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FAQs about Marine Crabs 1

Related Articles: Crabs, Hermit Crabs

Related FAQs: Marine Crabs 2, Marine Crabs 3Marine Crabs 4, By Species/Group:  Arrow CrabsEmerald Green Crabs, Decorator Crabs/Sponge Crabs, Fiddler Crabs, Pom Pom Crabs, Sally Lightfoots, & FAQs on: Marine Crab Identification, Crab Behavior, Marine Crab Selection, Marine Crab Compatibility, Marine Crab Systems, Marine Crab Feeding, Marine Crab Reproduction, Marine Crab Disease, Emerald Green, Mithrax/Mithraculus Crabs, Micro-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,

Cancer antennarius

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

The Price of Getting Crabs Hi guys, back again! I love talking to you people! <we love you too, dear> As you may have guessed from past e-mails, I am in need of many things for my reef tank. New Skimmer, more LR, more sand, etc. But I just realized there is another thing I am lacking in my reef environment, sand sifters, crabs, snails. I remember reading AND hearing that these little inverts are about the most important part of a reef,  next to LR. Is this so? <They are extremely important to the overall health of your sand bed.> I only have about 15 or so snails, nothing else since my wild caught crabs all died. Which also leads me to this question: Can you guys recommend a site where I can purchase on line? I went to many of the links on your web page Rob, but after about 35 minutes of clicking here and there, I decided to just go to the experts! I will say that I went to WWW.GARF.ORG and they had what appears to be a pretty good deal compare to the $3.99 a piece  price tag at my local shop for crabs, they had a price of about $1.00 a piece for an assortment of crabs and snails. Of course I would hope that these inverts are very healthy and of good size. Can you do better?? <I have heard good things about the detritivore kits from http://www.inlandaquatics.com/  This should inoculate your sand with a nice variety of sand sifting creatures.  -Steven Pro> Let me know what you all think, and thank you very much for your speedy help as always! Pam  

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 Saddlebacked 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>

Re: more feeding <<JasonC here...>> I also got a Blue Boxer Crab, I could not find much Information about them. Any ideas what they eat. <<just about anything they run into, or that runs into them...>> My LFS said brine shrimp <<that would work. Cheers, J -- >>

Sally Light Foot? Hi Bob. I was reading about the Percnon gibbesi, the Nimble Spray Crab on your site. Is this crab also known as the Sally Light Foot crab? <Mmm, maybe... perhaps sold, labeled as this by some... though the "real" Sally Lightfoot Crab is Grapsus grapsus> Does it need to be able to get out of the water periodically? <Yes> Any further tips on keeping this crab healthy? <Do use your search engines here. Not much that is practical/husbandry known about these crabs. Bob Fenner> Gracias. Zimmy

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>

Crab misidentification, correction on WWM Mr. Fenner, You have a picture of the Pacific rock crab, Cancer antennarius, labeled as a Dungeness crab, Cancer magister at your site: http://www.wetwebmedia.com/swcrabs.htm <Thanks much for this i.d. Will post your msg., the correction tomorrow. Bob Fenner> Chris Hunt Marine Scientist SAIC-Science Applications International Corporation

Big Ole Crab This is probably the strangest question you will get all day! While cleaning the pool in the back yard I discovered the biggest crab I have ever seen running around on the bottom. It is about 8-10 inches wide with two very large claws. It's body is light tan with a purple tint and the claws have a tint of blue to them. I don't know how long it has been there but would like to get it out and turn it loose in it's proper environment. Do you think he is salt water of fresh? We live fairly close to both but have never seen anything quite like him before. <Bizarre... maybe someone is pulling a prank... I would remove the crab (with a big net) and set it out near the beach. It will return to the sea if this is where it belongs. Bob Fenner>

Dungeness crab R & D Hi Robert, Thanks for the comments and advice my previous email about observing Dungeness crab behavior in and out of our traps. We'll be able to get filter seawater from the Seattle Aquarium which is nice since it is only 3 miles away. We'll need about 3,500 gallons. <Do consider, study the need to bolster alkalinity. The facilities I help with use simple baking soda, sodium bicarbonate (Arm & Hammer) here... Inexpensive, readily available... to boost alkalinity, maintain pH at a safe level... otherwise, w/o much in the way of soluble substrate present/water flowing over... even with 3,500 gallons these values can slip dangerously, quickly...> Any idea on how much air we need aerate the pool and keep the environment good for active crab activity ?? <Not much if it's just one, a few crabs in this volume... I would use a sump (separate container, like a big Rubbermaid tote... horse/cow drinking size.) to have the water overflow from the main system (run it through a protein skimmer (will aerate here par excellence) then through some sort of biological filtration (to convert ammonia/ammonium from crab wastes (produced continuously whether you feed or not, and from your demo. baits...). Perhaps a good idea to have a few "Aquarium Service" companies come out and bid on the mechanicals, install... to get their ideas. Bob Fenner, www.WetWebMedia.com> Thanks, Ed

