Shrimp and Crabs dying

I have a 75 gallon tank that is doing well. The fish and the corals (several species of polyps, mushrooms, and a colony of Xenias) look healthy. Over the last year I've added 2 cleaner shrimp and 1 emerald crab. One of the shrimp lasted for several weeks the other (much smaller) for 3-4 days. The emerald was added recently and I spotted for about a week, but the other day I noticed its carapace on the sand. Is it possible that I have a predator that is targeting these inverts (I've never heard any clicking)? If so, how do I find it? Any other possibilities? I'm reluctant to add any others until I sort out the problem.

Thanks

 

Don't crabs molt? Was it possible you saw a molted carapace?

 

well, I have a big coral banded shrimp in my 10 gallon tank. When he molds it sometimes takes me some time to see, which one is the real one, and which is just the skin. It looks like a perfect duplicate with every single antenna there.
It's easy to think the actual shrimp died.

 

Hi BBell! what fish do you have? If you got a trigger or wrasse could be the ones you have are predatory and likes crabs and shrimps. Generally cleaners are not eaten but I've seen Groupers eat cleaners (yeah, the Lysmata kind). Nasty beasts. Same with dwarf groupers and soldier fishes.

 

Thanks for you input

It is possible that the carapace that i've seen has been molted. I'll keep looking for the crab

No predatory fish: blue damsel, pseudochromis, percula clown and recently added a Clarkii (and yes the percula is displaying some territorial agression, but I think they're working it out).

Am I right to assume that if the water quality is good for the Xenia's it should be fine for the other species?

 

puffers eat crustaceans, too, but i guess you don't have any puffers.

maybe you can do a water test for nitrates? or have you used any copper-based medications recently?

 

BTW long ago i read an article by Toonen-biogeek about too much iodine supplementation which kills crustaceans. It causes toxins on the animal, so the animals try to remove it by molting rather too frequently that it fails to regenerate and dies.

 

I was fooled by a shell from a sally light foot the day after I bought it. Looked and felt just like the crab, until she came crawling aroung the rock. Even the lsf was fooled. They were about to give me a new one.

 

lol u shoulda taken it