What are Mangroves?
Mangroves are woody trees and shrubs that form dense, low-growing forests in coastal areas. These plants occur in the intertidal zone; an area of the coastline where water levels fluctuate because of changing tides. They are considered to be terrestrial plants that have the unique ability to thrive on the edge of the marine environment where salty soil typically dehydrates plant tissues, and seawater floods the soil, making it unstable for plant roots to grow. Nevertheless, over evolutionary time, mangroves have adapted to thrive in and around the intertidal zone where most other plants cannot.
So what is really important about mangrove forests? Sure, they’re unique, but why should people care? Because these plants are adapted to grow under conditions that are too harsh for other terrestrial species, they provide a number of extremely important ecosystem services that most other plants cannot. Ecosystem services are functions of the natural environment that benefit the lives of human beings and promote a healthier planet. The ecosystem services listed below reveal the significance of mangrove conservation and are just a few ways these forests contribute to the stability of our changing world.
Mangroves all over the world are threatened due to rapid coastal development which has stripped away important habitat. Many trees and forests have been uprooted leaving areas of land exposed and forcing thousands of species to find a new home.
1. Critical Habitat for Terrestrial and Marine Species
The upper reaches of mangrove forests form a canopy of leaves and branches that provides an important space for numerous bird species, including herons, egrets, ibis, spoonbill, and some migratory birds, to nest and breed. Certain species of monkey and tree climbing crabs also take advantage of this leafy home to find food and shelter.
At the base of the mangrove forest, a specialized root system extends into the soil, and in the case of the red mangrove, Rhizophora mangle, its prop roots stretch into the water column to create protective nursery habitat for larvae and juveniles of many marine organisms. Commercial species including shrimp, crabs, snapper, and surgeonfish rely on mangrove roots for a safe secluded environment to reproduce and deposit their eggs. Hatched and developing young benefit from the safety of mangrove roots that serve as a way to hide from predators, and offer a hard surface for small sponges and barnacles to attach.
A surprising number of marine animals that live among mangrove roots are actually considered to be reef and seagrass species because once they become young adults, many fish, crustaceans, and snails, will leave the safety and comfort of mangroves to complete the rest of their lifecycle on the barrier reef or nestled in seagrass. It is important to understand how animals are changing over the course of their life and moving between habitat types because without the healthy growth of mangroves, many animals that contribute to the biodiversity of seagrass beds and coral reefs would lack a safe place to begin their life.
2. Prevention of Erosion
Mangroves prevent erosion by structuring the soil and building up land area, but exactly how are these plants able to do this?
Because the soil in coastal areas is water-logged and soggy, it is unstable and requires support to remain intact. The roots of mangroves do just that, and create a network that holds soil particles in place. This provides critical stability to the surrounding environment. Without mangrove roots acting as anchors in the sediment, coastal areas would be more vulnerable to erosion.
In addition, the growth of mangroves reduces the flow of water because their mass interrupts the movement of currents. By slowing current speeds, mangroves encourage material in the water column like sand, silt, or clay, to concentrate around their roots and settle. Overtime, the settling of these particles builds up additional land area. By maintaining the structural integrity of the soil and accumulating land area, mangroves promote a healthy future for coastlines around the world that are presently threatened by sea level rise.
Protection from Storms
Mangroves are also great at absorbing energy from large waves and storms that would otherwise strip away coastal areas, thus damaging local development and wildlife. These forests act as a buffer against generous amounts of wind and strong waves that accompany environmental hazards such as tropical storms and hurricanes.
The removal of and damage to mangrove forests exposes areas of the coastline that are vulnerable without them including coastal cities and towns, private homes, and all kinds of terrestrial habitat. As our climate continues to change and temperatures increase, hurricanes are becoming more intense and frequent. More than ever, we need the help of mangroves to protect our coasts, and subsequently the livelihoods of many people who live in these areas, like Roatan.
3. Water Quality and Filtration
Mangroves influence the quality of seawater in three main ways; directly through the
structure and function of their roots, and indirectly by promoting the growth of other water-filtering organisms.
The ability of mangrove roots to slow current speeds and effectively settle drifting particles improves water clarity for important photosynthesizers who require an abundance of sunlight to penetrate the water column. Photosynthesizers that occur adjacent to mangroves and benefit from clear water include seagrasses and corals.
Function of their roots
In addition, the roots of mangroves influence the quality of seawater by filtering nutrients and pollutants. Specialized tissues are able to absorb excess nutrients and toxins like heavy metals. This is important because in many aquatic systems a surplus of nutrients from run-off called eutrophication may cause damage to ecosystems, and toxins like metals can concentrate inside living organisms and can kill or seriously harm those individuals. Because we rely on fish, molluscs, and crustaceans as a major source of food, we may ingest these harmful metals and compounds by eating polluted animal tissues. The good news is, mangroves play a role in filtering toxins and minimizing the effects of these metals and other hazardous compounds. By protecting mangroves we allow them to clean our seawater and protect our daily health.
Growth of other water-filtering organisms - Oyster Reefs
A unique way mangrove forests indirectly control water quality is by promoting the growth of filter feeders like oysters, whose microscopic larvae require the conditions near mangrove roots to settle on the muddy bottom and begin to grow. Oyster reefs and beds are associated with mangroves and play an important role in maintaining the quality of seawater because these molluscs are also able to filter pollutants and clear sediment particles from the water column. Healthy mangroves means abundant oyster populations, and oysters mean cleaner, clearer water.
4. Reduction of GreenHouse Gases
Mangroves are photosynthetic organisms, and like all other plants they absorb carbon dioxide (CO2) through their leaves in order to produce oxygen. When CO2 is removed from the atmosphere by mangroves it becomes concentrated in their roots, and may be stored in the soil for long periods of time. The storage of CO2 is called carbon sequestration, and mangrove forests like all other forests have the ability to sequester tonnes from the atmosphere each day.
Carbon storage in the marine environment is called blue carbon, and is a promising way nature can combat excessive greenhouse gas emissions of atmospheric CO2. The removal of CO2 from the atmosphere is important because it helps to reduce the effects of climate change and global warming. Maintaining and restoring coastlines inhabited by mangroves is becoming more important each day, and scientists believe these unique and resilient plants can lead us into a greener, cleaner future.
What can YOU DO to help?
In Roatan there are several opportunities to learn about mangroves and help forests thrive.
Schedule an environmental talk for your school or business, Contact us
Go online and research the importance of mangroves
Spread the word!
Written by: Grace Iverson