Crab Skeleton Bob, what is with your accuracy? <Have been credited, accused, cursed/blessed with intuition> You were right on, not that there was a smiling cat, but the Banggai was unfortunately lost. Have you witnessed the spontaneous loss of this hardy fish, and if not what could it mean for the rest of my stock (going to perform water change tonight)? <Good idea to execute this change> But here's the question. I know how much I stocked the tank. . . There were four crabs total in there. Three Mithrax and one Sally Lightfoot. When my girlfriend was getting the Banggai out of the tank while I was at work, she also discovered (on its back) what she described as the Sally Lightfoot crab dead. But then when I got home I spotted him eating happily. . .  <Likely just a shed exoskeleton... best to leave these in place (maybe behind the rocks) for the animals to ingest, re-use> Also, all of the other crabs were spotted at the same time in other parts of the tank, four crabs total. Do these guys do the same thing that my cleaner shrimp do with their skeletons??  <Yes> Could this specimen come from the rock? <Doubtful> You're the best, separate query on the way. <Mmm. Bob Fenner>

Dungeness crab (holding facility/gear) Hi Robert, <Howdy> Our company manufactures crab and lobster traps. We're purchasing a 12' wide x 31" high wading pool to set up as a crab observation tool. We want to watch Dungeness crab, and perhaps lobster later, as they crawl into our traps and try to get out. We make some entrance devices for the traps that we would like to observe as to their effectiveness. Our web site is www.neptunemarineproducts.com. <Neat> Any advice on how extensive of a system I will need to keep the crab alive and active would be appreciated. I suspect we would only need a couple of weeks to observe the crab's behaviour in relation to our entrances. After that, a crab feed! <Take a look here: http://wetwebmedia.com/cntfiltbiz.htm re centralized filtration systems in the ornamental aquatics business... same gear, principles apply... and any/all else on our site (www.WetWebMedia.com) that is linked, is unknown to you... And make it known if I can be of further help... Am tempted to suggest a "skid unit" more for the pool industry than a more expensive "live holding system" unit here... If cost is a concern... But would like to know that I/we weren't otherwise changing the test animal/prey's behavior by neglecting good water quality. Bob Fenner> Sincerely, Ed Wyman

What else? (crab, lighting questions) Bob, I have a question that I was hoping you could help me with. My tank is a 46 gallon bow front containing approx. 30 pounds of live rock, some cleaner crabs/snails, and few feisty little damsels. (I also received a small greenish crab reminiscent of an emerald crab but with stockier claws and orange eyes that is nocturnal as a free gift with a larger piece of live rock; so far he has been quite the little gentleman) <Keep your eye on this recruit> The filtration consists of a Magnum canister hang-on with a bio-wheel, a Visi-jet protein skimmer, and two small powerheads (one submersed the other hanging). The tank is 36" in length and is currently lit by one normal 30watt 50/50 by Coralife. The tank has been up for about 6 months. After extensive research and keeping a close eye on the chemical balance and salinity I have decided to move into a reef tank but have run into a problem with lighting. There is no canopy to fit this odd shaped tank. <Better, best to fashion one of your own> I have read that power compacts (possibly a smart lamp) could be used but am concerned with the heat atop the tank. It is covered by a glass tank top which the strip sits on. Do compact flour. give off enough heat for me to worry about heat fluctuations or the top cover glass breaking on my tank?  <Not to the extent of breaking the tank, no.> Let me know what you think; I respect your opinion. Thank you, Mike Stewart <We might want to talk/chat about specifics... design... but ballasting (electronic) can be easily remoted... Do read over Ozreef's for input on construction...: http://www.ozreef.org/> PS: I realize 46 is rather small for a reef (40 being your personal minimum) but it was a gift from my wife. I would hate to give it up until we could afford a nice size tank of larger range with a fitting canopy. <I understand. Be chatting my friend. Bob Fenner> Michael L. Stewart

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

Stowaway Crab Robert, I purchased a finger leather coral and subsequently discovered a small stowaway crab on the live rock to which the leather was attached. He was black and about the size of my pinky fingernail. Well he disappeared for about 6 months and then showed up significantly larger. He has very large black front claws, his body is about the size of a half dollar and is dark brown with white lines. His legs are brown and hairy. I recently lost a plate coral and wonder if he is responsible. <Possible> Any idea what type of crab he might be? Is he a pest in a reef tank? If so, how do I catch him? <Only the last... please read over the www.WetWebMedia.com site under "marine crabs" and associated FAQs. Bob Fenner> Your incites are appreciated Karen O'Reilly

