Blue Zoo: Sand Bubbler Crab


Featuring one amazing marine animal per week.

Imagine you’re walking across a beach and you see something like this:


Photo by Rob and Stephanie Levy via Flickr, Creative Commons License. 

What’s going on? Who could be capable of creating such delicate sand art?

The creative culprit is an unassuming critter – the sand bubbler crab. There are several species of sand bubbler crabs. They are very small (often less than a centimenter, and all belong to two genera, Scopimera and Dotilla. They can be found on sandy beaches ranging throughout the greater Indo-Pacific region.


Photo by Dcubillas via Wikimedia Commons, Creative Commons License. 

The intricate feat of creating sand bubbles is the result of a simple necessity: the crab has to eat! While the motivation for doing it is simple, the mechanics are not. The crab feeds on the organic matter in sand – plankton left behind by the tide, meiofauna (animals that live between sand grains), and detritus (non-living organic particles).


Photo by Dcubillas via Wikimedia Commons, Creative Commons License. 

In order to get that organic matter it feeds on, the crab uses its claws and mouthparts to scoop up small amounts of sand. It eats up the organic matter on the sand particles, essentially “cleaning” the sand. As it works, it forms little balls of clean sand that it leaves behind.

In the video below, you can take a closer look:

The patterns left by these crabs can vary. The crab lives in a burrow and works during low tide.They tend to work radially from the entrance to their burrow, going gradually farther away, and they often leave little paths open through which to scurry back to the burrow when necessary.


Photo by Cory via Wikimedia Commons, Creative Commons License. 

When the tide rises again, it hides in its burrow with a pocket of air to breathe. Its bubbles are wiped away by the waves, and the tide deposits a fresh supply of plankton and detritus, and the crab can start over.


Photo by Rob and Stephanie Levy via Flickr, Creative Commons License. 

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