Thriving Areas in Temperate Coastal Systems: Novel Insights for Marine Conservation

Resilience is a crucial property of ecosystems experiencing accelerated degradation in natural environments. While the functional characteristics of ecosystems play a significant role in shaping their resilience, the development of functional approaches in marine conservation has been largely overlooked. In light of this deficiency, we simultaneously consider the functional richness and redundancy of marine fish communities associated with rocky reefs to uncover and characterise the thriving and struggling areas. Location: Five marine ecoregions in southern Europe. Methods: We collected data on the density of reef-associated marine fish species using the Reef Life Survey's standardised protocol. Based on these data, we estimated the functional richness and redundancy using four key functional traits: dietary patterns, gregariousness, position in the water column, and substrate preference. Next, we applied a predictive approach by using the XGBoost algorithm to estimate these functional metrics across the study area, including areas where in situ data were unavailable. Subsequently, to identify threshold points in the predictions, we employed decision trees, enabling us to unveil thriving and struggling areas. Results: Our results indicate that the proportion of thriving areas (26.7%) is similar to that of struggling areas (26.5%), and that their distribution is heterogeneous across the ecoregions. We also find that these thriving areas are distinguished by lower values of human density, fishing pressure, chlorophyll concentrations, and they also exhibit a higher protection status compared to struggling areas. Main Conclusions: In the current context of declining resilience, it is essential to address the functional dimension of biodiversity to unveil thriving and struggling areas, thereby highlighting the regions that require prioritisation in conservation and restoration efforts. Our findings offer critical information for policymakers and governments at local, regional, and national levels, pinpointing priority areas to enhance marine resilience and prevent the ongoing loss of this vital ecosystem property.