Seabird island ecosystem recovery through an isotopic lens

Abstract

**Abstract:** Seabirds are island ecosystem engineers. They transport nutrients from the marine environment to islands, influencing terrestrial community composition and food web structure and function. Globally seabirds are at risk, with invasive mammals their greatest threat. Declines in seabird populations pose a critical threat to many island ecosystems. Eradications of invasive mammals on islands are increasingly being undertaken to protect seabird populations and conserve island ecosystems. Assessing how these island ecosystems respond is essential for assessing whether desired conservation outcomes are being achieved, for identifying when active ecosystem restoration interventions are required and for providing feedback to eradication funders and stakeholders. However, it is challenging to do so. Ideally, long-term multi-species monitoring, both pre and post-eradication would provide the basis for assessing ecosystem recovery. Globally, monitoring following invasive species eradications is sporadic. Due to ecological complexity and financial and logistical challenges monitoring is often restricted to assessing select species responses. We are investigating the use of stable isotope analysis as a cost- and time-effective assessment technique for evaluating ecosystem recovery. Stable isotope analysis is well established as a technique for tracing nutrient flow through food webs. Stable isotope signatures provide integrative insights into ecosystem structure and function, without needing detailed field work on all ecosystem components. We are undertaking a large-scale natural experiment utilising over 30 islands around Australia, New Zealand and the sub-Antarctic. We are using nitrogen stable isotopes to trace flows of seabird-derived nutrients through food webs on islands at various stages following invasive mammal eradication. Comparisons will be made with never-invaded and still-invaded islands to investigate the progression of eradicated island ecosystem recovery. We are also investigating an array of temporal, spatial and environmental variables also likely to influence stable isotope levels to explain additional noise in the isotope data and ensure comparable sampling between islands is possible. **Authors:** Penelope Pascoe¹, Holly Jones², Rowan Trebilco³, Mark Hindell¹, Justine Shaw⁴, Christine Weldrick¹ ¹University of Tasmania, ²Northern Illinois University, ³CSIRO, ⁴The University of Queensland