Methods for the manipulation of host-associated microbes in habitat forming macroalgaeReef-associated Biodiversity

Alexander Harry McGrath¹, Luca Rindi¹, Ezequiel Marzinelli^2,3, Benedetti-Cecchi¹

¹Universita di Pisa, Italy - ²University of Sydney, Australia - ³Sydney Institute of Marine Science, Australia

There is growing evidence that microbes associated with eukaryotic hosts are critically important for their function and persistence within a changing ocean. Whilst there are a number of methods that have been applied successfully to explore host-microbe interactions, these have primarily been ex-situ and in model species. However, to truly understand the significance and ubiquity of microbial communities in host function, they must be studied in the natural ecological setting of the host. For hosts that form the biogenic habitat of ecosystems, a consistent approach is needed if we are to understand the importance of host-microbe interactions in mediating the persistence of the ecosystems they support. Using multiple habitat-forming macroalgal hosts we developed a series of protocols to conduct manipulative experiments both inter- and sub-tidally using antimicrobials. Microbial disruption caused significant decreases in host photosynthetic yield, a trend which was consistent across algal species. Importantly, our experimental approach showed no discernable effect of the methods used to apply treatment. Overall our methods provide a promising avenue for exploration of both host-microbe interactions and density dependent processes in macroalgal forests in-situ.