Microalgae and Meiofauna Induce Heterogeneous Biostabilization in Marine Sediments

Transport of non‐cohesive sediments affects monitoring and navigating coastal waters, yet prediction is confounded by extracellular polymeric substances (EPS) produced by microbes and microalgae. EPS binds the surface layer of seafloor sediments together in a biomat, increasing the hydrodynamic forces required to initiate sediment motion. Meiofauna (benthic animals <1 mm) consume both EPS and microalgae, potentially affecting biostabilization. We investigated the biostabilizing effects of microalgal EPS on non‐cohesive sediments over time in no‐fauna, low‐fauna, and high‐fauna treatments and compared them to xanthan gum, a bacterial polymer commonly used as an EPS proxy in lab studies. Our data indicate that biomat stabilization increases as biomat age, resulting in higher critical shear stresses required to initiate floc mobility than clean sand erosion. High concentrations of meiofauna reduced overall biomat surface area erosion compared with no‐ and low‐fauna mats. We found that the initiation of motion in diatom biomats is spatially heterogeneous and occurs over a range of shear stresses. Diatom EPS biostabilization is not accurately approximated by xanthan gum, which has been historically used as a proxy in laboratory investigations. Improving predictions of coastal sediment transport may require the consideration of biological systems at appropriately complex spatial and temporal scales.