This is a static version of the conservation advice for this site, generated on 20/09/2019.
Please check the latest advice for this site at https://designatedsites.naturalengland.org.uk/
Natural England Conservation Advice for Marine Protected Areas
Plymouth Sound and Estuaries SAC

Natural England guidance

This site collection contains Natural England's conservation advice for this site. It fulfils Natural England’s responsibility under the Conservation of Habitats and Species Regulations 2017 (as amended), to give advice on how to further the conservation objectives for the site, identify the activities that are capable of affecting the qualifying features and the processes which they are dependent upon.

Natural England's conservation advice for this site is made up of a number of components. You will need to consider: Additional information for consideration:

Site information

Overarching site: Plymouth Sound and Estuaries Marine Protected Area
Site name: Plymouth Sound and Estuaries SAC
Designation type: SAC
Site identification: UK0013111
Latest designation date: 1 April 2005
Qualifying features
(click to see site specific description):

Allis shad (Alosa alosa)

Allis shad is a member of the herring family which is found along the south coast of the UK. Allis shad are rare and populations are declining in Europe (Joint Nature Conservation Committee (JNCC), 2015). These declines can be linked to anthropogenic activities such as the creation of physical barriers like damns and weirs (Limburg and Waldman, 2009)(Jolly et al., 2012). Whilst the overall population is declining a spawning stock of Allis shad still exists in the Tamar (Hillman, 2003).

Shad grow in coastal waters and then migrate up estuaries to spawn. Almost all adults die after spawning (Joint Nature Conservation Committee (JNCC), 2015). Relatively little is known about the stock in the Tamar. There is one known spawning ground on the Tamar which is located just below the Gunnislake Weir. It is thought that the weir acts as a barrier to most individuals and the shad migrating upstream find the nearest suitable habitat downstream of the weir to spawn (Hillman, 2003). The suitable spawning habitat consists of gravelly substrates in relatively shallow areas with low water flow(Joint Nature Conservation Committee (JNCC), 2015).

In the 2016 SAC Condition Assessment the feature was found to be in unfavourable condition (Natural England, 2016).

SubFeatures

Subtidal coarse sediment

Subtidal mixed sediments

Subtidal sand

Water column


Atlantic salt meadows (Glauco-Puccinellietalia maritimae)

Saltmarsh in the Plymouth Sound and Estuaries SAC is both regionally and nationally important. Salt meadows are uncommon in the Southwest, making the Plymouth area regionally important to numerous species reliant on these habitats. This includes wading birds such as avocet (Recurvirostra avosetta) and little egret (Egretta garzetta).

Extensive areas of saltmarsh can be found bordering the tidal mud banks in the broader reaches of the Tamar, Tavy, in St. John’s Lake and particularly on the Lynher Estuary.

The steep-sided banks associated with the Plymouth ria system result in an absence of typical saltmarsh zones (Seebold, 2013) (Natural England, 2014). Upper saltmarsh communities dominate, and often contain common saltmarsh-grass (Puccinellia maritima), red fescue (Festuca rubra) and sea couch (Elymus pycanthus) (Curtis, 2010). Two nationally scarce grass species are found in the Tamar-Tavy estuaries: stiff saltmarsh grass (Puccinellia rupestris) and bulbous foxtail (Alopecurus bulbosus) (Curtis, 2010). Importantly, the Tamar supports the only UK population of the triangular club rush (Schoenoplectus triqueter) (English Nature, 2000).

In the 2016 SAC Condition Assessment the feature was found to be in favourable condition. The feature was assessed using SSSI Favourable Condition Tables (Natural England, 2016).


Estuaries

Estuarine habitats were central to the designation of the Plymouth Sound and Estuaries SAC, and this site is considered to be one of the best areas in the UK for this habitat feature (English Nature, 2000). The importance of this estuarine complex is attributable to a number of factors, not least the variety and extent of different habitat types, and the presence of nationally rare species and communities (English Nature, 2000). The upper parts of the Tamar and Lynher estuaries exhibit one of the best examples in the UK of salinity graded communities, because the estuarine gradient has not been interrupted by locks or weirs (English Nature, 2000).

The rivers Tamar, Tavy, Lynher and Yealm have major estuaries within the site; all are tidally influenced, and display the classic topographical characteristics of ria estuary systems. There are smaller estuarine creeks branching off each of the larger estuaries such as Tamerton Lake on the Tamar and the River Tiddy on the Lynher. The Yealm is almost entirely natural, it has not been diverted or dammed and is unusual in the low levels of freshwater it receives, meaning that marine communities typical of full salinity seawater penetrate a significant distance up the estuary.

The watercourses all display a relatively high degree of naturalness, having largely escaped the construction of dams and weirs that have been detrimental to the wildlife and the physiographic processes of many of the UK’s other estuaries (English Nature, 2000). There is also variety between the rivers in terms of salinity and sediment load, with differing catchment areas resulting in different freshwater inputs. Consequently species assemblages vary between locations within the site. The estuaries are particularly important for fish and bird species and parts of the Tamar, Lynher and St John’s Lake are also designated as a Special Protection Area. Migratory fish such as Atlantic salmon (Salmo salar), European eel (Anguilla anguilla), sea trout (Salmo trutta) and Allis shad (Alsoa alosa) use the estuaries as a route to their breeding grounds. They are also a nursery area for some fish species such as bass.

In the 2016 SAC Condition Assessment the feature was found to be in favourable condition in 1161.40 ha and unfavourable condition in 762.37 ha in the Tamar estuary. 198.46 ha of the feature was not assessed (Natural England, 2016).

In the 2016 SAC Condition Assessment the feature was found to be in favourable condition in 12.36 ha and unfavourable condition in 115.41 ha in the Yealm estuary. 27.14 ha of the feature was not assessed (Natural England, 2016).

SubFeatures

Atlantic salt meadows (Glauco-Puccinellietalia maritimae)

Saltmarsh in the Plymouth Sound and Estuaries SAC is both regionally and nationally important. Salt meadows are scarce within the Southwest, making the Plymouth area regionally important to numerous species reliant on these habitats. This includes wading birds such as avocet (Recurvirostra avosetta) and little egret (Egretta garzetta). Extensive areas of saltmarsh can be found bordering the tidal mud banks in the broader reaches of the Tamar, Tavy, in St. John’s Lake and particularly on the Lynher Estuary.

The steep-sided banks associated with the Plymouth ria system result in an absence of typical saltmarsh zones (Joint Nature Conservation Committee (JNCC), 2014) (Natural England, 2014). Upper saltmarsh communities dominate, and often contain common saltmarsh-grass (Puccinellia maritima), red fescue (Festuca rubra) and sea couch (Elymus pycanthus) (Curtis, 2010). Two nationally scarce grass species are found in the Tamar-Tavy estuaries: stiff saltmarsh grass (Puccinellia rupestris) and bulbous foxtail (Alopecurus bulbosus) (Curtis, 2010). Importantly, the Tamar supports the only UK population of the triangular club rush (Schoenoplectus triqueter) (English Nature, 2000).

The 2016 SAC Condition Assessment found this subfeature to be in favourable condition in both the Tamar and Yealm estuaries (Natural England, 2016).


Circalittoral rock

The circalittoral reefs of the Plymouth Sound and Estuaries SAC support rich faunal dominated communities which were considered important for the designation of the site. This was particularly owing to the number of rare and unusual species and habitats found within the site (English Nature, 2000).

The depth at which circalittoral rock is found is dependent on the water clarity at any location. In the turbid waters of the estuarine Tamar circalittoral rock can be found in very shallow water depths. Where turbid waters and wave sheltered conditions continue into the Inner Sound dense communities that ordinarily would be algal dominated can be found (Vance, 2014). The tide-scoured hydrodynamic regime, along with the verticality of the reef structures, also prevents an excessive build-up of silt and delivers nutrient rich waters to the reefs. Steep sided circalittoral limestone reefs can found along the northern shore of the Sound and important sites include Devil’s Point, Eastern Kings and Firestone Bay (Vance, 2014). In the Outer Sound, with increasing water clarity the circalittoral zone is pushed deeper from the surface. Increasing exposure to wave action also dictates changes in community structure, however, the rocky reefs continue to support diverse assemblages. Circalittoral rocky reefs, typically of creviced slate occur in areas off Wembury, the Mewstone, Penlee Point and south of the Breakwater.

