What exactly is a Mangrove?
A mangrove is a tree or shrub species that lives along rivers, ocean shores, or estuaries in the tropics and subtropics. These trees are also classified as halophytes, or plants that thrive in salty conditions. They are able to grow in environments that many plants would never be able to survive in, living in water that is 100 times higher in salt content than other plants can tolerate. Saltiness aside, they are also able to survive two floods a day, where most trees would die simply from the excessive water. Mangroves are most commonly found in mud, sand, peat, and coral rock grounds. Mangroves are fast growing trees that can reach up to 25 meters in just a few years.
Types of Mangroves
Currently, there are 80 known species of mangroves, 60 of which are only found coasts between high and low tide lines. Multiple species of mangroves can be found dwelling in a mangrove forest in their own niches. Some mangroves, those that can handle complete tidal soakings, can be found completely submerged within the open sea. Others thrive in drier, more salty environments are typically found further away from the shoreline. The rest of the species can be found living along riverbanks much further inland, only as long as the freshwater is met by the tides from the ocean. Of the seven major types of Mangroves, there are three dominant ones. These include the red, black and white types. These three species combined work to stabilize shorelines. provide buffers from storm surges, capture debris, and provide essential breeding grounds for a wide variety of marine and terrestrial life.
Red Mangroves ‘Red Mango’ (Rhizophora mangle)
Rhizophora mangle (red mangrove) by James St. John under CC BY 2.0.
Red mangroves are most typically found closet to the oceans and can be identified by their prop root system. Prop roots are there to stabilize the tree and are also called stilt roots because they allow the the tree to rise above the water line. These roots also contain a waxy substance that helps to keep the salt from the water out. The seeds of red mangroves need about 16 to 30 months to mature into seedlings before being released from the mother tree. These types of mangroves are also very sensitive to cutting and trimming. If approximately more than 50% of the trees leaves are removed, the tree will in turn die. Red mangroves are commonly cut down for their bark which is used in leatherwork.
Black Mangroves ‘Courida’ (Avicenna germinas)
Black-Mangrove pneumatophores by Homer Edward Price under CC BY 2.0.
Black mangroves can easily be identified by their protruding roots which are specifically designed for oxygen uptake. These roots can still intake oxygen even when completely submerged. This type grows well in high saline areas and are most commonly found living in isolated groups or forests. Black mangroves produce large amounts of seeds annually and are viviparous plants. By definition, viviparous means the seeds germinate while still attached to the parent trees. The seeds are typically viable for up to a year after they are released. These trees are very hardy and are able to excrete their absorbed salt they absorbed from their thick leaves. Their name comes from the color of their trunk and heartwood. Black mangroves typically grow in areas just above high tide. They are considered to be the most important type of mangrove and because of that, they are typically the most common in many areas. Their seeds, when cooked properly can be edible and placed in a delicious meal.
White Mangroves (Laguncularia racemosa)
White Mangroves by Katja Schulz under CC BY 2.0.
White mangroves are the shortest species of mangroves in comparison to the other two types described here. They are also the most “terrestrial looking” since their roots cannot be seen. As seen in the diagram above, this type is typically found furthest back from the tide line in marshes and swamps. Their leaves are adapted with “glands” that allow for the passage of salt water from inside the tree to outside. The leaves are often coated with white salt crystals, which is where the trees get their common name from. These seedlings are thrown off the seed-shell and then become photosynthetic above the around, relatively close to the trunks. The white type coppices very well in comparison to the red and black mangroves.
Why are they so important?
Briefly mentioned earlier, mangroves are essential breedings grounds for many coral dwelling species, as well as providing an irreplaceable home for many birds, mammals, and other wildlife. These trees also have the ability to increase water quality and remove pollution by filtering material. Of late, many mangroves forests are being removed to build shore front properties, resorts and other vacation spots and commercial use. Mangrove areas dwelling close to these properties are also often removed because they are thought of as being gross, swamp like, and non-ascetically pleasing pieces of land. Many of the individuals removing these glorious environments don’t understand the level of importance they provide to so many species, including our own.
These trees are the foundation of the complex marine food chains and detrital food cycle. Mangroves are close to the beginning of the food cycle, starting with the dropping of their leaves. Once their leaves fall, fungi and bacteria are able to immediately move in and colonize, therefor converting difficult to digest carbon compounds into nitrogen rich detritus material. This then turns to food for small animals such as worms, snails, shrimp,mussels, etc. These small organisms then serve as food for crabs, fish, followed by birds and other larger carnivores. Many species that rely on the existence of mangroves are currently endangered or threatened. Mangroves also provide great protection from the storm surges and other environmental factors.
Food chain by Google Image under public domain.
Another major importance of thriving mangroves, specifically the red prop root type, is the habitat for fish species and other invertebrates they provide. Data research now shows that prop root environments are equally if not more important for juveniles than sea grass beds in relative areas. Many fish lay their eggs within the entangled roots of mangroves and they are able to obtain the necessary nutrients in these areas. Mangroves also provide shelter for these growing organisms. Their roots systems are often complex and intertwined, meaning larger predators are not able to access them.
Among the mangroves, Utila, Honduras by Dave C. under CC BY 2.0.
What effects does removing them have?
More than 35% of the worlds mangroves are already gone. Many people find them to be either gross, or smelly, which is why they typically remove them for either agricultural, tourist, or other human wishes. Mangroves are also commonly cut down and used as firewood, construction wood, wood chips, and many other reasons. Although harvesting has been going on for years, most of the time now, it is no longer sustainable. Damns and irrigation also have huge, negative effects on mangroves by reducing the amount of water reach the trees as well as the sanitation of the water. If freshwater gets into the mangroves, this can also cause the mangroves to dry out. Over fishing also has extremely negative effects on mangrove forests, as described in Jaime Marsh’s post Unsustainable Fishing. The destruction of coral reefs also has an affect on mangrove populations. When coral reefs are destroyed, so is the first line of defense for strong waves and currents. This then removes many of the needed nutrients found in the sediment that the trees need to grow as well as wash away the seedlings mangroves will drop. Another agricultural affect is the use of pesticides and pollutants. Climate change, affecting most of the world, also affects mangroves. Climate changes makes unstable sea levels, making the trees very sensitive to change. The negative affects of climate change is better described in Haley Zanga’s post Is Global Warming Real? All of these factors contribute to the loss of mangroves, which are essential breeding grounds, but further serving as the foundation of marine life web systems.
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