Small-scale habitat complexity preserves ecosystem services on coral reefs

1. Coral reef habitat quality is declining in many locations because of heatwaves (coral bleaching) and other disturbances. Reef-building corals provide refuge from predation, so declining complexity restricts the transfer of energy to upper trophic levels.2. We use a size-based ecosystem model to test systematically the effects of refuge at specific sizes and the impacts of distributions of refuges that vary in size. Outcomes are assessed in terms of ecosystem service provision.3. Simulations indicate that refuge sheltering fish between 5 and 10 cm in length enhances fish biomass and fisheries productivity, for example, increasing herbivore biomass by up to 80%.4. We identify and present a range of refuge profiles that can theoretically improve ecosystem service provision by as much as sixfold. Profiles where refuge availability decreases with increasing fish size consistently outrank other designs.5. Synthesis and application: These results highlight how critical small-scale refuge is for coral reefs, and how we might design artificial reefs to maximise service provision.