Australia’s coast is vast and diverse. It is the sixth largest of any nation, and contains a variety of habitat types, including sandy beaches and dunes, rocky shores, tidal flats, and estuaries and bays. Our coast is intimately linked to our national economy, industry, arts, social lifestyle and cultural identity, with more than 85 per cent of Australians living within 50 kilometres of the sea. We do, however, risk ‘loving our coast to death’, as its amenities and resources attract intensive human use. Most of Australia’s population growth is near the coast, and we rely on the coast for almost all our international trade. The coast is subject to pressures operating on a range of spatial and temporal scales, and it is the cumulative and interactive effects of these pressures that determine human impacts on coastal ecosystems. Now, more than ever, it is important that we understand the environmental consequences of how we use the coast, but significant gaps remain in our understanding of the state of coastal health. Urbanisation, agriculture and resource extraction have already modified much of the coast, and impacts associated with climate change are beginning to emerge. There is still much to protect, however, even in heavily modified ecosystems. Australia is also fortunate to retain large stretches of relatively untouched coast, containing ecosystems with exceptional natural values.
Current pressures on the coast are largely related to land use and climate change, and the state and trends of coastal biodiversity are tightly linked to these pressures. Eastern and southern coasts are most affected by urbanisation and agriculture, whereas resource extraction has grown as a pressure in the less modified west and north-west. Urban and agricultural land use cause habitat loss, habitat fragmentation, loss of native biodiversity, and contamination of coastal land and waterways. Resource extraction has increased in the past few years, with the mining boom causing severe, but highly localised, habitat loss and degradation. Trade associated with resource-extraction activities is also linked to the introduction of invasive species. The ecological integrity of the dynamic land–water interface is diminished through continued development of shorelines and the spread of invasive species. Aquatic habitats are affected by the alteration of flow and water quality through upstream development, modification of entrance dynamics, andr climate-related changes in precipitation patterns. Many of the ecological services and processes that ecological communities deliver and depend on are disrupted by human-driven deterioration of the coast. For example, widespread nutrient enrichment of coastal waterways has substantially altered the processes of nutrient cycling, sulfur metabolism and carbon fixation. Destruction of critical nursing, roosting and nesting sites has broad-reaching ramifications for species that rely on networks of sites to maintain populations (e.g. shorebirds). Critical habitat-forming species groups, such as saltmarsh, seagrass and shellfish, have failed to fully recover from extensive historical losses, although restoration programs are currently under way.
The outlook for the coast focuses on the escalating trajectory of climate-related pressures. These are expected to become increasingly prominent, and, unlike most other pressures, affect the entire coast. Since 2011, climate change has manifested as increased frequencies of marine heatwaves and severe storms, such as the Ningaloo heatwave and tropical cyclone Yasi of 2011, and the 2016 marine heatwave that caused severe bleaching in large sections of the northern Great Barrier Reef. Sea level rise is a key pressure that Australia is only just beginning to experience, and one that will have increasingly conspicuous impacts in future decades. If greenhouse gas production is not rapidly reduced, the rate of sea level rise is predicted to reach almost 12 millimetres per year or higher by 2100, depending on the behaviour of the Antarctic ice shelves. Increased sea level will not only shift the position of intertidal and aquatic habitats, it will also cause extensive erosion and recession. Of particular concern are low-lying islands, which are highly vulnerable to even small changes in sea level. For urban centres, options for human populations to cope with sea level rise include managed retreat, or engineering the coast to withstand impacts. However, engineering coastlines can also have negative impacts on coastal ecosystems. The key challenge in the short term is to implement strategies to mitigate the effects of climate change, while conserving the natural integrity of the coast.