What happened to my Emerald Crabs???

[Tennyson]

I have had three Emerald Crabs since I started my reef tank which was about 4 to 5 months ago. One of the biggest died a couple weeks ago, adn I haven't seen the other two for a long time. There isn't that much algae in the tank, but theres enough to go out and eat. Could they be sleeping the whole time? Molting for a really really long time (about 2-3 weeks or more)?

Any info is helpful

 

[FloatingFish]

They usually come out at night. I have a couple in my tank. I thought they were gone until I had to move some rocks and found them.