Ecological benefits and Habitat-specific fish responses in a small fully protected urban MPA

This study assesses the reserve effect on fish assemblages within the Larvotto Marine Protected Area (MPA), a small, fully protected, and highly enforced urban MPA, established in 1976 in Monaco (Mediterranean Sea), a highly urbanised coastal zone. Using a five-year dataset from underwater visual censuses, we analysed fish density, size, and biomass across two key habitats: artificial rocky substrates and Posidonia oceanica meadows, comparing data from within the MPA to nearby unprotected areas. Results show a pronounced habitat-specific response, with significantly higher fish biomass on artificial substrates inside the MPA, while Posidonia oceanica meadows displayed no significant biomass difference between protected and unprotected zones. These findings demonstrate that well-enforced MPAs in urbanized settings can deliver substantial ecological benefits, providing valuable insights for policymakers and advancing our understanding of MPAs in complex coastal environments. Integrating urban MPAs into broader conservation frameworks could enhance the ecological resilience of coastal ecosystems by complementing “residual” MPAs typically located in less disturbed areas. This approach can help reconcile the intensifying use of coastal zones with ambitious 2030 global conservation targets, contributing meaningfully toward the effective protection of 30% of Earth’s surface.