Figure 4.

A new model for host detection by coral pathogens. The coral surface represents an intense source of molecules, such as DMSP, that diffuse (yellow gradient) away from the surface and out into the surrounding water, thereby establishing chemical gradients that motile bacterial pathogens (not to scale) can use to navigate toward their host. The striking prevalence of motility among putative coral pathogens (Supplementary Table S1), together with the strength of the chemical signals at the coral surface relative to typical signals in the water column, indicate that the advanced motility adaptations described here could be a widespread phenotype associated with coral disease.