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Intertidal and subtidal ecosystems

Estuarine ecosystems are those with oceanic water which is diluted with freshwater run-off from the land. Marine ecosystems are those with oceanic water. Intertidal ecosystems differ from subtidal ecosystems based on the biophysical attribute of inundation and are therefore easier to map.

Estuarine and marine wetlands are a subset of estuarine and marine ecosystems which only extend to six metres below the lowest astronomical tide. The six metre depth contour is unsurveyed for most of the Queensland coast and the extent of freshwater influence is variable over time, making the extent of estuarine and marine wetland boundaries difficult to determine.

Seagrass at Urangan, Photo by N Kastner

Quick facts

The Great Barrier
Reef Seabed Biodiversity project[4] found that, after algae, sponges formed the most abundant group, then ascidians, with cnidarians and bryozoans favouring high current and harder substrates.

About intertidal and subtidal ecosystems

Intertidal and subtidal ecosystems may be composed of parts of both estuarine systems and marine systems[1][2]. Subtidal ecosystems are always submerged due to tidal influence, whereas intertidal ecosystems are found between the high tide and low tide, experiencing fluctuating influences of land and sea[3].

Intertidal ecosystems are a dynamic complex of plant, animal and micro-organism communities and their non-living environment that interact as a functioning unit, and are exposed at low tides (e.g. mangroves or saltmarsh on muddy substrate). Subtidal ecosystems on the sea floor remains continuously submerged. Tidal inundation is a major characteristic of these ecosystems and this and other biophysical attributes of benthic habitats can be used to classify and map benthic habitats.

Intertidal and subtidal attributes and types

Attributes for the purpose of classification (e.g. Intertidal and Subtidal Classification scheme) cover a range of themes including terrain, substrate, energy, hydrology (physical/chemical) and biota.

Ecosystem type descriptions provides a hierarchical list of ecosystem types described in terms of their combinations of attributes.

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  1. ^ Aquatic Ecosystems Task Group (2012), Aquatic Ecosystems Toolkit, Module 2: Interim Australian National Aquatic Ecosystem (ANAE) Classification Framework, Australian Government Department of Sustainability, Environment, Water, Population and Communities, Canberra..
  2. ^ Cowardin, LM, Carter, FC & LaRoe, ET (1979), 'Classification of wetlands and deepwater habitats of the United States.', Fish an dWildlif Service, vol. FWS/OBS-79131, Fish and Wildlife Services, Washington, DC.
  3. ^ OzCoasts (2015), Glossary. [online], OzCoasts (Geoscience Australia) 2015. Available at: [Accessed 21 June 2017].
  4. ^ Pitcher, RCR, Doherty, PPJ, Arnold, PP, Hooper, JJNA & Gribble, NNA (2007), Seabed biodiversity on the continental shelf of the Great Barrier Reef World Heritage Area, CSIRO Marine and Atmospheric Research.

Last updated: 4 September 2019

This page should be cited as:

Department of Environment and Science, Queensland (2019) Intertidal and subtidal ecosystems, WetlandInfo website, accessed 2 February 2022. Available at:

Queensland Government
WetlandInfo   —   Department of Environment and Science