Small Isles possible MPA - Application of the MPA ... · Scottish MPA Project ... We have used the terminology set out in the Selection Guidelines to describe ... SS.SMu.CFiMu.MegMax

Scottish MPA Project

Assessment against the MPA Selection Guidelines

SMALL ISLES POSSIBLE NATURE CONSERVATION MPA

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Document version control

Version Date Author Reason / Comments

Version 1 21/02/2013 Siobhan Mannion, Ben James, Ian Bainbridge, Laura Clark, John Baxter,and Andy Douse

Revised protected feature / possible MPA format, updating original MPA search location format (ver. 11).

Version 2 06/03/2013 Laura Clark Review and minor edits.

Version 3 22/05/2013 Ben James Review.

Version 4 28/05/2013 John Baxter QA review.

Version 5 29/05/2013 Ben James Refinements in response to initial QA review. Finalisation for SNH Scientific Advisory Committee.

Version 6 10/06/2013 Ben James Insertion of updated map following application of boundary setting principles.

Version 7 26/06/2013 Ben James Refinements following SNH Scientific Advisory Committee review.

Version 8 08/07/2013 John Baxter Final proof check and sign-off on behalf of SNH. Clearance to issue.

Distribution list

Format Version Issue date Issued to

Electronic 6 12/06/2013 SNH Scientific Advisory Committee members.

Electronic 8 10/07/2013 Marine Scotland officials.

Electronic 8 24/07/2013 SNH web publication [B1209026 / 27(#27)].

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Purpose

This document provides details of the assessment of the Small Isles possible Nature Conservation MPA against the Scottish MPA Selection Guidelines. It presents the assessment for each of the proposed protected features.

We have used the terminology set out in the Selection Guidelines to describe the five main stages in the assessment process from the identification of MPA search locations through to the development of MPA proposals. This area has now become a possible Nature Conservation MPA because, following advice from SNH and/or JNCC, Scottish Ministers have decided to consult on whether it should be formally designated.

The main terms used are described below.

MPA search location - this describes a location identified at stage 1 until it passes the assessment at stage 4.

Potential area for an MPA - if an MPA search location passes the assessment at stage 4 it goes on to become a potential area for an MPA for consideration at stage 5.

MPA proposal - a potential area for an MPA that has passed the assessment at stage 5 and which has been formally recommended for designation by SNH and/or JNCC to Scottish Ministers.

Possible MPA - an MPA proposal approved by Scottish Ministers for public consultation. From this time the location is given policy protection as if it were designated.

MPA search features - specified marine habitats, species and large-scale features that underpin the selection of Nature Conservation MPAs.

Geodiversity features - specified geodiversity interests of the Scottish seabed categorised under themed ‘blocks’ that are analogous to the MPA search features for biodiversity.

Representative features - habitats and/or species which are not MPA search features or key geodiversity features. They have been assessed to determine whether they would add to the broader representativity of the network.

Proposed protected feature - any feature (habitats, species, large-scale features and/or geodiversity features) which has been proposed by SNH and/or JNCC for designation as part of a Nature Conservation MPA.

History of development

The Small Isles possible Nature Conservation MPA was identified for seven MPA search features (black guillemot; burrowed mud; fan mussel aggregations; horse mussel beds; northern feather star aggregations on mixed substrata; northern sea fan and sponge communities; shelf deeps) and one geodiversity feature (Quaternary of Scotland). Circalittoral sand and mud communities and white cluster anemones are not MPA search features but have been recommended as proposed protected features because we consider that they would add to the broader representativity of the Scottish MPA network (i.e. representative features).

The Small Isles possible Nature Conservation MPA fully encompasses the Sound of Canna third-party MPA proposal from the Small Isles Community Council. That proposal also identified burrowing anemones and a broader infralittoral reefs category. These features are not MPA search features (only individual burrowing anemones have been recorded rather than aggregations) and are not included in the detailed assessment.

Details of supporting evidence are provided in the Small Isles data confidence assessment.

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SMALL ISLES POSSIBLE NATURE CONSERVATION MPA - APPLICATION OF THE MPA SELECTION GUIDELINES

Stage 1 - Identifying search locations that would address any significant gaps in the conservation of MPA search features1

Summary of assessment

The possible MPA encompasses a range of MPA search features, including a number considered to be under threat / declining in Scottish waters. The shelf deeps feature that extends from the Sound of Canna north towards Skye is of functional significance, providing the necessary structure and substrates to support a diverse assemblage of finer resolution habitats and species, including the most extensive known aggregation of fan mussels in UK waters within the Sound of Canna.

Detailed assessment

Proposed protected features Guideline 1a Presence of key features [MPA search features and geodiversity equivalents]

Guideline 1b Presence of features under threat

and/or subject to rapid decline

Guideline 1c Functional significance for the overall health and diversity of

Scottish seas

Biodiversity

Black guillemot

Burrowed mud OSPAR T&D2

Circalittoral sand and mud communities3 Representative feature

Fan mussel aggregations T&D4

Horse mussel beds OSPAR T&D

Northern feather star aggregations on mixed substrata T&D

Northern sea fan and sponge communities T&D

Shelf deeps

White cluster anemones Representative feature

Geodiversity

Quaternary of Scotland (glaciated channels/troughs, glacial lineations, meltwater channels, moraines, rock basins, streamlined bedforms)

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1 All proposed protected features of the possible MPA are listed in the stage 1 detailed assessment table and subsequently assessed against the MPA Selection Guidelines

(wherever practicable) to facilitate read across to SNH and JNCC’s formal 2012 MPA network advice (SNH and JNCC, 2012). 2 OSPAR list of Threatened and/or Declining species and habitats (see OSPAR, 2008 a & b). 3 Comprising ‘Amphiura filiformis, Mysella bidentata and Abra nitida in circalittoral sandy mud’ (SS.SMu.CSaMu.AfilMysAnit - A5.351) and ‘Deep circalittoral sand’

(SS.SSa.OSa - A5.27). 4 Feature considered to be under threat and/or in decline in Scottish waters (see http://www.snh.org.uk/pdfs/publications/commissioned_reports/388.pdf for further details).

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Maps of the Small Isles possible MPA showing the known distribution of proposed protected features

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Stage 2 - Prioritisation of search locations according to the qualities of the MPA search features they contain


The Small Isles possible MPA encompasses a diverse range of proposed protected features distributed within a complex and varied geological setting. The proposed protected features are integrally linked and many of the seabed habitats exhibit a high level of natural biological diversity. For some of the features there are no known equivalents - the largest fan mussel aggregation in UK waters and the deepest horse mussel bed in Scotland - but these may in fact represent relict examples of features that were once more widely distributed across Scotland’s seas. The features range in scale, with large areas of burrowed mud habitat with tall seapens overlying widely distributed coarse mixed muddy sediments, through to smaller discrete areas with northern sea fans and white cluster anemones. A number of the seabed habitats and species are considered sensitive to a range of pressures and at a regional level are considered to be at medium to high risk of significant damage by human activity. On the basis of current evidence, the features present within the possible MPA are thought to be in a natural state and largely undisturbed. All of the five Stage 2 guidelines have been met.

