Condition of intertidal seagrass communities in coastal waters determined using Water Environment Regulations methods.
The targets covering the condition of intertidal seagrass communities have been achieved in the Celtic Seas and Greater North Sea UK Marine Strategy sub-regions, although the target was not achieved in one of the constituent Regional Seas: Eastern English Channel. Data coverage is limited and there is low confidence in the assessment results.
Background
UK Target on intertidal seagrass quality
This indicator is used to assess progress against the Water Environment Regulations (WER) ecological status boundaries and areas of unacceptable impact, which are components of the sediment habitats targets, set in the UK Marine Strategy Part One (Defra, 2019).
Key pressures and impacts
The WER seagrass indicator is designed primarily to detect impacts from hydromorphological pressures arising from activities such as sediment transport, navigation, and flood protection, and to a lesser extent, increased nutrient concentrations (eutrophication).
Risk assessment information used in the UKMS assessments was derived by the UK WER monitoring authorities to support the Cycle One River Basin Management Plan (RBMP) classifications by identifying pressures considered likely to cause water bodies to fail to achieve their WER environmental objectives. These identified 83 of the 467 coastal water bodies as ‘At risk’ or ‘Probably at risk’ of failing to meet their objectives due to hydromorphological pressures.
Measures taken to address the impacts
Measures to protect benthic habitats are set out in the UK Marine Strategy Part Three. These include those related to the Habitats Regulations, WER River Basin Management Plans, Urban Wastewater Treatment Regulations, Nitrate Pollution Prevention Regulations, OSPAR measures on species and habitats, Marine Spatial Planning, land management schemes, catchment sensitive farming and European Marine Site management schemes.
Monitoring, assessment and regional cooperation
Areas that have been assessed
Progress against the UK target was assessed for the Celtic Seas and the Greater North Sea UK Marine Strategy sub-regions and their constituent UK Regional Seas set out in Charting Progress 2 (CP2) (UKMMAS, 2010). These areas were assessed in the 2018 UK Marine Strategy assessments.
Monitoring and assessment methods
Routine monitoring of intertidal seagrass is undertaken using methods developed under the WER. The intertidal seagrass tool is a multi-metric index based on seagrass bed extent loss, annual/five-yearly average shoot density loss and species loss as a proportion of a historic reference which are combined to derive an Ecological Quality Ratio (EQR).
Assessment thresholds
The indicator quality threshold is defined as the boundary for WER Good Ecological Status (EQR ≥0.60) or Good Ecological Potential (for Heavily Modified Water Bodies (HMWBs)). The UK Marine Strategy assessment target is met where the assessed surface area achieving the quality threshold meets the extent threshold of 95%.
Regional cooperation
WER seagrass indicator assessments are included within OSPAR Quality Status Report benthic habitat community condition assessments. WER ecological status boundaries were set through Intercalibration with Member States of the North-East Atlantic Geographical Intercalibration Group (NEAGIG).
Further information
The Water Environment Regulations intertidal seagrass tool is a multi-metric indicator derived from the following measurements of the seagrass communities within a water body:
Taxonomic composition: This compares the number of observed species with the number of historically recorded species. In the UK we recognise the seagrasses Zostera noltii, Zostera marina and Zostera angustifolia (the latter is regarded as an intertidal version of Z. marina but treated as a separate taxon for WFD), plus widgeon grass Ruppia spp. As Ruppia spp are very difficult to identify, we only identify Ruppia to genus level. This gives a total of 4 possible taxa.
Shoot density/% cover loss: This is the estimated percentage cover of seagrass in the survey area relative to the historic percentage cover of that site.
Spatial extent change: This is the percentage loss or gain of the total area of the seagrass beds in the waterbody. A stressed waterbody would exhibit a decrease in seagrass bed size, shoot density and the number of species. This decline allows space for other more tolerant species (such as opportunistic macroalgae) to grow. Opportunistic macroalgae can then dominate the area leading to the die-back of the seagrass bed. An undisturbed seagrass bed will be healthy & dense with no loss of historic indicator species. Beds should maintain their size or grow, though we must take natural variation into account. The changes in these measurements from a reference year are recorded. For baseline data no rolling mean can be calculated.
