Convergent stochastic assembly governs reef biofilm microbiomes across ecologically distinct benthic substrates

Abstract

Understanding the processes that shape microbial biodiversity and community structure is a key objective of the field of microbial ecology. The processes driving assembly of benthic biofilm bacteria on functionally important reef substrates, such as crustose coralline algae (CCA) and calcium carbonate, are not well understood, despite their critical contributions to the maintenance of biodiversity and ecosystem function on reefs. To characterize the patterns of community assembly and biogeography on these substrates, climax biofilm bacterial communities from 11 reef sites were collected, and full 16S small subunit rRNA genes were sequenced. Though CCA- and carbonate-associated communities demonstrated different diversity, composition, and correlations with environmental conditions, communities on both substrates were assembled according to similar processes. Stochastic processes dominated assembly on both substrates, primarily drift with moderate influence from dispersal limitation and selection. Sub-communities of habitat generalists and specialists, as well as rare and abundant taxa, experienced disparate patterns of assembly that remained consistent between substrates, highlighting the importance of individual taxa traits in shaping community assembly. These results provide insight into the factors shaping benthic biofilm bacterial assembly and biogeography in a tropical reef ecosystem and contribute to understanding of reef resilience in the face of environmental change.