huh this fish seems to have done a lot less damage than i had expected. since you mention the really bright poop... have you ever tried putting the poop under actinic only lighting and see if it fluoresces? im actually half serious
I don't see it having any use for the coral's fluorescent pigments so maybe they pass largely undigested (although i would be greatly surprised if they haven't been denatured and are nonfunctional)?