Detailed assessment

Guideline 2a The search location contains combinations of features, rather than single isolated features, especially if those features are functionally linked

The possible MPA supports ten proposed protected features; comprising seven MPA search features (at a range of scales), multiple interests under the Quaternary of Scotland geodiversity feature and two representative seabed habitat/species features. This biological diversity is a result of the geomorphological composition of the area with its complex volcanic and glacial history giving rise to a range of environmental conditions. Subglacial lineations and other glacially eroded features in bedrock highs around the Isles of Canna and Rum preserve the direction of ice sheet movement. Physical features include glacially over-deepened rock basins and linear troughs with steep, and in places rocky sides, moraines, drowned wave-cut platforms, small embayments and sublittoral basalt cliffs. The area is subject to grades of wave exposure ranging from exposed in the west and south to more sheltered northern coasts and moderate tidal streams. Several of the proposed protected features in the area are linked5.

- Many of the seabed habitat features are situated within the area of shelf deeps that extends through the Sound of Canna into the channel between the Small Isles and Skye. The confirmed distribution of burrowed mud around the margins of this large-scale feature reflects limitations in sampling to date - the deepest central section is yet to be assessed in detail.

- Within the seabed habitats themselves there is a clear association between the fan mussels Atrina fragilis, horse mussels Modiolus modiolus and burrowed mud, as the last contains both mussel species within the Sound of Canna. Northern feather star aggregations are also found on the burrowed mud. The fan mussels and horse mussels provide some stability in the sediment whilst the bioturbation created by the megafaunal burrowers may increase the food supply for the suspension feeding mussels and feather stars.

- Boulders supporting northern sea fan and sponge communities are present on the floor of the Sound of Canna and to the east of the Oigh-sgeir Bank adjacent to burrowed mud and associated seabed habitats. The white cluster anemone Parazoanthus anguicomus (not a feature that is considered to be under threat and/or in decline in Scottish waters) is commonly associated with the northern sea fan and sponge habitats.

Guideline met.

5 This term refers to linkages between features and also the wider marine ecosystem in Scottish waters and is not the same as functional significance used in relation to

Guideline 1c.

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Interpretation of the burrowed mud MPA search feature

This summary overview is provided to aid interpretation of the terminology used within this technical assessment. Further details on the burrowed mud MPA search feature are available online at - http://www.scotland.gov.uk/Resource/0039/00394205.doc. The burrowed mud feature encompasses five components considered to be of particular relevance in a Scottish context: two component biotopes (relevant biotope6 codes provided in bold text below) and three specific species:

Biotope - “Seapens and burrowing megafauna in circalittoral fine mud” (SS.SMu.CFiMu.SpnMeg) Biotope - “Burrowing megafauna and the mud volcano worm Maxmuelleria lankesteri” (SS.SMu.CFiMu.MegMax) Species - Funiculina quadrangularis (the tall seapen) Species - Pachycerianthus multiplicatus (the fireworks anemone) Species - Maera loveni (a mud burrowing amphipod)

Guideline 2b The search location contains example(s) of features with a high natural biological diversity

Burrowed mud The following components of the burrowed mud MPA search feature have been recorded within the possible MPA - seapens and burrowing megafauna (SS.SMu.CFiMu.SpnMeg biotope); the tall seapen Funiculina quadrangularis; and scattered records of the fireworks anemone Pachycerianthus multiplicatus. Within the Sound of Canna the burrowed mud habitat has been ascribed to the SS.SMu.CFiMu.MegMax and SS.SMu.CFiMu.SpnMeg biotopes by different authors (Howson et al., 2012; Moore, 2012). In the absence of any records of the characterising mud volcano worm Maxmuelleria lankesteri it is considered that the primary burrowed mud biotope within the sound is actually SS.SMu.CFiMu.SpnMeg, albeit with a low abundance (or complete absence in some records) of seapens. The tall seapen has been recorded within the northern section of the sound (with records assigned to the sub-biotope SS.SMu.CFiMu.SpnMeg.Fun) and in two locations in 2011 a substrate of scattered stones and shells on burrowed mud supported fields of northern feather stars together with tall and phosphorescent seapens. In the channel between the Small Isles and Skye, soft burrowed mud was widely recorded in 2011 at depths of 55 - 178 m, characterised by dense thalassinid shrimp and langoustine Nephrops norvegicus burrows and high numbers of Funiculina quadrangularis (generally Frequent7 or Common but locally Abundant) and Pennatula phosphorea (SS.SMu.CFiMu.SpnMeg.Fun) (Moore, 2012). To the east of the Oigh-sgeir Bank in the southern approaches to the Sound of Canna, mud burrowed by Nephrops norvegicus, thalassinid shrimps and probably the angular crab Goneplax rhomboides was widely distributed, generally with Occasional seapens (SS.SMu.CFiMu.SpnMeg), although Funiculina quadrangularis was Common locally to the south-east of Oigh-sgeir (SS.SMu.CFiMu.SpnMeg.Fun). It recent surveys it proved impossible to correlate specific infaunal communities directly with the burrowed mud habitat observed on the remote video footage. The majority of the samples collected within the Sound of Canna in 2010 comprised coarse sandy sediments (SS.SSa.OSa.OfusAfil) or sandy mud (SS.SMu.CSaMu.AfilMysAnit).

6 Further details on the UK marine habitat classification are available online at http://jncc.defra.gov.uk/page-5931 7 For details of the SACFOR scale used for reporting the abundance of marine benthic flora and fauna in biological surveys see Hiscock (1996).

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Burrowed mud cont.

These biotopes are incorporated within the circalittoral sand and mud communities proposed protected feature (see below). The infaunal communities present beneath the mud veneer were diverse, supporting a large number of species (see Howson et al., 2012). Up to 92 taxa were recorded from a single grab and diversity indices calculated ranged from 2.88 to 3.5 (Shannon Wiener H’). Although not directly comparable, the values associated with the infaunal component of this SS.SMu.CFiMu.SpnMeg biotope are equivalent to, or higher than, those from more typical muddier substrates in other locations (e.g. Loch Sunart had 30 taxa in a single grab and H’ of 2.84 - Bates et al., 2004). These findings were corroborated in 2011 when additional samples were taken within the Sound of Canna (assigned to gravelly sands to slightly gravelly muddy sands) and similarly within the northern (muddy sands) and southern approaches (muddy sands and one sandy mud record) to the sound. Species richness was highest in the Sound of Canna samples (Axelsson et al., 2012).

