Habitat account - Marine, coastal and halophytic habitats
1160 Large shallow inlets and bays
Background to selection
|Distribution of SACs/SCIs/cSACs with habitat 1160 Large shallow inlets and bays. Click image for enlarged map.|
Description and ecological characteristics
Large shallow inlets and bays are habitat complexes which comprise an interdependent mosaic of subtidal and intertidal habitats. Several of these habitat types (1140 Mudflats and sandflats not covered by sea water at low tide, 1110 Sandbanks which are slightly covered by sea water all the time and 1170 Reefs) are listed as Annex I habitats in their own right.
Large shallow inlets and bays are large indentations of the coast, generally more sheltered from wave action than the open coast. They are relatively shallow (with water less than 30 m over most of the area), and in contrast to 1130 estuaries, generally have much lower freshwater influence. In the UK, three main sub-types can be identified that meet the Annex I definition:
- Embayment. A type of marine inlet where the line of the coast typically follows a concave sweep between rocky headlands, sometimes with only a narrow entrance to the embayment.
- Fjardic sea loch. A series of shallow basins connected to the sea via shallow, sometimes intertidal, sills. Fjards are found in areas of low-lying ground which have been subject to glacial scouring. They have a highly irregular outline, no main channel and lack the high relief and U-shaped cross-section of fjordic sea lochs.
- Ria. A drowned river valley in an area of high relief; most have resulted from the post-glacial rise in relative sea level. In Scotland this sub-type is called a voe.
Large shallow inlets and bays vary widely in habitat and species diversity according to their geographic location, size, shape, form and geology. There is considerable variation between hard (rock) and soft (sediment) coasts. The degree of wave exposure is a critical factor in determining habitat and species diversity, affecting communities both on the shore and in the sublittoral zone. The range of plants and animals associated with this habitat type is therefore very wide. The issue of site size is also important, as larger sites tend to encompass the greatest variety of constituent habitats and have the greatest potential for maintenance of ecosystem integrity.
Intertidal rock communities may be dominated by wracks Fucus spp., particularly in more sheltered locations. Extensive beds of mussels Mytilus edulis may be present on mixed substrates. Sediment shores vary widely, depending on the degree of exposure. Very exposed conditions may result in shingle beaches, whilst less-exposed shores may consist of clean sand, and in sheltered conditions shores may consist of fine sand and mud. Very exposed sediment shores are generally unable to support animal populations. On less-exposed shores, communities of crustaceans and polychaete worms develop, while shores of fine sand and mud are characterised by polychaete and bivalve communities and beds of eelgrass Zostera spp. In the sheltered conditions of Scottish fjards, loose-lying mats of green algae and the unattached wrack Ascophyllum nodosum ecad mackaii may occur.
In the sublittoral zone, more exposed rocky coasts support forests of kelp Laminaria hyperborea, with forests of sugar kelp L. saccharina occurring in more sheltered conditions. Communities of ephemeral algae and maerl (including Phymatolithon calcareum and Lithothamnion corallioides) may be present on wave-exposed or tide-swept coasts, whilst sheltered shallow sediments may be covered by communities of filamentous red and brown algae, by loose-lying mats of algae, or by beds of eelgrass Zostera marina.
Animal-dominated rocky communities in the sublittoral zone also vary according to local conditions of wave exposure and tidal streams. On more wave-exposed coasts, soft corals, anemones, sponges, sea-fans, featherstars and hydroids may be dominant, whilst more sheltered coasts support different species of sponges, hydroids, brachiopods and solitary ascidians. A particular feature of rias and fjards is the presence of sublittoral rock in conditions of strong tidal flow but negligible or no wave action. Particular growth forms of sponges and ascidians, as well as specific biotopes, occur in these unusual conditions. In tide-swept areas communities of hydroid and bryozoan turfs or beds of brittlestars may be dominant. Beds of horse mussel Modiolus modiolus characterise some seabeds. Animal-dominated sediment communities range from gravels and coarse sands dominated by burrowing sea cucumbers, large bivalves and heart-urchins, through finer sediments supporting communities of polychaetes and small bivalves, to fine muds with beds of sea-pens, large burrowing crustaceans and bottom-dwelling fish.
European status and distribution
Large shallow inlets and bays are widespread throughout the coasts of Europe, although their specific character varies significantly from region to region. Fjardic sea lochs are scarce outside the UK, whilst rias are a particular feature of France and northern Spain as well as Britain.
