Starfish - Friend or Foe

[PapaFishRocks]

This little dude hitched a ride on my latest Zoa frag purchase. Little guy is only 1/4”

Keep or banish?

 

[Slocke]

This little dude hitched a ride on my latest Zoa frag purchase. Little guy is only 1/4”

Keep or banish?

Asterina starfish. Usually good eating mostly detritus and algae but can sometimes go for corals and/or overwhelm a tank.

 

[ISpeakForTheSeas]

Depends on your preference-some people view them as too risky, while others view them as good CUC:

Personally, I like them, but they do tend to reproduce very quickly.

I've heard some species eat corals and others don't - I've seen convincing evidence for one species (a very darkly colored one), and one piece of somewhat convincing evidence for one different species, but the vast majority of these guys seem to be at least mostly safe.

With regards to whether or not the average "Asterina" (technically Aquilonastra - Asterina is a separate genus within the Asterinidae family) eat corals, it might be a species specific thing, it might be a you have way too many starfish so they're out of other food options thing, it might be they're eating the slime coat/mucus on the coral rather than the coral itself (see below), or they might just opportunistically eat unhealthy corals. Based on how starfish eat, it seems plausible to me that it may also be coincidental (i.e. the star goes to eat something off the coral and the coral just happens to be one that is able to be negatively effected by the star's everted stomach). Regardless, Zoas are just about the only coral I've heard about regular "Asterina" stars potentially going after with any sort of frequency.

A quote I like to refer to for this:

It's an Aquilonastra spp. starfish and is a great scavenger. I see them with anywhere from 4 to 12 legs. 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.

 

[Slocke]

Depends on your preference-some people view them as too risky, while others view them as good CUC:

I always forget the true name.

For me they were great until one day I think I had too many for my algae. They then needed a new food source and they turned on the corals.

 

[exnisstech]

These little guys alway end up in my tanks somehow. They haven't really bothered anything but get annoying once they move to the front glass. At that point I start removing them by scraping them off with a net. As far as part of a cuc they don't do anything but leave small trails on the glass in my tanks. I think it would take thousands to do anything.
I have heard of certain ones eating zoas but have no first hand experience of that.