We are testing a new beta website for gov.scot go to new site

Scotland's Marine Atlas: Information for The National Marine Plan

Listen

INSHORE AND SHELF SUBTIDAL SEDIMENTS

Inshore subtidal sediments include shingle, gravel, sand and mud extending to the depth at which there is no effect from waves, typically around 50-70m. The shelf sediments extend to around 200m depth. Inshore subtidal sediments also include lagoons and maerl, a red seaweed with a hard chalky skeleton that forms small twig-like nodules which accumulate to form loosely interlocking beds, creating the ideal habitat for a diverse community of organisms.

Inshore subtidal and shelf sediments cover an extensive area of the sea bed. The east coast of Scotland in general has a relatively narrow fringe of largely sandy sediments with mud in the inner firths but there are more extensive areas of sand and mixed sediments in the Moray Firth and around the Orkney Islands. There is an extensive area of shallow sand in the south-west of Scotland off the coast of Dumfries and Galloway, whilst much of the sea bed in the Minches and many of the west coast sea lochs is of mud. These differences are the result of differences in depth, wave exposure and tidal currents with the mud habitats occurring in the deeper more sheltered areas. Much of the sea bed out to the continental shelf break comprises subtidal sediment.

Pressures

These habitats and the species that live within then are particularly vulnerable to damage from dredging and bottom trawling. Other potentially damaging activities would include disturbance from seabed development, anchoring and pollution.

Priority marine features

Burrowing sea anemone - Arachnanthus sarsi
Northern feather star - Leptometra celtica
Fan mussel - Atrina pectinata
Heart cockle - Glossus humanus
Ocean quahog - Arctica islandica
Burrowed mud
Maerl beds
Maerl or coarse shell gravel with burrowing sea cucumbers
Inshore deep mud with burrowing heart urchins
Shallow tide-swept coarse sands with burrowing bivalves
Seagrass beds
Low or variable salinity habitats

Broad habitat shallow subtidal sediments

Broad habitat shallow subtidal sediments

Broad habitat shelf subtidal sediments

Broad habitat shelf subtidal sediments

Burrowing sea anemone
Arachnanthus sarsi

This large tube-dwelling sea anemone lives buried in mud, sand or shelly mud between 10 and 36m depth. There are scattered records from St Kilda, the Inner and Outer Hebrides and the Firth of Lorn with one further record from Shetland. It is considered nationally rare at the UK scale and Scottish populations may be of international importance as the majority of the records are from Scotland. Populations appear to be isolated and fragmented and recruitment is likely to be sporadic.

Pressures

The main pressures are from dredging and demersal fishing.

Burrowing sea anemone
© Bernard Picton

Burrowing sea anemone map

Northern feather star
Leptometra celtica

Commonly found on sediment, shell, gravel or bedrock from 40 to 200m depth, it can on occasions form very dense aggregations on the sea bed. The majority of records from the UK are from the west and north coasts of Scotland and Shetland.

Pressures

The main pressures are from dredging and demersal fishing.

Northern feather star
© SNH

Northern feather star map

Fan mussel
Atrina pectinata

The fan mussel is one of Britain's largest molluscs growing up to 48cm in length it is found embedded in the sediment with one end protruding into the water column. It is one of the most endangered molluscs in the UK and considered nationally scarce, with over 50% of recent records from Scottish waters on the western and northern coasts. The densest known bed of fan mussels has been discovered recently in a dredge spoil disposal site off Canna.

Pressures

Fan mussels are particularly sensitive to damage from scallop dredging and other mobile fishing gear.

Fan mussel
© Sue Scott/ SNH

Fan mussel map

Heart cockle
Glossus humanus

This large heart shaped cockle is found in undisturbed soft muds typically below 50m depth. It is likely to be under-recorded at present and may be more abundant, especially offshore, than the scattered records suggest. The Scottish records are all from the west coast and off the Hebrides and represent 80% of UK records.

Pressures

The heart cockle is threatened by dredging and demersal fishing activities.

Heart cockle map

Ocean quahog
Arctica
islandica

The ocean quahog is the longest living mollusc known, and may live for over 400 years. It is most commonly found in sandy and muddy sediments between 10 and 280m depth from all around Scotland, mainly offshore in the east of Scotland and northern North Sea. Seventy percent of the British records occur in Scotland but it is now in decline.

Pressures

It is at risk from mechanical damage particularly caused by bottom fishing gear.

Ocean quahog
© Paul Kay

Ocean quahog map

Burrowed mud

In areas where this habitat is undisturbed it is extensively burrowed by several species including the commercially important Norway lobster ( Nephrops norvegicus). It also supports a number of characteristic and important species such as the fireworks anemone ( Pachycerianthus multiplicatus) and the tall sea pen ( Funiculina quadrangularis). This habitat type is concentrated within Scottish waters. Ninety-five percent of UK records of inshore and deep burrowed mud are from the northern North Sea and the sea lochs of western Scotland and the Hebrides and are of international importance.

