Condition of Benthic Habitat Communities: Assessment of Coastal Habitats in relation to Nutrient and/or Organic Enrichment

The biological quality elements required for the integrated assessment of ecological status (European Union Water Framework Directive (WFD), Annex V) of coastal waters are phytoplankton, macroalgae, angiosperms and benthic fauna (Solheim et al., 2012).

The WFD requires that standardised methods are used for monitoring biological quality elements, and that the good status class boundaries for each biological quality element are intercalibrated across Member States sharing similar types of water body.

The WFD requires that the overall ecological status of a water body is determined by the results for the biological or physicochemical quality element, with the worst class determined by any of the biological quality elements. This is called the ‘one out - all out’ principle. The rationale for this is to avoid averaging the impacts on different quality elements due to different pressures and therefore overlook some significant pressures, and also to provide sufficient protection for the most sensitive quality element to a significant pressure.

By definition, the WFD aims to assess ‘water quality’ of water bodies through quality elements such as benthic invertebrates or macroflora. Benthic habitat communities are thus mainly assessed for the WFD to reflect the main pressures in the coastal zone, such as direct or indirect effects of nutrient and / or organic enrichment as a result of nutrients inputs from land-based sources and through riverine inputs. Contaminants are generally assessed in sediment. For these reasons, WFD monitoring was generally designed to focus on the effects of nutrient and / or organic enrichment. This does not mean that the indices used are not in themselves sensitive to other pressure types. Currently several statistical indices that are used, notably those including a species sensitivity classification, have been developed and calibrated to assess nutrient and / or organic enrichment. The European Union Marine Strategy Framework Directive (MSFD) requires a reconsideration and adaptation of monitoring, to take into account and assess other pressure types (both inshore and offshore).

Diversity indices and species richness indices, as well as sensitivity / tolerance species classification systems, have long been used to assess the qualitative state of benthic habitat communities. The development of Benthic Indices (BI), combining these indices and classifications, was made mandatory by the WFD. Species composition and relative abundance of the benthic habitat community are basic common metrics. Multi-metric BI classically contains diversity indices, species richness indices and / or the proportions of sensitive, tolerant and opportunistic species. Species sensitivity is a proxy used to quantify disturbance for some pressures on a benthic habitat community: either as a direct or indirect effect of nutrient or organic enrichment, oxygen depletion, sand extraction or hydrological changes. This requires a good knowledge (for the communities and species assessed) of natural spatial and temporal scales of variation and sensitivity to a specific pressure gradient.

Multi-dimensional deviation in community structure from a reference condition, aims to link pressure (for management issues) and pressure-impact calibration of indices (level of disturbance / resilience). This is set up with various pressures types at the community level, by combining biological and pressure data. Analysis of sensitivity is then elaborated at community level rather than species level. This is an important distinction and a point of attention for further development by experts and implementation for management issues (i.e. specific parameters / metrics to be monitored).

The results of the assessment of Biological Quality Elements ‘Benthic Invertebrates’ and ‘Macroalgae and Angiosperms’ in coastal waters were requested through a data call to national contacts. Most of the status reports are from the second assessment cycle of the WFD (2010–2015), although assessment results for Ireland and Wales date from the first cycle (2009). Information was also requested on the indices used and the monitoring stations in coastal water bodies. Information on the methodology of the various benthic indices (sampling strategy, data evaluation, reference conditions, detected pressures) was mainly derived from the WISER (Water Bodies in Europe - integrative systems to assess ecological status and recovery) methods database and intercalibration reports (Birk et al., 2010; van Hoey et al., 2015). Detailed assessment methods and intercalibration exercise are available from the European Commission.

Guidelines for specific monitoring and assessment methods are described in Annex 2 of the CEMP guidelines (OSPAR, in prep.).

Birk S., Strackbein J. & D. Hering, D. (2010): WISER methods database. Version: March 2011. Available at http://www.wiser.eu/results/method-database/

OSPAR (in prep) BH2 CEMP guidelines for all references of generic and specific (BH2-A and BH2-B) monitoring and assessment methods

Solheim, A.L., Peterlin, M., Kodeš, V., Spiteri, C., Collins, R.P., et al. (2012). Ecological and chemical status and pressures in European Waters – Thematic assessment for EEA Water 2012 Report. EEA/NSV/10/002. 146p.

Van Hoey G., Bonne W. & Salas Herrero F. (2015): Intercalibration report for benthic invertebrate fauna of the North East Atlantic Geographical intercalibration group for Coastal Waters. (NEA 1/26), ILVO MEDEDELING 191.