UK status and distribution Click to view UK distribution of this habitat
The habitat type is widespread around the UK, but some sub-types are localised in their distribution. Rias occur only in southern Wales, south-west England, and Shetland (where they are known as voes), and fjards are restricted to western Scotland and Northern Ireland.
Site selection rationale
Sites have been selected to represent the range of sub-types, geographical range and ecological variation of this highly variable Annex I type. Selection has favoured larger sites, which tend to encompass the greatest variety of constituent habitats. Particular attention has been paid to the selection of rias and fjardic sea lochs, sub-types of the habitat for which the UK has a high proportion of the total EU resource.
|Berwickshire and North Northumberland Coast||Northumberland; Scottish Borders|
|Whilst predominantly rocky, this extensive and diverse stretch of coastline has several characteristic, sediment-dominated embayments in north-east England, including Budle Bay, Beadnell Bay and Embleton Bay. Each of these areas is relatively exposed and uniform in nature and is characterised by crustacean /polychaete- and bivalve/polychaete-biotopes. Budle Bay is adjacent and continuous with the bay to the north between the island of Lindisfarne and the mainland. This area forms one of the most extensive areas of sandflats between the Firth of Forth and the Wash, and these are some of the richest examples of these biotopes in north-east England. In the sublittoral, Beadnell and Embleton Bays form a sandy break in the otherwise continuous reef habitat in this site. These areas are characterised by extensive areas of clean sand with often dense populations of the heart urchin Echinocardium cordatum, and razor clams Ensis siliqua and E. arcuatus.|
|Carmarthen Bay and Estuaries/ Bae Caerfyrddin ac Aberoedd||Abertawe/ Swansea; Caerfyrddin/ Carmarthenshire; Penfro/ Pembrokeshire|
|Carmarthen Bay, off the south Wales coast is an extensive shallow bay. Throughout the bay physical conditions vary considerably. Salinity varies from low (at the estuaries) to fully marine, there are gradients in wave action from sheltered to exposed, and strong tides sweep exposed headlands whilst other areas are sheltered from currents. There is a wide range of seabed types, including mud, sand and rock, although the majority of the seabed is sandy. The sediment supports a large number of species, including bivalve molluscs, worms, burrowing urchins, brittlestars and sand-stars.|
|Fal and Helford||Cornwall|
|This site is a ria system in south-west England that supports a wide range of communities representative of marine inlets and shallow bays. The rias of the Fal and Helford have only a low freshwater input and as a result the area contains a range of fully marine habitats from extremely sheltered in the inlets to the wave-exposed, tide-swept open coast. There is a particularly diverse algal flora and a number of warm-water species are present. The area supports extensive and rich sediment communities, which include the largest and most south-westerly maerl Phymatolithon calcareum bed in the UK.|
|Loch Laxford, on the west coast of Scotland, is a complex fjard with numerous small islands and side branches that include two subsidiary lochs. It is an excellent example of large shallow inlets and bays and contains a wide variety of marine habitats and communities. The outermost part of the site is very exposed, but the many reefs and islands near to the narrow loch entrance result in sheltered conditions over most of the loch. The most important area for sediments, a sheltered littoral inlet at the head of the loch, contains the only extensive sheltered sediment shore in the northern part of the west coast. The soft muds of the inner subsidiary loch, Loch a’Chadh-Fi, contain particularly dense beds of the anemone Sagartiogeton laceratus, and the snake blenny Lumpenus lumpretaeformis (which usually occurs in burrows in deeper water) is also common here. In the outer more exposed reaches of the site, coarser sediments predominate supporting sea cucumbers, hydroids, heart-urchins and bivalves. Beds of maerl Phymatolithon calcareum, with their associated species-rich communities, also occur in various channels of the loch.|
|Loch nam Madadh||Western Isles / Na h-Eileanan an Iar|