Filstar XP2 canister filter Hey Bob, I would like to add the new Filstar system by Rena to my established 30 gallon reef set-up (about 1year). I believe my Eclipse 3 system is not powerful enough anymore (What do you think?). <A good addition as a reef filter system> I have been adding more corals lately and believe it's time for a filtration change. I was wondering which steps I need to take when changing filtration systems.  <Run both... if not continuously, at least for a month> I was mainly worried with biological lose and possible nitrate increase. Your input is always appreciated in such technical matters. Look forward to your advice. Thank You, Jason <Be chatting my friend. Bob Fenner>

Re: Filstar XP2 canister filter and Sally light foot Bob, Thanks for the reply. I just came home and found my Sally Light Foot on its back, its not so light anymore. <Actually lighter> I added a frog spawn and a blue Linckia starfish 2 days ago, would that cause the crab to die or do you think its was its time.  <Who knows? What do you think?> It seemed to be very active until today?? also my pipe coral and long tentacle anemone are touching each other, should I keep some distance between them??  <Yes> Plus my pipe coral doesn't look so hot. <It's losing. Bob Fenner> Thanks, Jason

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 ofthe 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>

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

Ghost crab care Dear Bob Fenner; My parents recently brought back two ghost crabs from the beach in a 20 gal tank with sand for my kids. Where can I find some general info. on crab care (besides hermit crabs)?  <Look on the Net under the genus "Ocypode"> The main thing that I need help with is what to do to replace/clean their sand. Any info will be greatly appreciated. Please send any info. to . Thanks, Chris Colby <Not easily kept in captivity. Bob Fenner>

Crabs First thank you for your help in other areas of my fish tank. This site is quickly becoming invaluable for a research/learn what you can nut like me. <Good company> But.... I wish that I had found this site earlier (but we only recently got on the net....we are so out of touch!) <But catching up quickly!> I have been going on my dealer's advice with all my critters currently housed in my tank, but after reading your articles some of my faith has been shattered. I was told that deco crabs were detritus eaters and rarely bothered anything in the tank, but from what I have read in your articles is that this can be the vicious monster that it looks! <Yes, unfortunately> And so far it has proven true. For a while all was well, he his and I would occasionally see him sitting on a rock at night, nothing was eaten or bothered. Then I bought a blue star fish. Pretty little thing, one of those things that I really wanted and went out of my way to make sure that my dealer knew it. So I brought this beauty home, acclimated him slowly and then plopped him into my tank, where he promptly "oozed" under a rock and disappeared. A couple days later I noticed that he had bites on him, two of them suspiciously the size of my Singapore angels mouth. At that point my husband wanted to get rid of the angel, "We never see him". But I see him and I love him.  <A great aquarium species... best of the genus Chaetodonoplus> So first I took my rocks apart to make sure the deco was o.k. cause I thought for sure that the angel might get him too...ha ha ha. (By the way I suspected the angel because I saw him taste my anemone and my sea cucumber once...though he never did it again) So I moved the star to an area that the angel would never be able to reach. down flat and under the rock that the star was attached to...there, now he's safe... not!!!! Two days later I woke up and found bits of blue flesh on the sand and a star that was losing his leg and had several more bites on him. So then I got to thinking. Angels don't go out at night, so what does? The only really nocturnal thing that I had at that time was the deco.....huh. After reading your articles I am sure this is what happened. The star went back to my dealer for a little r&r in his live rock tank with nothing meaner then feather worms.  <Neat> And now.....well he just did in my cute half tame emerald. I used to hand feed the little fellow. And if he was still hungry he'd grab my feeding tube and reach up in for some more...I got him on some rock, so financially he was no loss. But I don't count money, just lives. <Good for you, the planet> And the weird thing was that before the emerald died he started spitting this weird goop out of his mouth, that eventually covered him.  <Oh, oh> I took him out and found that his whole abdomen was missing and I could see his lungs. Have you ever heard of these crabs spitting goo?  <Reminds me of cheesy "B" or less movies with the "done in" actors regurgitating whatever... suspect your Emerald/Mithrax wasn't faking...> It was clear and stringy and reminded me of the stuff that some animals use to catch food. Or maybe what spawning looks like, except he wasn't spawning.... Any way thanks for all the help. And as for the deco crab.....he's going back for a trade on something far less likely to chew on everything in site! Maybe a rock... <Much safer. 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! I'm in a state of confusion and disbelief. I recently got an arrow crab to ensure that I didn't have any bristle worms and I'm pretty sure that I now regret the purchase. I used to have quite a plump 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, I'm 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 I'm pretty sure it molted, but I'm 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 question I've got a question regarding Schizophrys dama (decorator crab). about how many species are in this genus, <this genus of the family Majidae, the Sea Toads, has at least a dozen described species, but several more undescribed as yet... and some majids are not "decorator crabs" per se... and other families contain "decorator" types...> and are they all in the same genus because they 'decorate', or is it for other reasons.  <Other, morphological reasons> I started a 125g reef tank about 5 months ago and I'm going for a semi regionally accurate system going from the south of the barrier reef to a bit west of Australia (Christmas island). the furthest east ill go is Fiji, and the furthest north ill go is southern Indonesia. <Like the way you put this> anyways, I think the whole idea of decorator crabs is pretty cool and I'm trying to find out some information about them. are their any species that fit in that region that you can think of? perhaps some or the kind that use anemones as their main defense system? perhaps boxer crabs? any help would be neat <Best way to approach this IMO/E is to select for the animals on the basis of where they were actually collected... Schizophrys are not "reef safe" as the case with most all crabs... Do look into "The Modern Coral Reef Aquarium, volume 3" here... for about the most up-to-date, complete coverage of potential decapod additions. Sven and Alf's website link can be found on the WWM sites Link Pages.> Jon Trowbridge oh, I've seen some online places that sell anemone decorators and I'm wondering s they sell the baby anemones on them, do they (anemones) usually end up living? or would I get a bag with a crab and a lot of goo.... <The associated anemones live/ship about as well as their hosts... both generally arrive in good condition. Bob Fenner>

