The Living Mud; The Rise and Fall of a Mangrove Forest ¦ Part 4 ¦ SLICE EARTH

Tide after tide, the new mud deposits are consolidated by the mucus the diatoms produce. Layer by layer, the level of the mudflats rises progressively. The frequency of flooding, which used to be regular, becomes more and more sporadic over shorter periods of time during the highest of spring tides. The surface of the mudflat changes drastically as it's being increasingly exposed to the sun and the wind. It dries out and starts to crackle. Desiccation cracks appear. It may seem like an insignificant detail, but this transformation will upset this ecosystem. Soon, these cracks will become traps and enable astonishing wetland trees to grow, which marks the birth of amphibious mangrove forests. The mangrove trees lining the mudflats form an extraordinary type of forest in which the trees feel perfectly at home on soft and salty soil, poor in oxygen. In French Guiana, the two dominant mangrove species along the seafront are the Avicennia and the Laguncularia. These trees have developed a remarkable system for reproducing and dispersing. Their fruits are hydrochorus. They float and survive for long periods of time at the surface of the water, which carries them away from shady areas where they would otherwise have no chance of developing since the leaves of fully grown trees intercept all the solar energy. The fruit is carried in by the rising tide, then transported out to sea during the ebb tide. It washes up further out on the mud flats exposed to direct sunlight, then gets picked up again, and so forth in a constant back and forth cycle. All the fruit? Not quite. Some of them will wash ashore for good and stay trapped in the desiccation cracks. As soon as the fruit makes contact with the soil, it opens up to allow the inner seed to develop. This seed is viviparis. It germinates while still inside the fruit, and there's a perfectly good reason for this. It needs to take root as quickly as possible to withstand the waves of the ocean's next offensive. The conditions are ideal for seeds to sprout. Sunlight acts as an energy source, plus they have access to water and organic matter stuck inside the mud cracks. In a matter of weeks, a new mangrove forest is born on the mudflat. These young, well-rooted mangrove trees are strong enough to withstand the impact of waves and currents, and in less than a year, they'll be producing new fruit. Millions of small shrubs crowd the space and create a whole new phenomenon to the mudflat – shade. Their leaves absorb almost all solar energy, and very few rays of sunlight are able to reach the ground. Consequences are radical. The now energy-deprived algae, source of the entire food chain, will be progressively eliminated. Their disappearance will cause the migration of all the species which depended on them to feed. Life is now slowly leaving this forest, composed of a single species of tree, the Avicennia. They all share the same origin and are exactly the same age. This extraordinary uniformity comes as a result of the very particular way in which the seeds develop after having been carried onto the mud flats by tides. Besides, the silt soil now contains very little oxygen as it is composed of compacted and hardened clay. There is no possible access to fresh air. To make up for the lack of oxygen, the Avicennia grow special breathing roots out of their main roots very early on as to take in oxygen from the atmosphere the same way divers use a snorkel. They are called pneumatophores, and they grow all over. Enters through tiny pores known as lenticels, which open up to let the oxygen in when they're out of water. In this mangrove forest, these thousands of identical trees are involved in a silent but fierce competition. It is about being the tallest before any other tree in order to benefit from more solar energy, water, and nutrients. The mangrove trees' incredible adaptations still aren't enough, because like any other plant, it needs water. Unfortunately, the seafront only offers salt water. In order to absorb this water, the mangrove trees produce tannins, a complex organic compound which helps them overcome the salt concentration around their roots. But as the water makes its way up to the leaves, the salinity of sap increases to the point that the stomatal pores should close up. Only the stomata, these microscopic organelles all over the leaves, are essential to photosynthesis and plant breathing, because they allow gas exchange to take place with the air. To prevent the stomata from closing up, mangrove trees have developed a seemingly simple but highly sophisticated response. Their leaves are covered in glands, which is how they get rid of excess salt and release it in the form of crystals. Rain pouring on the leaves finishes off the cleaning process. But the high concentration of tannins, which enables the trees to absorb salt water, has a major impact on the forest. Their leaves are extremely toxic, a highly effective strategy for protecting themselves from herbivores. In this mangrove forest, there's very little apparent life, only the sound of insects, a few birds chirping, and the wind rustling through the leaves. While just a few meters away on the mud flat, crabs and birds continue to swarm galore. Has animal life suddenly disappeared from this environment? Not entirely. An extremely rare, if not legendary mammal, for it can only be seen once in a blue moon, seems to find the resources it needs in the mangrove. The Virginia deer, also known as the whitetail. Against all odds, it feeds on mangrove leaves. The evolution of its digestive system and microbial flora has made it possible for the deer to digest the toxic substances supposed to protect the trees from herbivores. As a result, the presence of these animals attracts another mammal with a completely different diet, but equally difficult to observe. The jaguar, South America's largest wildcat. The mangrove is full of surprises. While the forest is known for providing shelter to shorebirds during high tide, it also turns out to be a great feeding spot for the flaming scarlet ibises. Most of the leaves and dead wood are trapped by the pneumatophores. The slow degradation of vegetation therefore takes place where it falls. Carbon gradually builds up in the surface layer of the soil, while nitrogen and phosphorus are released to enrich rainwater. During heavy rainfalls, These nutrients are washed down to the mudflat. Once again, the mangrove forest plays a crucial role. Thanks to their roots, mangrove trees are able to capture nitrogen and phosphorus from the depths of the soil, then release them once their leaves have decomposed, fertilizing the mudflats in the process. With its outstanding and undefeated capacity to adjust to dire conditions and after growing at lightning speed, the mangrove forest is now dying of old age. Throughout its lifetime, it has photosynthesized significant volumes of organic carbon out of atmospheric carbon dioxide. It has also provided copious amounts of nutrition for the mudflats, a powerful source of life. In the fight against global warming, mangrove forests all over the world serve as highly effective natural wells for trapping carbon from the atmosphere And helping life flourish by fertilizing mudflats, thus feeding shrimp, Fish and human beings alike. In addition, they constitute highly effective natural reefs against heavy swells and tsunamis. Mangroves must be preserved and protected at all costs.