I have had 3-4, maybe even 5 different species of these (and they are not in the Asterina genus, they are in Aquilonastra), and none have ever eaten any corals. I’ve seen a lot of people claim that they eat corals, but I’ve never seen actual proof, it seems to me that if it was such a common thing, it would be easy to prove. They won’t get out of control so long as you don’t over feed and keep nutrients in check (having lots of algae and an inadequate CuC will lead to more of them, but population will stay low if there isn’t an abundance of food). Also, this is not a mutation or disfigured star fish, they reproduce by growing new arms and then fragmenting themselves, they split sort of similar to anemones and corals (though they are echinoderms not cnidarians, but same concept). Personally I like them, but I like most harmless hitchhikers, all of the microfauna from good live rock is half of what makes reef tanks interesting. If you want to get rid of them, go for it, it’s your tank, but IMO they are harmless if beneficial (they can get into places to eat algae that a lot of other members of your CuC can’t get to). Also, even if you have a massive population, harlequin shrimp will go through them quickly (they eat the tube feet of star fish, not the whole thing) and then slowly starve to death. There is nothing sadder than watching a usually active animal become completely sedentary because it’s trying to conserve energy because it’s starving. Their population would be much better controlled by limiting nutrients, not feeding too much, and having a robust CuC.
en.m.wikipedia.org
