Carbonate framework and sediment production across island-fringing coral reef habitats and a natural nutrient gradient

at shallow reefs), little variation among atolls, and a limited response to nutrients. Sediment composition was dominated by reef framework constituents (coral and crustose coralline algae), with secondary contributions from Halimeda, molluscs and benthic foraminifera. Beach sediments resembled shallow reef sediments, both showing increased Halimeda near nutrient-enriched reefs due to past calcareous algal blooms. Our findings demonstrate how different spatial scales and seabird-derived nutrients modulate carbonate production in remote reef island systems.