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Mangrove coasts: a muddy story (Part 2)

11-Apr-2013

By Han Winterwerp - 

In my previous blog, I have tried to explain the importance of mangrove mud coasts. Of course, these coasts are beautiful, exotic environments, with rare species, such as the mud skipper and numerous crabs, as well as rare birds.
 

For some, their beauty alone would be sufficient reason to protect these ecosystems. For mankind, it is their so-called ecosystem services that should urge their conservation. For instance, it is estimated that 50% of all commercial fish caught in tropical waters depends on the spawning and nursery functions of mangrove forests.


Mudskipper, by Yus Rusila Noor

 

Yet, mangrove mud coasts are under severe pressure. Mangrove trees are sometimes cut for extravagant reasons, such as the production of charcoal for barbecuing – this charcoal gives a very exotic flavour to your meal. Entire mangrove forests are transformed into fish and shrimp ponds, for huge rapid profits for a few. And last but not least, mangrove forests are lost because of well-intended but poorly planned restoration efforts, with failure rates at an unprecedented scale. In my next blogs, I will explain why these restoration efforts were so unsuccessful.

Horseshoe crab, by Vera Coelho


In the 1950s, the global area of mangrove forests still measured about 32 million hectares, decreasing to 18.8 million in 1980, and further declining to 15.2 million hectares in 2005. In the Philippines, for instance, two-thirds of the original 334,000 ha mangrove forest were converted into fish ponds.

The loss of this valuable habitat is a disaster in itself. But the problems are in fact much larger. With the loss of the coastal mangrove forests, coastal erosion rates become huge, also in coastlines which were previously accreting (i.e, gaining sediment). Dramatic examples can be found along the north coast of Java, which was once renowned for its extensive and dense mangrove forests. Today, little forest is left. Erosion rates are dramatic, even up to 100 m/year, as shown in the photograph below.

Estimated land loss of 200-900 meters between 2003 (blue line) and 2012 (orange line) due to erosion in Demak District, Central Java, Indonesia. Google Earth image.

 

Han Winterwerp works for the Dutch research institute Deltares and is a professor at the Delft University of Technology, where he teaches and develops instruments to measure and predict the behaviour and properties of mud. He specialises in the behaviour of mud in open waters.

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