While on your live aboard dive trip in the tropics, your cruise director will certainly bring you to one white sandy beautiful beach. Have you ever noticed hundreds of tiny sand balls patterned around a tiny hole by a crab?
With a body color resembling sand, the crabs are easy to miss. However, you won’t miss the sophisticated patterns they make on the beach. Sand bubbler crabs are in fact hunting for microscopic life, called meiofauna, living in the damp sand. They work at breakneck speed passing sand grains into their mouth filtering out all the meiofauna and kicking aside the waste rolled into little cleaned sand grain balls. By doing this, they avoid sifting the same sand twice. The crab will clean every grain of sand within a meter of its burrow, creating tiny galaxies drawings.
To protect their territory, males will perform a funny dancing choreography to show their dominance to the other crabs. They straighten their legs, stand tall, and stretch their claws high above the body. Then they pull all their limbs back in quickly to go into attack-mode position.
The crabs work fast because they can only sieve when the sand is damp. Once high tide is back, they simply return to their burrows and await the next tide. You can almost tell how long the tide has been out by the patterns of their sand balls. The more intricate the pattern of sand balls, the longer the tide has been out.
So, next time you are on the beach and you see such patterns on the beach, do have a closer look to check them out! It’s quite funny to watch these tiny crabs tossing the sand balls behind.