Sea Urchin

[VengefulSakhmet]

Has anyone ever heard of a sea urchin killing hermit crabs and snails? A week ago I purchased a pretty little white sea urchin and I've noticed a couple of dead hermit crabs in my tank as of late. I had done my research and talked to the guy at the LFS and both resources claimed he'd only eat algae, but I'm a little concerned. Everyone had seemed to be happily coexisting when recently I noticed a dead hermit crab carcas and the sea urchin seemed to have a new seashell hat. Is this just a coincidence and my new urchin is grabby?

 

[Blown 346]

They can kill snails, crabs and fish that are unsuspecting.

 

[VengefulSakhmet]

terrific...I have a slow killer in my tank...at least he'll be easy to grab

 

[bertoni]

I can't imagine how a small sea urchin could catch a hermit crab. What type of urchin is it? Can you post a picture?

 

[ACBlinky]

My guess is you're seeing molts, and the shells he's carrying around are some of the extras you no doubt threw in for the hermits to grow into. My pincushion urchin carries around 3-4 shells at a time and doesn't bother any of the snails and hermits (some are very small, some large) in his tank.

 

[VengefulSakhmet]

definetly not molts...I've seen my cleaner shrimp do that. The sea urchin had a new shell and there was a dead hermit crab. He moves terribly fast for a sea urchin. He cruises up and down my coral in a minute. He looks a lot like this:

Pseudoboletia indiana

<img src="http://www.coralreefnetwork.com/stender/marine/echinoderms/urchins/indiana.jpg">

It apparently is the pebble collecting urchin, but his new collection of shells bothers me.

 

[bertoni]

Urchins often collect items like that. My tuxedo urchin did that regularly. It's not a sign of predation. I don't see how an urchin like that could capture a hermit crab. Their diet tends towards algae and sessile invertebrates.

 

[Blown 346]

I have seen them eat fish, starfish etc. I cant say if it truly did this but since I have seen it, I cant say it wont.

 

[roader247]

I've had one very much like that one mine is a little more purple though, he will pick up shells and other thing and tote them around but has not ever got any hermits I've had him about 3 years.

 

[Alaskan Reefer]

My diadema (black longspine urchin) is about the size of a large canteloupe, and in 4 years of having him I've never seen him eat anything except coraline, hair algae, and zoanthids.

 

[VengefulSakhmet]

Well, I found out the truth. There were a few snails and hermits that had shells that I particularly remember being alive disappear and today I witnessed him capture and eat a whole turbo snail. Yeah, we took a nice little trip to the LFS and I traded him in to replace a few of my critters. I'm happy to be free of the little devil, but I think he took out a couple of my firefish. I noticed him hanging around their sleeping chambers lately and 2 are MIA while the remaining two ( a coupled pair ) seem to be wary of going back in. I have a glass cover, so jumping was not an option and after seeing him take out and eat the turbo in a 1/2 hr I have no doubt he could eat a sleeping fish. Never again will I buy an urchin.

 

[ACBlinky]

There's another thread floating around (maybe in the invert forum) about this. There ARE urchins that will eat meaty items, apparantly some can even sneak up on sleeping fish, but they're not nearly as common as the algae-eating varieties. Mine is a 'pincushion' (Lytechinus vaniegatus) and, other than rearranging the rockwork occasionally, he seems harmless. Sorry yours ended up being a predator, that's lousy. Don't let that sour you on urchins though, they really are fun pets.