Condition of Benthic Habitat Communities: the Common Conceptual Approach

D1 - Biological Diversity

D5 - Eutrophication

D6 - Seafloor Integrity

D1.6 - Habitat condition

D5.3 - Indirect effects of nutrient enrichment

D6.2 - Condition of benthic community

Benthic habitats are essential for marine life. Assessing their condition against all pressure types is a huge new challenge for science and management. Initial assessment results are available for two pressure types. Further development of this common approach will integrate assessment results and include additional habitat types and pressures.

Area assessed

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Background

Benthic habitats 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 is a reflection of the combined effects of all the pressures to which they are subject.

This study presents the concept for a common approach for evaluating the condition of benthic habitats and their communities. 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 an early stage of development and this concept will be further elaborated prior to the next OSPAR Quality Status Report and subsequent assessments.

Key
A Assessed and reported under the European Union Water Framework Directive (WFD)
Considered under the European Union Marine Strategy Framework Directive (MSFD)
P Partially assessed in the Intermediate Assessment 2017
Main risks (potentially widespread across the OSPAR Maritime Area)
Relationship identified but not currently assessed

Benthic Habitat (courtesy of Scottish Natural Heritage)

Table 1: Relationships between habitat and pressure types, and how / if the relationships are currently assessed or considered Relationships of broad habitat types, based on the revised EU Marine Strategy Framework Directive (MSFD) – Commission Decision (2017/848/EU), and OSPAR / MSFD pressure categories.
Broad Habitat Type Broad Pressure Type
Physical damage Removal of species Hydrological changes Eutrophication (nutrients or organic matter) Non-indigenous species Contaminants Litter Energy, including underwater noise
Littoral rock and biogenic reef A
Littoral sediment A
Infralittoral rock and biogenic reef A
Infralittoral sediment P A
Circalittoral rock and biogenic reef A
Circalittoral sediment P A
Offshore circalittoral rock and biogenic reef
Offshore circalittoral sediment P P P
Upper bathyal rock and biogenic reef
Upper bathyal sediment
Lower bathyal rock and biogenic reef
Lower bathyal sediment
Abyssal

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.

Results

For the Intermediate Assessment (IA) 2017 only two condition versus pressure interactions have sufficiently developed methodologies and data availability to undertake assessments in the line with the common conceptual approach. These are coastal habitats in relation to nutrient and / or organic enrichment and species diversity in subtidal sediments in the Southern North Sea versus abrasion (by bottom trawling fisheries). 

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 Ecosystem Assessment Outlook.

 

Conclusion

Assessing the condition of benthic habitats against all pressure types within the OSPAR Maritime Area is a huge new 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.

This indicator will require further development for the next assessment cycle, to include additional condition versus pressure relationships (for all OSPAR and European Union Marine Strategy Framework Directive (MSFD) purposes). An action plan to achieve this is summarised and referred in the knowledge gaps (extended) section and in EcApRHA action plan.

Application to Arctic Waters and the Wider Atlantic seems conceptually possible and feasibility could be further tested if relevant datasets are made available.

Depending on prioritisation of habitat / pressure types to be assessed in each sea area, and available resources and monitoring (and pressure data), this indicator could be progressively implemented towards its full potential.

This indicator does not aim to cover spatially all geographical areas of a sub-region, which would imply high monitoring costs. For a wide sub-regional scale assessment, this indicator will have to be used in combination with the indicator Extent of Physical Damage to Predominant and Special Habitats. The results from this assessment could be used to better design (and increase efficiencies) in monitoring. Furthermore, the application of a ‘risk-based’ approach allows for cost-efficiencies, through ground-truthing and quantifying potential impacts, which can then be extrapolated to the assessment of wide-scale disturbances.

The detailed technical method to combine these Indicators, for an integrated assessment, is still under development (refer to knowledge gaps, extended section) but the principle is to use this indicator to calibrate (quantify) the state / pressure relationship used in matrices for large-scale assessment, for each habitat and pressure type. For this assessment cycle, the effect of co-occurring pressures is not assessed, because the effect of each pressure type has to be understood before studying multiple effects. By considering numerous pressure types, the impacts from individual pressures are more difficult to distinguish and thus the implementation of adequate management measures is challenging. Partitioning individual pressures per habitat type enables the identification and exploration of individual threats to specific habitat types, and for targeted management to be implemented where required.

