Saltmarsh

Context

Coastal saltmarshes in the UK (also known as 'merse' in Scotland) comprise the upper, vegetated portions of intertidal mudflats, lying approximately between mean high water neap tides and mean high water spring tides.
 
Saltmarshes are usually restricted to comparatively sheltered locations in five main physiographic situations: in estuaries, in saline lagoons, behind barrier islands, at the heads of sea lochs, and on beach plains.  The development of saltmarsh vegetation is dependent on the presence of intertidal mudflats.  Communities are additionally affected by differences in climate, the particle size of the sediment and, within estuaries, by decreasing salinity in the upper reaches.
 
The characteristic vegetation consists of a limited number of halophytic (salt tolerant) species adapted to regular immersion by the tides.  A natural saltmarsh system shows a clear zonation according to the frequency of inundation.  At the lowest level the pioneer glassworts Salicornia spp. can withstand immersion by as many as 600 tides per year, while transitional species of the upper marsh can only withstand occasional inundation.
 
Saltmarshes are an important resource for wading birds and wildfowl.  Areas with high structural and plant diversity, particularly where freshwater seepages provide a transition from fresh to brackish conditions, are particularly important for invertebrates.  Saltmarshes also provide sheltered nursery sites for several species of fish.
 
SSSIs can be notified if they qualify under criteria outlined in Section 3 of Chapter 1 Coastlands of the Guidelines for Selection of Biological SSSIs.  In Northern Ireland, ASSIs are selected on a very similar basis – the Guidelines for the selection of Biological ASSIs in Northern Ireland is an addendum to the SSSI guidelines rather than an alternative 
 

Summary statistics

  SAC A/SSSI Total
Favourable condition 43% 62% 58%
Main monitoring coverage E, S, NI E, S, NI  
Reported assessments 28 118 146
Completeness of assessments 67% unknown  
Distribution of features     UK
 

Number of assessments reported by country and site type

Country SAC SSSI/ASSI
England 21 57
Scotland 4 53
Wales 1 0
Northern Ireland 2 8
United Kingdom 28 118
 

Natura features

List of Natura 2000 interest features within this reporting category

Interest feature name  
Formal name Informal name No. of assessments reported Total no. of features % assessed
Spartina swards (Spartinion maritimae) Cord-grass swards 2 2 100%
Atlantic salt meadows (Glauco-Puccinellietalia maritimae) Atlantic salt meadows 15 24 63%
Mediterranean and thermo-Atlantic halophilous scrubs (Sarcocornetea fruticosi) Mediterranean saltmarsh scrub 4 4 100%
Salicornia and other annuals colonising mud and sand Glasswort and other annuals colonising mud and sand 7 12 58%
 
Natura 2000 comprises Special Protection Areas (under the Birds Directive) and Special Areas for Conservation (under the Habitats and Species Directive). The list presented here includes all of the qualifying interest features under these Directives, and shows the proportion of these features for which a condition assessment has been made.
 

SSSI features

List of SSSI and ASSI interest features in this reporting category

Interest feature name  
Formal name Informal name No. of assessments reported
Coastal saltmarsh Salicornia and other annuals colonising mud and sand 2
Coastal saltmarsh Coastal saltmarsh 2
Coastal saltmarsh Atlantic salt meadows (Glauco-Puccinellietalia maritimae) 3
Coastal saltmarsh 1
Littoral sediment Littoral sediment 30
Saltmarsh Saltmarsh 53
Saltmarsh 27
 
This list has not been fully standardised at a UK level yet. It is intended to show the principal constituent "feature types" for this reporting category.
 

Maps - distribution

UK distibution of reported interest features

Distribution of reported interest features.

Map showing the locations of the 10km squares in which at least one condition assessment has been reported. It does not show features that have not yet been assessed.

 

Maps - Natura

Distribution of SAC features showing assessments of favourability Condition of SAC features, with those currently reported as unfavourable-recovering shown as favourable
Current condition of SAC features
Distribution of SAC features showing assessments of favourability (where unfavourable-recovering is counted as unfavourable).
Condition of SAC features, with those currently reported as unfavourable-recovering shown as favourable
The implication of the unfavourable-recovering condition assessments is that at some point in the future these features should become favourable. This map shows the effect of that recovery by counting the favourable and unfavourable-recovering assessments together.

 

IMPORTANT NOTE: we do not have information on the timescale of the predicted recovery, which may be influenced by many past, natural and human related factors. A sustained sympathetic management regime is more likely to result in favourable condition being attained.

