In Puerto Rico, a more recent and potential threat to the coral reefs is the increasing abundance of Ramicrusta spp . Ramicrusta, an encrusting red alga, forms a thin, crustose layer that spreads over the substrate and can grow over the living tissues of corals . Ramicrusta was the dominant substrate category at many shallow east coast reefs (e.g., Fajardo, Culebra, and Vieques), reaching a cover (±SE) as high as 63.0 ± 5.8%. At present, herbivorous fishes, like parrotfish and surgeonfish, have not been observed eating Ramicrusta . However, Diadema antillarum , a keystone herbivore, has been witnessed eating Ramicrusta in the laboratory and the field. The goal of this project was to increase reef resilience by increasing the population densities of Diadema on reefs by restocking lab-cultured urchins . The objective was to enhance herbivory and decrease algal cover, especially Ramicrusta . During the summer months (May to October), Diadema settlers were collected on settlement plates set along the shelf edge in La Parguera, Puerto Rico. Settlers (0.4 mm to 1.0 mm test diameter) were brought back to the lab and grown out in aquaria and raceways. Lab-raised Diadema were transferred to reefs once the urchins reach a size sufficient to reduce mortality (2.0 cm to 4.0 cm test diameter) . In August 2018, 480 Diadema were restocked to two reefs highly impacted by Ramicrusta in Fajardo, Cayo Diablo and Los Lobos. Within two months, Ramicrusta cover was significantly reduced by 63 % at reefs restocked with Diadema . T he substrate inside the experimental plots was charact erized by more available space and turf algae, which allows the settlement and colonization of corals and other benthic organisms. In August 2019, another 510 lab-reared Diadema will be transferred to two more reefs in Culebra. The r estocking of Diadema may be an effective tool to mitigate Ramicrusta c over, decrease algal cover and overall enhance reef health .