Knowledge Gaps

Further methodological development is required to 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 to address some of these knowledge gaps has been adopted as a result of the OSPAR EcApRHA project.

The need for further method development, and the lack of adequate data or access to existing data (biological, environmental, pressure), compromise the establishment of clear and accurate state-pressure relationships, and thus the possibility to define accurate assessment values at the OSPAR scale. However, such an assessment could be undertaken in those areas where there is sufficient data. The lack of data is due to both lack of appropriate monitoring (for example, for offshore habitats) and barriers to data flows.

Barriers and Gaps

Method Development

Baseline data (‘reference’ with low or least disturbance) are lacking at the OSPAR scale for many habitats exposed to abrasion by bottom-trawling fisheries. This compromises our ability to identify a sustainable condition for those habitats, which are under continuously high pressure levels. ‘Pristine’ baselines (no disturbance) are lacking for most of the habitats; this compromises our knowledge of the potential best condition of natural habitat communities. It is not practical or feasible to use this pristine state as an environmental target everywhere, but it is useful for understanding the natural dynamic and recovery potential of a given habitat. Increasing the establishment and management of Marine Protected Areas (including Marine Natura 2000 sites), notably including ‘no take or low pressure areas’ could help provide data in the future, for the relevant habitat types.

Cumulative Effects

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. According to the actual gaps in knowledge on benthic habitat communities, it will be necessary to first understand and quantify the effects of each pressure type, where data are available, before investigating and understanding the effects of cumulative pressures (such as whether they are synergistic or antagonistic). This is an important requirement because many habitats are exposed to multiple pressures. Monitoring of benthic habitats exposed to cumulative pressures, where management measures aim progressively for a more sustainable use, even for one pressure type, would help to better understand this in the future.

Data Use and Availability

Many potentially relevant data exist but are not all available (e.g. fishing pressure data at fine spatial resolution, or biological data from marine research and marine industry).

Many biological datasets exist, but few have associated data on pressure at a compatible spatial and temporal scale.

Most OSPAR Contracting Parties undertake large-scale marine benthic monitoring (at least for the European Union Water Framework Directive). Finer scale networks of state-pressure relationship assessment areas are more heterogeneous and should be further investigated. Developing coordinated monitoring – or better still, joint monitoring – would be more cost-efficient and would ensure coherence and robustness for an assessment at a sub-regional scale.

Each country currently stores its own monitoring data, so common methodology (and tools) still needs to be developed. The need for this should be anticipated and relevant work should be coordinated at a sub-regional scale to ensure coherence and facilitate the computation of data for indicator assessment.

Cost-effectiveness

This common approach is an ‘umbrella’ for several sub-assessments. It is based on existing and anticipated monitoring requirements (for OSPAR, the European Union Marine Strategy Framework Directive (MSFD), other European Directives, and the Common Fisheries Policy) and will therefore be cost-efficient if coordinated.

Further Development and Roadmap

The indicators for ‘Condition of Benthic Habitat Communities’ and ‘Extent of Physical Damage to Predominant and Special Habitats, are the only OSPAR-wide commonly agreed benthic habitat indicators. A regional (wide-scale) monitoring strategy and technical guidance are partly in place and implemented for some coastal habitats and for nutrient input pressure (European Union Water Framework Directive (WFD)). This monitoring strategy should be further coordinated, extended offshore and adapted for (finer-scale) assessment areas, to progressively take into account and assess effects of other types of pressure on each benthic habitat type. As geographical (nested) scales are identified, assessment methods would be progressively adapted and described.

An action plan identifying gaps, barriers and solutions to further develop OSPAR benthic indicators, and an integrated assessment for the next assessment cycle, is available in EcApRHA(ecosystem approach to (sub) regional habitat assessments) research programme deliverables.

In future assessments, consideration could be given to applying this common approach to other habitat types, such as those listed in the European Union Habitats Directive, and on OSPAR’s List of Threatened and/or Declining Species and Habitats (OSPAR Agreement 2008-06).