Key: Proportion of assessed features on 10km squares that are favourable:

Natura map legend - Key: proportion of assessed features on 10km squares that are favourable

 

Details of how these maps were produced

 

Maps - SSSI

Current condition of SSSI/ASSI features Condition of SSSI/ASSI features, with those currently reported as unfavourable-recovering shown as favourable
Current condition of SSSI/ASSI features
Distribution of SSSI/ASSI features showing assessments of favourability (where unfavourable-recovering is counted as unfavourable).
Condition of SSSI/ASSI features, with those currently reported as unfavourable-recovering shown as favourable
The implication of the unfavourable-recovering condition assessments is that at some point in the future these features should become favourable. This map shows the effect of that recovery by counting the favourable and unfavourable-recovering assessments together.

 

IMPORTANT NOTE: we do not have information on the timescale of the predicted recovery, which may be influenced by many past, natural and human related factors. A sustained sympathetic management regime is more likely to result in favourable condition being attained.

Key: Proportion of assessed features on 10km squares that are favourable:

SSSI map legend - Proportion of assessed features on 10km squares that are favourable

 

Details of how these maps were produced

 

Condition summary

Reporting category condition summary on Natura 2000 sites and SSSI

This lists the 10 different condition assessments and presents a bar chart showing the number of features within the SSSI series and the Natura 2000 series (either SPA for bird features or SAC for features other than birds). Note that for Natura 2000 we are able to estimate the number of features that have not been assessed during the 6 year reporting period - we are unable to do this for SSSI/ASSI because we do not have an overall list of notified interest features for these designations.

 

NB favourable unclassified and unfavourable unclassified have been used in this first six year cycle to get around difficulties in identifying trends in condition as common standards monitoring is implemented. It is expected that these categories will not be used for subsequent assessments of a feature.

 

Condition assessment - Natura 2000 features

The number and proportion of assessments for Natura 2000 (SAC and SPA) interest features falling into each of the condition categories
The number and proportion of assessments for Natura 2000 (SAC and SPA) interest features falling into each of the condition categories. Note that the �unfavourable� category includes all reports of unfavourable condition except �unfavourable recovering� which is shown as a separate segment.
 

Condition assessment - SSSI features

The number and proportion of assessments for SSSI/ASSI interest features falling into each of the condition categories
The number and proportion of assessments for SSSI/ASSI interest features falling into each of the condition categories. Note that the �unfavourable� category includes all reports of unfavourable condition except �unfavourable recovering� which is shown as a separate segment.
 

Adverse activities

The number of interest features where an activity has been reported as being implicated in the "unfavourable" condition of a feature
The number of interest features where an activity has been reported as being implicated in the "unfavourable" condition of a feature. More than one adverse activity may be reported for each feature.
 

Management measures

The measures summary bar chart lists the management measures relevant to the reporting category
For each "measure" the chart shows the number of interest features where that measure has been taken on a site to improve or maintain the condition of an interest feature. More than one measure may be reported for each feature assessed.
 

Interpretation

58% of saltmarsh features reported are in favourable condition.  This is about the average for marine and coastal features, above the average for all habitat features and just above the average for all features combined.  62% of A/SSSI features reported are in favourable condition and 6% are unfavourable-recovering.  43% of the SAC features reported are in favourable condition.  Data from the SAC series indicate that the 'Salicornia' feature seems to be in poorer condition than the 'Atlantic saltmeadow' feature. 
 
Coastal squeeze is a major cause of unfavourable condition in this reporting category.  Coastal squeeze occurs when sea defences prevent vegetation migrating landwards in response to sea-level rise.  The result is a loss of shoreline habitats.  Inappropriate coastal management includes the use of rock armour or groynes that interrupt sediment transport along the coast and therefore natural coastal processes.  Coastal squeeze and inappropriate coastal management are being addressed in England through shoreline management plans, estuary strategies and through other mechanisms such as high level biodiversity targets within the Environment Agency.  However, much of this has a long lead-in time and outcomes will be constrained by strategic considerations outwith the control of the country conservation agencies. 
 
Water quality also affects habitats in the intertidal zone.  Pollution arises from point sources, such as sewage treatment outfalls, or diffuse sources such as agricultural run-off.  This is in part being addressed through a review of consents for discharges being carried out and for plans to increase tertiary treatment in waste water treatment works.  Recent work indicates water quality may be more important for the condition of saltmarshes and mudflats than hitherto recognised, and links between condition assessments and water quality issues need to be strengthened. 
 
Agricultural operations may also cause unfavourable condition, as can under- or over-grazing.  Saltmarshes are affected by the difficulties of obtaining sustainable grazing at appropriate levels in such areas.