There are a number of important burrowed mud communities and species:

Seapens and burrowing megafauna in circalittoral fine mud

Burrowing megafauna and Maxmuelleria lankesteri in circalittoral mud

Tall seapen - Funiculina quadrangularis

Fireworks anemone - Pachycerianthus multiplicatus

Mud burrowing amphipod - Maera loveni

Nephrops emerging from burrow

Nephrops emerging from burrow
© Paul Kay

Seapens and burrowing megafauna in circalittoral fine mud

Extensively distributed throughout the sea lochs of the west coast, Hebrides and voes of Shetland it occurs at depths of between 10-100m. It supports a diverse burrowing fauna and in particular various seapens in the deeper, sheltered areas. The majority of the UK records are from Scotland.

Pressures

The habitat is vulnerable to the direct effects from fish farms (smothering, nutrient enrichment and chemical pollution) as well as from trawling for Nephrops which can cause severe physical disturbance and damage.

Seapens and burrowing megafauna in circalittoral fine mud
© Sue Scott

Seapens and burrowing megafauna in circalittoral fine mud map

Burrowing megafauna and Maxmuelleria lankesteri in circalittoral mud

Found at depths of 10-100m in sheltered and extremely sheltered conditions in sea lochs on the west coast of Scotland and the Outer Hebrides. The great majority of UK records are from Scotland.

Pressures

Bottom trawling and creeling are likely to cause severe physical disturbance, and chemical pollution from fish farms is also potentially damaging.

Burrowing megafauna and Maxmuelleria lankesteri in circalittoral mud
© David Hughes

Burrowing megafauna and Maxmuelleria lankesteri in circalittoral mud map

Tall sea pen
Funiculina quadrangularis

Found in deep sheltered waters up to 200m depth it has also been recorded from as shallow as 20m in some sea lochs. In the UK it is almost entirely restricted to western Scotland and the Hebrides; Scottish populations are considered of global importance.

Pressures

Tall sea pens are extremely sensitive to physical disturbance especially from mobile fishing gear and to a lesser degree from creels.

Tall sea pen

© Sue Scott

Tall sea pen map

Fireworks anemone
Pachycerianthus multiplicatus

This large burrowing sea anemone lives in a long thick tube buried in mud or muddy sand at depths of 10-130m in very sheltered areas. It is restricted to a number of sea lochs on the west coast of Scotland. It is nationally scarce in the UK, Scottish populations represent 95% of all records and are of international and possibly global importance.

Pressures

The fireworks anemone is highly sensitive to mechanical damage from mobile fishing gear particularly trawling for Nephrops and to a lesser degree from creels.

Fireworks anemone
© Sue Scott

Fireworks anemone map

Maera loveni

This amphipod lives in burrows in muds in depths of 20-400m. It is a northern cold water species that has reached its southern limit in Scotland where it is sparsely distributed around the coast. Ninety-five percent of British records are from sea lochs and the northern North Sea.

Maera loveni map

Maerl beds

Maerl beds are found along the entire west coast of Britain but the vast majority are in Scotland where they are widespread along the west coast, the Hebrides and the Northern Isles and together represent about 30% of all maerl beds in north-west Europe. Maerl is extremely slow growing and some of the extensive beds may be over 1000 years old. Maerl beds create a complex, open structure that supports diverse associated communities of red seaweeds and animals such as sea firs, scallops, brittlestars, sea cucumbers and tube dwelling sea anemones and including the juvenile stages of a range of commercially important species.

Pressures

Maerl beds are extremely sensitive to physical disturbance and smothering, as a result of scallop dredging, bottom trawling, aquaculture and extraction as a fertiliser.

Maerl beds
© Sue Scott

Maerl beds map

Maerl or coarse shell gravel with burrowing sea cucumbers

This habitat is found along the west coast of Scotland and the Outer Hebrides with occasional records for the Northern Isles and the Isle of May on the east coast. The gravel sea cucumber ( Neopentadactyla mixta) can be found in high densities within the gravel, maerl, coarse sand mixture along with scallops, brittlestars, crabs and dragonets.

Pressures

It is especially sensitive to physical disturbance from scallop dredging or maerl extraction.

Maerl or coarse shell gravel with burrowing sea cucumbers
© Ben James/ SNH

Maerl or coarse shell gravel with burrowing sea cucumbers map

Inshore deep mud with burrowing heart urchins

The deep silty-muddy basins of some sea lochs support a community dominated by the heart urchin ( Brissopsis lyrifera) and the brittlestar Amphiura chiajei as well as supporting various burrowing polychaete worms and bivalves and prawns. The majority of records are from Scotland from various sea lochs on the west coast and Outer Hebrides.

