Integrating local ecological knowledge and scientific surveys: a pathway to understanding benthic mesophotic ecosystems

Abstract Marine ecosystems face increasing anthropogenic pressures, highlighting the need for effective conservation strategies such as Marine Protected Areas (MPAs). Knowledge gaps are particularly evident in mesophotic ecosystems (MEs), which provide vital ecological functions but are difficult to study due to logistical and technological challenges. This study explores the role of Local Ecological Knowledge (LEK) as a complementary tool to Remote Operated Vehicle (ROV) surveys for characterising MEs in Northern Portugal. We conducted 59 interviews with fishers to gather information on species distribution, depth ranges, habitat associations, and conservation views. Simultaneously, 187 ROV dives recorded species presence and habitat features. Fishers reported a high diversity of species, including several Vulnerable Marine Ecosystem (VME) indicators, some absent from ROV observations, thus expanding biodiversity records for the region. Comparisons revealed both overlaps and discrepancies, emphasising the complementarity of LEK and ROV methods. Fishers broadly recognised the ecological importance of corals and sponges and showed support for conservation measures, although opinions varied among different fishing groups. Our findings demonstrate that combining LEK with scientific surveys improves biodiversity assessments, helps identify key conservation areas, and fosters collaborative efforts to protect mesophotic ecosystems amidst increasing human impacts.