Values of taxonomic composition, shoot density/percent cover loss and change in spatial extent were calculated to determine what these would be for undisturbed waters (reference conditions). The observed results are then compared with the reference condition values and combined to calculate the Ecological Quality Ratio (EQR) which operates between zero and one. EQR values close to one indicate angiosperm communities are close to their natural state; those near to zero indicate a high level of pollution or disturbance. The EQR is used to categorise the water body into one of the five Ecological Quality Status classes as required by the WER:
High status: ≥ 0.8
Good status: 0.6 ≤ 0.8
Moderate status: 0.4 ≤ 0.6
Poor status: 0.2 ≤ 0.4
Bad status: <0.2
Further details on the WER intertidal seagrass tool are available at the WER UK Technical Advisory Group (UKTAG) website:
Assessment method
Baseline setting
The WER seagrass indicator reference conditions have been used for the UK Marine Strategy baseline. Reference conditions are based on i) the maximum number of recorded taxa under total seagrass bed extent reference conditions ii) the greatest seagrass bed extent recorded within the WFD Cycle One RBMPs (or expert judgment if appropriate) and iii) the maximum seagrass shoot density recorded within the WFD Cycle One RBMPs. This complies with the approaches to setting baselines for UK Marine Strategy as outlined by the Intersessional Correspondence Group on Biodiversity Assessment and Monitoring (ICG COBAM) (OSPAR Commission, 2012) as:
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a state in which the anthropogenic influences on species and habitats are considered to be negligible.
-
a state in the past, based on a time-series dataset for a specific species or habitat, selecting the period in the dataset which is considered to reflect least impacted conditions.
Quality and extent targets
The target of Good Ecological Status or Good Ecological Potential (where mitigation measures against the modification features are considered sufficient for HMWBs) as defined for the WER is being applied as the indicator quality threshold for the UK Marine Strategy assessments. The extent target is met where ≥95% of the surface area of the assessed intertidal seagrass communities within a Regional Sea meet the quality threshold. Seagrass beds are priority habitats within the UK Biodiversity Action Plan (BAP), so this target conforms to those relating to the assessed surface area achieving an acceptable condition recommended by WFD-UKTAG (2007) for High Ecological Status and the Habitats Regulations target for Favourable Condition.
This may be reviewed and revised in future assessment cycles.
Aggregation approach
The approach to aggregating the WER water body classifications to UK Regional Sea assessments is shown below. Please note: UK Marine Strategy assessments are based on the data and processes used for the WER water body classifications within the 2021 Cycle Three River Basin Management Plan (RBMP) assessments and exclude changes to the classifications as a result of subsequent investigations.
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Seagrass WER classification results for coastal water bodies from the 2021 Cycle Three RBMPs were collated at the survey level from the UK WER monitoring authorities. The percentage cover of assessed seagrass beds at each WER ecological status class were calculated within each Regional Sea. The assessments use data derived WER classification results for use in the WER Cycle Three RBMP and exclude those rolled forwards from previous classifications.
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Seagrass beds categorised as ‘Bad’, ‘Poor’ or ‘Moderate’ ecological status under WER were categorised as being below the indicator quality target, with those at ‘Good’ or ‘High’ ecological status categorised as being above the indicator quality target.
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The final UK Regional Sea assessment is calculated as the total extent of seagrass beds within all classified water bodies which meets the indicator quality target as a percentage of the maximum recorded seagrass bed extent (based on either historic or recent data). The overall indicator target is achieved when the extent of classified seagrass meeting the quality target is 95% of all classified intertidal seagrass beds within a Regional Sea.
Please note: the method for setting the seagrass indicator baseline has been updated from the use of the historical seagrass bed extent in the 2018 assessments to the use of the maximum recorded seagrass bed extent in the current assessment.
Confidence assessment
The approach to determining confidence in the Regional Sea assessments is based on the extent to which the indicator and associated assessments fulfil certain criteria which impact the extent to which the assessment represents the available habitat relevant to the indicator, the extent to which the indicator can identify the overall effect of the relevant pressures and the confidence in the assessment result being above/below the indicator target. The confidence assessment method was developed for the 2018 Marine Strategy assessments. Confidence thresholds were arbitrarily set based on an equal division of the range of values for each criterion. Details of the criteria are provided in Table 1.