Pressures

The community is particularly vulnerable to damage from benthic trawling for Nephrops which may result in the removal of heart urchins and other sensitive species such as seapens.

Inshore deep mud with burrowing heart urchins
© Paul Kay

Inshore deep mud with burrowing heart urchins map

Shallow tide-swept coarse sands with burrowing bivalves

Coarse gravelly sand on exposed coasts extending down to around 20m supports an abundance of burrowing bivalve molluscs, particularly Tellina spp. and surf clams, and polychaete worms, tanaids and sand hoppers. It has a very limited distribution with most records from Shetland and a few from Orkney, the west coast of Scotland and Outer Hebrides. Scottish records are probably of national importance at the UK scale.

Pressures

It is likely to be targeted for scallop dredging and surf clam fisheries and whilst the overall habitat is relatively robust these slow growing molluscs are sensitive to overfishing and physical disturbance.

Shallow tide-swept coarse sands with burrowing bivalves

© Paul Kay

Shallow tide-swept coarse sands with burrowing bivalves map

Seagrass beds

Subtidal seagrass beds of the eelgrass Zostera marina are considered nationally scarce and found on the west coast of Scotland extending up to the Northern Isles with a few records from the east coast in more sheltered bays and firths. The eelgrass stabilises the underlying sediment and absorbs a proportion of the wave energy as well as being a nursery area for many commercially important species of fish. Scotland holds about 20% of the seagrass beds in north-west Europe with many being considered degraded following significant declines.

Pressures

Seagrass beds are particularly vulnerable to physical damage from anchors, nutrient enrichment and increasing turbidity that reduces the available light.

Seagrass beds
© Sue Scott

Seagrass beds map

Low or variable salinity habitats

Saline lagoons are shallow, coastal water bodies with varying salinity and support a diverse assemblage of specialised species that are able to tolerate the wide range of environmental conditions that exist within these habitats. Scotland contains the largest proportion of saline lagoons in the UK with 150 recorded covering around 3,900 hectares.

Low or variable salinity habitats
© Sue Scott

Low or variable salinity habitats map

There are a number of priority marine habitats and very rare and endemic species:

Faunal communities on variable or reduced salinity infralittoral rock

Very few records of this habitat exists. Examples include Firth of Forth, Shetland and Outer Hebrides and some west coast sea lochs. Typically it comprises dense beds of blue mussels which support barnacles, sea firs and sea mats.

Kelp in variable or reduced salinity

Very few records occur outside Scotland where it is found in saline lagoons in Orkney, Shetland, the Hebrides and west coast of Scotland. The habitat is dominated by sugar kelp and various red and green seaweeds and is only found on very wave sheltered bedrock and boulders.

Submerged fucoids, green or red seaweeds (low salinity infralittoral rock)

This is a characteristic lagoon community dominated by dense seaweeds with a very restricted fauna due to the low salinity. It is unique to Scotland where there are numerous records from the Outer Hebrides, Orkney and Shetland. Scotland is of national importance for this habitat.

Sublittoral mud in low or reduced salinity (lagoons)

This is a very characteristic lagoon community comprising various short-lived species such as blow lugworms and mud shrimps. The beaked tasselweed ( Ruppia) may also be present. Only a few records of this habitat exist outside Scotland where it is found in the Outer Hebrides, Shetland and within the Beauly Firth.

Baltic stonewort (Chara balthica)

Status: Found in three locations in the Outer Hebrides the Scottish populations are likely to be of national importance but threatened by habitat loss. Listed as Vulnerable on the Red Data Book of Britain and Ireland.

Bird's-nest stonewort (Tolypella nidifica)

Status: Scottish records from Loch of Stenness, Orkney and Loch an Duin and Loch an Strumore in the Outer Hebrides are the only British records. This species is declining throughout Europe. These sites are of national and probably international importance. Listed as Endangered on the Red Data Book of Britain and Ireland.

Foxtail stonewort (Lamprothamnium papulosum)

Recorded from North and South Uist in the Outer Hebrides. Of national importance with the Hebridean sites thought to represent the most secure global stronghold for this species. Listed as Near Threatened on the Red Data Book of Britain and Ireland.

Small brackish water snail (Hydrobia acuta neglecta)

Scattered records of this small snail occur on the west coast, the Outer Hebrides, Orkney and Shetland and in Montrose Basin on the east coast.

Pressures

Saline lagoons are threatened by a range of activities such as coastal development, land claim, water abstraction etc. that can either completely destroy the habitat or change it through altering the water flow and salinity regime. They are fragile habitats susceptible to sea-level rise and pollution as well as extreme weather events such as storms.

Submerged fucoids, green or red seaweeds

Submerged fucoids, green or red seaweeds
© JNCC

Baltic stonewort

Baltic stonewort
© Sue Scott

Bird's-nest stonewort

Bird's-nest stonewort
© Sue Scott/ SNH