Crab question Hello Bob- I recently purchased a bright pink hard coral from a mail order company. After placing it in my reef tank I noticed a very small crab approx. 1/8th of an inch from claw to claw that came with the coral and appears to be guarding the coral as his territory. If anything comes within range of the coral the crab gets between the object and his coral with his tiny claws extended. I have searched every internet sight I can find, to see what type of crab this could be and am hoping you may have an idea. He is mostly white with rust red claws. Thanks for any info Sincerely, Carol Gibbs <A few possibilities here... and do agree with your assessment... this crab is likely "guarding its turf"... For starter's, of works that are widely available, see Allen and Steene's "Indo-Pacific Guide" under both corals of the genera Porites, Pocillopora and crustaceans/decapods... 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>

Lightfoot Crab Just a quick update--the sally lightfoot crab that lost a claw and two right legs molted today and has all his legs back! (Hmm, as I had told you... neat trick eh?) I had been offering him frozen krill on the end of a skewer every other day or so since the "accident" to ensure he was getting plenty to eat and to speed up the growth/molting process. Looks like everything is going to be fine on that front! (Ah good) I also caught a glimpse of the peppermint shrimp last weekend--he's been hiding out in the back of the tank, apparently, and has not become a lightfoot meal, yet. (Also good news) The new tank is on order. I'm building the sump/refugium (30 gal) this weekend. Everything else has been ordered or has already arrived. I'm sure I'll have a question or two once this whole process really starts cooking, but I've also found a newsgroup with some pretty experienced reef keepers who have been very helpful as well. (Ahh!) Take care. Chat again soon. --James D (Bob Fenner, in Cabo San Lucas)

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>

Sad crab just the other day my anemone crab started its monthly molt. it usually takes about a day or so to complete the process (most of it is at night). so anyways, this time was a total bungle. this is the third day and its been having problems with the molt. I feared it would suffocate on the first day so I -carefully- aided in the removal of its top main shell (don't know the technical term). I broke just enough off so that its gills weren't covered and left the rest up to it. well the molt is pretty much over with, but the crab had to ditch both of its main claws and about 50% of its legs. it only has one of its 'filter' claws. as far as I can tell both sets of oral pincers are ok, so it can eat. anyways id rather write this one off and ditch it, but alas I've grow fond of the little bugger. I placed him near anoutcropping of rock so that it has something to hold on to (otherwise its pretty much on its back or drifting around). and I'm dropping some roe very close to him every now and again. I know crabs can recover from loss of limbs, but this is pretty bad. it definitely wouldn't last in the wild. got any advice? <Don't help animals in ecdysis... they can/will molt in due time... on their own... Keep track of alkalinity and biomineral content with these animals and make available materials (rock, substrate) that they can/will incorporate in their diet for purposes of biomineralization. Provide plenty of cover of different size hiding spaces...> thanks Jon Trowbridge ps. no other 'animals' in there except some corals and a few urchins/snails. nobody will bug it. perhaps there's a Ca problem? I'm using Kalk as well (iodide/strontium/CoralVite/Coralaccel). <So... are these at reasonable levels? Bob Fenner>