Table 1: Confidence assessment criteria for the UK Regional Sea WER intertidal seagrass indicator assessments.
|
CP2 Regional Sea confidence assessment criteria |
Low |
Medium |
High |
|
Spatial coverage of classification data
This criterion indicates the extent to which WER water bodies within a Regional Sea are classified by the indicator. High proportion of water bodies classified within a Regional Sea corresponds to high confidence in the UK Marine Strategy assessment. |
<33.3% of WER water bodies assessed |
33.3% - 66.6% of water bodies assessed |
>66.6% of water bodies assessed |
|
Spatial coverage of pressures
This criterion provides a measure of the extent to which the classified WER water bodies correspond to the presence of relevant pressures (as determined through the WER risk assessments), indicating the potential of the WER classifications to detect the associated impacts of such pressures. High coverage of the areas exposed to pressure (i.e. those considered at risk of failing to achieve GES under WER) by the WER water body classifications corresponds to high confidence within the Regional Sea scale Marine Strategy assessment. |
<33.3% of At Risk/Probably At Risk water bodies (WBs) assessed |
33.3% - 66.6% of At Risk/Probably At Risk WBs assessed |
>66.6% of At Risk/Probably At Risk WBs assessed |
|
Indicator level agreement (Cohen's Kappa) between assessment results and pressure from Risk Assessments
Cohen’s Kappa agreement provides an indication of the extent to which the indicator WER classifications correspond to the risk assessments at the water body level. Agreement between water bodies categorised as ‘At Risk’ or ’Probably At Risk’ and those at less than Good Ecological Status is calculated using all water body data. High confidence in the UK Marine Strategy assessments corresponds to high agreement between the indicator classifications and risk assessment results. Low correspondence may be indicative of either low sensitivity of the indicator to the pressure or indicative of a low correspondence between the risk assessment results and the true extent of the pressure (further investigation recommended). |
<0.333 |
0.333 - 0.666 |
>0.666 |
|
Variability of assessment results
This criterion is a measure of the variability of the different WER water body classifications within a Regional Sea scale UK Marine Strategy assessment. Low variability in the WER classifications corresponds with high confidence in the assessment. |
<66.6% of assessment units (seagrass bed extent) within same WER status |
66.6% - 83.3% of assessment unit (seagrass bed extent) at same status |
>83.3% of assessment units (seagrass bed extent) at same status |
|
Proximity of observed extent to extent threshold
This criterion is a measure of the magnitude of the difference between the observed extent meeting the quality target and the extent threshold. Large differences between the observed extent meeting the quality target and the extent threshold corresponds to high confidence in the UK Regional Sea scale UK Marine Strategy assessment. |
BAP Priority habitats: assessment within 1.66% of target |
BAP Priority habitats: assessment within 1.66% - 3.33% of target |
BAP Priority habitats: assessment >3.33% of target |
The overall confidence assessment is based on the lowest extent to which the criteria are fulfilled (one-out-all-out).
Deviations by WER Monitoring Authorities
Seagrass data were collected for use in the WER Cycle Three RBMP classifications by the Department of Agriculture, Environment and Rural Affairs (DAERA) of Northern Ireland, the Environment Agency (EA) of England and Natural Resources Wales (NRW) only. All monitoring authorities applied the assessment methods as described within the UKTAG method statement.
Results
Results and assessment of progress
Latest findings
Status assessment
Assessments are based on aggregated coastal water body classifications derived for the 2021 Cycle Three UK RBMPs. The results of the aggregated intertidal seagrass indicator assessment for the UK Marine Strategy sub-regions and Regional Seas are presented in Table 2 and Figure 1.
Table 2: Proportion of total assessed seagrass bed extent meeting the indicator quality threshold with corresponding assessment result and confidence for each UK Regional Sea and corresponding Marine Strategy sub-region summary.
