FAQs about Sea Urchins, Sand Dollar Feeding Related Articles: Sea Urchins,  Related FAQs: Urchins 1,  Urchins 2,  Urchins 3, Urchin Identification, Urchin Behavior, Urchin Compatibility, Urchin Selection, Urchin System, Urchin Disease, Urchin Reproduction,  Eucidaris thouarsii (Valenciennes 1846), Slate Pencil Urchin. Family Cidaridae. Galapagos pic.

Urchin eating Chaeto  2/16/10
I have had an urchin in my refugium for quite some time. It never occurred to me that the urchin may be the reason my Chaeto isn't showing the rapid growth that I've experienced with Chaeto in the past. Are urchins known to eat Chaeto? Love the site. Thanks!
<Mmm, yep. Bob Fenner>

Flesh Eating Urchin, Urchin Snack? 1/15/09 Hi Guys, <and gals> Good morning! <Hi Ginger> I searched WWM and couldn't find an answer to my question, so here goes. We have a 45 gallon tank, water levels normal. <Parameters normal?> We have live rock and a few fishy friends including crabs, a blenny, a goby, 2 clowns, a butterfly fish and an urchin. Last night we (including my ultra shocked 7 and 9 year old children) watched our butterfly fish swim right into our sea urchin, which we believe is a Diadema savignyi (Long Spined Sea Urchin). Of course, as you'd imagine, it was quite dramatic to watch what appeared to be blood spread where it had been poked and watched the butterfly fish swim around sideways and lay down at the bottom of the tank sporadically, as it (and we) awaited its death. Understandably, the children were very upset, and we used it as an opportunity to discuss ecosystems and how they work. After they went to bed, I waited for it to die so that I could remove it before the morning came, but it didn't. It actually had a few moments of normal swimming, and while I knew it probably wouldn't have survived until morning, I didn't feel right taking it out while it was still alive. I'll never forget the first thing I heard this morning when I woke up; desperate voices cried, "Mom, wake up! The urchin is EATING TAD! HE'S EATING IT! SAVE HIM!" I dragged myself downstairs to see, and sure enough, the urchin was on top of the now deceased fish and looked quite happy. Another ecosystem chat ensued, but fell upon deaf ears. My question is, should I allow nature to take its course, or should I remove our deceased friend to prevent the water levels from taking a turn for the worst? <I would remove the fish.> And by the way, I thought these urchins were herbivores? <They will eat meat if given the opportunity. The spines of this urchin are venomous so it did not surprise me that the fish died and do be careful when maintaining the tank, you will not like getting poked with their spines.> Thanks for the help; it's appreciated. <You're welcome. James (Salty Dog)> Ginger

