Benthos habitat quality assessment for the North Sea: joint GES assessments require a coordinated monitoring

The Marine Strategy Framework Directive aims at joint assessments of the good environmental status (GES) of our seas. Since monitoring programs and indicators are performed and developed on a national scale, it is a key challenge to maximize the compatibility between the separate national MSFD assessments, requiring harmonization and inter-calibration. Such a common assessment framework is being drafted for the benthic habitat within the EU-project ‘Joint Monitoring Program for the North Sea and Celtic Sea’. The existence of a wide variety of benthic indicators, which need to be inter-calibrated for assessment purpose, should not hamper the harmonization of the monitoring. Analysis of a compiled North Sea benthos dataset showed that the highest confidence, i.e. the ability to detect changes, can be reached when collecting habitat stratified species-abundance data by means of harmonized protocols, with the effort per stratum related to the size of the stratum and the variance in benthic characteristics per stratum. Such a data collection design can be cost-effectively implemented when ongoing monitoring at the national scale becomes incorporated into joint/coordinated monitoring at EU level. However, ongoing monitoring often has a long tradition, which may lead to institutional and/or country specific reluctance (skills, expertise, technology) to deviate from business as usual. Nevertheless, the implementation of a North Sea wide minimum’ benthic sampling design, which complement the national driven monitoring schemes, will inevitably lead to better integrated monitoring and allow for a thorough joint GES assessment.