Anyone ever heard of this?

[perfectdark]

Ok this past weekend I added a few new creatures to my tank one is (or shall I say was) a Pincushion Urchin (Mespilia globulus). Acclimation went fine 1-1/2 hours actually and he seemed ok for the first day. All of a sudden the second night I see it on the aquarium glass moving around making its way to the sand bed and accross to the other side of the tank. I diverted my attention for a while and came back about 2 hours later. Not really noticing anything out of the ordinary I started taking pictures of my tank. Then I noticed it, an Emerald green crab hanging on the urchin. I thought at first that he was just picking at his exoskelteton little things here and there. Then I noticed he'd been there a long time so, I tried to move him off. The little @#$%&* put up a fight , and a good one at that. I get him off and he actually tore apart the urchin using its claws to snip its (mantle I guess you would call it) away from its body and ate him.

I was to late to save him so I left it as it was and in a 1/2 hour the crab was inside the urchin having a meal.

I have a post here with pics and there is one that has a LG feather duster on it. If you look past the duster to the left you can see the urchin, and the reflection in the glass you can see the crab on it.
Is this common? :notsure:

 

[clay12340]

Crabs are opportunistic omnivores. If they are hungry or something looks tasty they will eat just about anything. They don't differentiate between nuisance algae and expensive tank resident.

 

[perfectdark]

Ok so I inquired a bit more about the litte "tude" of my Emerald Green Crab. I totally agree with what you said and dont doubt for a min he saw an opportunity and exploited it. My only concern is 1st was the Urchin sick to begin with? IMO unlikely, he was moving around with no apparent issues, on the glass trucking along. Although its possible It just didnt look unhealthy, all his little spines were out he was on the glass for a while and then started to move along the sand bed. Thats when the attack came. So, my second concern was the tenacity of the crab his reluctance to give up. I know crabs by nature are pretty bold and have an attitude but somthing about this one that struck me as odd. Most of the time when I put something in the tank, they hide under rocks and wait till im gone, big things make them nervous. This guy acted like he did not care what was pulling him off he was fighting for his meal, it was brutal. I was told that its possible that he could of been protein starved and from time to time its not a bad idea to throw a piece of meat in the tank for your crabs. Something like Raw Shrimp, fish or chopped clams all are ok, not a lot just a small piece every now and then.
Is that common to do? Do any of you feed your crabs with a solid meat of any kind. I know when I give my fish their food the crabs grab some here and there of the Formula 1 frozen.

 

[jake123]

I feed my crabs every 2-3 days some sinking shrimp pellets..
I have 12 hermits and 1 emerald.
I put in 4-6 pellets.
If you have not fed your inverts before, It's great to watch. They come running!!

 

[perfectdark]

Yea I did that last night for the first time. It was cool they came out form everywhere, and destroyed it in about 20 mins.

 

[blueram]

Originally Posted by Jake123
I feed my crabs every 2-3 days some sinking shrimp pellets..
I have 12 hermits and 1 emerald.
I put in 4-6 pellets.
If you have not fed your inverts before, It's great to watch. They come running!!
What's the name of the food you feed your crabs with?
Cheers

 

[clay12340]

I typically feed my clean up crew a few shavings of scallop or clam or a bit of frozen mysis once a week or so. I only keep 1 hermit crab, but the bristle worms and nass snails come out of the rockwork en masse.
I have very little in the way of fish in my tank, so I supplement the little guys diets. It is definitely fun to watch.