How coral reefs can sustain their extreme biomass of large reef fishes has continued to puzzle scientists. By living fast and dying young, small, bottom-dwelling (‘cryptobenthic’) reef fishes have been suggested as an important part of coral reef productivity, fuelling the foodweb. Yet, cryptobenthic fish communities are strongly dependent on environmental conditions, and as such their role in driving productivity of the foodweb may change substantially if the environment surrounding them is altered. Environmental conditions on coral reefs are dramatically influenced by the presence of seabird colonies that provide a steady influx of ocean-derived nutrients to islands (through their droppings), which leach out to surrounding coral reefs. However, how the presence or absence (typically driven by the presence of rats) of seabirds may affect cryptobenthic fish communities on surrounding reefs and their role in feeding the many predatory fishes on coral reefs is currently unknown. This study will investigate whether seabirds alter coral reef food-webs through cryptobenthic fish communities and to what extent these changes are reversible. Specifically, the project seeks to answer the following questions: 1) do cryptobenthic communities differ between rat-infested and seabird-dominated islands?; 2) does this affect the productivity role of cryptobenthic fishes for larger predators?; 3) do cryptobenthic fishes tend to replenish their own populations on a reef, or distribute among reefs?; and 4) how does this affect the overall productivity of reefs adjacent to rat-infested vs. seabird-dominated islands? The questions will be tackled using field-based data collection on cryptobenthic fish communities, laboratory techniques in mass spectrometry and population genetics, and analyses of population and community dynamics. Mentoring and professional development opportunities will be provided by leading researchers at Lancaster University, Bangor University, and the University of Texas at Austin, and extensive opportunities for external development via workshops, conferences, and lab visits will be offered.