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FAQs about Marine Crab Compatibility, Removal Strategies... 1

Related Articles: Crabs, Hermit Crabs

Related FAQs: Marine Crab Compatibility 2, Marine Crab Compatibility 3, Marine Crabs 1, Marine Crabs 2, Marine Crabs 3Marine Crabs 4, Marine Crab Identification, Marine Crab Selection, Marine Crab Systems, Marine Crab Feeding, Marine Crab Reproduction, Marine Crab DiseaseMicro-Crustaceans, Amphipods, Copepods, Mysids, Hermit Crabs, Shrimps, Cleaner Shrimps, Banded Coral Shrimp, Mantis Shrimp, Anemone Eating ShrimpCrustacean Identification, Crustacean Selection, Crustacean Behavior, Crustacean Compatibility, Crustacean Systems, Crustacean Feeding, Crustacean Disease, Crustacean Reproduction,

Hi Bob,
I keep seeing a strange looking crab in my aquarium, in fact I have seen quite a few now as I often look into my aquarium when the halides have gone out and there are only a few blue T5 tubes on.. One is fairly small, about 1 inch across and has red eyes. The other is quite a bit larger being about 4 inches across its shell and is absolutely covered in hairs, which makes it look even larger. The larger crab has been growing steadily and is now quite a formidable size. I have a mixture of fish and easy to keep soft corals, polyps etc. I have noticed that the crabs seem to be eating at the same time as the fish get fed- taking brine shrimp, Mysis and anything else they can get their claws on. This to me makes me think that they are not causing trouble and are happy living along side the other residents in the tank, have you any thoughts on this subject and whether these crabs are safe to keep? Thanks
Peter Johnston 

<I do have strong opinions here Peter. Most all crabs could be kindly called general omnivores, meaning they'll consume most anything (and everything!) organic they can get their greedy claws on. To put this bluntly, I dont trust decapods to do anything but seek out and try to consume all life in an aquarium if they're in the least bit hungry; hence my stock admonition to not trust any of them, particularly larger individuals, species. At the very least I urge you to keep constant vigilance if having crabs in your system/s, and do make sure they are being fed If it were me, mine, I would bait, trap out the larger one/s and remove them to a sump, possibly their own system. Not to alarm you, but it has been my long-and-constant observation that marine crabs of all kinds/species always become opportunistic, chewing on sessile invertebrates of all kinds, even catching, killing and consuming sleeping fishes in time. I do urge caution. Even largely herbivorous crabs will attack other reef life. >

Snack Crab - 08/20/05 I am crest-fallen this evening. <<That doesn't sound good...>> I have found my anemone crab, fresh after a molt, with only 2 and a half legs and 1 food strainer. (Sorry I don't know what the proper name for their feather like filter feeder appendage.) <<Feather-like filter feeder appendage works for me.>> It has no claws and therefore no way to defend itself. <<Not much "defending" with these little guys...is what the anemone is for.>> It had recently taken up residence under my Cynarina after finding my coloured bulb anemone too tough to keep up with. <<Likely it was expelled by the clowns you list below.>> I need to know if I should euthanize this wonderful little crab or if there is a chance that it will grow back the missing limbs. <<If it can feed and avoid predation, it should be able to regenerate the lost limbs.  It may take several molts before all is back to normal.>> It has been in the tank for 9 months and has done very well (12th molt).  The only tank mates it has are a 2 inch blood shrimp, a 3 inch banded boxing shrimp, 3 inch sally light foot crab, 3 common clowns, a 5 inch regal blue tang, a 6 inch blonde Naso tang, a 3 inch yellow tang, 3 inch neon Dottyback, small green mandarin and a ton of hermits and serpent stars. <<Oh my!  Please tell me this isn't a 75 gallon tank!>> The only thing that I believe could do the damage is the boxer. <<Nope...actually, just about everything you list, with the exception of the mandarin, might make a snack of a small crab fresh after a molt.  The other crustaceans, the Dottyback, and the clowns would be my first suspects...in that order.>> I have taken the crab out and put him in the sump for now. Is there any chance of a recovery? <<With time and protection.>> Thanks in advance once again. Pete Fearful <<Regards, EricR>>

Lybia tesselata question Hi! Is it true that a pompom boxing crab (Lybia tesselata) is going to eat a starfish and that I have to choose between getting a pompom crab or a starfish (was thinking of a Fromia) in my system? Thanks! Dominique <I suspect Lybia spp. may indeed be opportunistic omnivores as most decapods... but if kept well fed, you're likely facing better then 50:50 odds here. Bob Fenner> 

Oddball crabs 5/2/05 Hello WWM crew. I manage the fish room in a large Canadian LFS chain, as well as being a hobbyist. I tend to try ordering in some oddball or unusual inverts. Anyway, recently we received some interesting crab species; Mithrax pilosus, M. commensalis, and some inch wide Pitho species. I can find only vague biology reports on the internet and was hoping that one of your crew may have some experience with these species in the aquarium. I have the largest Pitho in my reef tank (don't worry, no small fish : ), where it spends most of the time buried in the corner. I was hoping as Majidae types they would be more or less "reef safe". Simon Luffman  <My general rule of thumb is to not trust any crabs in reef tanks. Almost all are opportunistic omnivores that will take a bite out of nearly anything, and have no qualms about tearing apart another living thing to extract a small tasty morsel inside. While I don't have a lot of experience with any of these species, I would suspect that the Mithrax sp. that you list look like (an is confirmed by the name "commensalis") commensal species. Commensals are notably safer in reef tanks, but may suffer without their ecological "other half". In short, I would recommend that you let your customers know to keep an eye on these guys. Also, while ordering oddballs may make life interesting, it is a sure way to end up with (and support the trade of) unsuitable species. Best Regards. AdamC.>

Crab/Eel Compatibility Hello!  <Hello April> My husband recently introduced a sally lightfoot crab to our 50 gallon breeder reef tank. We noticed the other day he was missing a leg. Today we noticed he is missing two more legs. We also have a juvenile snowflake eel, 3 different types of damsels and a turbo snail...as I have said this is a reef tank. We did have 2 turbo snails but one has seemed to disappear. Is the eel trying to feed in the crab? Could that be why the missing legs? The boy at the pet store told my husband that eels and the crab would be fine together.  <I think the boy at the pet store needs further training. Crabs are a delicacy for eels.>  Also, I thought I read somewhere that this crab needs to get out of the water once in awhile...is that true?  <No>  What could explain the missing snail.. <Maybe died? Is the shell in the tank?>  This eel is very small. He leaves the damsels alone. If we can't have the crab in the tank with the eel then what can we get to eat the algae that wont be the eel's dinner? There is starting to be a lot of algae growing on the sides of the tank. We have never done a reef tank before. Just eels. Thanks for any help you can give.  <On the Wet Web Media Google search, type in the keyword "algae control". You will find plenty of info there to help you out. James (Salty Dog)>

Sally Lightfoots? Hello once again mi amigos- <Buenos noches> Do Sally Light foots eat coral? <Percnon gibbesi? Not usually... but do cause some damage, closing by walking over them> A salesman stopped me from buying one for my reef tank. He said that they eat soft coral. I already have one in the tank, great scavenger and all, and was looking to add a new one. Should I be worried about the one I have? Thanks, Mark <Not worried... but as with almost all crabs, I'd keep an eye on it. Bob Fenner>

- Crab & Clicking - I have a 75 gallon reef tank with rock that was previously in my other two tanks that was moved over. The only things that have been added recently have been corals that are either on tiny rocks, or no rocks at all. The problem is that we have a mystery crab. This thing is huge to have never seen before. I do night patrol on a regular basis with a flashlight and have never come across it before. It is a "true crab" with large fat claws and is rusty red color and white splotches. It's about two inches across.  <Sounds like perhaps a shame-faced crab.>  It seems that it is eating my snails on a regular basis. The bottoms of the snail shells are removed, cut out, to see the spiral inside. There are several like this that have appeared recently. For the last four months or so, we have heard a clicking pretty regularly from the left side of our tank. This is where this crab has been living. I know your answer to the clicking is going to be a pistol shrimp, but no sign of that either.  <Pistol shrimp are pretty secretive.>  One of my emerald crabs also had three legs removed last week. Whatever this crab is, it's getting along ok with my coral banded shrimp. They seem to be living in the same vicinity. Any clues or thoughts you may have would be helpful and how do I get it out of my tank?  <I'd try and trap the crab... it's not going to do you any favors by staying in the tank. Check with your LFS to see if they have a trap they can rent you. Use your night prowling time to bait the trap with something meaty and bag the crab.> Thanks, Jennifer  <Cheers, J -- > 

