Join Date: Nov 2011
Location: Long Beach, Maryland
That is a bacterial bloom and is very common on new driftwood. Leave it be and it will go away, it is harmless. If it is dense and lumpy it could also be some resin (sap) from the wood, but your description sounds like a bacterial bloom. It is cause by the bacteria feeding on a thin layer of soft wood.
Again, don't worry, it will clear up on it's own, and don't bother trying to clean it off, it would most likely come back.