Acropora crab

[chariton]

Hello I recently bought an acropora coral and inside of it it was a coral crab. Looks like cymo crab. My question is should I keep it there or I ll have to take it away because as I can see it eats polyps from coral. Any advise?

 

[fishywishy]

looks like coral crab to me. You can just leave it in there, they don't harm the corals.

 

[chariton]

looks like coral crab to me. You can just leave it in there, they don't harm the corals.

If you see the picture or the video there are some white spots on the acropora. These are polyps missing and they are on the places that crab eats that’s why I asked. Do you think these polyps will regenerate?

 

[fishywishy]

If you see the picture or the video there are some white spots on the acropora. These are polyps missing and they are on the places that crab eats that’s why I asked. Do you think these polyps will regenerate?

Oh, then maybe you should remove it. Coral crabs dont eat the corals they eat the stuff on the corals.

 

[chariton]

Oh, then maybe you should remove it. Cymo crabs dont eat the corals they eat the stuff on the corals.

That’s why I posted the video too. Cause it looks like cymo but I am not sure. And as far as I know cymo not harming corals

 

[fishywishy]

That’s why I posted the video too. Cause it looks like cymo but I am not sure. And as far as I know cymo not harming corals

Im pretty sure you can keep it in there if you want, i think cymo crabs eat the corals but aren’t necessarily bad in small numbers but i could be wrong @ISpeakForTheSeas

 

[ISpeakForTheSeas]

Im pretty sure you can keep it in there if you want, i think cymo crabs eat the corals but aren’t necessarily bad in small numbers but i could be wrong @ISpeakForTheSeas

That's pretty accurate:

The crab may be a Cymo sp. such as Cymo melanodactylus - they're obligate commensals with Acropora corals, and their relationship with them seems a bit mixed; they reportedly do very, very little damage to the coral, and they seem to help keep the corals healthy if the coral is diseased.

Looks like a Cymo sp., possibly C. andreossyi or C. melanodactylus (this one if it has black claws):

That said, there are also reports like the one linked below where the crabs may be responsible for killing coral colonies.

Are infestations of Cymo melanodactylus killing Acropora cytherea in the Chagos archipelago? - Coral Reefs

link.springer.com

However, the corals dying may have been caused by a few separate things:
-Overpopulation of crabs
-Disease
-Bleaching
-Etc.

If the corals were dying for reasons unrelated to the crabs, however, then the crabs may have been trying to protect the healthy colonies by consuming the sick/dying ones.

So, the crab is essentially typically a beneficial parasite; if the coral is small or struggling in your tank, then the crab could very well kill it, but if it's large and doing well, it should be fine to keep.

Probably Cymo andreossyi - generally not one you'd want in an aquarium, but at least somewhat beneficial in the wild:

they're somewhat parasitic on their host corals; in small numbers on big colonies, they're helpful, but in large numbers and/or on small colonies, they may kill the colony.