Circalittoral sand and mud communities

This proposed protected feature comprises deep circalittoral sand (assigned to the SS.SSa.OSa biotope complex) with brittlestars Amphiura filiformis and the sea potato Echinocardium cordatum in circalittoral clean or slightly muddy sand (SS.SMu.CSaMu.AfilMysAnit biotope). Records of the feature within the possible MPA have been derived primarily from quantitative infaunal samples targeted initially at the surficial, overlying burrowed mud feature (see above). Within the Sound of Canna, the finer resolution biotope SS.SSa.OSa.OfusAfil (Owenia fusiformis and Amphiura filiformis in offshore circalittoral sand or muddy sand) was recorded at seven of the grab stations sampled in 2010 (Howson et al., 2012). The samples had a rich fauna with a total of 194 species recorded, 63 of these occurring in three or more of the samples. The diversity indices calculated ranged from 2.88 to 3.92 with a mean of 3.4 (Shannon Wiener H’). The sediments were very mixed but were predominantly sand with 10 - 30 % mud (Howson et al., 2012). Four infaunal samples collected in 2011 were assigned to the coarser resolution biotope complex SS.SSa.OSa. Three of the samples were taken within the shelf deeps area to the north of the Sound of Canna (ranging from 205 - 230 m depth; mean H’ = 2.48) and the fourth record was at the southern entrance to the sound in 120 m (H’ = 3.46). Northern feather stars were recorded within the grab sample taken at this location. An additional 2011 sampling station within the Sound of Canna was assigned to the SS.SSa.OSa.OfusAfil biotope (Axelsson et al., 2012). The second component biotope of this proposed protected feature, SS.SMu.CSaMu.AfilMysAnit, was found in slightly muddier sediments throughout the Sound of Canna (Axelsson et al., 2012; Howson et al., 2012). The biotope is species rich and diverse (total taxa 245, mean taxa 59, mean H’ 3.4).

Fan mussel aggregations

This guideline applies only to seabed habitats - this feature is an aggregation of a low / limited mobility species but details of associated / adjacent habitats known from this possible MPA are provided for reference. There are no other known fan mussel aggregations in UK waters with which to meaningfully compare indices of natural biological diversity. However, whilst the fan mussels are generally scattered, with individuals in the denser patches occurring at densities of 1 - 4 m-2, occasionally in clumps, it is clear (from video footage) that the epibiotic diversity is considerably higher amongst the fan mussels than in adjacent areas (Howson et al., 2012). The byssal threads stabilise the sediment and the mussel shells provide a substrate for an associated fauna, apparently dominated by hydroids such as Nemertesia ramosa and Halecium halecinum. Other members of the fauna include colonies of the calcareous tubeworm Salmacina dysteri, burrowing anemones, the fan worm Sabella pavonina, and the brittlestars Ophiocomina nigra and Ophiothrix fragilis, with evidence of the infaunal community comprising many small holes in the sediment, some housing bivalve siphons, and holothurian tentacle crowns (Moore and Roberts, 2011). Infaunal samples collected from within the main fan mussel aggregation in 2011 were assigned to mixed coarse and muddy sand communities, namely the SS.SMu.CSaMu.AfilMysAnit and SS.SSa.OSa.OfusAfil biotopes.

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Fan mussel aggregations cont.

From the video records the fan mussel aggregation appeared structurally comparable with a horse mussel bed supporting a low density of Modiolus modiolus. Infaunally the three samples collected (184 - 242 m) were less diverse than the horse mussel bed into which this habitat merges in the south, but were comparable with the composition of the ‘burrowed mud’ infauna. Diversity indices ranged from 2.44 to 3.61 (Shannon Wiener H’). The infauna was characterised by Abundant Amphiura filiformis brittlestars, the bivalves Abra nitida and Kurtiella bidentata, and polychaetes such as Owenia fusiformis and Nephtys spp. (Axelsson et al., 2012).

Horse mussel beds To the south of the main fan mussel aggregation within the Sound of Canna, the substrate of muddy sand with broken and whole shell material supports a horse mussel Modiolus modiolus bed, consisting of clumps of abundant mussels, mostly or completely buried, with just the posterior shell tip and mantle edge visible at the sediment surface (Moore and Roberts, 2011). The shells support an associated fauna dominated by hydroids and sponges, including N. ramosa, H. halecinum and Iophon hyndmani?, terebellid worms and O. nigra. From the video footage the infauna was seen to include Frequent fan mussels, as well as fan worms Myxicola infundibulum and holothurians, and the epifauna also included S. pavonina, dead man’s fingers Alcyonium digitatum, the cushion star Hippasteria phrygiana and Frequent hake, Merluccius merluccius. This deep, probably moderately tide-swept, fine sediment habitat is dominated by infaunal and semi infaunal Modiolus and is not readily ascribable to existing Modiolus bed biotopes but has strongest affinities with SS.SBR.SMus.ModCvar (although this is generally associated with sheltered, shallow locations). The atypical nature of this horse mussel bed may be a result of the depth (range 160 m - 250 m) and the degree of sediment-immersion of much of the Modiolus population. This is the deepest known example of this habitat in Scottish waters. Deep Modiolus beds around the UK are generally associated with mixed coarse sediment communities, including venerid bivalves, and are attributable to SS.SBR.SMus.ModMx (Connor et al., 2004). Six infaunal samples collected from the horse mussel bed in 2011 (depths ranging from 210 - 250 m) were indeed assigned to the SS.SBR.SMus.ModMx biotope on the basis of the infaunal species composition. The samples were all highly diverse with up to 95 taxa recorded from a single grab (range 69 - 95) and diversity indices calculated ranged from 3.38 to 3.99 (Shannon Wiener H’). These figures correlate with values presented in Mair et al. (2000) for Modiolus clump samples from other locations (e.g. Busta Voe S = 65; H’ = 3.5 / Loch Alsh S = 100; H’ = 4.5). The samples contained moderately high numbers of live horse mussels (3 - 20 individuals per 0.1 m2) and the rich infaunal community was observed to support a high density of polychaete species (Axelsson et al., 2012).

