NB10b: Extent of key semi-natural habitats: coastal habitats

Scotland’s coastline is extensive (about 18,000km) and, as a result of geology, glaciation and large variation in tidal range and wave exposure, exceptionally diverse. It also contains over 790 islands.  The relative lack of development in areas such as the Highlands and Islands means that many coastal habitats are in an outstanding condition (Ellis & Munro, 2004).

Scotland’s coastal habitats are particularly noted for their extensive dune systems including machair which is found only in Scotland and Ireland and is one of the rarest habitats in Europe.  Much of Scotland’s machair is now internationally recognised for its conservation importance, and is included in Natura 2000, the EU network of protected areas under the Habitats Directive (H.R. Wallingford, 2012). Scotland’s coastline is also noted for its salt marshes which are structurally and biologically distinct from those in England (Ellis & Munro, 2004).

Coastal habitats provide a range of ecosystem services of significant benefit to the economy and society, including carbon sequestration, flood protection and seascapes that support tourism (Jones et al, 2011). The total value of the ecosystem services provided by the UK’s coast is estimated at £48 billion (adjusted to 2003 values).  The ecosystem services of greatest financial value are tourism and leisure (cultural) and coastal defence (regulating), but the relative importance of these services differs according to location (ibid).

Climate change will impact coastal habitats in a number of ways. Sea level rise will cause inundation, accelerated erosion, more frequent and extensive flooding and saline intrusion. The ability of coastal habitats to provide sea defence will come under increasing pressure (Ellis & Munro, 2004). The dynamic, natural state of coastal margin habitats that supports their rich biodiversity depends on the key natural processes of supply and transport of sediment. The supply of sediment may be affected by sea level rise and coastal erosion; this may be either positive or negative subject to the local context. In either case, there will be an impact on the extent or character of habitats necessitating a management response (Jones et al, 2013).

This indicator measures the extent of coastal habitats in Scotland, and reports on the five coastal priority habitat types recognised by the UK Biodiversity Action Plan: 1) coastal sand dunes, 2) coastal saltmarsh, 3) coastal vegetated shingle, 4) maritime cliff and slopes, and 5) machair.

Related indicators:

NB10a Extent of key semi-natural habitats: terrestrial

NB11 Extent of key habitats: deep peat

Table 1 Estimated extent of coastal priority habitat types

Table 1 shows the estimated extent of the five coastal priority habitat types in Scotland (with UK figures for comparison) recognised by the UK Biodiversity Action Plan.

Data on the extent of coastal habitats is compiled from a variety of sources, and differing definitions or classifications of habitats (Jones et al, 2011). Therefore there are still significant knowledge gaps for some habitats. Alternative estimates are also included in Table 1 where available.

Coastal sand dunes: 50,000 ha

The sand dune vegetation survey of Scotland (Dargie, 1997-2000) included both coastal sand dune and machair. Some known small areas of sand dunes were not included (Ellis & Munro, 2004).

Coastal salt marsh: TBA

From 2010-2012 all known saltmarshes larger than 3 hectares were surveyed across the Scottish mainland and islands, compiling the first comprehensive national survey of this habitat. All saltmarsh and brackish swamp has been mapped using the National Vegetation Classification (Haynes, 2016).

Coastal vegetated shingle: 1,120 ha

Due to the lack of comprehensive data on the extent of coastal vegetated shingle in Scotland, Scottish Natural Heritage (SNH) commissioned an inventory to draw together existing data, supported by field validation work across a number of sites (Murdock et al, 2011; Murdock et al, 2014).

Maritime cliff and slopes:  1,778.5 km

There are uncertainties in existing data. The estimate produced by Posford Duvivier Environment (1988, in Ellis & Munro, 2004) correlates well with OS 1:50,000 maps however it does not include some known cliff areas, e.g. on the Berwickshire coast (Ellis & Munro, 2004). The current estimate of 1,778.5 km accounts for just under 10% of Scotland’s total estimated coastline.

Machair: 18,452 ha

The estimated extent of machair is from an unpublished dataset held by Stewart Angus, based on Dargie’s (2000) Sand Dune Vegetation Survey of Scotland. Accurate and consistent measurement of machair is difficult because of the difficulty of classifying machair habitat at the edges of its range (Ellis & Munro, 2004).

Sea level rise and climate change, together with pollution and continued development pressures, present a major threat to our coastal margins in the coming decades. Vulnerability to such threats is increased by the linear nature of the habitat; it is subjected to pressure from every side (Jones et al, 2011). Climate change therefore impacts them not only through changes in temperature, rainfall and the frequency and severity of storms, but also through sea level rise and coastal erosion (Jones et al, 2013). Increased frequency of gales and storm surges may also change the structure of coastal habitats (Ellis & Munro, 2004).

Coastal erosion is currently occurring on about 12% of the Scottish coastline, one of the lowest levels in Europe (H.R. Wallingford, 2012); however changes in rates of erosion and accretion may lead to habitat loss, particularly where landward migration of sand dunes and salt marshes is constrained by coastal defence structures and other development (coastal squeeze). Coastal erosion is a particular problem for Scotland’s inner and developed firths that are composed of soft coastlines and rare habitats (Ellis & Munro, 2004). The composition and range of shallow marine habitats may therefore change as sea levels increase. 

Future losses will increase throughout the UK as storm erosion events increase in magnitude and sea-level rise further outstrips isostatic readjustment.

Appropriate management may enhance both biodiversity and other ecosystem services. Sustainable management options include:

• Allowing Coastal Margin habitats room to migrate inland with rising sea levels in order to mitigate coastal squeeze (‘managed realignment’).
• Managing sediment supply by allowing erosion to contribute new sediment to the coast, and allowing natural transport processes to proceed where possible.

Maintaining or encouraging natural formation of early successional habitats where these are threatened or have disappeared (Jones et al, 2011).