What are those holes on the Cauliflower coral?

Close up of the crab hole (photo by Ryan Tabata)

Have you ever noticed those small holes, usually pink around the rims, on Cauliflower coral?  It’s actually made by a crab.  The crab (Utinomiella dimorpha), referred to as the Cauliflower Coral Crab or Kahe Point Crab, is small, only up to 1/4 of an inch.  You can see a picture of what it looks like here.  Not all Cauliflower Corals are invaded by these crabs.  You may see one coral head with one or more of these little crabs, next to a coral head without any crabs at all!  These pinkish holes are different from the pink spots/zits that you may see on other corals (Porites spp).  Those are caused by a trematode infection.