Subtidal habitats

The results of this trial assessment demonstrated changes to the diversity of the benthic communities in relation to fishing pressure, particularly in coastal waters of the Southern North Sea. However, there was insufficient data to estimate whether the associated UK target had been achieved.

Background

UK target on condition of benthic communities

This indicator aims to assess progress against the following qualitative target set for predominant seafloor habitats in the Marine Strategy Part One (HM Government, 2012): the level of exposure to pressure at the level of the Marine Strategy Framework Directive sub-regions should not result in more than Moderate Impact/vulnerability of the habitat (dependent on the sensitivity of the habitat to this pressure).

Key pressures and impacts

The main pressures on benthic habitat and community condition are disturbance of the seabed and extraction of species by fisheries, nutrient and organic enrichment, sedimentation (for example, from dumping of dredged material or extraction of aggregates) and contaminants. The indicator primarily addresses fishing pressure.

Measures taken to address the impacts

Measures to protect benthic communities are set out in the UK Marine Strategy Part Three (HM Government, 2015). Measures include: the Common Fisheries Policy, Marine Spatial Planning, OSPAR recommendations to protect OSPAR Threatened and Declining habitats, and the establishment of an ecologically coherent network of Marine Protected Areas.

Monitoring, assessment and regional co-operation

Areas that have been assessed

The assessment was limited to the southern sub-region of the Greater North Sea and included the waters of Belgium, Denmark, Germany, the Netherlands and the United Kingdom (Figure 1).

Figure 1. The Southern North Sea encompasses the waters of the United Kingdom, Belgium, the Netherlands, Germany, and Denmark. The blue symbols indicate the benthos monitoring samples.

Monitoring and assessment methods

Species richness and abundance are used to calculate a diversity index. This index is used to assess the quality of benthic communities under different levels of fishing pressure. Changes in diversity alongside fisheries pressure gradients are evaluated against reference values. The approach is built upon 15 years of international Water Framework Directive marine benthos experience. Infaunal data collected using grab and box core sampling from monitoring programmes for the period 2010 to 2015 have been used for these analyses. However, a full quantitative assessment of the Marine Strategy Framework Directive sub-region was not possible at this stage due to data limitations and early stages of indicator development. In the future, we expect this condition indicator to be used to calibrate and ground truth modelled based indicators, in particular, the extent of physical damage to predominant and special habitats indicator

Assessment thresholds

No assessment thresholds have been applied due to the early stages of development of this indicator.

Regional co-operation

The UK has participated in this assessment for this OSPAR sub-region of the Greater North Sea, and the UK results are being used in the Intermediate Assessment 2017 (OSPAR Commission, 2017)

Results

Findings from the 2012 UK Initial Assessment

In 2012, a method using expert judgement found that the spatial extent of damage from bottom fisheries was considered to outweigh contributions from other sources of damage to the seabed (HM Government, 2012).

Latest findings

Status Assessment

For all assessment areas, the diversity value showed significant changes in relation to fishing pressures (Figure 2). It should be noted that data transformation was required due to the wide variations in the sources of data available. Furthermore, the lack of suitable data for this analysis in UK waters means that a full assessment was not possible.

Figure 2. Relation between the fisheries pressure (subsurface) and the normalized Margalef diversity value, as demonstrated using all available benthos data in the Southern North Sea showing that the benthic community condition decreases (lower normalized Margalef index value) when the fisheries pressure increases.

The initial results show that the shallow coastal areas of Belgium, Germany, and the Netherlands, have a relatively lower condition compared to deeper offshore areas. Several UK areas showed a relatively high benthic condition, although the results have a low confidence as reference conditions for those offshore areas will need to be refined.

Trend Assessment

Unknown: The indicator was not considered as part of the 2012 Initial Assessment.

Conclusions

The UK target has not been applied due to data limitations within the Marine Strategy Framework Directive sub-region.

The selected diversity index assessed the benthic community quality for a range of assessment areas in the Southern North Sea and showed clear differences between different assessment areas. Coastal areas usually showed lower benthic quality.

This is the first time that a diversity index to assess changes in benthic communities has been applied on such a broad geographical scale. The UK target was not applied due to data limitations within the Marine Strategy Framework Directive sub-region, but it may apply to other UK regions in the next assessment cycle.

Knowledge gaps

The main knowledge gaps are:

the lack of reference values for environmental variables needed to assess benthic community and habitat condition
the influence of associated pressures such as nutrient enrichment, sedimentation, and heavy metals, particularly in offshore waters.

References

HM Government (2012) ‘Marine Strategy Part One: UK Initial Assessment and Good Environmental Status’ (viewed on 5 July 2018)

HM Government (2015) ‘Marine Strategy Part Three: UK Programme of Measures’ December 2015 (viewed on 5 July 2018)

OSPAR Commission (2017) ‘Intermediate Assessment 2017' Condition of Benthic Habitat Communities: Subtidal Habitats of the Southern North Sea’ (viewed on 16 January 2019)

Acknowledgements

Assessment Metadata

Please contact marinestrategy@defra.gov.uk for metadata information

Recommended reference for this indicator assessment

Phillips, G.¹, McGruer, K.¹, Crook, D.², Doria, L.³, Herbon, C.³, Khan, J.⁴, Mackie, T.⁵, O’Reilly, M.⁴, Singleton, G.³ & Young, C.⁵ 2018. Condition of soft sediment invertebrate communities in coastal waters determined using Water Framework Directive methods*. Marine Online Assessment Tool, available at: https://moat.cefas.co.uk/biodiversity-food-webs-and-marine-protected-areas/benthic-habitats/subtidal-habitats/

*Adapted from OSPAR Intermediate Assessment 2017 on Subtidal Habitats of the Southern North Sea

¹Environment Agency

²Natural Resources Wales

³Joint Nature Conservation Committee

⁴Scottish Environment Protection Agency

⁵Department of Environment, Agriculture & Rural Affairs, Northern Ireland