Please visit our Sponsors

FAQs about Decorator/Sponge Crabs

Related Articles: Crabs, Arrow CrabsHermit Crabs

Related FAQs: Marine Crabs 1, Marine Crabs 2Marine Crabs 3, Marine Crabs 4, By Species/Group:  Arrow CrabsEmerald Green 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 Shrimp Crustacean Identification, Crustacean Selection, Crustacean Behavior, Crustacean Compatibility, Crustacean Systems, Crustacean Feeding, Crustacean Disease, Crustacean Reproduction,

Lethargic decorator crab      7/20/16
Hello! I am a beginner saltwater enthusiast. My son gave me a 30 gallon saltwater tank for my birthday and we are building the tank together.
<A great project>
Currently we have live rock, 2 clown fish, orchid dotty, flame angel,
<Yikes; this needs more room>
lawnmower blenny,
<And this fish in time>
2 emerald crabs
<Keep your eyes on these; fish-eaters>
and recently added a decorator crab.
<This too>
He doesn't move around the tank but stays huddled up under a rock all the time.
<Pretty much what they do in the wild during the day-light hours>
After 2 days of no movement I thought he was dead and tried to remove him from the tank but he started moving lol. Well it's been another 2 days and he still hasn't left that spot. I read that decorator crabs are nocturnal and started turning the light off at night, but still he doesn't move! My water test is ok, the other fish and crabs are doing well and are active. Am I doing something wrong or should I be looking for some kind of illness or parasite on this little guy?
<Do you dose iodide-ate? You need to w/ these decapods. See WWM re>
Please let me know what I can do to get this little guy up and moving around the tank. Thank you��
<The I2 may do it on its own, otherwise... time going by; practice feeding by day. Bob Fenner>
Re: Lethargic decorator crab      7/20/16

So I need to provide iodine supplements for the crabs and then provide a food source high in iodine for them?
<One or the other. Likely best to use a commercial prep: http://www.seachem.com/reef-iodide.php

Brittle Stars Living Inside Decorator Crab -- 10/19/2009
<Hey Allison!>
A decorator crab that I have has a few holes in its exoskeleton on its legs. I assumed it was from another crab or fish picking on it. Then yesterday I took a closer look and saw there was several tiny white brittle stars crawling from out of the holes as if they have taken up house.
<Mmm, not good...>
Do you think they are eating the crab inside out?
Is there a way to get ride of the stars without killing the crab?
<He is likely on the way out already, unfortunately.>
Would the crab be OK if I just left him be? Any info would be greatly appreciated.
Thanks Allison
<Well Allison, brittle stars are a common part of an 'unpurchased clean-up crew' -- if you're seeing them invading the crab already, its likely already too late. Does the crab still move? If its becoming more and more lethargic, I would definitely remove it before it fouls the water...

Decorator Crab; Feeding And Compatibility 8/30/09
Okay, so my roomy and I recently set up a 25 gallon salt water aquarium consisting of crushed coral and about 8 lbs of live rock. We decided to throw in a Spider Decorator Crab to entertain us while we
wait for the tank to finish curing and ammonia levels to get as close as possible to zero :) (we made sure they were pretty darn close to nil before adding the crab).
Squeegee, as we named him, seems pretty content, scavenging the tank for whatever he can find on the live rock, not-to-mention the assortment of tropical flakes that we throw in on a day-to-day basis.
This leads me to my first question. Are the flakes enough for the crab to eat and if so how many should I be throwing in there? Also, would feeding the crab ghost shrimp be okay (if so how many a night)?
<Ghost shrimp are fine, maybe one every other day depending on the crab's size. Kind of pricey for crab food.>
And lastly, Is there a more ideal (and cheap?!) sustenance we could be feeding it?
<Flakes are fine and about as cheap as you can get. A few flakes per day should keep him happy. Crabs are opportunistic scavengers and will eat most anything they can find.>
Finally, as far as compatibility goes... the tank was originally intended for a Snowflake Eel (no fish) which we'll be getting as soon as the tank is ready. Do you think a young (6in) Snowflake would attack/devour Squeegee?
<A excellent chance for this to happen as crabs and shrimp are their main diet in nature. Do be aware that your tank will eventually be too small for keeping a Snowflake Moray in good health.>
Would there be any way that we can get them accustomed to each other with adequate feeding long enough so that they can coexist for some extended period of time?
<No. Do read here. http://www.wetwebmedia.com/snowflakemoray.htm>
Thank you!
<You're welcome. James (Salty Dog)>

