Spatial variation of bacterial and fungal communities of estuarine seagrass leaf microbiomes

The health of seagrass plants, and thereby the ecosystems they form, is linked to their associated microbial communities. However, the role of the microbiome in holobiont function and health remains poorly understood for most seagrass species and environmental pressures, and there is, therefore, a need to better understand the drivers behind the formation of and external influences on the seagrass microbiome. Using a core microbiome framework, we characterised the leaf microbiomes of 6 estuarine seagrass populations after a precipitation event to explore how the microbiomes vary across different sites and salinities over a regional spatial scale. We found that each estuary had distinct core bacterial community structures (beta-diversity), but shared a more similar fungal core community structure. We hypothesise that the differences in the bacterial members of the microbiomes among estuaries are generally the result of each estuary being influenced by unique watersheds and sources of prokaryotes. In contrast, the similarity in the core fungal communities suggests that the eukaryotic components of the microbiomes are likely under selection or result from similar colonisation pathway(s). We also found that the bacterial taxa driving the differences among estuaries were linked to the salinity of the estuary, likely due to (1) the general epibiotic nature of colonisation (i.e. watershed source and exposure) and (2) members or functional groups within the leaf microbiome assisting seagrasses in coping with the extreme salinities. These results are valuable for linking microbiomes to the resilience of seagrasses living within dynamic estuaries experiencing a range of physicochemical pressures.