Spider crab with a Decorating Fetish Date: Thu, 3 Feb 2005 Hello, thank you all for all you do. My Spider crab was banished from my 55 ga tank because he decided to mow down a colony of polyps and stick them on his ENTIRE body. Anyway he was transferred to my 15 gallon next to it.  When I was looking at my tanks the other day, I noticed my Long tentacle anemone moving. After looking a little harder I seen the spider crab "digging in" at the base of it. I left the house for an hour or so and when I came back, the spider crab had stuck the anemone on its body. The pink skunk clown was still swimming in its tentacles and the anemone crab was clinched to the base. The really unbelievable part is the crab is only the size of a hockey puck and the anemone is the size of a softball. I guess my question is, Ever heard of such a thing?  Corey  <Corey what I believe you have is what is called an anemone crab. These crabs will stick anemones to themselves which serve as protection for them. I think what you have is unique and I would leave it alone. James (Salty Dog)>

Emerald Crab Compatibility I have a 29 gallon with a lot of bubble algae and a button polyp, to get rid of the algae the LFS recommended a emerald crab. However he seems to spend more time clawing at my polyp, I haven't seen any damage yet, but I worry he has a sweet tooth for the coral instead of the algae, should I take him out? Or is it true these crabs are completely coral safe?<Lochlan, no need to remove the Emerald Crab. Your Emerald Crab will do much of his bubble popping after the lights go down.  There is no guarantee that each individual crab will remove bubble algae.  Give it some time and see what happens.  James (Salty Dog)>

Small Tang and Mithrax? Ok this will be my shortest question ever. <Ha!> In my saltwater system, I have a Yellow-Tailed Blue Tang (he's only about 1.5" ~ just a baby)... he sometimes sleeps (hangs out at night) up in a corner by the heater, sometimes almost laying down flat on my rockwork, and sometimes laying down flat on the sand.   <Typical> During the day he swims around and is an aggressive feeder.  I am assuming his nighttime habits are normal? <Yes> I was wanting to get an emerald crab (Mithrax).  With my very small tang sometimes laying on the sand bed or rockwork, should this be a concern for being preyed upon by a Mithrax?? <A possible threat should the crab be hungry, larger...> I have heard that they are opportunistic scavengers that may attack fish if they can get their hands on them.  The other fish I have I am not concerned about as they have all lived with a Mithrax before. Your thoughts? <Mmm, what is your rationale for including a Mithraculus crab? If just to have a crab, I'd skip it... if for algae control, I'd seek out other means> As well, what is a good sand sifter for a reef aquarium? <Posted on WWM> Ruling out sandsifting star because my tank is likely too small at 90 gallons (maybe 5sqft of actual open sandbed).  Scooter Blenny? Thanks Dave <Please use the Search tool, Indices on WetWebMedia.com re these questions. Bob Fenner>

Crabs as Thieves (1/11/05) I have had problems with my hermits stealing food from my Blastomussa and Candycane corals. They climb up on them and pick at their mouths all day after I feed them. Is this harmless behaviour or could they damage the corals? <As long as they do not appear to be doing physical damage to the corals, it is probably not harmful. They will likely continue to get adequate nutrition. Any crab can be a problem for corals in the aquarium setting.> Any advice on prevention? <The only way to do this is to remove the crabs.> Thanks for your help. Cord. <Hope this helps. Steve Allen>

Clowns, Crabs Thanks a lot for the fast response.  I actually received two responses on my letter!  Not bad! <Well, not bad if we agreed!> I don't see a plump belly or any rock cleaning going on, But she did eat a few flakes last night after I sent the E-mail.. so hopefully everything is going to be ok. <I am sure it will.  Switching brands of food or trying tempting treats like frozen Mysis often help too.> These two fish have been "side by side shimmying" since I first laid eyes on them in the stores tank,  they are always doing the "Cichlid Shimmy" as I came to think of it over several years of raising cichlids.  Hopefully this is a good sign. Anyways, I plan to get the Wilkerson book ASAP. <Sounds like love!  The Wilkerson book is one of my favorites.  It is easy to read, but packed with practical info.> Ahhh... what big crabs are scary?  Did you mean the mystery crabs (both of which were under the size of a quarter when I last saw them...one was brown and bumpy, the other was almost white and buries himself in the sand, actually got him with a bag of live sand) or the large "spider Crab" which I am told is a total scavenger... I watched him for a long time in the store and never  saw any untoward behaviour.  This still remains true 4 or 5 months in my tank... the only time I've ever seen him even touch anything else is when a hermit crab was hanging onto it's leg... it tried to shake it off, making NO move to kill it.  It is possible that one or both of the mystery crabs ate my Firefish about 9 months ago, as it disappeared without a trace (actually, so did a peppermint shrimp) but it is also possible that my anemone got them....or they jumped (you know... horrible, horrible freedom!).  Should I be overly concerned about any of these crabs?  Perhaps I should try to catch them, if they're still alive. <I personally don't trust any crabs, even supposedly "reef safe" hermits.  Their usefulness really doesn't outweigh their risks.  I have seen crabs tear apart corals and anemone for food, and they are quite capable of killing fish, especially at night.  In the case of your Firefish and shrimp, I would guess jumping and anemone food to be the most likely scenarios.> The reason I asked about the immobile brittle star is that I have a serpent star that crawls all over, day and night, but even in the middle of the night the Brittlestar only pokes the tips of his legs out, he's been under that rock for nearly a year to the best of my knowledge. Thanks again... Tom <There are many brittle stars that live a very sedentary lifestyle.  They nestle down into a hole in a rock or crevice and wait for food to come to them.  As long as you see that it is alive, there is nothing to worry about.  If it isn't getting enough food, it will move to a new spot.  If you are really worried, you could target feed it small morsels of food to be sure that it is getting enough.  Best Regards.  AdamC.>

Mystery crab I had a nice xenia piece growing rather well in my tank and overnight I lost about 2/3 of the coral. I did an exhaustive search and never found a thing other than a stowaway crab that I never purchased.  I did some research and found out that it is most likely a Eriphia smithi crab, aka: red eyed reef crab, aka: liar crab. it is about the same size as my emerald crab, but reddish brown with red eyes. I've heard from web users that it is a carnivore and that it has probably been the cause of my missing snail phenomenon as well as my disappearing xenia trick. <May well be> unfortunately no one knows anything about the animal other than "he's bad" and its "carnivorous" all I can find on the web is in Russian.  and despite all the vodka I drink, I still cannot decipher the Russian. <Heee! Maybe try Babelfish (the program, not a drink)> if you have any info or links for me to read id very much appreciate the help.  I removed the crab and placed him in my fuge just to be safe. <Good move> but id like to know before I buy any more livestock if that was probably the cause of my problem.  the only thing else in my tank is:  green Brittlestar, percula clown, blue legged hermits, yellow tang, and assorted snails. <None of these likely implicated> any help would be appreciated. Edwin <I also know very little concerning this crab... or speak/read Russian... I do hope that its removal solves your mystery. In the meanwhile, do keep your eyes open, maybe take a peek during the night with a small flashlight to see if there's something else mal-lurking. Bob Fenner>

Sally eat/lightfoot Hello again! I think I botched up....I added a sally lightfoot crab to my tank the other day. So far so good, but after reading a bit on the net, well, now I'm worried! My tank has mostly half grown damsels and I don't want them eaten!! Do you think if I target feed the crab it will be okay or should I get it out now?  I feel like an idiot because I know enough to read up on things before buying them but every once in a while I lose my sanity..... Thanks for your help, Barb <Barb, we all make mistakes, don't worry about it.  I think that target feeding of the crab will be a great idea.  If your tank is big enough and there is enough food source the crab won't be a problem.  It you notice some of the damsels missing then take the crab out.  Consider this a lesson and don't worry.  You haven't lost anything yet.  MikeB>

Crab Problem Hi - <Hello there> I have a reef tank, which is doing quite well.  In the process of getting it set up, I bought a "cleaning crew" of assorted critters, including emerald crabs.  It appears that the crabs are catching and eating some of the small fish in the tank - this in spite of my feeding them raw shrimp 2 or 3 times a week.  Is there an easy way of catching the crabs so that I can remove them from the tank?  I do not want to beak down all of the live rock to get them.  Thanks. - Bruce <Some folks have luck making a "feeding sink" of a glass tray, jar on its side, with meaty bait (e.g. a cocktail shrimp sans sauce)... and lifting out when enough of the little buggers are in there. Bob Fenner>  

Mystery Crab have looked everywhere I have been watching this crab for awhile and no luck. I finally had to pull it out of my tank after it attacked my sea apple. Please let me know if it is ok to dispose of this crab or is it a breed of interest. <All are breeds of interest (to me), but this one needs to be out of reach of sessile invertebrates (like in a sump or a rough and tumble fish only system). Bob Fenner> Thanks in advance,

New to Saltwater + Coral How about an Arrow Crab with other species? Will kill off cleaner shrimp? Hermit crabs? >>>I'd steer clear of the arrow crabs. Jim

