As Z stated, many fish and other inverts will eat shrimp. They are a delicacy to others besides us humans You have to be careful and know about the eating habits/potential of your current livestock before adding anything new, whether it be new animals or corals.

Also, sometimes you may think a shrimp is dead as it is dissappeared or you see what looks like it's skin floating around the tank. Shrimp can be very good at hiding and they can also shed their exoskeleton (shell). Depending on the water parameters and nutrients, they can molt frequently and will tend to hide for awhile after they do as they are most vulnerable during this time.

Hope that helps