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/

Mounts Bay MCZ

Last updated: 13th September 2019

Supplementary advice

The Supplementary Advice on Conservation Objectives (SACOs) present attributes which are ecological characteristics or requirements of the designated species and habitats within a site. The listed attributes are considered to be those which best describe the site’s ecological integrity and which if safeguarded will enable achievement of the Conservation Objectives. These attributes have a target which is either quantified or qualified depending on the available evidence.

The target identifies as far as possible the desired state to be achieved for the attribute. In many cases, the attribute targets show if the current objective is to either ‘maintain’ or ‘recover’ the attribute.

Where there is no evidence to determine a marine feature’s condition, a vulnerability assessment, which includes sensitivity and exposure information for features and activities in a site, has been used as a proxy for condition. Evidence used in preparing the SACO has been cited with hyperlinks included where possible. Where references have not been provided, Natural England has applied ecological knowledge and expert judgement.

Some, but not all, of these attributes can also be used for regular monitoring of the condition of the designated features. The attributes selected for monitoring the features, and the standards used to assess their condition, are listed in separate monitoring documents, which will be available from Natural England. As condition assessment information becomes available, the conservation advice package will be reviewed accordingly.

When to use

You should use this information, along with the conservation objectives and case-specific advice issued by Natural England when developing, proposing or assessing an activity, plan or project that may affect the site.

Any proposals or operations which may affect the site or its features should be designed so they do not adversely affect any of the attributes in the SACO or achievement of the conservation objectives.

Feature target

‘Maintain’ targets do not preclude the need for management, now or in the future, to avoid a significant risk of damage or deterioration to the feature. The supporting and/or explanatory notes in the SACOs set out why the target was chosen and any relevant site based supporting information. This is based on the best available information, including that gathered during monitoring of the feature’s current condition.
Feature/Subfeature nameAttributeTargetSeasonSupporting notes
High energy intertidal rockDistribution: presence and spatial distribution of biological communitiesMaintain the presence and spatial distribution of intertidal rock communities.N/AA variety of communities make up the habitat. Listed component communities reflect the habitat's overall character and conservation interest. Communities are described as biotopes using EUNIS or the Marine Habitat Classification. Communities include, but are not limited to, those that are notable or representative of the feature. Representative communities include, for example, those covering large areas and notable communities include those that are rare, scarce or particularly sensitive to pressure. Changes to the spatial distribution of communities across the feature could highlight changes to the overall feature (Joint Nature Conservation Committee (JNCC), 2004).
Site-specifics:

8 high energy habitat types were recorded within this MCZ during the 2013/2014 intertidal verification survey (Curtis, 2014):

  • A1.112 Chthamalus spp. on exposed upper eulittoral rock
  • A1.1122 Chthamalus spp. and Lichina pygmaea on steep exposed upper eulittoral rock
  • A1.122 Corallina officinalis on exposed to moderately exposed lower eulittoral rock
  • A1.1221 Corallina officinalis and Mastocarpus stellatus on exposed to moderately exposed lower eulittoral rock
  • A1.1222 Corallina officinalis, Himanthalia elongata and Patella ulyssiponensis on very exposed lower eulittoral rock
  • A1.123 Himanthalia elongata and red seaweeds on exposed lower eulittoral rock
  • A1.125 Mastocarpus stellatus and Chondrus crispus on very exposed to moderately exposed lower eulittoral rock
  • A1.126 Osmundea pinnatifida on moderately exposed mid eulittoral rock

The A1.112 biotope was present around London Rocks; between Trenow Cove and Basore Point; in a continuous stretch between the Greeb and Perran Sands (including Maen-du Point) and from the east of Perran Sands to the east of Trevean Cove. The A1.1122 sub-biotope was recorded continuously between Trevean Cove and Cudden Point, with smaller patches at Basore Point and on the east side of St Michael's Mount as well as just to the west of the causeway to the Mount. Great Hogus was found to be dominated by this biotope.

