What crabs aren't evil... (other than a dead one!)
one thats fed. In most cases, animals have a "preferred food" and will eat that whenever it's available. if it's not available, it still wants to survive and will take whatever it can get. If your crabs have enough of its preferred food it will leave your other critters alone.
In regards to the bubble algae; I like them! 8O I've only pulled out a few that have gotten extremely large (3-4 inches in diameter) but have left the rest alone and I do not have a problem with them in my tank (as in i don't have very many). My 55 has probably.. 3 or 4 that might be around 1" and maybe a dozen or so less than 1/2" (which is hardly noticeable) If you're going to remove them then the sooner the better. Their skin is quite firm, but the larger they get the thinner their skin becomes. Simply grab hold of them and twist slightly while wiggling them back and forth until their root lets go of the rock.