Crab eating Acropora?!

whixley101 · Apr 22, 2014

Earlier in the week I notice another crab in one of my Acropora. Great, right? This one did not have a hard shell or spoon shaped pinchers like the other ones I have. This particular crab is "hairy" and blends in to the green milli really well with the tan hairy appearance. Over the past couple of days I have notice healthy tissue missing. So long story short(three days of panic and combing the web), I noticed today that he appeared to be pinching and eating healthy polyps. I have attach the best picture I could find as a representation of what this one looks like. I have never had an Acropora crab not be beneficial, but I refuse to believe my wife and I are crazy. I had to grab her as well to make sure I was not seeing things! Again, any help is much appreciated before this guy meets my porcelain tank.

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Naiad · Apr 22, 2014

That is not an acro friendly crab! They will eat the acro and move on to the next. Not really a symbiotic relationship.

Mike&Terry · Apr 22, 2014

That is a cymo sp. crab. They are commensal coral crabs and will do best with larger coral colonies as they do eat a few polyps here and there. We have a couple in our reef and have found them to be beneficial to our larger colonies. You may want to check out this thread: https://www.reef2reef.com/forums/general-invert-forum/92842-commensal-crabs-love-em-hate-em.html

If you decide to remove the crab, see if anyone in your local club wants it before you kill it.

Naiad · Apr 22, 2014

I am amazed you can keep these guys in captivity without destroying your acros. You must have amazing growth.

Mike&Terry · Apr 22, 2014

Naiad said:
I am amazed you can keep these guys in captivity without destroying your acros. You must have amazing growth.

We've kept these crabs for years and from what we've observed, their coral "grooming" encourages new growth.

whixley101 · Apr 22, 2014

This milli colony is about 5x4 and where it has eaten is very clean but coralites(sp) are not destroyed. If new growth will come at the affect area, this might be interesting or a total failure?!

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whixley101 · Apr 23, 2014

Anyone else with an opinion? I am have a lot of trouble finding info on this guy

Naiad · Apr 23, 2014

I would see if it grows back! When I worked at a Lfs these guys would be problems but then the acros where stressed and may not have been able to recover properly. Good to learn that they can be kept if the coral is in good health.

reeffirstaid · Apr 23, 2014

I've had this crab appear on several frags. I soaked them in a high iodine coral dip, and that killed the crab. They do consume polyps and can wreak havok on a frag.

Naiad · Apr 23, 2014

reeffirstaid said:
I've had this crab appear on several frags. I soaked them in a high iodine coral dip, and that killed the crab. They do consume polyps and can wreak havok on a frag.

Yea I think they would need a well established colony.