Crab trapping 11/8/04 I have just finished cycling my new 400 gallon tank. The live rock used was fresh and uncured, collected on a night dive and placed in my tank the same morning. The problem is that these rocks are infested with little crabs, every rock seems to have a little crab hiding inside and there are 80 rocks in this aquarium. <great hardy scavengers for fish only tanks... but high risk for a reef tank> I have tried setting some traps but I am not catching much. If there were only one or two crabs in this aquarium I'd persist with the traps until I had caught them but it seems futile with the large amount of crabs I am dealing with here. <the mistake in part I suspect was putting them in a tank with a substrate where they can/could dig in. Like curing rock... LR placed in a bare-bottomed (QT) tank and propped up on grates allows for such critters to be lured to the bottom but they have difficulty scurrying back up the PVC pipe legs> Do you have suggestions for dealing with this problem? <with or without a sand bottom... the common trick is stinky meaty food tied up in a nylon satchel and sunk in the bottom of a wide mouthed glass jar overnight. The crabs have a tough time scurrying up the sides of a glass jar wall> The tank is fully cycled and does not contain any livestock yet, apart from the hitchhikers that came with the live rock. Thanks!, Timon <other trapping tips in the WWM archives if you'll kindly take the time to look/learn. Anthony>

Trapping crabs in marine aquaria 11/10/04 Hi Anthony! <hey, bro> You know what? I tried the wide mouth glass jar and have caught 3 crabs in the last 24 hours with one trap. <heehee... once in a while, I do know what I'm talking about <G>. the thing with glass jars is that crabs have pointy little legs for clinging to rock, which do not scurry up glass very well. And they cant swim :p> I was using a Tupperware box with a large hole in the top before and that didn't work. I have found placing the jar about half an inch under a flat overhanging rock works really well. I am optimistic about trapping now and am going to set 10 traps today. <you go!> The trap also seems to catch the interest of other creatures. Check out the worm hanging from the rock in the attached photo! I have seen these worms in my tank before but only about 2" sticking out of the rocks, I didn't realize how long these worms are until I saw it hanging into this jar today. This is a little disturbing. Any idea what it is and do I want to get these out of my tank too? Thanks for your help Anthony. Timon <no worries on the worms unless they get very large (literally approaching a foot. Most Errantiate Polychaetes are beneficial infauna of marine substrates. And contrary to popular belief, they do not blossom to plague proportions unless there is an (over-fed) food source. kindly, Anthony>

A Crab Dilemma Fish and Wives Hey guys! <Hi, Mike D here>  My name is Abby. Your web site is FABULOUS and has given me SO much valuable info.  I am a hobby "newbie" with a 46 gallon bow up for 2 months, all water parameters including alkalinity and calcium perfect.  About 30 pounds of live rock in the tank getting nice and purple.  Have two small percula clowns, six line wrasse, one mushroom coral, one small leather coral both doing well.  3 scarlet hermits, 9 turbo(?) snails who mostly stay on the glass and about 18 tiny snails that like the aragonite substrate.   Planning to add a royal Gramma soon.<That sounds like a plan to me.> A quick question...I have read extensively on your relative dislike of crabs in a marine set-up.<That's reefers in general, while I personally love them and don't consider a tank whole without some.>  The only thing I am now worried about is the fact that I did add a quarter size and growing (I think)  Emerald Crab last week at the suggestion of my LFS guru who I really do like and trust.  I had a huge plant growth on my live rock which the crab did dutifully remove for me.  Problem is the crab frequently hides under my Mushroom coral.   He just seems to sit there, doesn't seem to be harassing it in any serious way.   But here's why I am worried.  The coral never "bellows" out nice and full when he's under there like it usually does when the lights are on.  Is he bothering it?<This is possible, as some coral respond negatively to being touched by anything.> Can he hurt it?<Can he? Yes, most often by attempting to move it as he grows in an attempt to make a lair for himself.>  Now that he has already eaten most of the plant life in my tank, what should I feed it to keep him from turning to my corals or fish for his supper?<Any meaty food is fine, with best results often obtained by "spot feeding" the animal with a pair or tweezers, making sure it gets enough to keep it healthy. Predation on corals themselves is rare to nonexistent, while trapping a fish in a crevice is quite possible if it's severely malnourished.>  If he gets much bigger do I remove it?<That's always an option, although most rarely get larger than a dime to nickel sized shell.> I almost never see it unless it is under the mushroom, so how the heck am I going to get it out?<A small glass jar with a piece of shrimp, fish or chicken crab bait of chicle in the south) placed inside and left overnight often works. If it's sitting mouth up, the crab can't climb back up the smooth sides once it's gone in for the meal, then you simply remove the jar the next morning.> Saw your bottle technique but am unclear how that will work.  Won't the fishes swim into the bottle too?  (I should have gotten a tang to help resolve my plant problem I guess)<Yes, the fish will swim in too, but the trick here is to use a piece of bait too large for the fish to pull out...they'll nibble, then simply swim back out. As to the tangs, the problem is often that you get attached to them while small and all eventually grow too large for a tank the size of yours, so you probably did the wise thing, plus your crab may never present a problem, particularly if you can build or arrange a cave that he really likes, away from the coral. If fed consistently in the same location, they often end up staying there.> Also, what happens to the red hermits if I do not provide bigger shells for them to "grow" into.<Luckily, if you're referring to the red-legged hermits, they never get very large. If, on the other hand, you're referring to the type often seen with the blue speckles, they can grow up to the size of the Emerald Crab or larger and present the same problems.> I don't want big crabs in my system right?<Correct. With the shells, they are even clumsier than your other crab and literally bulldoze their way through whatever blocks their intended path.>  But will they die without a new host shell?<Actually, they will often fight to the death over the largest shell, but the best suggestion is to simply ask your LFS if they'll take them back when they grow (many will) and then replace them with the smaller red-legged or blue-legged varieties that remain small.> ANY input you can give me would be REALLY appreciated! THANK YOU!! THANK YOU!!<Hope this helps a little.> -Abby

Cucumber & Crab Question Hello Bob. I was just reading over your "Crabs for Marine Aquarium" article trying to ID a little guy I found hitchhiking on my new Tigertail Cucumber; low and behold, it would appear you've encountered this precise situation before. Apparently, I have a Lissocarcinus sp. just like the one in your photo (from N. Sulawesi). <Neat> Although I can not tell for certain from the image, it appears to be the same kind of cucumber. The crab seems quite intent on staying with the cucumber both in your photo and my tank. Thus I am very curious about the relationship between my two new guests. Would you happen to know more about it? Is it perhaps symbiotic? Parasitic? Or just a coincidence? Thanks for your time. <Very likely this is more of a commensal to mutualistic relationship... with at least the crab benefiting (getting towed about, likely avoiding some types of predation) and not harming the Cucumber host. Bob Fenner> Emerald Crab I purchased a emerald crab a week ago and every night since, he has decided to set up camp in my leather tree..  I don't think he is hurting any thing because it continues to open .any thoughts >>>No worries, it shouldn't bother the coral Jim<<<

Re: Emerald crab Killing my fish? Thanks, Steve for the reply.  The Perculas were very small (3/4") as was the Catalina goby.  The mandarin, however, was larger (about 2") but, as you know, they move around slowly. <Yes... Steve's out till mid-month...> Tried the flashlight thing a few times...nothing.  I will try again.  I have a new trap going in tonight, and I plan to bait it with a larger piece of shrimp or clam perhaps. I will keep you all posted.  Thanks again for the reply. --Dave-- <Persistence pays... good hunting. Bob Fenner>

Re: Emerald crab Killing my fish? Thanks for the response...from the man himself...how exciting!  Just started reading Reef Invertebrates...awesome book! <Happy to find it useful, of interest to you> So far my 2 Cleaner Shrimp enter the trap and graze on the bait. (I use fresh 1/2 shrimp & a piece of clam from the local store.) <Think I'd go in there...> No sign of the Mithrax, but I will keep on trying.  Should I be removing any animals (like the shrimp) during this process? <Yes> Should I move and corals and rock around? (I would hate to mess with the aquascaping.)  Also, how persistent do I get; do I do this everyday for a month if necessary?  Am I using the right bait? <No, yes, yes> If this fails, what next?  Ultimately, will I need to break the tank down and rebuild or do I just live without fish forever?  (That would stink.) <... perhaps remove all the rock...> Again, thanks...any further help will be greatly appreciated! --Dave-- <Be chatting, Bob Fenner>

