While searching for frogs in Goa’s Bondla Wildlife Sanctuary, Keerthi Krutha chances upon thousands of crabs on the move.
Photo: Keerthi Krutha.
‘Earthworms you ate
With your outer skeleton covered with calcium carbonate
With two claws and eight feet,
You crawled in thousands on the street
How do u manage to live in the stream and the river
How do u manage to live in the sea and the ocean?
Why and how? I wonder I wonder’
To me, crabs are an incredibly fascinating group of underexplored organisms which require more attention. Especially in India, there are so many facets to them waiting to be explored. Taxonomic studies on crabs in the country are gaining popularity and there are many species waiting to be unearthed. They are a group of organisms which also demand studies that focus on their eco-system services and ecology. Results from studies focusing on their specific roles and life history stages will act as evidence to prevent careless acts of pollution and human disturbance.
In India, only one species, the Coconut Crab Birguslatro from the Nicobar Islands is protected under Schedule I of the Wild Life Protection Act (1972). It is common practice for local villagers to poison a pond or lake to catch fish easily. Sadly, I was witness to one such eerie sight at a tank in Melkote, Karnataka, in August 2014. The bodies of the crabs had become brittle and turned white.
Photo: Keerthi Krutha.
In October of 2012, a colleague and I were walking in Goa’s Bondla Wildlife Sanctuary on the lookout for frogs. The road was tarred yet kaccha and dotted with innumerable potholes. It was one of those mid-mornings when the rain had had its way and the sun was out bright, the sky was an azure blue with clouds interspersed like little white puff-balls, the plants were glimmering in the light and when I looked at them I felt like they were smiling at me. Except for the music of the stream gushing by the roadside all else was quiet. The stream was covered with an overhanging curtain of Cyathea ferns.
Here, we were surprised to encounter thousands of crabs scurrying towards the stream! I was struck with curiosity as to their source. Careful not to step on any of them, we began photographing and video-graphing the crabs, and whenever a vehicle came by we stopped it and began rushing the crabs into the stream before letting the vehicle pass. After spending about an hour at the site, we crossed the 20m. wide crab frenzy and went on our way, wondering why these crabs were on the move. On re-inspection at nightfall, the numbers had reduced and the road was covered with bits and pieces of dead crabs killed by vehicular traffic. As is the way the forces of nature work, nothing went waste and ants were diligently carrying away the carcasses.
On that same night, we saw a large purple colored crab, now known to science as Ghatiana atropurpura, carrying a dead earthworm up a tree. On subsequent days, my encounters with crabs became more common, especially under boulders submerged in the stream. A rule which I learnt for finding crabs is that the size of a crab is directly proportional to the size of the boulder it's under. The larger the boulder, the larger the crab.
The question of why the crabs were travelling en masse lingered in my mind. A little research threw light on the encounter. I learnt that the crabs I had seen at Bondla belonged to the Gecarcinucidae family and that crabs migrate in large numbers at particular times of the year to spawn. At this time, crabs that dwell in burrows in forested areas travel to a nearby water body to mate and release their eggs. Spawning is known to be initiated during wet months and is directly related to the phases of the moon. It is common among both marine and freshwater crabs. One such famous ‘crab-crossing’ event is of the Christmas Island red crab on Australia’s Christmas islands. Their government has taken the initiative to make ‘crab-fences’ out of aluminum to funnel the crabs into underpasses or over a five-meter high bridge to allow the safe passage of the crabs during their migration.
Photo: Keerthi Krutha.
Three families from India have been assessed by the IUCN Red List. Red List assessments are a process by which experts classify each species based on their taxonomic validity and threats so that they can prioritize them for conservation action. The three families from India that are included in the IUCN Red List are Coenobitidae, Gecarcinucidae and Potamidae which add up to a total of 82 species. Of these 82 species, three species are presently vulnerable to extinction with their major threats being urbanization and pollution from pesticides.
Sanctuary Asia’s Young Naturalist of 2015, Keerthi Krutha is a conservationist working on herpetofauna and community based conservation.