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International audience; The Northeast Atlantic, a highly productive maritime area, has been exposed to a wide range of direct human pressures, such as fishing, shipping, coastal development, pollution, and non-indigenous species (NIS) introductions, in addition to anthropogenically-driven global climate change. Nonetheless, this regional sea supports a high diversity of species and habitats, whose functioning provides a variety of ecosystem services, essential for human welfare. In 2017, OSPAR, the Northeast Atlantic Regional Seas Commission, delivered an assessment of marine biodiversity for the Northeast Atlantic, including that of benthic temperate reef communities. This assessment examined biodiversity indicators separately to identify changes in Northeast Atlantic biodiversity. Here, we expand on this work and for the first time, a semi-quantitative approach is applied to evaluate holistically the state of Northeast Atlantic benthic marine biodiversity, including benthic-pelagic coupling and xeno-biodiversity (i.e. NIS). Our analysis reveals widespread degradation in marine benthic ecosystems and biodiversity, much of which is likely the result of cumulative effects of multiple human activities, such as overexploitation, the introduction of NIS, and climate change. The status of many indicators, however, is uncertain due to gaps in data, unclear pressure-state relationships, and the non-linear influence of some pressures on biodiversity indicators. Lessons learned from this regional assessment will drive future improvement methods to progress towards a better integrated assessment of wide-scale marine benthic ecosystems Synergies between science and policy throughout the assessment process were identified as a critical enabler to delivering holistic and scientifically-robust biodiversity assessments.

Anthropogenic activities have transformed the pelagic habitat in the last decades with profound implications for its essential functions. While the EU-Marine Strategy Framework Directive 2008/56/EC and the Commission Decision (EU) 2017/848 have set criteria and methodological standards for the assessment and determination of Good Environmental Status (GES) for pelagic habitats in EU waters, there is strong evidence that Member States have not yet harmonized the pelagic GES assessment across EU marine waters. Today, pelagic habitats are assessed by evaluating whether good status is achieved by each of the pelagic indicators, but this approach fails to observe the high variability of the pelagic environment. To this end, GES is not estimated at pelagic habitats scale but only for each individual indicator. This paper synthesises the latest developments on pelagic habitats assessment and identifies the main factors limiting the consistency of the assessment across Member States: i) coarse spatial and temporal scales of sampling effort as regards to the pelagic habitat dynamics, ii) little consideration of the whole range of plankton (and, to some extent, of zooplankton) size and trophic spectra, iii) lack of integrated hydro-biogeochemical and biological studies and collaboration among experts from different scientific fields, iv) limited availability of pressure-based indicators, and v) lack of integration methods of the pelagic indicators’ status for the GES determination. This analysis demonstrates the importance of maintaining a consistent sampling frequency and a spatially extensive network of stations across the gradient of anthropogenic pressures, where spatial environmental data can help objectively extrapolating field data., The authors would like to thank the Pelagic Habitats Experts, part of the MSFD Biodiversity Expert Network for the fruitful discussions on the harmonisation of the MSFD assessment and monitoring for pelagic habitats. CM, MP, JND, and AP were funded by the Joint Research Centre of Ispra (Italy). IV wishes to acknowledge support from the program “Monitoring and recording the situation of the marine sub-regions of Greece / Upgrading and functional updating of the MSFD monitoring network”, funded by national and EU funds under National Strategic Reference Framework 2014–2020 (MIS 5010880), and the European project ABIOMMED: Support coherent and coordinated assessment of biodiversity and measures across Mediterranean for the next 6-year cycle of MSFD implementation, funded by DG Environment (11.0661/2020/839620/SUB/ENV.C2), coordinator Dr. Kalliopi Pagou, HCMR.

This report reviews the current situation as regards to the Marine Strategy Framework Directive (MSFD) Descriptor 1 (Biodiversity) for pelagic habitats and serves as a basis for a workshop with Member States experts and scientists that will be held on March 9-10 2021. Recommendations are in the concluding section. Pelagic habitats cover the 71% of Earth’s surface and play an essential role in regulating temperature on land, producing oxygen and food. They are also a management challenge where the alterations of their physical, chemical and biological characteristics negatively impact their ecosystem functioning and services (e.g. provisioning services). To address these challenges, the MSFD has required the assessment of pelagic habitats against environmental targets to reach Good Environmental Status (GES). A key step in the pelagic habitat assessment is a thorough understanding of its physical, chemical and biological processes and the drivers that underlie the spatiotemporal variability in its ecologically relevant ecosystem components. However, pelagic assessments to date have not sufficiently addressed the functional and structural characteristics of pelagic habitats processes, which is limiting our ability to inform on their environmental status and to disentangle the anthropogenic drivers. This report evaluates previously published work on pelagic habitats assessments considering the actions and targets to meet the MSFD requirements. To do this, the report (i) summarises the main drivers of variation in pelagic habitat characterization; (ii) reviews the common empirical approaches used to assess pelagic habitats, the advantages, and challenges; and finally (iii) exposes a set of recommendations for characterising pelagic habitats in EU waters. Since the pelagic habitats are made of a highly dynamic fluid, appropriate spatiotemporal scales regarding data and methods must be considered to assess their GES. This applies in particular to the selected indicators to propose the effective and quantifiable GES targets that need to be reached.