Biofilms: An Extra Coat on Macroalgae

Biofilms are a mixture of complex communities of organisms mostly composed of diverse bacteria that vary depending on the surrounding environmental conditions induced by physical and chemical factors. In biofilms, symbionts play major roles in the relationship among organisms by the production of bioactive molecules involved in quorum sensing signaling. A cohesive structure of a multi‐layer of extracellular polymeric substances (EPS) such as polysaccharides and proteins is the base of biofilm structural organization. Biofilms can be found in a variety of habitats, on free‐living, on the surface of other organisms or inert surfaces, both in aquatic as well as terrestrial environments. The importance of macroalgae in marine ecosystems is unquestionable. They are main key players along ocean coastlines, contributing to the overall primary production and providing shelter as well as food to many forms of life which can vary from microbes to large fish and mammals. Macroalgae are intimately associated with a huge microbi‐ al community coating their surface. As this microenvironment is very rich both in terms of biodiversity and food availability, life in it is very complex and competitive. The microorganisms, bacteria, archaea, fungi, microalgae like diatoms and protozoa, play fundamental roles in the development, defence and metabolism of the macroalgae. They benefit from the availability of diverse organic carbon sources commonly produced by the algae. In this chapter, we intend to do a comprehensive revision of the actual state of the art of the biofilm community of macroalgae focusing on biodiversity, role played by both the microbiome and the host in this ecological system and its regulation namely through the quorum sensing. Furthermore, biofilm‐related biotechnological applications, their role in macroalgae diseases and their influence in neighbor organisms will be also addressed.