Hitchhiker Crab ID Please

[Tetra1]

I found this crab lurking in my tank and he started out tiny a year ago. I have since broke down that tank and got a new one and was able to capture him. He came in on my ulva lettuce and I need to know if he is good or bad because I don't want to put a pest in my new tank. Please help. Thanks.

 

[Joeganja]

It's an Emerald Crab. He's actually good believe it or not eats algae like crazy. And is reef Safe