Abstract. Spatial nutrients subsidies between ecosystems can be key to ecosystem structure and productivity. For example, seabirds feeding in the open ocean can deposit large quantities of nutrients onto islands when roosting or breeding, which may enhance plant biomass, and the demographics of island fauna. However, if these spatial nutrient inputs extend out to coral reef environments and how they influence the system is poorly understood. Here, we utilise a rare natural experiment, where some islands in the Chagos Archipelago are rat infested with few birds, while others are rat free with abundant bird colonies. This scenario translates to marked differences in nitrogen delivery to the islands. Using stable isotopes of Nitrogen, we show how islands with seabirds have a dramatically heavier nitrogen signature and abundance in soils and new growth leaves of coastal shrubs. While attenuating with distance from shore, these differences were apparent in halimeda and sponges on the reef flat, and in turf algae and damselfish (Plectroglyphidodon lacrymatus) muscle on the reef crest. The damselfish on reefs adjacent to the rat free islands were growing at faster rates compared to fish adjacent to rat infested islands. Reef fish communities adjacent to rat free islands had higher biomass of all feeding groups, with overall biomass 50% greater that rat infested islands. Collectively, this study demonstrates a spatial nutrient subsidy to the reef ecosystems adjacent to rat free islands, which enhance the productivity of the reef fish community. Invasive rats have disrupted this natural dynamic, highlighting rat eradication as a high priority for conservation in remote oceanic islands.

Biography. Nick is a Professor of Marine Ecology and Royal Society Research Fellow at the Lancaster Environment Centre, Lancaster University. He tackles large-scale ecological and social-ecological coral reef issues under the overarching themes of climate change, human use and resilience. He has assessed the impacts of climate induced coral bleaching on coral reef fish assemblages, fisheries and ecosystem stability. He has studied the patterns and processes by which degraded coral reefs recover, and how this can be influenced by management. He has worked extensively on the ecological ramifications of coral reef fisheries and various approaches to their management. Nick was a Research Fellow in the Centre from 2008-2015, and remains an Adjunct professor.