Squelchy mud. Tangled roots. Hot. Humid. Wet. Mangroves aren’t the most inviting ecosystem. But after a talk by our friends at EcoScience to celebrate World Wetlands Day, I’m definitely interested to take the plunge and learn more.
“Mangrove” refers to the habitat as well as the plants that live between the sea and land, flooded by sea tides. A mangrove may be a tree, a shrub, a palm, or a fern, but all of them are able to tolerate excess salt and air-less soils, coming together to form mangrove forests along coastlines, rivers and estuaries.
Originally from South East Asia, mangrove fruits, seeds and seedlings floated upon ocean currents, some for more than a year, before taking root in India, Africa, the Americas and Australia. 42% of mangrove forests found in Australia have taken root in the Territory, and comprise 32 different plant species.
Nineteen of these plant species can be found in Darwin Harbour, and all of them in the little patch that is Ludmilla Bay. They are joined by more than 150 species of molluscs, birds found nowhere else on Earth, more than 70 species of worms, and fish that shelter amongst the roots for breeding and nursing their young, including a Top End favourite, the barramundi. New species are still being discovered in our mangrove communities. But when some of these species, in particular a snail, are no bigger than 1.5 mm, it’s not surprising there are critters hiding in the mud and roots, waiting to be unearthed and unraveled. For those species that have been uncovered:
- There’s one species of ant that hides in air pockets as the tide rises, but if need be, can hold its breath for 3.5 hours!
- One gastropod can drill a hole through the shell of its prey. Its drill-like vice becomes a straw, as it slurps up the soft-bodied prey for consumption.
- A mud lobster, which is actually a shrimp and not a lobster, eats tiny pieces of organic matter in the mud. Mud lobsters have to process huge amounts to get enough nutrition, so mud is piled high around their burrow and can reach up to 3 metres!A tree climbing mangrove snail doesn’t like getting its shell wet. They climb trees one or two hours before the incoming tide. Once the waters recede, they shimmy down to feast upon anything left behind, like seagrasses.
- And there’s even a fish adapted to breathing air that will drown if held underwater!
Mangroves are globally threatened. 35% of the world’s mangroves are already gone and in some Asian countries, like India and the Philippines, they have been reduced by 50%. This has led to increased flooding and wider devastation from tropical cyclones. Our mangrove forests aren’t tall in comparison to some 30 metre giants in Asia, but they are our shield against cyclones, they bear the brunt of a storm’s wrath.
They are also drowning. Sea levels in the Top End are rising 7 mm every year. Mangrove forests are currently adapting by retreating and moving further inland. Animals are retreating with their favourite mangrove zone too, but will they keep pace?
Our mangroves in the Top End are considered to be the most pristine, globally. Together we need to ensure they stay that way; for the protection they offer our coastline, for the filtering service they provide our waters, for the nursery grounds they provide our favourite fish, and for all the weird and wonderful creatures that call our mangrove forests home.
If you missed this mangrove walk, stay tuned as another will be organised for mid-year. Come along, test your eyesight and see how many coin-size creatures you can spot.