Crab ID 4/14/09
I bought this crab at my LFS. They said he is reef safe, and a sponge crab.
After looking up a sponge crab, I realized that he is certainly something else... but can't determine what.
He has very small pinchers, like a shrimp might.
Any ideas?
<I concur that it is unlikely a sponge crab. With not much detail in the pics, my best guest would be a Stenorhynchus species, commonly known as decorator crabs, and they are not entirely reef safe. Like all crabs, they are opportunistic feeders and will eat what ever they can catch/find. Caution here
my friend. Since Mr. Fenner's second home is on the reefs, I will ask for his input here.>
<<My Standard Spiel here re Decapods period... Cave Crabem! (beware the crab). RMF>>
Thanks so very much!
<You're welcome. James (Salty Dog)>

Decorator crabs. Comp.  04/03/09
Hi, i have 2 decorator crabs in one 30 gallon tank, they were fine when i brought them home a few weeks ago and were small. Once they got a little bit bigger it seems they try to eat everything.
<What they do>
I have never dealt with this type of decorator. It's the sponge decorator variety of crab.
<There's more than one species...>
Should i get rid of both or just one?
<... what do you want to have else-wise?>
I planned on getting a different species that i have had experience with but not this one. I was given these two when i ordered a different type of decorator.
<Mmm, I'd likely trade both in... you will have "issues" with one, two... in any case. Bob Fenner> 

Decorator crab... something growing on it... no pic... Uhhh?  3/23/07 I have read up about as much as my brain can absorb, <Mmm, may I be excused, my brain is full?> but I have something on the back of my decorator crab, other than the many things that looks like he put on its back purposely and can not identify. It has spread from maybe a small percentage of the crab's body to about a third over a period of 5 to 6 weeks. <A fast grower!> It is clear to white in color with very small specks of bright orange. <Hmm, maybe a sponge?> I don't know if it is a disease or maybe even a flatworm. <Unlikely, I think.> It doesn't seem to  bother the crab, but it is getting closer to the crab's eyes and  mouth. <Hopefully, the crab will be able to prevent this from being a problem.> Any info would very helpful. <Can't really tell you much without a photo.> Sorry I couldn't send an image, if I can find a camera with close enough lenses I will send you a pic.   <Check to see if your camera has a macro setting, looks like a small flower, will allow you to take close ups.> Thanks, <Welcome -Mich> Jeremy