| UK MS sub-region | Extent meeting quality threshold (EQR ≥ 0.6) | Extent threshold met (≥ 05%) | Assessment summary | Regional Sea | Extent meeting quality threshold (EQR ≥0.6) | Extent threshold met (≥ 95%) | Confidence |
| Greater North Sea | 98.8 % | ✅ | Target met for the sub-region (low confidence). | 1. Northern North Sea* | 100.0 % | ✅ | Low |
| 2. Southern North Sea | No Data | - | - | ||||
| 3. Eastern English Channel | 86.7 % | ❌ | Low | ||||
| Celtic Sea | 97.9 % | ✅ | Target met for the sub-region (low confidence). | 4. Western Channel and Celtic Seas | 97.2 % | ✅ | Low |
| 5. Irish Sea | 98.2 % | - | Low | ||||
| 6. Minches and Western Scotland | No data | - | - | ||||
| 7. Scottish Continental Shelf | No data | - | - | ||||
| 8. Atlantic North-West Approaches, Rockall Trough and Faeroe/Shetland Channel | Suitable habitat absent | - | - | ||||
| 9. Shared waters between N Ireland and Rep of Ireland | 100.0 % | ✅ | Low |
The indicator target has been met for both UK Marine Strategy sub-regions and all constituent Regional Seas, with the quality threshold having been met for the majority of the contributing water bodies. This indicates that the activities which might cause impact to intertidal seagrass communities may be operating at a level which are not causing a deleterious effect. Four Regional Seas have not been assessed due to either an absence of intertidal habitat which is required by the indicator or an absence of existing WER classification data. The natural conditions required for seagrass beds to exist limits their occurrence in coastal water bodies.
The confidence for WER intertidal seagrass indicator assessments has been categorised as low for all assessments, primarily due to low spatial coverage of the WER assessment results, and low coverage of water bodies categorised as being ‘At Risk’ or ‘Probably At Risk’ from diffuse source pollution and morphological alteration pressures from the WER Risk Assessments that were classified under WER. Agreement between intertidal seagrass assessment results and risk assessment results is low, potentially indicating either a low correlation between the indicator to morphological alteration/diffuse source pollution pressures (either due to variability in the indicator or the criteria used for the risk assessments) or a discrepancy between the threshold required to trigger a water body being categorised as ‘At Risk’ or ‘Probably At Risk’ and the indicator quality target threshold.
Findings from the 2012 and 2018 UK assessments
This indicator was not considered as part of the 2012 Initial Assessment. The 2018 UK assessment concluded that the targets covering the area of intertidal seagrass communities at an acceptable condition had largely been achieved in both the Greater North Sea and Celtic Seas UK Marine Strategy sub-regions. The assessment results were assigned low confidence.
The detailed 2018 assessment is available via the UK Marine Monitoring & Assessment Strategy (UKMMAS) Marine Online Assessment Tool:
Trend assessment
The aggregated WER intertidal seagrass results were not considered as part of the 2012 Initial Assessment.
The intertidal seagrass assessment results remain unchanged between the 2018 and current assessment for the Celtic Sea and Greater North Sea sub-regions, with the indicator target continuing to likely be achieved. Results remain the same for all regional seas except the Eastern English Channel which now fails to achieve the extent threshold due to an update in the indicator baseline setting methodology. The assigned confidence remains low for both sub-regions and all Regional Seas between the two assessments. Data availability has increased, with the number of water body assessments increasing from eight in the 2018 assessments to 12 in the current assessments.
Figure 1: UK Regional Seas with corresponding assessment results indicating locations of coastal water bodies used for RBMP Cycle Three WER intertidal seagrass classifications with corresponding ecological status.
Further information
The assessment is based on aggregated results from the classifications derived for the UK Cycle Three RBMPs. The method is based on the intertidal seagrass assemblages and considered responsive to hydromorphological and nutrient enrichment pressures from inshore activities.
The indicator determines the impact on the ecological quality of seagrass communities of intertidal habitats by combining measures of seagrass bed extent loss, annual/five-yearly average shoot density loss, and species loss as a proportion of a historic reference. The average of the three metrics is combined within an Ecological Quality Ratio (EQR). Metrics are calculated at the level of the WER water body using data collected within a six-year period. The water body assessments indicate the extent to which the entire intertidal seagrass community deviates from reference conditions and relates this to the boundary between Moderate and Good Ecological Status to identify whether the water body has achieved the target of Good Ecological Status. The extent target is met where ≥95% (priority habitat threshold) of the assessed surface area meets the quality target of Good or High Ecological Status or Good Ecological Potential.
A summary of the data used for each UK Marine Strategy sub-region and Regional Sea WER seagrass indicator assessment is provided in Table 3. Individual WER water body information with associated Third Cycle RBMP seagrass classification results is provided in Table 4.
