Emerald Crab -yay or nay?

[Europhyllia]

I have been thinking of getting an Emerald Crab mostly because I hear they eat bubble algae. They also seem kind of interesting.
What's everybody's opinion on them?

My main concerns are these:


will harm/eat fish or other critters
will not eat bubble algae
will be tough to catch if he causes any trouble


I think I read somewhere that females aren't as prone to start causing trouble but I don't remember how to figure out the boy/girl thing on crabs.

[Mr Cob]

These are the only type of crabs I keep. I tossed the hermits over a year ago, got tired of them killing snails and messing with frag glue etc.

So, yes, I'm a big fan of emeralds. I trade them out when they get big though. I have never lost a fish to a emerald that I know of. I get rid of them when they are big because they can easily move things. Most of my corals are mounted so no worries there but they can move small pieces of live rock easily if they are large enough. 80% of mine have always eaten bubble algae (i don't know how I came to that percentage...I just guessed).

My wife and I enjoy watching them eat. They will also eat hair algae and clean rocks. It's cool to watch them grab pieces with their claws and then bring to the mouth.

Cool addition IMO.

[Europhyllia]

So you would say they're easy to catch? They don't hide? Remember I got a lot of rock with a lot of tunnels, caves, etc.

[Mr Cob]

Oh trust me I have a lot of tunnels! I also have a 29" deep tank both top to bottom and front to back. They are easy to catch in my experience because mine all come out when the MH goes off. When I have just my blue LEDs on they are out and I can grab them easily. You can also put something near their claw like some macro algae and they will clamp down on it and you can pull them up to the surface.

The big ones are the easy ones to catch. I have never had a problem catching them when they are large. But, that's me... others may have different stories. The small ones are a little more difficult to catch.

[Rychek]

Emerald crabs won't be a center piece in your tank because they prefer the dark, but, like Rob said, they aren't that hard to catch. I've been meaning to get some for my bubble algae infestation.

[phippsj]

I LOVE the emerald crabs. They are tons of fun to watch. I have no bubble algae at all.

[Europhyllia]

Looks like I might have to make a trip into town tomorrow. They're pretty common, right? Any sponsor store should have them?

[Rychek]

They are a general stocking item for most of the stores. Calling to check availability is always a wise thing to do though.

[Europhyllia]

Should I get one or more than one?
Mr Cob what do you do with them when they are big? And how fast do they grow?

[Mr Cob]

I get rid of them every 6 months or so. I keep about 3-5 in my tank. I only have 2 right now. I always try to buy smaller ones so they stay with me longer. I'm pretty sure most people just keep them and don't really care about their size, I'm probably extra cautious then I need to be but I'm also very particular about things.

I normally take them to the lfs for donation or store credit. But...the last one was HUGE a few months ago so I had to post him up for grabs and another member picked him up.

[Europhyllia]

Hm. I kind of get attached to my critters. Plus I still want Ed to get me some Trimma gobies (tiny gobies that only get to be about an inch long).
I don't want my trimmas to be crab snacks...

[Mr Cob]

I have a tiny yellow watchman goby...

Anyways... I guess the possibility is there but in my opinion it's unlikely that an emerald will become a problem if it has plenty of alage to eat....maybe I've never had a problem though because I don't keep the big ones.

We'll see who else chimes in with experiences.

[Goofball310]

Emerald crabs are oportunity eaters and will usually only eat fish if they are dying or dead.

[Rychek]

The only emerald crab I had was small and grew very, very slowly (less than doubling his size in a year). I had a brown mythrax crab (was sold to me as being the same as an emerald) that grew very, very fast (more than doubled his size in a matter of months).

[FireWater]

I have kept several Emerald crabs with little problem. I have only had one out of a dozen or so that liked to pull at polyps. I currently have 4 in my 90g and they range in size from dime to quarter across their shell. I have found that their growth is relative to water quality kind of like shrimp - molting often if they are enjoying life. I would also reccomend that any and all frags are glued down - I don't think they intentionally do it, but they will move and knock stuff over like a snail or hermit does.
I was told to look at their joints to tell male from female. Males tend to be larger in the joints and claws also more colorful (red) in the joint area. I have never found out for sure if this is true - i don't speak crab and never looked to see which undies they were wearing

[ShAgMaN]

I never had a prob with emeralds but I do get paranoid once they get big and trade them.

I know this is a little off subject, but I was wondering if anyone has tried the strawberry crabs. They look just like an emerald but are light red/pink. They look cool but I was wondering if the ate/grew the same.

[apedroza]

I had 2 that both seemed to love picking at zoa polyps!!

[Europhyllia]

I had 2 that both seemed to love picking at zoa polyps!!
did you have algae?

[phippsj]

I had 2 that both seemed to love picking at zoa polyps!!

It is possible they were going for small sponge and algae that grew between the zoa's /polyps. Mine did that but I never noticed any harm or missing zoas.

