Mangrove Forest

By Liliana Usvat

At the intersection of land and sea, mangrove forests support a wealth of life, from starfish to people, and may be more important to the health of the planet than we ever realized.

Land Extension

Mangrove forests thrive near the mouths of large rivers where river deltas provide lots of sediment (sand and mud). Mangrove roots collect sediments and slow the water’s flow, helping to protect the coastline and preventing erosion.  Over time, the roots can collect enough debris and mud to extend the edge of the coastline further out.

These plants are also land builders par excellence. Some Aborigines in northern Australia believe one mangrove species resembles their primal ancestor, Giyapara, who walked across the mudflats and brought the tree into existence. The plants’ interlocking roots stop river borne sediments from coursing out to sea, and their trunks and branches serve as a palisade that diminishes the erosive power of waves.

Species of Plants

There are some 70 species from two dozen families—among them palm, hibiscus, holly, plumbago, acanthus, legumes, and myrtle. They range from prostrate shrubs to 200-foot-high (60 meters) timber trees. Though most prolific in Southeast Asia, where they are thought to have originated, mangroves circle the globe.

Most live within 30 degrees of the Equator, but a few hardy types have adapted to temperate climates, and one lives as far from the tropical sun as New Zealand. Wherever they live, they share one thing in common: They’re brilliant adapters. Each mangrove has an ultrafiltration system to keep much of the salt out and a complex root system that allows it to survive in the intertidal zone. Some have snorkel-like roots called pneumatophores that stick out of the mud to help them take in air; others use prop roots or buttresses to keep their trunks upright in the soft sediments at tide’s edge.

Animals

A wide diversity of animals is found in mangrove swamps. Since these estuarine swamps are constantly replenished with nutrients transported by fresh water runoff from the land and flushed by the ebb and flow of the tides, they support a bursting population of bacteria and other decomposers and filter feeders. These ecosystems sustain billions of worms, protozoa, barnacles (Balanus spp.), oysters (Crassostrea spp.), and other invertebrates. These organisms in turn feed fish and shrimp, which support wading birds, pelicans, and the endangered Crocodile.

Mangrove forests are teeming with life. Shorebirds, crab-eating monkeys, and fishing cats all make the mangrove home. Mangroves provide a safe haven and  a nursery for a variety of fish, birds, crustaceans, and shellfish.

There are 15.9 million hectares (over 60,000 square miles) of mangrove forests in the warm waters of tropical oceans all over the world. Along the Atlantic coast they are found from Florida all the way down to Argentina. Mangroves grow on both the western and eastern coasts of Africa. They stretch into India, Burma, and south-east Asia. Mangrove forests are also common in New Zealand and Australia.

Conservation Policies

Many governments have realized how necessary mangroves really are to the overall environment and have adopted mangrove restoration and conservation programs. Strict legislation to protect mangroves is in place in many countries.

Tsunami Protectors

Mangroves form dense barriers against storms and tsunamis, saving lives and protecting property. They also provide us with many other important benefits—more than many people may realize. For example, mangroves produce seafood, fruits, medicines, fiber, and wood. They stabilize shores by trapping sediments and building land. They improve water quality by filtering runoff and polluted waters. They protect the climate by absorbing carbon dioxide and reducing the amount of greenhouse gas. All in all, researchers estimate, the world’s mangrove forests provide human communities with many billions of dollars worth of free services.

Aboriginal Australian Use of Mangroves

Prior to the arrival of Europeans, just over 200 years ago, Aboriginal and Torres Strait Islander communities of coastal areas managed all of Australia’s mangroves.

Sustainable use of Mangrove Forest

Many natural resource products were gathered from mangroves and used by Indigenous peoples in a sustainable way for more than 40,000 years. Over this time, Indigenous people left little, or no, significant impact on these ecosystems. These ecosystems continue to have high cultural significance.

Furthermore, many Indigenous foods are still obtained from mangrove environments, including boring bivalves, clams, mud crabs, mangrove worms, and of course the fish, Barramundi and Mangrove Jack. Certain mangrove plants are also used as food, like Avicennia marina fruit.

