Investigating the influence of tourism on the Wadden Sea using a multi-layer social-ecological network

Coastal zones are the epicentre of significant social, cultural, and economic development worldwide. A human activity with increasing importance for coastal ecosystems is the expanding tourism sector, a core economic activity, one of the fastest-growing sectors worldwide and included in the list of cultural ecosystem services. The World Heritage Site of the Wadden Sea, located in the south-eastern North Sea, belongs to the coastal ecosystems of outstanding value and is a highly attractive area for tourism. Given the complexity of potential ecological, social, and socio-economic relationships involved in tourism, single-discipline studies fall short in capturing the full range of interactions between tourism's economic value and its ecological influences. To bridge the gap between these social and ecological aspects, a comprehensive approach utilising Social-Ecological Systems (SES) has been suggested by different authors and employed to study human-nature linkages. Social-ecological networks (SENs) provide a suitable tool to study SES, utilising language, methods, and models common in both natural and social sciences. Hence, we used a SEN approach to study tourism's ecological, and socio-economic relations in the Wadden Sea with the aim to provide a holistic picture of the relationships between tourism and ecological nodes, socio-economic nodes, other ecosystem services, and threats that might influence the area's natural value. We constructed a multi-layer social-ecological network with 30 nodes and 147 edges representing to our knowledge the first SEN approach in the Wadden Sea. With a total degree of 37, tourism was the most connected node in the SEN, with numerous direct and indirect relationships to nodes from the same and other layers indicating a huge potential for cascade effects. Furthermore, we identified 12 loops in the network related to tourism that could result in positive or negative feedbacks. Furthermore, critical data and knowledge gaps were revealed to fully capture the complexity of tourism interaction in the Wadden Sea. By highlighting the interconnectedness of tourism, ecosystem services, and anthropogenic threats, this study provides guidance for sustainable management practices that can preserve the Wadden Sea for future generations.