Circalittoral reefs in the estuaries support faunal communities typified by the presence of the breadcrumb sponge (Halichondria panicea), which is widespread in the central and lower estuary (Ware and Meadows, 2011). Further upstream it is possible to find a species poor assemblage, defined by the hydroid (Cordylophora caspia), the bryozoan (Electra crustulenta) and the barnacle (Balanus crenatus). This community, a result of very low but still variable salinity, is nationally rare and therefore regarded as important to conserve despite its lack of diversity (Tyler-Walters, 2002).

The soft limestone reefs of the Inner Sound harbour a rich infauna and are extensively burrowed by the wrinkled rock borer (Hiatella arctica) and bristleworms (Polydora spp.) They are also colonised by sessile invertebrates such as the structurally fragile sea beard hydroid (Nemertesia antennina), and the hydroid (Nemertesia ramosa). These species only occur in water this shallow when there is a full absence of physical abrasion (Vance, 2014). Reefs in the Outer Sound are geologically varied and provide diverse habitats supporting rich assemblages that can be characterised by dead man’s fingers (Alcyonium digitatum) (English Nature, 2000).

The 2016 SAC Condition Assessment found this subfeature to be in favourable condition in the Tamar estuary (Natural England, 2016).


Infralittoral rock

Infralittoral rock and other hard substrata in the Plymouth Sound and Estuaries SAC incorporates bedrock outcrops and mixed boulder and cobble communities in the shallow subtidal. Infralittoral reefs frequently connect with those in the intertidal zone, and the reefs in the deeper or more turbid water of the circalittoral zone.

There are two main infralittoral rock habitats within the Plymouth Sound and Estuaries SAC; kelp forest communities, which can be found from the inner Sound to the open coast on reefs in the photic zone and a more unusual habitat, formed of bedrock, boulders and cobble in the estuarine Tamar. One such area is beneath and in the vicinity of the Tamar Bridge (Ware and Meadows, 2011). Important sites include the Mewstone, Penlee Point and Duke Rock.

The estuarine bedrock, boulder and cobbles in the Tamar support a number of fucoid and filamentous algae, which tend to be found no deeper than 1m below chart datum due to the turbidity of the water (Moore et al., 1999). In contrast, the clearer waters of the Sound allow kelp to dominate extensive rocky areas of the infralittoral. The most common species is tangle kelp (Laminaria hyperborea), and this habitat-defining seaweed can form extensive dense underwater forests along with other kelp species, including the southern species (Laminaria ochroleuca) and red seaweeds.

The 2016 SAC Condition Assessment found this subfeature to be in favourable condition in the Tamar estuary (Natural England, 2016).


Intertidal mixed sediments

Littoral mixed sediments range from muds with gravel and sand components to mixed sediments with pebbles, gravels, sands and mud in more even proportions. Littoral mixed sediments are important feeding areas for birds such as the avocet (Recurvirostra avosetta) and little egret (Egretta garzetta).

Littoral mixed sediments occur in small areas at various locations throughout the Plymouth Sound and Estuaries SAC. These areas range from close to the Sound (e.g. Cawsand, Conger Point, Pier Cove, Outer Broady Cove, Rame Head, Heybrook Bay, and Wembury) up to the mid-upper reaches of the estuaries including the Lynher Estuary (on the northern shore near Wivelscombe Lake) and the Tamar-Tavy Estuary (near Warren Point, east of Tamerton Bridge, and in the upper reaches between Cotehele Bridge and Chapel Farm).

The most abundant species in these littoral mixed sediments are typically polychaetes such as (Hediste diversicolor, Nephtys hombergii, and Streblospio shrubsolii), and the oligochaete (Tubificoides benedii). Also present are the amphipod (Corophium volutator), the gastropod (Hydrobia ulvae), and the bivalve (Macoma balthica).

The river Yealm supports the most interesting littoral mixed sediment communities. For instance, north of Shortaflete Creek, rich muddy gravel supports abundant peacock worm (Sabella pavonina), common cockle (Cerastoderma edule), orange sponge (Hymeniacidon perleve) and common shore crab (Carcinus maenas communities).

The 2016 SAC Condition Assessment found this subfeature to be in unfavourable condition in the Tamar estuary (Natural England, 2016).


Intertidal mud

Littoral mud is perhaps the most visible of the described features in the Plymouth Sound and Estuaries SAC. When the area was designated for protection the site was judged as supporting a significant presence of this habitat. In each of the estuaries at low tide extensive mudflats extend from the main riverine channels out to saltmarsh and other transitional habitats. These areas are very important as feeding grounds for birds such as the avocet (Recurvirostra avosetta) and little egret (Egretta garzetta).

Littoral mud habitats can be found on the Tamar, Tavy, Lynher, and Yealm estuaries, as well as in St. John’s Lake. The largest littoral mudflats on the Yealm are in an area called the Broad Ooze which supports ragworm (Hediste diversicolor), common cockle (Cerastoderma edule) and the sand mason worm (Lanice conchilega) (Moore et al., 1999). On muddy shores in lower salinity conditions, in the sheltered regions of all the other estuaries, oligochaete worms and ragworms frequently make up a large proportion of the infaunal community. These areas include the sheltered inlet of Tamerton Lake, Kingsmill Lake and Saltmill Creek (Bunker et al., 2002). Another dominant community consists of ragworm and the peppery furrow shell (Scrobicularia plana), in reduced salinity on muddy shores. This biotope was recorded as dominating many of the mud flats across the estuaries (Bunker et al., 2002).

The 2016 SAC Condition Assessment found this subfeature to be in favourable condition in the Tamar estuary and unfavourable condition in the Yealm estuary (Natural England, 2016).


Intertidal rock

Representatives of every littoral life form (Foster-Smith and Bunker, 1997) and habitat complex type (Connor et al., 1997) have been recorded within Plymouth Sound and Estuaries SAC. Intertidal reef habitats are an essential component of the protected area (Bunker et al., 2002). Within the site sheltered limestone reefs can be found, these are particularly important as this is one of only two coastal areas in southwest Britain with Devonian limestone (English Nature, 2000).

Intertidal rock can be found along most of the coast of Plymouth Sound, with further areas throughout the estuaries where boulders and other hard substrata exist. Sheltered limestone reefs are found along the northern shore of the Sound, from Devil’s Point to Batten Bay. The area from Mount Batten to Dunstone Point is also important for this intertidal limestone habitat, which is extensively burrowed in places by rock boring invertebrates. Under-boulder communities, a Priority Habitat, are also an important feature on rocky shores around the Sound, such as at Jennycliff Bay (English Nature, 2000c,(Bunker et al., 2002). Many other sites with littoral rocky reef habitat can be found around Plymouth Sound and Wembury Bay; including at Wembury Point and Penlee Point.

The Great Mewstone provides a microcosm of littoral reef habitats that can be found in Plymouth Sound, exhibiting exceptional variety in a small area due to the distinct changes in wave exposure around the islet (Bunker et al., 2002). The reefs are formed of Devonian sandstones, slates and limestone. These hard substrates link with the reefs of the infralittoral and deeper circalittoral zones and outcrops also intersperse with areas of sediment. Other hard littoral substrata within the site include estuarine cobbles and boulders, where communities tolerant to reduced salinity develop.

The littoral reefs within the Yealm Estuary are also of note. This aquatic system receives low freshwater inputs which means that marine reef species can survive as far north as Steer Point and Newton Creek, where it is still possible to find rocks with limpets (Patella spp.), barnacles (Semibalanus balanoides and Elminius modestus) and the common flat periwinkle (Littorina obtusata) (Moore et al., 1999). Boulders and other hard substrata in the tidal reaches of all of the estuaries are also colonised by a variety of seaweeds such as bladder wrack (Fucus vesiculosus), channelled wrack (Pelvetia canaliculata), knotted wrack (Ascophyllum nodosum), and toothed wrack ( Fucus serratus) (Curtis, 2010).

The 2016 SAC Condition Assessment found this subfeature to be in favourable condition in the Tamar estuary and unfavourable condition in the Yealm estuary (Natural England, 2016).


Intertidal seagrass beds

Littoral seagrass beds had disappeared from St John’s Lake at the time of the site’s designation, so were not considered an interest feature of the site in their own right. However, they are an important subfeature of the intertidal mudflats and sandflats feature. The disappearance of these beds, which were first recorded in 1872 (Hocking et al., 2002), then in the 1950s (Wilson, 1958) and 1986 (Burd, 1986) is described as dramatic (Marine Nature Conservation Review (MNCR), 1996).