- Hairy Crabs - Hello! <Hi.> I came across your page from a Google search and I am going to tell you it was a great help.. I am still lost but I did feel better knowing that other people are having issues with crabs hitchhiking into there tank. I am told that crabs lay eggs and it takes up to 60 days to hatch... is this true? <Hmm... am not really an expert on crab reproduction, but the egg laying part sounds correct, but no idea how long they take to hatch. Seems a bit long.> I am enclosing 2 pictures of my HAIRY crab… one is bigger than this one... and I did not think to take a pic, I have found two (2) of them so far… I am not sure if I should keep them …. <What else is in your tank that might be in jeopardy because of the crab? If you can't think of anything, I'd keep them...> And this was the best description that I read… (reported on your site) Thanks for your assistance… West <Cheers, J -- >

Hairy Crab reef safe? No thanks :) 8/11/04 Hello, I know you folks get buried under ID requests, but I thought I would add one more anyway.  This little fellow, about ? to ? of an inch across the caprice, hitch-hiked a ride in some Marshall Island live rock I bought about a month ago.  Fortunately, he was fairly easy to catch and is now living in my 15 gallon refugium.  I would really like to know what kind of crab he is, any ideas?  In addition to the pic, I can add that the tips of his claws are black, (rock crab?) and he is covered in dense, white bristly hair. <the ID is difficult from a pic as it is... and in this case, the subject does not fill the frame of a clear/high-res shot. It may be a moot point though... crabs like this are categorically scavengers and fairly far from being reef safe. Do look at the claws/pincers: form follows function! There's a hobby saying too that hairy or black tipped clawed crabs are dangerous with invertebrates and small fishes. Truth be told, again, though... most all crabs are not reef safe - opportunistic scavengers indeed> I intend to keep him, although I can’t let him stay in the display tank, so my options are the sump (40 gallons total) likely in refugium chamber because the live rock chamber would give him access to the skimmer.  I also have a 29 gallon quarantine tank, but since I am going to cycle new additions and live rock through there, I don’t see that as an option. Nonetheless, knowing what kind of crab he is will help me prepare a better permanent home for him. Thank you for your help! <no worries... offer it a variety of meaty fare with some greens/algae and keep separate from small fishes and corals. Anthony>

Stars and Emeralds Hello I am josh <Hi, MikeD here> I have a 55 gallon reef tank, about three months old. I also have a orange starfish, xenia, button polyps, and branching star polyps. A month after I got live rock I purchased a brittle starfish, it is black with red/orange under and on tip of tentacles and black with bristles on its back. I was just wondering if it would disturb other stuff in my tank like fish or shrimp because I was going to get a pair of cleaner shrimp.<This species ought to be fine, but keep in mind that many to most brittle/serpent stars actually perish because people expect them to just "find" food, something they can't do in an average reef tank. I suggest spot feeding with a bit of meaty food 2-3 times weekly, usually easy to do if you just look for the waving tentacles which are really saying, "FEED ME!"> I have read other articles that the green bristle will but nothing on a brittle star.<This is one of the larger and more predatory species, thus often thought of as a bad actor. Well fed specimens rarely attack fish> Also I just purchased a emerald/Mithrax crab. Will he hurt corals or anything else.<The answer here is YES if it, too isn't fed. Although they can and will eat some forms of algae, all crabs have substantial appetites and if they can't scavenge then they'll become predators. Again, spot feeding a Mithrax crab 3-4 times a week will often assure other tank mates are left alone. As far as corals, the biggest problem is often that a large crab is extremely strong, the "Hercules" of the reef and if a coral or shell is in its way, large specimens often merely move the offending obstruction> I understand when he gets bigger he can but he is the size of a quarter. Also how fast will he grow.<If adequately fed, it should molt every 1-3 months until it reaches about 1/2" across then will often slow to 2-3 times yearly.> Thanks.<You're welcome> 

Pom-pom/Boxer Crab (Lybia sp.) 6/5/04 Hi guys, I have been considering purchasing a Pom-Pom crab and was wondering if they would be safe around corals such as some Zoo's and leathers? The tank will only have 2 baby Banggai Cardinals as my LFS (who is a fellow reefer turned LFS) has a breeding pair. I'm on your site all the time and just finished reading Reef Invertebrates by Calfo and Fenner (which I quote on our local reef club site all the time) and would be no where without all of your information. Thanks, Kris Willard <These crabs should be safe with your inverts. Do beware that they could become a snack for predatory fish and that they may be seldom seen in a large tank. Best regards. Adam.> 

-The White Spotted Crab of Mystery- is the white spotted crab harmful to feather dusters or live rock. <I suppose that would depend on what kind of crab you're talking about, the common name of that critter doesn't give me much to go on.> I just picked up two for my 77 gallon marine aquarium as I have some brown algae and a turbo snail. <It's unlikely that this critter is an algae grazer, it's probably carnivorous.> The pet store lady says they will be fine with live rock while their competition says they will hurt feather dusters. <Can you get a picture of this beast? It sounds likely that the critters living in/around your rock may be in trouble, you may want to separate it until you get an ID. -Kevin>  Thank you Lori Cowry Questions Hey Crew, <Hello Peter> Firstly thanks for all the great info available on your site - it's helped me many times in the past. <Glad to realize> My questions are about Cowries. I've had one of these wonderful creatures for about a year now until the recent tragedy. Normally he moves along the walls of the tank and over the live rock at night and attaches himself to the wall during the day. I noticed about 5 or so days ago that he was his side on the bottom of the tank resting against the wall and he had gone right back into his shell. Upon closer inspection I saw one of our small crabs (probably about 1.5 - 2.0cm across) picking around near him. I didn't see the crab attack the cowry and looked to be trying the eat the algae under him. <Doubtful> I moved the Cowry away from the crab just in case and later that night the cowry seemed fine and had gone back to exploring the tank. This was until about 2 days ago...in the morning the cowry was attached the to the side of the tank as he normally would be. I changed about 10% of the water in the tank that morning. As the cowry was attached near the top of the tank, this left him out of the water for a minute or two - should I have moved him down into the water? <No, I wouldn't have> A few hours later I noticed the cowry had fallen from the side of the tank and was back in his shell. I left him alone as he was close enough to the side of the tank to move if he needed to. The cowry stayed in his shell for about 2 days until this morning. When I got up the lights of the tank were still off but the cowry shell had been moved but he was still in his shell. Then about 20 min.s after I noticed he had been moved again but this time the cowry was out of his shell. <!> I grabbed a torch so I could see what was going on and saw a crab ripping at the exposed cowry with another crab waiting near by. <The animal had been removed from its shell either forcibly or post dying> Sorry for the long description, now to my questions: Do you have any idea what may have killed the cowry? Could have been the first crab, water quality or old age? <Yes to any, combination of the above or other factors> Do you think he had actually been dead for about 2 days and the crabs had gotten him out of the shell so they could have a feed? <Very likely already dead> Do you know how long cowries normally live for? <Yes... I collect Cypraeids (their shells, but am familiar with their life history), several years... some larger species for decades> He had plenty of algae to feed on so starvation shouldn't be the problem. I also don't think my problem is water quality as I've had the cowry for a year and followed the same procedures with water changes throughout, although you never know. I'd love to get another cowry but I am a bit concerned that the same may happen again. Thanks in advance for your help. Peter <I suspect that having crabs in the same system with this animal were a large part of the reason for its loss. Bob Fenner>

Disappearing fish 3/2/04 The fish did not jump out, I have completely checked all around my tank and overflows and no sign. Water parameters are fine. I am really not sure what to do. I would like to get more fish but am afraid of something getting them. I forgot to mention the Sally Lightfoot crab I have could he be killing the fish? He is about 4" across. <Aha!  A prime suspect.  Sally's are well known to prey on fish if they have the opportunity.  The fish you lost tend to lock themselves into rocks or bury in the sand at night.  This protects them well from predatory fish, but makes them sitting ducks for a large sally lightfoot.  I have a policy of excluding all crabs from my reef tanks, and would absolutely banish the sally lightfoot.> Whatever it is I am losing them at night. and not to jumping out. How would I "dose with peroxide"? for the Aiptasia. Thanks again Aaron  <The best way to peroxide Aiptasia is with a needle and syringe (look at hobby shops).  Since writing before, I have come across a new product called "Joe's Juice".  It comes with a syringe and is remarkably effective.  Best of luck!  Adam>

Gall crab 1/13/04 I have what I believe to be a female gall crab living in my closed brain coral.  Should she be removed? Thanks much! Jeff Wagner <they are rarely a problem my friend... the coral will usually grow around them. If your coral exhibits normal polyp cycles and feeding... no worries. Anthony> Crab Compatibility Hello, <Good Afternoon! Ryan Bowen with you today> I have been cruising around WWM looking for an answer to this question and cannot seem to find one. <Fire away> I have a skunk cleaner shrimp (Lysmata amboinensis) who I love dearly. <I have the same> He has even learned to run up the side of the tank and take food out of the eye-dropper when I'm feeding my false Perc.  (Could have knocked me over with a feather the first time that happened!!)  Is this common? <Yes!  These animals learn feeding behavior quickly> Anyway, I have recently become interested in purchasing several hermit crabs (probably blue-legged hermits - Clibanarius tricolor) because they're just so darn cute! <In my opinion, the best choice for hermits> Other inhabitants of the 40Long tank include the previously mentioned false Percula, a yellow tang, a Mexican turbo snail, a Nerites snail, and 2 Cerith snails.  Would a few hermit crabs (no more than 5) be OK to add to this mix? <Be fine> Or is someone going to get picked on or eaten?  If these hermits wouldn't work, or even if they would, are there other species of hermits that would be safe to add?  <They'll fit in nicely.  Please provide empty shells for them, as they'll need bigger quarters as they age.  If you don't provide them, it'll be off the back of your snails!  Cheers, Ryan> Thanks a bunch!  Love your site!!

