Crabs feel the pinch
Monday 27 July 2009
The “vultures” of our river systems are at risk from extinction, reveals new research.
The IUCN Red List assessment, led by scientists from ZSL and Northern Michigan University discovered that about one sixth of all freshwater crab species are threatened with extinction, with habitat loss and pollution to blame.
Just like vultures, freshwater crabs play a vital role in the recycling of animal and plant remains that helps maintain the long-term health of tropical aquatic ecosystems. The disappearance of freshwater crabs from these ecosystems would break the nutrient cycle and could seriously affect other animals that feed on them from fish to people.
“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.
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 and even climate regulation.”
Freshwater crabs are the main catch for small-scale fisheries in many parts of the tropics and often provide the primary source of protein for local people.
The decline of these crustaceans could lead to the collapse of local fisheries, and this could have a profound effect on the economy of the villages that depend on them.
“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,” said freshwater crab biologist, Dr. Neil Cumberlidge of Northern Michigan University.
Freshwater crabs may not be fussy about what they eat, but they are extremely choosy about where they live.
The new study showed that the diversity of crab species is highest in tropical rainforests as they have the most favourable habitats and the trees act as natural water filters.
Most threatened species of freshwater crabs were shown to be highly sensitive to habitat loss, pollution, and water siltation.
The increasing destruction of rainforests and freshwater ecosystems throughout the tropics means that these crabs need urgent protection.
This study is the first global extinction assessment for any group of freshwater invertebrates.
The study provides a valuable source of information for the governments of the 122 countries where these threatened species occur, not least because these nations have pledged to reduce biodiversity loss ahead of the Convention on Biological Diversity meeting next year.
‘Freshwater crabs and the biodiversity crisis: Importance, threats, status and conservation challenges’ is published in Biological Conservation.