If we take a quick look at the history of Mumbai, we realise that the city today is formed by reclaiming and connecting the seven southern islands of erstwhile Mumbai, viz Colaba, Little Colaba, Bombay, Mazagaon, Parel, Worli and Mahim, to the larger islands of Salsette and Trombay Islands in the north. What most of us don’t realise is that, Mumbai, even today after massive reclamation, is an island. Sadly, neither we nor our urban planners behave like islanders. This lack of respect for our geography and the limitation of resources it imposes on the possibility of urban and industrial growth put our city's environment and biodiversity at a huge risk.
Fiddler crabs are one of the most important detrivores (creatures feeding on dead matter) and perform the ecological role of bioturbulators or tillers
On hearing about the announcement of the coastal road and trans-harbour link towards Nhava Sheva, my first reaction was, “What will happen to all the marine diversity found along the coast of Mumbai?” I'm a big fan of the coastline and sea, as I think all islanders should be. I have taken literally hundreds of students and adults for beach and mangrove walks right from Colaba in the south to Haji Ali, Sewri, Dadar, Mahim, Juhu, Vikhroli, Mulund, Manori, Gorai, Uttan and further up till Vasai and Palghar, too. These sandy and rocky beaches harbour diverse creatures, and the most 'looked-at’ or appreciated species tend to be the various shells - conches and clams. And sadly for me, my favourite marine crabs are least focussed on. I fell in love with marine crabs (Brachyurans) during my college days when I found a 1957 research publication (booklet) of the Department of Fisheries, Bombay titled Marine Crabs of Bombay State, written by Dr B F Chhapghar. The booklet covered 81species of marine crabs found right from Okha (now Gujarat) down till Karwar (now Karnataka). The coloured plates and detailed sketches just drew me to that group of creatures. And that’s how I began crab watching. They were intriguing and peculiar with their 10 stilted legs and pincers, Ferrari-like foldable eyes; deep burrows and rolled up sand balls. But among all these crabs, I found the fiddler crabs to be the most unusual.
Fiddler crabs belong to the genus Uca. Also called calling crabs, they are semi-terrestrial and unique in a way that the males possess one abnormally enlarged claw or chela (pincher). The males use this claw to wave and challenge other male crabs and to signal to potential females. The size of the male crab’s claw and his vigorous wave indicates higher strength and virility — which is preferred by females. It is not uncommon to see thousands of red, creamish or yellow fiddler crabs arm-wrestling and combating other males during low tide in a mangrove mudflat. Accidents are common and if a male loses his large claw, the smaller claw grows in successive moults. And thus, we see fiddler crabs that are left-handed and right-handed. In females, both the claws are small and of the same size.
The name ‘fiddler crab’ doesn’t come from the wave or large claw. It comes from the smaller claw’s unusual habit of picking up dead and decaying food under the protection of the bigger claw - this looks like the crab is playing a fiddle. Fiddler crabs are one of the most important detrivores (creatures feeding on dead matter) and perform the ecological role of bioturbulators or tillers. They dig deep burrows, throw the sand above the ground in the shape of balls. They, then, take the food and dead material deep into the marshes which allows oxygenation, cycling of soil and prevents anaerobic conditions, which can kill the roots of mangrove plants.
Predators such as gulls, herons and jackals regularly feed on these fiddler crabs. But a much bigger threat to their survival is the rapidly increasing oil leakages from the engines of fishing boats, slicks caused by collisions of crude oil container ships and deep sea drilling and dredging for fossil fuels. The oil not only covers the book gills of adults, thus choking them but also coats and kills the eggs laid on the sea bed and the floating larvae of the crabs. It will be an over-simplification to state that fiddler crabs are the lifeline of mangrove and coastal ecosystems. So the next time, if you chance upon fiddler crabs waving frantically at you, remember that it doesn’t mean they are panicking and signalling for help. In fact, they may well be warning us humans, that with the destruction of mangroves, creeks, coastlines and seas, and disappearance of fiddler crabs, we may be waving goodbye to our own race.