Strange symptoms in reef fish

Recently a large number of fish species has been observed carrying signs of what could be a disease. Two types have been observed and herbivorous fish seem most affected. The first "disease" was historically observed on surgeonfish (A. bahianus), but is now also occuring on several species of grunts and hamlets. Indiviuals affected are covered by dark, round patches, usually dark grey/ black in color, that can occur all over their body. Examples of this "disease" are shown  in [...]