Disruption of host-associated and benthic microbiota affects reproductive output and settlement of a habitat-forming...

The reproduction and establishment of habitat-forming species are key processes affecting their persistence and associated biodiversity. In marine systems, microbial communities associated with habitat-forming macroalgae can influence various aspects of host performance; however, the role of these microorganisms in influencing macroalgal reproduction and settlement is poorly understood. Using a dominant habitat-forming macroalga on Australian rocky shores, Hormosira banksii, we manipulated host- and benthic-associated microbiota to determine the relative importance of microorganisms to reproductive output (number of viable eggs released) and settlement (settlement and morphogenesis of algal zygotes). Disruption of the host microbiota using antibiotics decreased reproductive output after 2 weeks, with the effect dependent on the type of antibiotic used. Disruption of host- and benthic-associated microbiota, in combination, caused a significant decrease in settlement of H. banksii zygotes, with the combined disruption having the greatest impact on settlement success. Our results demonstrate the importance of host-associated microbiota in macroalgal reproduction and an interactive effect of host- and benthic-associated microbiota on settlement-a key ecological process with important implications for host fitness and potentially ecosystem persistence.