pressures and management

Island biosecurity across states and territories differs widely, leading to inconsistencies in island conservation and management. There is limited national coordination and, in many cases, absence of any actions or regulations to manage the arrival, detection and eradication of invasive species. Responses to climate-change-driven impacts have mostly been restricted to protection of human communities and associated infrastructure, with little recognition of the need to also protect environmental assets.

Some remote islands, which to date have been largely unaffected by human activities, are now facing pressures from resource extraction and processing, particularly in north-western Australia. Islands in the Pacific, Indian and Southern Oceans, and the Coral and Timor Seas, as parts of Australia’s external territories, are strategically important for defence and border protection. Near-offshore islands are under increasing pressure from tourism and recreation.

While there is a paucity of data and condition monitoring, the overall state of Australia’s offshore islands is highly variable and remains of concern. Globally (Szabo et al. 2012, Tershy et al. 2015) and in Australia (Woinarski et al. 2019), the proportional extinction rate of island biodiversity far surpasses that of continental areas. The biodiversity of many Australian islands is currently in rapid decline (Garnett & G.B. 2020); notably, the 3 most recent confirmed extinctions in Australia have been of island endemic species – the Christmas Island pipistrelle, Christmas Island forest skink and Bramble Cay melomys (Woinarski et al. 2017). Conversely, some of the most impressive recent recoveries of biodiversity (including threatened species) have been on islands from which invasive species have been eradicated – for example, Macquarie Island (Springer 2018) – because eradication of invasive species is much more achievable in island settings than in mainland areas.

Management of many islands as Indigenous Protected Areas and native title (Mabo) determinations has helped Indigenous peoples to maintain their connections to island and sea Country, and to continue their cultural practices, customs, lore, stories, songlines, totems and languages. Given Indigenous peoples thrived through the last great period of climate change, the Holocene, there is opportunity for modern Australia to learn from them in planning and implementing a response to the current climate change.

There is also much to learn from the new suite of contemporary whole-of-island management approaches, such as those taken on Lord Howe, Macquarie and Dirk Hartog islands, that are proving highly successful. Managing interests and conflicts between island users is also integral to island management, and cooperation of all parties involved is essential if management is to be successful (Bryant et al. 2021). Provided the Traditional Owners and local communities are kept embedded and involved from the initial stages of planning, the focus of effective island partnerships can shift from managing the threats to threat mitigation. However, island managers will need additional resources to ensure that the management of key threats is sustained and community ownership and longevity in conservation initiatives are maintained.

A national, coordinated approach is required to ensure the long-term conservation of Australian islands. Assessing island risks and using key island indices to monitor trends in island condition offers one approach for policy-makers to understand and interpret condition over time. Island management requires a multidisciplinary approach supported by comprehensive evidence and funding, and a decision-support system that can simplify the numerous actions involved in protecting island values nationally, while recognising that size alone is not a valid criterion for determining island priority. Designating islands containing important nature conservation values as Matters of National Environmental Significance or Threatened Ecological Communities under the EPBC Act could impose safeguards and improve conservation efforts (Woinarski et al. 2018).