|Loch nam Madadh (Loch Maddy) is representative of fjardic sea lochs on the coast of north-west Scotland. This site is exceptionally complex. It is predominantly shallow, with deeper water only in its entrance, and wave exposure grades from moderately exposed to extremely sheltered in the inner basins. There are numerous rocks and islands and at least 22 shallow sills and associated basins. The fjardic marine biotopes on this site are more diverse than on any other known site in the EU. There is a particularly wide variety of shallow tide-swept reef and sediment habitats and communities. Some of the holothurian species found in abundance on soft mud in the inner basins, such as the sea cucumber Labidoplax media, are considered rare elsewhere. There are dense beds of knotted wrack Ascophyllum nodosum ecad mackaii and a variety of kelp forest types that illustrate the wave exposure gradient in the loch. There are transitions to a complex system of lagoons, which have been selected in their own right as Annex I type 1150 Coastal lagoons.|
|Luce Bay and Sands||Dumfries and Galloway|
|Luce Bay and Sands represents a high-quality large shallow inlet and bay. The sediments within Luce Bay range from mixed-sized boulders, deep sediments and highly mobile fringing sands, all of which support rich plant and animal communities typical of a large embayment in south-west Scotland. Water depths in Luce Bay are shallow, ranging from 0-10 m fringing the coastline and at the head of the bay. Shallow depths extend further out into the bay where the major sandbanks are located along the western and northern shores. The water deepens to 20 m at the site boundary between the two headlands. Most of the intertidal area of the bay comprises small boulders, often resting on sediment. Some larger boulders on the lower shores have spaces beneath and between them which provide shelter for false Irish moss Mastocarpus stellatus and permit rich under-boulder communities to develop, including ascidians, sponges and crustose coralline algae. In the subtidal area mixed boulders and sediment harbour a shallow-water community of sparse kelp Laminaria hyperborea and sea-oak Halidrys siliquosa, red algae and the dahlia anemone Urticina felina, typical of sand-influenced hard substrata. Much of the central part of Luce Bay consists of slightly deeper-water sediments that support a rich community of polychaete worms, bivalves, echinoderms, brittlestars, particularly Ophiura spp. The holothurian Labidoplax digitata has also been recorded in the bay. At Mull of Galloway in the west and Scare Rocks near the seaward boundary of the bay, tide-swept rocky reefs support L. hyperborea on shallow sublittoral rocks and very rich sponge- and hydroid-dominated communities below 10 m.|
|Morecambe Bay||Cumbria; Lancashire|
|Morecambe Bay in north-west England is the second-largest embayment in the UK, after the Wash. It is a large, very shallow, predominantly sandy bay bordered on the south by the channel of the Lune estuary and on the north by Walney Channel. At low tide vast areas of intertidal sandflats are exposed, with small areas of mudflat, particularly in the upper reaches of the associated estuaries. The sediments of the bay are mobile and support a range of community types, from those typical of open coasts (mobile, well-sorted fine sands), grading through sheltered sandy sediments to low-salinity sands and muds in the upper reaches. Apart from the areas of intertidal flats and subtidal sandbanks, Morecambe Bay supports exceptionally large beds of mussels Mytilus edulis on exposed ‘scars’ of boulder and cobble, and small areas of 1170 Reefs with fucoid algal communities. Of particular note is the rich community of sponges and other associated fauna on tide-swept pebbles and cobbles at the southern end of Walney Channel.|
|Pembrokeshire Marine/ Sir Benfro Forol||Penfro/ Pembrokeshire|
|Pembrokeshire Marine in south-west Wales includes Milford Haven, one of the best examples of a ria in the UK, and the wide, shallow, predominantly sandy embayment of St Brides Bay. The wide range of environmental conditions, particularly seabed substrates, tidal streams and salinity gradients, supports high community and species diversity. The species-richness of sediment communities throughout Milford Haven is particularly high, with intertidal sandy/muddy areas supporting extensive beds of narrow-leaved eelgrass Zostera angustifolia. High-salinity water and rocky substrates penetrate far upstream, and communities characteristic of fully saline conditions occur. A wide range of subtidal and intertidal rocky habitats are present, from rocky reefs and boulders to rich underboulders, crevices, overhangs and pools.|
|Pen Llyn a`r Sarnau/ Lleyn Peninsula and the Sarnau||Ceredigion; Gwynedd; Powys|
