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

Host-associated microbial communities have been widely acknowledged as being fundamentally important for normal host function and performance. Whilst there is evidence that microbial communities associated with habitat-forming macroalgae can strongly influence various aspects of host performance, to have a deeper understanding of these effects we need to understand the role of host-associated microbiota on the fitness of the host, throughout its entire life cycle. We addressed these issues 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 of the host. Disruption of the host microbiota using antibiotics decreased reproductive output after two weeks, with the effect dependent on the type of antibiotic used. Disruption of host- and benthic-associated microbiota, independently and in combination, caused a significant decrease in settlement of Hormosira-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 for a dominant habitat forming alga. Thus microbiota affect key ecological processes with important implications for host fitness and potentially ecosystem persistence.

Methods
Data collected from an experiment run at Cape Banks Aquatic Reserve on algal reproductive output and settlement in response to microbial disruption. Data are Microbial community responses (16S Phyloseq) and host responses (Response variables). The various steps within the DADA2 pipeline are also included here, as well as the code to generate the plots and analyses.

Design was as follows - Host treatments 4 (Antibiotics 2; Antibiotics 3; Control and Procedural control) and tile treatments 5 (AB2; AB3; Control; Procedural control and Autoclaving).