Is this a tiny crab on my coral?

This little critter *and by little I mean it looks like a speck when not zoomed in* came on my favia brain frag. Upon arrival it was bright yellow but has since turned orange. Is he a danger to my corals? It seems to be eating something constantly. I'm slightly afraid that it may be the coral. Any help would be appreciated. Here is a video .. ok I cannot post a link because I have a 0 post count. Arrgh.