Climate change will affect coastal habitats directly and the extent of impact may be increased by the cumulative effects of other threats. Because they are often located close to population centres and industry, coastal habitats tend to be highly vulnerable to other impacts such as degraded water quality and coastal development.
Coastal habitats include estuaries (areas where fresh and salt water mix), mangroves, salt marshes, beaches, wetlands, seagrass meadows and nearshore waters and reefs. These habitats form vital connections between land and sea.
Coastal habitats perform the following vital functions in the Great Barrier Reef ecosystem:
- Provide coastal protection and function as essential pathways and filters for materials that move from the land into the marine environment. Such materials include fresh water, soil (or sediment) particles, nutrients and pollutants
- Act as crucial nursery grounds for many animals like fish and crabs
- Act as links in the life cycles of species that migrate between marine and freshwater environments.
Sea level rise
Coastal and estuarine habitats are diverse, and are closely linked through the movements of materials, animals and plants. The effects of climate change on any part of the coastal environment will be passed on through these linkages.
Rising sea levels, for example, will increase the movement of salt water into freshwater wetlands. It will also affect the balance of coastal erosion and sediment build-up and tidal connections between land and sea. Changes such as these will affect both resident and migrant animals and plants, with flow-on consequences for neighbouring habitats.
The direction and extent of impacts will depend on how rising sea levels interact with altered patterns of rainfall and flooding.
Altered rainfall patterns
It is the mixing of fresh and salt water that gives estuaries their unique characters. If patterns of rainfall and flooding change it will have wide-ranging consequences for estuarine and other coastal habitats.
The timing, size and variability of rain events determine the patterns of freshwater flow to these habitats. Such flows are vital for supplying the essential nutrients that support coastal productivity, but can also lead to poor water quality. As water passes downstream through river catchments, it accumulates nutrients, soil and pollutants, which end up in estuaries and coastal waters.
For this reason it is rainfall patterns, in combination with human land use, that determine the extent to which coastal habitats and coral reefs are exposed to poor water quality. Changes to rainfall patterns caused by global warming will therefore directly affect water quality on the Great Barrier Reef.
Severe weather events
Estuaries and other coastal habitats are constantly changing. For example, sediments washed from the land accumulate over time in estuaries are flushed out to sea by large floods and then accumulate again.
The animals and plants that live in coastal and estuarine environments have adapted to cope with, and in some cases depend on, these occasional disturbances. However, changes to how often such events occur, how severe they are or how long they last could disrupt the normal cycle of variability to which animals and plants have adapted.