Human activity endangers coral health around the world. A new algal threat is taking advantage of coral’s already precarious situation in the Caribbean and making it even harder for reef ecosystems to grow. Just-published research details how an aggressive, golden-brown, crust-like alga is rapidly overgrowing shallow reefs, taking the place of coral that was damaged by extreme storms and exacerbating the damage caused by ocean acidification, disease, pollution, and bleaching.