In 1986 Zostera noltii and Z. angustifolia (now considered to be Z. marina) were recorded as abundant across an extensive bed in the south west of St John’s Lake, but had disappeared completely in 1997. However, in 1999 several patchy beds of Zostera noltii were recorded in St John’s Lake (Hocking et al., 2002) and in 2010 a large bed of intertidal seagrass was recorded in a similar location. These reports suggest that the bed is somewhat ephemeral in nature.

Zostera marina has also previously been recorded in intertidal areas at Drake’s Island and Cawsand Bay, but has disappeared from these areas since 1967 (Hocking et al., 2002).

The 2016 SAC Condition Assessment found this subfeature to be in unfavourable condition in the Tamar estuary (Natural England, 2016).


Subtidal mixed sediments

Plymouth Sound and Estuaries SAC is an exceptional site, in part owing to the huge range of substrata within its boundaries. This includes muddy sediments from the rivers, marine sands, and harder materials contributed by the underlying geology of Devonian slates and limestone. The sublittoral mixed sediment habitats can involve a number of these components and are made up of a combination of muds, shells, sands, gravels, pebbles and cobbles.

Sublittoral mixed sediments can be found widely across the site and are a subfeature of estuaries, large shallow inlets and bays and sandbanks. In Plymouth Sound, mixed sediments occur at varying water depths and can be exposed to a range of tidal streams and wave action. The mixed substrata provide a range of niches supporting a variety of species assemblages. In the estuarine environment filamentous algae is abundant on cobbles, shells and muddy sediments such as off Ballast Pound (Hiscock and Moore, 1986). Seagrass (Zostera marina) also colonises sublittoral mixed sediments within the site.

The 2016 SAC Condition Assessment found this subfeature to be in unfavourable condition in both the Tamar and Yealm estuaries (Natural England, 2016).


Subtidal mud

Sublittoral mud is formed from fine sands, silts and clays that have been washed down river by the Tamar, Tavy, Lynher and Yealm and settle in areas of low water flow within the river estuaries and the Sound. Subtidal mud was noted as an important subfeature of the site at the time of designation, due to its high productivity and its contribution to the overall functioning of the system.

The larger areas of sublittoral mud are located directly inside the Breakwater, in the shelter of Cawsand Bay and to the north and east of Drake Island. Sublittoral mud is present throughout the main river channels of the estuaries and is often contiguous with the intertidal mudflats. The main riverine channels provide refuge and feeding grounds for mobile benthic species, including fish such as sole (Solea solea), which can move up onto the littoral mudflats to feed with the rising tide. Sublittoral mud is found in a range of salinities and depths throughout the site and supports various communities, predominantly infaunal, at different locations. These muddy substrata often adjoin areas of coarser sand, gravel and cobble and where they mix they form the subfeature subtidal mixed sediments.

The abundance of invertebrate life is demonstrative of the general quality of sublittoral muddy sediment habitats in the Plymouth Sound and Estuaries SAC. However, there are large pockets of contaminated sediment within the site. This is mostly due to historical mining activity in the Tamar Valley, which during the 19th century was producing half of the world’s arsenic, and some other heavy metals associated with the activities of the port. For example, some of the components that were widely used in antifouling paint on ships are particularly harmful and persistent in the natural environment. The concentrations of heavy metals in the muddy sediments are highest in the Tamar-Tavy estuaries and decrease further out into the Sound (Langston et al., 2003). Biological communities associated with contaminated sediments tend to be impoverished.

The 2016 SAC Condition Assessment found this subfeature to be in unfavourable condition in both the Tamar and Yealm estuaries (Natural England, 2016).


Subtidal sand

Sublittoral sand is an important subfeature of subtidal sandbanks for which the site was designated. It occurs in patches in Plymouth Sound and around the mouth of the Yealm Estuary. The largest patch is found near Cawsand Bay in Plymouth Sound. There tends to be no clear boundary between sublittoral sand and other sublittoral sediment habitats which have higher levels of mud or gravel components.

Sublittoral sand may be colonised by eelgrass (Zostera marina) where conditions are suitable, such as north of Drake’s Island. Sublittoral sands in the inner part of Plymouth Sound have been described as silt- free and supporting a community that showed no identifiable estuarine influence (Moore et al., 1999). Sublittoral sand occurs at a range of depths across the outer part of the SAC.


Subtidal seagrass beds

Seagrass (Zostera marina) beds in the Yealm Estuary with their rich associated flora and fauna were one of the prime considerations in the designation of the site. Severe declines have occurred in the past to this once widespread habitat and recovery has been patchy. The habitat is nationally scarce and the south west is one of its main strongholds.

Extensive beds of seagrass (Zostera marina) can found on tide swept sandbanks at the mouth of the River Yealm, at Cawsand Bay, Tomb Rock near Wembury and off the northern side of Drake’s Island. Two further beds located in Firestone Bay and Jennycliff Bay have a patchier distribution of seagrass and exhibit a more ephemeral nature (Curtis, 2012). Leaf blades within the site have been recorded as up to 1.5m in length and many of the old leaves have numerous attached epiphytic species. Survey divers have reported some bald areas in the bed at Drake’s Island but also a number of new seedlings, which is very uncommon for seagrass (Sharrock, 2012).

The seagrass beds at Red Cove North in the mouth of the Yealm are an excellent example of this habitat type and surveys here have identified many associated species. This includes the hydroids (Obelia geniculata and Kirchenpauria pinnata, as well as two species of stalked jellyfish. Both of these stalked jellyfish (Lucernariopsis campanulata and a Haliclystus sp.) are UK Priority Species (Curtis, 2012). Seahorses are also present in the seagrass beds in Plymouth Sound (Sabatini and Ballerstedt, 2007).

The 2016 SAC Condition Assessment found this subfeature to be in favourable condition in the Yealm estuary (Natural England, 2016).



Large shallow inlets and bays

Only two sites in the south west are designated for their large shallow inlets and bays, and Plymouth Sound and Estuaries SAC is the largest. This site, along with the Fal and Helford SAC, are the only rias that are protected for this feature in England. The large shallow inlets and bays in Plymouth Sound and Estuaries SAC support a wide diversity of habitats and species for a number of reasons. In particular the range of exposures, topography, geology and tidal streams within the site provide a variety of niches. The south westerly position of the site means that seawater temperatures allow the existence of species that have a southerly distribution.

The large shallow inlets and bays feature of this site is found in the outer part of the site and includes all of Plymouth Sound and Wembury Bay up to the mouths of the Tamar and Yealm estuaries. This feature includes a range of sediment and rock sub-features.

In the 2016 SAC Condition Assessment the feature was found to be in favourable condition in 979.03 ha and unfavourable condition in 1234.56 ha. 475.71 ha of the feature was not assesed (Natural England, 2016).

SubFeatures

Circalittoral rock

The circalittoral reefs of the Plymouth Sound and Estuaries SAC support rich faunal dominated communities which were considered important for the designation of the site. This was particularly owing to the number of rare and unusual species and habitats found within the site (English Nature, 2000).

The depth at which circalittoral rock is found is dependent on the water clarity at any location. In the turbid waters of the estuarine Tamar circalittoral rock can be found in very shallow water depths. Where turbid waters and wave sheltered conditions continue into the Inner Sound dense communities that ordinarily would be algal dominated can be found (Vance, 2014). The tide-scoured hydrodynamic regime, along with the verticality of the reef structures, also prevents an excessive build-up of silt and delivers nutrient rich waters to the reefs. Steep sided circalittoral limestone reefs can found along the northern shore of the Sound and important sites include Devil’s Point, Eastern Kings and Firestone Bay (Vance, 2014). In the Outer Sound, with increasing water clarity the circalittoral zone is pushed deeper from the surface. Increasing exposure to wave action also dictates changes in community structure, however, the rocky reefs continue to support diverse assemblages. Circalittoral rocky reefs, typically of creviced slate occur in areas off Wembury, the Mewstone, Penlee Point and south of the Breakwater.

Circalittoral reefs in the estuaries support faunal communities typified by the presence of the breadcrumb sponge (Halichondria panicea), which is widespread in the central and lower estuary (Ware and Meadows, 2011). Further upstream it is possible to find a species poor assemblage, defined by the hydroid (Cordylophora caspia), the bryozoan (Electra crustulenta) and the barnacle (Balanus crenatus). This community, a result of very low but still variable salinity, is nationally rare and therefore regarded as important to conserve despite its lack of diversity (Tyler-Walters, 2002).

