Everything You Need to Know About Mangroves

Mangroves form a mysterious ecosystem on the boundaries of our green landscape and warm oceans. These aquatic trees can be found fringing the coastlines of Africa, South East Asia, Australia and all the way down the Atlantic coastline from Florida to Argentina. For those who haven’t had the chance to visit these dense, tangled forests, mangroves are filled with salt-tolerant trees and shrubs which manage to thrive in shallow, salty and muddy waters. Many mangroves flourish near the mouths of rivers where saltwater and freshwater meet. Very often these areas are tidal, with each incoming tide bringing with it nutrients and plankton which float in the calmer lagoons created by the mangrove trees. Following shortly behind this influx of food is a massive array of species which make these ecosystems home to spectacular biodiversity. Young sharks and fish arrive to breed and often the youngsters remain here as they grow, safe from large predators, powerful waves and strong currents. Many species of our endangered turtles enjoy floating underneath the leaves while birds such as pelicans and herons often touch down from above. On the Galapagos Islands, even penguins live amongst the twisted roots while mangrove finches, one of Darwin’s famous finches which he used to support his theory of evolution, spend much of their time here too. Even monkeys clamber and play about in the dry higher branches. However, despite mangroves only totalling 0.4% of planet Earth’s forests, they are disappearing up to four times faster than their land-based counterparts. Yet many believe that each hectare of mangrove forest is worth tens of thousands of dollars each year due to the many benefits they provide humans. Let’s take a look at how mangroves improve our daily lives.

With mangroves providing hotspots for biodiversity, it should come as no surprise that many of the fish and shellfish our fishing industry catches are likely to have been born and raised in the safe waters of a mangrove. Coral reefs, which are renowned for an abundance of fish, often lie close to mangrove forests and so the species we catch and sell from reefs has quite often relied on the mangroves to successfully raise their young in areas full of food and lacking predators. In this way, these miniature woodland ecosystems contribute millions to the economy each year, while many others who live close to the shoreline often depend on the fish purely for daily food and their main source of protein. The 200 million people who live on the stretches of coastline hugged by mangroves also benefit from their service as a coastal defence. Mangrove trees grow with a massive clump of twisted, deep roots which allow them to stand tall amongst boisterous waves. When storm surges or powerful waves start barrelling towards the coastline, mangroves act as a natural barrier which slow the waves and allow some of their energy to dissipate before they hit our seashores. This also means any erosion to our shorelines is slowed, helping delay the impacts of rising sea levels.

However, that is not all mangroves do in our plight to halt climate change. These trees are a fantastic store of carbon dioxide and actually take in carbon up to four times faster than our much heralded tropical rainforests like the Amazon. During their lifetime, the leaves on the trees and shrubs absorb carbon dioxide through the process of photosynthesis and store it in their leaves, roots and trunks. When these beings die off, they take the carbon with them and fall into the deep mud which surrounds their roots. As the soil where mangroves grow is often or always covered in water, the dead trees fall into an area with low oxygen levels which means their decay is extremely slow. This allows the carbon they hold to be stored with them underwater rather than released quickly back into the atmosphere. As mangroves are chopped down or lost, the carbon they hold is quickly emitted back out into the air, increasing our emissions. Mangroves have been used for centuries by local communities with their wood failing to rot or succumb to insects, meaning villages often use it to build their houses and boats. Traditionally, the bark also provided dye whilst the leaves were used for tea, tobacco, medicine and livestock feed, all essentials in the tiny, often forgotten, communities which lived in isolated patches of coastline.

Finally, mangroves also help improve water quality, allowing clear water to travel out to sea and surround our delicate corals. With mangroves’ dense network of roots standing at the mouth of the river, the water is forced to slow down and move more gently. This makes it easier for sediment such as mud and sand to be deposited whilst pollutants and heavy metals in the water also become trapped, preventing them travelling far out to sea in the currents.