Urchin Hitchhiker: Pencil Urchin - 1/31/08 Hello Crew! <Hi Andy!> About 4 weeks ago, I purchased a large piece of cured Fiji rock to round out my LR aquascape. It is a neat piece, with a big, winding hole running the length of the piece. Even though my LFS claims that the water in the LR tanks are not mixed with other water, I have seen fish in the tanks from time to time, so I placed the LR in my 30 gallon QT for 2 weeks just to be on the safe side. During QT, I can't say that I stared at the LR much other than when checking water parameters, etc. After the QT period, I placed the LR in my tank. About 2 days later, I was shining a flashlight into my tank to check out the nighttime goings on. When I shined the light in the hole of the new piece of LR, I noticed an urchin that is about 2" in diameter (body) (thankfully, the lack of acclimation--twice--didn't kill it!). From browsing WWM, I can confidently tell you that it's some type of pencil urchin, either a Eucidaris tribuloides or a Heterocentrotus mamillatus (my guess, since the LR is pacific, but it has characteristics of the former). <Okay> It is very elusive, so I haven't been able to get a picture of it (or even a good look at it). In fact, for about a week (and apparently, the entire time it was in QT) it didn't move from the cave. Since then, it has made an appearance outside the cave, but only briefly and then on the underside of this same piece of LR. It has now moved back into the cave (who knows where it goes at night). <It goes out to eat! These urchins are nocturnal foragers that, once they've found a nice little protected spot, tend to use it as their "home base". They wedge themselves into place during the day with the help of their thick spines.> My research leads me to believe that it likely poses little risk to its other tank mates--a Sailfin tang, a Gold Stripe Maroon Clown, a Brown Combtooth Blenny, a Royal Gramma, a Copperband Butterfly, 2 cleaner shrimps, 15 or so mushrooms, some type of tree coral (I keep meaning to send in a pic for an ID), a Lemnalia tree coral, two small colonies of pulsing Xenia, and a Trachyphyllia geoffroyi. My tank is 110 gallons, with about 90 lbs of LR, under-the-cabinet trickle filter (in which I run activated carbon that I change out every 2 weeks), a 30 gallon fuge (LR, a huge tuft of Chaeto, and 5" DSB (with about 1 billion bristle/fire worms) on a reverse daylight cycle), and a Coral Life Super Skimmer. My water parameters are: ammonia, nitrite, nitrate and phosphate all 0, temp 80*F, Alk is 3.5 meq/L, pH is 8.3, calcium is 400, and spg is 1.026 (I have a Salifert I2 test kit and a SeaChem iodine test kit, both of which show no appreciable levels, even after dosing with Kent Iodine over a period of days--I've since stopped adding Iodine until I can figure this out). <Good thinking. Please read over the FAQ's here at WWM, starting here: http://www.wetwebmedia.com/iodfaqs.htm > I use RO/DI water (mixed/circulated days in advance of water changes). <Excellent> I dose, as needed, with ESV B-Ionic 2-part buffer. Probably more than you need to know, but . . . <Hey, it's better to have too much information in these queries than too little!> So, to my questions . . . I'm a little worried about this guy starving, because he doesn't seem to move around much and there's not much on the new piece of LR to feast on. <Hmmmm, well he's undoubtedly moving about at night to feed. That's typical for these urchins. What we don't know is which species it is. Some are mostly herbivorous, while others dine on corals, sponges, tunicates, bryozoans, snails, etc. Some even employ those spines to trap/kill fish, shrimp, and other organisms.> I have tons of coralline algae (too much), but the urchin doesn't seem interested in finding it. An attempt to plant Nori would meet with immediate failure, as the Sailfin Tang and Blenny would make quick work of it. <Well, the good news is that these fish aren't nocturnal. I'd rubberband some Nori, or a seaweed sheet, to a rock and place it near the cave after the lights go out.> I have shrimp pellets that I use to feed my fuge--should I try dropping some of those in the display at night? <You could certainly give this, or a bit of clam/squid/etc a try. It's going to be tough though, to keep the shrimp and/or any other nighttime critters from running off with it. To get around this, try to put the food as close to the urchin as you can, and give the shrimp their own little bits to distract them. Is it normal for these urchins to remain fairly stationary? <During the day, yes, very normal.> I would think not. Also, am I correct that the urchin poses little risk to my sessile inverts? <Again, depends on the species/individual. These urchins are generally not considered reef safe. Not only because they can be predatory, but because they tend to bump into things with resulting damage to corals and sometimes your carefully arranged aquascape! For more information/photos on this family of urchins, please see these WWM links: http://www.wetwebmedia.com/urchinsii.htm http://www.wetwebmedia.com/urchinfdgfaqs.htm > Thanks for the help/info. Andy <You're very welcome, Andy. Take care. -Lynn

Purple Spined Sea Urchin... Arbacia punctulata   7/30/07 Hi Crew. <Hi Rick, Mich here.> I was walking the beach in Florida the other day on the Gulf of Mexico side and found a purple spined sea urchin. <Lucky you... the walking on the beach part... I seem to be good at finding urchins with my feet! Ouch!> I did a web search on them and they are, according to them Arbacia punctulata- purple spined sea urchin. <Is endemic to Florida, and generally live on rocky bottoms as opposed to sandy bottoms.> I was thinking about putting him in my FOWLR tank. Is he safe? <Mmm, I doubt that you will be able to provide suitable nutrition for him. These animals typically eat sessile invertebrates which he will likely consume your current tank population quite quickly. Gut content analyses have show bryozoans, hydroids, barnacles and tunicates and limited algae. The algae are typically only those growing on the rubble. but the diet is usually more heavily weighted with animal matter> I have a coral shrimp and a tang. goby and clown. Right now I have him in my QT tank. Would he benefit my tank? <I don't think the tank would benefit nor do I think it the urchin would benefit. I think it would be best to return him to where he was found.> I also found some large hermit crabs, about 2 1/2 inches and was wondering if these would be good substrate cleaners? <A big no go there! Usually any large hermit crabs are highly predatory, capable of killing fish and even well protected animals such as urchins.> Those I didn't bring home <Wise.> but the urchin was too pretty to pass up and they do sell them locally. <I do not have personal experience with this species, but from what I have read, I obviously have concerns, perhaps those in your local market may be able to guide you better, but with the information I found describing the typical diets of these urchins, I would be concerned about starvation. More here: http://www.int-res.com/articles/meps2005/295/m295p171.pdf > Thanks for all info past and present you guys are great and make my hobby so much easier. Rick <You're welcome and thank you for the kind words. Mich>