Detritivores and crabs 12/16/03 Oh Helpful Gurus-     I have *about* 3/4 of an inch of crushed coral substrate that needs more maintenance. I change water / siphon 4 gallons once a week in a 55 gal. I am thinking of getting something in the way of detritivores. I imagine this means snails. However, I have a hermit crab that is a pretty good size, perhaps 1.5". Am I wrong thinking the crab will eat any snails I introduce?   <you are correct... the hermit is a calculated risk and likely to eat some desirable invertebrates. Few are truly reef safe.> Is a crab this size just an all-around bother? <yes> I have a fish-only tank and plan to keep it that way, so the rest is not a problem. Small picture attached for fun and reference. Thanks! Lance <do consider instead one of those outstanding Amblygobius phalaena Bullet/Dragon gobies. Truly outstanding for sand sifting and hardy too. Anthony>

Hawaiian Strawberry crab Compatibility? Hi,    First  I would to thank you guys for having such an awesome site with tons of helpful info on it. <thanks kindly> Second since there are tons of crabs out their I will tell you all I know about this critter. Name: Hawaiian Strawberry Crab (Liomera sp.) Max Size: 2 inches   Description: Body is bright pink with white spots on the shell and black on the tips of the claws. I would like to know if you guys think the crab would be ok with some pom pom crabs (Lybia tesselata), sexy shrimp (Thor amboinensis) , small clown goby, and corals.  Thanks for the help, Teige <IMO, it is not ultimately reef safe (nor is the Lybia) and will likely harass or irritate (if not nibble/consume) desirable benthic invertebrates. Very few crabs are truly reef safe - they are categorically opportunistic predators. Anthony>

Carpet Anemone with crab problems - 12/9/03 oh yeah, your reply on the carpet....  no nibbling from the crabs.  I had a large crab, and it took a huge chunk out of it, as well as swallowed a feather duster one lonely night. <Hmmm. What kind of crab??> As you might think, the large crab is no longer with me......<understood if you are sure the crab was a the likely suspect>  Since then (about 4 weeks), the carpet anemone has stared growing it's tentacles back. <Fantastic! ~Paul> GR Bad Crab? Hi Scott <Hey there!> I have noticed a crab in my tank that has come along with my live rock. It is pretty tiny lives in one of the holes in the live rock. Would this guy be harmful o my fish, don't wanna spend on fish and then the crab dude chomps them up. <Well, it's hard to be sure without a positive ID as to the species. Many crabs can be harmless to fishes; others can be quite dangerous. If you could provide a pic, we might be able to make a positive ID on it...> If it is ok to keep the crab, what should I be feeding the bugger, he is already living for 2 weeks and I have not fed him anything yet? <Well, many crabs are harmless scavengers, subsisting on what they can pull from the rock. If he's made it this far, chances are he is finding what he needs to subsist on. I wouldn't be too concerned here.> Thanks Ziad <My pleasure! Regards, Scott F>

Sally Lightfoot Cannibalism WWM Crab-Crew: I've had 2 of these Sally Lightfoots (sometimes called Urchin Crabs?) for about 3 months, introduced within a few days of each other. They've kept to opposite ends of my 100-gallon reefer and occasionally would bump into each other but not even seem to notice or care. Yesterday, the larger one jumped and dismembered the smaller one, eating most of the soft fleshy stuff. Crabs legs and eyeballs were flying everywhere (my two cleaner shrimp went nuts and gobbled these flying body parts with much glee.) Can you explain why what I thought were peaceful crabs, and were appearing to be so, all of a sudden became quite nasty? <Sally lightfoot are not peaceful crabs when not enough food is around they will eat anything they can get there claws on> And, the smallest fish I have is a common Firefish; should I be concerned that this could be its next target? <yes> I'm starting to understand now why no one with much reef experience can safely recommend any crab of any size large enough to cause this gruesome chaos. <good luck Mike H> thanks, SLC

- Anemone Crab in Disguise? - Good morning Bob, <Actually, JasonC here this morning...> I have been visiting your website off and on for about a year and found it to be very informative.  I am relatively new to the marine aquarium hobby (had fresh water systems for 15 years).  The question I have is: I bought a Porcelain anemone crab about 3 months ago and he/she has taken up residence with my long tentacle anemone, however the anemone has started to move around a lot and seems to be in bad health now.  Can this be from the crab? <Is a possibility, but there are likely other issues as well.> If so how do I get the crab a way from the anemone until I find a home for him? <Remove it by hand.> Thanks in advance for help, Bill <Cheers, J -- >

Crabs in coral 9/9/03 Hi, there. I am a devoted fan of your website, esp. the FAQs, which I read daily. Thanks for all of your time and devotion to helping the not-so-experienced out there. <thanks kindly> I had a question regarding two mysterious crab-like organisms that are now in my tank.   I know that you guys like pictures for identification, but these crabs blend in too well with the sand to get a good close-up. These 0.5 inch, creamy white "crabs" have very small legs, no apparent claws, and have quite a large body in comparison to leg length. Eye stalks are not discernible. They are not agile creatures and spend a good deal of time sitting on their backs. <sounding like one of many possible Xanthid crab species> Evidently they were living between a piece of soft coral and its hard skeleton. A portion of this coral recently receded and there were two indentations carved into the skeleton where the crabs had been living (I saw them in their respective coral homes). When the crabs left the coral (which ultimately died), they took with them some tentacle pieces, which they either were eating or decorating themselves with. <yikes. Indeed... there are destructive species> Now, sans LPS coral, they live in my sandbed and ride on top of my sandsifting star occasionally. Have you heard of any crabs making a permanent residence in LPS corals? <many do, yes> After removing the skeleton from the tank and scrubbing it, I now believe that the coral had grown around the crabs. <a combination of crabs teasing/training it and natural growth> Could they be commensal? Parasitic obligate LPS feeders? Would you recommend removing them? (I have no other LPS, SPS,  or any other cnidarians, as this was my only one that died. I am thinking of some green star polyps for the future, though.) Thanks for an incredible resource. -McGreggor Crowley <I would consider removing them to a refugium... they may be decorator species and will be rather destructive in time. Do send a pic if possible for a better ID. Best regards, Anthony>

-Arrow crabs: Good or bad?- Dear WWM Arrow-Crab guru: <(Removes anemone guru hat in favor of arrow crab guru fez) Kevin here!> I've heard more conflicting advice about these marine spiders than just about any other invert out there. <K, I'll set you straight> The advice ranges from 'completely harmless and very beneficial' to 'devil-spawn that will kill everything in your tank.' <I don't see how they're of much benefit besides aesthetics. They generally do more harm than good.> Searching your site for FAQs also leaves me confused (very easy to do), and several books I have also give conflicting advice. Just looking at the creature at my LFS would lead one to believe they are dangerous and malevolent, but my Aunt Martha looked the same way and she was relatively harmless. <I just forwarded this email to her... ;) > Besides being rumored to munch on feather duster worms ... <Which they do, with much gusto> have any of you actually observed an Arrow Crab in action in a reef tank for any length of time? <Sure have. I have seen then take out green Chromis (as in grab a healthy one out of the water column!), yank hermits from their homes, and other assorted nasty stuff. I find them to be of little benefit besides the scavenging that they do. Just like any other crab, they're opportunistic feeders and are pretty well equipped to take out small critters. And to top it off, Bob's blurb from a crab article: 'Stenorhynchus seticornis (Herbst 1788), the Caribbean Arrow Crab. Not to be trusted with small to medium fish tank-mates (may spear with rostrum, otherwise consume). Safe with hardy native corals and anemones, larger fishes.' Hope this helps! -Kevin> Any advice would be 'swell.' Thanks, SLC

- Battle of the Reef Invertebrates - Crew: I have a snail and a hermit crab seemingly stuck together.  It looks like the snail was upside down and the crab tried to go in there, and the snail retracted and caught one of the crab legs in there.  What, if anything, should I do? <I'd leave them be... the snail will either drop the crab or the crab will drop the claw which will then grow back with successive molts.> Thanks, Rich <Cheers, J -- >

