Emerald crabs. . are they predatory?

[toohipnoob]

Got a 24g Nano, in it's 2nd year, as a noob has several blow-ups/die off, but settling back down. I don't have many corals but trying to improve. Nothing unusual in the fish category, irrelevant to question. I have a lot of hermit crabs and nassarius snails for clean-up duty. Also have recently added some emerald crabs, about 3-4, largest about 1/2". Not sure if male or female, seem to have medium sized claws so could be males. Not sure if crab gender is part of the concern. I had just added peppermint shrimp to hopefully eat my aiptasia that's breaking out, and the next day can't find it. Then I find an emerald chowing down on my expensive cleaner shrimp, who was healthy. I'm highly suspecting the emerald crab(s).

I've researched all the forums, (I love researching info!) but there's too much of a mix of rationale. I agree, these guys are opportunists and will eat dead fish and invertebrates, and live critters won't stand around for a crab to start munching on them. I like that aspect of the crabs. . clean up of dead critters. But I can't afford to have them killing my livestock. Fish seem to quick and tough for crabs to kill (yes, I've heard otherwise), but a delicate peppermint or cleaner shrimp with all it's legs and tentacles would be easy to latch on to. What I'd like to know for sure. . is can these emerald crabs, as small as they are, be predatory to actually kill a reasonably healthy shrimp?

It would be easy (well not really to catch them) to simply remove them (some I hear put them in the back sump? with chaeto?), but I'd like to keep the emeralds for clean up, especially since I have an outbreak of hair algae (my lamp bulbs are over 18 months old), and I hear they're good for that. But I can't live with them, if they kill delicate shrimp. Guess it's either the shrimp or the crabs? If I get a confident fact they can or will kill small shrimp, even fish. . then they're gone. Appreciate direct experiences or knowledge.

Thanks. . still a noob at this.

 

[gemini9]

I have an emerald in my 30 and he's peaceful. He's a food theif and may steal the food from others, lol but they are harmless. The only thing that would concern me would be having more than one in a smaller aquarium because they can be territorial towards their own kind. I don't think an emerald would be able to catch a healthy fish anyway. Crabs are kinda slow. It's my guess, the peppermint was already dead before the emerald got it.

My emerald doesn't seem to pay any attention to my hair algae.

 

[toohipnoob]

I have an emerald in my 30 and he's peaceful. He's a food theif and may steal the food from others, lol but they are harmless. The only thing that would concern me would be having more than one in a smaller aquarium because they can be territorial towards their own kind. I don't think an emerald would be able to catch a healthy fish anyway. Crabs are kinda slow. It's my guess, the peppermint was already dead before the emerald got it.

My emerald doesn't seem to pay any attention to my hair algae.

I would agree, but this is like the third shrimp (one cleaner, two peppermints) that have either disappeared or I find their carcass (I know what a molt looks like). This cleaner shrimp was healthy for the longest time, and I had maybe one or two emeralds (hard to keep track they hide and die under the rocks), then I got two more, and right after that. . I find one of them on my freshly killed cleaner shrimp. I really, really want to keep them. . they are cool to watch, and unique critters. . but I don't see them eating hair algae (I think caused by my nearly 2 year old bulbs). Next research how to clean off hair algae, with out disturbing corals or removing "good bacteria". Someone mentioned hydrogen peroxide, but that's scary. I think sometimes I look for natural fixes, which are causing more problems then fixes! Thanks for the reply.

 

[5Bucks]

I have a couple of Emeralds. One of them about twice the size of the other. Fairly certain he's been preying on some Turbo Snails. Started finding empty shells - 2 in the last couple of weeks. Never saw him do it. Then last night saw him attack a Conch. He was unsuccessful but tried getting at the soft underbelly and in thru the point where the Conch sticks the tube out. He gave up on the meaty parts and then started cleaning the algae off the shell of the Conch. Maybe I need to feed him more. He loves the dried sheet algae. He's a real character, waves his claws around when I'm near the tank kinda asking to be fed. Other Emeralds I've had have been very shy. This big boy is out all the time. I have a coral banded and they stay away from each other.

 

[catlinth]

I have a pair of emeralds in my 30 gallon. For the most part, they are peaceful. They will steal food from my corals from time to time but, my skunk cleaner shrimp is much worse for doing that. I did have some problems with them eating tentacles from my Duncan but, they stopped when I moved the Duncan to a different spot in the tank. Now, they are more likely to hide under the Duncan. My emeralds have recently learned that they can ride my snails to get at algae on the glass when I have been neglectful in keeping the glass clean.

 

[haleyf1024]

My emerald never bothers or eats any coral in my tank (zoas, birdsnest, mushrooms, etc etc.) And I have to agree with the comment on the skunk shrimp being worse for food stealing, lol. He doesn't bother my RBTA either. But, he is very outgoing and gets hand fed mysis and krill so maybe that is why mine doesn't bother coral or my hermits/snails?

 

[glb]

My emeralds took out a few shrimp and snails in my nano, so I don't use them in my tank anymore.