Table 3: Summary of the data used for the UK Marine Strategy WER seagrass indicator Regional Sea assessments.
|
Regional Sea |
Regional Sea |
Total area (sq km) |
RS Total WB area (sq km) |
Assessed WB Count |
Assessed WB Area (Km2) |
Assessed Area (% of total) |
Assessed HMWBs |
Assessed 'At Risk' WER WBs (Morph) |
Assessed 'At Risk' WER WBs (Diffuse) |
|
Greater North Sea |
1. Northern North Sea |
181,551.6 |
8,164.8 |
1 |
30.4 |
0.4 |
0 |
0 |
1 |
|
Greater North Sea |
3. Eastern English Channel |
21,970.8 |
1,903.5 |
2 |
284 |
14.9 |
1 |
2 |
2 |
|
Celtic Sea |
4. Western Channel and Celtic Seas |
93,959.8 |
5,086.4 |
3 |
130.6 |
2.6 |
0 |
2 |
2 |
|
Celtic Sea |
5. Irish Sea |
38,647.4 |
10,014.0 |
4 |
418 |
4.2 |
1 |
4 |
3 |
|
Celtic Sea |
9. Shared waters between N Ireland and Rep of Ireland |
353.5 |
271.7 |
2 |
211 |
77.7 |
0 |
2 |
2 |
Table 4: Summary of WER water body pressure information and WER seagrass tool classification results aggregated to the Regional Sea UK Marine Strategy assessments.
|
Regional Sea |
Agency |
Water body name |
HMWB |
At Risk/ Probably At Risk from Diffuse Source Pollution pressure |
At Risk/ Probably At Risk from Morphological alteration pressures |
Seagrass Baseline Extent (Ha) |
Seagrass Current Extent (Ha) |
Water body EQR |
WER status |
|
1. Northern North Sea |
EA |
Holy Island & Budle Bay |
No |
Yes |
No |
699.4 |
699.4 |
0.84 |
High |
|
3. Eastern English Channel |
EA |
Solent |
Yes |
Yes |
Yes |
65.5 |
56.0 |
0.83 |
High |
|
3. Eastern English Channel |
EA |
Tor Bay |
No |
Yes |
Yes |
6.1 |
6.1 |
0.97 |
High |
|
4. Western Channel and Celtic Seas |
EA |
PLYMOUTH SOUND |
No |
Yes |
Yes |
50.3 |
50.3 |
0.97 |
High |
|
4. Western Channel and Celtic Seas |
NRW |
Burry Inlet Outer |
No |
No |
No |
3.0 |
0.4 |
0.43 |
Moderate |
|
4. Western Channel and Celtic Seas |
NRW |
Milford Haven Outer |
No |
Yes |
Yes |
54.3 |
54.3 |
0.87 |
High |
|
5. Irish Sea |
DAERA |
Dundrum Bay Inner |
No |
Yes |
Yes |
13.3 |
8.8 |
0.61 |
Good |
|
5. Irish Sea |
DAERA |
Larne Lough South |
No |
No |
Yes |
28.9 |
28.9 |
0.97 |
High |
|
5. Irish Sea |
DAERA |
Strangford Lough North |
No |
Yes |
Yes |
951.9 |
951.9 |
0.94 |
High |
|
5. Irish Sea |
EA |
Morecambe Bay |
Yes |
Yes |
Yes |
65.0 |
50.1 |
0.86 |
High |
|
9. Shared waters between N Ireland and Rep of Ireland |
DAERA |
Carlingford Lough |
No |
Yes |
Yes |
33.2 |
33.2 |
0.97 |
High |
|
9. Shared waters between N Ireland and Rep of Ireland |
DAERA |
Lough Foyle |
- |
Yes |
Yes |
270.0 |
270.0 |
0.95 |
High |
The UK WER risk assessments identified a total of 19% (90 of the 467 assessed) of coastal water bodies are ‘At Risk’ or ‘Probably at Risk’ of failing to meet their environmental objectives due to morphological alterations and diffuse source pollution (including nutrient enrichment) pressures. The WER risk assessments have not been updated between the 2018 and current assessments so variations in pressures influential to seagrass status cannot be evaluated.
Detailed assessment results for each UK Marine Strategy sub-region are presented for each of their component UK Regional Sea. The UK Marine Strategy sub-regions comprise of their component Regional Seas as follows:
Greater North Sea UK Marine Strategy sub-region:
1. Northern North Sea
2. Southern North Sea
3. Eastern English Channel
Celtic Sea UK Marine Strategy sub-region:
4. Western Channel & Celtic Seas
5. Irish Sea
6. Minches and Western Scotland
7. Scottish Continental Shelf
8. Atlantic North-West Approaches, Rockall Trough and Faeroe/Shetland Channel
9. Shared waters between N Ireland and Rep of Ireland
Northern North Sea
The overall risk of the Northern North Sea failing to meet the target for seagrass can be considered as low. The Northern North Sea assessment consists of a single WER water body intertidal seagrass assessment, classified as WER High Ecological Status, indicating that seagrass communities are above the indicator quality target (Figure 2). The quality threshold has been achieved for 100% of the baseline surface area for the Northern North Sea, therefore achieving the 95% extent target for the Regional Sea.
