I hate Emerald crabs

erk · Dec 11, 2014

So, as the title says, I hate emerald crabs. I bought 2 to try and get the bubble algae that is cropping up under control as I manually remove the stuff I can see. Well, one of these things decided it wanted corals instead and ate the single mouth out of a booger sized chalice frag I bought. The chalice was doing great and growing quickly before this happened. Is there a chance it will heal and keep growing or will it most likely fade away?

Z06-Hec · Dec 11, 2014

cant answer that, but i can agree... Emerald crabs are advertised as reef safe and are not.
I had one when they sold to me said it only eats algae and stuff and crap in the sand... yeah right...
I saw it nipping at fish left and right... It also went to town on my chocolate star, chunks at a time.
One of my damsels hated that... one day the crab was dead... i assume one of the damsels got ****** and ate it. all i saw was an empty shell.
I was pretty shocked though.

erk · Dec 11, 2014

Yeah, I'm shocked at how blatantly they attack my fish and such. Guess I'll have to figure out catching them and sticking them in the sump.

BlueZreef · Dec 11, 2014

I pulled mine out when I was up one night and looked at the tank with a flashlight and one was taking food out an open brains mouth....he went to the sump after that. I would suggest a foxface for bubble control instead if possible.

Your chalice could heal up, give it time and easy on the light.

erk · Dec 11, 2014

OK, Ill lower my lights a bit and try to catch those crabs. I have 29 gal tank, so if I get a foxface I'll get a small one to try out. I am firmly planning to upgrade to a 90 cube sometime in the middle of next year.

Webslinger · Dec 11, 2014

I have 2 small emerald crabs about the size of a nickle and I love them!!. The are the best cuc in my tank by far. They leave eveything alone. hope they stay that way!

Baldguy · Dec 11, 2014

I had one perch on top of my favorite duncan plucking tentacles off one after the other. Too the sump that one went.

rworegon · Dec 11, 2014

emeralds are definitely a hit and miss proposition. The females tend to be somewhat less aggressive and unpredictable but when they are small its hard to sex them. I've tried them a few times in the past but never had any luck.

GHill762 · Dec 11, 2014

loved my emerald until I got a clam, immediately started tearing the mantle when I put the clam in the tank. I then banished it to the sump and only saw it once after that.. pretty sure he's gone now..

TarHeelReefer22 · Dec 11, 2014

Like any crab they are opportunistic eaters and if there is a coral in bad shape it will eat dying flesh. Also, nipping at fish sounds like you have fish in there that are showing interest in inverts in which case can you blame the crab for protecting itself? I have had two in my current tank that have been in there for over a year now and aside from being clumsy when grazing I have not seen any interest in coral. Previous to this I had one that was in my tank for over 3 years and I will advise when they get to a large size they should be replaced with smaller ones.

Jmcdaniel0 · Dec 11, 2014

I rarely see mine. I check him, at night sometimes, he just wanders about eating junk off my rocks, never seen him bother anything else.

WindeyD · Dec 11, 2014

I have had several pairs of emeralds, never have had any issues with them molesting corals but they will certainly take down some snails if they can't find enough food. I feed mine manually once a week and mine have been good inhabitants. I consider most crabs and shrimp to be reef safe with caution.

erk · Dec 11, 2014

TarHeelReefer22 said:
Like any crab they are opportunistic eaters and if there is a coral in bad shape it will eat dying flesh. Also, nipping at fish sounds like you have fish in there that are showing interest in inverts in which case can you blame the crab for protecting itself? I have had two in my current tank that have been in there for over a year now and aside from being clumsy when grazing I have not seen any interest in coral. Previous to this I had one that was in my tank for over 3 years and I will advise when they get to a large size they should be replaced with smaller ones.

The chalice that the crab ate was definitely in great shape. Very reactive and always put its tentacles out when feeding. The crab literally ate just the mouth. Maybe the coral had captured some food and wanted to take it away. As for fish that want to eat it, it was flaring at firefish, chromis, a clown, and a small blenny. I definitely agree that any crabs will take advantage of things that stand still long enough and emerald crabs are no exception.

erk · Dec 11, 2014

I checked the chalice frag and while I can see skeleton in the center the rest of the flesh is inflating and looks pretty good. I think it might recover.

erk · Dec 12, 2014

I just caught both crabs on my frag rack chowing down on corals. I have noticed a large reduction in bubble algae so I think they are moving onto the corals. I caught one, hopefully the other one will stick to the bubble algae for awhile.

Sully · Dec 12, 2014

Always amazing at the amount of blame people place on the things they put in their tank.

Tab28 · Dec 12, 2014

Emerald crabs are no different than any other living creature. If they are hungry they will eat. If they are eating your corals you are not providing them with enough food. They will rather grab a piece if food on the sand bed than rip it off something that gives more resistance. Even a reef safe fish will resort to eating at coral if it is hungry. If you do not have enough food on sand bed. Do not get any invertebrates. There is a reason many tanks that are low nutrient do not have fish or most types of invertebrates. They require food. Uneaten food and digested food byproducts means higher nutrients.

A fox face will get too big for a 90 gallon and knock over things. They scare easily and freak out. They will also nip at LPS if not given enough food. What the fish believes is enough food not what you think is enough food.

Pacman · Dec 12, 2014

I had one that decide that it did not like my hammer coral , caught him ripping the tentacles off , wasn't eating them either just destroying the coral. By the time I figured out it was the crab I lost the coral.