They are some the ocean's tiniest inhabitants. On coral reefs, microorganisms are copious creatures. But in a world that's invisible to the naked eye, drastic changes are taking place. Throughout Florida, scientists painstakingly work to identify key players within this microbial community. Recent breakthroughs revealed a direct link between a human pathogen and a devastating coral disease. With corals under immense stress, experts are using advanced genetic tools and a former aquarium "pest" to better comprehend these microscopic organisms. With experimental sites in the lab and in the sea, what will microbes reveal about coral health? How do human activities impact the microbial balance on the reef?