Assembly and ecological succession of bacterial communities on sand grains
Marine microbial communities in coastal sediments are some of the richest and densest communities known and play a major role in global elemental cycles. The composition of these benthic communities, which mostly live sheltered within the cracks of grains, depends on the physicochemical characteristics of the sediment, a pattern that suggests strong environmental selection. Yet, individual sand grains also host a substantial number of rare taxa, which suggests local stochasticity. To test whether environmental selection dominates over stochasticity during the first stages of community assembly, we followed the succession of bacteria on individual sand grains in a microcosm experiment. Bacterial community composition on sand grains followed strikingly similar trajectories and converged over time: Vibrionaceae dominated within six hours, followed by Rhodobacteraceae and Alteromonadaceae after one day and, later, by Flavobacteriaceae and Saprospiraceae. We propose that reproducible community assembly emerges from the physical structure of grains, from high dispersal of the species pool, and from averaging communities across cracks. Sand grains may therefore function as a collection of smaller, semi-independent communities whose overall composition is more predictable than that of any individual crack. Our results are consistent with a framework in which selection dominates over stochasticity, and further suggest that microbial communities in coastal sediments may be more predictable than previously thought.
Marine microbial communities in coastal sediments are some of the richest and densest communities known and play a major role in global elemental cycles. The composition of these benthic communities, which mostly live sheltered within the cracks of grains, depends on the physicochemical characteristics of the sediment, a pattern that suggests strong environmental selection. Yet, individual sand grains also host a substantial number of rare taxa, which suggests local stochasticity. To test whether environmental selection dominates over stochasticity during the first stages of community assembly, we followed the succession of bacteria on individual sand grains in a microcosm experiment. Bacterial community composition on sand grains followed strikingly similar trajectories and converged over time: Vibrionaceae dominated within six hours, followed by Rhodobacteraceae and Alteromonadaceae after one day and, later, by Flavobacteriaceae and Saprospiraceae. We propose that reproducible community assembly emerges from the physical structure of grains, from high dispersal of the species pool, and from averaging communities across cracks. Sand grains may therefore function as a collection of smaller, semi-independent communities whose overall composition is more predictable than that of any individual crack. Our results are consistent with a framework in which selection dominates over stochasticity, and further suggest that microbial communities in coastal sediments may be more predictable than previously thought.