Looks like Green hair algae. If you can, take it out, put it in a bucket with some tank water, and scrub it off with a toothbrush. If you can't remove it, scrub it off while siphoning out what comes off with some airline tubing.
Emerald crabs will eat it too, but they can be a problem picking at other things as well. Some snails will also eat it, to a degree.