Early ecological responses of bentho-demersal communities to new Fishery No-Take Zones in the NW Mediterranean: evidence of passive restoration

Abstract Fishery No-Take Zones (FNTZs) are increasingly being used as a spatial management tool to promote marine habitat recovery and enhance the sustainable use of fishery resources. To evaluate their effectiveness in shelf edge and upper continental slope habitats, a characterization of sessile and motile fauna within eleven FNTZs implemented along the Catalan margin was conducted. Surveys were conducted between 2023 and 2024 using Remote Operated Vehicle (ROV) video-transects across two depth ranges (100–300 m and > 300 m), covering both protected and adjacent Control areas. Sessile and motile fauna were analyzed separately, to assess the different responses in organisms with different life strategies. Results revealed that the effects of protection varied across depths and locations. Sessile fauna exhibited significantly higher densities, and diversity in several FNTZs, especially at the shelf edge, while motile fauna displayed less consistent trends. Community analyses showed differences between protected and control sites, with FNTZs hosting more habitat-forming species opposed to motile species which were more represented in Control areas. Despite initial signs of structural differentiation, results indicate that ecological recovery in soft-sediment at this depth remains slow and spatially variable, likely restricted by the habitat physical degradation consequence of decades of trawling. This research provides the first regional-scale, non-destructive assessment of FNTZs effectiveness on Mediterranean soft sediments and establishes critical reference data for future monitoring.