Are emerald mithrax crabs 'reef safe' with SPS ? NO !

[ekovalsky]

I recently added two fairly small emerald crabs (males with large claws) to my 250g tank to eliminate a few bubble algae I've seen. Next day I noticed a few branches of an SPS coral (A. millipora) with complete tissue loss and exposed skeleton. Thinking I had either a case of a RTN-like disease or an predator nudibranch I stayed up late last night and frequently checked on it with a flashlight. Well I find one of the new crabs on this coral, picking flesh with its claws. The other was on the adjacent coral (A. Sarmentosa) doing the same thing, with a small area of skeleton exposed right next to where he was eating. These corals are healthy and did not have algae growing on them, or excessive slime. Like most of my other SPS these two corals came from Divers Den. Some have arrived with small symbiotic crabs which I have generally left alone. I did find a predator nudibranch on a klyxium leather coral I bought from them, which I removed before it did much damage.

Anyway since these buggers were on the corals, and I had not yet glued them in place, they were easy to remove. There has been no progression of tissue loss since. I'm not sure the damaged areas will recover, but the healthy/uneaten branches should be fine I think.

By the way I don't have an excessive cleanup crew i.e. hermits and snails, just enough to do the job. There was plenty for these emerald crabs to eat on the 400+ lbs of live rock in the system. I actually put one back in the tank and watched him climb right back up to the A. sarmentosa and resume his feast... he was subsequently placed into the high flow-chaeto-sediment trap section of my sump/fuge and introduced to the giant hermit crab (smuggled back from Bora Bora) I keep in there. The other was put in the low flow - plankton generation section of the sump/fuge. If I need him to mow down some valonia in the future I can probably find him in there.