CANCOR investigated how N₂-fixing microbial associations support productivity in tropical coral reef ecosystems, which remained highly productive despite being surrounded by nutrient-poor (oligotrophic) waters. Key reef primary producers—such as corals, macroalgae, and turf algae—and reef substrates—including sands, dead coral, and rocky surfaces—hosted nitrogen-fixing microbes whose ecological role was poorly understood. The project quantified carbon and nitrogen fixation by these reef producers and examined the biogeochemical coupling between carbon and nitrogen cycles. It also evaluated how environmental factors influenced these processes, providing new insights into the microbial mechanisms that sustain reef ecosystem functioning.