I have been wondering the same thing, and nobody has been able to give me an answer. Nevertheless, I think Clown Trigger is probably correct. I had numerous decorator shrimp in my reef tank: 3-4 candy-stripers, 4 scarlets, and a golden coral banded. After a couple of years, my population started to dwindle, and now I have none. I would say 2-3 years at the most.