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Condition of Benthic Habitat Communities: The Common Conceptual Approach

Assessing the condition of benthic habitat communities against all pressure types is a challenge. Current results are based on the "Margalef species diversity index" and "Assessment of some coastal habitats in relation to nutrient and/or organic enrichment". Only a few habitats and pressure types are included in these assessments, further development is needed.


Benthic habitats (Figure 1) are essential for marine life, because marine species rely directly or indirectly on the seafloor to feed, hide, rest or reproduce. Benthic habitats are characterised by animal and plant communities with no or slow mobility when compared to fish or marine mammals. The whole benthic community is therefore exposed when a pressure occurs. As a result, the condition (quality status) of benthic habitats reflects the combined effects of all the pressures to which they are subject.

The concept for a common approach for evaluating the condition of benthic habitats and their communities is presented. The application of this common approach has been endorsed by OSPAR for the Greater North Sea, Celtic Seas, and Bay of Biscay and Iberian Coast through the adoption of a Common Indicator. It has been recognised that to assess the impact of each human pressure on the condition of each benthic habitat type, along a pressure-impact gradient, requires specific assessment methodology and scales (Table 1). The aim is to inform management of human activities with as full an understanding as possible of the relative effects of different pressures on benthic habitats and their communities. For example, which habitats are affected, where, by how much and for how long.

OSPAR-wide assessments of benthic habitats are at a relatively recent stage of development and this concept will be further elaborated prior to the next OSPAR Quality Status Report and subsequent assessments.

Figure 1: Horse mussel beds (Modiolus modiolus) © Scottish Natural Heritage

Figure 1: Horse mussel beds (Modiolus modiolus) © Scottish Natural Heritage

Table 1: Relationships between habitat and pressure types, and how / if the relationships are currently assessed or considered. Relationships based on the revised EU Marine Strategy Framework Directive (MSFD) – Commission Decision (2017/848/EU), and OSPAR / MSFD pressure categories

Use of this common approach to evaluate the quality of benthic habitat communities, according to each pressure type along a pressure-impact gradient, has been endorsed for the Greater North Sea, Celtic Seas, and Bay of Biscay and Iberian Coast. Preliminary testing demonstrated that it is conceptually applicable to all habitat types but has only been applied to selected habitat types for the Intermediate Assessment (IA) 2017. Further testing is required to conclude on the relevance and performance of each metric and statistical index, depending on the habitat and pressure types assessed (Table 1).

The colours in the table matrix identify where a particular pressure versus habitat relationship is considered within European Union Directives. The ambition of this indicator is both to draw on existing assessments and to complement this material with new data and knowledge in order to provide better understanding of the overall condition of the benthic habitat community.

Biological and environmental data are quantitatively sampled (such as by grabs, cores, quadrat) at community scale (for example, at least at EUNIS Level 5 for sublittoral sand or infralittoral rocks). The EUNIS habitat classification is a system to classify types of habitat at several nested levels. The higher the level, the more detail and sub-types of habitat are included.

Table 1 identifies the main pressures, with the potential for widespread impacts, for each habitat type at EUNIS (European Nature Information System) Level 2 in the OSPAR Maritime Area. The broad pressure and habitat types (EUNIS Level 2) presented in Table 1 are summarised, however, to assess the condition of habitats versus pressures in the marine environment, relationships should be considered at a finer scale. Monitoring, assessment and reporting should be completed per pressure and habitat type. The cumulative effect of co-occurring pressures (different types of pressure at the same place and in the same time range) is not currently assessed.

This indicator aims to assess and quantify the relationship between state and pressure. The indicator requires the following types of data, at relevant and compatible spatial and temporal scales: biological data (community species abundance), environmental data (substrate and water characteristics), and pressure data (type, intensity, frequency).

Monitoring and assessment scale should be adapted depending on each habitat and pressure type, from the site scale (100 m) to regional assessment scale (100 km).