Northern feather star aggregations on mixed substrata

This guideline applies only to seabed habitats - this feature is an aggregation of a low / limited mobility species but details of associated / adjacent habitats known from this possible MPA are provided for reference. No quantitative infaunal data exist with which to compare indices of natural biological diversity within the varied habitats that support aggregations of northern feather stars Leptometra celtica. Dense aggregations of the species on mixed substrata have been recorded at a number of locations within the Sound of Canna (Howson et al., 2012), to the south-east of Oigh-sgeir on mud and scattered stones (in association with burrowed mud and tall seapens) and to the north of the channel between the Small Isles and Skye (Moore, 2012). From remote video footage the substratum appears to comprise a mixture of occasional boulders with some cobbles and shell on burrowed mud or muddy fine sand. There were generally more species present on the sediment surface (epibiotic) than in the adjacent areas classified as burrowed mud. Species included the rugose squat lobster Munida rugosa and edible crab Cancer pagurus with the burrowing anemones Cerianthus lloydii and Sagartiogeton laceratus. Pagurus prideaux hermit crabs with their Adamsia carciniopados anemone cloaks were Frequent and Pecten maximus, Neptunea antiqua, Echinus esculentus and Luidia ciliaris were present. The more unusual northern species of Luidia starfish, L. sarsi, was seen at several stations.

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Northern feather star aggregations on mixed substrata cont.

Where there were boulders, the cup coral Caryophyllia smithii was invariably present, Swiftia pallida was present at low abundance (Rare) and there were axinellid sponges, particularly Axinella infundibuliformis (i.e. the boulders supported the northern sea fan and sponge communities proposed protected feature). Other species recorded included the bryozoan Porella compressa, the hydroid Nemertesia antennina and the white cluster anemone Parazoanthus anguicomus (a proposed protected feature in its own right when occurring as dense aggregations or in association with the northern sea fan and sponge communities feature). Species characteristic of the adjacent and sometimes underlying burrowed mud were also found within the northern feather star aggregation habitat such as the seapens Funiculina quadrangularis and Pennatula phosphorea.

Northern sea fan and sponge communities [& white cluster anemones]

All four component habitats and species of the ‘northern sea fan and sponge communities’ MPA search feature have been recorded within the Small Isles possible MPA. The northern sea fan Swiftia pallida is widely distributed, occurring on bedrock cliffs and on boulders and rocky outcrops in the deeper parts of the Sound of Canna, and generally at sufficiently high density, in association with axinellid sponges, to characterise the biotope as CR.MCR.EcCr.CarSwi.LgAs, which includes the white cluster anemone Parazoanthus anguicomus at a number of sites. The deep sponge community CR.HCR.DpSp.PhaAxi has been recorded at four locations, including in deep water on the slope of the extensive Oigh-sgeir Bank, situated to the south-west of Canna between 60 - 97 m and in the south-western approaches to the Sound of Canna. At these locations the faunal crust community on bedrock, boulders and cobbles is accompanied by a fairly rich sponge fauna dominated by Axinella infundibuliformis and / or Phakellia ventilabrum, together with some branching erect species e.g. Polymastia boletiformis, the bryozoan Porella compressa and patches of Swiftia pallida (Moore, 2012). The CR.HCR.XFa.SwiLgAs biotope was assigned to diver records collected on the vertical cliffs off Canna in 2010 (Howson et al., 2012). The examples of this proposed protected feature present within the sound are comparatively species-rich. Comparisons with similar habitats (using the same diver sampling methods) in the Firth of Lorn indicate that around 25% more species were recorded from the Sound of Canna (39 to 46 species per station, total species number of 85, compared with 25 to 30 per station and total number of 62 for the Firth of Lorn). The Canna cliffs and deep water sites have not been surveyed in detail, with diver sampling currently restricted to a small area (Howson et al., 2012).

2b - Result Guideline met.

Guideline 2c The search location contains coherent examples of features, rather than smaller, potentially more fragmented ones

Black guillemot Black guillemots breed along the rocky coastline of Rum and Canna where suitable nesting habitat exists (almost exclusively cliff nesters utilising crevices, holes under rocks and other concealed locations - SNH, 2012), foraging in inshore areas off the coast. The species has been present on the Small Isles since at least the mid-19th century (when recording began); though numbers may have been lower than at present (Evans and Flower, 1967). The Seabird 2000 census (sampling undertaken in 2000) estimated approximately 850 individuals which equates to ca. 2.2% of the GB population - Mitchell et al., 2004). This figure is comparable (well within normal count variability) with the 1989 Seabird Colony Register count of 800 birds (Lloyd et al., 1991). The provisional results of survey work undertaken in 2013 suggest that numbers have remained fairly stable on Canna where 214 birds were counted, whilst on Rum there was an increase from 642 in 2000 to 1,013 in 2013 (a total of 1,227 breeding black guillemots within the possible MPA). However, no firm conclusions can be drawn because the rise in numbers is also within normal count variability.

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Burrowed mud The megafaunal communities associated with the burrowed mud habitat in the Small Isles possible MPA are typical for the physiographic setting (open coast / coastal island groups) on the west coast of Scotland with thalassinid shrimp and Nephrops norvegicus burrows and varying densities of tall and phosphorescent seapens (Moore, 2012). The infaunal communities are somewhat atypical within the Sound of Canna and the shelf deeps to the north of the sound, where they are representative of the coarser gravelly sandy sediments underlying a muddy veneer. To the south of the sound the burrowed mud habitats support a more typical infaunal mud community. The burrowed mud habitat is the most widely distributed feature within the possible MPA, covering the largest area of seabed of the different proposed protected features. The habitat runs along the east of Oigh-sgeir Bank, up through the Sound of Canna and opens out across the deeps to the north in the channel between the Small Isles and Skye. The habitat is likely to be present in a series of discrete areas (four such areas were identified within the Sound of Canna in Howson et al., 2012) but fragmentation of the habitat is considered minimal. The precise area of burrowed mud within the possible MPA has not been calculated. However, it is likely to be in the order of 30-45 km2 (13 km2 was identified within the Sound of Canna alone in 2010 - Howson et al., 2012). There has been very little research on seapen and burrowing megafaunal communities to assess their natural spatial and temporal variability. Hill et al. (2010) assessed the potential viability of these habitats and concluded that whilst only very large areas (1,962 km2) would protect all the life-cycle stages of most of the constituent fauna, an area of 500 m2 would be suitable for the maintenance of most species (no data were available for seapens). In the absence of significant disturbance, the burrowed mud habitat is considered stable and expected to persist.