The A1.1221 sub-biotope was restricted to ‘The Greeb’ which projects out from Perranuthnoe. The A1.1222 sub-biotope occupied a much broader expanse of the lower shore at the eastern end of the site, between Favel’s Hole and Cudden Point. The A1.123 biotope was found at the most western extent of the site, in the lee of Long Rock. It was also found to the northeast of St Michael’s Mount.

The A1.125 biotope was recorded on the southern shores of St. Michaels Mount and Great Hogus, as well as on a few isolated rocks north of Long Rock and on Maen-du Point near Perranuthnoe. The distribution of the A1.126 biotope was restricted to the eastern shore of St. Michael’s Mount and the rock around Basore Point in the middle of the MCZ.

Additional rockpool biotopes were recorded within areas of high energy rock, including 'Coralline crusts and Corallina officianalis in shallow rockpools' (A1.4111) near Stackhouse Cove and 'Bifurcaria bifurcata in shallow eulittoral rockpools' (A1.4113) in the eastern end of the site near Arch Zawn and Stackhouse Cove. 'Enteromorpha spp. on freshwater-influenced and/or unstable upper eulittoral rock' (A1.451) and 'Porphyra purpurea or Enteromorpha spp. on sand-scoured mid or lower eulittoral rock' (A1.452) were also found around Trevean Cove.


The target has been set in accordance with the MCZ General Management Approach, based on application of the vulnerability assessment, from the time of designation. The GMA has been tailored to specific attributes according to the likely impacts.

High energy infralittoral rockDistribution: presence and spatial distribution of biological communitiesMaintain the presence and spatial distribution of infralittoral rock communities.N/AA variety of communities make up the habitat. Listed component communities reflect the habitat's overall character and conservation interest. Communities are described as biotopes using EUNIS or the Marine Habitat Classification. Communities include, but are not limited to, those that are notable or representative of the feature. Representative communities include, for example, those covering large areas and notable communities include those that are rare, scarce or particularly sensitive to pressure. Changes to the spatial distribution of communities across the feature could highlight changes to the overall feature (Joint Nature Conservation Committee (JNCC), 2004).
Site-specifics:

The A3.1 biotope Laminaria hyperborea with dense foliose red seaweeds was identified in the verification survey undertaken in 2013 (Godsell et al., 2013).


The target has been set in accordance with the MCZ General Management Approach, based on application of the vulnerability assessment, from the time of designation. The GMA has been tailored to specific attributes according to the likely impacts.

Moderate energy infralittoral rockDistribution: presence and spatial distribution of biological communitiesMaintain the presence and spatial distribution of infralittoral rock communities.N/AA variety of communities make up the habitat. Listed component communities reflect the habitat's overall character and conservation interest. Communities are described as biotopes using EUNIS or the Marine Habitat Classification. Communities include, but are not limited to, those that are notable or representative of the feature. Representative communities include, for example, those covering large areas and notable communities include those that are rare, scarce or particularly sensitive to pressure. Changes to the spatial distribution of communities across the feature could highlight changes to the overall feature (Joint Nature Conservation Committee (JNCC), 2004).
Site-specifics:

Kelp and red seaweeds (both foliose and coralline) have been identified on this feature as well as orange encrusting sponges (Arnold and Green, 2017).


The target has been set in accordance with the MCZ General Management Approach, based on application of the vulnerability assessment, from the time of designation. The GMA has been tailored to specific attributes according to the likely impacts.