 

[3Twinklets]

They can be a pest if they are hungry. I feed my tank well so have never had a problem

 

[catlinth]

They can be a pest if they are hungry. I feed my tank well so have never had a problem

I agree. Plus, it is fun watching them go nuts when you give them small bits of nori.

 

[Wiz]

They have flat claws. I dont see how they would kill snails or shrimp. I have one in my 40b. Had 3 in my 90. They are clumsy, and strong. Occasionally causing rock slides or popping a plug out of place. But I have never in 8 years of reefing seen them "attack" another inhabitant. Not saying I'm right. But I would bet your losing shrimp and snails for another reason. Either water issues or another predator. My 2 cents.

 

[Wiz]

And I stare at my tank on average 2 hours a day or so. And spotlight with a red bulb after lights have been out a while every night before bed.

 

[Wiz]

Got a 24g Nano, in it's 2nd year, as a noob has several blow-ups/die off, but settling back down. I don't have many corals but trying to improve. Nothing unusual in the fish category, irrelevant to question. I have a lot of hermit crabs and nassarius snails for clean-up duty. Also have recently added some emerald crabs, about 3-4, largest about 1/2". Not sure if male or female, seem to have medium sized claws so could be males. Not sure if crab gender is part of the concern. I had just added peppermint shrimp to hopefully eat my aiptasia that's breaking out, and the next day can't find it. Then I find an emerald chowing down on my expensive cleaner shrimp, who was healthy. I'm highly suspecting the emerald crab(s).

I've researched all the forums, (I love researching info!) but there's too much of a mix of rationale. I agree, these guys are opportunists and will eat dead fish and invertebrates, and live critters won't stand around for a crab to start munching on them. I like that aspect of the crabs. . clean up of dead critters. But I can't afford to have them killing my livestock. Fish seem to quick and tough for crabs to kill (yes, I've heard otherwise), but a delicate peppermint or cleaner shrimp with all it's legs and tentacles would be easy to latch on to. What I'd like to know for sure. . is can these emerald crabs, as small as they are, be predatory to actually kill a reasonably healthy shrimp?

It would be easy (well not really to catch them) to simply remove them (some I hear put them in the back sump? with chaeto?), but I'd like to keep the emeralds for clean up, especially since I have an outbreak of hair algae (my lamp bulbs are over 18 months old), and I hear they're good for that. But I can't live with them, if they kill delicate shrimp. Guess it's either the shrimp or the crabs? If I get a confident fact they can or will kill small shrimp, even fish. . then they're gone. Appreciate direct experiences or knowledge.

Thanks. . still a noob at this.

Also I have 2 fire shrimp a scarlet shrimp and over 100 snails easy in my 40b. So he has plenty of opertunity. At night I watch him walk right over my sleeping purple firefish without a glance. I would not blame the emeralds unless you see it with your own eyes.

 

[toohipnoob]

Thanks for all the replies. While I don't think they're actively predatory, they're definitely opportunists, and maybe a weakened, slow moving fish or shrimp is that opportunity when also hungry? I don't feel it's a slam dunk they won't kill to eat if opportunity or the drive is there, but so far I haven't relocated them to my sump as some have suggested. One died, the big one, and I still have two smaller ones. I have them for cleanup, and I noticed the other day my two Kupang Damsels are down to one. Can't find the body, but I'm sure the crabs are doing their job faster than the water can do decomposing them. Same happened to an expensive Diamond Goby I bought for cleanup. Just disappeared. Don't want to lift live rock and disturb the sand bed. . did that intentionally and the hydrogen-sulpheric buildup killed everything. So I just watch for the obvious bodies, and let the clean up crew do their job. Also it's pretty obvious you can't watch these critter's 24/7 to check their behavior, sometimes it's just coming to conclusions on evidence you come across. Fun hobby, but expensive, and VERY technical using both science and art!

 

[Wiz]

Thanks for all the replies. While I don't think they're actively predatory, they're definitely opportunists, and maybe a weakened, slow moving fish or shrimp is that opportunity when also hungry? I don't feel it's a slam dunk they won't kill to eat if opportunity or the drive is there, but so far I haven't relocated them to my sump as some have suggested. One died, the big one, and I still have two smaller ones. I have them for cleanup, and I noticed the other day my two Kupang Damsels are down to one. Can't find the body, but I'm sure the crabs are doing their job faster than the water can do decomposing them. Same happened to an expensive Diamond Goby I bought for cleanup. Just disappeared. Don't want to lift live rock and disturb the sand bed. . did that intentionally and the hydrogen-sulpheric buildup killed everything. So I just watch for the obvious bodies, and let the clean up crew do their job. Also it's pretty obvious you can't watch these critter's 24/7 to check their behavior, sometimes it's just coming to conclusions on evidence you come across. Fun hobby, but expensive, and VERY technical using both science and art!

So you lost snails, shrimp, fish, and even one of the questionable emeralds. I would bet there's a water quality issue.