If the stringy looking moss is floating, I'd rake it off the top and dispose of it OR wait and hope it blows to a non-bed shore and rake it off there. The bedded fish will get a bit upset during the raking process, but damage will be minimal to non existent.

If the moss is on the bottom, I'd leave it alone during spawning UNLESS you think you have more than enough reproduction to begin with, but then the question should be "how much should I disturb the spawning process?".

Fish on!,
Noel