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Coral Eating Starfish

By Various Authors. Posted to reef-l emailing list, Friday the 23rd to Sunday the 25th of March 2001.

Scott Crumpton

This is an observation -- not fact.

One of my Organ Pipe colonies ( Tubipora musica ?) has been losing polyps over the last six months to the point where it only has about three left. I haven't been home much during this time and was wondering what was going on.

The other night I noticed two starfish completing wrapped around and covering the polyps. The starfish are those white/gray/tan speckled little buggers with only a couple of about eight legs. They are probably a cm across.

I remember GARF saying something about this but I considered the source. Most of the time these things are all over the place, on the rocks, sand, snail shells, glass. But this time they were on the polyps which are completely healthy until they disappear.

What are the chances they are the culprit? Educated answers only -- we've seen enough guesses on these types of subjects.

Kevin McDonald

Sorry to hear about your polyps, but I can't say I've ever seen that before. Since you mention GARF, I'm guessing you're talking about the brittle stars they sell. I have many of these kind in my tank - High Res. close-up photo's of IA's stars.

In fact I just got some more from Inland Aquatics last week. I've had these stars in my systems for 3 years now. Never seen them eat anything they weren't supposed to (detrious or food). I've purchsed stars similar to these from GARF as well, and never had a problem. I don't know the exact name/species, but I'm sure Morgan Lidster or one of the other folks at Inland would help you with some information about them.

Keith Langdon

GARF must have a far different species that looks just like mine. I have had these in my tanks for the last 6yrs and never see them eat a thing besides the algae. I literally have a thousand of the things in my tank. You mostly see them in the morning covering everything except living animals. When the lights come on they are only a few here and there. They multiply by dropping off a couple arms and regrowing. Sold a dozen of them at auction for $6.00 yesterday! ;)

Rob Toonen

One of my Organ Pipe colonies (Tubipora musica?) has been losing polyps ... The other night I noticed two starfish completing wrapped around and covering the polyps. ... probably a cm across. I remember GARF saying something about this... What are the chances they are the culprit? Educated answers only -- we've seen enough guesses on these types of subjects.

Scott, you will probably not find any "educated answers" (or at least consensus) on these stars, and part of the reason for a lack of agreement is that there are almost certain to be several species of similar small stars that are impossible to tell apart in practice. There are a variety of tiny sea stars in the genus Asterina that all look more-or-less the same but in practice they may have very different habits in aquaria. In fact, depending on the source, several named species of these tiny asexual sea stars may or may not be valid or all belong to one variable species. Even experts on sea star biology do not agree on how many species there are or whether variation in prey habitats seen among these animals is a result of variable behavior, environmental triggers or species preferences.

The sea stars listed on the GARF site ( ) are really quite huge in comparison to most that I have seen in aquaria (and that you describe here). Species like Asterina cepheus , A.burtoni and A. gibbosa can all be pretty variable in color, shape and size depending on how much asexual reproduction they undergo, but for the most part, all of them are thought to be opportunistic predators and scavengers. I would say that, like some large errant polychaetes, the likelihood of them causing a problem (such as eating a coral) is likely to be a direct consequence of their size and level of hunger -- a starving animal is less picky about their diet than one that is reasonable well-fed. Of course, there is always the possibility that these stars are also attracted to the scent of decay, and your experience with this coral is not uncommon for people without these stars in their tanks as well -- these stars use chemical stimuli to track food, and will be much better at determining when a polyp is failing than you are. My guess is that as soon as a polyp starts to fail the stars in the area immediately respond by coming over to feed on it, but that's moving into the "enough guesses" zone again ;)

My original guess for an ID on these stars based on the picture was A. gibbosa , which can easily get more than 2 inches in diameter. Being a very hardy and common sea star that is an efficient opportunistic predator and gets reasonably large, it's likely that this star could do some real damage if it became abundant in a reef tank. The sea star pictured by GARF has subsequently been ID'ed with the help of Gerald Heslinga ( ) as Asterina anomala , but I am not familiar with this name, and cannot find any references to this species in the scientific literature, so I am unsure what relationship (if any) it shares with A. gibbosa .

A. cepheus tend to stay less than 2" but is still a relatively large sea star that preys on sessile marine invertebrates (corals among them) and there is a smaller morph (perhaps a separate species, but that is still a topic of debate) that typically has six arms rather than 5 when fully mature, and tends to remain less than 1 cm or so (about 1/4") in diameter. This smaller morph/species is my best guess at the ID of the mystery stars in our tanks so far, and seems to be relatively harmless in the majority of tanks, but that doesn't mean they don't have the potential to cause problems given the right conditions. The irregularly shaped animals result from asexual reproduction by fission (the stars arms crawl off in different directions and pull the body in half - the body then regenerates the missing portion of the body resulting in the star being asymmetrical), and these stars can rapidly reproduce given suitable conditions and enough food.

I know plenty of people that have had these stars in their tanks without problem for many years. The reports on the GARF website regarding the taste of their sea stars for certain SPS are pretty dire, however, so it's worthwhile keeping an eye on them to make sure that you don't have a problem with them. Again, although these stars are opportunistic carnivores, my guess is that problems with them in the tank are a result of size, population density, and feeding regime of the tank in question. I would say that in general, people who have relatively few of these stars, or have only the stars of the small variety (never get more than 1/2"), almost always report "they don't seem to cause any visible problems in my tank..."

If you find that they grow larger than 1/4 to 1/2" or you are convinced that these stars are the source the problem with your Tubipora (as opposed to cleaning up a slowly failing colony), though, there have been successful reports of using the Harlequin Shrimp to remove these cryptic stars (e.g., also on the GARF site ). If you're really set on removing these sea stars from your tank, that is probably the best way to go, because these stars are primarily nocturnal and so cryptic that you're almost guaranteed to miss some in any manual removal attempt. The Harlequin Shrimp will do a much better job than you will in finding all the sea stars in your tank if you're determined to remove them, but when sea stars become scarce in your tank, you'll need to start buying small sea stars to feed the shrimp, because I have never heard of one being kept alive for any length of time without sea stars on which to feed....

Created by liquid
Last modified 2006-11-24 18:40