Acro crab id

[robdog]

I found these two crabs in the same piece of acro and was wondering if they are good or bad species? They live among my prized acros.

 

[robdog]

feom my research so far, Im leaning toward the small sharp claw one not harming my acros but the hairy one might go in the sump.

 

[nsteinca]

I believe the one on the bottom is a bandit acropora crab. My understanding is they are reef safe and have a symbiotic relationship with SPS corals. I had one come in on a chunky frag once. Saw it for maybe a week and then think my sixline wrasse put an end to him lol. Not sure about the top one

 

[robdog]

I believe the one on the bottom is a bandit acropora crab. My understanding is they are reef safe and have a symbiotic relationship with SPS corals. I had one come in on a chunky frag once. Saw it for maybe a week and then think my sixline wrasse put an end to him lol. Not sure about the top one

Thanks for the info. I think you are right. I have released the bandit crab back in the tank and it is doing fine. The other one is on a chunk of acro in my sump for the moment as I think it might be a gorilla crab.

 

[ISpeakForTheSeas]

I found these two crabs in the same piece of acro and was wondering if they are good or bad species? They live among my prized acros.

The top crab is Cymo melanodactylus - probably not a keeper, but pretty neat:

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:

https://aquadocs.org/bitstream/handle/1834/9351/Cymo%20andreossyi.pdf?sequence=1&isAllowed=y

The bottom crab is Trapezia guttata - it's a keeper.

 

[robdog]

Thanks very much for that. The trapezia guttata has found a good spot in one of my acros and also has at least one other buddy in there. A great looking little crab.