Camposcia retusa... decorator crab, comp.     2/16/07 Hi Crew <Angel> I have a question regarding the above.  I have bought one, I suppose it was a bit of an impulse buy as I wasn't planning on getting one, <Mmm, you're learning...> I'd never heard of one, but I saw it and was fascinated.  The shop didn't give me the Latin name but from pictures I have seen on the internet it is definitely this one.  It is approximately 10 cm in diameter from tip of leg to tip of leg. <Yikes... Giganto!> So he is fairly large compared to my other shrimp and hermits. So basically I have a tank set up with fish, shrimp (dancing) and hermits (red ones) waiting for my new and improved 700 L new Christmas present tank to cycle. <Wow! Send your Santa my way!> It is a reef set up in that I have live rock in it, 2 types of algae plants, under tank sump, skimmer (thinking of getting an ozonizer to make the water crystal, but that is another question for the future may be).  Any way as I have told Bob F in a past email, my LFS only gets small stocks of marine life and quarantines them for about 6 weeks before selling them and I am very good friends with him and the manager and know that all their stock is disease and parasite free. <Mmm, just my usual cautionary note here re... Most all stores, wholesalers even... can't actually promise such... there is just too much going on... mixed nets, containers, staff... to warrant that contamination hasn't occurred, that new livestock coming/going haven't passed things on...> So I took the crab home and very excitedly put it (Kev) straight into the new tank (acclimatizing obviously).  Kev is doing really well, but now that I have seen him trundling around and realized how big he is, although small claws, <...> I am worried about what damage he may do to my fish and hermits when I put them in.  My LFS friend said watch with small fish and shrimp, but now I am worried what would be classed as small relative to his size and eating habits. <Ah, yes>   My smallest fish at the minute is a young clown who is approximately 5 cm.   So at the moment I am holding back on transferring my buddies into the new tank.   <You are wise here> I know that in the aquarium world you cannot be certain of anything, but I thought you probably know more about their track record for compatibility than most.  On a positive note though the Caulerpa sp. I bought had some hitchhiker xenia on it and so I have attached this to the rock and he hasn't demolished it and only took a little, so maybe Kev is the caring type. <Or not caring for Pulsing Soft Corals... as the present "menu item">    Have had no replies on the chat forums so its over to you!   Thanks in advance Angela (WWM fan). Please let Bob know that his book CMA is brill!!   <Much good help with this tome. I would definitely keep your eye on Kev... and a spot in a refugium to move it/him too not if, but when he becomes too much of a tankmate sampler. Bob Fenner>
Re: Camposcia retusa comp.    02/17/07
Hi Bob <Am everting my lips in my best... well... semi-okay impersonation of MickJ... "Angie..."> Thanks for the swift reply. <Welcome> Would you say he is probably too big for the rest of my fish and crabs who are in shells of about 4 cm?  Give it to me straight, don't spare my feelings! My largest fishes are: 12 cm blue Cheeked goby 12 cm long Midas blenny 8 cm long Regal Tang I know that I can return him, sad though I would be.  But I don't want to be unfair to my other fish friends. <Mmm... if it t'were me, I would return this Decorator... Too likely to be heartbreaks down the line> What do you mean by "Much good help with this one tome." <Oh, the publisher, James Lawrence is a pet-fish and publishing genius... a delight to work with him and the Microcosm crew> Angela in a dilemma. <BobF, in a heat to get out and work on the garden walk/run the dogs...>
Re: Camposcia retusa comp.    02/17/07
Thanks for that, he will be going back to the shop tomorrow, but he will be in good hands. <Ah, good> From Angela (named after Carly Simons "Angie baby"). Night time here so off to bed. Good night from rainy Manchester.. <Sleep tight... from nice/sunny (today) southern California. BobF>

Sponge Crab Questions (4/16/04)  I have a 1 1/2 inch sponge crab that I am keeping in a 20L aquarium right now with a few fish..... I call him "Sponge Bob." Bob is a cute little fellow but I know very little about his dietary requirements. He is eating small pieces of silver side right now. What else would give him a good balanced diet? I assume, like most crabs he is not reef safe, right? <Exceedingly unsafe and very destructive.> I would love to put him in my Harlequin Shrimp tank ( it has a few limpets too) but fear he might hurt them, would he? <Quoting Calfo & Fenner, they "have no place with a casual marine aquarist or in mixed invertebrate reef aquariums.> He lost his sponge and is currently carrying around a small piece of green 3M Brillo pad on his back........I call him "Brillo Bob," now:) Thanks for the help! Janey <These crabs do tend to be omnivorous with a leaning toward meaty foods. I had a hard time finding much info. I'd suggest you search the terms "sponge crab" and "Dromid" on WWM & Google to get more info. Steve Allen.>

