Agrochemical pollution and habitat degradation: Grave threat to freshwater crabs
By Ranmini Gunasekara
Agrochemical pollution and habitat degradation are some of the most serious threats faced by endemic freshwater crabs, noted the Sixth National Report on the Biodiversity Profile of Sri Lanka to the Convention of Biological Diversity.
According to the Report, out of the 51 species of crabs in the country, 50 of them are endemic, whilst 23 of these endemic varieties are point endemics (endemic species of fauna or flora unique to one specific location).
It further stated that manmade activities, increased land clearance in the highlands which leads to the erosion of river banks and the accidental catching of crabs by fishermen, were some of the other major threats faced by these species.
Moreover, it stated that water diversion from mountain streams for human settlement, agriculture and energy generation, results in the frequent drying up of streamlets and marshes, the typical habitats for freshwater crabs. The Report also stated that crab habitats are threatened by gem mining and solid waste dumping as well.
Speaking to Ceylon Today, Biologist Dinesh Gabadage who was also a contributor to the Report, said that most endemic crabs are in the wet zone.
“You can find most endemic crab species from Colombo, Galle, Matara, and Nuwara Eliya. Areas like Ritigala and Knuckles are also very important to endemic crabs. When it comes to the Central Hill areas, agrochemicals have become a severe problem for crabs, and the same can be said for crabs living in paddy fields.”
He further added that another major problem was the obstruction of crab nest holes due to solid waste dumping, erosion and landfilling.
“When you cut trees near rivers, the banks of the river tend to erode, and these erosions then end up covering the nest holes of crabs. When this happens, they will have no way to come out and they will die. We have observed this in a lot of places where the crab gets trapped inside their nest hole due to erosion, and die inside,” he said.
Gabadage added that he has also observed crab mating behaviour change during the past decades and added that this could be due to the change in monsoonal weather patterns owing to climate change.