The Jack Barnes Mangrove Boardwalk located off Airport Avenue on the way to Cairns Airport is closed until further notice.
The boardwalk was opened in February 1988 to commemorate the Queensland Bicentennial and is is named in honour of Dr Jack Barnes, a well known marine biologist with a lifelong interest in box jellyfish and the mangrove environment.
The Jack Barnes Mangrove Boardwalk offers two walks through different zones of mangrove forest including a mature stand of Stilt mangroves that can reach heights of 30 metres. Along the walk, you can see 11 of the 29 mangrove species found in Cairns, as well as epiphytes such as ant plants, basket ferns and golden orchids. As the tide rises and falls a myriad of crustaceans, fish and birds adapted to life in this special place can be observed.
Worldwide there are 69 recognised species of mangroves belonging to 20 plant families. Queensland has 34 species and 3 hybrids while Cairns has 29 species.
Mangroves are trees and shrubs adapted for survival in the intertidal zone.
They occur throughout the tropics on sheltered shores, in estuaries and lagoons where salt water penetrates, along sandy or rocky beaches and on coral that has been covered by a layer of sand or mud. Mangrove swamps can vary from a few metres in width to several hundred metres or more depending on the suitability of the area. A few species occur outside the
tropical regions where habitat and conditions are suitable.
Once regarded as sandfly and mosquito infected swamps of little or no value to society, many mangrove areas were destroyed by landfill or used as garbage dumps. All Queensland mangroves are now protected environments under State and Federal legislation.
The mangrove ecosystem
These highly complex and productive intertidal ecosystems support a range of complicated food webs and are nursery areas for a wide range of commercial and recreational fish and invertebrates.
Decaying mangrove leaves and organic materials provide nourishment for algae and microscopic organisms. These are food for shrimp, prawns and filter feeding molluscs such as oysters and clams, crabs, including mud and fiddler crabs, who in their turn are a food source for large fish species, such as Barramundi, Jewfish, Threadfin, Bream and Mangrove Jack. This environment is well populated with a variety of birds and insects.
Many recreational and commercial species that are normally found in the open ocean and on the coral reefs return annually to the mangrove creeks to spawn. Their larvae and juveniles which also include various prawn species, remain in these nursery areas protected by the stems, branches and roots of mangroves from predators and wave movement until they are
mature enough to move out to sea. Adult sea-mullet live and spawn at sea, but their fertilised eggs and larvae along with those of a variety of reef fish are swept into the mangroves where they develop through their early stages.
At low tide mudskippers and fiddler crabs emerge to graze on the nutrient rich mudflats. As the tide flow changes garfish and mullet feed on food caught by the flowing water, while large whelks and other shellfish feed on decomposing vegetation and a variety of small animals.
Surviving in salt water
Mangroves have special features that allow them to survive in salt water and deliver needed oxygen to their large root systems. Mangroves in common with some swamp plants have developed aerial root systems which form a radial pattern around the base of the tree.
These exposed roots allow the plant to absorb oxygen from the air and transport it down to the roots. The roots also act as stabilisers holding the plant erect in soft muddy conditions. The trees get rid of the salt that manages to invade their system by storing it in leaves that turn yellow and die. Another way is to excrete the salt out onto the surface of leaves where rain can wash it off.
Many mangroves germinate seedlings from their fruit while they are still attached to the parent plant. These mangroves are commonly referred to as“Viviparous”.
Seedlings can take as long as 12 months to fully develop, they then fall into the surrounding water and float on the high tide, coming to rest in a bare patch of mud where they send down roots and grow to maturity. Some seedlings can drift on the tides for many kilometres, establishing new colonies far from their origins.