Threats to their habitats worldwide, including here, are killing off species
Amresh Gunasingham, Straits Times 8 Aug 09;
ONE in six - or 1,000 species - freshwater crabs known to thrive in the tropics of Asia, Africa and South America is in danger of going extinct, an international team of experts has warned.
The study, led by scientists from the Zoological Society of London and Northern Michigan University, said the loss of natural forest to land development and agriculture had impacted almost every habitat in which freshwater crabs live.
The crabs are known to thrive in habitats ranging from lowland forests to mountains such as rivers, streams, waterfalls and wetlands.
The conservation of freshwater crabs relies heavily on preserving patches of natural forest large enough to maintain good water quality, because many species are extremely sensitive to polluted or silted water and cannot survive exposure, the researchers explained.
The crabs help maintain tropical aquatic ecosystems by recycling animal and plant remains, for example, and their disappearance could adversely affect the nutrient cycles, while having knock-on effects on water quality, animal population and human communities.
The scientists conducted the research - the first global assessment of the extinction risk for any group of freshwater invertebrates - for the International Union for Conservation of Nature Red List of Threatened Species.
The Red List categorises different animal and plant species according to extinction risk.
Crab species in South-east Asia are the most at risk from habitat destruction, pollution and drainage. In Singapore, six freshwater crab species are known to exist, three of which are not found elsewhere in the world. And crabs here are not immune to these threats.
For example, the Johora singaporensis is considered a critically endangered species. This species had previously been known to thrive in a 39ha patch of forest at the Bukit Timah Nature Reserve, but grew close to extinction last year.
A fragile ecosystem has meant the protected area has not been spared the effects of acid rain or climate change, said Professor Peter Ng, director of the Raffles Museum of Biodiversity Research.
Researchers from the National University of Singapore and National Parks Board are studying the changing conditions in water streams found at Bukit Timah Hill.
The international study, which was published in the journal Biological Conservation, serves as an important reminder of the need to monitor endemic species, said Prof Ng.
Such a programme is lacking here, and efforts should be stepped up before it is too late, he said.
'Our Singapore crabs represent many of the species found in China, India and other parts of the world...Most of them are right at the edge of a cliff right now,' he said.
'If we kick a little harder, they will go down.'