Urchin foods 7/15/05 What is the diet (what do they eat) of an Asthenosoma ijimai, Diadema   paucispinum, Asthenosoma Varium and a Astropyga radia <Please see Baensch Marine Atlas, Marine Invertebrates v.2. Bob Fenner>

Hungry Urchin? (11/21/04) Hi <Hello. Steve Allen with you tonight.> I've been reading your brilliant Marine section for months & wonder if you can help with an urgent problem. Our reef tank is about 6 months old. One of our early purchases was a lovely little black spiny sea urchin. He helped clean up the tank as it cycled & settled down. We have very little "nuisance" algae now & are beginning to wonder is "Spike" is hungry... <I'm not sure if they get "hungry" per se, but rather they eat anything the deem edible that is in their path. The pretty much eat all the time.> Two nights ago he ate our small but healthy pulsing xenia, last night he had a go at the Gorgonia. <Did you see it eat these or are you guessing?> We always have seaweed in the tank for him, the Mithrax crabs & the tangs (& most of the other fish who also seem to eat it) which he seems quite happy with in the day but obviously gets bored with at night. We have only recently started putting soft corals in the tank although have had green star polyps in the tank for about 4 months - he's shown no interest in that! We think we're going to have to take him back to the LFS unless you can suggest any other solution. Any advice welcome. <If the urchin is eating these desirable organisms, your only option is to take it back. There is no way to compel or persuade it not to.> Thanks, Mandy Thomas <Good luck.>

Lobophora (Brown Wafer Algae) Eating Urchins Trying not to bother you guys, but time to go to the experts. <MikeD here and not an expert, but a long time urchin aficionado> 75G FOWLR DAS H99 in-tank sump/skimmer Lights - 2x40W NO (today replaced 9 month old 50/50, and 11 month old full spectrum with Coralife 50/50 and 10000K)<It was time> NO2/NO3 0.0 pH 8.1 Believe I have the nutrients under control, using RO/DI and have a good size patch of Halimeda that I crop.<Sounds good> Lobophora is taking over my tank. After agonizing over what urchin to get, settled on a Blue Tuxedo after seeing a monster size Long Spine. Well, after watching the Blue Tux eat coralline for a week and going out of it's way to not even touch the Lobophora, it's now decided to spite me by packing around pieces of it.<It's not spiting you, but rather, like many short-spined urchins, camouflaging itself to escape notice of fish predators, such as triggerfish.> Talked to the LFS and they are willing to exchange for a Diadema. Diadema questions: -how realistic a Diadema will eat Lobophora?<It depends on whether it is obtainable or growing on irregular surfaces that the urchin can't easily adhere to.  Flat, open surfaces will almost always be preferentially grazed due to the ease with which the tube feet can hang on.  Many will learn to go to the surface of the water to be hand fed, should you so desire.> -they're ~5" diameter now, how big, how fast?<This depends upon available food within reach, the type of food and the water chemistry.  Urchins were long used as "miner's canaries" to monitor water parameters before the advent of cheap, easy, reliable test kits, proceeding to shed their spines as water conditions deteriorate long before most fish show adverse reactions.> -how does a Long Spine's appetite for coralline compare to a Blue Tux?<Again, it depends upon what's easiest to reach, although if it helps any, the Long Spine's aren't usually camouflagers.> -can they be exposed to air (transferring to quarantine)? For short periods. The waste discharge hole (anus) in the top usually prevents trapped air bubbles.> -if the Long Spines a bust, how do I handle the Lobophora?< Pruning with tweezers and shears is what I usually resort to.  Foxfaces will usually remove ALL vegetation to an extent that makes most tangs look like carnivores.> Mark in snowy Edmonton, Alberta,<Brrrrrrrr>

