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In Sydney Harbour there are two species of mangrove, the Grey Mangrove Avicennia marina and the River Mangrove Aegiceras corniculatum. Major concentrations of mangroves can be found along the Lane Cove River, Parramatta River, Homebush Bay and Duck River, with other stands in Tarban Creek and the upper reaches of Middle Harbour.
Mangroves are true plants, with roots, stems and leaves that have become specially adapted for life in seawater. Mangroves are among those very few land plants that can live in inter-tidal areas and can tolerate a constantly changing mixture of salt and fresh water. They survive in salty water by preventing their roots from absorbing too much salt and pumping out any excess salt through special glands in their leaves.
Unlike other trees, many mangroves can breathe through their roots. They do this by extending their underground roots through the surface of the mud to form aerial roots called 'pneumatophores'. Pneumatophores can often be seen sticking out above the water and mud under mangroves, especially during low tide.
Wetlands and mangroves are a very important part of the natural environment of Sydney Harbour. They play a critical role in providing shelter, food, breeding and roosting areas for a diversity of wildlife. They are also valuable in nutrient recycling, improving water quality, recharging ground water, flood control, erosion control and stabilisation of river banks.
Mangroves have suffered from a very poor reputation in the past, and have often been considered unpleasant and unsafe areas, which are best avoided. Even up until very recently, mangrove swamps were often considered undesirable and frequently cut down. The shallow muddy areas left were then filled in providing land for houses with good views and waterfront parks. Many people now realise just how important mangrove swamps are and they are finally being preserved and protected.
Mangroves provide a quiet muddy habitat for a large variety of fish and marine invertebrates. During the rising tide many fish enter mangrove forests in search of food, remaining in the forest during high tide and leaving again as the tide goes out. Many commerically important fish such as leatherjacket, flounder, Sea Mullet, Yellowfin Bream Acanthopagrus australis, Luderick Girella tricuspidata and Dusky Flathead Platycephalus fuscus spend much of their juvenile life in mangrove creeks before moving out into deeper water as adults. Other fish particularly common in the mangrove forest around Sydney are Common Toadfish Tetractenos hamiltoni, Estuary Catfish Cnidoglanis macrocephalus and Striped Scat or Striped Butterfish Selenotoca multifasciata.
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