Mangrove Forests | JONATHAN BIRD'S BLUE WORLD

Most people come here to yap in the middle of the Pacific Ocean, to dive on beautiful coral reefs and meet the manta rays. I noticed that 90% of the island is covered in these beautiful, lush mangrove forests. So I got special permission from the chief of Baychell Village to explore the mangroves. Hi, I'm Jonathan Bird and welcome to my world! Mangroves are a type of plant living in the tidal coastal areas between sea and land. All share the trait of being able to tolerate partial submersion in saltwater and poor oxygen content in the ground where their roots penetrate. Mangroves only grow in the tropics, like these rich mangrove forests in Yap. Mangroves are extremely important for several reasons. They serve as a buffer zone between the ocean and the shore. Their roots hold the shoreline together, limiting erosion and attenuating the waves. In effect, they form a protective barrier between the ocean and the land. Second and perhaps more importantly, mangroves serve as a refuge for marine life. The tangled maze of roots in the mangrove forest creates a confusing shallow water labyrinth. Taking refuge in this protective maze, many animals survive here when they couldn't survive anywhere else. The mangrove is a nursery for juvenile fish and invertebrates. In the protection of the calm, sheltered waters of the mangroves away from predators, the juvenile fish find food and safety. Without the mangrove nursery, life on the reefs would be in trouble. Mangroves live in saltwater, which is a tough environment for a plant. The roots are designed to soak up the water and exclude as much salt as possible in the process. They have little filters built into their cells. But the plants still take in a fair amount of salt, and they have to get rid of it or it will kill the tree. And they get rid of it by concentrating it in their leaves. Some mangrove trees excrete the salt out through the leaf as a crystal, which is then washed away by rain. You can taste the salt on the leaves. Other trees concentrate the salt in older leaves, which then turn yellow and fall off, taking the salt with them. All those leaves land in the water, sink to the bottom and decompose. The mud has a high concentration of bacteria to break down all the organic material. These bubbles on the bottom are mostly methane, the by-product of decomposition. The bacteria consume the leaves, releasing nutrients that wash out to sea every day on the receding tide. So the mangroves are an important food and nutrient source for animals and plants on the reefs and in the open ocean. Most trees have their roots completely underground. Mangrove trees have their roots coming up out of the water, into the air like this. That's because the soil down below the water here is a black muck that is high in bacteria, has very little oxygen in it, so the roots can't absorb any oxygen. So when they come up into the air, they absorb the oxygen directly through their skin. Partially submerged conditions in mangrove forests make it hard for traditional seeds to take root, so reproduction requires special seeds. This is a mangrove seed. The seed part is up here, but it has a long root already on it. When it falls off the tree, it floats like a cork with this part up and this part down. When it floats into shallow water, this part will go right into the soft bottom and the leaves will come out the top and you have an instant mangrove tree, ready to start growing. This adaptation allows a seed to take root in shallow water, with the root in the bottom and the leaves at the surface. Exploring the mangroves, I realize not only how fascinating this habitat is, but important as well. It's imperative that as coastal development continues, care is taken not to overlook the importance and beauty of the mangrove forests—the nurseries of the reefs. They are not just part of the land or part of the ocean, but a critically important link between these two worlds.