Emerald Crabs vs SPS

[Reefahholic]

I love the way emerald crabs clean rocks. Their pincher’s are perfectly made to pick a rock clean. However, they always seem to eat the base of my Acro’s. I’m just wondering if anybody else has this problem are do they just appear to eat corals, but stop after they taste a few. For sure I’ve had several eat almost 1/2 of the base of an Acro that I’d rather keep.


I guess what I’m trying to ask is how long does it take for them to stop messing with corals. Do they eventually stop or will they just keep eating SPS. How many people here still keep them without problems? Maybe they need supplemental feeding’s?

 

[Jay Hemdal Verified Community Expert]

I love the way emerald crabs clean rocks. Their pincher’s are perfectly made to pick a rock clean. However, they always seem to eat the base of my Acro’s. I’m just wondering if anybody else has this problem are do they just appear to eat corals, but stop after they taste a few. For sure I’ve had several eat almost 1/2 of the base of an Acro that I’d rather keep.


I guess what I’m trying to ask is how long does it take for them to stop messing with corals. Do they eventually stop or will they just keep eating SPS. How many people here still keep them without problems? Maybe they need supplemental feeding’s?

In Patrick Colin's 1970's Caribbean Reef Invertebrates book, he writes that Mithrax/emerald crabs have been documented at eating Porites coral at a rate of up 10 polyps per minute. Based on that, I've avoided keeping them with SPS.....

Jay

 

[386reeftrader]

IME, once they’ve got the taste for SPS there’s no end to it. You could always remove the bad one and try a batch of new ones.

I also don’t keep them anymore for this reason

 

[exnisstech]

I did not know this about emeralds. I have one in a smaller sps tank but I only see it after lights out. I think I'll try to remove it just to be safe. I have to manually remove bubble algae as it appears so the crab isn't doing what I added it to do anyway.

 

[GarrettT]

I made the switch to Pitho crabs a long time ago. No longer have issues with corals. I supplemental feed every other day. Makes a difference.

 

[David_CO]

mine killed my beautiful rainbow splice, he would only eat it super late at night. never again in an SPS tank

 

[jkcoral]

Emerald crabs are a headache. A less popular, but awesome alternative is the Pitho crab.

Emerald crabs always end up causing some type of trouble and can/will eat coral.

 

[jda]

I have never had emeralds eat any coral. I do make sure that they have food. They do not eat coral in Florida, but any of us would rather than starve. I have seen them eating things out of the slime coat.

 

[386reeftrader]

I have never had emeralds eat any coral. I do make sure that they have food. They do not eat coral in Florida, but any of us would rather than starve. I have seen them eating things out of the slime coat.

What makes you say they don’t eat coral in FL?

 

[jda]

I was at an hour long talk about crabs in the Caribbean reefs at the St Louis aquarium club and the presenter was a biologist studying crabs. They never observed them to eat corals in the wild. I also have never had them eat corals in my tanks.

I have no doubt that they could eat coral rather than starve. Many things eat terrible things rather than starve.

 

[386reeftrader]

I was at an hour long talk about crabs in the Caribbean reefs at the St Louis aquarium club and the presenter was a biologist studying crabs. They never observed them to eat corals in the wild. I also have never had them eat corals in my tanks.

I have no doubt that they could eat coral rather than starve. Many things eat terrible things rather than starve.

Agreed, there’s no doubt an endless supply of algae for them to eat in the wild, so observing them eat corals would be rare. My experience with emeralds that I’ve collected here in FL is that they can become voracious SPS eaters, not from lack of food.. Maybe the finer branched indo/pacific corals are tasty to them? It’s definitely an acquired trait, not all of them will do this but once they start they do not stop IME

 

[jda]

They eat more than algae. The scavenge for all kinds of things in the wild. Make sure that some pellets or flake float down there to feed them, shrimp, etc.

 

[Reefahholic]

Emerald crabs are a headache. A less popular, but awesome alternative is the Pitho crab.

Emerald crabs always end up causing some type of trouble and can/will eat coral.

Are Pitho’s that good?! Seems two of you guy prefer them. I need to try some. Hmm…

 

[Reefahholic]

Agreed, there’s no doubt an endless supply of algae for them to eat in the wild, so observing them eat corals would be rare. My experience with emeralds that I’ve collected here in FL is that they can become voracious SPS eaters, not from lack of food.. Maybe the finer branched indo/pacific corals are tasty to them? It’s definitely an acquired trait, not all of them will do this but once they start they do not stop IME

I’ve bought some twice and they went after the bases for sure. I think maybe they’re just too dumb to know the difference or maybe they really like the sweet taste of Acropora tissue. Lol

 

[Reefahholic]

I just want something to scrape my
Rocks well. Maybe I should look into a different option. Jda, which urchin is the most active in the day and night?

 

[jkcoral]

Are Pitho’s that good?! Seems two of you guy prefer them. I need to try some. Hmm…

I have been reefing for over 20 years, and just got my first pitho crabs about a month ago. Hands down the best crabs I have ever had in terms of cleaning ability (especially pesky bubble algae) and being well behaved. They also happen to look pretty neat!

 

[GarrettT]

Are Pitho’s that good?! Seems two of you guy prefer them. I need to try some. Hmm…

I’ve seen them go after my acro’s polyps multiple times when underfed, but for whatever reason, they never do any damage, unlike my emeralds. Now when I see it happening I just leave it alone knowing the coral will be unfazed.

 

[blecki]

I just want something to scrape my
Rocks well. Maybe I should look into a different option. Jda, which urchin is the most active in the day and night?

Not sure urchins are capable of sleeping. My pincushion just eats nonstop, day and night, and occasionally swings by the frag rack to pick out a hat. Leaves the rocks bone white, but of course he can't get into the crevices.

Anyway I've never had an issue with emeralds eating coral but I also don't keep anything fancy. No acros at all, only some hardy montis and stylos. Everything else in my tank is soft. I did have to remove an emerald crab from my nano tank because it had gotten big enough to be a threat to sleeping fish, but that crab is now doing fine in the 230 gallon. I have three in there and don't have any issues, and the only algae growth is in areas they can't reach. I feed heavily to make sure enough gets down to my engineer gobies so there's plenty for them to scavenge. I see it the same way as my yellow tang that ate all my acans years ago - they normally don't see the SPS as food, but once they find out it tastes good it's impossible to make them stop and you'll have to decide which animal you want to keep.

Has anyone successfully mixed pithos and emerald crabs? I kind of want to try one out, but not going to catch the emeralds to do it.

 

[Acros]

I have caught my emerald crab nipping at my TGC Cherry Bomb and my ASD Rainbow. Oddly enough, neither coral are affected by it. They don’t even retract their polyps while this happens.

 

[Reefahholic]

I have been reefing for over 20 years, and just got my first pitho crabs about a month ago. Hands down the best crabs I have ever had in terms of cleaning ability (especially pesky bubble algae) and being well behaved. They also happen to look pretty neat!

Where’s the best place to order?