Mangroves of Toondah Harbour

Grey mangroves at the edge of Cassim Island.

I love mangroves. I find them to be fascinating examples of adaptation, and admire the way they shape and influence entire coastlines and ecosystems. 

Salt crystals on a yellow mangrove leaf.

Here in South-east Queensland, we have seven species of them (eight, if you count a species of fern), so I also appreciate how beginner-friendly they are when it comes to plant identification, as there are not too many to sort through.

Unfortunately, despite their immense environmental and economic value, mangroves are sadly not championed by the general public in the same way that rainforests, coral reefs and other ecosystems are. Governments and developers use this to their advantage, feeling comfortable in destroying coastal wetlands for the sake of marinas, canal estates and the like. A situation just like this is currently playing out in Cleveland, where a proposed development threatens Toondah Harbour and surrounds.

Swamp tiger (Danaus affinis) on a river mangrove.

This blog post examines the different mangrove species that can be seen in the Toondah Harbour area, and provides tips on how to tell them apart, but may also be useful for other mangrove communities in South-east Queensland. 

Grey mangrove (Avicennia marina)
This is the most common local mangrove, a beautiful, spreading tree with olive-green leaves and pale, whitish-grey bark. Like many mangroves, it has special above-ground roots that increase the amount of surface area exposed to essential atmospheric gases. For this particular species, these roots look like a dense carpet of little grey fingers; next time you see the roots out on a mudflat, look at the distance between them and the tree they belong to—it can be quite considerable!

Grey mangrove leaves; INSET: above-ground roots

The fruit of this species is a walnut-sized, green capsule that can be seen floating throughout Moreton Bay. The tree itself is abundant at Toondah Harbour and grows around all the bay islands, including Cassim Island. It provides shelter for roosting birds, and acts as a nursery for fish species around which multi-million dollar industries are based.

Red mangrove (Rhizophora stylosa)
This is my favourite mangrove, thanks to the amazing stilt roots that arch out from the tree trunk! No other local species of mangrove has roots quite like it, but if you want to double check that you’ve got the ID correct, look under the thick fleshy leaves and you should see lots of tiny little spots.

Red mangrove, Oyster Point; INSET: leaf detail.

To my mind, this is the quintessential ‘tropical’ mangrove, and when the tide is in around those beautiful roots, I almost half expect to see a box jellyfish or saltwater crocodile swimming amongst them!

At Toondah Harbour, this species mixes in with the grey mangrove and is fairly common, even growing on the side of the vehicle ferry ramp. Elsewhere in our local area, the red mangrove frequents sandy river banks in places like Noosa and Tweed Heads.

River mangrove (Aegiceras corniculatum)
As the name implies, this species is common along the tidal reaches of rivers, but at Toondah Harbour, it also grows in dense thickets on the claypan behind Nandeebie Park. 

River mangrove flowers allegedly smell like rotting bananas!

River mangroves can be recognised by their thick and shrubby growth form and oval leaves, as well as by their abundant white flowers that appear in spring and summer. 

Orange mangrove (Bruguiera gymnorhiza)
This is a beautiful and strange mangrove, because its appearance makes it seem as though someone has planted a lush rainforest tree in the wrong environment. In fact, one of my first encounters with this tree along the Maroochy River led me to believe I was seeing a fig, thanks to the thick green leaves, stipules and scarred branches. This tree can also be recognised by its peculiar, red, ‘plastic-looking’ flowers. 

Orange mangrove leaf and flower close-up.

At Toondah Harbour, I found only a small example of this tree near the edge of the saltmarsh, but larger specimens grow out on bay islands like Karragarra.

Orange mangrove growing at the edge of the saltmarsh near Nandeebie Park.

An interesting fact that changed the way I thought of mangroves is that few of the trees are closely related, and the word ‘mangrove’ is simply an ecological term in much the same way that rainforest is. With this in mind, the beautiful fern (Acrostichum speciosum) that grows in tidal wetlands can also be referred to as a mangrove, and it too can be found at Toondah Harbour.

Yellow mangrove (Ceriops tagal)
There is an area around the margin of most mangrove wetlands where sedges and grasses can grow thanks to the slightly less salty conditions, and this is where the yellow mangrove is found. It is usually a small shrub, with yellowish-green leaves that point upwards. The base of the plant flanges out in a chunky little buttress shape.

Yellow mangrove at the bottom right, with grey mangroves behind and to the left.

Milky mangrove (Excoecaria agallocha)
The mangrove which seems to tolerate tidal inundation the least in South-east Queensland is the milky mangrove. It grows in dry sand, often in the company of trees not considered to be mangroves, such as the beach hibiscus (Hibiscus tiliaceus) and tuckeroo (Cupaniopsis anacardioides).

Milky mangrove leaf detail.

The milky mangrove can grow fairly tall, and the specimens at Toondah Harbour (adjacent to the footpath near Oyster Point) are about six or seven metres in height. 

The leaves seem to point in all directions off the stem, and the ID can be confirmed by plucking a leaf to see a milky-white poison form where the tissue has broken. Take care around this tree: Aboriginal people have a name for it that translates as ‘blind-your-eye’, and it can blister sensitive skin.

Close-up of the poisonous white latex on a milky mangrove leaf.

There is one other mangrove species found in South-east Queensland called the black mangrove (Lumnitzera racemosa). It is at the southern limit of its distribution in the Redlands and I have never seen it for myself, but it may occur at Toondah Harbour. It grows as a small shrub with leaves that have a distinctive notched tip.

Once the different varieties of mangroves can be told apart, their ecosystem suddenly has much more character and nuance. The next time you find yourself at Toondah Harbour, or at one of South-east Queensland’s other coastal wetlands, I hope you take a second look at these remarkable plants and let your newfound knowledge form a connection to them.

Red mangrove, growing beside the ferry terminal at Toondah Harbour.