Nature-based adaptation in human dominated coastal ecosystems

Ecosystems along river-to-sea continuums face urgent challenges that demand swift restoration interventions, often exceeding the data availability, collection and testing capacity. This makes expert- and consensus-based approaches vital for guiding decisions, particularly in data-scarce coastal regions. With the aim to provide practical guidance for assessing the applicability of different restoration techniques, this study involved a group of 23 experts from various European and Mediterranean regions to evaluate 49 restoration techniques tested recently in nine sites, representing diverse coastal ecosystems. Through a Delphi-based expert elicitation, a series of gray, hybrid, and green restoration techniques was assessed in terms of their structural and functional performance. Additionally, the assessment of the pressures affecting the regions allowed exploring the restoration techniques' resilience to both natural and anthropogenic pressures and impacts. Results from the data collected so far suggest that, while green restoration techniques are environmentally friendly and significantly support natural processes, their limited scale of influence makes them vulnerable when pressures are strong or widespread on the ecosystem. This often leads to opting for hybrid or engineering-based solutions for restoration, as they provide a more robust structure and longevity albeit with reduced capacity to foster natural processes. This result underscores a critical dilemma: while green and/or integrated solutions can help mitigate human-induced impacts and digital tools may support decision-making, restoration efforts alone may sometimes be insufficient if the underlying anthropogenic pressures on human-dominated coastal ecosystems remain unaddressed. Subsequently, the identified techniques and their performance evaluated under current and future conditions have been compiled into an open-source, interactive digital tool, designed to assist decision-makers and practitioners in selecting the most suitable restoration strategies by leveraging the knowledge acquired through ongoing experiences in coastal restoration. This digital platform not only facilitates access to information but also enables the integration of new data on emerging techniques, making it a dynamic and evolving resource for coastal restoration management.