Townsville SOE home page

Habitat 7. Mangroves

Mangroves are an important, widespread coastal ecosystem that plays a vital role in the biological productivity of Australia’s coastal waters.

Mangrove forests are diverse communities growing in the intertidal zone along tropical to subtropical coastal rivers, estuaries and bays and may also be found growing in carbonate sediments on reef islands.

Mangroves have specially adapted to their dynamic salty environments, being subjected to high fluctuations in salinity, experiencing high levels when inundated by sea water and experiencing relative low levels of salinity when heavy rains or floods expose the plants to fresh water. The soils of the intertidal zone are usually soft, muddy and anaerobic.

The type of mangrove species that will occur is dependant upon relevant levels of particular environmental factors such as salinity, nutrient availability and oxygen levels in the soil and wave energy. Therefore a species distribution, known as zonation will occur. For example, less salt tolerant species will often occur high in the intertidal zone (closer to the land), where as species highly tolerant of salty conditions will occur lower in the intertidal zone.

Mangrove Swamp Mangrove Swamp
Click to enlarge

Mangrove Characteristics
To survive in soft, salty, oxygen deficient soils Mangroves have developed many adaptations.

To overcome often anaerobic soils some mangrove plants have developed structures called pneumatophores. These are above ground roots that are filled with a sponge-like tissue that is covered by a bark with holes that allows oxygen to be transferred to the extensive below ground root system. There are four different types of pneumatophore:

    1. tilt or prop type
    2. Snorkel or peg type
    3. Knee type
    4. Ribbon or plank type

The roots also provide the advantage of structural support in often soft, muddy soils.

Another characteristic trait of the Mangroves is an ability to desalinise, to an extent, the water it uses by excluding most of the salt by a membrane in the cells at the root surface. The salt that does enter the plant is then stored in the leaves and as a result the Mangrove will have high concentrations of salt in the leaves. In some species such as the Grey Mangrove the salt is excreted from special leaf glands, while in other species the salt is simply stored until the leaf dies and is shed. Due to the limited availability of freshwater in the intertidal zone, Mangroves can reduce the evaporation rate, thus conserving the fresh water by restricting the opening of their stomata and varying the orientation of their leaves, away from the harsh sun.

Mangrove Ecosystem
Mangrove forests are also an important ecosystem due to their position, at the interface between marine and terrestrial environments, forming part of an ecosystem that supports an abundant array of life through the food chain that starts with the Mangroves. The nutrient rich leaves which are shed from the Mangrove are broken down by fungi and bacteria or are eaten by small animals such as the crustaceans, molluscs and fish that live within the Mangrove floor. The nutrients also feed the plants, plankton and algae all forming part of a complex mangrove ecosystem. Few animals use mangroves as their only habitat. Some live primarily in the mangroves, while others move in and out of the mangroves seasonally, at different stages of their life cycle or even at different daily times dependant on the tide.

Search the Natural Assets Database
Habitat Name Landform
Mangrove low forest Tidal channel
locations seen (11)  ..  vegetation (17)  ..  mammals (4)  ..  birds (44)  ..  reptiles/frogs (6)  ..

Townsville City Council Home PageCouncil's Environment Management Services