30 Apr 2017 16:42 IST

Kerala crab in a treehouse

Kani tribals in the Western Ghats helped discover a new species of tree crabs

For years, the Kani tribesmen have watched long-legged crab-like creatures darting up trees in the southernmost parts of the Western Ghats, near the Agasthyamala Biosphere Reserve in Kerala. They called them maranjandu (tree crab), little knowing that no tree-living crab species had ever been identified in India. World over, only three species of fully arboreal crabs had been identified — in Sri Lanka, Madagascar and Borneo.

Finally, when researchers from Kerala University’s department of aquatic biology and fisheries conducted a survey of freshwater crabs in the Western Ghats about two years ago, the Kani tribesmen told them — after some prodding — about the ‘crab-like creatures’ in the hollows of large trees. They described how, when they manage to catch the crab, they boil it in oil to treat skin disease in children. The researchers launched a hunt for them and, soon, the first tree crab species was identified in India.

“The Kani tribesmen are keen observers of nature. But they won’t talk about what they have seen unless they are asked specifically. You have to spend a few days with them and build a rapport,” says A Biju Kumar, head of the department and the research team. During the search for the tree crab, though the tribesmen managed to spot them early, they could catch one only after many days, he says.

The hunt for a pair

Not every tree can be a home for these crabs. They prefer those with wide girths and large cavities that can hold enough water. Such water-filled cavities (phytotelms) are seen only in a few trees. The tribesmen identify the presence of such cavities at the treetop from the debris the crabs push out of them; and the appearance of air bubbles near the water surface are sure signs of crab presence.

In early September last year, Kumar received a call from one of the tribesmen that they had finally caught one of the crabs. They had to first clear out around seven-eight litres of water from the tree cavity. When Kumar and his research student Smrithy Raj reached the Kottur forests, they found the crab safe in a water-filled bottle.

“It turned out to be a female. If it is a species that has been identified and described earlier, we need just a female to confirm it’s the same species. But for a species that could be a new one, we need the male too to describe it, as the male reproductive organ is one of the identifying characteristics of the species,” says Kumar.

Before long, a male crab was caught too. From the elongated legs, the researchers were able to conclude that this was a species of tree crabs that was different from those identified in Sri Lanka, Madagascar and Borneo. Another strange coincidence helped the team confirm the find without wasting any time.

Just that week, Kerala University happened to be hosting Peter KL Ng, head of the Lee Kong Chian Natural History Museum at the National University of Singapore. An expert who had identified and described the other three known tree crab species, he was in town for a Crab Taxonomy Workshop.

It took him just one look to identify the Kerala tree crab as a new genus. Its colours were striking — much of the dorsal part of the body and legs were bluish-black, with bright orange markings on the abdomen and lower half of the claws, while the joints of the legs were orange. The shell was found to be swollen, thus creating enough space to retain water during the height of summer.

Naming ceremony

Next was the task of choosing a name under the binomial nomenclature — the use of two terms to denote a species, where the first indicates the genus and the second the specific epithet. To honour the Kani tribesmen for their role in identifying the species it was named Kani maranjandu, thus retaining the name by which the tribesmen had known it.

The specimens were then deposited with the Zoological Survey of India for evaluation. The genus was finally described in the April issue of the Journal of Crustacean Biology, a peer-reviewed, quarterly scientific publication from the Oxford University.

Kumar says the crab’s discovery is important in the context of the conservation of the Western Ghats Biodiversity Hotspot, as the species can well serve as ecological indicators — namely, reflect the health of the ecosystem. As water-holding hollows in large trees are essential for the crab’s survival, the conservation of such trees assumes importance, especially given the degraded forest ecosystems of the Western Ghats. It also highlights how little we know about the biodiversity of these forests and the need for extensive studies.

Although there has long been extensive research in the Western Ghats, it has mostly concentrated on wildlife and plants. There has been very little focus on crabs, and this probably explains why the tree crab went unnoticed for so long. Even the seven-eight new freshwater crab species identified in this region were by foreign researchers.

Kumar’s team is now preparing for research in other areas of the Western Ghats in Kerala. Recently they got a call from the Aaralam forest in Kannur, from someone who claimed to have spotted a species of crab similar to the newly identified Kani maranjandu. More unexplored water-filled cavities atop random trees are beckoning.

(The article first appeared in The Hindu BusinessLine's BLInk.)

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