Urchin Question (10/4/04) Hello! <Hi! Steve Allen with you tonight.> I have a question about a purple urchin. <Do you know the scientific name, purple is a rather common color among urchins.> I recently got him and he used to cruise all over the tank. Now I notice he keeps falling off the walls and he ends up upside down then I have a hard time getting him latched on again. <this is worrisome. They usually adhere firmly.> I have to prop him up but his spines keep him from being flush with the tank on the underside. Is he sick? I am thinking he's malnourished cause I don't feed him anything separate. I feed flake food and frozen krill and I also have some type of algae in the tank that floats around and is also starting to attach to a rock I have. <Do you have coralline? Urchins eat algae off of rocks.> Is this enough food? <Most urchins eat detritus and usually do not require supplemental feeding unless the tank is incredibly clean.> I read that you suggest that stuff from the oriental food place, is there anything else that I can buy in a regular store? <I'm a big fan of Sea Veggies for tangs and other herbivores. Spirulina wafers might work.> Thank you for your help. My urchin will be grateful!!! <Hope this helps. You can try these feeding options, but I'd also recommend checking all of your water parameters and making sure that you keep steady, ocean water chemistry. Echinoderms to best with pH and SG at normal seawater values and very stable.>

Long spined sea urchin... excellent algae grazers 2/11/04 I just bought a long spined sea urchin a couple of days ago.  I was told at the pet shop that they eat algae off the glass of the aquarium and fine particles in the sand.   <they were exactly correct> Now I have been reading on the internet that it was in the past common practice for divers to kill sea urchins because of the negative effect they have on the reefs.   <not exactly... urchins are direly needed for reef health (as evidenced by the struggles of the Caribbean and other reefs without them). The only reference I can think of is in reference to the stupid practice of fisheries (for kelp) killing them. But that was for $/commerce... not reef health> I have a small amount of live rock in my 75 gallon aquarium (about 15lbs) Would I be wasting my time getting anymore?   <few are needed. Stick with what you have likely> I have been getting live rock a little at a time when I see neat pieces.  My last question is, will starfish destroy a reef tank too? <depends on the starfish... brittle and serpent stars are safe... most others are not. Read more about them here on our website and in our new book "Reef Invertebrates" by Calfo and Fenner. Anthony>

Urchin saves the day - eating Dictyota 2/2/04 Hello again Anthony, I wanted to give you an update about our Dictyota problem. Our urchin is now eating it. :) <outstanding to hear. I do love those urchins> We could not be more happy to see the right upper half of the tank free from this plague. Slowly the little urchin is going to town on it. Mark took a picture of the urchin to the SeaBay meeting but he never got the chance to show it to you. <Awww... no worries. DO send it here if you like> We are now sure it must be a long spined urchin. I hope he keeps up eating the Dictyota. If it eats all of micro algae will it be happy to eat any coralline algae? We don't want it to starve. <hmmm... tough to say. If so, I don't think it will survive on it. Fortunately, they will scavenge food bits. Offer an algae based frozen food and likely it will be fine (2-3 times weekly) after the nuisance algae is gone> Sincerely, Clair & Mark Dawson <best regards, my friends. Anthony>

Question on pencil urchin Hello does my pencil urchin eat algae because I've heard that they will eat my coralline algae? is this true? Also does my decorator crab eat algae? Thanks you WWM Crew. < Your urchin does eat algae along with any thing he can forage.  There is a very good chance he will eat your coralline.  The crab is a omnivore and will eat a wide variety of foods. Cody>

