The mold or algae on the roof shingles is most likely an algae called gloeocapsa magma, or as it is more commonly referred to as blue-green or black algae. Algae is actually a solid deposit of spores and dirt.
Wash roof shingles with a soft bristle brush or broom (no metal brushes) with a detergent like TSP, Spic & Span, Top Job, Simple Green etc. This removes most of the solids. Fully rinse the roof.
There are also algae & mold resistant roof shingles available for humid climates near oceans and rainy areas of the globe.
Another treatment for avoiding the black streaks is to install Zinc metal strips at the top of your roof near the ridge caps above the algae prone areas. These zinc metal strips affect the water and help avoid the black roof streaks in many cases.
There are companies that specialize in this black streak roof cleaning service and will take care of this for you. Feel free to CallMosby.com or 314-909-1800 for help with this. Learn more about Mosby roof services.