The circalittoral sand and mud communities feature has a widespread distribution within the Sound of Canna (Howson et al., 2012) and has also been recorded to the north and south of the sound (Axelsson et al., 2012). The precise area of this feature within the possible MPA has not been calculated but it is likely to exceed 20 km2 (16 km2 was identified within the Sound of Canna alone in 2010; comprising ca. 6 km2 of SS.SSa.OSa.OfusAfil and ca. 10 km2 of SS.SMu.CSaMu.AfilMysAnit - Howson et al., 2012). The SS.SSa.OSa.OfusAfil samples aligned well with the description provided for this biotope within the national classification (Connor et al., 2004), dominated by the brittlestar Amphiura filiformis with several polychaete species (Pholoe inornata Chaetozone sp., Spiophanes kroyeri, Lumbrineris gracilis and Galthowenia oculata) in addition to the tube building O. fusiformis. The anemone Edwardsia claparedii was present in all of the samples and the bivalves Timoclea ovata and Thyasira flexuosa were found in the majority. The sea cucumber Labidoplax buski was also present. The SS.SMu.CSaMu.AfilMysAnit biotope was characterised by large numbers of the brittlestars Amphiura filiformis and Amphiura chiajei, the bivalve Abra nitida, and polychaetes including Notomastus latericeus, Lumbrineris gracilis, Spiophanes kroyeri and Diplocirrus glaucus. The home range of the species thought to be characteristic of this feature would be encompassed by an area less than 10 km2. However, it should be noted that information is lacking for a number of species and is identified as being of low confidence for others so this value should be treated with some caution (Hill et al., 2010). The majority of species identified as being faithful and frequent residents of the feature have a larval phase in their development and so are capable of dispersing over large distances. In the absence of significant disturbance, the feature is considered stable and expected to persist.


Records of individual fan mussels are scarce and the fan mussel aggregation within the Sound of Canna (covering an estimated 2 km2) represents the largest known aggregation in the UK. It is likely that future accounts of the typicalness will use the Sound of Canna example of this habitat as a reference. There is no information regarding the area required to maintain a minimum viable population of fan mussels. The species is believed to have a larval dispersal potential of 4-10 km (Hill et al., 2010).

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Fan mussel aggregations cont.

The longevity of A. fragilis is unknown but a related Mediterranean species is reported to live for up to 18 years. Shell growth is believed to be relatively slow (around 3-4 cm per year). Successional / cyclical tendencies will only become apparent over time (subject to ongoing surveillance) however, the presence of this feature and an absence of disturbance would suggest a stable environment. Fragmentation is evident towards the southern extremities of the fan mussel aggregation (Howson et al., 2012).

Horse mussel beds The horse mussel bed present in the deepest section of the Sound of Canna, adjacent to and intermingled with the fan mussel aggregation, is considered a somewhat atypical example of the habitat because of the depth (160 - 250 m - the deepest recorded example in Scottish waters) and the degree of sediment-immersion of much of the Modiolus population (Moore and Roberts, 2011; Axelsson et al., 2012). However, a study by Mair et al. (2000) concluded that whilst some species are fairly ubiquitous in their distribution within Modiolus beds, the faunal community which establishes may differ significantly according to the location and environmental conditions present. The characteristic infaunal species aligned well with those specified within the SS.SBR.SMus.ModMx biotope description (Connor et al., 2004) including the polychaete worms Glycera lapidum, Paradoneis lyra, Aonides paucibranchiata, Laonice bahusiensis, Lumbrineris spp., Mediomastus fragilis, syllid worms such as Exogone spp. and bivalve molluscs such as Spisula elliptica and Timoclea ovata. The level of fragmentation found within this feature across the UK is highly variable. M. modiolus can occur as relatively small, dense beds of epifaunal mussels. In some sea lochs and open sea areas, extensive expanses of seabed are covered in scattered clumps of M. modiolus. The total extent of the bed within the Sound of Canna is unknown (it may continue to the south in the deepest and as yet un-surveyed section of the sound) but existing records of the feature are currently restricted to a reasonably tightly defined area with high densities of horse mussels (3 - 20 individuals per 0.1 m2 - Axelsson et al., 2012). No specific information is available on the size of area required to ensure the viability of this feature. Horse mussels are long-lived species, with individuals over 25 years old frequent in British populations and occasional records of specimens up to 35 years old (Hill et al., 2010). Maximum ages are thought likely to be in excess of 50 years (Anwar et al., 1990). Temporal variability of horse mussel beds has not been well studied but in the absence of regular disturbance and despite intermittent and variable recruitment, they appear to be fairly stable in the long-term with beds known from the same location for 80+ years (Seed and Brown, 1975; Anwar et al., 1990; Hill et al., 2010).


The dense fields of the northern feather star L. celtica observed on the surface of mud and muddy sand substrates with scattered cobbles and boulders are considered typical. They are broadly comparable with other recently observed examples of this feature from the Little Minch, Little Loch Broom, and off the mouth of Loch Gairloch (Moore et al., 2011; Moore, 2012). The examples of this feature within the Sound of Canna appear to be present on more variable substrates, with a greater number of species representative of burrowed mud, such as seapens (both tall and phosphorescent) and burrowing anemones (Cerianthus lloydii and Sagartiogeton laceratus), intermingled with larger boulders supporting Swiftia pallida, the cup coral Caryophyllia smithii and the white cluster anemone Parazoanthus anguicomus. Species that are widely-distributed across the possible MPA include the erect calcareous bryozoan Porella compressa, the rugose squat lobster Munida sarsi, the coral worm Salmacina dysteri, a number of starfish species and the edible sea urchin Echinus esculentus. Although the total area of this feature within the possible MPA is currently unknown, the five discrete areas recorded within the Sound of Canna in 2010 were estimated to cover ca 0.5 km2 (Howson et al., 2012). Little is known about the biology and reproduction of L. celtica so it is not clear how large an area is required to support a viable population. Similarly, no information is available on the longevity of the species. Current records are spread across the possible MPA so some degree of fragmentation may be concluded.

13



The northern sea fan and sponge communities present within the possible MPA are considered typical. As well as supporting the characterising northern sea fan Swiftia pallida, areas of habitat (assigned to the CR.MCR.EcCr.CarSwi.LgAs and CR.HCR.XFa.SwiLgAs biotopes) support cup corals Caryophyllia smithii, often in large numbers, dead man’s fingers Alcyonium digitatum, white cluster anemones Parazoanthus anguicomus and axinellid sponges. In accordance with the JNCC biotope descriptions (Connor et al., 2004) bryozoan crusts were present on rock surfaces and echinoderms were frequent including Echinus esculentus, Luidia ciliaris, Henricia sp. and occasionally Leptometra celtica. At a few sites with a significant tidal stream, the jewel anemone Corynactis viridis covered the boulders. With increasing depth the abundance of sea fans declined and the axinellid sponges Axinella infundibuliformis and / or Phakellia ventilabrum started to dominate the community (characterising species of the CR.HCR.DpSp.PhaAxi component biotope). The species composition of the deep sponge community also aligned well with that listed in the national habitat classification and is comparable with other recently observed examples of this feature from the Shiant East Bank and Little Minch (Moore, 2012). It is not possible to define a minimum viable population of northern sea fans. Thought to be self sustaining, they have short-lived larvae and limited potential for larval dispersal (Hill et al., 2010). The life-span of S. pallida is estimated to be between 11 and 20 years (Wilding and Wilson, 2009). No information is available on the typical level of fragmentation for northern sea fan and sponge communities. There are scattered records of the feature across the possible MPA, with even the smallest rocky outcrops on the deep floor of the Sound of Canna supporting variants of the habitat. The total area covered by the feature is currently unknown but the examples present within the Sound of Canna were estimated to cover ca. 1.4 km2 (Howson et al., 2012).

