Hi all --
I really think we need to stop using the name Asterina. As of a couple of years ago there were 26 genera in the family Asterinidae. I tried to identify some specimens & got hopelessly lost due to the complexity of the characters used to separate the genera (which could be saying more about my non-polychaete ID skills than anything else!). Anyway, they are very difficult to separate even at the generic level. The small, asexually reproducing species are spread among several genera so maybe it's best to just say "asterinid", which means a member of the family. Food preferences aren't know for most species. For those that have been studied, preferences vary from herbivore to predator to scavenger to grazer to sifter depending on the species and I bet they will switch foods if starving.
The only way to know for sure that a particular star is a coral predator is to put it in a container with a healthy coral and see what it does. Otherwise there are several different scenarios. The top two, already mentioned above, are: The coral is sick/damaged due to other reasons and the star is scavenging necrotic tissue OR the star - especially if there's a ton of them - may not have enough food so they're going for whatever is available.
Once upon a time I read through a couple years' worth of asterinid posts, trying to find some kind of clues as to which ones were peaceful reef citizens & which were predators. In general, the small white ones were sediment & micro-film grazers while the predators tended to be larger & more colorful. Not always, but generally. I found the GARF posts a little single minded as they seemed to say that all small, asterinids belonged to a single species & were predators which just isn't true.
But just to be on the safe side, Ryan, since your star is colored and you did find it on a coral, maybe you should start removing them. Donate them to someone who has harlequins to feed.
There was one very interesting post - can't remember who wrote it or where, sorry - about a possible correlation between asterinids & zoa-eating nudis. The poster never had nudis but did have lots of asterinids. At some point he decided to remove the stars. Once he did the nudis started showing up & devastating his zoas. There were no other changes in his tank that could explain it so he stopped removing the stars & the nudis disappeared again. One post doesn't prove a relationship but it would be really intriguing if other people noticed the same thing.
Look similar to what is in mine, but ID on these guys can be very tough. If you did a side by side comparison, then you are off to a good start. Hope there aren't too many more in there.