Possibly an Aggressive Rock Crab - 8/20/03 Good Morning, <cheers> This is my first time using this website and asking a question, so I apologize if this has already been asked.  I looked and couldn't find anything in the FAQs. <no worries... welcome, and thanks for trying to find your own way <G>> I have a 125 gallon tank with a large amount of live rock, a 4-bar damsel, a velvet damsel, a large dog face puffer and two recently added rock crabs of medium to large size. At least I was told they were rock crabs, they don't look like the few pictures I have seen.  Their mandibles are quite narrow and the photos I have seen of rock crabs show large mandibles.  The first problem appeared when one of the crabs was missing a mandible and arm after being in the tank for 2 days.   <these crabs are puffer food by any definition to make matter worse in the long run> I noticed that the crabs were fighting a lot and figured they were staking out territory and this had been the cause.  After about 5 days the other crab was missing a leg and they were still going at it.  Both act aggressive if you get close to the glass.  It has now been over a week and I have witnessed one of the crabs going after the dog face puffer while he was eating.   <heehee... too funny>

Cleaner Shrimp >Hello, >>Good morning, Marina here. >I am having some trouble with my 30 Gallon tank.  We have multiple Featherdusters, some mushrooms, 30 lbs live rock, 1 clown fish, 1 pygmy angel, 2 green Chromis, 1 Pseudochromis, 1 sally lightfoot.  The problem is we have tried on 2 occasions to have a scarlet cleaner shrimp.  The first one we found in the morning missing part of it's tail.  The last one we found with the sally lightfoot starting to eat it under one the rocks.  Is the sally lightfoot known to go after scarlet shrimp?   >>The crab is known to cause trouble, not specifically to scarlet cleaners, but to any fish or invertebrate it finds tasty.  Otherwise I would surmise you have a mantis, but it would have nailed the crab, so I don't think this is the case.  The Sally lightfoot crab (a common name given to more than one species of crab--some of them quite destructive in a home reef), is known to be unpredictable at best.  This one has proven its propensity and preference for the tiny lobster you attempted.  I suggest STRONGLY that you discontinue placing small, unprotected crustaceans in the same tank.  I would expect that the reef-safe hermits would stand a better chance against this predator.  C'est la vies, eh? >Is the sally just eating the shrimp and the shrimp is dying from other circumstances?  Water levels check out and everyone else looks healthy. >>Again, very doubtful, I place the blame squarely on the crab.  Best of luck to you, Doug!  Marina

Red crab is eating my xenia. Hi Bob, <Anthony Calfo in your service> I recently set up a 70 gal reef take to replace my existing 30 gal. I purchased about 50 lbs. of Fiji live rock from a local retailer which of course came with many pleasant surprises.  <yes...many such joys with fresh live rock> The tank has been running for about 5 months now. About 2 months ago I placed some green star polyps that are doing fantastic. Based on the success of the star polyps I figured I could start transplanting the rest of my corals into the new tank. I started with a small xenia and a Sarcophyton. This morning when I looked the xenia was gone and the Sarcophyton had a bite taken out of it. I looked with a flash light in the holes in the live rock and saw a red crab munching on the xenia.  <Arghhh> The crab is roughly the size and shape of an emerald crab but it' s bright red. Any idea what kind of crab this is and is it a notorious problem in reef systems.  <actually, most crabs including emerald crabs can be predatory in reefs. Most all are opportunistic predators. So... if hungry enough <G>> Other suspects are a 6 line and a peppermint shrimp. Any advice is appreciated. <the crab is by far the likely candidate. Do remove and resist even most "safe" crabs if you want great diversity of microorganisms in live rock and sand> Thanks John Allen <best regards, Anthony>

Have you ever heard of this happening? Hello Bob, I've written in the past to ask questions about the upkeep of my Nano reef, but this time I have more of an anecdote to relate. Night before last, I spotted my happy, well-fed and well-adjusted ocellaris clownfish, which was about 1.5" long, apparently 'wedged' between two rocks. Thinking (naively) that he had swum into a spot from which he could not escape, I tried to use a feeding prong to ease him free. After several minutes of prying, I almost had him free, when a frustrated green Mithrax crab reached out of his crevice and pulled him back in! It appears my emerald crab had caught and killed the clownfish, and was in the very early stages of consuming him. I know I caught him right after the fact, since the fish's eyes were clear, his color was good, but his gills were still when I finally freed him from the tank. Have you ever heard of such a thing happening? Thanks for your time. Josh <Yes. Unfortunately, Mithrax/Emerald Green Crabs are not entirely the benign, strictly algae-eating creatures some folks make them out to be... They will indeed eat fishes when they are large, hungry enough to catch them. Only small crabs of this genus are to be tried, trusted. Bob Fenner>

Question regarding Mithrax and Sally Lightfoot Crabs It appears that either a newly added Mithrax or Sally Lightfoot Crab killed two of the shrimp in my 60 gallon tank. My guess is the Mithrax but I would appreciate your opinion. <Yes, this does happen with both crab species... they are not "simple herbivores"... not nearly as opportunistic as some crab species... but still...> Also is there a way to catch the offending crab without dismantling the tank. <You can try baiting, trapping... per "crustacean" removal sections on our site: www.WetWebMedia.com> Thanks for your input. Mark Hill <Good hunting my friend. Bob Fenner>

A Bunch of stuff, with the Crab the "butler" who did it Hello Mr. Fenner, I emailed you about a month ago when I received some "extras" anemones in a recent fish shipment because it took the company so long. I really appreciate your advice and gave them to my local aquarium store. The white beaded is living in an employees tank and doing great paired up with an anemone fish, I was thrilled. <Very good to hear/read> The other pink tip is a permanent residence at the store and has his good/bad days. I just received my first two pair of Seahorses on April 2. Tank bred and raised on frozen Mysis shrimp, I just got my first problem with trapped air bubbles in one males pouch. I think! <Very common... and can be real trouble> I have also read about trapped air bubbles under the skin or ingested and/or problems with undissolved gases in your water affecting buoyancy. <Yes> I recently discovered a very large, very red crab, he must have hidden very well indeed, will this guy threaten my horses? <Possibly, yes... if hungry, for sure> I also had a arrow crab and peppermint shrimp who disappeared (eaten) and I'm thinking this red guy is the culprit. <Likely...> I looked at the pictures of the crabs on your section but didn't see any like him. Very large front claws( mandibles?), white horizontal stripes down his legs, no shell (like hermits). <Would take a few lifetimes to assemble such an index... with images... a worthy goal... I put a few on as I pass through, get new images...> Is there a trap I can use to get him if he poses a threat? <Yes, or a tethered bait... see the WWM site re pests/removal here...> He has buried himself under my 100 lb.. of Live rock, haha, I can't move it. I also have a 55 gal. brackish and would love to see more inf. on the various fish, especially puffers, no one seem to know how they breed etc.. <Need to get to this section... there is a nice Scat article in FAMA this issue (May)...> I also have another question and have asked my aquarium store but no one else has seen it. I have a variety of different crabs all small but the previously mentioned one, one type however, pale red, hairy legs & body goes up to the very top of my live rock and spits-spews out white dots (bugs? eggs?) they swirl around for a few days and then are gone. What is it doing?  <Don't know... maybe reproductive dispersal...> Once I noticed hundreds of plankton-type white organisms swimming around for days, then gone. I hear of people talking about calcium etc... are these just worries for the reef aquarist? <Concerns? Yes... one of many possible ways of judging water quality... an important variable...> Currently I only check for pH, ammonia, nitrates, nitrites, salinity. I do have live sand, rock, fan worms, gorgonians, some kinds of corals, but I'm looking at a species only tank with a few Dragonets, BTW what do Dragonets eat exactly? <A wide range of interstitial fauna... crustaceans, worms, mollusks and more that live in, between sand grains... the water column...> Sorry for so many questions. I'm amazed at your wide range of knowledge on so many different topic. Thank you for your time and patience, its greatly appreciated. <You are welcome my friend. Let your curiosity and wonder lead you to further study, enjoyment. Bob Fenner>

Mithrax Crabs... no carte blanche guarantees... Hello Mr. Fenner In your previous writing's on your site you have stated that the Mithrax crabs are good bubble algae and Bryopsis eaters. I very much would like to have a few in my 120 Berlin system. Will they be ok with my red leg, and blue leg crabs and all of my corals? How many would you recommend for my tank? As always , I am grateful for your site, books and advise. Thank you , and take care. <I would try four or so small individuals of the Emerald Crab <Mithrax> here... but no guarantees... there are numerous cases of this species trying out other crabs, even corals from time to time... Get one inch or so individuals... chances are they will leave your other life alone. Bob Fenner>

