• chemical ecology;
  • epiphytes;
  • settlement cues;
  • fouling;
  • natural antifoulants;
  • biofilms;
  • bacterial signalling

The surfaces of macroalgal thalli are colonized by planktonic propagules (larvae, spores, cells, etc.) from a wide diversity of eukaryotes and prokaryotes. Colonization (here defined broadly to include processes such as settlement, attachment, metamorphosis, biofilm formation, and infection) of seaweed surfaces can be both induced and inhibited by metabolites produced at those surfaces. However, detailed examples of chemically mediated interactions at seaweed surfaces for which chemical cues have been characterized, quantified in situ, a biological effect determined, and the consequences to the demography of the seaweeds or colonizers demonstrated are very rare. Here we briefly review the literature on both deterrents (“natural antifoulants”) and inducers of colonization and on interactions at seaweed surfaces between the hosts and associated bacterial biofilms. One theme that emerges is the strong need to integrate ecology, cell biology, and chemistry to understand the distribution of surface-active molecules in situ and their ecological consequences. This multidisciplinary approach is further emphasized for research on biofilms on seaweeds, where recently developed molecular tools for characterizing bacterial communities are opening up an entire new area of marine chemical ecology. Finally, we emphasize an integrated approach to the topic, as we believe that many aspects of somewhat disparate fields including, for example, induction of larval settlement, algal pathogenesis, and the molecular biology of bacterial signaling can be usefully viewed within the overall framework of chemical mediation of surface colonization.