Mangroves have enormous ecological significance, both to the functioning of the natural environment and to humans. As a coastal species, mangroves act as both barriers, preventing soil erosion and protecting inhabitants from storms, and biofilters for nutrients in upland runoff, such as nitrogen and phosphorous. Mangrove forests form the basis of a detrital food chain, where the fallen leaves provide coastal waters with much of their productivity. This high level of productivity contributes to the wide array of species that inhabit mangroves or use them as refuges, migration sites, and nurseries. Many threatened and endangered species inhabit mangrove forests, such as the Royal Bengal tigers, manatees, and sea turtles. Hundreds of bird species have been identified in mangrove forests, and many species of tropical and sub-tropical marine species, such as fish and crustaceans, spend some part of their lives in mangrove wetlands as juveniles. And the biodiversity doesn’t end there! Mangroves are also home to snakes, lizards, and insects – which are actually the most abundant (both in numbers and species) above the tide.
© Leo Thom – fisherman in the Sundarbans
In addition to their adaptation to salty conditions, mangroves have also evolved innovative reproductive strategies. Mangrove embryos grow directly on the parent tree, and are dropped as propagules only once fully developed. Some propagules may take root in the soil beneath the parent tree, but others may float for an extended period of time before anchoring to the shore.
Recent research has also indicated that mangroves are incredible carbon sinks, sequestering more carbon than any of their terrestrial counterparts. Mangrove forests sequester approximately 1.5 metric tons/hectare/yr of carbon, or 3.7 lbs/acre/day of carbon (1336 lbs/acre/yr). Mangrove substrate may contain 20-25% carbon, which may also help explain the high productivity and biodiversity of these ecosystems.
The provision of habitat for aquatic and terrestrial fauna and flora cannot be overlooked. Mangrove systems are critically important habitats for a wide range of aquatic species, including fish, shrimp, molluscs and crabs, providing nursery, feeding and refuge areas and underpinning coastal food webs that support many commercial harvests, local subsistence harvests, and other sustainable uses such as limited timber and firewood harvests, local medicine production and other important local uses.
Mangrove ecosystems are also important habitats for a wide range of birds and insect species, and lesser numbers of mammals and reptile species, providing nesting, feeding, and refuge areas.
Other ecosystem services provided by mangroves include:
- Guatemala Rhizophora aerial rootsprotection from strong winds & waves;
- Mangroves’ protective buffer zone helps shield coastlines from storm damage and wave action, minimizing damage to property and losses of life from hurricanes and storms.
- soil stabilization & erosion protection;
- The stability mangroves provide is essential for preventing shoreline erosion. By acting as buffers catching materials washed downstream, they help stabilize land elevation by sediment accretion, thereby balancing sediment loss. In regions where these coastal fringe forests have been cleared, tremendous problems of erosion and siltation have arisen.
- nutrient retention and water quality improvement through filtration of sediments and pollutants;
- Mangroves have been useful in treating effluent, as the plants absorb excess nitrates and phosphates, thereby preventing contamination of nearshore waters.
- flood mitigation;
- sequestration of carbon dioxide;
- Mangroves absorb carbon dioxide and store carbon in their sediments, thereby lessening the impacts of global warming; and
Protection of associated marine ecosystems
Sea grass beds and coral reefs depend on healthy mangroves to filter sediments and provide nursery grounds for resident species.
Traditional and indigenous coastal populations have found sustenance from mangroves, collecting products and resources in a sustainable manner for hundreds or even thousands of years, including:
- fibers & dyes
- construction materials