The technical principle underpinning this assessment is to detect and quantify the impact of a pressure by a deviation (of values of the computed statistical index) compared to (simultaneously assessed) reference stations (defined as under least-damage condition), per habitat type.

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), which combine the aforementioned indices and classifications, was made mandatory by the Water Framework Directive (WFD). Species composition and relative abundance of the benthic habitat community are basic common metrics. Multi-metric BI classically contain diversity indices, species richness indices and / or 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 and / 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.

In order to undertake an assessment to meet OSPAR and European Union Marine Strategy Framework Directive (MSFD) requirements, there are many gaps in knowledge of benthic habitats that require research, for example benthic habitat community and sensitivity classification for several habitats’ types and the characteristics of pressure types (for example, physical, contaminants and biological pressures).

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 pressure 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 collection of biological, environmental and (semi-) quantitative pressure data along a pressure gradient is a key step to calculate this metric and to validate the pressure-impact evaluation for an effective multi-metric index.

This common approach has the potential to assess a wide range of environmental aspects and provide more information by looking at them together, than could be gained from assessing each aspect individually.

Further framework development for this indicator (methods, monitoring, data flows) is needed to address all potential MSFD / OSPAR purposes. This indicator should include a necessary flexibility (both for metrics and indices) to consider the wide range of applications to different habitat types, to target offshore habitats and to assess sensitivity / tolerance to various pressure types.

Further sub-assessments (for example on contaminants and sediment extraction or dumping) are being developed outside the OSPAR works and are likely to be incorporated into future OSPAR assessments. Future assessments would then be combined as components of an ‘umbrella’ assessment to provide an overall view of the condition of benthic habitats in the North-East Atlantic.

The sub-assessment sheets will follow specific assessment methodology depending on the habitat and pressure types (for now ‘Condition of benthic habitat communities: assessment of some coastal habitats in relation to nutrient and/or organic enrichment’ and ‘Condition of Benthic Habitat Communities: Margalef diversity in region II (Greater North Sea)'). For the purposes of the QSR 2023, this assessment sheet sets out the proposed method for assessment of the indicator overall.

This indicator needs to be developed in close coordination with other benthic indicators, to ensure complementarity and avoid redundancies, that is, ‘typical species composition’, ‘physical disturbance of benthic habitats’ and other indicators that are still under development (such as ‘area of habitat loss’ and ‘size-frequency distribution of bivalve or other sensitive / indicator species’).

Guidelines for generic monitoring and assessment methods are described in the CEMP Guideline; including detailed technical specifications. These documents are regularly updated, according to the work conducted for the development, testing and implementation of this indicator. An applied research programme: The ecosystem approach to (sub) regional habitat assessments EcApRHA and NEA PANACEA projects were co-financed by the European Union and coordinated through OSPAR to address gaps in biodiversity indicator development. It has enabled the further development of several benthic indicators. In addition, these projects have also enabled links between indicators (methods, scales, monitoring and data requirements), including investigation of an integrated method for an overall assessment of benthic habitats, to be developed (Elliott et al., 2017a, 2017b, 2018).


Currently, only two conditions versus pressure interactions have sufficiently developed methodologies and data availability to undertake assessments in line with the common conceptual approach. These are ‘Condition of benthic habitat communities: assessment of some coastal habitats in relation to nutrient and/or organic enrichment’ and ‘ Condition of Benthic Habitat Communities: Margalef diversity in OSPAR Region II (Greater North Sea) '.

In the future, to have a better understanding of pressures on the seabed, the assessment of benthic habitats will include results from a range of assessments of specific pressures. Each set of results will differ depending on which pressure type (and thus, specific associated assessment scale) is considered. The cumulative effect of co-occurring pressures (different types of pressure at the same place and in the same time range) is not currently assessed. Further development will take place over the next assessment cycle (depending on progress in developing methods to integrate assessments and other indicators) to provide an overall understanding of the condition of benthic habitats in the North-East Atlantic.

Progress on developing cumulative effects assessment is also addressed under the benthic habitat thematic assessment.


