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Please quote as: Lancaster, J. (Ed.), McCallum, S., Lowe A.C., Taylor, E., Chapman A. & Pomfret, J. (2014). Development of detailed ecological guidance to support the application of the Scottish MPA selection guidelines in Scotland’s seas. Scottish Natural Heritage Commissioned Report No.491. Maerl Beds – supplementary document. Maerl Beds Biotopes: SS.SMp.Mrl.Lcor Lithothamnion corallioides maerl beds on infralittoral muddy gravel. SS.SMp.Mrl.Lgla Lithothamnion glaciale maerl beds in tide-swept variable salinity infralittoral gravel. ` SS.SMp.Mrl.Pcal Phymatolithon calcareum maerl beds in infralittoral clean gravel or coarse sand. Sub-biotopes: SS.SMp.Mrl.Pcal.R Phymatolithon calcareum maerl beds with red seaweeds in shallow infralittoral clean gravel or coarse sand. SS.SMp.Mrl.Pcal.Nmix Phymatolithon calcareum maerl beds with Neopentadactyla mixta and other echinoderms in deeper infralittoral clean gravel or coarse sand. Territorial/Offshore waters: Territorial Maerl is calcareous red algae that grow as nodules (occasionally crusts) forming dense, but relatively open beds of algal gravel. Maerl beds, including dead maerl, have a complex open structure formed by interlocking maerl thalli allowing water to circulate, providing perfect conditions for a diverse community of organisms to exist. The maerl provides an attachment site for animals such as feather stars, hydroids and bryozoans. The loose structure provides shelter for small gastropods, crustaceans, bivalves and juvenile fish, and the infauna includes many bivalves such as Mya truncata and Dosinia exoleta. Epifauna include small Crustacea (Farnham & Bishop, 1985; Jones et al., 2000). Red seaweeds, sea firs and scallops may also colonise the surface. Many species have a high specificity to maerl beds, such as species of polychaetes (e.g. Glycera lapidum, Sphaerodorum gracilis and Polygordius lacteus) and amphipods (e.g. Parametaphoxus fultoni, Atylus vedlomensis and Animoceradocus semiserratus) (BIOMAERL team, 1999). Several species of algae are almost entirely restricted to calcareous habitats and are characteristically found in maerl beds (e.g. Halymenia latifolia, Scinaia turgida, Gelidiella calcicola, Gelidium maggsiae and Cruoria cruoriaeformis) (Birkett et al., 1998). Studies of the faunal composition from within maerl beds have shown that they often exist as isolated islands of high benthic diversity and biomass (BIOMAERL team, 1999). Maerl beds add considerable biological diversity to an area as well as adding value to other ecosystem functions. For example Hauton et al. (2003), commented that undamaged maerl grounds can be of long-term benefit to fisheries, acting as reproductive reservoirs for future generations of commercially important species, e.g. cod, edible crabs and scallops. Functional Links Functional links and associations with Priority Marine Features Flame shell beds: Nests of the flame shell Limaria hians are often found in conjunction with maerl (Hall-Spencer et al., 2003). L. hians binds maerl together with its byssal threads, helping to stabilise the maerl bed (Birkett et al., 1998). Maerl or coarse shell gravel with burrowing sea cucumbers: Areas of predominantly dead maerl and other coarse gravels with burrowing sea cucumbers often occur on the edge of maerl beds. Native oyster (Ostrea edulis): Maerl beds have been suggested as important nursery areas for native oysters, Ostrea edulis (Hall-Spencer et al., 2003). Horse mussel beds: Modiolus modiolus binds maerl together with its byssal threads, helping to stabilise the maerl bed (Birkett et al., 1998). Functional links and associations with wider Scottish marine ecosystem Maerl beds provide feeding areas for juvenile gadoid fish such as Atlantic cod (HallSpencer et al., 2003; Kamenos et al., 2004a). Maerl beds act as important nursery areas for commercially valuable molluscs such as scallops (Pecten maximus and Aequipecten opercularis) and razor shells (Ensis spp.) (Birkett et al., 1998; Hall-Spencer et al., 2003; Kamenos et al., 2004b,c) and also crustacea (Cancer pagurus). Maerl is important in calcium carbonate cycling, providing a source for other coastal habitats, e.g. beaches and dunes (Birkett et al., 1998). Deep burrowers and tube dwellers (e.g. Cerianthus sp., Sabella sp., Chaetopterus sp. and Upogebia sp.) can stabilise the underlying sediment upon which maerl beds develop (Birkett et al., 1998). Biological Diversity Habitat/Biotope description for Scottish waters There are four