The tide is low. Thin brushstroke clouds are dissipating in the March sky. It is one of those days at Elliot’s beach in Chennai when adult horn-eyed ghost crabs (Ocypode brevicornis) gang up and stroll together on the surf, where the foam is formed by breaking waves. Here and there, a few slow down, stop to inspect debris or pick up a morsel from the sand. Silhouettes of Caspian terns send some sprinting sideways into the waves, only to tip-toe out later. There are about thirty of them in a loose group, all strolling at the same pace and in the same direction, and there are one or two more groups further ahead. My friend Vikas and I follow the patrol along the shore. He lugs a massive telephoto lens under the midday sun — pointing it every few minutes at some bird in the sky, like a ghost crab’s eye.
Down this beach, past the fishing hamlets of Urur Kuppam and Olcott Kuppam, and beyond the forest department’s turtle hatchery, is the Adyar river’s estuary. The crab troop begins to scatter as we approach the river, where egrets and sand plovers are standing in the swash zone (where waves break) foraging wedge clams.
Dark chocolate-brown mudflat stretches form the cheeks of the river’s mouth where different ghost crabs show up — red ghost crabs (Ocypode macrocera). The young ones are drab brown, but the adults are red as cherries. They are not beachcombers like their sibling species, but sand-sifters. They live away from the wave action, forage organic matter from the mud and leave a trail of near-polygonal chunks of processed soil outside their burrows. Reds are shy and seldom venture more than a metre from their lairs. At the estuary, the river flows into the sea carrying the shadows of the city. Waves foam at its mouth, and the water is sometimes greenish, smelling of algal broth and effluents. A broken bridge juts over it. A bunch of college youth stand at its precipice and take selfies. The bridge stands in three disjunct pieces as a testimony to the temperament of this river-sea junction. In the 1970s, a flood shattered most of the bridge and sent its fragments into the Bay of Bengal. Yet, the Greater Chennai Corporation is considering another road over the estuary that will evict the fishing hamlets that have been here for centuries. Under the bridge’s southern fragment, fields of fiddler crabs appear as the tide falls. Ring-legged fiddlers (Austruca annulipes) and fluorescent blue variegated fiddlers (Austruca variegate) wave the larger of their claws vehemently over their heads. If you keep silent, you can hear the air murmur with pincer sounds. The Students’ Sea Turtle Conservation Network has recorded over two hundred olive ridley sea turtles nesting on this beach in winter.
The horn-eyed ghost crabs are now loosely dispersed; many have begun their return stroll away from the river towards the beach again. Two have found a beached eel carcass and are cleaning its spine out disc by disc. Another one crouches among the waves, feigning dead for a while — eye-stalks drooping, legs collapsed — but then jumps to life and zips off into the sea when we approach too closely.
A fisherman and his young boy cross us with a bag of ghost crabs they have just dug out from the intertidal zone. They tell us that stew made of them is an important food for breastfeeding mothers in their hamlet. Paa nandu, karuvaali nandu, kuzhi nandu are some local Tamil names for ghost crabs. Their meat is used as fish bait; it is also strewn on the shore at low tide to lure lugworms to the surface.
Fisherfolk say that these creatures are good weather-forecasters. If a crab chucks sand at a distance from its burrow as it digs, then the weather will be calm. If it throws sand cautiously close or stays inside its burrow all day, then strong winds, rain or tidal surges can be expected.
To me, the life and physiology of ghost crabs (subfamily Ocypodinae) is sheer science fiction or the stuff of mythology. They are everyday company, yet their utter “otherworldliness” fascinates me immensely. Ghost crabs are coastal chimeras, edge-of-the-world denizens, living on the foggy cusp of land, sea, sand, and sky. They have lungs and gills to breathe in both air and water. They can hear and drink with the setae (hair) on their feet, speak in pincer signs, stridulations, and gut rumbles. They have panoramic 360-degree vision, and the cylindrical retinas atop their eerie, ghostly periscope eyes can see you coming from 50 metres away. For a ghost crab, the horizon is not a mere line in the sky but a full circle. They can be forward-strolling on the shore and instantly change direction and skedaddle sideways when they want to, dashing off at 15 kmph — faster than any land crustacean. They move and live and breed to lunar rhythms — feeling the moon’s tug in their blood thickening and thinning, moulting and growing during full and new moon phases. Watch them throughout the day, and their mooniness becomes more apparent. They change the colour of their carapaces according to background brightness — paler during the day and near full moons, distinctly darker at night and near new moons. They are compulsory company to all of Chennai’s beachgoers. They may cross your path, scurry into your slippers, scour the leftovers from food shacks and picnics. But their indispensability to a sandy beach ecosystem remains entirely unsung among the general public.
Beach sand has very little microbial life in it. A washed-up eel or a stargazer can lie rotting there for weeks if ignored. If not for ghost crabs — the principal beach clean-up squads and public health officers of sandy shores – beaches would be less livable and hygienic places for numerous life forms, including us. They are crucial scavengers here, the vultures of sandy coastal ecosystems. A 2014 study in the journal of Oceanography and Marine Biology by biologists Serena Lucrezi and Thomas Sclacher shows that ghost crabs facilitate the major transfer of energy from marine ecosystems into sandy and dune habitat food webs, making them a keystone species.
I also like to call them land pirates in the most crabbish, voguish sense. They snatch hatching baby sea turtles crawling to the ocean, steal shorebird eggs and chicks, and if times are hard, they may even eat each other. Their burrowing bio-turbates the sand — mixes up and distributes minerals and nutrients — making the subsoil more livable for wedge clams, olive sea snails, lugworms, mole crabs, purse crabs, ribbon bullia, and many other creatures of Chennai’s intertidal zone. Rivers bring sediment. Wind and waves make the beach over millennia. These ten-legged beach-keepers have been the beach’s indispensable maintenance crew.
Out of the estuary, a mullet torpedos three feet above the water, catches the sun’s glint, and splashes back in. A hermit crab examines a discarded pill bottle. A fisherman drags out his hand-cast net, which has caught shivering silver bellies and mackerel. A small cloud of little stints come into view over the ocean, “shshing” softly overhead as they swerve down into the creek. Down on Earth, tower snails have screwed themselves upside down into the tidal flats, their black opercula (lid) facing the sky as they wait for the tide to rise. Numerous discarded face masks wash up at the river mouth, some ear-loops entangled on razor clams, murex shells, and dismembered pincers. Four beached sand stars lie in a square, mysteriously outside a ghost crab burrow. The creature must have been dragging them towards its lair before the sand thudded with giant bipedal footsteps, making it abandon them for the time being and vanish into the ground.