Methodological elements for optimising the spatial monitoring design to support regional benthic ecosystem assessments

Benthic habitat condition assessments are arequirement under various environmental directives.The Marine Strategy Framework Directive (MSFD),for example, challenges member states in a Europeansea region to perform comparable assessments ofgood environmental status and improve coherenceof their monitoring programmes by 2020. Currently,North Sea countries operate independent monitoringprogrammes using nationally defined assessment areas. Lack of an agreed OSPAR or EU scale monitoring method and programme has been identified asa priority science need. This paper proposes a methodfor the development of a coherent and efficient spatial sampling design for benthic habitats on regionallevel and gives advice on optimal monitoring effortto get more accurate assessments. We use ecologically relevant assessment areas (strata) across nationalborders and test spatial sample allocation methods. Furthermore, we investigate the number of samplesneeded in each stratum to reduce the variance forestimating mean number of taxa and abundance.The stratification needs to take into account the spatial heterogeneity of the entire ecosystem. The totalsample effort is optimal when sample allocation takesinto account the size and benthic variability withinthose strata. Change point analysis helps to find abalance between sampling effort and precision of thebenthic parameter estimate. A joint sampling designfor the North Sea could be generated by combiningcurrent efforts, and where needed adapting existingnational programmes. This serves a coordinated, region-wide, benthic condition status assessment andstrengthens regional cooperation to fulfil multiplemonitoring tasks, with a scientifically underpinnedcommon approach.