Biologically, coasts are an interface between the biota of the oceans and the land, including biota of freshwater systems that mingle with salt water in estuaries. The transition between terrestrial and marine environments represents one of the sharpest changes in habitat for living organisms found on Earth. It produces unique flora and fauna adapted to deal with unique environmental challenges. One of those challenges is that the border between terrestrial and marine systems is constantly changing; it is set to become even more variable with the effects of climate change in coming decades. Geomorphology is also unique and dynamic.
Australian coastal environments include a range of ecosystems that contain habitat for a variety of species. Habitats include mangroves, saltmarshes, saltflats, seagrass beds, beaches, dunes, estuaries, intertidal mudflats, gulfs, bays and coastal wetlands. Nearshore and offshore marine habitats are potentially impacted by human coastal settlements and activities. Coasts, especially the mouths of rivers, are where valuable resources such as high-quality soils accumulate, and where people practise agriculture and a range of other resource-based industries, as well as enjoying the amenity of these places.
Australia’s population is focused strongly around its coastline, especially around the estuaries of major river systems. These areas include good shipping and boating facilities, as well as prime agricultural land. Australians have been concentrated on the coast since the beginning of European settlement. Before then, coastal Aboriginal people had lifestyles that differed from those of Aboriginal people living inland, although goods, stories and practices were exchanged between coastal and inland people.
Concentration of people around the coasts puts pressure on coastal ecosystems. It also complicates the management of these systems because several major demands on the land come into potential conflict with each other: demand for urban development at the waterline; demand for agricultural production on fertile floodplains; increasing demand for inshore areas for food production (aquaculture); increasing recreational use, including fishing and boating; and demand for conservation of nature for both its intrinsic values and the benefits it provides for humans through water filtration, regulation of river flows, provision of food and provision of cultural values. Coastal ports are also prime sites for entry of invasive pests and diseases.
Governance issues are highly complex in coastal areas. The importance of coastal assets means that many interest groups place demands on local, state and national governments. The responsibilities and authorities of these three levels of government overlap at times, which can lead to conflict if objectives differ between levels of government. Issues can be inadequately addressed if it is unclear where responsibilities lie, with one level of government expecting another to take responsibility and action. Resourcing can often be a major issue at all levels, especially when the desires of coastal residents outstrip funding, including land rates.
Coastal environments are where the dynamics of future change will be writ large on the landscape and ecosystems. Many aspects of climate change will directly affect the coast: sea level rise; changing wind patterns; changes in the frequency and magnitude of cyclones, storms, tidal surges and rainfall events; changes in erosion and sediment transport; and changes in nearshore ocean currents. The effects of changes in the nature and amount of trade with other countries will be felt in coastal ports, with flow-on effects on local economies and lifestyles. All these will drive change in ecosystems and human values at the waterline, where even small changes in sea level and the quality of water can have major effects on the species that live where the sea and the land overlap.