Mystery hitchhiker crab risk...

[Antony®]

I haven't taken a picture, but a little crab just appeared the other day, and although it seems that most here are anti crab, I was wondering if it will be worth tearing apart my tank to remove him. He is about the size of a dime including his legs, white, with very thin black stripes on his legs, slightly fuzzy, with black pinchers. I wouldn't even know he's there, but he seems to have taken up residence in a live rock with a colony of xenia. The type of xenia is the one that looks like tan palm trees, the fans almost an inch across. The reason I ask, is that the xenia today was very unhappy looking, and I don't know if the crab is killing it, or the xenia is just unhappy with him poking around the bases of them. Is my description of him enough to anyone to be able to ID him, or do I really need to try to get a pic of him? Anyway, I'd rather not tear into my tank, but I'd rather do it now if he is a troublemaker.

[Ninong]

If the carapace is white, it might be a good guy. Maybe it's a commensal crab that lost its coral host? Or anemone host. Keep an eye out to see if you can figure out what it's up to. Maybe you should check your tank after dark with a flashlight.

Most of what you read about people not liking crabs applies to hermit crabs, which are not true crabs anyway. Hermit crabs have a lot of good qualities but they also kill snails and eat beneficial sand bed epi- and infauna.

True crabs that come in as hitchhikers usually fall into two categories: those that are commensal with certain corals and those that are not. Commensal crabs defend their host corals against predators, such as the crown of thorns sea star.

A crab with a white carapace might be a harmless porcelain crab. Keep an eye out and see if you can see what's going on. You will want to actually catch it in the act if you think it is doing harm.

In the meantime, I wouldn't lose any sleep over it.



P.S. -- As a general rule, most hitchhiker crabs are bad guys but I can't think of any of the bad guys that have a white carapace.

[kronos5]

Sounds like good Advice

[Antony®]

Besides the damage if any, it's the idea of him getting big and mean too.
If he stays small and minds his beeswax, I'm fine with him.