Magical Mud and the Giant Sieve
Mud is all part of the mangrove experience.
In fact, its why many of us avoid the mangroves altogether - that and those annoying mosquitoes! Next to the flamboyance of our coral reefs, mangroves seem extremely unglamorous. Most people drive by them every-day and don't even cast them a second glance.
But it's unfair to judge mangroves at face value. There's something a little magical about sitting in a mangrove forest. In the stillness, qari emerge from their secret burrows to snatch at fallen leaves, a belo flaps it wings in the canopy overhead and flashes of silvery fish can be seen flitting through the drowned city of mangrove roots. To appreciate the worth of these odd-looking plants, we have to take time to look a little closer - beyond the mud and the mosquitoes.
Much like people, plants look for great real estate to take root, perhaps produce a few seeds and start a small brood of saplings that will live nearby and produce saplings of their own. For most plants, this 'utopia' is usually a place with lots of fresh water and nutrient-rich soil.
Space is limited and the best that most can manage is a few individuals living in a mixed community of plants - unless of course, a plant is innovative.
Mangroves have managed this so well that they are able to grow in areas where many other types of plants can't - where the land meets the sea. The extreme change in salt and tides, coupled with a suffocating, muddy substrate, make this area undesirable for most plants but provides the perfect opportunity/fit for mangroves to flourish undisturbed.
To survive in this shifting environment, these enterprising plants have developed some unique features. - one of these being their exposed roots. The thick mud below the plant does not hold much oxygen, so the roots are forced to break above the muddy surface like a 'snorkel' and take in oxygen directly from the surrounding air. The roots, which grow above the ground - are dotted with tiny 'lenticles' (a much fancier word for 'air vents') which help the plants breathe in the mud and water.
Another important function of this complex root system is to anchor them to the soft mud so that the plant can survive the ebb & flow of the tides. By intertwining its roots with other nearby mangrove plants, into a flexible matt of anchors, they are better able to withstand the waves, thereby reducing wave energy from direct impact on the coastline and protect the coastline from severe erosion. In many cases, beaches also form behind mangroves as waves become sluggish and deposit their sandy sediment.
Where mangroves grow in large numbers, this mass of tangled roots acts as a permeable barrier to waves - letting the water be carried through the root system but significantly slowing its flow. Any soil or heavy metal carried by the water, settles to the bottom, adding a fine layer of soft sediment to the muddy bottom. In this way, the mangrove roots act as a giant sieve - filtering the water of soil sediments, leaving the clearer water to travel further out into the coastal waters.
Clear water is linked to how plants make their food. Tiny algae in sea grass and corals are central to marine food chains. To grow, algae need sunlight and carbon-dioxide. After heavy rainfall, rivers often become choked with soil sediment and extend like long brown fingers far out to sea. A lot of sediment in the water creates a curtain, reducing the amount of sunlight that reaches the marine algae, affecting their ability to produce food. If this sediment settles off-shore, it could threaten the long-term health of the reef.
Our natural environment is not just a 'pretty face'. Every fish, every coral, every bird and every tree is part of an intricate web of inter- connecting parts. Each has a specific job to do in keeping balance within this system - a balance which has taken centuries to adapt to and perfect.
So the next time you pass by a mangrove swamp, don't scrunch your nose up at the pungent smell but rather reflect on the abundance of marine life within that supplies our fisheries, the complexity of mangrove mud and the genius of this amazing coastal plant.
This is the first article in a series supporting the National Mangrove Awareness Campaign in Fiji. Stephanie Robinson is the Coordinator of the AusAID Building Resilience to Climate Change Programme at WWF South Pacific.