2c - Result Guideline met.

Guideline 2d The search location contains features considered least damaged / more natural, rather than those heavily modified by human activity

Black guillemot Areas of nesting habitat within the possible MPA are essentially unmodified. Black guillemot numbers have remained reasonably stable on Canna across the three most recent counts, with numbers around Rum potentially increasing in 2013 (preliminary results) suggesting that the population has not been adversely affected by human activity. Both islands are mink-free (non-native American mink is a major predator of black guillemots). The brown rat population of Canna has been eradicated in the last decade, and current work is seeking to evaluate the impacts of this species on seabird populations on Rum.

Burrowed mud The analysis of video samples collected in 2011 concluded that the burrowed mud proposed protected feature may have been trawled in some areas, including along the eastern side of the Sound of Canna and to the south of Sanday. It is therefore likely that the burrowed mud habitat represents a mixture of natural and modified areas. One indicator of disturbance / modification may be the absence of seapens in these areas (which are only found in small numbers and in scattered locations) (Howson et al., 2012).


This feature occurs primarily under a veneer of burrowed mud, a habitat which appears to have been modified by human activity in some areas. However, no indicators of change / damage to this underlying habitat were reported in the most recent surveys (Axelsson et al., 2012 and Howson et al., 2012) and the feature is therefore considered to be in a natural state.

14

Guideline 2d The search location contains features considered least damaged / more natural, rather than those heavily modified by human activity


The fan mussels were first recorded during routine Marine Scotland Science (MSS) monitoring of the licensed dredge spoil site in the Sound of Canna in 2009. Video sampling undertaken in 2010 and 2011 showed that the fan mussels support a much wider range of species than is present on the surrounding sediment, with sponges, ophiuroids and crustaceans apparent. In light of the diverse epifaunal community and the sensitivity of the fan mussels themselves, it is highly probable that the aggregation is both natural and largely undisturbed (Howson et al., 2012).

Horse mussel beds Given the sensitivity of horse mussels and the diverse associated epifaunal and infaunal communities present, the feature is considered to be largely undisturbed.


Little is known about the expected composition and longevity of northern feather star aggregations. Aggregations may be the result of a single settlement event and / or they may be self-sustaining. Regardless, the fragile nature of the species would suggest that the areas that continue to support these aggregations are relatively undisturbed (Howson et al., 2012).


The northern sea fan and sponge communities appear undisturbed with a diverse flora and fauna. Northern sea fans Swiftia pallida were recorded on sloping bedrock and cliffs and in deep water on isolated boulder piles in 2010 and 2011 (Howson et al., 2012; Moore, 2012). S. pallida and a number of other species in these communities, such as the branching sponges, are fragile, slow growing and long-lived and it is therefore probable that they have been undisturbed for some time (Howson et al., 2012).

Geodiversity features

The components of the Quaternary of Scotland geodiversity feature were formed through glacial action ca. 15,000 years ago (Howe et al., 2012). They are robust, entirely natural in origin and are not considered to have been modified by human activity.

2d - Result Guideline met.

Guideline 2e The search location contains features considered to be at risk8 of significant damage by human activity

Black guillemot The Small Isles possible MPA lies within the West MPA region9. On the basis of a risk assessment undertaken at the level of the MPA region, there is considered to be a medium risk of significant damage to this feature arising from human activity (a cumulative assessment considering the range of activities known to be taking place in the MPA region). Within the region, non-native species colonisation e.g. American mink, is considered to present a high risk to the black guillemot populations. The brown rat eradication on Canna has helped reduce, and further research on Rum will help evaluate, the risks from predation by rats. Seaweed harvesting and shipping present medium risks and the risks of damage from marine energy production (wave and tidal turbines and associated infrastructure), fishing and aquaculture-related activities are considered to be low.

8 Information on the sensitivity of the MPA search features to pressures and their associated activities was taken from Tillin et al. (2010). The degree to which an MPA

search feature is exposed to activities / pressures to which it is sensitive in each MPA region was assessed to provide a qualitative measure of risk. Risk assessments for the various activities were examined to produce an overall qualitative risk assessment by MPA region. The conclusions may therefore not reflect the level of risk at the scale of the possible MPA. Site-specific activities and pressures are considered in further detail within the management options paper produced for this possible MPA.

9 The seas around Scotland were split into five MPA regions (East, North, West, South-west and Far West) at the outset of the MPA Project to aid the identification of MPA search locations and the preliminary appraisal of these against the MPA Selection Guidelines (e.g. the completion of regional risk assessments). This approach provided a useful framework for the initial stages of assessment. Within SNH and JNCC’s formal MPA network advice (SNH and JNCC, 2012) the MPA proposals and remaining MPA search locations were then cast within the context of broader OSPAR regions.

15

Guideline 2e The search location contains features considered to be at risk of significant damage by human activity

Burrowed mud On the basis of the cumulative regional risk assessment, there is considered to be a medium risk of significant damage to this feature arising from human activity. This is largely as a result of potential exposure to pressures associated with demersal fishing activity and aquaculture (finfish and shellfish farming).


Regional risk assessments have not been completed for representative features. However, information is available on the likely sensitivity of this feature (based on SS.SMu.CSaMu.AfilMysAnit biotope) to pressures arising from human activity. The feature is considered to be moderately sensitive to substratum loss, changes in water flow rate and increases in wave exposure. It is considered to have a low sensitivity to abrasion and physical disturbance and a very low sensitivity to increases in turbidity (Hill, 2004).


On the basis of the cumulative regional risk assessment, there is considered to be a medium-high risk of significant damage to this feature arising from human activity. This is largely as a result of potential exposure to pressures associated with demersal fishing activity (primarily otter trawling and scallop dredging).

Horse mussel beds On the basis of the cumulative regional risk assessment, there is considered to be at medium risk of significant damage to this feature arising from human activity. Within the region, demersal fishing activity (hydraulic dredging for bivalves, otter trawling and scallop dredging) are considered to present a high risk to horse mussel beds. Seaweed harvesting, some other fishing methods (creels and pots; and dive fisheries) and aquaculture (finfish and shellfish farming) present medium risks.


On the basis of the cumulative regional risk assessment, there is considered to be at low-medium risk of significant damage to this feature arising from human activity. This is largely a result of exposure to pressures associated with demersal fishing activity.


