knee roots of orange mangrove

Maroochy Wetland Sanctuary

The word “swamp” brings to mind all manner of oozy and disgusting things, but mangrove “swamps” are one of my favourite ecosystems. So much so that I spent the Honours year of my Science degree doing a research project on mangrove ecology. If you share my enthusiasm for tidal wetlands, the Maroochy Wetland Sanctuary and Bilai Environmental Education Centre in Bli Bli is a wonderful place to visit.

I took my Mum to the Sanctuary on a hot, hot summer weekend. It was pretty quiet that weekend. I think everyone else was at the beach or hanging out somewhere air-conditioned. We only saw 6 other people, including the volunteer at the education centre.

Mum and I were both quite impressed with the Education Centre. They’ve packed a lot of interesting displays into a fairly small space. The big display case in the middle of the room holds a multitude of fascinating objects. Make sure you open each of the drawers to find everything inside.

The microscope is fantastic. There are samples of snake skin, leaves, feathers and other bits and pieces that you can look at under the microscope, which displays on the large monitor on the wall. You could also bring back any treasures you find along the way and look at them, too. I know what I want for Christmas this year!

In one corner, there’s a wall of rotating boxes and an array of buttons that switch on recordings of local birds. I’m sure kids would have just as much fun as I did pressing all the buttons to hear and compare bird calls for all the local species.

Before you leave the Education Centre there are two things you absolutely must do: make use of the complimentary Aerogard and grab a copy of the self-guided walk brochure that the Maroochy Wetlands Sanctuary Support Group has put together.

A boardwalk winds its way through a variety of coastal ecosystems including wet eucalypt forest, open casuarina forest and mangrove shrub land to end at a pontoon on the Maroochy River. The board walk is 2m wide and is fully wheelchair accessible for the entire 900m path. It’s a flat, even surface that would allow any one to be able to explore the Sanctuary.

As you walk along the boardwalk, keep an eye out for the numbered tiles at the edges. Each number corresponds to a site description in the self guided walk brochure. There is a lot of interesting information in the brochure. I learned that “bilai” is the aboriginal word for Casuarina glauca, the swamp she-oak that you will see along the way. To make plurals they repeat the word, so bilai bilai means many swamp she-oaks and this is where the local area of Bli Bli gets its name.

You’ve probably seen Hibiscus tileacous (cotton tree) in the parks along the Maroochy River. There are some particularly big old trees in the park at Cotton Tree and kids love climbing them. But here in the Sanctuary, the cotton trees are quite tall and spindly because they are in a forest environment and have to grow upward to compete for sunlight. Their leaves have so many holes in them from being eaten by caterpillars and beetles that they look like lace.

Hibiscus tiliaceous (cotton tree)

Through the casuarina forest and into the landward edge of the mangrove forest you’ll walk through an extensive stand of Acrostichum speciosum (mangrove fern). This is the only fern that grows on the floor of mangrove forests. The fronds are very long, so the ferns can grow to about 2m high. It’s quite amazing to see such thick expanses of them.

I find mangrove ecosystems fascinating because they are so different from any other type of ecosystem. They are found in the inter-tidal zone, right on the edge between the land and the sea, and have characteristics of both land and marine environments. It’s a challenging place for plants to live, and mangroves have some quirky features that have adapted them to live there.

Mangroves are extremely salt tolerant. They can happily grow in salt water environments that would kill most other plants. Some mangroves, like Aegiceras corniculatum (river mangrove) and Avicennia Marina (grey mangrove), have salt glands in their leaves. These mangroves take up salty water and secrete the salt through the glands on their leaves. You can see salt crystals on the Aegiceras leaves in the photo above. Some mangroves can also accumulate the salt in their leaves until the leaves die and fall off and others can take up water while preventing the entry of salt through their roots.

The way that mangroves produce “seeds” is also quite different to most other plants. In many (but not all) mangrove species, the seed actually germinates while it is still on the tree, forming large and buoyant propagules. When they fall off the parent tree the propagules float away on the tide allowing the species to disperse into new areas. When the propagule washes up in a suitable location, its large size and advanced state of development allows the mangrove seedling to establish very quickly.

The intertidal zone is very wet. At high tide everything is under water and even at low tide the soil is wet and boggy. Most plants would die in waterlogged conditions like this, but mangroves have adaptations that allow their roots to “breathe”. Brugiera gymnorhiza (orange mangrove) has “knee roots”. These knobbly roots grow up out of the soil and then down again. Avicennia marina (grey mangrove) has pneumatophores, thin roots that stick straight up in the air. There are other types of mangrove roots, but these are the main ones you’ll see in the Sanctuary.

The knee roots and pneumatophores act like snorkels. They hold part of the mangrove’s root system out of the soil so that, even though most of the root system is still in the waterlogged soil, at low tide the roots can get air. These roots also have special cells called lenticels and aerenchyma that help them to take in air.

If you take the bird hide loop of the boardwalk you will come to a platform that has bench seats and a tall slatted timber wall. This wall is the hide. It will keep you camouflaged from birds and crabs feeding on the banks of the waterway. It’s a nice shady spot to stop for a while and watch the crabs darting in and out of their holes.

Along this section of the boardwalk you’ll see a grassy area of Sporobolus virginicus (salt water couch). The self guided walk brochure says that you might see swamp wallabies grazing here. We weren’t lucky enough to see any, but it’s worth keeping an eye out for them.

At the very end of the boardwalk you will come to a pontoon on the Maroochy River. If you look north (to the left), you can see Mount Coolum. This is a lovely place to sit and watch the boats go by and you might be luck and see one of the many water birds that live in the area.

Accessibility

The entire site is very accessible. There are ramps to access the Environmental Education Centre and the toilet block. The boardwalk is 2m in width, has a very even surface and extends the full 900m distance out to the pontoon. The pontoon can be accessed by a ramp although care should be taken if you go onto the pontoon as there are no rails or barriers on the edges.

How to get there

From Bli Bli, turn off David Low Way at the round about near Sunshine Castle and follow Bli Bli Road. The rest of the way is quite well signed, so keep an eye out for the brown tourist signs. At the next round about turn into Willis Road, then turn right into Lefoes Road. Turn right into Sports Road at the sports ground and follow this all the way to the Maroochy Wetland Sanctuary car park.

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