Medicine

Mangrove plants are also a source of medicines. For instance, the ashes from burnt Ceriops australis and Camptostemon schultzii wood is used to heal sores and infections, while the bark of Avicennia marina is used to treat stingray stings.

Seeds of Mangrove

Several species of viviparous mangrove plants produce seeds which have a buoyant outer coating.   The seed floats until it reaches a favored water salinity (not too salty, not too fresh).   When the salinity is right, the coating peels off, and the seed sinks to the bottom.   With luck, it will take hold and grow.   Other species produce seedlings which stay attached to the mangrove plant while a stem and some roots grow out of either side of the seed.

After the seed has developed its “starter” root and stem, it falls into the water.   In the buoyancy of salt water, the whole seedling floats horizontally on the tides and currents.   But when the seedling reaches brackish coastal water, the less buoyant root sinks, flipping the whole seedling to a vertical position where the root can hopefully touch bottom and take hold.   While not all mangrove trees utilize vivipary, they all seem to produce large seeds or fruits which can survive a long time, suggesting that sometimes these seeds or fruits float for quite a while in “suspended animation” until they find a suitable place to germinate.

Destruction of the Mangrove Forest

But, in just in the last decade, at least 35 percent of the world’s mangroves have been destroyed. That’s a rate of loss that exceeds the disappearance of tropical rainforests.

Petroleum is the primary mangrove pollutant in the Caribbean.   Drilling and shipping of petroleum products in and around the Caribbean proves a constant peril to mangroves.   In 1962, the Argea Prima, an oil tanker, spilled about 3.7 million gallons (approx. 14 million liters) of crude oil near the coast of Puerto Rico, killing a large amount of mangroves and associated fauna.   Over 25 years later, hydrocarbon residues were still measured at this site in the soil, and the surviving mangroves had numerous mutated seedlings caused by the toxic spill.   This is but one of many examples of how tragically an oil spill can damage mangroves.

Currently, the Caribbean is losing mangroves at a rate of about one percent per year.   Most of the loss is on mainlands (like Venezuela, Columbia and Panama) rather than islands, although the Bahamas have lost nearly half their mangroves in the past ten years.   People sometimes lament the loss of pretty mangroves, but rarely do they realize just how hard the destruction impacts the reef and the shoreline.   Loss of mangroves effects not just mangrove fishing, but productivity on the reefs as well.

The colorful coral reefs and pretty fishes of the Caribbean may get more people’s attention than the mangroves, but without the mangroves, life cannot continue to flourish on the reefs as it does now.   It is imperative that as development of coastal areas continues, care is taken not to overlook the importance of the mangrove forests, the nurseries of the reefs.

Mangroves bring wildlife back to Senegal coast

The habitat was destroyed through decades of illegal logging in mangrove forests for firewood and building.

Since 2006, reforestation has revived 12,000 hectares (30,000 acres) of mangrove in Senegal — an area larger than the city of Paris — mainly in Casamance but also in the north and centre of the country, according to official figures.

“There has been nothing here since the 1960s and 70s. Replanting is bringing back the mangrove,” said Simeon Diatta, the chief of Diakene Diole village near the Guinea-Bissau border, pointing at riverside vegetation.

“I am struck by the extraordinary success that this initiative represents,” French Development Minister Pascal Canfin said on a recent visit to Casamance, descriving the programme as “model for Senegal, Africa and the world”.

“With the return of the mangrove, people are catching a lot of fish and oysters. Women are selling them on and making a lot of money,” Diakene Diola resident Simeon Diatta told AFP.

The mangrove, which thrives in salt water, is important for trade in forestry and fishery products.

The swamps provide a nursery area for many marine species, most of which are important for food such as fish, crabs and shrimp.

In the nearby village of Diakene Ouolof, resident Mariama Tine said “everything was dead” before the replanting programme began.

“The mangroves stopped the advance of salt and we were able to recover rice fields. There were no fish here before but we are starting to get a lot of them, along with oysters and ark clams,” she said.

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