Assessing the ecological and aesthetic effectiveness of restoration interventions on coralligenous reefs

Abstract

Although tools for actively restoring marine habitats have advanced considerably, the capacity and timeframes for ecosystem recovery remain uncertain. Time and funding constraints, and lacking metrics to quantify the recovery process, represent the primary obstacles to evaluating restoration success. Here, we assess the recolonization dynamics of bare coralligenous reefs and the effectiveness of restoration actions, consisting of disturbance removal and transplantation of Eunicella cavolini and Paramuricea clavata colonies, following the Costa Concordia shipwreck disaster. We quantified transplantation efforts and assessed community dynamics, diversity, and aesthetic value at impacted and nearby control sites. Recolonization patterns were slow, characterized by an increase in species richness over time. Perennial encrusting algae led the recolonization of bare surfaces. Transplanted colonies showed a high survival rate and an increase in density and cover; in contrast, no natural recruitment was observed on the monitored reefs. The impacted reefs exhibited a steady increase in ecological metrics, although their values remained significantly lower than those of the control sites. Conversely, by 2020, the aesthetic value of the reefs in the impacted site had equaled that of the control sites. This work provides empirical evidence that disturbance removal and transplantation of erect-structuring species can support the recovery of structure and aesthetic perception of coralligenous reefs. Full recovery is unfeasible in a short time, underscoring the importance of long-term protection and monitoring efforts. Assessing the effectiveness of restoration initiatives should include evaluating their impact on cultural ecosystem services.