Question on sea urchin diet Hi again, I was told by the LFS that a pencil urchin which i already bought only eats algae and sometimes coralline algae. <neither is true at all... although more urchins than not do eat microalgae nicely. The pencil urchin is too often sold for algae control and it starves instead in most aquaria... it has decided carnivorous inclinations. Eating thawed meaty foods and sinking pellets is much better for it> Today i woke up to enjoy my tank and too my horror my urchin was eating my starfish leg?! Is that normal hope he doesn't die seeing as the star fish was 19.99 and the pencil urchin was 6.99. <although I'm a bit "put off" by your valuation of creature's lives in relation to how much money you've spent on them, I can tell you that the urchin did not attack and kill your starfish... the urchin is merely a meaty scavenger. Your starfish aborted a leg or is dying for another reason altogether. If the starfish is new and/or has not been quarantined then you may have your answer already>> will the urchin do this to my mushrooms and polyps? <not likely... and please be sure to research these animals needs in advance of a purchase. Merely taking the word of a clerk that is trying to sell you something is not your best route as a consumer.> I hope not anyways tell me what you think so i can get rid of it. thanks JM <wow... please do browse the archives... and consider getting a good book or two to keep on hand. Mike Paletta "New Marine Aquarium" is a good start. Fenner's :Conscientious Marine Aquarist" will put you on an even better track. Borneman for corals ("Aquarium Corals"). Best regards, Anthony>

Re: question on sea urchin Thanks so he wont eat my soft coral i have lots of algae in my tank green hair that he eats as far as the starfish he's still alive and scavenging the bottom with a hub for one leg where can i buy Fenner's book? I've always wanted a book is it packed with reef info or only certain animals? thanks JM <many places to buy Bobs book... signed copies can be found here: http://www.disaquatics.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=DA&Product_Code=TCMAS best regards, Anthony>

Sea Urchin Hi I recently purchased a sea urchin for my tank which contains some corals, clown fish, snails, shrimps an hermit crabs. However I'm concerned as to its eating habits. I currently feed flake food and pellets. From what I can understand, they normally feed on algae and plankton of which I do not think there is enough. I can buy jars of Zooplankton - would this be suitable ? Thanks in advance. Ghufar Razaq >> Instead, get your hands on some "sheet algae" from an oriental food store (or that section of your Supermarket)... and place a part of this down near the edge/under the urchin... Most species are macro or micro-phagous herbivores... they eat small and large algae in the wild. Bob Fenner

Sea Urchin Hi Mr. Fenner, <Howdy> I have been researching this hobby for about 5 months now and just now getting started.. I purchased 20lbs. of live rock (from the Gulf) from my LFS and I have seen 2 sea urchins and was wondering how to remove them without harming them, but keep the nice flat rock they inhabit. <Place some foodstuffs you think they might be attracted to (like some sheet algae from the oriental food store/section tied to a stone in a strip (like with a rubber band) near them... and wait till they more off> Also on the same rock I want to remove 2 cone snails and a Limpet. Can you suggest a way to do this without harming the animal.. <The cones I would just move forward/backward by hand net... the Limpet... more difficult to extricate... gingerly with a knife that is sharp only on one side. Quickly slid, sharp side down under the foot...> Thanks for your advice, Chris Thompson <You're welcome. Bob Fenner. Who has removed many Archaeogastropoda like this... to eat them!>

