Pollution and habitat loss are wiping out the freshwater crab, one of the essential guardians of the world's river systems, according to researchers from the Zoological Society of London.
The Telegraph 27 Jul 09
A sixth of all the world's freshwater crab species are now considered threatened with extinction.
The scavenging creatures help to keep tropical aquatic ecosystems healthy by recycling animal and plant remains. But now the crabs are said to be feeling the pinch.
Their disappearance would break the nutrient cycle and have knock-on effects on water quality, animal populations, and human communities.
Freshwater crabs are the main catch for small-scale fisheries in many parts of the tropics and often provide a primary source of protein for local people.
They are also an important food source for fish and other animals.
Dr Ben Collen, from the Zoological Society of London (ZSL), who co-led a new assessment of freshwater crab populations worldwide said: "The loss of freshwater crabs threatens to interrupt the processes that provide benefits to humans such as nutrient cycling and maintaining water quality.
"We must set clear goals to reverse these trends and ensure that our enduring legacy is not to wipe out the small things that provide us with great benefits, such as nutrient cycling and even climate regulation."
Colleague Dr Neil Cumberlidge, of Northern Michigan University in the US, said: "A wide range of predators - such as mongooses, herons, snakes, and catfish - depend on freshwater crabs for their survival, and when the crabs go, these species may follow. For example, we know that the disappearance of crabs from a river ecosystem in Kenya caused the otter population that fed on them to crash."
The British and US scientists conducted the research for the IUCN (International Union for Conservation of Nature) Red List of Threatened Species.
The Red List categorises different animal and plant species according to extinction risk.
Species falling into the "vulnerable", "endangered" and "critically endangered" categories are said to be threatened with extinction.
Freshwater crabs 'feel the pinch'
Matt Walker, BBC News 27 Jul 09;
Two thirds of all species of freshwater crab maybe at risk of going extinct, with one in six species particularly vulnerable, according to a new survey.
That makes freshwater crabs among the most threatened of all groups of animals assessed so far.
The study is the first global assessment of the extinction risk for any group of freshwater invertebrates.
Crab species in southeast Asia are the most at risk, from habitat destruction, pollution and drainage.
Scientists from the Zoological Society of London and Northern Michigan University led the survey, which produced the first World Conservation Union (IUCN) Red List assessment of the 1280 known species of freshwater crab.
Of those, the survey found that 227 species should be considered as near threatened, vulnerable, endangered or critically endangered.
For another 628 species, not enough data exists to adequately assess their future, says the survey published in the journal Biological Conservation.
However, while the most optimistic scenario is that 16% of all species are at risk, the worst case scenario suggests the figure could be as high as 65%, or two-thirds of all species.
Keystone species
Freshwater crabs are essential to many freshwater ecosystems. Some feed on fallen leaves and algae, while other species help cycle nutrients by eating vast quantities of detritus.
The crabs themselves are an important source of food for a range of birds such as herons and kingfishers, reptiles such as monitor lizards and crocodiles and amphibians such as frogs and toads. Mammals that like to dine on freshwater crabs include otters, mongooses, civets as well as wild boar and even macaque monkeys.
Because most species require pristine water to survive, they are also excellent indicators of good water quality.
But species are increasingly being impacted by habitat destruction and pollution.
Most vulnerable are crabs living in southeast Asia, which is also home to the greatest diversity of species.
For example, 40 of 50 species living in Sri Lanka are threatened.
Those species that live a semi-terrestrial life, breathing air, living in burrows and dividing their time between water and land, appear most at risk, possibly because their habitats are most easily disturbed by human activities.
No species are yet known to have gone extinct, but some species such as the terrestrial crab Thaipotamon siamese and the waterfall crab Demanietta manii from Thailand have not been seen alive for over a century, and their original habitats have since been built over by urban developments.
The loss of natural forest to land development and agriculture has also impacted almost every habitat in which freshwater crabs live, the report notes.
The proportion of freshwater crabs threatened with extinction is equal to that of reef-building corals, and exceeds that of all other groups that have been assessed except for amphibians.
"We must set clear goals to reverse these trends and ensure that our enduring legacy is not to wipe out the small things that provide us with great benefits, such as nutrient cycling," says Ben Collen, one the survey scientists from the Zoological Society of London.
