Plant-based biofilters with seaweeds or periphyton efficiently remove the excess nitrogen in mariculture effluent while forming a protein-rich biomass. Yet, little is known about the microbial assemblies in such biofilters. Metacommunity theory, the study of communities spatially connected via dispersal, is among the central pillars of microbial ecology. It evaluates which of the four paradigms of patch dynamic, species sorting, mass effects, or neutral model best explains community dynamics.
While theoretical research endorsed the neutral model in aquatic environments, empirical studies primarily support mass effects and species sorting paradigms. Here, we study metacommunity theory in a two-step biofilter with Ulva fasciata for ammonia removal and a sequenced marine periphyton biofilter for polishing and nitrate removal. During five weeks, microbial assemblies in the three patches of Ulva, periphyton, and water were analyzed following 16S rRNA gene amplicon sequencing.
Our results of community structure, diversity, and functionality support the argument that species sorting, operating through environmental heterogeneity, is the central force that drove microbial community dynamics in all three habitats. Determinism was a leading force across all patches, highest in Ulva, medium in the ambient water, and lowest in periphyton. This trend coincides with community diversity, suggesting that a less diverse environment tends to impose a more selective force and vice versa. Function-wise, genes related to nitrogen and sulfur metabolisms were higher in periphyton than in the water and Ulva assemblies. Our results proved against the common thinking that mass effects would overrule in such a small-scale aquatic system.