Educational Material

Mangroves - Precious habitat or prime real estate?

National Parks Association of NSW believes that NSW marine parks need REAL protection in No-take Sanctuaries. By protecting our mangroves, seagrasses, salt marshes, rocky shores, sponge gardens, sandy bottoms, sandy beaches, coral reefs, and open oceans we will help conserve our marine biodiversity and ensure that our fisheries are healthy and productive.

Mangroves are trees and shrubs forming forests in the intertidal mud flats along the shores of estuaries. In these sheltered waters they usually grow in the region between the saltmarshes and seagrass beds. What is left of the mangroves of NSW is a valuable resource that must be urgently protected.

NPA is campaigning for a system of marine sanctuaries to be established which together include at least 20% of the total area of each marine habitat type within both the Commonwealth and State Territorial Seas.

NSW Mangrove Species
There are five species of mangroves in NSW. The Grey Mangrove and the River Mangrove are the most common on the NSW coast.

The River Mangrove is a shrub found from the Tweed River south to Merimbula. The Grey Mangrove is a large tree found along the entire coast. Three others - the Red Mangrove, the Large-leaved Mangrove and the Milky Mangrove - are located only in the northern estuaries of NSW.

Special Features of Mangroves
Mangroves are terrestrial trees, which have adapted to living in soft muddy sediments with a large salt content and little oxygen, and are covered twice a day by salt water.

Adapting to Salt Water
Most plants die in salty soils. Mangroves have evolved processes to cope with salt:
· Secretion - some mangroves, such as the Grey and River Mangroves, take up salty water through their roots and excrete the excess salt through their leaves;
· Exclusion - salt-excluders are able to take up water only from the mud, without the salt. All mangroves of NSW exclude salt to some extent.
· Accumulation - many mangroves, such as the Milky Mangrove, accumulate salt in older tissues, which are then shed as they become laden with salt.

Aeration
Many mangroves, such as the Grey Mangrove, have aerial roots (pneumatophores). These roots protrude above the mud bottom as open-ended pipes and are used to absorb oxygen from the air.

Seed Dispersal
Mangrove seeds float, and are shaped so that they can anchor themselves into a soft substrate where they can start to grow. Because the young plant must compete with the adults for light, growth is often fairly slow at first - it can be many years before an opening in the overhead canopy allows a young seedling enough light to grow.

Importance of Mangroves

Animal Habitat
Mangroves are permanent or temporary habitats for many aquatic and land animals.
They are also important nursery grounds for juvenile fish. As the tide rises and submerges the mangrove flats, numerous fish move in to find food and shelter.
The floor of the mangrove forest is a habitat for extensive numbers of crabs and molluscs. Dense colonies of oysters encrust the base of trees, and limpets, crabs and worms live among the oysters. Three commercially important crustaceans - king prawns, blue swimmer crabs and mud crabs, live in mangroves. In the canopy of the trees live webs of golden-orb weaver spiders, ants and beetles. At dusk, many birds come to mangroves to roost, or a colony of fruit bats may fly in to feed on the mangrove flowers and fruits. In tropical areas you may find goannas or snakes living in mangrove habitats.

A Source of Food
A single square kilometre of mangrove forest contributes about 600 tonnes of plant material each year to the estuarine food chain.

Microscopic fungi and bacteria first break down the mangrove litter. Animals such as mullet, prawns and crabs eat this decomposing material.

Foreshore Buffering
Mangroves grow between the estuary and the surrounding land and buffer the waterway from the direct effect of run-off waters, by filtering pollutants from the land run-off. Thus mangroves help maintain estuarine water quality and reduce siltation in waterways.

Mangroves Have Been Sold Out as Prime Real Estate
Mangroves, saltmarshes and seagrass beds are often seen as prime sites for coastal developments. Mangrove forests have in the past been inexpensive real estate for development, as the community had not perceived the ecological importance of mangroves.

Threats to Mangrove Habitats
In the past, flood mitigation works have meant the construction of barriers that prevent tidal flow, or the draining of wetlands resulting in the lost of vast areas of mangroves. Mangroves have been seen as unproductive swamp and used as rubbish dumps, and as feeding grounds for cattle.

Local governments and individuals have reclaimed mangrove habitats and carried out devastating dredging and waterfront development in these vital fragile ecosystems.

Indiscriminate cutting and clearing of mangroves is prohibited, however people have all too often cleared mangroves simply for a better view of the river.
There is no point protecting individual marine species if we are not protecting the habitats they need to survive

20% of each NSW Marine Habitat Type Needs Real Protection in No-take Marine Sanctuaries.
At least 20% of each NSW marine habitat type needs FULL protection in No-take Sanctuaries.

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