Legless Lightfoot One of my Sally Lightfoot crabs molted yesterday. However, today he is missing one front claw and two of his legs on the right side. Is it common for these crabs to lose legs in connection with a molt? Or is something amiss here? <Hmm, sometimes in ecdysis/molting some limbs are not formed due to nutritional reasons... perhaps other factors... but in most cases like this, "someone" was munching the inopportune animal during the "hiding phase" of rehardening its new exoskeleton... it can/will "re-make" these lost limbs next molt...> In case you don't recall, one night I saw a different crab in the tank that must have come in on the LR. The damaged lightfoot is now "guarding" a hole in the LR, and I can see the two front claws of the "mystery crab" at the entrance to the hole. Occasionally the lightfoot will "pick" at the other crab's claws. Are there any species of crabs that eat other crabs? <Many> This "mystery crab" was pretty small before, but is it possible that as he's getting bigger he's munching on the Lightfoots? Or is this loss of legs just something that sometimes happens when they molt? <More likely the former. Bob Fenner>

Black Crab Dear Sir, I have a 55 gal reef tank approx. 7 mos. old. I was feeding my fish one evening and noticed a couple of hairy legs beneath my chubby plate coral. wait till lights out and came back in the room after lights out. The thing I was a crab sort of looks like a sally light foot but smaller but its coal black very shiny and has hairy legs with white spots. I did not buy it so I think it came in with my rock. But it has been staying under my chubby until it died and I wondered if that crab anything to do with it. <Doubtful> I've talk to aquarium shop but they can't help me. I just wanted to know this this species eats corals and leathers if so I, I need to get it removed!! Thank you, Gary! <Good question, but I too cannot identify this crustacean from your description. Perhaps by chance you might find something similar in books concerning these decapods at a large local library? Bob Fenner, who would just remove it "on general principles" if it were more than a couple of inches in diameter.>

Can an arrow crab live without claws? Hello Mr. Fenner! First of all, thanks for offering your services! (I really appreciate your expertise.) <Glad to be here, help> I bought a large arrow crab a few months ago and it only had one claw. (Since I have a set-up that makes it easy for him/her to obtain food, I thought it wouldn't be a problem.) <Likely not> However, last night, he lost his other claw. I couldn't find it anywhere and was wondering if you could tell me if he'll a.) be able to survive? b.) How it might have happened? <b. a tussle of some sort, a. likely yes> I have a 60-gallon hex. with live rock and all I have are 5 small green Chromis and 1 yellow damsel. I also have 4 hermits and some Astreas. This past weekend, I purchased a Sally Lightfoot as it was recommended to me as a good and harmless algae grazer. Might it have been that? (Could a Sally Lightfoot take on a large one-clawed arrow crab? Would it?) <Yes...> Thanks for any insight you could provide me with. <Next molt your Stenorhynchus will likely have something in the way of claws back... and then next... a bit more> PS - Two weeks ago, I noticed one of his legs on the tank bottom. (I suspect he was molting since he still had 6 legs.) <Sounds like a miniature crustacean version of "Clash of the Titans"... I would separate these two if you have the facilities> Best, Declan Procaccini <Be chatting, Bob Fenner>

Arrow crabs Mr. Fenner I placed an arrow crab in my aquarium in hopes that it would rid my live rock of bristle worms. but recently, if been reading that these crabs could attack fish or even other crustaceans or invertebrates. is this possible? <Yes, unfortunately... for their size these oddities can/do become predaceous toward fishes, other invertebrates> the crab we have doesn't seem to bother anyone. should I remove it, or just keep a cautious eye on it. <The latter IMO. You will likely see signs (scraped fishes, stalking behavior) before outright missing livestock. Bob Fenner> thank you

Lightfoots OK--now you'll really know what a greenhorn I am. When I got home this evening, I pulled another "dead" sally lightfoot crab out of the bottom of the tank. Before I ran a barrage of water tests, however, I counted them--and there were three crabs on the rocks--and we started with three. Now I know what an empty exoskeleton looks like after a crab molts. I guess they're happy and growing. . . <No worries... glad to read, know... and do leave these cast off exoskeletons in the tank for a week or two... sometimes consumed, incorporated by the shedding animals to augment their new ones> On another note--I guess I need to build a calcium reactor, and soon. Tonight I dosed the aquarium with the Tropic Marin Bio-Calcium. It's a powder product, if you're not familiar with it, and the instructions say to just put the powder in the tank by sprinkling it on top of the water.  <Very familiar with the product and company... both are excellent> The hammer coral, moon coral and finger leather were unaffected--in fact, all three of them seemed to love the Ca boost and extended their polyps even further. The moon extended its tentacles about an inch, and some of the hammer polyps were an inch long as well. However, the pagoda got what looked like "blisters" all over it and the flesh looked very irritated, and the bubble and Goniopora (I know--bad choice. . .), and toadstool leather all retracted completely. Is a sudden increase in Ca likely to cause such a reaction in these species?  <Yes... a few things at play here... like you state, sudden increase in calcium, but also pH (locally), and physical irritation (irrespective of how well the product appears to dissolve... Best to pre-dissolve, introduce the new material by way of a filter, sump... and slowly (perhaps rig up a drip bottle or siphon of airline tubing...> (Based on the label instructions, Ca was increased roughly 35 ppm by the dose.) Any permanent damage?  <Not likely, unless the animals health was impugned before use... but more nicks toward the negative...> (They all seem okay now, after several hours--but no reason to put them through any stress if I can dose the Ca gradually, on a daily basis, and by first dissolving the Ca in the top-off water--or better yet, by building a reactor.) <Ah yes... the process continues.> Thanks once again for your thoughts. <You're welcome my friend. Bob Fenner>

Cleaners The cleaner shrimp are doing fine. However, when I got home yesterday, my smallest sally lightfoot crab was decimated at the bottom of the tank,missing several legs. Is it likely the Lysmatas are the culprits? From reading about these shrimp on the site, my guess would be that they got hungry and decided to snack on the crab. <Very unlikely... crustaceans know who to avoid... and Lysmatas are pathetically slow compared to this genus of crabs... You may have a Stomatopod... Alpheid... hungrier fish... or just a sick/dead Sally...> Hope you're doing well--got your book on Monday and it's been a great reference--very informational and easy to read. Thanks for your contributions--and for the section describing the terrible use of cyanide to collect fishes. I'll certainly ask about the origin of every specimen I buy in the future. <Ahh, deeply gratifying. Thank you. Bob Fenner> Talk again soon! James A. Deets

Percnon gibbesi Hi Bob - I recently walked into the LFS and, as described in your chapter on crustaceans, scurrying around inside a display tank were a half dozen Percnon gibbesi with an accompanying "Sally Lightfoot Crabs" I.D. sign. The Nimbles really do deserve their correct common name and fascinated ... I bought one. Nimble Sally has been in QT for two weeks and I'm getting ready to move it into my display. The only behavior that I've found curious has been the specimen rubbing its legs together; occasionally "wiping" it's face with legs or claws; and rubbing / "scratching" its back on the piece of rock I keep in non-fish QT. Are these unusual habits for Ms. Nimble?  <Not at all... general cleaning> Recently, I found a discarded exoskeleton ... does the itchy behavior precede a molting event?  <Perhaps ecdysis (fancy schmancy term) is related... but maybe not> Should the abandoned shell be regarded as a decay/ammonia threat and removed from the tank? <I'd leave in for a few days... little ammonia/protein in it... and like many crustaceans your Percnon may consume it for mineral et al. content to build new exoskeleton> Finally, should crabs receive the "freshwater dip" treatment prescribed for fish? <Not most, and not this one> Thanks for your help - Tom <Thank you for your input and asking. Bob Fenner>

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>

Arrow Crab Hi Bob, Thank you for your previous advice, and your current work to help us becoming a "conscientious marine aquarist" (loved your book!). I am currently in the process of ordering your new book---although an on-line form would be more convenient :-). <Thank you times three... Agreed... wish we did have the capability... but then, it would take away the fun and good I can do answering queries, maintaining and building the site... maybe some day soon, or better, hopeful that the pet-fish publishing world (it is small!) will "wake up, smell the java", and get more of my works (and several friends) into print, distribution, sales... In the meanwhile, nothing really wrong with snail-mail... Will get you the book in, um, maybe a week total transit time from you sending order to receiving it.> I wanted to have your expert opinion on the arrow crab (Stenorhynchus sp.). I just completed the initial phase (cycling) for a 90 gal. reef system. I envisioned to have mushrooms, star polyps, soft corals, cleaner shrimps, scarlet hermit crabs, and a few fish (orchid Dottyback, flame angel, and yellow or Kole tang). My questions are as follows: 1) Is it safe to add an arrow crab in my system I envisioned? <Maybe... depends on what you're going to put in with it... and thanks for prompting me... have my "crab" slides and reference works, old articles, on the tables here... re-did the shrimp, cleaner shrimp, fw shrimp... and lobster sections of WWM the last few days... and am on to the crabs today....!> 2) Does the arrow crab have a history of surviving/thrive in a captive environment? <Yes, but...> 3) What is a typical diet for an arrow crab? <Most anything it can get its claws on... which is considerable as this animal gets bigger. Have seen them eat Butterflyfishes in captivity...> 4) Where can I find more information regarding the arrow crab? <Take a look at the www.WetWebMedia.com site in a couple of days... for the references listed there... I'll be looking through the bibliographic tools at my disposal (online), and be adding the "pet-fish" references there as well> As always, any information will be greatly appreciated. Thanks, Dan <Chat with you soon my friend. Bob Fenner>

