Condition of Benthic Habitat Communities: the Common Conceptual Approach

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 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 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 take into account 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 (on contaminants and sediment extraction or dumping) are being developed outside the IA 2017, 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 (for example ‘ Condition of Benthic Habitat Communities: Subtidal Habitats of the Southern North Sea ') will follow specific assessment methodology depending on the habitat and pressure types. For the purposes of the IA 2017, 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 damage of predominant and special 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 currently being developed and will be described in the CEMP guidelines (OSPAR, in prep.), which will include detailed technical specifications. This section will be updated in 2018 to reflect these changes.

Technical specification of all common OSPAR benthic habitat indicators and detailed methods and testing results will be described in OSPAR CEMP Guidelines (OSPAR, in prep.). 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  project was a co-financed European Union project coordinated by OSPAR to address gaps in biodiversity indicator development. It has enabled the further development of this indicator. In addition the EcApRHA project has enabled links between indicators (methods, scales, monitoring and data requirements), including investigation of an integrated method for an overall assessment of benthic habitat, to be developed.