Motile epipelic diatoms exhibit dynamic aggregation behaviour altered under oxidative perturbation

Epipelic diatoms continuously adjust their position within sediments, yet how individual motility contributes to the spatial organization and temporal dynamics of collective aggregation and how this behaviour responds to environmental conditions remain poorly understood. We resuspended a natural assemblage dominated by Pleurosigma strigosum and Gyrosigma balticum in filtered seawater and monitored aggregation dynamics over 72 h under a dark control condition or under 24 h exposure to a nominal initial H2O2 concentration of 400 umol L-1, followed by a 48 h post-exposure period. Time-lapse imaging and quantitative image analysis revealed rapid aggregation and continuous remodeling into dynamic, spatially complex multicellular networks. In the control, aggregate number declined from 11,767 to 3,237 and surface coverage from 24.4% to 10.3%, with pronounced temporal fluctuations. Under H2O2, aggregation followed a distinct, less variable trajectory, with fewer aggregates and persistent differences following the cessation of H2O2 exposure. These observations suggest that dynamic aggregation behaviour may contribute to biofilm organization and resilience, while not distinguishing active regulation from emergent cell-cell-matrix interactions.