Wednesday, June 6, 2007
Mud and Mangroves
Looking over the narrow bridge that spans Sandy Creek I realised it was almost time for LowTide Day as there was an unusually wide expanse of thick, deep, oozy mud along the creek bank, far wider than I had seen before. LowTide Day is significant as it commemorates the day with the lowest tide around the globe.
The LowTide event was started in 1995 by the organisation riverOcean Foundation located in southern England. It is a recognition of the intimate connection between river and ocean, salt and fresh water, and the incoming-outflowing movement of the tides. All round the UK coast, on the continent and in other coastal areas in different places around the world, communities organise discovery walks, rock pool rambles, local 'fayres', and run workshops on habitat restoration, sustainable fishing and marine and coastal conservation.
Through exploring the intertidal zone, experiencing the ebb and flow of the tides, and learning about the delicate balance of coastal and riverine ecosystems, local communities celebrate the pull of the moon and sun on the interflow of waters from one side of the planet to the other.
Witnessing the rhythmic movement of tides along Sandy Creek and the Brisbane River puts me in touch with this global event, where patterns of life, human, land and water, intermingle and flourish. Places like this where diverse ecosystems meet are known as 'ecotones', in-between spaces of rich abundance and high fecundity where plants and animals have learned to adapt and thrive amongst the constant interchange of fresh and salt waters.
One of the most amazing of plants that survives within this edgy transition zone is the mangrove. These very clever trees live in the saltiest of environments. How? One way is through their super-smart leaves which can excrete the salt that has accumulated in the trunk and roots, while other mangrove species are able to prevent the salt from entering their systems.
The salty terrain has also created a unique form of mangrove propagation known as viviparity (bringing forth live young). After pollination, the seeds, which would die in saltwater, germinate and develop into seedlings while still attached to the parent plant. Eventually these seedlings (or propogules) drop off the trunk, sink into mud and take root. And the roots of mangroves are its other very clever function. They reach upwards, exposed to the air because the swampy conditions create an anerobic environment that stifles oxygen reaching the tree-roots.
The mangroves act as a buffer, a permeable boundary between water and land. Like environmental sentinels they protect the land from potentially devastating and surging waters. Studies on the effect of tsunamis and hurricanes in coastal areas show that mangrove forests, as well as fringing coral reefs, help to moderate the overwhelming effects of severe ocean and coastal storms by providing what's described as a bioshield.
But overdevelopment, the growth of coastal tourism, widespread agriculture and the explosion of aquaculture projects have placed tremendous presssure on the mangrove tidal zone. For example, the Science and Development Network reports that 'mangrove replanting programmes in India and Indonesia are struggling in the face of pressure from developers wanting to build shrimp farms'.
In this mangrove microcosm along the Brisbane River, there is also the threat of development in the air. Condominiums are mooted. The community is fighting back. All along the river freeways and high rise apartment blocks have encroached the wild spaces, so this tiny fragment of bush is precious and needs to be cared for.
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