Gall Crabs – Coral-Inhabiting Micro Crabs of Okinawa

Gall crabs are coral-dwelling crabs that spend their entire life living inside a hole of the hard coral. These micro crabs are only 7mm-10mm in size.  They are hard to find and photograph due to their small size.

Gall crab in coral

Gall crab in Favia Coral © Shawn Miller

These tiny crabs are considered to be safe keepers or guardians of the hard coral. The gall crabs defend against coral eating predators such as starfish and snails. The coral provides shelter and food, making it an ideal habitat for the micro coral-dwelling gall crab. I have found these crabs in a variety of coral species in Okinawa. They are usually found in shallow water corals, but recently I found a healthy colony of crabs at sixty-five feet.

Gall crab, Maeda point

Gall crab claws out © Shawn Miller

Large algae covered gall crab

Large algae covered gall crab © Shawn Miller

Gall crab closeup  by Shaw Miller

Gall crab closeup © Shawn Miller

If you’re lucky you might see a gall crab searching for food during the night.

Unidentified gall crab

Unidentified gall crab © Shawn Miller

Gall crab searching for food

Gall crab searching for food © Shawn Miller

Unidentified gall crab © Shawn Miller

Unidentified gall crab © Shawn Miller

The only reason I found this beauty was because she was leaving the gall to release her eggs.

DSC_6209Some of the gall crabs fluoresce using the specialized Light & Motion Nightsea underwater blue light.

Gall crab fluorescence

After the crabs die, the galls become a new shelter opportunity for snails, fish, and reef crabs.

Prime Coral real estate

Prime Coral real estate © Shawn Miller

Bicolor blenny in coral - fish of okinawa

Bicolor blenny in coral © Shawn Miller

Yaeyama blenny

Yaeyama blenny © Shawn Miller

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Blenny in coral gall © Shawn Miller

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Blenny in coral gall © Shawn Miller

I found this hard coral washed up on Iheya Island. Look close and you can see that hole made by the gall crab.

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Stony coral and gall

My Mission: To Document and Preserve the Wildlife of the Ryukyu Islands

This site is also designed to help people identify the beautiful animals of Okinawa, basically  to serve as an online nature reference guide. If you would like to make a contribution to support my mission, please click on the donation link  paypal.me/maketheswitch4nature

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