Ecological implications of restoring degraded marine areas using Posidonia oceanica: assessment of plant contamination and fish fauna recovery

The potential of ecological restoration to re-establish ecosystem structure and function is globally recognised. However, the ecological implications of restoring polluted sites are rarely considered in the assessment of trajectories and recovery processes. Here we present two case studies of restoration of marine coastal areas carried out by transplanting the Mediterranean seagrass Posidonia oceanica from donor meadows to polluted marine areas with the aim of assessing, within six months from transplant: (i) trace element (TE) accumulation in P. oceanica in response to environmental contamination; (ii) fish fauna recovery. We found increased Cr, Cu and Hg accumulation in roots and As in leaves of transplanted plants, confirming that P. oceanica may act as a sink, sequestering TEs and potentially decreasing their availability, but also opening questions about the potential risk of remobilising buried contaminants. At the same time, fish assemblages showed signs of rapid recovery in both areas, i.e., an increase in species richness, abundance, and diversity from the first month after transplantation, indicating a rapid improvement in habitat provision function. Although the amount of TEs potentially transferable from P. oceanica to the ecosystem seems to be low in the study areas, further investigations including cost-benefit assessments of restoring polluted sites by transplanting seagrasses would improve current knowledge in support of efficient ecosystem-based coastal biodiversity management and conservation.