Sea urchins play a dual ecological and socio-economic role in Mediterranean rocky reefs. As key grazers, they can influence algal cover, benthic community structure and, under high grazing pressure, contribute to the persistence of simplified reef states. At the same time, commercial species such as Paracentrotus lividus support valuable small-scale fisheries, whose sustainability depends on maintaining viable populations and adequate gonad production. These two dimensions are often addressed separately: conservation actions tend to focus on reducing excessive grazing pressure, whereas fisheries management aims to prevent overexploitation and population collapse. However, both perspectives ultimately depend on defining the range of sea urchin abundance, size structure and productivity within which rocky reef ecosystems and fisheries can persist.

Here, we propose a three-threshold framework to support integrated management of sea urchin populations in Mediterranean rocky reefs. The first threshold identifies levels of sea urchin biomass or density above which grazing pressure may limit algal cover and reef recovery. The second defines the lower demographic limit below which harvested populations risk losing reproductive capacity, size structure and long-term viability. The third incorporates socio-economic constraints, including fishing effort, profitability, market value and governance capacity, which can either enable or prevent the implementation of ecological and fishery targets.

By linking habitat condition, population dynamics and fishery sustainability, this framework moves beyond single-objective management and provides a locally adaptable basis for ecosystem-based and adaptive management. Rather than treating sea urchins only as a threat to macroalgal assemblages or only as a fishery resource, the three-threshold approach frames them as a dynamic component of social-ecological systems. Maintaining sea urchin populations within this safe operating space may help reconcile biodiversity conservation, sustainable harvesting and the resilience of Mediterranean rocky reefs under increasing environmental and anthropogenic pressures.