Trouble with tribbles Anthony, First let me start by reporting the best reef conditions I have ever had. Thanks to you and yours, water is better, skimmer is functioning properly, rock and inverts are thriving, and the reef is reefier! (Did I just coin a word?) <sounds delicious!> You guys ought to wear capes!  <I used to wear one... but apparently it is unlawful to do so without wearing any other garment of clothing while standing in a park fountain> Yes, reefier. Has a nice ring to it. I'll be using that one again.) <just ducky! <winky>> I was scraping algae off the glass this morning for the first time in a couple of weeks, (snails are apparently getting lazy) and I noticed what looked like very tiny white bugs scampering around in the algae. Then I noticed that there were none left on any place I had scraped, and only collecting on spots I had missed. Upon closer examination, I could almost make out a tadpole (sperm) shape, they were white and definitely moving of there own free will.  <perhaps you've discovered the secret ingredient in some of the vital/snake oil reef supplements?> I stopped scraping to avoid possibly wiping out a colony of something cool. Any idea what they might be? <well... many desirable microorganisms...amphipods, copepods and the like. Do look up some of Shimek's or Moe's drawings/photos of such critters. Very desirable though I'm sure> Also, a couple of weeks ago, against my better judgment, I bought a really cool long spined urchin. I took the advice of a reef store that said........"Sure he'll eat your precious coralline algae, but upon doing so, they expel the spores thus repopulating/propagating the species." Is this BS?  <Hahahahahahhhahhahhahhahhahahhhahhah...........> <Ha... ha....he....hehe...he....hahahahahahahhahhahhahahhahhaahah> <woooo...hooooo...ha...hooo. Ahe...heheh. Ahem....> <Pat,...I do not believe that explanation by your LFS was entirely correct <tear>> I have noticed a whole lot of chewing going on. Can this little monster actually chew down my reef? or is the new coralline growth I'm starting to see (on the snails of all places) evidence of this. I hand picked all 75lbs ( and counting) of my rock for it's abundant coralline/calcareous growth and I'd hate to see it all devoured by this aquatic tribbles, as cool as he is. <in fact, I agree that the long-spine urchin is pretty cool. Yes they can eat some coralline algae...but  no, they do not shoot "Magic" coralline algae spores out of their bungholes....hahahahahahahah...heheheheh, wooohooooo. Oh, yeah! I got to get the name of that sales clerk and thank him for that one <smile>! Anyway... my take on the urchin/live rock deal is that I would recommend them for tanks that for whatever reason grow enough microalgae for them to graze. In such cases their presence serves the greater good. Else, they eat more coralline algae than most people can grow. If you see that exposed white carbonate material on the rock than pink, etc corallines sprouting...pull the urchin. Else, enjoy it>> Hey anyway, have 65 nice days in a row. If they ever come out with a small porous statue of you, I will surely sink it in the tank so as it seeds, my animals can all have someone to worship.  <I'm actually hoping they manufacture my likeness in one of those springy tassel dolls that you can mount on the dashboard of your car. But if you do submerge a statue of me in the tank, please cultivate some long hair algae on my head so that I look taller> As always, thank you. -Pat <with kind regards, Anthony>

Re: Something is Eating Coralline By far, the most awesome gods, you are right! I have a pincushion and a pencil urchin. That's what is eating the coralline. poor giant emerald crab, I caught him and threw him into another tank. I guess I could put him back now...urchins...ugh. <<while I appreciate the kind words, I can assure you, I am quite human and make many more mistakes than any god should. But where were we?? Urchins... yes... they are like self-propelled Brillo-pads.>> yes, I supplement calcium and drip Kalk at night and etc, etc. little coralline dots growing everywhere else. <<Ahh good, well we've now solved the mystery of the missing coralline so no worries about the calcium.>> which urchin to remove or both? <<Well, depends just how much of the coralline they are removing - if you can live with a little loss - recall this is food for them - then keep them. I'm sure you can find balance there somewhere.>> can I put him/them into a tank with a giant carpet and two clowns? <<sure.>> another subject...cuz gods can do more than one thing at a time. <<well, actually, I'm done with that previous thing so... sorry to disappoint, but... one thing at a time here ;-) >> how do the fish retain color. I buy clowns from ORA and they are BRILLIANT. then they gradually turn regular color. what do they feed them. <<A better question to ask would be, what do you feed them?>> I am truly blessed to have such bright and attentive gods to watch over me.\reneeRN <<Cheers, J -- >>

Supplementing Black Sea Urchin Diets Hello, <<Hello to you...>> Great site; as always. <<Thank you although I can't bask in the glory alone - this is the work of many people of which I am just the Garbage Scout Captain.>> I read up on your site concerning sea urchin diet.. (they eat anything apparently)? <<Not anything, but anything algae based... even coralline.>> I have reasonable green algae growth, and purple coralline is starting to grow as well.  What additional foods can I feed the urchin? <<Oh that is a difficult question because it's hard to clue them in - how does one ring the dinner bell for an urchin? You could leave things around but it's likely someone else more swift of foot and opportunistic will snag it. Best to just keep that algae growing, perhaps try to encourage other macro algae to grow in the tank.>> Do I put the food adjacent to it? <<You could try, but odds just as good that it would head in the other direction.>> Or under it or what? <<You see why this is not an easy question to answer... in your best interest not to disturb it so under it wouldn't work so well either. Best to just leave it to its own devices.>> I assume I would do this right before the lights go out? <<I don't think urchins care so much... my tuxedo urchin is busy 24/7.>> Thanks again Bob, you are the ANSWER MAN!! <<Wait! I'm not Bob... what does that make me?>>