Figure 2: Outline of the Northern North Sea Regional Sea inshore indicating seagrass UK Marine Strategy assessment result and location and ecological status of the corresponding WER water bodies.
The WER risk assessments categorized the water body within the assessment as ‘At Risk’ or ‘Probably At Risk’ of failing to achieve the seagrass indicator quality target as a result of morphological alterations and/or diffuse source pollution pressures. The Northern North Sea regional sea intersects with a total of 72 water bodies, with eight of these water bodies considered 'At Risk' from morphological alterations and/or diffuse source pollution pressures which have not been assessed with the seagrass indicator.
When considering indicator quality targets for HMWBs (WER Good Ecological Potential (GEP)), none of the water bodies assessed as below the indicator quality target are categorised as HMWBs, so meeting a target of WER GEP is not considered.
The overall confidence in the Northern North Sea regional sea seagrass assessment is categorised as low. This is based on the low spatial coverage of the assessment data (one out of 72 water bodies within the region), low spatial coverage of 'At Risk' or 'Probably At Risk' water bodies in terms of morphological alterations and/or diffuse source pollution pressures (one out of nine water bodies within the region) and the lack of agreement between the seagrass indicator and morphological alterations and/or diffuse source pollution pressure Risk Assessment results (Kappa agreement of -0.18).
Eastern English Channel
The overall risk of the Eastern English Channel failing to meet the target for seagrass can be considered as high. Whilst both WER assessments within the Eastern English Channel indicate that seagrass communities are above the indicator quality target (both classified as WER High Ecological Status), a reduction in seagrass extent in contrast to the baseline has resulted in the quality threshold having been achieved for only 86.75% of the baseline surface area for the Eastern English Channel, therefore failing to meet the 95% extent target for the Regional Sea (Figure 3).
Figure 3: Outline of the Eastern English Channel Regional Sea inshore indicating seagrass UK Marine Strategy assessment result and location and ecological status of the corresponding WER water bodies.
The corresponding risk assessments categorise both water bodies as ‘At Risk’ or ‘Probably At Risk’ of failing to achieve the indicator quality target as a result of morphological alterations and/or diffuse source pollution pressures. However, the regional sea intersects with a total of 11 water bodies, with nine water bodies existing within the Eastern English Channel which are considered 'At Risk' from morphological alterations and/or diffuse source pollution pressures which have not been assessed with the seagrass indicator.
The overall confidence in the Eastern English Channel regional sea seagrass assessment is categorised as low. This is based on the low spatial coverage of the assessment data (two out of 11 water bodies within the region), the low spatial coverage of 'At Risk' or 'Probably At Risk' water bodies in terms of morphological alterations and/or diffuse source pollution pressures (two out of 11 water bodies within the region) and the lack of agreement between the seagrass indicator and morphological alterations and/or diffuse source pollution pressure Risk Assessment results (Kappa agreement of -0.18).
Western Channel & Celtic Seas
The overall risk of the Western Channel & Celtic Seas failing to meet the target for seagrass can be considered as low. The majority of WER assessments within the Western Channel & Celtic Seas indicate that seagrass communities are above the indicator quality target, with water bodies predominantly being at WER High Ecological Status (two of the three water bodies) with the remainder at WER Moderate Ecological Status (Figure 4). The quality threshold has been achieved for 97.24% of the baseline surface area for the Western Channel & Celtic Seas, therefore meeting the 95% extent target for the Regional Sea.
Figure 4: Outline of the Western Channel & Celtic Seas Regional Sea inshore indicating seagrass UK Marine Strategy assessment result and location and ecological status of the corresponding WER water bodies.
