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60% of freshwater crabs could face extinction

Rainbow crab by Neil Hepworth.

A new survey has found that 60% of the world’s freshwater crabs might be in danger of becoming extinct.

The survey, which was undertaken by scientists at the Zoological Society of London (ZSL) and the University of Michigan, was released in the first IUCN (International Union for Conservation of Nature) Red List review for freshwater crabs and the first ever global assessment of the extinction risks for any group of freshwater invertebrates.

Of the 1280 identified species of freshwater crab, 227 species were classed as at risk, endangered or critically endangered and another 628 other species had not enough information available to properly evaluate them.

At risk
The best case scenario of the survey which was released in the journal Biological Conservation is that 16% of all species are at risk, however, at worst this survey could mean that 65% of all species are at risk.

This makes freshwater crabs one of the most threatened of all groups of animals assessed so far.

Most of the vulnerable crabs are found in Southeast Asia with 40 out of the 50 species in Sri Lanka threatened alone but out of the 122 countries that have populations of freshwater crabs, 43 have species in need of protection.

Threats include habitat destruction, deforestation, pollution and drainage of natural habitats for agriculture.

These problems also have knock on effects to the freshwater ecosystem.

Scavengers
Crabs often consume fallen leaves, algae and detritus and in this way help to cycle nutrients, and thus maintain quality, throughout their natural environment.

The crabs are also an important source of food for a wide range of birds, reptiles, mammals, amphibians and indeed humans! In addition, their need for pristine water conditions makes them an excellent indicator of good water quality.

No species have been confirmed 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 100 years, and their original habitats have since been built over by houses.

More threatened than corals
This study means that that the proportion of threatened freshwater crabs is equal to that of the much more publicised coral reefs and exceeds that of all other groups except amphibians.

“The loss of freshwater crabs threatens to interrupt the processes that provide benefits to humans such as nutrient cycling and maintaining water quality” said ZSL's Dr. Ben Collen on their website.

He adds “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."

For more information see: ‘Freshwater crabs and the biodiversity crisis: Importance, threats, status and conservation challenges’ Biological Conservation.

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