Diatom Motility: From gliding on sea ice to active nematics on intertidal mudflats

Diatoms are photosynthetic single-cell algae, accounting for ~20% Earth's carbon fixation. In this talk, I will discuss their dynamic behaviors in two critical ecosystems: cryosphere and coastal mudflat [1-2]. First, I will show our findings from a 45-day Arctic expedition. We customized sub-zero microscopy to observe diatoms dwelling within porous sea ice. We find that these ice diatoms exhibit robust motility down to –15 °C and possess the unique ability to glide across ice surfaces, a capability that temperate counterparts completely lose upon contact with ice. Combining experiments with thermo-hydrodynamic modeling, we show adaptive strategies that enable gliding motility in cold environments. Turning to the collective regime, I will discuss our recent findings that diatoms self-organize into an ecosystem‑scale active nematic phase spanning tens of meters on coastal mudflats. Within these carpets, self‑propagating trigger waves spontaneously arise: diatoms abruptly accelerate and glide along their common alignment direction, causing a local density depletion that interrupts the nematic pattern behind the passing wavefront. Surprisingly, we find that the mucilage secreted by diatoms onto the substrate encodes a mechanical memory, allowing the restoration of the nematic pattern after being perturbed by the wave. These results show how diatoms adapt and re-engineer their surroundings, opening a distinct physical perspective for understanding ecosystem stability in rapidly changing environments.