The soft limestone reefs of the Inner Sound harbour a rich infauna and are extensively burrowed by the wrinkled rock borer (Hiatella arctica) and bristleworms (Polydora spp.) They are also colonised by sessile invertebrates such as the structurally fragile sea beard hydroid (Nemertesia antennina), and the hydroid (Nemertesia ramosa). These species only occur in water this shallow when there is a full absence of physical abrasion (Vance, 2014). Reefs in the Outer Sound are geologically varied and provide diverse habitats supporting rich assemblages that can be characterised by dead man’s fingers (Alcyonium digitatum) (English Nature, 2000).

The 2016 SAC Condition Assessment found this subfeature to be in favourable condition (Natural England, 2016).


Infralittoral rock

Infralittoral rock and other hard substrata in the Plymouth Sound and Estuaries SAC incorporates bedrock outcrops and mixed boulder and cobble communities in the shallow subtidal. Infralittoral reefs frequently connect with those in the intertidal zone, and the reefs in the deeper or more turbid water of the circalittoral zone.

There are two main infralittoral rock habitats within the Plymouth Sound and Estuaries SAC; kelp forest communities, which can be found from the inner Sound to the open coast on reefs in the photic zone and a more unusual habitat, formed of bedrock, boulders and cobble in the estuarine Tamar. One such area is beneath and in the vicinity of the Tamar Bridge (Ware and Meadows, 2011). Important sites include the Mewstone, Penlee Point and Duke Rock.

The estuarine bedrock, boulder and cobbles in the Tamar support a number of fucoid and filamentous algae, which tend to be found no deeper than 1m below chart datum due to the turbidity of the water (Moore et al., 1999). In contrast, the clearer waters of the Sound allow kelp to dominate extensive rocky areas of the infralittoral. The most common species is tangle kelp (Laminaria hyperborea), and this habitat-defining seaweed can form extensive dense underwater forests along with other kelp species, including the southern species (Laminaria ochroleuca) and red seaweeds.

The 2016 SAC Condition Assessment found this subfeature to be in favourable condition (Natural England, 2016).


Intertidal rock

Representatives of every littoral life form (Foster-Smith and Bunker, 1997) and habitat complex type (Connor et al., 1997) have been recorded within Plymouth Sound and Estuaries SAC. Intertidal reef habitats are an essential component of the protected area (Bunker et al., 2002). Within the site sheltered limestone reefs can be found, these are particularly important as this is one of only two coastal areas in southwest Britain with Devonian limestone (English Nature, 2000).

Intertidal rock can be found along most of the coast of Plymouth Sound, with further areas throughout the estuaries where boulders and other hard substrata exist. Sheltered limestone reefs are found along the northern shore of the Sound, from Devil’s Point to Batten Bay. The area from Mount Batten to Dunstone Point is also important for this intertidal limestone habitat, which is extensively burrowed in places by rock boring invertebrates. Under-boulder communities, a Priority Habitat, are also an important feature on rocky shores around the Sound, such as at Jennycliff Bay (English Nature, 2000c,(Bunker et al., 2002). Many other sites with littoral rocky reef habitat can be found around Plymouth Sound and Wembury Bay; including at Wembury Point and Penlee Point.

The Great Mewstone provides a microcosm of littoral reef habitats that can be found in Plymouth Sound, exhibiting exceptional variety in a small area due to the distinct changes in wave exposure around the islet (Bunker et al., 2002). The reefs are formed of Devonian sandstones, slates and limestone. These hard substrates link with the reefs of the infralittoral and deeper circalittoral zones and outcrops also intersperse with areas of sediment. Other hard littoral substrata within the site include estuarine cobbles and boulders, where communities tolerant to reduced salinity develop.

The littoral reefs within the Yealm Estuary are also of note. This aquatic system receives low freshwater inputs which means that marine reef species can survive as far north as Steer Point and Newton Creek, where it is still possible to find rocks with limpets (Patella spp.), barnacles (Semibalanus balanoides and Elminius modestus) and the common flat periwinkle (Littorina obtusata) (Moore et al., 1999). Boulders and other hard substrata in the tidal reaches of all of the estuaries are also colonised by a variety of seaweeds such as bladder wrack (Fucus vesiculosus), channelled wrack (Pelvetia canaliculata), knotted wrack (Ascophyllum nodosum), and toothed wrack ( Fucus serratus) (Curtis, 2010).

The 2016 SAC Condition Assessment found this subfeature to be in favourable condition (Natural England, 2016).


Subtidal coarse sediment

At the time of designation the site was noted for its communities living on mixed cobble, pebble and gravel habitats. Sublittoral coarse sediment, comprised of unstable gravels and cobbles is typically found in high energy areas of the site. There are patches of this subfeature across Plymouth Sound in varying water depths. It does not occur in the estuaries of the site.

In places the coarse sediment is a dynamic habitat where storms can easily move cobbles and tidal flows scour rocks and gravels with loose sand. Species are therefore well adapted to periodic disturbance and communities of scour tolerant ephemeral red algae colonise pebbles and cobbles such as those near Duke Rock (Howson et al., 2005). This includes the nationally scarce seaweed cleaved wart weed (Gracilaria multipartita) (Hiscock and Moore, 1986).

The 2016 SAC Condition Assessment found this subfeature to be in unfavourable condition (Natural England, 2016).


Subtidal mixed sediments

Plymouth Sound and Estuaries SAC is an exceptional site, in part owing to the huge range of substrata within its boundaries. This includes muddy sediments from the rivers, marine sands, and harder materials contributed by the underlying geology of Devonian slates and limestone. The sublittoral mixed sediment habitats can involve a number of these components and are made up of a combination of muds, shells, sands, gravels, pebbles and cobbles.

Sublittoral mixed sediments can be found widely across the site and are a subfeature of estuaries, large shallow inlets and bays and sandbanks. In Plymouth Sound, mixed sediments occur at varying water depths and can be exposed to a range of tidal streams and wave action. The mixed substrata provide a range of niches supporting a variety of species assemblages. In the estuarine environment filamentous algae is abundant on cobbles, shells and muddy sediments such as off Ballast Pound (Hiscock and Moore, 1986). Seagrass (Zostera marina) also colonises sublittoral mixed sediments within the site.

The 2016 SAC Condition Assessment found this subfeature to be in unfavourable condition (Natural England, 2016).


Subtidal mud

Sublittoral mud is formed from fine sands, silts and clays that have been washed down river by the Tamar, Tavy, Lynher and Yealm and settle in areas of low water flow within the river estuaries and the Sound. Subtidal mud was noted as an important subfeature of the site at the time of designation, due to its high productivity and its contribution to the overall functioning of the system.

The larger areas of sublittoral mud are located directly inside the Breakwater, in the shelter of Cawsand Bay and to the north and east of Drake Island. Sublittoral mud is present throughout the main river channels of the estuaries and is often contiguous with the intertidal mudflats. The main riverine channels provide refuge and feeding grounds for mobile benthic species, including fish such as sole (Solea solea), which can move up onto the littoral mudflats to feed with the rising tide. Sublittoral mud is found in a range of salinities and depths throughout the site and supports various communities, predominantly infaunal, at different locations. These muddy substrata often adjoin areas of coarser sand, gravel and cobble and where they mix they form the subfeature subtidal mixed sediments.

The abundance of invertebrate life is demonstrative of the general quality of sublittoral muddy sediment habitats in the Plymouth Sound and Estuaries SAC. However, there are large pockets of contaminated sediment within the site. This is mostly due to historical mining activity in the Tamar Valley, which during the 19th century was producing half of the world’s arsenic, and some other heavy metals associated with the activities of the port. For example, some of the components that were widely used in antifouling paint on ships are particularly harmful and persistent in the natural environment. The concentrations of heavy metals in the muddy sediments are highest in the Tamar-Tavy estuaries and decrease further out into the Sound (Langston et al., 2003). Biological communities associated with contaminated sediments tend to be impoverished.

The 2016 SAC Condition Assessment found this subfeature to be in unfavourable condition (Natural England, 2016).


Subtidal sand

Sublittoral sand is an important subfeature of subtidal sandbanks for which the site was designated. It occurs in patches in Plymouth Sound and around the mouth of the Yealm Estuary. The largest patch is found near Cawsand Bay in Plymouth Sound. There tends to be no clear boundary between sublittoral sand and other sublittoral sediment habitats which have higher levels of mud or gravel components. Sublittoral sand may be colonised by eelgrass (Zostera marina) where conditions are suitable, such as north of Drake’s Island.