Decorator Crab Woes [Not A Question; More Of An FYI]  - 04/26/06 Hi Gang, <Hey there>    I had an unfortunate event yesterday with a decorator crab that I wanted to share in case anyone else is considering getting one of these creatures.   <Share away, we love this stuff!>    My partner and I have had our aquarium for about two months now and are having a great time with it.   <Wonderful!> We're very pleased with it's results and with our damsels.  We made the decision over the weekend after positive tests that it was time to increase our stock from two damsels to a couple of shrimp, a crab and a Nudibranch.   <Be very wary with the last.  These do not survive so well in captivity.  Most times they perish fairly quickly.> So we set off to the pet store and in our ventures wound up getting a starfish, a decorator crab, two cleaner shrimp, a blood shrimp and a Nudibranch.  All was right with the world.    We got them home; floated them <Tell you the truth, you should float them, but drip acclimate them.> and put them in the tank still under the illusion that everything was great.  With amazing speed (which tends to happen in this hobby I've found) everything went horribly, horribly wrong.  Our tank is a forty-five gallon bow-front with 15 pounds of live rock, a three inch live sand substrate and giant piece of dead coral to provide hiding places.  With the rocks and the coral, there are a ton of places for the guys to hide.  As we expected, the decorator crab started off nice and leisurely picking up stuff from the tank as we were expecting him to do.  When he came across the blood shrimp, which had perched itself on top of one of our live rocks, he apparently didn't like him there and quite simply attacked him.  The blood shrimp having a brain the size of, well, a shrimp tried to fend his territory.   <Ha! This isn't uncommon though.> You can guess which one won.  The shrimp lost half of one leg on one side and one whole other leg from the other side . <Oh boy, probably tasty, but an expensive snack.> The decorator proceeded to make fast food of this delicious new meal and go back for seconds.  He started actively pursuing the blood shrimp.  Right before a second confrontation, during which I'm sure the crab would have killed the shrimp, I finally took the blood shrimp our of harms way and perched him on top of the coral where I though he would be out of the reach of the decorator crab.  Once again, all seemed well.    Concerned about the crabs aggressive behaviour (we'd gotten mixed reviews on this aspect of the decorator crab during our research); we decided to keep an eye on him for a bit after lights out.  While we were observing the tank; we noticed that the decorator crab had turned his attentions to the cleaner shrimp and was actively pursuing them; stalking, we're almost certain, with intent to kill.  Fortunately, they were small enough and fast enough to evade his reach.  Satisfied that he at least wouldn't decimate the rest of the aquarium, we made the decision to call it a night and started debating taking him back to the pet store the next morning.    Sometime during the night he managed to get to the blood shrimp again; this time dealing a fatal blow.   <Oh no!> The shrimps carapace was split down close to it's tail, two more legs were missing and one of his feeler antennae had been ripped in half.  He died shortly after we found him like that.  At that point we were pretty upset because we loved the shrimp (he was absolutely beautiful) and because he had cost us twenty dollars.  Where we were only debating returning the decorator, we made the decision at that point.  We figured it would only be a matter of time before he got his hands on the Nudibranch, the cleaners or the starfish (all of which had cost a grand total of $130.00).    I'm writing this to get the information out there if you guys see fit to publish it.   <Absolutely!> The research we did on the net was mixed with regard to aggressiveness of this species; although it tended towards them being relatively easy to keep and working well with other animals (possibly with the exception of SLOW moving inverts - I don't consider shrimp slow-moving but could be wrong about that).   <Sometimes they just have different personalities.  Info here or anywhere is based on the majority of cases, sometimes it may be different because each specimen is different.> Our experience says something very different.  This particular crab was extremely territorial and aggressive to the point he was actually hunting his tank mates.  It doesn't seem like a good choice in an aquarium where other crustaceans are housed.  We've since replaced him with a few snails and feel much better for the wear. <Great idea!>   Thanks for putting this out there for your readers and for the great work you guys continue to do at WWM. <No problem, best of luck in the future, Jen S.>   Warm regards,

Odd Crab 1/2/04 Sorry I didn't have a program to resize these.  Paint wouldn't let me. So, I'll only send 1 unless you want more. Info on the crab. Found along Florida Gulf Coast area (Tampa) Looks like a rock with legs and pincers. About 1 ? inches long. Narrow end of "shell" is where his eyes are. The shell is NOT an attached rock as his eyes are "built in" Any ideas? <cheers, Larry... your crab is "sponge crab" of the family Dromiidae. They are often decorator species, and they are never "reef safe" (very few if any crabs are in fact). Some sponge crabs have specialized diets or feeding habits. Survival in captivity is variable and runs the gamut. Best regards, Anthony>