Mystic Mithrax Dear Bob: I have a 155 gal tank started in Oct. 99. I have lots of live rock and also the live sand. I really haven't had much growth on it except some brown grass and my Mithrax crabs ate that. I think they are eating so much that nothing is growing. I got 10 of them. I have feather dusters, two anemones, some different corals(7) arrow crab, a clam, two metal halide lamps, skimmer, 350 magnum pump with charcoal, temp. 80%, water tests good, but: I just lost a large coral (star coral) that had been doing really good, before that a carnation coral, before that an elegance (2). It seems that the inhabitants I have now do well but new ones slowly die. I just purchased some plants from ff. and I'm hoping this will help. I also really like them. Can you help? I lovvvvvvvvvvvvvvvvve this hobby. Temp. 78 - 80 Brenda (thanks and I really appreciate your diary.) >> Yikes, ten Mithrax Crabs? You really should try to remove all but a couple or three of these... more are too many... a tough job I know. Is the Magnum (canister filter) all your filtration? Not sufficient for a 155 gallon system... Hopefully you have left off some gear, circulation mention. And the Carnation and Elegance choices were poor... they generally don't live... New animals slowly dying is a bad sign... Poor water quality, some sort of poisoning from inside (dead, dying organisms) or outside (supplements... what is your history here?)... The macro-algae ("live plants") you mention getting a step in the right direction... but do read over the Marine set-up and maintenance pieces stored at my site: www.wetwebmedia.com for insights into what's been done so far that is the cause of your losses. Once we get your system set-up and running properly, it will be far more fun and easier to maintain. Bob Fenner

Sally light foot Hey Bob I have a Sally light foot crab. Constantly busy eating algae etc. Also constantly shedding it's exo and growing. JUST HOW BIG IS THAT THING GONNA GET? It is already more than 9" from one leg tip to another. Do I have any thing to worry about its size and becoming a clumsy nuisance? I really like him or her, well it anyway. Kevin Johnson <Wowzah! this is a very large Sally Lightfoot Crab (Grapsus grapsus)... the biggest one I know of was (collected with difficulty in the wild) about ten centimeters/4" across its carapace (upper shell)... This is a very big crab for a reef tank... and though they mainly eat algae, this species has been recorded eating invertebrates... even capturing small land mammals... Bob Fenner>

Re: Sally light foot I am sorry I must have said it wrong. The crab is about 9" from the very tip end of one leg across to the very tip end of another. The body of it is about 1.25" across. Is it going to get much bigger. I don't want it eating my invertebrates. Right now it is very content on eating algae. Do I need to take this one to a pet store soon? Kevin Johnson <I understood the end to end part... those are some long legs! And I wouldn't trade this crab in if it was doing a good job, and leaving your other livestock alone. Bob Fenner>

Stowaway Crab I ordered some fish and corals from you a couple of weeks ago and everything is great. However, one of the things I ordered, a Pink Stylophora, had a stowaway. When I took it out of the bag, I saw a small crab hiding in the branches of the coral which looks like a Mithrax crab, except that it was red. I left the crab alone until I noticed that it appeared to be feeding on the polyps of the Stylophora at night. At that point I removed it from the Stylophora by blowing a powerhead on it. However, at that point, it looked  like many of the polyps at the base of the coral had been picked at or eaten. What is this crab? Should I get rid of it from the tank altogether? <Hmm, sorry, but not surprised to hear of such stowaways... I would give it the heave ho... Doesn't sound like a commensal... probably more trouble as time goes by. Bob Fenner>

WHAT TO FEED A DECORATOR CRAB... I BOUGHT A DECORATOR CRAB TWO WEEKS AGO AND HAVE JUST BEEN LETTING HIM FEED ON HIS OWN. I CAN NOT FIND ANY INFORMATION ON THEM THAT TELLS OF THERE DIETARY HABITS. HE IS IN A FISH ONLY TANK, DOES HE NEED LIVE ROCK TO USE FOR HIMSELF AND WILL HE EAT BROWN ALGAE. >> These animals are feeders on other invertebrates: worms, shrimp and other crustaceans... and a minimal amount of greenery... They can live pretty well on newer live rock inhabitants, in addition to meaty scraps from feeding your fishes and other invertebrates. Bob Fenner

