Please refer to: http://plantclinic.cornell.edu/FactSheets/artfungus/artilleryfungus.htm
After my house was built, I parked my boat on the edge of the woods line where the wood chips were blown when they were clearing the lot. This huge pile of oak and pine wood chips was decaying and I started to see these tiny, hard shelled, black spots appear on my boat, from the roof to the trailer. I thought it was some kind of insect poop but it wouldn't come off. I can scrape the hard shells off but a black tary substance is left that stains the fiberglass. I have a huge list of products I've tried and nothing touches these spots. It was the next year when I was lead to the above link and knew what I had. I've moved the boat and am trying to remove that huge pile.
I've tried: MEK, Acetone, Paint Thinner, Bleach, On-Off Bottom Cleaner(contains a mild acid), Rubbing Compounds and a slew of cleaners. Nothing touched these spots. I had a Marine Surveyor and a Boat Finisher look at them and I was told to use 1000 grit wet/dry sandpaper sanding wet followed by a rubbing compound, a polishing compound and a wax. My boat is a 22 foot hardtop and is now covered with these spots. My old body has a workout ahead of me. My boat is a 1990 and has seen a lot of sun so it's oxidized which didn't help. It should have been waxed more often. Second thought too late. Insurance won't cover it. They concider it a mold or mildew.

Please keep your toys away from piles of wood chips. I'd hate to see others go through this.

Look at the bright side, after you get done with the wet sanding and compounding, put some wax on and the boat will look brand new again! Another alternative would be to scrape and then paint the boat over the black spots.

Take a plastic puddy knife and knock the head off then hit with rubbing compound... I had 5-6 boats with this problem 2 years ago that got the fungus from wood chips in the yard... PIA big time....

Mr Clean Magic Eraser
Used this product to clean years of tree sap and other crap from the top of my work van. Nothing ele touched it. These eraser sponges worked with not too much elbow grease.

I would try 50% clorine bleach/water spray it on let is soak an 30 min-hour or so and blast with a pressure washer. This will kill anything. If your boat is other than white then I would try in small spot first. Don't let the stuff touch any metal.

If that doesn't work then burn the boat and collect insurance for a fire. (put the old gas in your truck before starting fire):buds:

This thread needs to be revisited. This Fungus is active in the Spring and Fall. Artillery Fungus or sometimes called Shotgun Fungus is caused by decaying wood chips. The spores from the decaying wood chips are propelled 20 feet in the air and are attracted towards the sun or anything that reflects the light like a white boat, vinyl siding on your house, white cars, motorhomes. In the case of my boat and one case of vinyl siding I heard of, the fungus CAN'T be removed. I'm using 1000 grit wet/dry sandpaper to remove it. My boat is a 22 foot with a hardtop and it's covered from the top to the keel.

Please refer to this link: http://plantclinic.cornell.edu/FactSheets/artfungus/artilleryfungus.htm

Please keep your toys away from wood chips.

Artillery fungus it is! I can also confirm there is no spray or solution that will get the stuff off. As I'm sure you have read it takes the right combination of sun and moisture and it loves the reflection of a nice white hull. I used rubbing compound to remove the sticky little dots from all the smooth gelcoat areas the non-skid areas was another issue and I just did the best I could there but some remain.

The problem at my house was the previous owner used free wood mulch from the town dump, it has way too much wood pulp which the fungus loves. So, before compounding my boat I had to remove all of the wood mulch. That was five years ago and I haven't had a problem since.

You need to knock the little pimple head off and rubbing compound on a rag with the tip of your finger...

I had 10 boats with the problem... lots of work

MTC - That is the exact process I used. Sore arms and hands after that ordeal.