Sublittoral sands in the inner part of Plymouth sound have been described as silt- free and supporting a community that showed no identifiable estuarine influence (Moore et al., 1999). Sublittoral sand occurs at a range of depths across the outer part of the SAC.

The 2016 SAC Condition Assessment found this subfeature to be in favourable condition (Natural England, 2016).


Subtidal seagrass beds

Seagrass (Zostera marina) beds in the Yealm Estuary with their rich associated flora and fauna were one of the prime considerations in the designation of the site. Severe declines have occurred in the past to this once widespread habitat and recovery has been patchy. The habitat is nationally scarce and the south west is one of its main strongholds.

Extensive beds of seagrass (Zostera marina) can found on tide swept sandbanks at the mouth of the River Yealm, at Cawsand Bay, Tomb Rock near Wembury and off the northern side of Drake’s Island. Two further beds located in Firestone Bay and Jennycliff Bay have a patchier distribution of seagrass and exhibit a more ephemeral nature (Curtis, 2012). Leaf blades within the site have been recorded as up to 1.5m in length and many of the old leaves have numerous attached epiphytic species. Survey divers have reported some bald areas in the bed at Drake’s Island but also a number of new seedlings, which is very uncommon for seagrass (Sharrock, 2012).

The seagrass beds at Red Cove North in the mouth of the Yealm are an excellent example of this habitat type and surveys here have identified many associated species. This includes the hydroids (Obelia geniculata and Kirchenpauria pinnata, as well as two species of stalked jellyfish. Both of these stalked jellyfish (Lucernariopsis campanulata and a Haliclystus sp.) are UK Priority Species (Curtis, 2012). It is also possible to find the two UK species of seahorses in the seagrass beds in Plymouth Sound, the short-snouted seahorse, Hippocampus hippocampus, and the spiny seahorse, Hippocampus guttulatus (Plymouth City Council, 2014).

The 2016 SAC Condition Assessment found this subfeature to be in favourable condition (Natural England, 2016).



Mudflats and sandflats not covered by seawater at low tide

The mudflats are a highly productive system forming a critical part of the food chain (English Nature, 2000). The mudflats contain extensive and varied infaunal communities, rich in bivalves and other invertebrates, and provide key feeding grounds for internationally important numbers of wintering wildfowl and waders.

Mudflats and sandflats are composed of a variety of sediments within the Plymouth Sound and Estuaries SAC, including littoral mud, littoral sand and muddy sand, littoral mixed sediments, and littoral coarse sediments. Muddy sediments border the main river channels and backwater embayments where slower flow rates have allowed suspended sands, silts and clays to become deposited. Important intertidal mudflat areas can be found above the Hamoaze in the Tamar-Tavy Estuaries, in the Lynher Estuary, and throughout the Yealm Estuary (Bunker et al., 2002)(Curtis, 2010)(Curtis, 2010). Areas of sand and muddy sand are also an important component of the estuaries, particularly in St. John’s Lake and the northern Lynher Estuary as well as the Tamar-Tavy Estuary. Additionally, extensive areas of sand and coarse sediments are found on beaches within the Sound (e.g. Cawsand, Bovisand, and Crownhill bays), and at Wembury Bay.

Sediments in the littoral zone provide habitat for the common or blue mussel (Mytilus edulis). Biogenic reefs formed of well-developed mussel beds can be found on the Tamar opposite Weir Point and along the shore of the estuary for more than a kilometre between Tamerton Lake and the Tamar Bridge. Mussel beds are also located at the tide-swept entrance to the Lynher Estuary. These beds support a rich variety of epifauna and flora including seaweeds, barnacles, sea squirts and sponges (Bunker et al., 2002).

In the 2016 SAC Condition Assessment the feature was found to be in favourable condition in 1412.09 ha and unfavourable condition in 70.09 ha (Natural England, 2016).

SubFeatures

Intertidal coarse sediment

Within the Plymouth Sound and Estuaries SAC, littoral coarse sediments are not as prevalent as at other sites in the southwest, especially compared to the long sections along the shore between Sidmouth (Devon) and Weymouth (Dorset) for example. Though largely found on open shores, littoral coarse sediments can also be found in low energy environments such as in the upper reaches of estuaries, where the outflow of riverine freshwater can wash out fine particulate matter. Plymouth Sound and Estuaries SAC has examples of littoral coarse sediments in both of these types of contrasting environments.

The largest areas of littoral coarse sediments are found along the shore in Wembury Bay. Smaller, more isolated areas of littoral coarse sediments are found in the upper reaches of the Tavy tributary within the Tamar-Tavy Estuary SSSI. Littoral coarse sediments are typically species-poor habitats, and this is true in the upper reaches of the Tavy River, where littoral coarse sediments were recorded as barren littoral shingle (Curtis, 2010).

The 2016 SAC Condition Assessment found this subfeature to be in favourable condition (Natural England, 2016).


Intertidal mixed sediments

Littoral mixed sediments range from muds with gravel and sand components to mixed sediments with pebbles, gravels, sands and mud in more even proportions. Littoral mixed sediments are important feeding areas for birds such as the avocet (Recurvirostra avosetta) and little egret (Egretta garzetta).

Littoral mixed sediments occur in small areas at various locations throughout the Plymouth Sound and Estuaries SAC. These areas range from close to the Sound (e.g., Cawsand, Conger Point, Pier Cove, Outer Broady Cove, Rame Head, Heybrook Bay, and Wembury) up to the mid-upper reaches of the estuaries including the Lynher Estuary (on the northern shore near Wivelscombe Lake) and the Tamar-Tavy Estuary (near Warren Point, east of Tamerton Bridge, and in the upper reaches between Cotehele Bridge and Chapel Farm).

The most abundant species in these littoral mixed sediments are typically polychaetes (Hediste diversicolor, Nephtys hombergii, and Streblospio shrubsolii) and the oligochaete (Tubificoides benedii). Also present are the amphipod (Corophium volutator), the gastropod (Hydrobia ulvae), and the bivalve (Macoma balthica).The river Yealm supports the most interesting littoral mixed sediment communities. For instance, north of Shortaflete Creek, rich muddy gravel supports abundant peacock worm (Sabella pavonina), common cockle (Cerastoderma edule), orange sponge (Hymeniacidon perleve) and common shore crab (Carcinus maenas) communities.

The 2016 SAC Condition Assessment found this subfeature to be in unfavourable condition (Natural England, 2016).


Intertidal mud

Littoral mud is perhaps the most visible of the described features in the Plymouth Sound and Estuaries SAC. When the area was designated for protection the site was judged as supporting a significant presence of this habitat. In each of the estuaries at low tide extensive mudflats extend from the main riverine channels out to saltmarsh and other transitional habitats. These areas are very important as feeding grounds for birds such as the avocet (Recurvirostra avosetta) and little egret (Egretta garzetta).

Littoral mud habitats can be found on the Tamar, Tavy, Lynher, and Yealm estuaries as well as in St. John’s Lake. The largest littoral mudflats on the Yealm are in an area called the Broad Ooze which supports ragworm (Hediste diversicolor), common cockle (Cerastoderma edule) and the sand mason worm (Lanice conchilega) (Moore et al., 1999). On muddy shores in lower salinity conditions, in sheltered regions of all the other estuaries, oligochaete worms and ragworm frequently make up a large proportion of the infaunal community. These areas include the sheltered inlet of Tamerton Lake, Kingsmill Lake and Saltmill Creek (Bunker et al., 2002). Another dominant community consists of ragworm and the peppery furrow shell (Scrobicularia plana), in reduced salinity on muddy shores. This biotope was recorded as dominating many of the mud flats across the estuaries (Bunker et al., 2002).

The 2016 SAC Condition Assessment found this subfeature to be in favourable condition (Natural England, 2016).


Intertidal sand and muddy sand

The subfeature littoral sand and muddy sand is found at various locations throughout the Plymouth Sound and Estuaries SAC, including both estuarine and bay environments. For example, an extensive estuarine area is found on either side of the river Tamar, extending northwards from the Tamar Bridge to where the Tamar and Tavy tributaries merge. Large areas are also found within the Lynher Estuary and St. John’s Lake, and to a lesser extent in the upper reaches of the Yealm Estuary near Steer Point. Within Plymouth Sound, the subfeature is found at numerous locations including at Bovisand Bay, Crownhill Bay, and beaches within Cawsand Bay.

