Long-term retention and density-dependent herbivory from Diadema antillarum following translocation onto a reef restoration site

Abstract

Most reported Diadema antillarum restocking has resulted in low survival and retention. These outcomes challenge conservation and restoration goals. A manipulative study was conducted to evaluate site retention, tandem coral-urchin restoration, and herbivory from 200 adult D. antillarum translocated to five experimental plots off Key Biscayne, Florida. Two additional plots were monitored as controls. Surveys revealed homogeneous dispersal over time, with overall retention of 94.5%, 79.5%, 56.0% and 22.5% at 1-, 7-, 84- and 267-days post-release, respectively. Rugosity significantly predicted urchin retention and plots with higher relief exhibited reduced emigration rates. Benthic image analysis revealed a significant decline in macroalgae relative to controls when urchin densities were above 0.15 m−2 but not at 0.04 m−2. Urchin plots experienced a 27% reduction in macroalgae from days 7 to 84. Results indicated higher long-term retention, especially within plots with greater relief, and evidence for ecologically significant herbivory following a single translocation event.