The Juan Fernández Archipelago (JFA) is a unique ecosystem due to its diversity and high endemism. In recent years there has been an increase in the populations of the endemic sea urchin Centrostephanus sylviae, generating negative impacts to the ecological and socio-economic systems of the archipelago. Here we describe the establishment of C. sylviae and the consequences of its overabundance on the subtidal communities, specifically around Robinson Crusoe and Santa Clara islands. The increase in abundance of C. sylviae and its community-level impacts (i.e., sessile benthic, macroinvertebrates, and fishes) were documented by visual surveys using scuba diving at various sites during January 2014 (12 sites), March 2017 (12 sites), March 2020 (4 sites), and January 2024 (7 sites). Over this time period the increase of C. sylviae abundance (~ 40-50%) was associated with a significant decrease in sessile biotic benthic cover and an increase in the percentage of barren grounds (40-95%). Additionally, a significant decrease in the abundance of the sea star Patiriella calcarata (100%) and the sea cucumber Mertensiothuria platei (80%) was observed, together with a decrease in the biomass of the endemic Juan Fernández wrasse Malapterus reticulatus (95%) and the endemic Juan Fernández trevally, Pseudocaranx chilensis (65%). Although the increase in urchin abundance has resulted in serious problems for the main economic activities of the archipelago (i.e., lobster fishery and recreational diving), it could also be considered an opportunity to diversify economic activity through the commercialization of the species, whose biological attributes make it an attractive gastronomic product. However, to create sustainable commercial exploitation, the ecological characteristics of the species and socioecological traits need to be understood to generate effective management and enforcement strategies. The results of the present study could serve as a baseline for exploring ongoing community changes in subtidal environments.