Tidal wetlands are sheltered waters along the coast which are affected by both tides and freshwater run-off. They occur around Australia in shallow, protected coastal areas, such as bays and estuaries. Tidal wetlands consist of salt marshes, mangroves and seagrass beds.
Tidal wetlands are one of the most productive ecosystems known. They produce large amounts of plant material which are broken down into detritus by the myriad of animals and micro-organisms which live in the sediments of wetlands. This material is the 'fuel' which drives our coastal ecosystems. Wetlands also harbour a whole range of animals at various stages in their life cycle, such as young marine organisms which come to feed at high tide and find shelter from larger predators.
Tidal wetlands function as 'kidneys', filtering and removing excess nutrients from the water that flows through them and preventing them from flowing out into coastal waters. This has been shown to be particularly important in coral reef areas. They also stabilise the coastline, preventing erosion during storms. In addition, wetlands act as nurseries for many species of fish and prawns.
Extensive areas of wetland are cleared for ports and marinas, residential and commercial developments and agricultural needs. For example, most of the sugarcane grown in Queensland is on reclaimed tidal wetlands.
Once wetlands are drained, the soil becomes extremely acidic and much of this acid enters the ground water when it rains. The acid is then washed into creeks, sometimes causing massive fish kills. Removal of wetlands also causes a loss of habitat for many plants and animals, and results in coastal erosion.
We have come a long way from the days when wetlands were regarded as smelly swamps to be cleared and filled. However, their biological and physical values are still often ignored. Recreating wetlands is not a viable option, and although mangroves, salt marsh and seagrasses have been transplanted with some success, wetlands are far more than just plants. Therefore, we should be conserving and enhancing many of our degraded wetlands, not clearing them.
Pat Hutchings
Marine Invertebrates
Australian Museum
Copyright © Australian Museum, 2003
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