Something is eating my brittle stars

Information on the tank and water quality:

FOWLR, 60 gallons, 48x13x24. About 80 pounds of live rock. 50 pounds fiji, the rest originally dry base rock, still becoming live currently.

While I don't believe my parameters are an issue, I will include them for the sake of providing complete information. My water parameters are currently:

Temperature: 78.6
Specific Gravity:[/U/ 1.023
Ammonia: 0
Nitrite: 0
Ph: 8.0
Nitrate: 15 (Has been holding steady there for the last few days, down from 20 at its highest, including during the cycle)
Phosphate: 0 <- I'd said .25, but that was as of my last test, currently they are at 0
Carbonate Hardness: 300

Stocklist (I added the cleanup crew first at the advice of a couple of books):

-15 dwarf crabs, some red legged, some blue
-20 assorted snails (Cerith and Nassarius snails)
-1 Peppermint Shrimp
-2 Serpent Brittle Sea Stars (I had 3, but one was already eaten yesterday)
-2 very small clownfish
-1 very small flame angel (the most recent addition)

The total "fish length" in the tank is about 2.5 inches. I was planning on keeping it there for a while. I only have 2 or 3 more small semi-aggressive fish I planned on adding for the whole tank, and was just going to let them grow for a while and let the tank mature before considering adding anything else. The Serpent Sea Stars have only been peaceful and hiding since they showed up.

The clownfish eat voraciously, and the flame angel has only recently realized that feeding time happens - but now that he does, he comes out from wherever he's hiding and jumps out at the food. All I had seen him do until a day or two ago is forage for algae off the live rock. The peppermint shrimp is the only invertebrate that really takes part/takes interest in feeding time.

The Problem:

Yesterday morning I woke up to one of my brittle stars completely mangled and almost dead. Today I just checked the tank and one of the brittle stars had left his home under a rock and had two of his arms bitten off halfway. I put a rock over him (not crushing him) so he could have a little protection as he is still alive, and then came on here.

This only seems to happen at night time. I have the fish and inverts line up and do a head count every morning and every night. So, who do you think the culprit is? The crabs? The flame angel? I even suspected the peppermint shrimp as I've seen him pull snails up off the sand and try to eat either the algae inside them or possibly eat them, though I've never seen him actually pull flesh out. I really don't think it's the clownfish. I almost can't imagine it's a one-fish/crab job because of how much was eaten in one sitting. The only aggression I've seen is between the hermits, and it mainly seems to be them fighting over who gets the shells I put in the tank for them to move into. They apparently really care about showing off, because I got some rather nice ones from a friend in Hawaii.

If it is the flame angelfish, does this mean that he's acquired the taste for invertebrates, and he will never be safe in the tank again, and needs to be gotten rid of? Agh. I just want to know so I can stop worrying and create a plan of action. If it was the angelfish, he would have had to wriggle sideways under the rock to get at him, I'd think.

 

If starfish are really stressed or have been through some pretty extreme water, temp or oxygen changes they will or can I should say drop all their arms and possibly die.
This happens alot after acclimation.

 

Well, one of them not only dropped arms, but appeared completely mangled. Is it possible that one of them dropped arms, then got mangled afterwards by an opportunistic fish/crab?

They have been fine for about a week or two? Is it possible that this is only now happening?

 

I had mine drop arms after about 3 weeks your tank is too small to sustain 2 stars long term.

Have they been climbing the glass? this usually means that they are starving. You can try to place some food underneath it, but they almost never come back after this sorry :-( LFS should stop selling them

 

jdameli1, no, they have been situated fine underneath rocks and haven't really moved at all. They've seemed happy up until this point. I think there's been plenty for them to eat.

Just out of curiosity, why was this moved from the ASAP forums? One brittle star was found dead yesterday, my 2nd brittle star was found with some tentacles missing today, and the third one is vulnerable to the same problem at any time now. This seems to me to be an emergency problem, not something I simply want a fast answer to, as the rules state. Also, I see other threads where someone's animal (including sea stars) is simply possibly ill and those threads weren't moved; surely trying to avoid a death of something warrants someone wanting a faster response? I've been up all night watching my tank and I've been very worried.

I'm not trying to be rude here, and I'm sorry if I come across that way, I just want to know what sort of situation it is appropriate to post in the ASAP section, then? Surely if imminent death of an animal isn't an emergency, then what exactly is?

 

If this is happening at night I would look for a predator like a mantis or possibly a crab.

 

Well, I haven't heard any of those clicking sounds that I hear mantis shrimp make, but I could very definitely suspect a crab. The only violence I have witnessed in my tank is crab-on-crab violence over shells, as I said, so I wouldn't be surprised if one or two of them were the culprits.

I guess this is a learning experience, but I really would prefer it if nobody had to die!

Thanks, both of you.