Decorating by eating others 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>

Crab cleaner ups or eater ups? 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... Bob Fenner>

To Mithrax or no Bob, Thanks for all your past help. I've read your book, (loved it) and have all your FFE Q/A in one doc for easy searching. Here's my questions.  I have a 75 with 4x96 CF Bulbs (2 6700, 2 7100) bulbs. I run them 14 hours a day. I've read different things on CF, what is your opinion on how frequently they should be changed? I've seen you recommend Mithrax crabs for reef tanks, and also seen the following quoted from Julian Sprung: Avoid Mithrax crabs. They may do a good job when real small but they grow real fast and cause damage . http://www.athiel.com/lib5/macna2.htm What problems could they cause? What should I NOT have them with? I am looking for a good sand stirrer. I had some white burrowing starfish, but they got eaten by my pacific or fire cleaner shrimp? Thanks! Marty < Good questions... ones that are tough to answer... Regarding the CF lamps, you'll have to check with your supplier...some have "effective lifetimes" about the same as (T-12) regular/old-fashioned fluorescents... on the order of 7,500 to 10,000 hours... and others up to 20,000 hours... And really, the only way to tell, irrespective of "doing the math" on how many hours you're running yours... that they need replacing is to use a PAR or lumen meter... IMO they should be replaced either at 80% of their calculated "effective lifetime" or at 80% of their output... The latter, the better judge.> "Avoid Mithrax crabs. They may do a good job when real small but they grow real fast and cause damage", this bit lifted from the URL you posted. But also see: From 'The Reef Aquarium, Vol. 1', Sprung and Delbeek, p279:  Mithrax crabs are good herbivores for large aquariums. Mithrax sculptus only grows to about 6.3 cm (2.5 inches), but is capable of capturing small fish. Some Mithrax species grow very large, and are therefore unsuitable for most Aquariums. Some species have been reported to eat Valonia. This crab is from the Caribbean. < So... I think these statements are confluent... that in the former Jules was referring to little reefs (ten gallons, like his), and in the book version of his opinions, larger systems. Some aquarists have reported that Mithrax crabs will eat polyps if hungry enough. I recommend that you start with only one and keep your eye on it to make sure it does no harm.  Bob Fenner >

Lightfoot, light some legs I have a sally lightfoot crab and he/she has lost 4 legs in three days, also all 4 legs fell off on one side. I have two emerald crabs, 1 three striped damsel, three blue damsels, 1 clown, hermit crabs, snails, . do I have the right fish combo or is my crab sick. please help!!! < Yikes... very unlikely that the legs have "just" fallen off. More likely pulled off... I'd guess by the other crabs (real: emeralds, and false: hermits)... or a more remote possibility that the animal has an internal problem (e.g. an infectious or parasitic disease). In any case, the prognosis is bleak to bleakest if you do nothing... if you can't move the Sally Lightfoot, do place it in a separate chemically inert container (outside power filter box?, plastic breeding net-trap?...) away from your other crustaceans...  Bob Fenner>

Mithrax, reef safe? I noticed that the Mithrax Crab will eat bubble algae. Are they safe for a reef tank and how many is necessary for a 90 gal tank with 90 lb. of live rock? Thanks.........Lin Smith < Of all crabs, this genus is amongst the best for reef use, though not totally "safe" (they can eat coralline/red algae, might try your other animals if hungry), but do often consume Valonia/bubble/pearl algae as well. I'd only use a couple... easier to remove a few if they've got to go than many. Bob Fenner>

Mean Crab disease I have recently started a reef tank 44 gal, pentagon, with some live rock and a few anemones. With the live rock I got a really mean crab that has now grown to almost 1.1/2" in diameter, and ate both the gobies I had in the tank, and I think some of the anemones. I don't really want to get rid of him (my 3 year old thinks he's "cool"), so I bought a dwarf lion, that is right now my only fish in the tank. Last night I noticed that the lion had little air bubbles all over him. When he was chasing his dinner a lot of the bubbles blew off, but then a few hours later they seemed to return. Is this a problem? < Hmm, might be, and may be related to the Crab that ate Cincinnati... Are there bubbles from air or water pumps just kind of floating around in the system? Lionfishes are quite slimy and these bubbles might be adhering to it from these sources... on the other hand maybe Mr. Crab is chasing/pinching the lion about at night, causing it to jet up to the surface... If it were me, I'd A) give that crab the heave-ho, B) Get less pinchable fishes to keep with it, C) A combo. of both... Bob Fenner>



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