On the basis of the cumulative regional risk assessment, there is considered to be at low-medium risk of significant damage to this feature arising from human activity. This is largely as a result of potential exposure to pressures associated with creel and pot fishing, otter trawling, scallop dredging, set netting and aquaculture (fin fish)-related activity (all considered to present a medium risk).

Geodiversity features

Regional risk assessments have not been completed for geodiversity features. However, information is available on the likely sensitivity of these features to pressures arising from human activity (Brooks, 2013). The glaciated channels/troughs and rock basins are highly resistant to human activities (having been formed originally by glacial scouring). These and the meltwater channels (possible tunnel valleys) are either considered not sensitive, or to have a low sensitivity, to pressures arising from human activities. The glacial lineations, streamlined bedforms and moraines are considered highly sensitive to removal of substrates and have a medium sensitivity to changes in tidal water flow, wave exposure and sub-surface abrasion. In the vast majority of instances, most pressures associated with marine anthropogenic activities will not be sufficient to impact geological and geomorphological seabed features (Brooks, 2013).

2e - Result Guideline met. This is not an assessment of activities that require management within the possible MPA. That assessment is provided in the management options paper.

16

Stage 3 - Assessing the appropriate scale of the search location in relation to search features10 it contains

Assessment

The size of the search location should be adapted where necessary to ensure it is suitable for maintaining the integrity of the features for which the MPA is being considered. Account should also be taken where relevant of the need for effective management of relevant activities

The size and shape of the possible MPA reflects the distribution and extent of the range of proposed biodiversity and geodiversity protected features. To the north, the boundary encompasses the northerly extent of the shelf deeps (comprised of rock basin and glaciated channel / trough component interests of the Quaternary of Scotland geodiversity feature), following their outer extent down the north-east coast of Rum. To the west, it reflects the distribution of the glacial lineations and moraines on the shallower bedrock plateau known as the Canna High (Brooks et al., 2013). A number of the seabed habitat interests are encompassed within the shelf deeps large-scale feature (e.g. the fan mussel aggregations, horse mussel bed, circalittoral sand and mud communities). Burrowed mud is more widely distributed across the possible MPA (and beyond). Within the Sound of Canna and to the north, the burrowed mud habitat overlies mixed coarse, and muddy, sand communities. The proposed boundary has been influenced by the distribution of the tall seapen, encompassing areas of suitable habitat to the south of Canna, up through the sound and around the margins of the shelf deeps to the north. The northern feather star aggregations on mixed substrata and the northern sea fan and sponge communities are encompassed by a combination of the burrowed mud habitat, the shelf deeps and, for the northern sea fan and sponge communities and white cluster anemones, the geodiversity features to the south-west of Canna (NB - the northern sea fan and sponge communities are found on rocky outcrops rather than directly on the burrowed mud). The possible MPA also incorporates the sea area used for foraging by breeding black guillemots and encompasses most of the marine extensions of the existing Rum, and Canna and Sanday Special Protection Areas (SPAs). It extends a minimum of 2 km from the coastline where they nest. Field studies and modelling work indicate that approximately 95% of all black guillemot foraging occurs within 2 km of the coastline where they nest (SNH, 2012). The breeding population is distributed around the rocky coastline of Rum, Canna and Sanday. Guideline met.

10 Setting the size and shape of a possible MPA considers the distribution of both MPA search features and relevant geodiversity features. The latter, which are analogous to

the biodiversity search features, were defined after the publication of the MPA Selection Guidelines (refer to Brooks et al., 2013).

17

Stage 4 - Assessing the potential effectiveness of managing features within a search location as part of a Nature Conservation MPA


The possible MPA passed the assessment against the Stage 4 guideline. This resulted in the original MPA search location progressing as a potential area for an MPA to Stage 5.

Detailed assessment

There is a high probability that management measures, and the ability to implement them, will deliver the objectives of the MPA

The conservation objective for the protected features within this possible MPA is to ‘conserve’. The features are considered to be in good condition. A number of activities are considered capable of affecting the proposed protected features (see 2e above) and there is therefore a need to consider whether additional management is required. Statutory mechanisms exist (e.g. Fisheries Orders or Marine Conservation Orders) to support the introduction of spatial / temporal measures to conserve the features within the possible MPA. For example, Fisheries Orders have already been used to underpin management of marine Special Areas of Conservation. There is therefore potential for management measures to be implemented successfully and the conservation objective of the MPA to be achieved. Further discussion is required with those involved in using the possible MPA to provide clarification on interactions between the protected features and known / potential activities / developments. Additional details are provided in the management options paper produced for this possible MPA.

18

Stage 5 - Assessment of the contribution of the potential area to the MPA network


Guideline met - if designated the possible MPA would make a significant contribution to the MPA network.

Detailed assessment

The potential area contributes significantly to the coherence of the MPA network in the seas around Scotland

Assessment of biodiversity features Feature Representation Replication Linkages Geographic range & variation Resilience

Black guillemot

Encompasses ca. 2.2% of the GB breeding population (based on the Seabird 2000 full census).

Provisional 2013 results suggest that numbers of birds may have increased.

Replication of this feature in the network is proposed within and between OSPAR Regions II and III (see SNH and JNCC, 2012).

Not applicable11

Provides an example of a moderately sheltered colony on the west coast. In the southern part of the species’ range.

Additional replication within the network is proposed because the population in Scotland, particularly along the west coast, is considered to be threatened as a result of predation by introduced mammalian predators (e.g. mink).

Burrowed mud

Tall seapens Funiculina quadrangularis.

Seapens and burrowing megafauna in circalittoral fine mud.

[SS.SMu.CFiMu.SpnMegbiotope]

Seapens and burrowing megafauna are included within possible MPAs / MPA search locations within OSPAR Regions II, III and V.

Tall seapens are proposed within possible MPAs / MPA search locations in Regions II and III, with replication proposed in Region III (SNH and JNCC, 2012).

Not applicable12

Middle of geographic range in Scotland for both components.

Open coast in parts. Tidal sound and island grouping.

Additional replication within the network is proposed because Scottish waters are of proportional importance for this OSPAR Threatened and/or Declining habitat.

Replication of the components would be delivered within the network through the possible MPAs. The Small Isles is one of two possible MPAs with tall seapens in OSPAR Region III.

11 Connectivity has only been considered for black guillemots within the Clyde Sea Sill possible MPA and the provision of linkages to Irish populations of this species. This is

because juvenile black guillemots tend not to move further than about 50 km from their natal colony (SNH, 2012). 12 The linkages part of the guideline has only been assessed in situations where there is a good understanding of the relationship between features in different areas to help

build connectivity into the network. There is currently little evidence on which to base assessments of linkages for seabed habitats and low or limited mobility species in Scotland’s seas. Whilst there is information available for some species on dispersion distances, this cannot be readily applied to areas with complicated hydrography. For this reason, Marine Scotland Science is currently completing work on connectivity which focuses on a number of seabed habitats and low or limited mobility species (see http://www.scotland.gov.uk/Resource/0038/00389468.doc for an outline of work being undertaken to consider connectivity within the Scottish MPA network).

