Black streaks on your roof are a harbinger of bad news, unfortunately. There’s nothing good to say about Gloeocapsa Magma, a hardy blue-green algae species that easily multiplies and spreads. Detrimental to your roof from any way you look at it, black streaks caused by Gloeocapsa Magma can really cause some damage to your shingles—and if left unchecked, it can reduce the expected lifespan of your whole roof.