Mangrove madness

Materials World magazine
,
1 Jan 2015

They provide hiding places for small fish, a barrier against aggressive waves and a home for tigers. What’s not to like about mangroves? Eoin Redahan reports. 

Who knew mangroves had such a sprawling reach? According to a recent announcement from Wetlands International, 210 million people benefit from mangrove-associated fisheries. But there is a lot more to these tree species than providing protection for small sea creatures.

Dr Mark Spalding is a Senior Marine Scientist at the Nature Conservancy, an organisation that protects ecologically important lands and waters, including mangroves. Spalding and his colleagues help restore mangrove populations, which have dwindled in the past 50 years. In recent decades, mangrove forests have been decimated to make way for intertidal shrimp farms, or reclaimed for agriculture and urban expansion. However, by razing these plantations, communities are doing away with a versatile resource.

Firstly, mangroves provide natural coastal barriers. Spalding explains their importance in fending the advances of angry seas. ‘Mangroves occur in places with a number of threats, such as wind, swell and waves,’ he says. ‘They are on the front line of tropical storms. If you have a thick enough stand of mangroves, it will slow these surges.’

Mangroves are built to stand where the soil is thin and salty water engulfs. To survive this, they have a complex above-ground root structure that allows them to survive in oxygen-deprived areas. Networks of spider-legged roots act like snorkels, sucking in and storing oxygen during high tide. This matted structure is also a haven to a variety of sea creatures, including crabs, prawns, mullet, herring, anchovy, snapper, oysters and groupers.

Spalding explains that these roots also trap sediment, which creates soft soils for molluscs and crustaceans to burrow in, and a hiding place from predators. As such, mangroves act as useful nursery for marine life.

Apart from bolstering fish populations, mangroves also provide a useful building material and fuel. According to Spalding, mangrove wood has been used as a building material for millennia, its rot resistance making it effective in everything from houses, pole wood and fish traps, while also providing excellent charcoal.

Despite being a versatile resource, mangrove populations have dwindled. But there is still hope, especially as they are so easy to grow. Simply snap a ‘propagule’ (effectively a ready growing seedling) from the tree, plonk it in the ground and it will grow. Spalding says, ‘You often don’t need to plant anything at all. If the intertidal conditions are right, the mangroves will multiply and fill the available space.’

That is the theory. As with many things in life, progress depends on convincing people. He says, ‘For me, the mangrove is the poster child of ecosystem services – it does so many things people benefit from. If only we could better tell that story, then people would stop damaging them.’

 

  • Mangroves grow in tropical and subtropical regions within 30° of the equator
  • 50% of forests have been lost since the middle of the 20th Century
  • US$12,392 annual economic value of one hectare
  • 15.2m hectares of mangrove cover the world’s tropical coasts

 

* Stats from wetlands.org