Variation in ecosystem services within biogenic reefs: The role of reef-building species under distinct hydrodynamic conditions

Abstract

To enhance the climate resilience of coastlines, measures are being implemented to protect and restore coastal ecosystems, such as biogenic reefs and dunes. These measures, known as Nature-based Solutions (NbS), provide protection against storms, coastal erosion, and flooding. They are also recognised for increasing biodiversity and delivering a range of ecosystem services (ES). This study investigated the ES provided by biogenic reefs composed of two reef-building species (Mytilus edulis and Lanice conchilega) under distinct hydrodynamic conditions. Three ES were assessed at two sites in the Belgian part of the North Sea: (1) coastal protection, (2) carbon sequestration, and (3) water quality regulation. The two sites have different hydrodynamic conditions due to their relative locations in relation to local sandbanks, making one site more exposed and the other more sheltered. The ES were quantified and monetised using in-situ measurements and literature data based on the SUstainable Marine Ecosystem Services (SUMES) model. The results suggest that the provision of ES in biogenic reefs is determined by multiple factors, including environmental conditions (e.g. hydrodynamics) and reef-building species. (1) Sediment accumulation was only observed under low hydrodynamic conditions, due to the higher settlement success of M. edulis and the presence of L. conchilega. (2) M. edulis “produces” carbon under both low and high hydrodynamic conditions, due to high respiration and biocalcification rates. However, low hydrodynamic conditions are more conducive to carbon burial, thus enhancing carbon sequestration. (3) M. edulis patches exhibited higher denitrification rates under low hydrodynamic conditions than under high hydrodynamic conditions or in L. conchilega patches, due to divergent macrobenthic functional diversity. In conclusion, the level of ES provision is determined by location and associated environmental conditions, as well as temporal and spatial variation in biogenic reefs and the physiological characteristics of reef builders. Therefore, both aspects need to be carefully considered when planning coastal protection measures and determining the provision of ES. Finally, when implementing NbS along high-energy coastlines, sheltered sites should be prioritised.