The WER risk assessments for the water bodies indicate two water bodies categorised as ‘At Risk’ or ‘Probably At Risk’ of failing to achieve the indicator quality target as a result of morphological alterations and/or diffuse source pollution pressures, with the remaining water body being ‘Not At Risk’ or ‘Probably Not At Risk’ of failing. However, the Western Channel & Celtic Seas regional sea intersects with a total of 25 water bodies, with 13 of these water bodies considered 'At Risk' from morphological alterations and/or diffuse source pollution pressures which have not been assessed with the seagrass indicator.
The water body assessed as below the indicator quality target is not categorised as a HMWB, so meeting a target of WER GEP is not considered.
The overall confidence in the Western Channel & Celtic Seas regional sea seagrass assessment is categorised as low. This is based on the low spatial coverage of the assessment data (three out of 25 water bodies within the region), the low spatial coverage of 'At Risk' or 'Probably At Risk' water bodies in terms of morphological alterations and/or diffuse source pollution pressures (two out of 15 water bodies within the region), the lack of agreement between the seagrass indicator and morphological alterations and/or diffuse source pollution pressure Risk Assessment results (Kappa agreement of -0.18), the close proximity of the assessment results to the indicator target.
Irish Sea
The overall risk of the Irish Sea failing to meet the target for seagrass can be considered as low. All WER assessments within the Irish Sea indicate that seagrass communities are above the indicator quality target, with water bodies predominantly being at WER High Ecological Status (three of the four water bodies) with the remainder at WER Ecological Status (Figure 5). The quality threshold has been achieved for 97.32% of the assessed surface area for the Irish Sea, therefore meeting the 95% extent target for the Regional Sea.
Figure 5: Outline of the Irish Sea Regional Sea inshore indicating seagrass UK Marine Strategy assessment result and location and ecological status of the corresponding WER water bodies.
The corresponding risk assessments for the water bodies categorise all four water bodies as ‘At Risk’ or ‘Probably At Risk’ of failing to achieve the indicator quality target as a result of morphological alterations and diffuse source pollution pressures. The Irish Sea intersects with a total of 66 water bodies, containing 24 water bodies which are considered 'At Risk' from morphological alterations and/or diffuse source pollution pressures which have not been assessed with the seagrass indicator.
When considering indicator quality targets for HMWBs (WER Good Ecological Potential), one water body (Morecambe Bay) within the assessment is a HMWB, but as the water body attained WER High Ecological Status, meeting a target of WER GEP is not considered.
The overall confidence in the Irish Sea regional sea seagrass assessment is categorised as low. This is based on the low spatial coverage of the assessment data (two out of 66 water bodies within the region), the low spatial coverage of 'At Risk' or 'Probably At Risk' water bodies in terms of morphological alterations and/or diffuse source pollution pressures (four out of 28 water bodies within the region), the lack of agreement between the seagrass indicator and morphological alterations and/or diffuse source pollution pressure Risk Assessment results (Kappa agreement of -0.18) and the high variability in WER water body status within the Irish Sea regional sea, the close proximity of the assessment results to the indicator target.
Shared waters between Northern Ireland and the Republic of Ireland
The overall risk of the Shared waters between Northern Ireland and the Republic of Ireland failing to meet the target for seagrass can be considered as low. The two WER assessments within the Shared waters between Northern Ireland and the Republic of Ireland indicate that seagrass communities are above the indicator quality target, with both water bodies being classified as WER High Ecological Status (Figure 6). The quality threshold has been achieved for 100% of the assessed surface area for the Shared waters between Northern Ireland and the Republic of Ireland, therefore meeting the 95% extent target for the Regional Sea.
Figure 6: Outline of the Shared waters between N Ireland and Rep of Ireland Regional Sea inshore indicating seagrass UK Marine Strategy assessment result and location and ecological status of the corresponding WER water bodies.
The corresponding risk assessments for the water bodies indicate both assessed water bodies are ‘At Risk’ or ‘Probably At Risk’ of failing to achieve the indicator quality target as a result of morphological alterations and diffuse source pollution pressures. The regional sea intersects with three water bodies in total. A further water body exist within the Shared waters between Northern Ireland and the Republic of Ireland which is considered 'At Risk' from morphological alterations and/or diffuse source pollution pressures which has not been assessed with the seagrass indicator.
The overall confidence in the Shared waters between Northern Ireland and the Republic of Ireland regional sea seagrass assessment is categorised as low. This is primarily based on the lack of agreement between the seagrass indicator and morphological alterations and/or diffuse source pollution pressure Risk Assessment results (Kappa agreement of -0.18).
