Those little echinoderms, what do they eat?

[Gig 'em @ NDstructible]

I'm hoping to start a good conversation on starfish in our reef tanks and their roles and impacts they have on our systems. Many people have encountered asterina starfish as hitchhikers and have been annoyed by there unsightly appearance. Some people have reported that the stars were predatory and preyed on their corals, while most people just don't know what the heck they eat. Linkia starfish also puzzle me as to what they eat. I'm sure they can be opportunistic feeders, but what do they eat when they're cruising around the tank?

Who here has experienced these little guys in your tank, and do you have any stories or observations of their impact on your tank ecosystem? Do they leave corals alone? Do you notice your tank has less algae with them? No affect on algae?

I have a Brute of about 200 pounds of live rock that I'm QTing right now and it has two species of asterina, one species is small and greenish color and they stay on top of the highest rocks, the other is the large tan variety. The larger asterina species like to hang out on the sides of the Brute trash can and lately the water has formed a biofilm on the surface and they have moved up to the surface and flipped over to basically float upside on the surface of the water. I am currently hypothesizing that these little guys graze on blooming biofilms, which explains why they are attracted to a fresh surface where bacteria are quickly colonizing and the surface of the water that has a high density population of bacteria. If this is true, then would these guys be beneficial for a tank by keeping biofilms and bacterial populations in check? I assume the smaller green asterinas get their color from grazing on algae, and there has been NO algae outbreaks in the Brute yet. So are these little guys great at keeping algae under control? If this is true, then I would think that these little guys, who most consider a nuisance, may prove to be much more beneficial to the overall bio-stability of our tanks than we give them credit for.

Thoughts? Ideas? Criticisms?

[FarmerTy]

I've had plenty of the tan varieties of asterinas in my tanks over the years. None I would consider predatory by any means and I've never had them "attack" a coral that wasn't sick and dying already. Not saying there might not be predatory ones out there but my opinion is most that get blamed for eating coral are just doing their job of cleaning up.

I've never had the green one's you speak of but I'm sure they are similar in role.

I've usually observed my starfish grazing on the rocks and glass walls and the presumptive conclusion in the reefing community is they are munching on biofilms.

I would guess the same for my blue and red linkia starfish. I can't even remember how long ago (6+ months) I bought them but the blue one is surprisingly spry and healthy looking still and the red one seems to be suffering a bit. I bought both as an experiment to see if my tank would even support them as I know they have dismal survival rates in captivity.

[Neon Reefer]

I "had" 2 types of Asterina starfish in my tank. One was the tan type and was harmless. The other was a grey species which ate my Acros. They seemed to love the plating Acros the best and ate one to pieces. That was until I got a Harlequin shrimp. Of course he dined on both types and now there are none.

[Gig 'em @ NDstructible]

I'm sure, like most animals, there are multiple species that look very similar and have evolved to have different diets. I'm sure there are some out there that are predatory, but I bet most are grazers and eat microbes and detritus.