Comparison of Sentinel of Seabed and Relative Benthic Status indicators' performance to assess the impact of bottom trawling on the epi-benthic communities in an overexploited Mediterranean basin

Trawl fishing activities are considered one of the main anthropogenic causes of disturbance and degradation of benthic habitats. Several risk-based indicators have been developed to assess trawling impacts on benthic communities. In this study, the Sentinel of Seabed (SoS) and the Relative Benthic Status (RBS) indicators were applied and compared to evaluate the impact of trawling on mega-epibenthic communities in the Adriatic Sea, one of the basins most impacted by bottom trawling. Biomass data were used to calculate sensitivity indices and then evaluate their responses to fishing pressure. The two risk-based assessments were also compared in terms of habitat sensitivity and impact estimates. Both the Sentinel of Seabed and the Relative Benthic Status declined sharply with increasing trawling pressure. They consistently identified muddy habitats as the most impacted, with an 88% loss of sentinel species and the lowest RBS values. The estimated quality thresholds for both approaches indicated a highly impacted scenario in the Northern Adriatic Sea, underscoring an urgent need to adopt adequate management measures to achieve Good Environmental Status (GES sensu Marine Strategy Directive 2008/56/EC). In addition, when quality thresholds are expressed as pressure thresholds, differences are observed between indicators, showing that SoS is more conservative, identifying lower trawling pressure as causing a shift from good to non-good status. Our findings underscore the importance of adopting integrated approaches that combine multiple indicators to evaluate sea floor integrity and support effective measures for a specific region in compliance with the requirements of the Marine Strategy Framework Directive. Such approach could be further extended to assess the condition of soft sediment habitats in the context of the Nature Restoration Regulation (Reg. EU 2024/1991).