Please refer to: http://plantclinic.cornell.edu/FactSheets/...lleryfungus.htm . This Fungus called Artillery Fungus or Shotgun Fungus is caused by decaying wood chips. When my house was built in 2003 they cleared the lot of trees, hauled off the logs and chipped the branches into a large pile in the woods. When I moved in, I parked my boat and trailer on a flat next to the woods where that pile was. Each time I parked the boat it was in the same location. The next year I started to notice these tiny, pinhead sized, hard shelled spots on my boat, trailer, on everything. When I scraped the spots, inside the hard shell was a black tarry substance that stained the fiberglass. I have a huge stockpile of products I've used to try to remove these stains with no luck. Things like: MEC, acetone, paint thinner, bleach, On/Off Bottom Cleaner(contains a mild acid) and various rubbing compounds, cleaners and spot removers. Again nothing worked. I called in a Marine Surveyor, he had never seen these spots and had no idea what it was. He recomended using 1000 grit wet/dry sandpaper sanding wet. I called in a boat finisher, again he had never seen these spots. He tried a 3M Rubbing Compound with a buffer with no luck. He then recomended 1000 grit wet/dry sandpaper sanding wet followed by rubbing compound followed by a polishing compound. I have since found an Orange Pumice Hand Cleaner, GoJo works well but still a lot of scrubbing. In the beginning, I had no idea what these spot were or where they came from. A lot of research on the internet and talks on forums lead the the link above. I since removed that pile of chips which was about 30 feet from my boat and 70 feet from my house. I also have these spots on the house vinyl siding. My boat is a 1990 that has seen a lot of hot California sun so it is quite oxidized which didn't help. I'm slowly making progress with these spots but it's a lot of scrubbing. Please keep wood chips away from your toys.