Found burrowing along the coastlines of the Indo-Pacific region, the tiny sand bubbler crab may initially look like an extremely fussy eater. Furiously gathering sand into its mouth, the creature then egests its ‘food’ from the top of its head at almost the same rate as it is eaten. In fact, the crab is filtering off the microscopic creatures and nutrients from the surface of sand particles, and egesting the grains which have been ‘licked clean’. These feeding habits bring a whole new meaning to the term ‘micro-diet’.
Emerging only at low tide, the creature works radially from the entrance of its burrow to gather its food, leaving a beautiful pattern of ‘sand bubbles’ in its wake. The crab is prone to predation from above by various sea birds, and so it always leaves itself a clear escape route back to its burrow, ready for use in times of emergency. However, some portions of crab populations have been observed abandoning their burrows. Studies have shown that these differences in behaviour can be due to individual crab size and whether or not they are pregnant. The more vulnerable individuals (ie those who are small or egg-bearing) are restricted to the typical radial patterning activities, whereas others can chose to move away from their burrow if the organic content of their surrounding sand is low.
Whatever the crab chooses to do with its precious little time at low tide, it works quickly before disappearing back inside its burrow, where it creates a small bubble of air to survive on while the tides rise once more.
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| Image courtesy of ISAKA Yoji |
NB The name 'sand bubbler crab' typically refers to crabs of the genera Scopimera and Dotilla in the family Dotilidae.
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