biotopes (and two sub-biotopes) described for maerl beds. Three biotopes (and two sub-biotopes) occur in Scottish waters, SS.SMp.Mrl.Pcal (and the sub biotopes SS.SMp.Mrl.Pcal.R and SS.SMp.Mrl.Pcal.Nmix), SS.SMp.Mrl.Lcor and SS.SMp.Mrl.Lgla The following biotope descriptions are taken directly from the Marine Habitat Classification Hierarchy (Connor et al., 2004). Where needed and possible, below each box, they are supplemented with additional information specific to Scotland from the scientific literature. Phymatolithon calcareum maerl beds in infralittoral clean gravel or coarse sand (SS.SMp.Mrl.Pcal) “Maerl beds characterised by P. calcareum in gravels and sands. Associated epiphytes may include red algae such as Dictyota dichotoma, Halarachnion ligulatum, Callophyllis laciniata, Cryptopleura ramosa, B. byssoides and Plocamium cartilagineum. Algal species may be anchored to the maerl or to dead bivalve shells 2 amongst the maerl. Polychaetes, such as Chaetopterus variopedatus, Lanice conchilega, Kefersteinia cirrata, Mediomastus fragilis, Chone duneri, Parametaphoxus fultoni and Grania sp. may be present. Gastropods such as Gibbula cineraria, Gibbula magus, Calyptraea chinensis Dikoleps pusilla and Onoba aculeus may also be present. Liocarcinus depurator and Liocarcinus corrugatus are often present, although they may be under-recorded; it would seem likely that robust infaunal bivalves such as Circomphalus casina, M. truncata, D. exoleta and other venerid bivalves are more widespread than available data currently suggests. It seems likely that stable wave-sheltered maerl beds with low currents may be separable from this biotope, having a generally thinner layer of maerl overlying a sandy /muddy substratum with a diverse cover of epiphytes but insufficient data currently exists on a national scale. Wave and current-exposed maerl beds, where thicker depths of maerl accumulate, frequently occur as waves and ridge / furrows arrangements. At some sites where P. calcareum occurs, there may be significant patches of maerl gravel containing the rare burrowing anemone Halcampoides elongatus; this may be a separate biotope, but insufficient data exists at present. Northern maerl beds in the UK do not appear to contain Lithothamnion corallioides but in south-west England and Ireland L. corallioides may occur to some extent in this biotope as well as Lcor1, where it dominates” (Connor et al., 2004). Whilst Connor et al. (2004) indicates that northern maerl beds do not appear to contain L. corallioides, there are records of this species in Scottish territorial waters (Jackson, 2007a). There are two sub-biotopes to SS.SMp.Mrl.Pcal which are described below: Phymatolithon calcareum maerl beds with red seaweeds in shallow infralittoral clean gravel or coarse sand (SS.SMp.Mrl.Pcal.R) “Upper infralittoral maerl beds characterised by P. calcareum in gravels and sand with a wide variety of associated red seaweeds. These algae typically include D. dichotoma, P. cartilagineum, Phycodrys rubens, Chondrus crispus, H. ligulatum, Chylocladia verticillata, Hypoglossum hypoglossoides and Nitophyllum punctum. These species are not restricted to maerl beds but their abundance on maerl beds differentiates this biotope from Pcal.Nmix2. Anthozoans and echinoderms are much less common in this biotope than in Pcal.Nmix2, which typically occurs deeper than this biotope” (Connor et al., 2004). Phymatolithon calcareum maerl beds with Neopentadactyla mixta and other echinoderms in deeper infralittoral clean gravel or coarse sand (SS.SMp.Mrl.Pcal.Nmix) “Lower infralittoral maerl beds characterised by P. calcareum in gravels and sand with a variety of associated echinoderms. The echinoderm N. mixta is frequently observed in this biotope. Other echinoderms such as Echinus esculentus, Ophiura 1 Lithothamnion corallioides maerl beds on infralittoral muddy gravel Phymatolithon calcareum maerl beds with Neopentadactylla mixta and other echinoderms in deeper infralittoral clean gravel or coarse sand 2 3 albida and rarely Luidia ciliaris may also be present. Red seaweed such as P. cartilagineum may be present but at a much lower abundance than in Pcal.R3 and with fewer species present. Other, more ubiquitous echinoderms such as Asterias rubens may also be found in low numbers throughout P. calcareum biotopes” (Connor et al., 2004). Lithothamnion corallioides (SS.SMp.Mrl.Lcor) maerl beds on infralittoral muddy gravel “Live maerl beds in sheltered, silty conditions which are dominated by L. corallioides with a variety of