Workshop to scope assessment methods to set thresholds and assess adverse effects on seabed habitats (WKBENTH2)

The Marine Strategy Framework Directive (MSFD) requires Member States to achieve good environmental status (GES) across their marine waters. The EU have requested ICES to advise on methods for assessing adverse effects on seabed habitats, through selection of relevant indicators for the assessment of benthic habitats and seafloor integrity and associated threshold values for GES in relation to Descriptor 6 – Seabed integrity under the MFSD. 

Two sets of criteria were developed to evaluate indicators and thresholds respectively for evaluation of suitability for assessing GES. 16 indicator and 12 threshold criteria were compiled and weighted by importance. The criteria were designed for evaluation at a subregional or regional level. The scoring for these criteria is meant as a guidance when choosing indicators and thresholds, so failure to meet one criterion will not necessarily prevent the use of the indicator or threshold in an assessment. The framework was evaluated for 6 indicators and for 11 methods for setting thresholds. The criteria were found to be useful for evaluation both indicators and thresholds. The process works most consistently when there are experts in the group on both the criteria themselves and on the indicators and thresholds. 

The MFSD Descriptor 6 determination of GES needs both a quality threshold (when are seabed habitats in a good state in a specific location) and an extent threshold (proportion of the assessment area that needs to have seabed habitats in good state). Eleven different methods for setting thresholds were identified, of which more are suitable for setting quality than for extent thresh-olds. Preferred methods identified an ecologically-motivated difference between a good and degraded state, rather than another transition. Quality thresholds based on the lower boundary of the range of natural variation were considered most promising. This approach can be used for most, but not all, indicators.

The WK collated a standardized dataset to test the specificity, sensitivity and/or responsiveness of sampling-based benthic indicators to pressure gradients for evaluation by WKBENTH3. Risk-based methods will be evaluated as maps and by scored sensitivity and impact score per MSFD habitat type and subdivision. Participants provided input into the selection of indicators for the compilation of indicators. A template was developed for documenting the characteristics of each indicator to facilitate the evaluation of the indicators.