JOIN USWalking on a sandy beach, you must have seen a ‘galaxy’ of designs made from tiny sand balls. Well, watch closely and you will see small burrows and tiny creatures popping out, looking around with watchful eyes. Well, say hello to the sand bubbler crab, nature’s very own artist par excellence. This little beach dweller is an expert sand sculptor and makes our beaches that much pretty with its ingenuity. It is a classic case of motivation. The intricate unintentional designs are born out of a simple necessity — filling their stomachs. A lot of attention is given to animals in the categories of huge size, strong body, fast feet, but the sand bubbler crab is surely an unsung hero when it comes to the art category.
Artful designers
Sand bubbler crabs belonging to the genera Scopimera and Dotilla are widely seen along the west coast of Karnataka. So far, eight species of Dotilla and 50 species of Scopimera are known. This shoreline harbours mainly three distinct habitats: sandy beaches, rocky shores and estuaries. The sandy bay of the coast is inhabited by innumerable creatures and sandy bubbler crabs are the most interesting ones. Sand bubbler crabs are small crustaceans, around one cm across the carapace and have something called gas windows on the merus of their legs.
These crabs dig burrows in sand and live inside them. During low tide, the crabs come out of their hiding spots and feed on the organic matter in the sand. The first sign of an emerging crab is a near circular hole — the opening of the burrow — from which the crab pops out to see if it is safe to emerge. Once satisfied, it re-enters the burrow and begins clearing it of all the sand.
The crab then uses its claws to scoop up small amounts of sand, eats up organic matter on each sand grain particle, rolls little balls of leftover sand and tosses them out. These are the remarkable-looking reminders which help them from searching for food in the same sand twice. These tiny balls of sand measure approximately 2-3 mm. The feeding activity continues till the high tide comes. During high tide, the balls get washed away and the sea waves replenish the sand with micronutrients. When the high tide subsides, crabs come out to start the process all over again.
The mating behaviour of these tiny creatures is amazing. They mate both on surface and inside burrows. Wandering males mate sequentially with resident females, whereas the resident males chase the females, capture them and take them to burrows. The surface copulation has higher success rate than the underground copulation.
These crabs are hard workers, never give up even when the tide washes away all the hard work. They are meticulously clean and excellent managers of time. Their burrows protect them from all predators. Clever and practical creatures, sand bubbler crabs push the sand balls away from the burrow, throwing them away from the burrow’s entrance.
Sea birds prey on sand bubblers on the beaches. Though there are no direct threats from humans to the population of sand bubblers, we speculate that the increasing number of motorised fishing boats which harbour on the sandy bay in the west coast and the resulting oil spillage might create extensive habitat loss for the sand bubbler crabs over a period of time.
One of the areas where these crabs face imminent threats is the Dhareshwara seashore. A decade ago, there were very few traditional fishing boats, but at present there are nearly 50 mechanised fishing boats at Dhareshwara alone. The sandy bay at this beach is getting continuously polluted due to boats’ oil spillage, which eventually triggers habitat loss. The disturbed ecological niche will subsequently hamper the food chain as well as harmonious living of these tiny creatures.
Next time you walk along the sandy beach, look for these intricate patterns of balls. Capture their dedicated work in your phone and watch the video on a stressful day. It can be quite a stress-buster! But remember, the crab’s eyes are watching you. Even a tiny bit of shade on the sand can alert the smart creature and it will quickly run to hide in its burrow.