While the subfeature is found in both estuarine and bay environments, the composition of the sediments differs between these two environments. For example, most prevalent in the Tamar-Tavy Estuary, Lynher Estuary and St. John’s Lake SSSIs is muddy sand dominated by bivalves and polychaetes. These include the cockle (Cerastoderma edule) and polychaetes (Pygospio elegans and Streblespio shrubsolli) (Curtis, 2010)(Curtis, 2010). In contrast, areas within the Sound are classified as medium to fine sand shores, dominated by amphipods and polychaetes (Natural England, 2010) (Moore et al., 1999).

The 2016 SAC Condition Assessment found this subfeature to be in favourable condition (Natural England, 2016).


Intertidal seagrass beds

Littoral seagrass beds had disappeared from St John’s Lake at the time of the site’s designation, so were not considered an interest feature of the site in their own right. However, they are an important subfeature of the intertidal mudflats and sandflats feature.

The disappearance of these beds, which were first recorded in 1872 (Hocking et al., 2002), then in the 1950s (Wilson, 1958) and 1986 (Burd, 1986) is described as dramatic (Marine Nature Conservation Review (MNCR), 1996). In 1986 Zostera noltii and Z. angustifolia (now considered to be Z. marina) were recorded as abundant across an extensive bed in the south west of St John’s Lake, but had disappeared completely in 1997. However, in 1999 several patchy beds of Zostera noltii were recorded in St John’s Lake (Hocking et al., 2002) and in 2010 a large bed of intertidal seagrass was recorded in a similar location. These reports suggest that the bed is somewhat ephemeral in nature.

Zostera marina has also previously been recorded in intertidal areas at Drake’s Island and Cawsand Bay, but has disappeared from these areas since 1967 (Hocking et al., 2002).

The 2016 SAC Condition Assessment found this subfeature to be in unfavourable condition (Natural England, 2016).



Reefs

The rocky reefs of the Plymouth Sound and Estuaries SAC are considered to be an excellent example of this habitat type within the UK. Reef communities within the Sound and Estuaries are defined by the south-westerly location of Plymouth, wave exposure and tidal flow, bathymetry, geology and the variance in salinity from the upper estuarine to the open coast (English Nature, 2000). This wide variety of abiotic factors encourages a diverse range of flora and fauna within a small geographical area (Howson et al., 2005).

Reefs are widespread in the Plymouth Sound and Estuaries SAC and can be divided into three sub-feature classifications: the intertidal, infralittoral and circalittoral. These sub-features frequently connect with one another and are interspersed with the variety of sediment habitats found in the area. A number of individual locations within the site have been identified as typifying important reef habitats. This includes circalittoral reefs in the outer Sound at Penlee Point and the Mewstone, and sites such as Eastern Kings and Devil’s Point along the northern shore of Inner Sound. Infralittoral rock habitats dominated by kelp communities can be found at Duke Rock, Cavehole Point and Tinker Shoal. The large tidal range in Plymouth - up to 5.85m - means that littoral reef habitats are an important element of the site. A typical example of a littoral reef structure is the shoreline of Jennycliff Bay.

Some of the richest reefs are in the wave-sheltered inner parts of the Sound, where vertical limestone walls rise up from a deep channel. Rich communities of sponge, hydroids, anemones and rock boring species have developed here. The shore at Wembury has been studied for many years and has a diverse range of intertidal life within its wave cut platforms and rockpools. Much of the shallow subtidal area within the site is dominated by kelp forest which is an important infralittoral habitat. A significant feature of the estuaries in the site is that a zonation of rocky habitats is found for an extended distance along the estuarine gradient. For example, in the area of the Tamar Bridge close to Saltash there is more than a mile of mixed substrata that includes bedrock, boulder and cobble reef. The reefs here, under varying and low salinity, are colonised by species that can cope with these challenging conditions, such as the hydroid (Cordylophora caspia), which is a brackish water specialist. In the Yealm Estuary marine reef species such as limpets (Patella spp.) can also be found a long way inland, due to the occurrence of suitable hard substrata and low freshwater inputs in this waterway (Moore et al., 1999).

In the 2016 SAC Condition Assessment the feature was found to be in favourable condition in 2376.83 ha and unfavourable condition in 18.72 ha (Natural England, 2016).

SubFeatures

Circalittoral rock

The circalittoral reefs of the Plymouth Sound and Estuaries SAC support rich faunal dominated communities which were considered important for the designation of the site. This was particularly owing to the number of rare and unusual species and habitats found within the site (English Nature, 2000).

The depth at which circalittoral rock is found is dependent on the water clarity at any location. In the turbid waters of the estuarine Tamar circalittoral rock can be found in very shallow water depths. Where turbid waters and wave sheltered conditions continue into the Inner Sound dense communities that ordinarily would be algal dominated can be found (Vance, 2014). The tide-scoured hydrodynamic regime, along with the verticality of the reef structures, also prevents an excessive build-up of silt and delivers nutrient rich waters to the reefs. Steep sided circalittoral limestone reefs can found along the northern shore of the Sound and important sites include Devil’s Point, Eastern Kings and Firestone Bay (Vance, 2014). In the Outer Sound, with increasing water clarity the circalittoral zone is pushed deeper from the surface. Increasing exposure to wave action also dictates changes in community structure, however, the rocky reefs continue to support diverse assemblages. Circalittoral rocky reefs, typically of creviced slate occur in areas off Wembury, the Mewstone, Penlee Point and south of the Breakwater.

Circalittoral reefs in the estuaries support faunal communities typified by the presence of the breadcrumb sponge (Halichondria panicea), which is widespread in the central and lower estuary (Ware and Meadows, 2011). Further upstream it is possible to find a species poor assemblage, defined by the hydroid (Cordylophora caspia), the bryozoan (Electra crustulenta) and the barnacle (Balanus crenatus). This community, a result of very low but still variable salinity, is nationally rare and therefore regarded as important to conserve despite its lack of diversity (Tyler-Walters, 2002).

The soft limestone reefs of the Inner Sound harbour a rich infauna and are extensively burrowed by the wrinkled rock borer (Hiatella arctica) and bristleworms (Polydora spp.) They are also colonised by sessile invertebrates such as the structurally fragile sea beard hydroid (Nemertesia antennina), and the hydroid (Nemertesia ramosa). These species only occur in water this shallow when there is a full absence of physical abrasion (Vance, 2014). Reefs in the Outer Sound are geologically varied and provide diverse habitats supporting rich assemblages that can be characterised by dead man’s fingers (Alcyonium digitatum) (English Nature, 2000).

The 2016 SAC Condition Assessment found this subfeature to be in favourable condition (Natural England, 2016).


Infralittoral rock

Infralittoral rock and other hard substrata in the Plymouth Sound and Estuaries SAC incorporates bedrock outcrops and mixed boulder and cobble communities in the shallow subtidal. Infralittoral reefs frequently connect with those in the intertidal zone, and the reefs in the deeper or more turbid water of the circalittoral zone.

There are two main infralittoral rock habitats within the Plymouth Sound and Estuaries SAC; kelp forest communities, which can be found from the inner Sound to the open coast on reefs in the photic zone and a more unusual habitat, formed of bedrock, boulders and cobble in the estuarine Tamar. One such area is beneath and in the vicinity of the Tamar Bridge (Ware and Meadows, 2011). Important sites include the Mewstone, Penlee Point and Duke Rock.

The estuarine bedrock, boulder and cobbles in the Tamar support a number of fucoid and filamentous algae, which tend to be found no deeper than 1m below chart datum due to the turbidity of the water (Moore et al., 1999). In contrast, the clearer waters of the Sound allow kelp to dominate extensive rocky areas of the infralittoral. The most common species is tangle kelp (Laminaria hyperborea), and this habitat-defining seaweed can form extensive dense underwater forests along with other kelp species, including the southern species (Laminaria ochroleuca) and red seaweeds.

The 2016 SAC Condition Assessment found this subfeature to be in favourable condition (Natural England, 2016).


Intertidal rock

Representatives of every littoral life form (Foster-Smith and Bunker, 1997) and habitat complex type (Connor et al., 1997) have been recorded within Plymouth Sound and Estuaries SAC. Intertidal reef habitats are an essential component of the protected area (Bunker et al., 2002). Within the site sheltered limestone reefs can be found, these are particularly important as this is one of only two coastal areas in southwest Britain with Devonian limestone (English Nature, 2000).