[hobogato]

i just picked up two small ones(emerald crabs) at reefs2u, i think they had at least two more

[Europhyllia]

Okay. Too wet and cold for me to venture out tonight but I'll call around and pick some up tomorrow. If it doesn't work out there's always the refugium... ;)

[allan]

I have one in my tank, only see him/her at night when I feed the acans. At one time I saw it under the acan rock bench pressing the rock up and down. Later that day the acan rock was on the sand bed upside down. Aside from that I've never had problems with them. Like Rob though I'm seriously thinking to get rid of my hermits as I've never seen so many empty snails shells in my tank.

Just a little off topic, but is the salifeet crab any better/worse than the emerald?

[Europhyllia]

Just a little off topic, but is the salifeet crab any better/worse than the emerald?

Is that short for Sally Lightfoot Crab? I've heard they can be very bad for other livestock.

[corruption]

I personally keep a couple TINY blue-leg hermits... And thats it for crabs. They're just too opportunistc and predatory for my tastes, with commensal crabs (such as acro crabs, etc) being one of the few exceptions i'd make.. Just my personal feelings on them, of course -- plenty of success stories include them in the mix :)

-Justin

[Third Coast Tropical]

In general, crabs can be sexed by looking at the bottom of their carapace (underside)...if the segemented part comes to a triangular point, then it is a male,...if the segmented part is more rounded, then it is a female.....wish I could draw a picture for you......

Now my disclaimer, this is true for most crabs, never sexed an emerald, but guessing it is similar

[Europhyllia]

Okay Third Coast, you wanna turn over some crabs with me tomorrow? :D

[Third Coast Tropical]

lol....can't tomorrow

the trick is...be faster than the crab

lol..no, there is a way to hold them and not get pinched, again, wish I could draw you a picture

good luck, I would think a store owner has experience handling them, and possibly even sexing them....

[Europhyllia]

Okay I got my crab sexing sheet printed out
http://www.reefstewardshipfoundation.org/forums/showthread.php?t=1278

Now I just need to get up the nerve to ask the LFS guys to let me see the underside of their crabs. :)

After reading around RC I am convinced I want a female.

[Mr Cob]

Kevin will do it at Reefs2u...LOL! I kind of want to see him do it... LOL!

[kkiel02]

lol ^ I wanna be there too.

[Europhyllia]

I think I might go somewhere for this where they won't recognize me... ;)

[Gseclipse02]

Just a little off topic, but is the salifeet crab any better/worse than the emerald?


worse crab to have IMO really aggressive


when i had one it would steal food from my LTA and one morning i found him eating my yellow tang :angry:


Kevin will do it at Reefs2u...LOL! I kind of want to see him do it... LOL!


LMAO haha watch out your crab might be violated with him lol jkjk

[Third Coast Tropical]

Those are good pictures to refer to Karin....exactly what I was talking about....I would feel a little strange asking to see the underside of a crab as well...but if it is what you want, then it must be done....

[Europhyllia]

l...but if it is what you want, then it must be done....
I like that attitude!

[Europhyllia]

crab sexing went great! Got two little female crabs, Veronica and Virgina :)

[Europhyllia]

okay I got the crabs but where's the fun you all have been promising?
After the first 24 hours I haven't seen them again!

[FireWater]

Pick up every rock in your tank and you will eventually find them.

Mine like to hide out most of the time - every once in a while I will see a green claw poke out of the rocks and grab at anything in reach. I get lucky every once in a while I they forget about hiding. Mine also run out when it is feeding time. So hopefully they will eventually settle in for you.

[jroescher]

They hide, and can hide well. I had an emerald crab a couple of years ago and eventually never saw it again. Recently I saw a green claw come out of nowhere in a rock and grab a piece of food. After watching for awhile, the whole crab came out. I haven't put anything new in my tank in a long time for him to have hitchhiked in.

[Mr Cob]

I don't think 24 hours is enough time for them to feel at home. I see mine all the time. Day and night but mostly night/actinic only. How many did you get anyways? How big too?

[Rychek]

Look at night with a red light. You'll see him.

[Europhyllia]

I don't think 24 hours is enough time for them to feel at home. I see mine all the time. Day and night but mostly night/actinic only. How many did you get anyways? How big too?

2 small females

The only red light I have is a chicken heat lamp... :blushing:

[saabtech]

now you all have me thinking about getting some emeralds.... but i dont have bubble algae. what else do they eat. (dont have any hair algae either) all i have is a little cyano in the sand

[jroescher]

Mine always just picked at the rocks like any other crab. Never touched bubble algae that I saw, but what little there was slowly went away.

[Double-O-Zilch]

They eat your tail spot blenny when you're not looking! I thick he may of had ich though. Not sure cause all I saw was bones and intestines. Thought it was a dead bristtleworm at first. I know my loves picking isopods off the glass and pretty much anything not glued down. He never stops picking at rocks and there is plenty of evidence he's eating.

[ErikH]

Emeralds are so neato. I love "Mr. Crabs" he's funny little guy.