Canopy Critters & Visiting Fauna
Australia’s mangroves provide key habitat for a diverse range of animals living in forest canopies. For instance, these canopies are home to pythons, tree snakes, lizards, spiders, innumerable insects, more than 16 species of ants, over 200 bird species, native rats, insectivorous bats, fruit bats and possums. New species and expanded distributional ranges are being found all the time. For instance, recent studies in Darwin Harbour identified 9 species of bats, at least 11 species of other mammals, 128 species of birds and around 3,000 species of invertebrates.
Like a number of these animals, some birds depend entirely on mangrove habitat for shelter, food, nesting and rearing their young. Many of these animals make significant contributions to mangrove forest structure and function. For instance, animal pollinators like bats, birds and insects, noted also in the section on floral adaptations, provide an essential service towards germination and successful regeneration of existing and new mangrove stands.
Other fauna like insect larvae, or caterpillars, consume leaf material and contribute to litter decomposition and recycling. Fruits are also infested and damaged by crabs, insects and rats, further affecting forest regenerative processes and aiding species selection, forest composition and structure.
Left - Flying foxes in Avicennia marina, bordering the Brisbane River estuary, Queensland.
- Leaves of Rhizophora stylosa being demolished by little green caterpillars.
- Shore birds roost in mangrove trees and feed amongst the roots.
Aquatic Fauna in the Muddy Mélange
Mangroves provide habitat also for a wide variety of aquatic animals and those living in the muddy sediments. These include saltwater crocodiles, molluscs, burrowing worms, polychaete mud worms, fish, various crustaceans and crabs. New species are still expected. For example, some authors suggest that about 20% of crab species in Australia’s mangroves remain unnamed.
In Darwin Harbour, a recent study identified 36 species of crustaceans and 31 species of molluscs. Other animals are less obvious, so it cannot be over-stated that there is still much to learn about the diversity of fauna in mangrove ecosystems. Another study of animals inhabiting decaying wood in mangrove forests in Australia found more than 120 species, including 17 species of insects, 16 species of crabs and polychaetes, and 12 species of ship worms.
Furthermore, sesarmid crabs have a keystone role in forest growth and development where they take large numbers of leaves below ground, aiding the retention and recycling of nutrients within mangrove forests. These leaves would otherwise have been flushed away and lost from the habitat with the next tide.
Some marine fauna are much better known, like the larger fishes, Barramundi and Mangrove Jack, that use mangroves during flooding tides. One unexpected faunal associate of mangroves are Green Turtles, Chelona mydas. These turtles on occasion eat mature fruits of Avicennia marina that they crop from the trees at high tide. Our knowledge of this important but novel activity is very limited, but it seems these turtles might also contribute to mangrove ecosystem processes.
Right - A healthy mud crab hunts amongst mangrove roots
- Crocodiles seem to love sunning themselves in stream edge Acanthus thickets.
- Grazing molluscs meander in the mud between the pneumatophores.