Supplementary material from "The effect of surface properties on the interactions of particles and marine mucous filters"

Suspension feeding, in which organisms filter particles from the water for nutrition, is a widespread and ecologically critical feeding strategy in aquatic ecosystems. Yet the principles governing particle capture remain unresolved. Mucus-based particle capture is widespread, and classic models typically describe it as a size-dependent sieve–like mesh of mucous nanofibers. Here, we show that for small particles, surface physicochemistry, not size alone, strongly influences capture success. Using polystyrene microspheres with tailored amphiphilic polymer coatings, we found that steric repulsion altered particle mobility within the mucous filter, reducing capture efficiency for submicron beads, while larger particles were retained regardless of coating. Cryo-SEM imaging revealed that, contrary to prevailing models, the ascidian mucous filter is a ~5 µm-thick continuous sheet rather than a nanofiber mesh. These findings call for a revision of suspension-feeding models to incorporate colloid–mucus interactions and bulk transport phenomena. Beyond advancing our understanding of plankton ecology, this work provides principles for the design of synthetic filtration systems that couple high efficiency with self-cleaning.