|The seabed of Tremadog Bay on the south side of the Lleyn Peninsula, north-west Wales, consists of a mosaic of different sediment types, which support a diverse mixture of plant and animal communities. Areas of cobbles and pebbles in shallow water support algal species that can tolerate sand-scour, such as Naccaria wiggii and Scinaia spp. There are patchy areas of maerl around St Tudwal’s Islands. Maerl has been found at only one other site in Wales, in Milford Haven. Burrowing animals, including bivalves, crabs, brittlestars, urchins and worms, dominate the muddier sediments in Tremadog Bay. There are also beds of eelgrass Zostera angustifolia and muddy gravel shores within Tremadog Bay, both uncommon habitats. The gravelly beach at Traeth Crugan supports the nationally rare amphipod Pectenogammarus planicrurus. Several unusual species that are more often seen in warmer Mediterranean waters have been found in Tremadog Bay, such as the bearded red seaweed Anotrichium barbatum and the mantis shrimp Rissoides desmaresti.|
|Plymouth Sound and Estuaries||Cornwall; Devon; Plymouth|
|Plymouth Sound and Estuaries on the south-west coast of England includes the rias of the rivers Tavy, Tamar, Lynher and Yealm. The first three of these join at the wide, rocky inlet of Plymouth Sound and the Yealm enters the adjacent Wembury Bay. The Yealm has good examples of habitats and communities characteristic of sheltered marine inlets with little freshwater input, including a range of sponge- and worm-dominated communities on lower shore mixed sediments. The Plymouth Sound complex has a high diversity of habitats and communities characteristic of different salinities, in contrast to the Fal and Helford. Some of these support extremely rich marine flora and fauna, which include abundant southern Mediterranean-Atlantic species rarely found in Britain, such as the carpet coral Hoplangia durotrix. Particularly notable habitats include (i) littoral and sublittoral limestone reefs extensively bored by bivalves and harbouring a rich fauna; (ii) offshore sublittoral tide-swept reefs; (iii) tide-swept limestone channels with animal communities rarely encountered in other marine inlets; and (iv) subtidal sediments with rich and often diverse invertebrate communities.|
|Strangford Lough on the east coast of Northern Ireland is an outstanding example of a large, enclosed fjardic sea lough. Sea water enters the Lough through a narrow entrance, expanding into a broad, mostly shallow basin that has a central deep channel (30-60 m deep), which carries rapid currents and causes great turbulence in some parts, particularly the Narrows. With a wide range of tidal stream strengths and depths, there is a remarkable marine fauna within Strangford Lough and it is one of the most diverse sea loughs in the UK. The communities present range from the very rich high-energy communities near the mouth, which depend on rapid tidal streams, to communities in extreme shelter where fine muds support burrowing brittlestars, Dublin Bay prawn Nephrops norvegicus, and a rich community associated with horse mussels Modiolus modiolus.|
|Sullom Voe||Shetland Islands|
|Sullom Voe in the Shetland Isles is the most northerly site in the UK to be selected as a representative of large shallow inlets and bays, and within the site series it is the only Scottish example of a ria (known locally as a ‘voe’). The boreal-arctic (northern) species-rich communities of Sullom Voe are restricted to Shetland voes and are not represented elsewhere in the SAC series. The intertidal sediments, confined to lagoons near the mouth of the voe, are colonised by a diverse faunal community including bivalves, polychaetes and the sea cucumber Leptosynapta inhaerens. Poorly-mixed, muddy sediments which characterise the sublittoral are colonised by horse mussels, sea-pens Virgularia sp. and diverse burrowing communities. A range of bivalves, polychaetes and amphipods can also be found in the organically enriched shell-sand, gravel and muddy-sand sediments.|
|The Wash and North Norfolk Coast||Lincolnshire; Norfolk|
|The Wash is the largest embayment in the UK, and represents Large shallow inlets and bays on the east coast of England. It is connected via sediment transfer systems to the north Norfolk coast. Together, the Wash and North Norfolk Coast form one of the most important marine areas in the UK and European North Sea coast, and include extensive areas of varying, but predominantly sandy, sediments subject to a range of conditions. Communities in the intertidal include those characterised by large numbers of polychaetes, bivalve and crustaceans. Sublittoral communities cover a diverse range from the shallow to the deeper parts of the embayments and include dense brittlestar beds and areas of an abundant reef-building worm (‘ross worm’) Sabellaria spinulosa. The embayment supports a variety of mobile species, including a range of fish and 1365 Common seal Phoca vitulina.|
SACs/SCIs/cSACs where this Annex I habitat is a qualifying feature, but not a primary reason for site selection
|Y Fenai a Bae Conwy/ Menai Strait and Conwy Bay||Conwy; Gwynedd; Ynys Môn/ Isle of Anglesey|
Many designated sites are on private land: the listing of a site in these pages does not imply any right of public access.