Intertidal coarse sedimentDistribution: presence and spatial distribution of biological communitiesMaintain the presence and spatial distribution of intertidal coarse sediment communities.N/AA variety of communities make up the habitat. Listed component communities reflect the habitat's overall character and conservation interest. Communities are described as biotopes using EUNIS or the Marine Habitat Classification. Communities include, but are not limited to, those that are notable or representative of the feature. Representative communities include, for example, those covering large areas and notable communities include those that are rare, scarce or particularly sensitive to pressure. Changes to the spatial distribution of communities across the feature could highlight changes to the overall feature (Joint Nature Conservation Committee (JNCC), 2004).
Site-specifics:

Infauna have been found to be extremely sparse within this feature, as is usual for this habitat type (A2.111 - Barren littoral shingle) which is fairly mobile and free-draining (Curtis, 2014). During the 2013/2014 verification survey only 4 taxa were recorded in this feature. One sample from the beach to the east of Basore Point was found to be completely barren. Enchytraeidae, Diptera pupa, Onoba semicostata, Nassarius incrassatus and Odostomia turrita were recorded in other samples taken from the beach to the east of St Michael's Mount and Top Tieb.


The target has been set in accordance with the MCZ General Management Approach, based on application of the vulnerability assessment, from the time of designation. The GMA has been tailored to specific attributes according to the likely impacts.

Moderate energy intertidal rockDistribution: presence and spatial distribution of biological communitiesMaintain the presence and spatial distribution of intertidal rock communities.N/AA variety of communities make up the habitat. Listed component communities reflect the habitat's overall character and conservation interest. Communities are described as biotopes using EUNIS or the Marine Habitat Classification. Communities include, but are not limited to, those that are notable or representative of the feature. Representative communities include, for example, those covering large areas and notable communities include those that are rare, scarce or particularly sensitive to pressure. Changes to the spatial distribution of communities across the feature could highlight changes to the overall feature (Joint Nature Conservation Committee (JNCC), 2004).
Site-specifics:

Several moderate energy biotopes were recorded within the site during the 2013/14 intertidal verification survey (Curtis, 2014).

'Pelvetia canaliculata and barnacles on moderately exposed littoral fringe rock' (A1.211) was found on the southern shore of St. Michael’s Mount and within Stackhouse Cove and on the western side of Cudden Point. This biotope was generally restricted to the largest rocky outcrops.

'Fucus spiralis on full salinity exposed to moderately exposed upper eulittoral rock' (A1.212) was limited to a small area inshore of St. Michael’s Mount, mosaicking with much smaller patches of the fucoid Pelvetia canaliculata and communities dominated by Fucus vesiculosus (A1.213) on the lower lying rocks. The high abundance of the western barnacle species Chthamalus montagui represents a regional variation of the biotope.

'Fucus vesiculosus and barnacle mosaics on moderately exposed mid eulittoral rock' (A1.213) was the most extensively distributed littoral rock habitat type throughout the site. Species composition was consistent with the EUNIS biotope description, with additional southern and western species including the barnacles Chthamalus montagui and Balanus perforatus, the purple topshell Gibbula umbilicalis and the brown algae Bifurcaria bifurcata present.

'Fucus serratus and red seaweeds on moderately exposed lower eulittoral rock' (A1.214) and the sub-biotope 'Fucus serratus and under-boulder fauna on exposed to moderately exposed lower eulittoral boulders' were widespread throughout the mid and lower shore of the site, being recorded at Long Rock, Great Hogus, St Michael's Mount (north-eastern side), Top Tieb, Little London, Trenow Cove to Basore Point and to the east of Maen-du Point.


The target has been set in accordance with the MCZ General Management Approach, based on application of the vulnerability assessment, from the time of designation. The GMA has been tailored to specific attributes according to the likely impacts.

Intertidal sand and muddy sandDistribution: presence and spatial distribution of biological communitiesMaintain the presence and spatial distribution of intertidal sand and muddy sand communities.N/AA variety of communities make up the habitat. Listed component communities reflect the habitat's overall character and conservation interest. Communities are described as biotopes using EUNIS or the Marine Habitat Classification. Communities include, but are not limited to, those that are notable or representative of the feature. Representative communities include, for example, those covering large areas and notable communities include those that are rare, scarce or particularly sensitive to pressure. Changes to the spatial distribution of communities across the feature could highlight changes to the overall feature (Joint Nature Conservation Committee (JNCC), 2004).
Site-specifics:

During the 2013/2014 interidal verification survey (Curtis, 2014) 4 intertidal sand and muddy sand biotopes were recorded within the site:

  • A2.211 - Talitrids on the upper shore and strandline
  • A2.2221 - Oligochaetes in full salinity littoral mobile sand
  • A2.223 – Amphipods and Scolelepis spp. in littoral medium-fine sand
  • A2.231 – Polychaetes in littoral fine sand

It should be noted that the feature was first surveyed in early December 2013 but following the initial survey severe storms between late January and mid February 2014 caused a significant change in the sediment character within the site. The biotope surveys were undertaken following the storm events.

The A2.211 biotope was present on the beaches in the west of the site and was found in patches abutting the constructed sea defences along the upper shore.

The A2.2221 sub-biotope communities were limited to the most exposed sediments found in in Trenow Cove and at Basore Point.

The A2.223 biotope was found mostly on the mid shore in areas where there was some shelter; for example on Marazion beach, Mounts Bay beach and Perran sands.

The A2.231 biotope occupied most of the broad sandy mid and lower shore banks found on the beaches of Marazion and Long Rock.


The target has been set in accordance with the MCZ General Management Approach, based on application of the vulnerability assessment, from the time of designation. The GMA has been tailored to specific attributes according to the likely impacts.

Seagrass bedsDistribution: presence and spatial distribution of biological communitiesMaintain the presence and spatial distribution of intertidal seagrass bed communities.N/AA variety of communities make up the habitat. Listed component communities reflect the habitat's overall character and conservation interest. Communities are described as biotopes using EUNIS or the Marine Habitat Classification. Communities include, but are not limited to, those that are notable or representative of the feature. Representative communities include, for example, those covering large areas and notable communities include those that are rare, scarce or particularly sensitive to pressure. Changes to the spatial distribution of communities across the feature, could highlight changes to the overall feature (Joint Nature Conservation Committee (JNCC), 2004). The communities supported by seagrass can vary enormously as seagrass can colonise any sediment from muddy to coarse. The unique sets of variables can support very different groups of infauna and epifauna communities.
Site-specifics:


The target has been set in accordance with the MCZ General Management Approach, based on application of the vulnerability assessment, from the time of designation. The GMA has been tailored to specific attributes according to the likely impacts.

Subtidal sandDistribution: presence and spatial distribution of biological communitiesMaintain the presence and spatial distribution of subtidal sand communities.N/AA variety of communities make up the habitat. Listed component communities reflect the habitat's overall character and conservation interest. Communities are described as biotopes using EUNIS or the Marine Habitat Classification. Communities include, but are not limited to, those that are notable or representative of the feature. Representative communities include, for example, those covering large areas and notable communities include those that are rare, scarce or particularly sensitive to pressure. Changes to the spatial distribution of communities across the feature could highlight changes to the overall feature (Joint Nature Conservation Committee (JNCC), 2004).
Site-specifics:

Samples taken in a 2016 survey (Arnold, 2017) have been recently analysed, and have found ‘Fabulina fabula and Magelona mirabilis with venerid bivalves and amphipods in infralittoral compacted fine muddy sand’ (A5.242) to be the most frequently occurring biotope within this feature (Arnold and Green, 2017). The biotope 'Nephtys cirrosa and Bathyporeia spp. in infralittoral sand' (A5.233) (which is indicative of sediments exposed to physical disturbance through wave action) was also present.


The target has been set in accordance with the MCZ General Management Approach, based on application of the vulnerability assessment, from the time of designation. The GMA has been tailored to specific attributes according to the likely impacts.

Seagrass bedsDistribution: presence and spatial distribution of biological communitiesMaintain the presence and spatial distribution of subtidal seagrass bed communitiesN/AA variety of communities make up the habitat. Listed component communities reflect the habitat's overall character and conservation interest. Communities are described as biotopes using EUNIS or the Marine Habitat Classification. Communities include, but are not limited to, those which are notable or representative of the feature. Representative communi