Intertidal rock can be found along most of the coast of Plymouth Sound, with further areas throughout the estuaries where boulders and other hard substrata exist. Sheltered limestone reefs are found along the northern shore of the Sound, from Devil’s Point to Batten Bay. The area from Mount Batten to Dunstone Point is also important for this intertidal limestone habitat, which is extensively burrowed in places by rock boring invertebrates. Under-boulder communities, a Priority Habitat, are also an important feature on rocky shores around the Sound, such as at Jennycliff Bay (English Nature, 2000c,(Bunker et al., 2002). Many other sites with littoral rocky reef habitat can be found around Plymouth Sound and Wembury Bay; including at Wembury Point and Penlee Point.

The Great Mewstone provides a microcosm of littoral reef habitats that can be found in Plymouth Sound, exhibiting exceptional variety in a small area due to the distinct changes in wave exposure around the islet (Bunker et al., 2002). The reefs are formed of Devonian sandstones, slates and limestone. These hard substrates link with the reefs of the infralittoral and deeper circalittoral zones and outcrops also intersperse with areas of sediment. Other hard littoral substrata within the site include estuarine cobbles and boulders, where communities tolerant to reduced salinity develop.

The littoral reefs within the Yealm Estuary are also of note. This aquatic system receives low freshwater inputs which means that marine reef species can survive as far north as Steer Point and Newton Creek, where it is still possible to find rocks with limpets (Patella spp.), barnacles (Semibalanus balanoides and Elminius modestus) and the common flat periwinkle (Littorina obtusata) (Moore et al., 1999). Boulders and other hard substrata in the tidal reaches of all of the estuaries are also colonised by a variety of seaweeds such as bladder wrack (Fucus vesiculosus), channelled wrack (Pelvetia canaliculata), knotted wrack (Ascophyllum nodosum), and toothed wrack ( Fucus serratus) (Curtis, 2010).

The 2016 SAC Condition Assessment found this subfeature to be in unfavourable condition (Natural England, 2016).



Sandbanks which are slightly covered by sea water all the time

In Plymouth Sound and Estuaries SAC the subtidal sandbanks feature is found in the outer, higher energy areas of the site such as around the mouth of the Yealm Estuary, in Cawsand Bay and in parts of Plymouth Sound. The sandbanks tend to be tideswept and are made up of a range of sediment types, from fine muddy sand to gravel, including mixed sediment. They support various communities including subtidal seagrass beds and a number of communities dominated by worms and burrowing molluscs. Sandbanks within the SAC are largely stable, not mobile and are not significantly elevated from the levels of the surrounding seabed.

In the 2016 SAC Condition Assessment the feature was found to be in favourable condition in 118.99 ha and unfavourable condition in 1356.87 ha (Natural England, 2016).

SubFeatures

Subtidal coarse sediment

At the time of designation the site was noted for its communities living on mixed cobble, pebble and gravel habitats. Sublittoral coarse sediment, comprised of unstable gravels and cobbles is typically found in high energy areas of the site. There are patches of this subfeature across Plymouth Sound in varying water depths. It does not occur in the estuaries of the site.

In places the coarse sediment is a dynamic habitat where storms can easily move cobbles and tidal flows scour rocks and gravels with loose sand. Species are therefore well adapted to periodic disturbance and communities of scour tolerant ephemeral red algae colonise pebbles and cobbles such as those near Duke Rock (Howson et al., 2005). This includes the nationally scarce red seaweed cleaved wart weed (Gracilaria multipartita) (Hiscock and Moore, 1986).

The 2016 SAC Condition Assessment found this subfeature to be in unfavourable condition (Natural England, 2016).


Subtidal mixed sediments

Plymouth Sound and Estuaries SAC is an exceptional site, in part owing to the huge range of substrata within its boundaries. This includes muddy sediments from the rivers, marine sands, and harder materials contributed by the underlying geology of Devonian slates and limestone. The sublittoral mixed sediment habitats can involve a number of these components and are made up of a combination of muds, shells, sands, gravels, pebbles and cobbles.

Sublittoral mixed sediments can be found widely across the site and are a subfeature of estuaries, large shallow inlets and bays and sandbanks. In Plymouth Sound, mixed sediments occur at varying water depths and can be exposed to a range of tidal streams and wave action. The mixed substrata provide a range of niches supporting a variety of species assemblages. In the estuarine environment filamentous algae is abundant on cobbles, shells and muddy sediments such as off Ballast Pound (Hiscock and Moore, 1986). Seagrass (Zostera marina) also colonises sublittoral mixed sediments within the site.

The 2016 SAC Condition Assessment found this subfeature to be in unfavourable condition (Natural England, 2016).


Subtidal mud

Sublittoral mud is formed from fine sands, silts and clays that have been washed down river by the Tamar, Tavy, Lynher and Yealm and settle in areas of low water flow within the river estuaries and the Sound. Subtidal mud was noted as an important subfeature of the site at the time of designation due to its high productivity and its contribution to the overall functioning of the system.

The larger areas of sublittoral mud are located directly inside the Breakwater, in the shelter of Cawsand Bay and to the north and east of Drake Island. Sublittoral mud is present throughout the main river channels of the estuaries and is often contiguous with the intertidal mudflats. The main riverine channels provide refuge and feeding grounds for mobile benthic species, including fish such as sole (Solea solea) which can move up onto the littoral mudflats to feed with the rising tide. Sublittoral mud is found at a range of salinities and depths throughout the site and supports various communities, predominantly infaunal, at different locations. These muddy substrata often adjoin areas of coarser sand, gravel and cobble and where they mix they form the subfeature subtidal mixed sediments.

The abundance of invertebrate life is demonstrative of the general quality of sublittoral muddy sediment habitats in the Plymouth Sound and Estuaries SAC. However there are large pockets of contaminated sediment within the site. This is mostly due to historical mining activity in the Tamar Valley, which during the 19th century was producing half the World’s arsenic, and some other heavy metals associated with the activities of the port. For example, some of the components that were widely used in antifouling paint on ships are particularly harmful and persistent in the natural environment. The concentrations of heavy metals in the muddy sediments are highest in the Tamar-Tavy estuaries and decrease further out into the Sound (Langston et al., 2003). Biological communities associated with contaminated sediments tend to be impoverished.

The 2016 SAC Condition Assessment found this subfeature to be in unfavourable condition (Natural England, 2016).


Subtidal sand

Sublittoral sand is an important subfeature of subtidal sandbanks for which the site was designated. It occurs in patches in Plymouth Sound and around the mouth of the Yealm Estuary. The largest patch is found near Cawsand Bay in Plymouth Sound. There tends to be no clear boundary between sublittoral sand and other sublittoral sediment habitats which have higher levels of mud or gravel components. Sublittoral sand may be colonised by eelgrass (Zostera marina) where conditions are suitable, such as north of Drake’s Island.

Sublittoral sands in the inner part of Plymouth sound have been described as silt- free and supporting a community that showed no identifiable estuarine influence (Moore et al., 1999). Sublittoral sand occurs at a range of depths across the outer part of the SAC.

The 2016 SAC Condition Assessment found this subfeature to be in favourable condition (Natural England, 2016).


Subtidal seagrass beds

Seagrass (Zostera marina) beds in the Yealm Estuary with their rich associated flora and fauna were one of the prime considerations in the designation of the site. Severe declines have occurred in the past to this once widespread habitat and recovery has been patchy. The habitat is nationally scarce and the south west is one of its main strongholds.

Extensive beds of seagrass (Zostera marina) can found on tide swept sandbanks at the mouth of the River Yealm, at Cawsand Bay, Tomb Rock near Wembury and off the northern side of Drake’s Island. Two further beds located in Firestone Bay and Jennycliff Bay have a patchier distribution of seagrass and exhibit a more ephemeral nature (Curtis, 2012). Leaf blades within the site have been recorded as up to 1.5m in length and many of the old leaves have numerous attached epiphytic species. Survey divers have reported some bald areas in the bed at Drake’s Island but also a number of new seedlings, which is very uncommon for seagrass (Sharrock, 2012).

The seagrass beds at Red Cove North in the mouth of the Yealm are an excellent example of this habitat type and surveys here have identified many associated species. This includes the hydroids (Obelia geniculata and Kirchenpauria pinnata), as well as two species of stalked jellyfish. Both of these stalked jellyfish (Lucernariopsis campanulata and a Haliclystus sp. Are UK Priority Species (Curtis, 2012). Seahorses are also present in the seagrass bed in Plymouth Sound (Sabatini and Ballerstedt, 2007).

The 2016 SAC Condition Assessment found this subfeature to be in favourable condition (Natural England, 2016).