Assessing the condition of benthic habitats against all pressure types within the OSPAR Maritime Area is a huge challenge for science and management. In only a few years, experts involved in Regional Seas Conventions have developed common approaches to assess the effects of each pressure type.

Currently two habitat pressure interactions have been assessed in line with the common conceptual approach, however work to develop assessment of other habitat and pressure types is promising. Further work is needed to address knowledge gaps, monitoring and data flow needs to ensure sufficient and adequate data for an effective region wide assessment. The added value of a common approach to assessing the condition of benthic habitat communities will be realised through its application in combination with other benthic indicators. This will provide fuller understanding of the extent of the effects of pressures on benthic habitats: i.e., which habitat is affected, where, by how much and for how long has it been impacted. More extensive data and the development of methods for assessments of additional pressure-habitat interactions should, in the future, provide clearer signals and identify clearer trends to inform management needs.

Knowledge Gaps

More benthic monitoring (Figure 2) and further methodological development is required to provide relevant data, adapt, operationalise and implement coherently this common conceptual approach for all pressure and habitat types. Although promising, this indicator requires more development and testing to be fully operational for all OSPAR and MSFD purposes for the next assessment. An action plan (Padegimas et al., 2017) to address some of these knowledge gaps has been adopted as a result of the OSPAR EcApRHA project, completed through NEA PANACEA project deliverables, to be included in the updated OSPAR Science Agenda.

Figure 2: Coastal survey and sampling equipment for benthic habitat monitoring

Figure 2: Coastal survey and sampling equipment for benthic habitat monitoring

Elliott, S.A.M., Guérin, L., Pesch, R., Schmitt, P., Meakins, B., Vina-Herbon, C., González-Irusta, J.M., de la Torriente, A., Serrano, A., 2018. Integrating benthic habitat indicators: Working towards an ecosystem approach. Marine Policy 90, 88-94.

Elliott, S.A.M., Arroyo, A.L., Safi, G., Ostle, C., Guérin, L., McQuatters-Gollop, A., Aubert, A., Artigas, F., Pesch, R., Schmitt, P., Vina-Herbon, C., Meakins, B., González-Irusta, J.M., Preciado, I., López-López, L., Punzón, A., de la Torriente, A., Serrano, A., Haraldsson, M., Capuzzo, E., Claquin, P., Kromkamp, J., Niquil, N., Judd, A., Padegimas, B., Corcoran, E., 2017b. Proposed approaches for indicator integration. EcApRHA deliverable WP4.1, ISBN: 978-1-911458-29-6.

Elliott, S.A.M., Guérin, L., Pesch, R., Schmitt, P., Meakins, B., Vina-Herbon, C., González-Irusta, J.M., de la Torriente, A., Serrano, A., 2017a. Applying a risk-based approach towards an integrated assessment of benthic habitat communities at a regional sea scale. EcApRHA deliverable WP4.1, ISBN: 978-1-911458-25-8.

Padegimas B., F. Artigas, N.L. Arroyo, A. Aubert, A. Budria, E. Capuzzo, E. Corcoran, S. A. M. Elliott, J. M., González-Irusta, L. Guérin, A. Judd, J., Kromkamp, 2017. Action Plan for the further implementation of habitat and food web indicators and progressing integrated assessments in OSPAR (sub) regions. EcApRHA deliverable WP5.6, ISBN: 978-1-911458-30-2.


Lead Authors: Laurent Guérin and Anna Lizińska 

Supporting Authors: Petra Schmitt, Sander Wijnhoven

Supported by: OSPAR Benthic Habitat Expert Group (OBHEG), Intersessional Correspondence Group on the Coordination of Biodiversity Assessment and Monitoring (ICG-COBAM), OSPAR Biodiversity Committee (BDC)


Guérin, L., Lizińska A., Schmitt P. and Wijnhoven, S. 2023. Condition of Benthic Habitat Communities – The Common Conceptual Approach. In: OSPAR, 2023: The 2023 Quality Status Report for the North-East Atlantic. OSPAR Commission, London.. Available at:

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