Children as citizen scientists at EXPO 2025 clarify geometry-dependent feeding mechanics in mushroom corals

Abstract Ciliary-mucus feeding of free-living Fungiidae (mushroom corals), in which coordinated ciliary currents transport food particles toward the oral aperture, remains poorly characterised despite over a century of descriptive study; understanding the physical determinants of particle transport has implications for coral heterotrophic nutrition and for the risk of plastic and debris ingestion in reef ecosystems. Using a citizen science protocol embedded in EXPO 2025 Osaka, 462 visitors placed standardised food particles on nine Fungiidae individuals at two orientations relative to the oral slit (0°: along slit axis; 90°: perpendicular) and filmed particle movement; 117 sessions provided per-video average transport speeds; orientation effects were compared with Mann-Whitney tests, and food particle effects were estimated with individual fixed-effects regression, accounting for repeated measurements per individual. Ninety-degree placement produced significantly faster transport than 0° in eight of nine individuals (Mann-Whitney U = 2305, P = 0.0010; paired Cohen’s d = 1.376), an effect not attributable to differential surface slope (CT-derived mean slope: 28.9° in both conditions; P = 0.973). Within individuals, food particle mass negatively predicted transport speed (fixed-effects β = −0.357 [95% CI: −0.548 to −0.166]); footprint area was significant in isolation (P = 0.0019) but not after adjustment for mass (P = 0.36), and composite mechanical stress was not independently predictive, suggesting gravitational load rather than contact extent is the primary mechanical constraint on ciliary transport. The citizen science programme achieved 97.4% participant satisfaction (Net Promoter Score: +57.7), and visitor-collected data yielded statistically robust, publication-quality results, demonstrating that non-specialist participants can reliably conduct controlled biomechanical observations. We propose the oral slit length–contact hypothesis, which posits that 90° placement may maximise simultaneous mucoadhesive contact along the full oral slit margin; this hypothesis offers a testable framework for future studies on particle capture in free-living corals and for evaluating whether coral feeding geometry affects energetic responses to environmental change. These findings also demonstrate that large-scale public events can generate rigorous mechanistic data alongside meaningful participant engagement, offering a replicable model for embedding citizen science in large-scale public programmes.