Mangroves may vanish in 100 years

Mangroves may vanish in 100 years
ST, Apr 14, 2010
World's mangrove species are threatened by rising sea levels and coastal developments
By Grace Chua

MANGROVE expert Jean Yong was strolling with his wife along Pasir Ris beach in 2003 when he chanced upon a delightful find.
The National Institute of Education plant physiologist had spotted a mangrove plant he could not identify.

The mystery mangrove turned out to be a Bruguiera hainesii or berus mata buaya (crocodile eye in Malay and named for the big knob-like protrusions on its tree trunks), one of the two rarest mangrove species in the world, with just two plants left in Singapore. The other is at Pulau Ubin.

The other rare species is the Sonneratia griffithii found in India and South-east Asia. It has not been found in Singapore.

There are fewer than 90 adult Bruguiera hainesii trees left worldwide: four in Vietnam and some 80 in Malaysia, and conservation organisation the International Union for Conservation of Nature (IUCN) considers them 'critically endangered'.

And it gets worse: The world's 70 species of mangroves, which are located along coastlines, may be set to get rarer, as they are threatened by sea-level rise and coastal developments. They are also being cleared for aquaculture such as prawn farms.

Effectively, mangrove forests may disappear in just 100 years. That is what Assistant Professor Yong and 20 other mangrove experts and IUCN scientists have warned about, in a report published last week in international biology journal PLoS ONE.

'Mangroves are at the worst place in the world - the transition between coastal and marine habitats, which face the most pressure,' Asst Prof Yong said.

By expert estimates, these tidal wetland ecosystems provide at least US$1.6 billion (S$2.2 billion) worth of services a year, such as protecting coastlines from erosion, improving water quality and providing habitats for commercial fish species.

Here, they can buffer the coastline from waves more effectively than concrete berms, and are home to snails, mudskippers, crabs and the birds that feed on these swamp-dwellers.

Singapore has about 500ha to 600ha of mangrove area, mainly at Sungei Buloh and Pulau Ubin, and with pockets at Labrador Park, Pasir Ris and other areas.

That figure is on the rise as conservation projects take root, but it is still a tiny fraction of the 6,400ha of mangroves the country had in 1953.

There are 36 species of 'true' mangroves (trees which usually grow only in tidal habitats) here, or just over half of all known species.

And what of the very rare Bruguiera hainesii trees here? The National Parks Board (NParks) is monitoring the health of Singapore's two specimens and its staff prune weeds around them to let sunlight through.

NParks' care is not limited to the rarest mangroves - it collects and cultivates young plants of 10 or so rare species, which are then replanted in national parks and reserves, explained Dr Lena Chan, deputy director of NParks' National Biodiversity Centre.

It will take time to see results, however.

Bruguiera hainesii are the 'slow giants' of the mangrove world, Asst Prof Yong said.

They grow up to 33m and may live as long as 300 years, but the seedlings grow less than 30cm a year.

So while reforestation of mangrove areas is an option, the paper's authors write, it is usually successful only when large numbers of fast-growing species are planted - other rare and slow-growing species cannot be replanted easily.

'Mangrove areas may be able to be rehabilitated in some regions, but species and ecosystems cannot be effectively restored.'

caiwj@sph.com.sg

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