Watch OUT for Emerald Crabs!

authentic · Feb 3, 2016

Noticed some chipping on the base of some of my SPS new growth so i got out my night LED flashlight and took a look...I bought a small emerald crab(1/2 the size of a penny)and there he was with its little pincers at the base of my frags nipping away.Looked up the stats online and sure enough it warned of this type of behavior..my tank is extremely clean and i guess there wasnt enough food for the little guy!

CodyRVA · Feb 3, 2016

Same thing happened to me. I had a pair that cleaned up a bunch of hair algae, but once it was gone... they started tearing through the zoas. :mad:

tankstudy · Feb 3, 2016

CodyRVA said:
Same thing happened to me. I had a pair that cleaned up a bunch of hair algae, but once it was gone... they started tearing through the zoas. :mad:

I found out the same way you did.

cginter · Feb 3, 2016

^^^ same happened to me a long time ago. They tore through my zoas.

aabjones888 · Feb 3, 2016

Same thing for me too, it sucks when w u start noticing ur coral disappear. There hard little guys to catch too.

CodyRVA · Feb 3, 2016

I put a raw piece of shrimp in a glass cup and leaned against a rock at a 45 degree angle and they went right for it. Had them both caught within an hour.

Triggreef · Feb 3, 2016

Luke anything else we keep they will try to do what they think is needed for survival. I keep hundreds of these crabs between all my tanks and seldom have an issue. I have however had one that went for the tips of an acro before. Not sure why but I did catch him doing it and he hasn't tried it again since. My tank is too big to have caught him. I see some in my stylos chasing polyps now and then but they don't do any damage.

As for zoas, they do cause them to temporarily close, but never actually eat polyps. They do clean very diligently in between the polyps. I have hundreds of zoas colonies many many crabs. Crabs don't eat them.

CodyRVA · Feb 3, 2016

Triggreef said:
Luke anything else we keep they will try to do what they think is needed for survival. I keep hundreds of these crabs between all my tanks and seldom have an issue. I have however had one that went for the tips of an acro before. Not sure why but I did catch him doing it and he hasn't tried it again since. My tank is too big to have caught him. I see some in my stylos chasing polyps now and then but they don't do any damage.

As for zoas, they do cause them to temporarily close, but never actually eat polyps. They do clean very diligently in between the polyps. I have hundreds of zoas colonies many many crabs. Crabs don't eat them.

They will eat zoas, I've seen them do it.

favites · Feb 3, 2016

Everyone's mileage may vary, but for me-- a crab is a crab is a crab....

one of the main reasons I don't put 'live rock' in my tank and dip everything else in Bayer hot sauce :>

cb684 · Feb 3, 2016

Got one eating the tip of acros in my tank too. Usually they freeze with light. I was able to catch the one that was damaging my acros pointing a flashlight at him and then using a net. It helps if a second person hold the flashlight.

Triggreef · Feb 3, 2016

CodyRVA said:
They will eat zoas, I've seen them do it.

No offense, I've seen people post videos on YouTube of their emerald eating their zoas. They definitely were not. Maybe you have a rogue agent. But like I said, I have hundreds of zoas, many colonies, many frags. They are often walking in the zoas eating stuff. But not eating the zoas.

I also keep about a dozen mithrax in my frag tank. I have gone through 250 frag plugs in the last couple months, about 90 percent of those are zoas. Tanks full in prep for frag farmers market. Every now and then I find an empty plug. But the zoas that came off it are at the bottom of the tank, not in crabs belly.

authentic · Feb 3, 2016

Crabs are opportunistic eaters!maybe I'll get a pom pom

Laker32 · Feb 3, 2016

Triggreef said:
Luke anything else we keep they will try to do what they think is needed for survival. I keep hundreds of these crabs between all my tanks and seldom have an issue. I have however had one that went for the tips of an acro before. Not sure why but I did catch him doing it and he hasn't tried it again since. My tank is too big to have caught him. I see some in my stylos chasing polyps now and then but they don't do any damage.

As for zoas, they do cause them to temporarily close, but never actually eat polyps. They do clean very diligently in between the polyps. I have hundreds of zoas colonies many many crabs. Crabs don't eat them.

I woke up one morning and found a large head missing from a Paly before, and I know my fish didn't bite it off. Emerald Crab could have been the only culprit.

Triggreef · Feb 3, 2016

Laker32 said:
I woke up one morning and found a large head missing from a Paly before, and I know my fish didn't bite it off. Emerald Crab could have been the only culprit.

Not going to argue the point all night here but I probably have more emerald crabs than anyone here. That said,

1. How do you know your fish didn't bite it off?

2. Sometimes zoas and paly also separate from the colony on their own. It happens.

Laker32 · Feb 3, 2016

Triggreef said:
Not going to argue the point all night here but I probably have more emerald crabs than anyone here. That said,

1. How do you know your fish didn't bite it off?

2. Sometimes zoas and paly also separate from the colony on their own. It happens.

Heads seperate and they leave the stock behind?

Triggreef · Feb 3, 2016

Laker32 said:
Heads seperate and they leave the stock behind?

Idk what can do that. But emerald crabs don't have scissors for claws. Their claws are actually like little cups at the end. Maybe a gorilla crab in your tank?

CodyRVA · Feb 4, 2016

Triggreef said:
No offense, I've seen people post videos on YouTube of their emerald eating their zoas. They definitely were not. Maybe you have a rogue agent. But like I said, I have hundreds of zoas, many colonies, many frags. They are often walking in the zoas eating stuff. But not eating the zoas.

I also keep about a dozen mithrax in my frag tank. I have gone through 250 frag plugs in the last couple months, about 90 percent of those are zoas. Tanks full in prep for frag farmers market. Every now and then I find an empty plug. But the zoas that came off it are at the bottom of the tank, not in crabs belly.

No offense taken, but like I said, I have witnessed this with my own eyes. Not picking around, or between, or cleaning zoas, legit tearing polyps into pieces and eating them. I'm not saying this is a common occurrence, merely that it CAN and HAS happened before, even if you yourself have not seen it take place, it's definitely possible. As mentioned, crabs are opportunistic, if food is scarce they will do what they must to survive.

Baby Ray · Feb 6, 2016

CodyRVA said:
Same thing happened to me. I had a pair that cleaned up a bunch of hair algae, but once it was gone... they started tearing through the zoas. :mad:

Same thing happened to me

Brainthestrong · Aug 16, 2016

CodyRVA said:
No offense taken, but like I said, I have witnessed this with my own eyes. Not picking around, or between, or cleaning zoas, legit tearing polyps into pieces and eating them. I'm not saying this is a common occurrence, merely that it CAN and HAS happened before, even if you yourself have not seen it take place, it's definitely possible. As mentioned, crabs are opportunistic, if food is scarce they will do what they must to survive.

I too witnessed my emerald tearing my zoa apart. It started to release a brown fluid.

Jimbo · Aug 16, 2016

I have seen my Emerald Crabs inside my Acros many times at night mostly. Never noticed any damage to the coral though. I'd assume if they were hungry enough, and being a crab, they would possibly eat almost anything.

Never had an issue with them myself though.