Our work has identified core seagrass leaf-associated microbiome communities, in particular fungal microbiome members which have been widely understudied in this ecosystem. We also detected a strong separation in both bacterial and fungal members of the microbiome communities across estuaries. The differential responses to site and salinity of the core members of both fungal and prokaryotic components of the microbiome communities suggests different selection pressures and colonisation routes that could be useful for linking microbiomes to the spatiotemporal changes within the estuary.