Despite all these invaluable benefits, 50% of Earth’s mangrove forests were destroyed by the end of the 20th century, with many of those that remain, now in a degraded condition. Yet what is threatening these precious ecosystems? As with our terrestrial forests, the biggest threat is clearance. In fact, mangroves are being cleared even faster than our beautiful tropical rainforests, yet somehow this environmental disaster fails to hit headlines. In place of these species rich forests, farm land is cultivated, harbours built, tourist infrastructure constructed or most commonly, shrimp farms are created. In many countries, shrimp farming is becoming an increasingly lucrative business and forests are cleared to make space for artificial ponds. However, even the remaining surrounding mangroves are impacted as to fill the ponds, farmers often create channels which funnel water away from forests and towards their farms. This means that water levels are lowered, causing mangrove trees to dry out whilst the lack of flowing water means less nutrients are delivered and their seeds fail to travel very far. With thousands of shrimp packed in tightly together, farms pump chemicals and antibiotics into their pools but these pollutants overspill into the surrounding seas and contaminate any plants or animals which may be living nearby. In fact, the average Asian shrimp farm is forced to shut after only 2-5 years due to localised pollution and disease whilst the mangroves that once stood in that spot could have provided years of income from the likes of eco-tourism. With regard to tourism, many mangroves have been overlooked as an attraction in comparison to their neighbouring bright reefs, yet slowly, the potential for sustainable snorkel tours taking visitors around the rich, calm lagoons of the mangroves is a growing prospect. Hopefully, soon mangroves will be an area of sustainable income whilst shrimp farms will be forced to comply with the increasing number of environmental standards which are being developed. In the meantime, the seafood choices you make as a consumer can have a massive impact over whether sustainable farms thrive or fail.

Other threats to these intertidal forests include the overuse of their wood as they are increasingly exploited for pulp, wood chip and charcoal in a way that is no longer sustainable. Multiple dams and irrigation channels are also being built upstream in many countries which reduces the amount of water reaching the trees whilst also altering the levels of salinity nearby. If the salt levels are too high, many cannot survive whilst low water levels leaves trees drying out in the tropical sun. Even the amount of sediment travelling down the river can either smother plants or leave them lacking essential nutrients. Sadly, mangroves haven’t managed to escape our pollution either with toxic chemicals impacting plant growth while plastic hinders the wildlife living between their gnarled roots. Being situated at the mouth of the river, mangroves are the front line receiving our deluge of chemical fertilisers, industrial waste and single-use plastic which is carried down by the rushing water.

Luckily however, there are many fantastic projects going on across the world in a battle to save these incredible, underrated ecosystems. Mangroves on the Indus River delta in Pakistan declined as trees were chopped down for fuel and camel feed but today, already 1.4 million seedlings have been planted, with those nestled in the soil 10 years ago now standing at six foot tall. Even the Pakistan Navy has recently pledged to plant one million more seeds in the area. In the past, much of the river water was diverted for irrigation which reduced the amount of sediment travelling to the coast which caused the delta to sink and the land which once grew melons, rice and bananas to become flooded with saltwater. To tackle this, 21,500 acres of mangroves have been rehabilitated to help reduce the impact of flooding whilst also encouraging wildlife to return to the area. In other countries such as Colombia and Tanzania, fantastic protected areas have been created to save remaining mangrove forests. Many women in local communities work in these intertidal areas collecting shells and clams to sell and so rely on the mangroves daily. The protected areas allow local people to continue to access their traditional materials but prohibit outsiders taking a share and making resource extraction unsustainable. These protected havens also provide locals with jobs in conservation whilst eco-tourists flock to witness our beautiful wildlife which hides in quiet lagoons. Sadly, mangroves are often forgotten about in our mission to save the ocean despite the essential role they play in our lives. Hopefully in the future, these environments will continue to see an increase in awareness and gain the essential protection they and their local wildlife deserve.

By Neve McCracken-Heywood