The coral surface represents an intense source of molecules, such as DMSP, that diffuse (yellow gradient) away from the surface, through the mucus layer and out into the surrounding water, thereby establishing chemical gradients that motile bacterial pathogens (not to scale) can use to navigate toward their host. Graphic / Glynn Gorick, Melissa Garren, Roman StockerCoral reefs, the most biodiverse ecosystems in the world’s oceans, are declining because of bleaching and disease. But little is known about the microscale interactions between the pathogens that cause disease and the weakened coral. Now CEE’s Professor Roman Stocker, postdoc Melissa Garren and grad student Kwangmin Son have identified one mechanism by which pathogenic bacteria identify their prey: The stressed coral produce up to five times more of a sulfurous compound called DMSP. The abundant DMSP appears to serve as a clarion call, inciting the pathogen cells, which sense the amplified chemical and charge in for attack, changing their swimming direction and speed as they home in on the weakened coral. Read a news release.