What are Mangroves?
Mangroves are not a single species of plant, but a collection of trees and shrubs that grow in coastal areas in tropical and subtropical climates. Their tangled roots grow above and below ground, forming dense thickets that are home to a huge variety of plants and animals.
Mangrove forests are among the world’s most productive ecosystems, providing food security, valuable timber production and coastal erosion defence, and are one of the most efficient and important carbon stores on the planet.
Where do mangroves grow?
Mangroves are halophytes, which means they are salt-tolerant plants that grow in waters with high salinity. Only two per cent of the world’s plants are halophytes.
They grow particularly well in brackish water, where salt water and freshwater bodies meet, and where the sediment has a high mud content. They can also survive in areas where seawater is highly concentrated, due to evaporation.
Mangroves are found in all the world’s equatorial regions. The largest population is in Indonesia, where mangrove trees cover around 23,000 square kilometres (14,000 square miles).
However, as average global temperatures rise, mangroves are also beginning to expand their range beyond the equator.
Why are mangroves so important?
Mangroves can absorb and store up to four times as much carbon in their root systems as mature tropical rainforests, according to a 2011 study in Nature Geoscience, making them a hugely valuable natural resource and key to combatting climate change.
The underwater habitat created by the mangrove roots, provides essential nursery grounds for thousands of different marine species, many of which are endangered. Species include algae, sponges, sharks, fish, reptiles, crustaceans such as crab and shrimp, and molluscs. Interestingly, scientists estimate that 80% of the global fish catch relies directly or indirectly on mangrove forests.
Many species of local and migratory birds use mangrove trees as feeding and nesting sites, and larger animals use these habitats to find their prey. For example, tigers live and hunt in the Sundarban mangrove forest in India.
The densely tangled roots are very effective at trapping sediment, heavy metals and other pollutants, so are essential to maintaining water quality. They create a natural barrier by dispersing wave energy, which protects coastlines from erosion and flooding, particularly in areas where sea levels are rising. The build-up of roots also helps to protect adjacent coral reefs and seagrass beds from being smothered by sediment.
Mangroves are also important for local rural communities, whose fishermen and farmers rely on the natural environment to provide food, building materials, fuel and medicinal ingredients for their families.
Why do we need to protect them?
Mangroves represent less than 0.4% of the world’s forest, but they are disappearing three to five times faster than forests such as the Amazon.
Threats to mangroves come from unregulated coastal developments for tourism and housing, particularly shrimp farming, and logging for timber and fuel. In addition, as natural water courses are destroyed or polluted, for example through the use of herbicides or disposal of plastics, entire mangrove ecosystems can be compromised.
How does the ASC help?
Mangroves often occur in areas where shrimp are farmed, and the ASC has included special provision in the ASC Shrimp Standard to ensure that these habitats are maintained. This is helping to reverse the perception that the growing global consumer demand for shrimp is fuelling an environmental crisis in some of the world’s poorest nations, through destruction of wetlands.
Of particular interest to ASC are the mangrove systems in countries including Vietnam, Ecuador, Indonesia, Honduras, Guatemala, Venezuela, Thailand, Mexico and India, where ASC certified shrimp farms are situated (2021).
To protect the ecosystem, the Shrimp Standard mandates that clearing of mangrove forests to provide land for a shrimp farm is prohibited, and in some cases, replanting of mangroves can be imposed as a condition of certification. Impacts to areas surrounding shrimp farms must be minimised, and there are also requirements related to the disposal of plastic waste and the monitoring of water quality.
Importantly, workers must be trained to be aware of and maintain a pristine environment, because a healthy mangrove system results in a healthy shrimp farm, and a healthy product for the consumer.
ASC is also extending its influence beyond farms with a project that provides local communities in Ecuador with economic incentives to look after and maintain their mangrove forests. The project, in collaboration with Conservation International, provides communities with education as well as funds, and aims to tackle the underlying economic incentives behind much mangrove destruction.