Coral spat survival on inshore reefs is enhanced by foul-release-coated seeding devices

Abstract Near shore coral reefs are increasingly characterised by high macroalgal biomass, elevated sedimentation and eutrophication, all of which limit coral recruitment and restoration success. Managing early life-stage bottlenecks is therefore critical for effective larval-based reef restoration. We evaluated whether a commercial non-biocidal foul-release coating (FRC) applied to ceramic coral seeding devices could reduce fouling accumulation and enhance coral spat survival on six macroalgal-influenced inshore reefs of the southern Great Barrier Reef (Keppel Islands), which are prone to high levels of eutrophication and sedimentation. Acropora millepora larvae were settled onto concrete tabs embedded within seeding devices with or without FRC treatment and deployed for 48 weeks across six sites. FRC treatment substantially reduced device fouling (24% vs 67% on controls) and more than doubled spat survival (49% vs 22% on controls). Survival declined sharply with increasing tab-level fouling, with predicted survival approaching zero under complete fouling. Device burial and sediment accumulation further reduced survival irrespective of device treatment, particularly at sites with high understorey macroalgal cover. In contrast, survival was generally higher in areas dominated by canopy-forming Sargassum spp. Our results demonstrate that early mortality driven by competition with other benthic organisms is a major bottleneck in larval-based restoration on inshore reefs and that non-biocidal FRC-treated devices can provide sustained protection against this competition. Integrating early fouling mitigation with site selection and device optimisation offers a practical, scalable strategy to enhance coral seeding outcomes on turbid, macroalgal-influenced reefs.