Basically all what was stated above is true about emeralds. I have one in my 55 reef without any issues. The issues start coming about when there isn't enough algae for them to eat, crabs are scavangers afterall. The biggest reason why mine doesn't nibble on my coral is because algae grows in my tank like a weed and it takes ro
, and a fuge to keep it down to where it is now. I have a lawnmower blenny, coral beauty, and the emerald crab, several blue legged hermits, and tons of snails that consume what does grow while I'm at work.