Saltmarsh and tidal flats

Saltmarshes and tidal flats occur in the intertidal zone, which is the area underwater at high tide and exposed to air at low tide. Tidal flats are large muddy or sandy areas that are inundated by the tide daily, where as saltmarshes are at the higher end of the intertidal zone, and are generally inundated less frequently. In Tasmania saltmarshes mainly occur in small patches and are generally found within bays and at the mouths of creeks and streams. Their extent depends upon the shape of the landscape, being largest in flat low-lying areas. Within the Derwent estuary the largest area of saltmarshes and tidal flats occurs in Ralphs Bay near Lauderdale. They are highly productive habitats provide food and shelter for a diverse suite of marine and terrestrial species, and also support the healthy functioning of estuaries.

Click on the images below to find out more about the typical plants and animals found in Derwent estuary tidal flats and saltmarshes.

The Habitat Atlas indicates that there are 11.4 square kilometres of sandy tidal flats/beaches remaining in the Derwent estuary (primarily in Ralphs Bay) and about 1 square kilometre of mudflats (in the upper estuary). The landward margins of tidal flats are often associated with salt marshes, containing a unique assemblage of succulents and other salt-tolerant plants

Did you know?

  • More than 10 species of wading birds feed on the sandy tidal flats of Ralphs Bay. Some of these birds migrate over 15,000 km each year, from their breeding sites in the northern hemisphere as far as Alaska and Siberia.

Things to explore - resources for teachers and students

  • Visit a tidal flat and salt marsh as part of a school trip, for example at Lauderdale or Arm End. How many different kinds of birds can you spot? Collect several tubs full of sand and filter these through a sieve. How many different kinds of invertebrates can you find?

Community types

Plants and animal species of saltmarsh and tidal flats occur in a range of different community types, largely distinguished by the vegetation types.


Key threats

Extensive loss of saltmarsh due to land reclamation and changes in land use mean that many remaining areas are often fragmented. Despite the significance of saltmarsh it is one of the most heavily impacted coastal habitats and are listed as an Endangered Ecological Community in some Australian states. Of critical importance to the future of these habitats are changes in relative sea level and in tidal range. Climate related threats require thoughtful re-zoning of land neighbouring saltmarshes to enable the land-ward transgression of these saline wetlands with sea level rise.

Saltmarshes are highly fragile and prone to disturbance, especially from:

  • motorbikes and cars
  • grazing from rabbits and livestock
  • illegal clearing
  • bushfire
  • weed invasion

For more information on threats to saltmarsh and other habitats in the Derwent estuary see our publications.


Educational resources and excursions

Pacific Gull

Restoring and promoting the Derwent estuary