Of Rats and Reefs

Seminar for ARC Centre of Excellence for Coral Reef Studies, 5 October 2020

When abundant, seabirds feeding in the open ocean transport large quantities of nutrients onto islands, enhancing the productivity of island fauna and flora. These nutrients can leach into nearshore waters enhancing the productivity and functioning of reef fish communities (Graham et al. 2018 Nature). However introduced pests, such as rats, have decimated seabird populations on 90% of the world’s islands. This talk will provide an overview of our ongoing work in this area. Following a major coral bleaching event, coral mortality was consistent between islands with and without seabird nutrient subsidies, but space was rapidly occupied by calcifying algae where seabirds were present (Benkwitt et al. 2019 GCB). Strong biodiversity-ecosystem function relationships of fish assemblages are maintained despite coral bleaching or rats depleting nutrient subsidies, but ecosystem functioning is reduced through different pathways by these stressors (Benkwitt et al. 2020 Nature Eco Evo). A demographic trade-off between investing in growth and fecundity is evident in parrotfish, with individuals around islands with many seabirds exhibiting faster growth, but lower size-based fecundity. Finally, rat eradications can lead to intermediate seabird population densities and reinstated nutrient subsidies to the marine environment over a decadal time frame.