Blue Linckia and catching evil Sally Lt foot? Hi Bob aka Lorenzo, Bob knows about my tank, but you seem like a nice knowledgeable guy so here goes. I would like to catch a nasty Sally light foot (my sister's name, I should have known :-)). Anyway it ate an otherwise healthy (but teeny- 1") False Perc. I am thinking I will replace with Clarkiis, but that's another story. <This does happen... Bob as Bob> Anyway he (or she) looks impossible to catch, so how do I do it? I looked on the FAQ and couldn't find anything. <You might be fortunate to bait this faster than lightning crustacean out with a meaty item tied to a stout thread or bit of fishing line... and net it out from there> Also looked on the FAQ, as if I catch the darn thing I am thinking about a Linckia star. The question I have is how established is my tank? Or would I need more time? About my system I have had it going since December. It is a forty gal breeder with 40 lbs or so of LR and 40 lbs sand (some live). Usual perimeters are: Temp 78-80 pH 8.2 Ammonia, Nitrites 0 nitrates under 10 Alk 3-4 Ca 390-450 Phos .1-.2 I use an Ecosystem 40 and have 144 watts PC. I have a MaxiJet 1000 for circulation. All creatures are doing well and include: Midas blenny, juvenile Sailfin tang (who is not long for the tank at his/her eating rate), a Common Cleaner, some Turbos, a regular mushroom, and a Rhodactis. No deaths or anything for months except the ill-fated clowns (one jumped out -- maybe spooked by Tang and the other was eaten :-o). I won't put any slow creature in until the SLF is out, but aside from that what do you think? <Would skip a Linckia for this small system... Look for a smaller Fromia Seastar species in its stead. Bob Fenner> --Jane J

Crab Control Bob, I discovered a crab in my 75g reef tank a couple of months ago which I assumed to have been a hitchhiker on my live rock. I didn't give it much thought at the time but I did some reading which indicated that some types of crabs can be detrimental to the tank including corals, hermit crabs, small fish, and snails. <Yes, many crab "recruits" can get large, become too destructive> Well - this weekend I saw him again for the first time in about a month and he is now about the width of a quarter, light brown (almost beige) color, and has a hairy appearance. I noticed that he has taken refuge on the bottom of the tank under a large piece of live rock. I monitored him for while and much to my chagrin observed him sneaking out from his refuge and capturing small Nassarius snails which he then transports back to his hideaway and assume he then consumes their meat if he can. <Likely> Given the obvious difficulty in trying to capture this nuisance - I'm writing you to ask for any insight you may have in trapping and removing this crab short of removing all my live rock to find him. <Do take a read through the FAQs on Crabs on our site: www.WetWebMedia.com as well as those on other crustacean groups... about baiting, trapping them out of established systems. I would probably be removing yours. Bob Fenner> Your thoughts would be appreciated.. Thanks,

Soft shell crab Hi port some living rock for my tropical marine tank 6 weeks later spotted some damaged coral. The culprit is a crap about 1.5 inches in size grey in colure with a soft shell there is no discarded empty shells in the tank .The crab hides during the day in a small hole the only time I see him is during the night. He is growing fast, can you tell me how large he will grow and is he a danger to my fish and anemones <Hmm, can't tell what this animal is species-wise... but would likely pull it (bait it, trap it out...)... some directions on how to go about this are posted on our site:  www.WetWebMedia.com. Bob Fenner>

Stow Away Crab Bob, I recently purchased your book from FFE and find it an excellent source for information and guidance.  <Thank you... much good help putting it together> I have referred to it countless times in the short time I have had it. But my question is in regards to a stow away crab. I just received a shipment of SPS corals from FFE for my 90 gal. reef. While the corals were acclimating I noticed in the bag with the Bird Nest coral that a small crab was hiding in the branches.  <Not uncommon> I looked on WWM and FFE as well as some bulletin boards, but have found no information on my specific crab.  <The site would have to be several times its current size... it will be...> It is red, has huge claw in relation to the it's body, and a thin yellowish band of color on each one of it's legs. I didn't know if it is safe for a reef tank, but doesn't seem like a good tank mate. I have a mated pair of gold strip maroons, Mandarin, 2 cleaner shrimp, and a lawnmower blenny. Thank you for making this hobby a much more enjoyable journey! <Thank you for sharing it with me. I would likely remove this "unknown" Decapod at my/your earliest convenience. Bob Fenner> Brad Stefanko

Arrow crab, good lord! am in a state of confusion and disbelief. I recently got an arrow crab to ensure that I didn't have any bristle worms and am pretty sure that I now regret the purchase. I used to have quite a plum little lion on my last tank that died from a nasty fight with pseudomonas and I had two peppermint shrimp in there for him to much on at will, also to give it something to do, hunting and all. anyways they made it into the second generation tank. only one survived and I've had it for quite some time. I saw it last night in full health (about two inches, a "big un" by ornamental peppermint sizes) and now my arrow crab has its maws on its exoskeleton. I haven't seen it for about a day now... perhaps its molted, that would be fine. but is there a chance that the arrow crab nailed it? my arrow is insanely aggressive towards anything (I've got 8 blue fin damsels, am a bit nervous there too. always do my morning count...). can a 4in leg span arrow tackle a 2in peppermint? <Absolutely... and it will eventually eat those Damsels as well...> Jon Trowbridge am pretty sure it molted, but am always nervous about the arrow. kinda wish I never got it. <You will be more sure about that sentiment soon... see the section on "Marine Crabs", Stenorhynchus on the WWM site... Bob Fenner>

Crab eating fish Dear Mr. Fenner, First, thank you so much for the time and information you offer fish hobbyists. Your book, Conscientious Marine Aquarist, has been a major asset. <Ah, thank you for your kind, encouraging words> I have had a 29 gallon saltwater tank since January of 2000. The first 2 residents were a sally lightfoot crab, and a pygmy angelfish, Centropyge argi. Both are still doing well. About 7 months ago, I added a Swiss guard Basslet, and have been very pleased with this fish as well....until today. <Oh oh> When I arrived home from work, I found the crab eating the Swiss guard. I can't say for certain that the crab killed the Basslet, only that he made a meal of him.  <You are right about the likely course of events> The crab is now approximately 4 inches across, leg to leg. Last November, I had a Gramma disappear from the tank, and at the time blamed it on the now-departed mantis. <Possible... Grammas are also great jumpers> My question is this: Will a sally lightfoot kill a fish if it is able to, and/or once it has eaten a fish, are any other small fish safe? <Yes, this species, especially when large can/will capture and consume fishes> I don't want to blame the crab unfairly-- I actually like the crab-- but am not willing to sacrifice fish to it either. <You may have to settle on just the inhabitants you have now... or look to getting a larger system with wary and aware larger fish species... Bob Fenner> Again, thank you. Sincerely, Owen Smith

Little help please (Giant Crab in Live Rock or as Live Rock...) Dear Mr. Fenner, It has been a week or so since I last mailed you. I must report some good news. My cleaner shrimp and tiny 1/2" neon goby are alive and well. :) <Ah, good to read> I did have an ammonia spike but a few water changes brought that down to zero. I am optimistic that adding that 15 pounds of live rock was a great help. I plan to add 15 more next month. <All sounds good> I wonder if you remember my saying how pleased I am with the live rock at my LFS. I have quite a large and amazing stowaway who I found just last night as more proof to the quality. The biggest crab I have ever seen. I went through WWM and found what I believe him to be. A Spider Decorator Crab. BIG!! I walked by my tank after lights off last night and thought I saw a big chunk of LR falling. Then I realized it was moving. and had claws. and mushrooms and sponges of the most amazing color on it's back and long legs. How I missed that monster when I was arranging the rock last week I have no clue. :) <Hope it behaves itself going forward> I have done some research last night to learn as much as I can about him/her. An algae muncher at night and dormant during the day. A terror of a beloved reef keeper because of it's need to adorn it's self. I haven't found anything stating it will do damage to live rock. Do you know if it could do that?  <Likely so to some degree> I have no coral or anything it would decorate with. :) I think I just need a little reassurance. Also I wanted to ask if I should have any other food for him/her to eat?  <I would try various foodstuffs to keep your crab, um, less crabby> Or do you think he might be better off somewhere else? <In all honesty, yes> In any event, I thought you might appreciate knowing what appeared from the LR I put it. I was amazed. :) Take care and best wishes, Josie <I won't gross you out... but have encountered hundreds of life forms on/in, as live rock... some wee-tiny, others... Bob Fenner>

