They like to eat the zoas that are recovering in my systems. The ones that arent the healthiest but still have a fighting chance. I have multiple photos of them wrapped around the tips of the polyps and the specific polyp their on always melts away after removing the starfish or the starfish eat a few polyps overnight.Asternia starfish. Harmless detritus and diatom grazer. A myth floats around that they eat zoas, but I've never seen this actually documented, or in my own aquarium.
If some do, it would be because the tank is too clean, but, again.... never seen this documented or in real experience.
Looks like you have a mushroom problem.No. It's an Aquilonastra spp. starfish and is a great scavenger. The whole discusion around them seems to me excellent examples of misidentification, mistaken behaviour and assumed causality based just on heresay without looking at the research. Asterina spp starfish are preditary but only reproduce sexually and are shortlived so while it's possible some might get into a tank even if it did happen it's not going to be around long. Aquilonastra are one of the uncommon species that reproduce fissiparous or by splitting so are easy to identify by the different sized legs regrown after splitting. They perform an important function not only feeding off algae films but also feeding off microbial films including those on corals (at least ones that don't sting). FYI the mucus coating on corals ages and corals have to periodicely shed it to renew it and maintian healthy microbial processes (Ref 1, Ref 2). If Aquilonastra are feeding on zoas or softies I'll argue they are either benign or even beneficial as they may be reducing the unhealthy older mucus which can be full of unhealthy microbes which the animal is trying to get rid of and are far more likely to be the actual problem.
Here's an example, this Toadstool is doing one of it's periodic sheddings. The Aquilonastra have been in this system for years but only climb onto the Toadstool when it's shedding. In the first picture you can see the old mucus film, Aquilonastra starfish and areas they have cleaned off. The second picture shows the Toadstool a week later.
People are just trying to be helpful.