Modeling bioerosion rates by Diadema antillarum populations to improve coral reef restoration in the Caribbean

Introduction The keystone herbivorous sea urchin Diadema antillarum was abundant throughout the Caribbean until the 1980s mortality event reduced populations and contributed to shifts toward algal-dominated coral reef states. Restoration of D. antillarum has since been used to reduce macroalgal cover and facilitate coral recruitment, but previous studies have not rigorously considered how D. antillarum restoration could increase coral reef bioerosion.Objectives Our objective was to create a user-friendly Excel tool to model bioerosion by non-restored and restored D. antillarum populations.Methods We combined a size-at-age population model with size-specific parameterizations of D. antillarum bioerosion rates to estimate current and future bioerosion.Results The non-restored 0.91 individuals m-2 population had a constant 0.87 kg CaCO3 m-2 year-1 bioerosion rate. The population starting with 5 individuals m-2 reached a max bioerosion rate of 4.53 kg CaCO3 m-2 year-1 after one year that declined to non-restored bioerosion rates by year 17. Adding 1 individual m-2 to the non-restored population reached a max bioerosion rate of 1.77 kg CaCO3 m-2 year-1 after one year before returning to pre-restoration bioerosion rates by year 17. Doubling the annual recruitment rate gradually increased bioerosion up to a constant 1.73 kg CaCO3 m-2 year-1 rate by year 14.Conclusions Restoring D. antillarum populations could accelerate losses in coral reef building if augmented bioerosion exceeds carbonate production by the facultative recruitment of reef-building corals. However, this effect would be temporary owing to D. antillarum populations returning to pre-restoration levels in the absence of continued restoration.