Crabs and lighting Bob Thank you for all your help I really appreciate having some one to ask all these questions to. I have two questions for you. I deal with Two LFS and I am getting conflicting information from them.  <If you keep asking me, you'll likely have a dozen!> One store tells me that emerald crabs are reef safe and will not eat corals, polyps, or fish the other store says that they will. <Hmm, here we go... Most of the time, small Mithrax crabs won't harm sessile invertebrates... But there are many cases of larger ones doing so...> So if you could resolve that question for me I would appreciate it. I have three in my 46 gal tank now so I need to know what to do. <This is a bunch in a small system... You, they will likely be okay for a good long time... as they shouldn't grow that much, that fast in such a setting> My other question is I have a 36in JBJ compact light with 4 36 watt 10K bulbs on my 46 gal tank. One LFS tells me that is plenty light for a brain and candy cane coral the other store says it is not enough and that I need metal halides. You are going to be the tie breaker please let me know your thoughts. <You have sufficient light... the shop has a hankering to sell you a chiller... Bob Fenner> Thank You Jason

Fiddler Crabs I have a 55 g. marine aquarium with 45 lbs. LR. I was recently given a VERY surprise present of a fiddler crab. I've never seen one of these mentioned in any marine article.  <On our site: http://wetwebmedia.com/swcrabs.htm> What do they eat?  <Meaty bits of this and that> Will they harm my fish (I am planning on a tank of blennies, gobies and other small fish) or invertebrates (snails, an emerald crab, and fan worms)? <Slow, sedentary to sessile invertebrates may be in trouble if your crab gets hungry...> And how will I keep this guy happy?  <Need to have a place to get out, dry a bit... and cover to hide in, reharden their exoskeleton during molting events. Bob Fenner> Thank you very much for your time. Mike Rathwell

Fiddler Crabs? Hi. Thanks for all your previous help in the past, both directly and through the creation of this site. <You're welcome> My problem is this. I have a 35 gal tank that I added 10 Trochus and 10 Astrea snails to about a month and a half ago. Since then they have slowly died off to the point of about six. I find many upside-down on the sand bed, and, up until now, I had thought they had fallen off the Live Rock. However, I had failed to realize that I had been given a "gift" of a Fiddler Crab about two weeks prior to the addition of the snails. <The "Trojan" gift crab...> At least that's what it was called, and it looks like one (has the eye stalks, but doesn't have the one, large claw--I'm assuming this is because its female. But the Bad News Bears and Walter Matthau taught us what happens when one assumes).  <Well put> After the addition of the Fiddler, it disappeared for months and I believed it to be dead due to lack of a place to dry out. However, a few nights ago I found it out and crawling around the rocks. My questions are these: Is this crab causing the demise of my snails?  <Maybe... are their bodies missing?> Will it hamper my plans to add more invertebrates (mushrooms, leather corals, star polyps, feather dusters, shrimp)? <Maybe... I would pull it> If it is...then how do I get rid of it because I haven't seen it except for that one night? Please excuse the long email, and thanks very much. Michael Rathwell BTW Kingsley from Aquarium Arts in Phoenix says hello. <Ah, say hello back for me please. I would "bite the proverbial bullet" and drain, take out the rock... and remove the crab at this point. Luckily a thirty five gallon is not "that big". Please see here: http://www.wetwebmedia.com/movingaq.htm re input on "moving" aquariums, about the same list of steps, tools, materials as you'll be doing. Bob Fenner>

Re: Fiddler Crabs? Thank you again. The snails did have their bodies removed, but could this have also been from decomposition? <Not that quick... a few days...> In response to your moving idea, could a trap not be rigged up with a little bit of bait?  <Yes... a few types described on our principal site: WetWebMedia.com> I have seen these mentioned on various internet sites for the removal of pesky bristleworms, violent Mithrax crabs, and other things. Would this sort of thing work for Fiddlers? <Possibly> Seeing as how the residents of my soon-to-be mini-reef are only 2 red Firefish, 1 smith's blenny, 1 Featherduster, and 6 (numbers slowly declining) snails the moving shouldn't be a problem, but I would rather not mess with restarting a tank (thoughts of re-cycling and ammonia spikes sicken me, <Shouldn't have to be recycled... just put back what was in there... including much of the "old" water> especially when only 1 week away from putting in the first corals). And to think...all of this work for a $4 crab! Thank you for your advice and help. Michael <Be chatting. Bob Fenner>

Emerald Green crab attacks! Hi Bob, I just got back from my favorite fish shops in Chicagoland. Realized I really do have more time than money. Any way, I saw something there I could not believe. I watched an Emerald crab reach out and snag a Saddleback Clownfish.  <This does happen... with size, hunger, Mithrax crabs will eat most anything> It grabbed him and drug him down and held the poor thing fast while it started to try to eat it! I quickly got an employee and its life was spared. (maybe) Is this normal or just a case a very hungry crab? I was thinking about picking up a few until that event. Thanks for your input on the lights. I just purchased the CSL ABS 4-65 watt Power Compact unit online. I also decided to buy a 75Ga. and sell the 55Ga. More room (width) for the lights, filters, livestock etc.. Just plain easier all the way around is you ask me. Oh, buy the way, do you need a 55Ga. tank. I know someone who is selling. <Do post this on the Chatforum: http://talk.wetwebfotos.com/ Bob Fenner> Thanks Zimmy

Mithrax (emerald) crab Dear Robert, I have a 25 gallon reef tank and thinking of getting a Mithrax (emerald) crab to help control hair algae; will it bother my Sally lightfoot crab? I have had her for close to a year, I would sure be sad if it were to be eaten. <This is a possibility, especially in such small quarters... but not too large a one> Also, I keep my tank from 74 to 78 degrees would an abalone do Ok and I do have a skimmer. Any help is greatly appreciated! <I would skip on the abalone. Please read over the mass of algae, control and related articles and FAQs stored on WWM: Index here: http://www.wetwebmedia.com/acidalkph.htm for much more on your choices. Bob Fenner>

Mithrax Crab / Bubble Algae Question Bob, About a month ago, I wrote to you about a bubble algae problem I was beginning to have. Well, now it is a huge problem. I have been trying to remove it by hand, but this seems to be a losing battle. In your reply to my earlier e-mail you mentioned that Mithrax sculptus, the Green/Emerald Crab is known to eat bubble algae so I'm thinking of adding one (or more) to my tank. My questions are. a) will it bother the banded coral shrimp and 2 common cleaner shrimps I have and b) will it bother / eat any corals or clams?? Also, any other ideas for eliminating this pesky algae would be greatly appreciated. Thanks for your help again! Phil in San Diego <Very rare to have Mithrax crabs bother other crustaceans, corals, or clams... try one per fifty gallons or so... and start small... like one inch across the carapace in size. Bob Fenner>

Question about getting rid of a crab Hi, I was wondering if you would have some advice for me. I have a pinkish crab the size of my thumb that lives in one of my base rocks and eats my snails. There is no practical way to get the rock out of the 80 gallon tank. Is there any way to get this crab out of the tank? A trap or some sort? He comes out occasionally late at night. I would appreciate any advice. Thank you. Jerry Hirsch. <I have successfully used a trap called the X-Terminator. It has a spring loaded closing door. -Steven Pro>

Uninvited Guest Hi Bob, <Hello> Last night I was enjoying my tank when to my surprise this thing just crawled out of a piece of live rock. I was quite startled seeing this as I didn't put it there or even know it was there.  <Keep looking... much more to see> I assume it came with the box of live rock that I a received this past summer, but this was the first time I had seen it and it quickly crawled back into the rock. Nonetheless, it is some sort of crab, a little smaller than a half-dollar, brown, and all hairy. In fact it looks like a tarantula. I unsuccessfully tried to find a picture on the web site and the Internet.  <The Web/Net is "not that complete" yet> I was wondering if you knew what type of crab it might be, or more importantly if I should get it out of the tank.  <Mmm, bait, trap... many possibilities as to species> Right now it is a fish only tank with a flame angel, purple tang, flame hawk, and an orange diamond goby. I also have some snails and hermit crabs and of course the live rock. The snails and hermit crabs are pretty new additions and I have found a few dead snails or should I say empty shells already. Wondering now if the hairy crab got them?? <Could be... though the fishes you list should be in no danger. Bob Fenner> Thanks! JJ

I bought a decorator crab a few days ago, and this morning it looked like he was trying to eat one of snails. Will the decorators eat the snails or any of my other livestock? (I have 3 tangs, a clown, 2 damsels, mushrooms, button polyps, daisy polyps, and anemones) <Yes, most crabs will gladly consume most anything in the way of food... live or otherwise... Do you know which species this is? Time to do some investigating... Bob Fenner>

Hi Bob, I ordered one of the large clean-up crew packages from FFExpress and the crabs ate all of the snails within a couple of days. I have never experienced or heard of this happening before and was just wondering if you would have any comments?? Thanks, Diane. <I do... my standard spiel re Decapod crustaceans... I don't trust any crab around anything it can get its greedy pincers around... They are almost all opportunistic omnivores.... eating most everything that can't get away if they get hungry...

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