Adaptations to
The tidal Zone

Australia’s mangroves show remarkable adaptations dealing with frequent saltwater inundation and varying climatic zones from arid to very wet. Mangroves share specialised attributes for growing with excess salt and saturated air-less soils. They also have special growth strategies to facilitate establishment and regeneration. One special attribute promoting sustainability and dispersal of mangroves is their unusual production of live young - vivipary. Such attributes have kept mangroves from extinction for more than 50 million years, and enabled them to occupy tidal areas around the world.

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Salt & Soaking Adaptations

Salt encrusted leaves

Mangroves collectively possess a unique combination of morphological and physiological attributes for living in the tidal environment. Mangrove soils are regularly water-logged and loaded with salt. High tides bring marine aquatic and estuarine conditions, while low tides expose mud and roots to aridity, heat and desiccation. Few other natural habitats are subject to such dramatic changes in abiotic variables - particularly regards the combined influences of tides, rainfall, runoff, waves, currents, climate and sea level change.

All these factors have notable and profound influences on the distribution and characteristics of Australia’s mangroves. Adaptations required for survival in this environment are shared in part by plants from at least three other habitat types, namely: deserts, rainforests and freshwater swamps.

Living with Salt

Mangroves, like desert plants, have special adaptations for growing in low moisture and high salt conditions. In estuarine and coastal environments, salinity levels of interstitial and flooding waters are often widely variable being affected by tidal fluctuations, seasonal rainfall and river flows.

Over time, a combination of strategies have shaped the diversity and character of the plants. One strategy for coping with high concentrations of salt is special salt-excreting glands on leaves. Another is the exclusion of salt from entering roots with water uptake. In general, each species has mechanisms to regulate levels of salt in sap. This is further assisted by ridding salt with old leaves, bark and wood.

Left - salt, encrusted on leaves of Aegiceras corniculatum, is expelled from salt glands in the leaves.

  • Roots Fallen leaves, wood loss and shedding foliage are ways to rid plants of salt.
  • Xylocarpus The deciduous habit of one species, Xylocarpus moluccensis, may be an extreme strategy for this species to expel salt.
High tide

Support in Soggy Soils

Mangroves have shallow root penetration and breathing roots because their soils are usually saturated and airless. Mangroves also have broad support structures, such as buttresses and sturdy prop roots, because the soils are often soft and unconsolidated. The features of shallow depth and support structures are well-known in tropical rainforests. Like freshwater swamp trees, mangroves also cope with water-saturated soils that limit gaseous exchange, by using special breathing roots. Some have shallow, sub-surface cable roots with many vertical, finger-like breathing roots, called pneumatophores. Other groups have no obvious physical adaptations except for numerous small air-breathing lenticels on their lower stems.

Right - flooding waters from tides and seasonal rains are a common feature of mangrove habitats.

  • Bark Pustular lenticels on the bark of Bruguiera gymnorhiza help the plant breath and exchange gases where roots grow in anaerobic sediments.
  • Root buttresses The Buttresses of Heritiera littoralis provide support for stem and foliage in soft and soggy mud.

Community Volunteers

A key feature of MangroveWatch is its close partnership between community volunteers and scientists from the James Cook University’s Mangrove Hub. Together they are systematically recording basic data as video and still imagery for assessments of estuarine habitat health.

Armed with expert support, training and advice, MangroveWatch volunteers in key regions are actively contributing to the monitoring of local estuaries and shorelines. An important goal in this phase of the program is to develop a network of like minded groups with the aim of producing public documents that describe important issues affecting local estuaries and mangroves, and their overall health.

Getting Involved

If you would like to find out more about us or if you like to initiate your own MangroveWatch group within your area, please contact someone at the Mangrove Hub. We will be happy to help.

  • Mangrove Hub Facilitator
  • Dr Norm Duke
  • MangroveWatch Ltd
    ABN: 44 153 297 771
  • PO Box 1250,
  • Elanora Q 4221
  • Mangrove Hub Email

Mangrove Watch Brochure

You can download our fact and information sheet (see link below) to get more information about the MangroveWatch programs.

Mangrove Watch Brochure