Re: Odd Crab ID 1/7/03  Anthony, I don't doubt you, but while searching on Dromiidae or sponge crab, every web site gives me this:  http://www.ciesm.org/atlas/Dromiaspinirostris.html  Or a very similar shaped crab.  <you are looking in the wrong place/ocean here my friend. Your crab did not come from the Med or coast of Italy... unless you can confirm that he is as hairy as I am and likes nearly as much garlic on his food <G>. The Dromiids are an enormous group with a remarkable number of species. You need to look at references in locales where your live rock/coral has come from. Most of these crabs come from the Atlantic. Often with live rock... other times collected deliberately ten stocked in dealers mixed holding systems and "hitch-hike">  This crab does NOT have anything on top of him  <the crab in your link above is indeed nothing like your>  The rock looking shape IS his shell, not something he's holding on to. >From the items I read, the back 2 legs "hold" items, but this guy's back 2 legs are normal, not sticking up. Any links on the net to a similar crab? Thanks again  <your crab truly is a sponge/spongy decorator/spider type crab. Look to Paul Humann's "Reef Creature" book and you will see your critter. Best regards, Anthony>
Re: Odd Crab ID 1/8/04 Anthony, Thanks again. <<always welcome my friend>> <you are looking in the wrong place/ocean here my friend. Your crab did not come from the Med or coast of Italy... unless you can confirm that he is as hairy as I am and likes nearly as much garlic on his food <G>. I'll have to try that.  Lasagna and spaghetti with garlic bread probably won't look very good in a salt water tank though.....  :) <<true... but the skimmate in the skimmer will be remarkable>> <your crab truly is a sponge/spongy decorator/spider type crab. Look to Paul Humann's "Reef Creature" book and you will see your critter.> Thanks for the tip and advice.  We'll look for that book!   <<The Humann series of books overall is amazing and well worth it. DO look at them all>> It's amazing. I've studied computer science, space science, earth science, mathematics and such, but the earth is so covered in ocean with such diverse life, that humans don't spend more time studying it! <<so true... the density of life in a square inch is simply staggering. In shared admiration of the sea, Anthony>

Decorator arrow crab- Hello I have an interested in getting a Decorator Arrow Crab <Hmmm, I'll assume Camposcia retusa?>, however I have heard they can be troublesome to other animals. <Mainly with sessile inverts that easily become body ornaments.> I have the following in my fish only tanks. 1 Blue Moon Angel 1 Yellow Tang 1 Starcki damsel 4 young Clownfish 2 Emerald crabs 4 Urchins 2 Serpent Stars 1 Orange Starfish about 15 Small Hermits About 20 snails 2 Blood Red Shrimp My tank is a 210 Gallon with 180 lbs of rock. Do you see any problem adding this Crab? <These guys are opportunistic carnivores, but shouldn't seek out and kill fellow tankmates. If what you are referring to is Stenorhynchus seticornis, then there is an added threat to tube worms and it can pick on just about anything. This one is the true arrow crab, but not a decorator. I hope this helps! -Kevin> Thank you for your time. Kurt

Re: Decorator crab Would you also approve my tolerance of a small decorator crab?  True he tears up some polyps and zoos from time to time, but I think that's good for the tank since the polyps and zoos end up getting seeded in other spots, plus the crab is kind of interesting. <You have my endorsement here. Perhaps you will help our species in self-governance one day... and soon I hope. Bob Fenner>

Strange Hat Hello Crew, <Howdy Paul> I hope the picture comes through clear enough.  I adjusted the contrast and brightness a bit on the image, didn't come out that great.  It was night time, so taking a picture in the dark is a bit tough.  Anyways, on this rock that has a few zoo polyps ( dark spots ), there is a crab.  My question: is that a sponge on his head? <Actually, more on this back (carapace)> Also, interesting worm in the background a well, maybe a peanut worm? <Looks like it to me as well. Bob Fenner>
Thanks, Paul

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 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>

Become a Sponsor Features:
Daily FAQs FW Daily FAQs SW Pix of the Day FW Pix of the Day New On WWM
Helpful Links Hobbyist Forum Calendars Admin Index Cover Images
Featured Sponsors: