An ecosystem that switches from land to marine every single day...

(Vansittart Bay)

The term ‘Mangrove’ refers to both a type of plant and an ecosystem. They tend to develop best in muddy estuaries, but they can also grow right on tropical beaches. When they grow in stands they make up a distinctive, easily recognised ecosystem. Unusually among flowering trees and plants, mangroves are defined by their ability to grow in the tidal zone on the edge of the sea. The mangrove community is often also characterized by patterns of zonation, with certain species living on the landward edge, while others tend to live on the seaward side.

While different mangrove genera have evolved once or twice out of many different families, the family Rhizophoraceae is actually dominated by them. Most of the members of the family tend to have round, smooth, shiny, leathery leaves with a short point, and are bunched together at the end of the branches. There is often a long terminal stipule. Most species of Rhizophora, Ceriops, and Bruguiera produce the distinctive long cigar-like seedlings propagules.


Rhizophora are well known and recognizable mangroves. This is largely due to their often elaborate prop root systems. In other respects it is typical of the rest of the family in having shiny, roundish leaves bunched at the end of the stems, small flowers, and long seedlings that often begin to grow on the parent tree.

rhizophora-tree-bloomfield(Cowrie Beach, Bloomfield, Australia)

One of the largest and most obvious flowers belongs to the 'White Apple Mangrove', Sonneratia alba. These fluffy flowers attract birds (such as honeyeaters) and insects by day and bats and moths by night. 

sonneratia-flower-horizontal-waterfalls-Apple Mangrove flower, Horizontal Waterfalls, Australia

The genus Xylocarpus (that have large round hard fruits which also give them the common name of ‘Cannonball Mangroves’), includes the ''Deciduous Mangrove'. This common name refers to the habit of the leaves going distinct red-orange before falling off. The reddish colour is in strong contrast to the other consistent greens of other surrounding mangrove species, all of which are not seasonally deciduous.

mangrove-cedar-kimberleyThe 'Deciduous Mangrove', along the Prince Regent River, western Australia.

The most widespread mangrove in Australasia, and the most widespread internationally longitudinally, is the Avicennia marina, 'Grey Mangrove'. It is found along coasts in the Indo-Pacific; found as far south as New Zealand. The tree has roots spread out laterally and grow stick-like projections through the mud.

avicennia-bloomfieldthe widespread Grey Mangrove, (Bloomfield coast)

Some species of jellyfish swim up river to breed. In areas with large tidal ranges, the outgoing tide may resulting in jellyfish hanging from mangrove tree branches like plastic bags.

PrincefreerickSeaJellySea-Jelly (Prince Frederick Harbour, Western Australia)

There are not that many species of insects in the mangroves compared to the adjacent forests and savannas, but it sometimes feel like it if you are getting attacked by annoying midges or mosquitoes.

mosquito-biting-me-maroochydooreThe author getting bitten by a mosquito that is filling up my blood (image by Damon Ramsey)

However, crustaceans are a very diverse and important group in the mangroves. In many ways, crabs and their relatives are the ecological equivalent of insects and other invertebrates in the forests, and they fill in a range of niches and come in as range of forms. There are species that live on tree trunks, others on muddy banks, and some swimming in open water. They can be predators, scavengers and grazers.  

PrinceFrederickFiddler2Flame Fiddler Crab (Prince Frederick harbour)

There are over 40 species of mudskippers. They are found along the coasts of the tropical Indo-Pacific, from eastern Africa, through Asia and into the Pacific. They are not found in the Atlantic, except for one species that occurs on the western coast of Africa. They are absent from the Caribbean.

Mudskippers are truly amphibious, living partly in and partly out of the water. Different genera have varying levels of adaptation to living either in or out of the water. They are referred to as ‘mudskippers’, as they do indeed skip across the mud, with a flick of their tail. They also drag themselves along with their well developed and strong pectoral fins. Mudskippers have bimodal respiration, which means they can breathe both in the water (with gills) and in air. When on shore, like the unrelated frogs, they can perform cutaneous respiration, breathing through the skin, and through the lining in their mouth and throat. This requires that they stay moist, so mudskippers are never too far from water, and which is why they may be seen to occasionally roll in puddles. They also inflate the opercular chambers with air and so look like they have huge ‘chipmunk-like cheeks’. Another remarkable feature associated with their amphibious lifestyle are their bulbous eyes. These are huge for the size of the fish, and sit atop their head, giving them the potential for almost 360 degrees view. This helps them keep watch for movement of potential predators, such as kingfishers and egrets. The eyes can be completely sucked back into the eye socket to keep them moist

Crocodylus porosus, 'Indo-Pacific/Salt-water Crocodile' is the biggest crocodilian in the world, also largest of all living reptiles. Also known as ‘Estuarine Crocodile’ or ‘Indo-Pacific Crocodile’, the first name reflecting its preferred habitat of estuaries, and the latter name reflecting its large geographical range throughout tropical Asia and the Pacific. They are the top predator of the Australasian mangroves. Crocodiles use different senses to interact with their environment and detect prey. As they hunt mostly at night, their eyes are sensitive to light. As with many nocturnal animals, after light passes through the front of the eye, it is reflected back by a layer of guanine crystals in the tapetum at the rear of the eye, to allow light another pass. This also causes the orange-red ‘eyeshine’ of crocodiles when spotlighted at night. 

crocodile-red-coneIndo-Pacific Crocodile (Red Cone Creek, WA)

The family Scolopacidae includes the 'Sandpipers', many of which are in their drab non-breeding colours when in the mangroves. Many species feed on the edge of the mudflats outside of the mangroves, but the 'Common Sandpiper' Actitus hypoleucos is frequently seen inside this ecosystem. They are small and display a distinctive bobbing up and down movement.

sandpiper-common-hunter-riverCommon Sandpiper, (Hunter River, WA).

The group of birds most commonly noticed by visitors to the Australasian mangroves are no doubt the Herons of the family Ardeidae. The Herons range in size and colour. There is the skulking grey-coloured 'Mangrove Heron', the huge 'Great-billed Heron' and the 'Little Egret', the latter of which is one of a number of species that are white and called 'Egrets'. This name comes from France where it was popular for the women to wear the feathers of white herons in their hats; the southern French term for herons Aigron and then the diminutive Aigrette, gaves us the name 'Egret'. Ladies: just take the legs off the bird before you put it on your head in a hat, or you might get a toe in your eye. 

heron-mangrove-sunshineMangrove Heron
egret-little-hunter'Little Egret' (Hunter River, Western Australia).
princeFrederickGreatBilledheronGreat-billed Heron

The colourful jewels of the green and brown mangroves are the Kingfishers of the family Alcedinidae.

talbot-azure'Azure Kingfisher' (Talbot Bay).
PrinceFrederickSacredKingfisher'Sacred Kingfisher' (Prince Frederick).

There are not too many mammals in the mangroves. The most obvious ones are the Flying Fox, that often camp here to sleep during the day. Several types of cetaceans visit the edge of the mangroves, but one of the resident mammals at high tide are the 'Dugong'. These quiet mammals are a flesh coloured rather formless lump.


Places to experience the Australasian mangroves

Australia has the fourth largest amount of mangroves in the world (after Indonesia, Brazil and Nigeria), so there are plenty of places to explore this habitat. Many of this places are quite accessible, being alongside towns, such as Broome and Cairns. Along the east coast there are areas such as Etty Bay. One of the most pristine areas of mangroves in Australia is along the north-west coast in the Kimberley, including the large Prince Frederick Harbour.

For a short guided walk through the subtropical mangroves of south-east Queensland, Australia

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