The challenge of setting restoration targets for macroalgal forests under climate changes

The process of site selection and spatial planning has received scarce attention in the scientific literature dealing
with marine restoration, suggesting the need to better address how spatial planning tools could guide restoration
interventions.
In this study, for the first time, the consequences of adopting different restoration targets and criteria on
spatial restoration prioritization have been assessed at a regional scale, including the consideration of climate
changes. We applied the decision-support tool Marxan, widely used in systematic conservation planning on
Mediterranean macroalgal forests. The loss of this habitat has been largely documented, with limited evidences
of natural recovery. Spatial priorities were identified under six planning scenarios, considering three main
restoration targets to reflect the objectives of the EU Biodiversity Strategy for 2030.
Results show that the number of suitable sites for restoration is very limited at basin scale, and targets are only
achieved when the recovery of 10% of regressing and extinct macroalgal forests is planned. Increasing targets
translates into including unsuitable areas for restoration in Marxan solutions, amplifying the risk of ineffective
interventions.
Our analysis supports macroalgal forests restoration and provides guiding principles and criteria to strengthen
the effectiveness of restoration actions across habitats. The constraints in finding suitable areas for restoration
are discussed, and recommendations to guide planning to support future restoration interventions are also
included.
The dataset produced for this study shows the information used as input for Marxan analysis. Rows of the dataset correspond to Planning Units (PU), i.e., the set of potential sites from which to select restoration areas. For each PU the following elements are provided: identification number (ID); longitude and latitude (X and Y); Habitat Suitability Model classification: values ranging in the [0,1] interval. PUs with values < 0.61 are classified as unsuitable for restoration; the frequency of Sea Surface Temperature Anomalies expressed as a percentage. PUs with values > 75 are classified as unsuitable for restoration; the level of Habitat Richness. Values ranging in the [0,1] interval; the distance to the closest divining facilities (in km); the distance to the closest location with previous experience on restoration activities (in km); the distance to the closest port (in km); distance to the closest International, National and Regional Marine Protect Areas (in km); the distance to the closest Marine Institute (CIESM), Marine Station (MARS) or Specially Protected Areas Regional Activity Centres (SPA/RAC) (in km); the distance to the closest facility (in km); the cost of restoration (in €); the status: 0 for included PUs, 3 for locked-out PUs; the restoration features; the reason for exclusion from the analysis.