19



High quality examples of the feature.

[SS.SSa.OSa and SS.SMu.CSaMu.AfilMysAnitbiotopes]

Replication of this feature in the network is proposed within OSPAR Region II (SS.SSa.OSa not represented; a single record of .AfilMysAnit currently encompassed by existing measures).

Not applicable12

Middle of geographic range in Scotland.

A representative feature. Not considered to be threatened and/or declining.

Recommended to ensure representation of the range of broad-scale habitats within the Scottish MPA network.


Only known example of an aggregation of this low / limited mobility species in Scotland’s seas.

The largest known aggregation in UK waters.

[no definitive biotope]

Replication of this feature is not currently possible. This is the only known example in Scotland’s seas (see SNH and JNCC, 2012).

Not applicable12

The only known example in Scotland’s seas.

Fan mussels are considered to be threatened and declining within Scotland’s seas. The possible MPA includes the largest recorded aggregation of this species in the UK.

Horse mussel beds

The deepest known horse mussel bed in Scottish waters.

[SS.SBR.SMus.ModCvar biotope]

Replication of this feature in the network is proposed within and between OSPAR Regions II and III (see SNH and JNCC, 2012).

Not applicable12

The deepest known horse mussel bed in Scottish waters.

Significant sediment-immersion of much of the horse mussel population. Interspersed with an aggregation of fan mussels.

Additional replication within the network is proposed because Scottish waters are of proportional importance for this OSPAR Threatened and/or Declining habitat.


Multiple small high quality examples of aggregations of this low / limited mobility species.

[no definitive biotope]

Replication is proposed within OSPAR Region III. It is not possible to replicate between regions because of the restricted distribution of aggregations of this species (see SNH and JNCC, 2012).

Not applicable12

Middle of geographic range in Scotland. Open coast examples of the feature which is distributed around a coastal island grouping.

Additional replication within OSPAR Region III is proposed to address the lack of replication between regions and because of the sensitivity of the feature.

20


Northern sea fan and sponge communities

High quality examples of the feature.

[CR.MCR.EcCr.CarSwi.LgAs CR.HCR.XFa.SwiLgAs, and CR.HCR.DpSp.PhaAxi biotopes]

Northern sea fan Swiftia pallida.

Replication of this feature in the network is proposed within OSPAR Regions III and between OSPAR Regions II and III (see SNH and JNCC, 2012).

Feature considered well represented within the existing protected area network (Carruthers et al., 2011).

Not applicable12

Middle of the geographic range for the feature in Scotland.

Not required to achieve adequacy because of the protection already provided by existing measures.

Examples of the feature within the Small Isles possible MPA are of high quality. Recommended to add to the integrity of the proposal and complement existing protection in Region III.

Shelf deeps A high quality example of a glacially scoured shelf deep.

Replication of this feature in the network is proposed within OSPAR Region III and between Regions II and III (see SNH and JNCC, 2012).

Not applicable12

Extends the geographic range of the feature within the MPA network to the west.

Shelf deeps are not considered to be threatened and/or declining.

The shelf deep within the existing Firth of Lorn SAC (the additional example providing replication within OSPAR Region III) is the only known example of a tidally-scoured deep in Scottish waters. Therefore the possible MPA complements existing protection.

White cluster anemones

Aggregations of the white cluster anemone Parazoanthus anguicomus.

Replication of this feature in the network is proposed within and between OSPAR Regions II and III.

Feature considered well represented within the existing protected area network.

Not applicable12

Middle of the geographic range for the feature in Scotland.

Not required to achieve adequacy because of the protection already provided by existing measures.

Examples of the feature within the Small Isles possible MPA are of high quality. Recommended to add to the integrity of the proposal and complement existing protection in Region III.

21

Assessment of geodiversity features

Geodiversity features13

The Small Isles possible MPA encompasses part of the Small Isles key geodiversity area (Brooks et al., 2013) providing representation of the Quaternary of Scotland feature. The geodiversity interest has two dimensions. It provides a representative example of varied structural and lithological control influencing the form of the geomorphological seabed features of the area. It is also a good representative example of features of glacial erosion associated with palaeo-ice streams, notably large-scale basins and glacial lineations. The area is underlain by different bedrocks which have variable levels of hardness. It is dominated by the complex pre-Quaternary geology which includes platforms of Torridonian rock, and outcrops of Jurassic rock associated with regional Mesozoic basins. Highly resistant Palaeogene volcanic structures also influence the terrestrial and submarine geomorphological features. The differing hardness of the rocks and the distribution of faults provide a variable substrate that was differentially eroded by multiple ice streams during the Quaternary period. Where ice flows were constricted, high subglacial water pressure caused over-deepening. Where ice flows were less constrained the erosive potential of the ice was much reduced. The Sound of Canna offers a fine example of such differential erosion. During periods with fast-flowing and advancing ice, over-deepened sections were cut, which extend to a depth of 248 m. During periods when the ice was stationary or retreating, the surrounding shallow areas were subjected to the deposition of glacial debris which formed moraines. The Canna High, a large submerged shelf extending south-west from Canna, is capped with a hard bedrock with grooved features, eroded by the streaming glacial ice. The orientation of the grooves reflects the palaeo-ice stream, which is largely from the north-east to the south-west. Towards the western edge this is deflected increasingly towards the south, which suggests ice from the Sea of the Hebrides joined the larger, faster lowing Minch ice stream. Ice-contact moraines have been found along the near-shore of Rum and south Skye. These 10 m high features lie in water depths of 30 - 80 m, which may indicate that modern tidal activity in the area has removed much of the localised geomorphological evidence of the offshore glacial limits. Collectively the suite of geomorphological features within the Small Isles possible MPA link the adjacent terrestrial glacial landform record with the near-shore and off-shore evidence of the wider ice sheet dynamics and collapse. In this sense these features link the British-Irish Ice Sheet (BIIS) with the Barra Fan located on the edge of the Continental Shelf. These recent investigations off Scotland’s west coast identify a complex development of geomorphological features before, during and since the last glaciation. These varied submarine features control and influence the hydrodynamics, substrates, habitats and species which occupy this area.

Sources: Howe et al. (2012); Brooks et al. (2013).

13 For geodiversity the stage 5 assessment primarily considers the potential contribution to the principal ‘networks’ of marine geodiversity interests present in Scottish waters

(representation).

22

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23

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