Sediment microbial communities associated with bioturbators around remnant oyster reefs

The effects of biodiversity on ecosystem function have gained significant interest as global species loss continues. In estuarine sediments, microbial communities and their capacity to cycle nitrogen is influenced by bioturbating benthic macrofauna (bioturbators) and the burrow structures they create. Oyster reefs also influence microbial communities and their function by enriching surrounding sediments, which can increase bioturbator activity and nitrogen cycling bacteria. However, the interactions between sediment microbes and bioturbators, and consequences for ecosystem functions have not been fully explored. This study sampled sediment microbial DNA and in situ flux measurements of oxygen and nitrogen to assess how bioturbator activity can modulate microbial biodiversity and function at six remnant oyster reefs along the east coast of Australia. While bioturbator burrows were found to have similar microbial community composition and functioning to that of the surrounding surface sediments, these communities were related to bioturbation activity measured as number of burrows. Moreover, bioturbation activity explained sediment oxygen consumption, while the composition of core microbial communities explained gas fluxes between sediments and water column. This study highlights the importance of microbial sediment diversity and the functional roles of bioturbators in influencing biogeochemical cycles in estuarine sediments.