Seabird Diversity and Biomass Enhance Cross-Ecosystem Nutrient Subsidies

Abstract

Here, we test how the biomass and biodiversity of seabirds breeding on islands influences the magnitude of their nutrient subsidies transferred to tropical islands and nearshore coral reefs. We first compare seabird-derived nitrogen values in terrestrial soil and leaves, and marine sponges, algae and fish across islands with a gradient of seabird biomass and species richness. Next, we test whether increased coral-reef fish biomass is associated with higher seabird biomass and/or diversity, which would indicate not only greater transfer of seabird-derived nutrients across multiple systems but also greater benefits. Finally, we examine the drivers of seabird biomass and biodiversity, then identify seabird species and functional traits most associated with areas of high seabird biomass, biodiversity, and nutrient transfer. Combined, these results can inform which management actions and outcomes should be a focus of seabird conservation efforts to restore consumer-derived nutrient subsidies to vulnerable tropical island and coral-reef ecosystems.