Conclusions
The targets for intertidal seagrass communities have been met for both the Celtic Seas and the Greater North Seas UK Marine Strategy sub-regions, although confidence in the assessment is low.
The hydromorphological pressures which impact the seagrass communities operate over small spatial scales with their effect being relatively localised. The indicator results are therefore likely to be of limited relevance to UK Marine Strategy sub-region and Regional Sea scale assessments, although effects of larger scale pressures such as eustatic sea level change should be considered. The majority of seagrass communities assessed meet the quality threshold. The Eastern English Channel has the lowest extent of intertidal seagrass meeting the quality target and fail to meet the indicator extent threshold. However, due to the indicator target having been met at the scale of UK Marine Strategy sub-region, there a likelihood that coastal intertidal seagrass communities are not being extensively impacted by hydromorphological or nutrient pressures within inshore coastal waters at broader scales.
As the seagrass assessments are based on intertidal communities, conclusions drawn relating to the effects of pressures should be limited to inshore pressures only. The results cannot provide directional trends in quality due to the low frequency of the data (subsequent assessments are required for this).
Broader spatial coverage of assessments would be required for a more comprehensive evaluation of the level to which hydromorphological or nutrient enrichment pressures may be impacting UK seagrass communities.
The results may inform data collection and research requirements to improve confidence and accuracy of future assessments.
Knowledge gaps
The knowledge gaps accompanying the assessments include the following:
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Assessments represent a small proportion of the overall UK coastline with WER classifications provided for 8 out of 467 coastal water bodies.
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WER seagrass classifications were not undertaken for Scotland for 2015-2021.
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Comprehensive Available Intertidal Habitat data for seagrass is not yet available. This is to be made available for the next assessment cycle.
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WER monitoring and assessment methods for sub-tidal seagrass communities are in development. These may be incorporated into subsequent WER and UK Marine Strategy assessments.
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Subtidal taxa observed at extreme low water are occasionally included, potentially elevating species richness.
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The assessments do not include non-WER classification data and excludes additional relevant data such as seagrass condition assessments and monitoring for Marine Protected Areas undertaken by the UK Conservation Agencies.
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It is recommended that the results of WER investigations are considered in future assessments.
References
Defra (2019). Marine Strategy Part One: UK Updated Assessment and Good Environmental Status. 23 October 2019. Accessed 10 July 2025. https://www.gov.uk/government/publications/marine-strategy-part-one-uk-updated-assessment-and-good-environmental-status.
Authors
Graham Phillips1
1Environment Agency
Assessment metadata
| Assessment Type | UK Marine Strategy Framework Directive Indicator Assessment |
|---|---|
D1 - Biological Diversity D6 – Seafloor Integrity | |
| Point of contact email | marinestrategy@defra.gov.uk |
| Metadata date | Tuesday, July 1, 2025 |
| Title | Condition of intertidal seagrass communities in coastal waters determined using Water Framework Directive methods. |
| Resource abstract | |
| Linkage | |
| Conditions applying to access and use | © Crown copyright, licenced under the Open Government Licence (OGL). |
| Assessment Lineage | |
| Indicator assessment results | |
| Dataset metadata | |
| Links to datasets identifiers | |
| Dataset DOI | Please contact marinestrategy@defra.gov.uk |
The Metadata are “data about the content, quality, condition, and other characteristics of data” (FGDC Content Standard for Digital Geospatial Metadata Workbook, Ver 2.0, May 1, 2000).
Metadata definitions
Assessment Lineage - description of data sets and method used to obtain the results of the assessment
Dataset – The datasets included in the assessment should be accessible, and reflect the exact copies or versions of the data used in the assessment. This means that if extracts from existing data were modified, filtered, or otherwise altered, then the modified data should be separately accessible, and described by metadata (acknowledging the originators of the raw data).
Dataset metadata – information on the data sources and characteristics of data sets used in the assessment (MEDIN and INSPIRE compliance).
Digital Object Identifier (DOI) – a persistent identifier to provide a link to a dataset (or other resource) on digital networks. Please note that persistent identifiers can be created/minted, even if a dataset is not directly available online.
Indicator assessment metadata – data and information about the content, quality, condition, and other characteristics of an indicator assessment.
MEDIN discovery metadata - a list of standardized information that accompanies a marine dataset and allows other people to find out what the dataset contains, where it was collected and how they can get hold of it.