Written by Christel Schultz
Putting down roots in changing tides and shifting sands is just part of coastal living. The transition zone between land and sea is a highly dynamic environment. Adapting to these conditions is necessary for survival. Mangroves have seemingly mastered this “double life” – they don’t just survive, they thrive!
Mangroves forests are found in or near water in coastal areas around the world. These trees and shrubs possess specialized root systems specific to their habitat. Aerial roots elevate the trunk and leaves above the water, allowing the plant to breathe. They create an anchor network, providing stability in a constantly shifting environment. The roots filter salt based on water conditions. Some species even exude salt crystals through their leaves.
There are over 50,000 square miles of mangrove forests in warm ocean waters along several continents. Mangroves are prevalent from Florida down the Atlantic coast of South America, around Australia and New Zealand, even Africa. They also grow in areas of Asia, India, and Burma. Some flourish in fresh or brackish (mix of fresh and salt) water. Thought to be the largest of its kind, the Sundarbans Forest is located at the mouth of the Ganges, Brahmaputra, and Megha Rivers in the Bay of Bengal. This area covers approximately 3,860 square miles and is recognized by the United Nations Educational, Scientific, and Cultural Organization (UNESCO) as a World Heritage Site.
Taking care of the neighborhood on and offshore
No matter the size, mangrove forests perform a number functions vital to the surrounding habitats and communities. These unique ecosystems are rich in biodiversity. A variety of marine life including shrimp, fish, and several species of sharks, use the mangrove root system as a nursery. A large volume of food in the form of smaller fish, organic matter, and even bacteria is available. Juveniles can safely roam around without the threat of larger predators. A healthy mangrove forest promotes an abundance of adult fish in the neighboring waters.
The complex root system does more than provide shelter and food for young animals. Soils from land, along with sand and silt particles in the water, become trapped in the root system. Nutrients in runoff may also be absorbed, preventing excessive plant growth detrimental to the ecosystem balance. Coastal erosion is thus minimized and the water is filtered. This is particularly important near coral reefs and seagrass beds where sediment deposits can choke out sunlight, prevent oxygen absorption and cause extensive damage.
Because mangroves are specially designed for their environment, they can withstand an array of weather conditions. Tropical storms, massive hurricanes and typhoons occur in coastal areas where mangrove forests are found. The dense mangrove network provides a great level of stability and resilience. The mangroves provide a significant level of protection by absorbing much of the wave action that would otherwise directly impact the coastline.
The mangroves also absorb and store carbon particularly well. They extract carbon from carbon dioxide to grow. When the leaves and old trees ultimately die, they fall down and decay. The stored carbon then becomes part of the saturated soils. Because sediment tends to accumulate in the mangrove root system, the carbon may be stored for centuries. Mangroves are responsible for 10 to 15% of carbon burial even though they comprise less than 2% of marine environments. One acre of mangrove forest can store about 1,450 pounds of carbon per year. This buried carbon stored underwater in coastal ecosystems is known as “blue carbon”.
Challenges facing the forest
Like rainforests and coral reef systems, mangroves are plagued by human impacts including deforestation and coastal development. Large tracts of land may be cleared for timber, agriculture, establishment of shipping ports and harbors. Removal of mangrove forests releases mass amounts of stored carbon back into the atmosphere. Construction and development along the coast often occurs quickly with little concern for impacts to the surrounding area. Dredging activities and large volumes of runoff can alter a habitat beyond its ability to rebound.
Hope for the future…
The importance of mangrove forests has become more recognized. Many countries have implemented laws to protect existing forests. Restoration and conservation programs like Mangroves for the Future and the Mangrove Alliance have been established. Various restoration methods have been tried, and the most effective techniques developed. After many failed attempts to reestablish growth, it was determined that mangrove seedlings do best when they are submerged for 30% of the time and dry for the remaining 70%. Robin Lewis discovered this in 1986 during restoration activities in Florida, and his method of planting has been successfully repeated in several countries. Educating locals about the importance of mangroves also encourages reforestation. Coastal communities can then sustain the environment that provides their home, food source and economy for the long term.