Marine Epibiosis: Concepts, Ecological Consequences and Host Defence

The sessile mode of life is widespread in a variety of marine phyla. Sessile life requires a stable substratum. On the benthos, motile life stages and sessile adults compete for rigid surfaces making non-living, i.e. inanimate, hard substratum a limited resource. Epibiosis is a direct consequence of surface limitation and results in spatially close associations between two or more living organisms belonging to the same or different species. These associations can be specifically guided by host chemistry resulting in species-specific symbiotic or pathogenic assemblages. Most colonizers, however, are non-specific substratum generalists. The ecological consequences for the overgrown host (basibiont) and the colonizer (epibiont) can be positive and negative. The predominantly disadvantageous nature of epibiosis by microorganisms for the basibiont has resulted in a variety of defence mechanisms against microcolonizers, including physical and chemical modes of action. Besides antimicrobial effects of secondary metabolites emanating from the host, recent studies increasingly demonstrate that epibiotic bacteria associated with the host deter growth and attachment of co-occurring bacterial species or new epibiotic colonizers competing for the same niche.