Past and recent evolution of the submerged beach, shoreline, and dune-beach morphology as a baseline to monitor a nature-based reef solution for coastal protection and marine biodiversity enhancement

In a context of sea level rise and the intensification of extreme wind events and storm surges, low coastal areas and sandy beaches experience intensified damages and erosion processes. Engineered hard solutions are often necessary to protect inhabitants and ports; however, a soft approach is desirable for natural coastal systems and beaches. The LIFE NatuReef project implements a solution based on the exploitation of the work of species that can be considered ecosystem engineers, as they are able to build reefs on sand beds along the coast, thereby protecting the shore and mitigating erosion. The construction of a limestone artificial reef near the Bevano outlet (Ravenna, Italy) will serve as the substrate for the development of populations of oysters (Ostrea edulis) and sabellariid worms (Sabellaria spinulosa), which are native species capable of building three-dimensional structures atop and around the original artificial reef. These structures retain sediments and dissipate wave energy, thereby counteracting coastal erosion. In this work, we present the activities and preliminary results of continuous monitoring conducted on the submerged beach and the dune-beach system. The activities aim to establish a baseline that, through a reconstruction of past and recent morphological evolution, defines the current state of the system. This provides qualitative and quantitative elements for assessing fundamental morphological features as well as for describing habitats of key importance as for example embryo-dune, foredune, and back-dune habitats. Integrating Global Navigation Satellite Systems (GNSS) observations and digital photogrammetry obtained from UAVs (Unmanned Aerial Vehicles), we created a detailed model of the dune-beach system. This information was corroborated with the distribution of vegetation species. The morphology of the submerged beach was retrieved using OpenSWAP vehicles equipped with multibeam, sub-bottom profiler, side-scan sonar and single-beam echosounder. The combination of results obtained from different methodologies provided a comprehensive picture of the morphology of the entire submerged-emerged beach and dune system at extremely high spatial resolution. Continuous monitoring of the system state through periodic surveys will yield quantitative results on the variations caused by the constructed reef in front of the beach, including detailed analyses of shoreline dynamics resulting from the surveys.