Lorna McKellar (@lornamckellar.bsky.social)

Workshop to evaluate options for setting seafloor quality thresholds (WKBENTH4) The Marine Strategy Framework Directive (MSFD) requires Member States to achieve good environmental status (GES) across their marine waters. The European Commission (EC) has requested ICES advice on the application of operational methods to support the TG Seabed proposal for quality thresholds for seafloor integrity (MSFD Descriptor 6, Criterion D6C5) in EU marine waters.The scientific findings generated by Workshop to evaluate options for setting seafloor thresholds (WKBENTH4) provide the technical basis for ICES to develop formal advice in response to the EC request, following an independent peer-review process.Worked examples were developed from an ICES data call compiling reference‑condition time series and pressure–state gradient datasets, either specifically focused on a specific pressure or of large spatial extent stratified by MSFD broad habitat type (Sections 2, 5 and 6). Six threshold methods were compared using ten criteria addressing their scientific basis, data and uncertainty, operational practicality, and management applicability (Section 7). This allowed Quality Threshold Values (QTVs) to be estimated for six indicators including biodiversity metrics (Species richness and Relative Margalef diversity), the most sensitive species fraction for the pressure of concern (Sentinals of the Seabed), and the total abundance/ biomass and sensitive species biomass based on longevity of species.Results showed (in Section 7) that QTVs varied more among indicators than among methods, indicating that indicator choice has a strong effect on threshold outcomes, more so than method selection. Integrating multiple indicators remains challenging (Section 8), however a comparative analysis of different threshold and indicator combinations for broad-habitat types (Section 7) revealed all selected QTV methods and indicators have value in establishing quality thresholds. Accordingly, it was concluded that the integration of indicators and QTV methods (Section 8) would benefit from a proposed multi‑level quality‑extent approach or framework that can utilise all available evidence most appropriate for the available data in a given region.A workflow was developed for selecting QTV methods based on data availability and threshold approach, applicable beyond the methods and indicators evaluated. These outputs support national and regional assessments of seafloor impacts, and three example implementation path-ways were presented (Section 7).WKBENTH4 concluded (Section 9) that “good condition” under the Nature Restoration Regulation (NRR) is broadly equivalent to Good Environmental Status (GES) under the Marine Strategy Framework Directive (MSFD) for benthic habitat types (Group 7). The assessment and threshold-setting methods developed for MSFD Descriptor 6 provide a practical and scientifically robust basis for evaluating habitat condition, supporting restoration monitoring, and strengthening cross-policy coherence between the MSFD and NRR. Notably, at least one of the approaches enables estimation of ecological recovery times under specific conditions, providing valuable information for monitoring design and assessment of progress over time.The findings of WKBENTH4 collectively provide an operational, evidence-based pathway for setting and applying quality thresholds that can support coherent implementation of both MSFD and NRR objectives across EU marine waters. https://ices-library.figshare.com/articles/report/Workshop_to_evaluate_options_for_setting_seafloor_quality_thresholds_WKBENTH4_/31898953?file=64519932