Shore dock (Rumex rupestris)

Shore dock occurs in two locations adjacent to the Plymouth Sound and Estuaries SAC: Rame and Wembury. At Rame, shore dock occurs along a 300 m long stretch of sand and shingle beach from south-east of Captain Blake’s Point to just north of Polhawn Cottages (McDonnell and King, 2000). The beach is backed by high eroding cliffs of head deposits which, together with the presence of freshwater seepages, are favoured habitats for this species. At Wembury, plants have been recorded growing in shingle at the back of the rocky shore, beneath almost vertical cliffs of head, between Wembury Point and Blackstone Rocks (McDonnell and King, 2000).

In the 2016 SAC Condition Assessment the feature was found to be in favourable condition. The assessment was carried out using SSSI Favourable Condition Tables (Natural England, 2016).


General information on the site features:
The generic information on the qualifying features is useful for understanding the qualifying features, and should be used in conjunction with the site specific information.
Designated area (ha): 6402.03
Component Sites of Special Scientific Interest (SSSI):
Overlapping Protected Areas:

Last updated: 20th March 2017

Background information and geography

Plymouth Sound and Estuaries SAC is located on the south coast of England and straddles the border between Devon and Cornwall. Plymouth Sound and its associated tributaries comprise a complex site of marine inlets. The high diversity of reef and sedimentary habitats, and salinity conditions, give rise to diverse communities representative of ria systems and some unusual features. These features include abundant southern Mediterranean-Atlantic species rarely found in Britain. It is also the only known spawning site for the Allis shad (Alosa alosa).

The extensive mudflats present throughout the SAC are a highly productive system, forming a critical part of the food chain. They contain extensive and varied infaunal communities, rich in bivalves and other invertebrates, and provide important feeding grounds for internationally important numbers of wildfowl.There are communities of slender sea pens (Virgularia mirabilis) in the subtidal muddy habitats north of the Breakwater, which is uncommon in the south of the country. Fan mussels (Atrina fragilis), a UK Priority species for conservation, have been recorded in the sediment around Plymouth Hoe. On the Yealm estuary at Cofflete creek the nationally scarce tentacled lagoon worm (Alkmaria romijni) has been recorded.

There are extensive and important areas of saltmarsh present, particularly on the Lynher Estuary, with natural transitions to reedbed and fringing woodland. Saltmarsh is an uncommon habitat in the south west and provides important roosting areas for birds. The triangular club rush (Schoenoplectus triqueter) is on the very edge of its range in the UK, with the Tamar having the only known population in England. The saltmarsh fringes act as nursery areas for juvenile bass (Dicentrarchus labrax) and other fish species.

The site is of particular importance for its reef communities which are home to a number of species of note. The Devonian limestone reef is of particular importance because this is one of only two sites in the south west with coastal Devonian limestone. The limestone reef is heavily bored by marine worms and bivalves. The nationally rare sponge (Dysidea pallescens) and the Weymouth carpet coral (Hoplangia durotrix) are found on sublittoral reefs in the site. Nationally scarce species; pink sea fan (Eunicella verrucosa), trumpet anemone (Aiptasia mutabilis), latticed corklet anemone (Cataphellia brodricii), scarlet and gold star coral (Balanophyllia regia) and orange light seasquirt (Pycnoclavella aurilucens) have all been recorded on reefs in the site. The nationally scarce hydroid (Hartlaubella gelatinosa) forms clumps on mixed substrata in the upper Tamar estuary.

Intertidal reefs with rockpools at Wembury, Penlee, Hooe Lake Point and the mouth of the Yealm support a nationally uncommon sponge, seasquirt and red algae community. The intertidal underboulder communities at Jennycliff are of note for their species richness.The crevice dwelling brittlestar (Ophiopsila aranea) has been recorded as abundant around the Mewstone, but is nationally rare across the UK. Several nationally rare and scarce seaweeds are also found within the site including; Bornetia secundiflora, Carpomitra costata, Gigartina pistillata, Gracilaria bursa-pastoris and Schmitzia hiscockiana.

Intertidal reefs with rockpools at Wembury, Penlee, Hooe Lake Point and the mouth of the Yealm support a nationally uncommon sponge, seasquirt and red algae community. The intertidal underboulder communities at Jennycliff are of note for their species richness.The crevice dwelling brittlestar (Ophiopsila aranea) has been recorded as abundant around the Mewstone, but is nationally rare. Several nationally rare and scarce seaweeds are also found within the site including Bornetia secundiflora, Carpomitra costata, Gigartina pistillata, Gracilaria bursa-pastoris and Schmitzia hiscockiana.

Site maps

Use the MAGIC website to see site maps, including habitats, species and other marine designations.

These maps are based on best available evidence, there are some caveats associated with the maps on MAGIC.

The dynamic nature of habitat features and supporting habitats for mobile species is illustrated where data is available, as new evidence becomes available these maps will be updated with our current knowledge of their known extent.



Conservation objectives

The site’s conservation objectives apply to the site and the individual species and/or assemblage of species for which the site has been classified (the "Qualifying features" listed above).

The objectives are to ensure that, subject to natural change, the integrity of the site is maintained or restored as appropriate, and that the site contributes to achieving the Favourable Conservation Status of its qualifying features, by maintaining or restoring:
  • the extent and distribution of qualifying natural habitats and habitats of the qualifying species
  • the structure and function (including typical species) of qualifying natural habitats
  • the structure and function of the habitats of the qualifying species
  • the supporting processes on which qualifying natural habitats and the habitats of qualifying species rely
  • the populations of each of the qualifying species
  • the distribution of qualifying species within the site

Qualifying features

Refer to the site information table above for the list of features within this site.

This should be read in conjunction with the accompanying supplementary advice section, which provides more detailed information to help achieve the objectives set out above, including which attributes should be maintained and which restored.

The conservation objectives apply under the Habitats Regulations, and must be considered during a Habitats Regulation Assessment, including an Appropriate Assessment.

The conservation objectives and accompanying supplementary advice provide a framework to inform the management and measures needed to conserve or restore the European site, and the prevention of deterioration and significant disturbance of its qualifying features.

Where the objectives are met, the site will be considered to show a high level of integrity, and to be contributing to achieving the aims of the Habitats Regulations.

Supplementary Advice on Conservation Objectives

See supplementary advice on conservation objectives for this site, which aim to describe the range of ecological attributes that are most likely to contribute to a site’s overall integrity.

Last updated: 15th March 2019


Advice on Operations

See the advice on operations for this site to view information on the sensitivity of features in this site to the pressures exerted by different activities.

Last updated: 13th September 2019


Advice on Seasonality

See the advice on seasonality for this site, to view the months in which each mobile feature occurs in this site.

Last updated: 20th March 2017


Feature Condition

In 2016, Natural England trialled and rolled out a new Marine Protected Area (MPA) condition assessment methodology that provides robust results and information on the condition of marine features designated within MPAs in England. With guidance from National teams and using all available evidence and condition monitoring data, Area Teams conduct these assessments following a standardised approach that assesses if the feature and sub feature conservation targets set for each MPA have been met.

To date, condition assessments have been completed for a number of features in a range of marine Special Areas of Conservation (SACs) by the National and Area Teams. Further marine habitat features in SACs and other MPAs will continue to be assessed in the future. The new method can now also be applied to complete habitat and species condition assessments for other MPAs in England, whilst still meeting the different processes in place to report on the results of condition of features in Marine Conservation Zones (MCZs) and Special Protection Areas (SPAs). Different processes are currently in place to decide and report on the condition of non-marine habitat and species features of SACs.

The main part of the assessment process is directly undertaken and stored here on Natural England’s Designated Sites View. The details for the most recent assessments of this site can be found here.

Management measures

If you are carrying out an environmental assessment, planning an operation or assessing an operation or proposal, it is important to consult with the following organisations where applicable. To find out if any management measures, byelaws or other restrictions apply to your activity see the management measure page or you can use the following links for more information.

The Marine Management Organisation license, regulate and plan marine activities in the seas around England and Wales so that they’re carried out in a sustainable way.
Environment Agency are responsible for regulating major industry and waste, water quality and resources, fisheries, inland river, estuary and harbour navigations, conservation and ecology.
Offshore Petroleum Regulator for the Environment and Decommissioning (OPRED) regulates oil and gas, CCS and gas storage activities in the marine environment.

Further information

For further information relating to this designated site you can refer to the following resources:
Site specific information: Other information:
For further information about this site contact: Natural England enquiries Telephone: 0300 060 3900. Email: enquiries@naturalengland.org.uk


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