Diagnosing Black Spots on a Mahogany Deck

If dark spots appear on unfinished mahogany decking, do they have to be removed prior to finishing?

The unfinished mahogany decking on a recently-built deck located in the northeastern U.S. has developed black spots. If you are familiar with this spotting problem and know how to deal with it, the PDB forum member who posed this question and posted this photo would appreciate your advice. Read more.