Emerald Mithrax Crabs and SPS corals

[bigevill]

A friend of mine has seen an emerald mithrax crab eating the flesh off of one of his SPS colonies. He thinks that the coral was dying first and that the crab is just cleaning up, but he has been told by others that these crabs can do this sometimes. I have read everywhere that these crabs are 100% safe with corals. Now to the defense of the crabs he may not be feeding them at all. He only has one fish in the tank right now and is not adding much food at all. They could be driven to eat whatever they can. I didnt want to say that though till I hear what everybody else has to say.

[bigevill]

nobody has anything for me here?

[emoore]

I have 2 emerald crabs and they dont eat my SPS. One does think he is an acropora crab and will sit in one of my acro's at night but I don't think he is eating it.

[Peter Eichler]

I have seen them crawl up on SPS plenty of times, whether they are eating mucus or detritus that may have settled on the coral or flesh from the coral is hard to say. Whenever I've seen them on an SPS coral I've tossed them in the sump or refugium so I don't know if they're really doing any damage. In short, I don't trust them totally, but I don't think they would do much damage before you notice there might be a problem with one.

On a side note, they've always been pretty useless when it comes to bubble algae IME so I don't see much use in them as part of a cleanup crew.

[airtime23]

I had two Emerald Crabs. The day I put them in the tank they started devouring my green star polyps...literally ripping them from the root and eating them!

Needless to say, I had to tear down part of my tank to get them out, but I did and took them right back to the LFS. IMO, they are NOT 100% reef safe.

[Frick-n-Frags]

I've used them for many years expressly for cleaning around stony corals. Over the years the have made me nervous a few times, seeming to find something that needs a lot of work on the surface of a coral. I never interfered, even when one rarely exposed a small patch of skeleton. The next day, the ding was always gone.

It is very difficult for a coral to overgrow like a bit of algae on a damaged tip, but the mithrax will pick that clean and the coral can close right over then. They also keep the margin along the growing encrusting edges clean. sometimes they work a little into the coral edge, but, once again, the coral doesn't have to fight with anything to spread.

I have seen a fuzzy black Acro crab at work. Once you see that, even an obnoxious mithrax is small change compared to watching something eat an Acro like a candy bar. And you can tell, the mithrax isn't out to munch the good parts of the coral like that thing was.

My only complaint is that they knock stuff around sometimes.
Big deal.

[thorsky]

I've had the same luck as Frick-n-Frags. My 2 Mithrax are fastidious algae cleaners, much better than any hermit or snail I've ever seen. When I first got them I was concerned as every night, within 15 minutes of the lights going out, they would take up residence in my SPS. One climes a finger on a porites and one lodges himself into a birdsnest. They still do it every night like clockwork. Doesn't seem to bother the corals at all.

[Tang Salad]

Originally posted by Peter Eichler
I have seen them crawl up on SPS plenty of times, whether they are eating mucus or detritus that may have settled on the coral or flesh from the coral is hard to say. Whenever I've seen them on an SPS coral I've tossed them in the sump or refugium so I don't know if they're really doing any damage. In short, I don't trust them totally, but I don't think they would do much damage before you notice there might be a problem with one.

Same here.

Originally posted by Peter Eichler
On a side note, they've always been pretty useless when it comes to bubble algae IME so I don't see much use in them as part of a cleanup crew.

Doubly same here! Although other people seem to have had luck with them eating Valonia. Just not me...

[PrangeWay]

I've had the same luck as Frick-n-Frags. My 2 Mithrax are fastidious algae cleaners, much better than any hermit or snail I've ever seen. When I first got them I was concerned as every night, within 15 minutes of the lights going out, they would take up residence in my SPS. One climes a finger on a porites and one lodges himself into a birdsnest. They still do it every night like clockwork. Doesn't seem to bother the corals at all.

This is my experience to. Always find one of them at night hanging on my branching porties (which grows like mad, so he's no affecting it).

PW

[Frick-n-Frags]

mine are basically worthless on bubble algaes too. I'll see some damage periodically. and they absolutely won't touch hair algae.

For me, they have only one very important function=clean around the corals.

[RichConley]

Originally posted by bigevill
A friend of mine has seen an emerald mithrax crab eating the flesh off of one of his SPS colonies. He thinks that the coral was dying first and that the crab is just cleaning up, but he has been told by others that these crabs can do this sometimes. I have read everywhere that these crabs are 100% safe with corals. Now to the defense of the crabs he may not be feeding them at all. He only has one fish in the tank right now and is not adding much food at all. They could be driven to eat whatever they can. I didnt want to say that though till I hear what everybody else has to say.

Thats another reason why overfeeding and overskimming are much better for a tank than underfeeding. Things will eat, whether you give them food or not.


I feed a lot...never have problems like this.

[rooroo]

I added two and have only ever seen one. He hides under rocks during the day and tends to rearrange small rocks as he likes. He doesn't eat anything though. Doesn't touch bubble algae either. I actually don't like him much and am thinking he needs to go soon.

[REEFRHEAD]

if got 7 in my big tank and they are excellent algae eaters, ive watched one mow down soo much long hair algae that i couldn't believe it. they are great when they are nice and small because they can get those small tips of their claws into small holes and eat everything on the surface of the rocks and anything it can reach in the rocks the only thing i have noticed is when they get larger they might like snacking on a polyp, but i always just made they move with my plastic stick and then they leave the coral alone and for the most part they dont harm snails or anything, but i should add that they do need alot of algae or they will turn to other things like polyps or baby mushrooms even small things that over populate most of our tanks anyways, never noticed any of them bother any of my montiporas or my acroporas i could see them cleaning off the algae growth near the base and any exposed skeleton for sure but the coral would regenarate over that clean area quick like eveyrone says soo keep watching you never know if you think your specific one is bothering your sps just trade him in for a smaller one to the lfs good luck catching him theres some great advise on the subject on here, i would say go with the tall glass 45 degree angle angainst rockwork and like piece of krill or mysis in the bottom and they will go right in and cant get out

[supervdl]

There are mixed reports throughout RC about these guys, but I personally - knock on wood - have not had any problem with my three emeralds. Model citizens so far - unlike my black sea urchin that mows through my SPS frags about once or twice the month.