Single-celled algae and marine bacteria live in a complex but largely unexplored relationship. Now, a new study shows that the surface of diatoms is a surprisingly diverse habitat for bacteria. A team from the University of Oldenburg was able to demonstrate for the first time that the surface displays distinct microscale biochemical variations. The colonization by different bacterial species is finely tuned to this structure. Since diatoms bind large amounts of carbon and form the basis of marine food webs, their relationship with bacteria is of fundamental importance for the climate and ecology of the oceans.