Last night I found this guy dead in my refugium: youtube . com/watch?v=kg_xncL61as&feature=g-upl (sorry apparently my message can't contain URLs until I have 5 posts)
Here's the story:
From April 6-10 I was on vacation in Florida. I left the tank alone without supervision which I didn't suspect would be a problem given that I almost never feed my tank any way. The tank is a 55 that's been up for a year, bought the whole thing used so it was very mature from day one. For about 9 months I've only had one fish, a female mandarin who remains fat and happy to this day just eating what the tank provides. The only thing I feed is a pair of skunk cleaner shrimp, maybe every 3 days I stick my hand in with some dried squid I get from Chinatown. That's enough to keep them continually pregnant.
So I get back from vacation and everything seems normal, except my urchin is sitting in the sand and he seems to have dropped some spikes around him. I pick him up to inspect and I notice that he doesn't have the little black tentacle feet that he used to have all around his mouth. I put him back on the coraline covered rock and leave him for the night. In the next day or two, I decide he's still not looking well, so I stick him in the refugium. There isn't any coralline down there for him to munch on, but there is some cheato and some other fuzzy red algae that perhaps he might enjoy eating. After 10 days or so, he's still alive and I don't see anymore dropped spikes, but he didn't seem to be moving much or sitting in a place with food. I put him back in the display for a few days, no better no worse. I put him back in the refigium, and he's dead in 2 days.
I don't think it was a water quality issue as I didn't feed the tank and I have another urchin that's doing fine. No other problems... I think that perhaps the shrimp got extra hungry and started munching on his tentacles. I also feel like when I came home the shrimp were acting funny towards him. Is this something anyone else has observed?? Do shrimp ever bother urchins?
The only thing I can attribute it to is that it didn't have enough food and it was an on going process, not just during the time you were away on vacation. Do you have much algae in your main tank or feed algae food to your urchin in the past? How long have you had the urchin?
As for the shrimp, I have not heard any type of feedback regarding shrimp preying on urchins as that is probably a mute point. I have never witnessed a shrimp killing an urchin in the many years I have been in the hobby or being employed at Puppy Center and Aquarium. With a sustainable food source, you shouldn't have had any problem especially since you don't have any Triggers, Holocanthus or Pomacanthus Angels or puffers that would eat them.
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