foliose and filamentous seaweeds. Live maerl is at least common but there may be noticeable amounts of dead maerl gravel and pebbles. Other species of maerl, such as P. calcareum and Phymatolithon purpureum, may also occur as a less abundant component. Species of seaweed such as D. dichotoma, H. ligulatum and Ulva spp. are often present, although are not restricted to this biotope, whereas Dudresnaya verticillata tends not to occur on other types of maerl beds. The anemones Anemonia viridis and Cerianthus lloydii, the polychaetes Notomastus latericeus and Caulleriella alata, the isopod Janira maculosa and the bivalve Hiatella arctica are typically found in this biotope whereas E. esculentus tends to occur more in other types of maerl. The seaweeds Saccharina latissima and Chorda filum may also be present in some habitats. This biotope has a southwestern distribution in Britain and Ireland. Sheltered, stable, fully saline maerl beds in the north of Great Britain (where L. corallioides has not been confirmed to occur) may need to be described as an analogous biotope to this one (see Pcal4)” (Connor et al., 2004). Whilst Connor et al. (2004) indicate in their biotope description for Pcal4 that northern maerl beds do not appear to contain L. corallioides, it is important to highlight that there are records of this species in Scottish territorial waters (Jackson, 2007a). Lithothamnion glaciale maerl beds in tide-swept variable salinity infralittoral gravel (SS.SMp.Mrl.Lgla) “Upper infralittoral tide-swept channels of coarse sediment in full or variable salinity conditions support distinctive beds of L. glaciale maerl 'rhodoliths'. P. calcareum may also be present as a more minor maerl component. Associated fauna and flora may include species found in other types of maerl beds (and elsewhere), e.g. Pomatoceros triqueter, C. lloydii, Sabella pavonina, C. variopedatus, L. conchilega, M. truncata, P. cartilagineum and P. rubens. Lgla5, however, also has a fauna that reflects the slightly reduced salinity conditions, e.g. Psammechinus miliaris is often present in high numbers along with other grazers such as chitons and Tectura spp. Hyas araneus, Ophiothrix fragilis, Ophiocomina nigra and the brown seaweed D. dichotoma are also typically present at sites. In Scotland, this biotope may show considerable variation but the community falls within the broad description defined here. This biotope can often be found at the upper end of Scottish sea lochs where the variable salinity of the habitat may not be immediately obvious” (Connor et al., 2004). 3 Phymatolithon calcareum maerl beds with red seaweeds in shallow infralittoral clean gravel or coarse sand 4 Phymatolithon calcareum maerl beds in infralittoral clean gravel or coarse sand 5 Lithothamnion glaciale maerl beds in tide-swept variable salinity infralittoral gravel 4 Species diversity Some of the most diverse examples of this search feature are described from the Sound of Arisaig on the west coast, where three maerl species were recorded along with a rich associated infauna (236 taxa) and epifauna (185 taxa) in five survey sites (Moore et al., 2004). One transect of 100m2 was conducted for epibiota in each of the five maerl sites surveyed. The most sheltered maerl sites were found in the inner region of Loch Ailort (biotope .Lgla5) and in the south channel of Loch Moidart (biotope .Pcal.R3) on silty sediments. These sites had the highest number of epibionts of the maerl habitats surveyed with 92 epibionts per 100m2 in both sites. Other sites containing the biotope .Pcal.R3 in the outer region of Loch Ailort and Loch Ceann Traigh had 77 and 67 associated epibionts respectively per 100m2. In Loch Moidart North Channel (biotope .Pcal4) there were 40 species of epibiont per 100m2 (Moore et al., 2004). In addition to this, core samples were taken for the infauna communities and details of the species richness and diversity by biotope are provided in Table 1. Moore et al. (2006) also conducted work in maerl beds in Loch nam Madadh SAC, where the number of epibiota taxa ranged from 46 to 100 per transect (100 m 2) for biotopes .Pcal4 and .Pcal.R3. The mean infauna abundance ranged from 1884 to 2880 individuals/0.1 m2. The mean number of infauna taxa ranged from 30 to 46 per 0.1 m2. Table 1. Species richness data for infauna for biotopes listed within this search feature (calculated from data in Moore et al., 2004) Biotope Mean abundance Mean no. of Mean Mean Shannonof infauna species per Pielou Wiener individuals per core evenness diversity (log2) 3 3 core (0.00167m ) (0.00167m ) SS.SMp.Mrl.Pcal 89 36 0.9 4.63 (site O3) SS.SMp.Mrl.Pcal.R 331 53 0.82 4.65 (sites C6, S6 and Z59) SS.SMp.Mrl.Lgla 123 52 0.91 5.21 (site Y10) 5 Key and characterising species These have been taken from JNCC’s biotope descriptions (Connor et al., 2004). Biotope type Key species for identification Phymatolithon calcareum Additional characterising species SS.SMp.Mrl.Pcal.R Phymatolithon calcareum Cerianthus lloydii, Chaetopterus variopedatus, Lanice conchilega, Pomatoceros triqueter, Pagurus bernhardus, Liocarcinus depurator, Gibbula cineraria, Asterias rubens, Echinus esculentus, Bonnemaisonia asparagoides, Cystoclonium purpureum, Plocamium cartilagineum, Lomentaria clavellosa, Nitophyllum punctatum, Phycodrys rubens, Brongniartella byssoides, Trailliella intricata, Dictyota dichotoma, Desmarestia aculeata, Desmarestia viridis, Chorda filum, Saccharina latissima, Ulva spp. SS.SMp.Mrl.Pcal.Nmix Phymatolithon calcareum and N. mixta Cerianthus lloydii, Chaetopterus variopedatus, Lanice conchilega, Pomatoceros triqueter, Pagurus bernhardus, Liocarcinus depurator, Gibbula magus, Tectura virginea, Pecten maximus, Ensis sp., Luidia ciliaris, Asterias rubens, Ophiura albida, Echinus esculentus, Pomatoschistus spp., Plocamium cartilagineum, Desmarestia viridis, Saccharina latissima. SS.SMp.Mrl.Lcor Lithothamnion corallioides Cerianthus lloydii, Anemonia viridis, Nematoda, Pisione remota, Harmothoe impar, Pholoe inornata, Glycera lapidum, Kefersteinia cirrata, Sphaerosyllis bulbosa, Lumbrineris gracilis, Protodorvillea kefersteini, Aonides paucibranchiata, Caulleriella alata, Mediomastus fragilis, Notomastus latericeus, Terebellidae, Lanice conchilega, Pista cristata, Nannonyx goesii, Microdeutopus versiculatus, Caprella acanthifera, Janira maculosa, Pagurus bernhardus, L. corrugatus, Liocarcinus depurator, Polyplacophora, Gibbula magus, Pecten maximus, Mysella bidentata, Parvicardium scabrum, Gari tellinella, Hiatella arctica, Asterias rubens, Marthasterias glacialis, Amphipholis squamata, Phymatolithon calcareum, Dudresnaya verticillata, Halarachnion, Dictyota dichotoma, Chorda filum, Saccharina latissima, Ulva spp. SS.SMp.Mrl.Lgla Lithothamnion glaciale Cerianthus lloydii, Pomatoceros triqueter, Pagurus bernhardus, Carcinus maenas, Gibbula. cineraria, Buccinum undatum, Ostrea edulis, Asterias rubens, Ophiothrix fragilis, Ophiocomina nigra, Psammechinus miliaris, Echinus esculentus, Corallina officinalis, Phymatolithon calcareum, Chondrus crispus, Trailliella intricata, Dictyota dichotoma, Chorda filum, Saccharina latissima. SS.SMp.Mrl.Pcal Porifera, Porifera indet crusts, Obelia dichotoma, Nemertea, Nematoda, Harmothoe impar, Kefersteinia cirrata, Eurysyllis tuberculata, Trypanosyllis coeliaca, Sphaerosyllis taylori, Aonides paucibranchiata, Mediomastus fragilis, Polycirrus, Chone duneri, Grania, Parametaphoxus fultoni, Socarnes erythrophthalmus, Austrosyrrhoe fimbriatus, Ceradocus semiserratus, Gammaropsis cornuta, Leptocheirus hirsutimanus, Leptocheirus pectinatus, Cymodoce truncata, Vaunthompsonia cristata, Cumella pygmaea, Nannastacus unguiculatus, Liocarcinus depurator, Gibbula cineraria, Dikoleps pusilla, Onoba aculeus, Crisia, Alcyonidium diaphanum, Scrupocellaria reptans, Escharoides coccinea, Microporella ciliata, Cellepora pumicosa, Asterias rubens, Amphipholis squamata, Clavelina lepadiformis, Didemnidae, Callionymus lyra, Hildenbrandia rubra, Corallinaceae, Corallina officinalis, Lithothamnion glaciale, Saccharina latissima. 6 Coherence Typicalness Maerl is a collective term for several species of calcified red seaweed which grow as unattached nodules, or rhodoliths, on sediments (OSPAR, 2008). They have a hard chalky skeleton and form small rounded nodules or short branched twig-like shapes called thalli (BIOMAERL team, 1999). In favourable conditions, these species can form extensive beds, typically 30% cover or more, mostly in coarse clean sediments of gravels and clean sands or muddy mixed sediments (OSPAR, 2008). Living, photosynthetically active maerl occupies the surface layer, while deeper layers of maerl are dead (but still an important habitat). The branching nodules of maerl form an interlocking but relatively open structure that provides a considerable surface area for attachment of other organisms. Maerl beds can be mobilised through high water movement, such as winter storms, as the thalli are not attached. However, some bivalves and burrowing species (e.g. Modiolus modiolus, Limaria hians, Cerianthus spp. & Sabella spp.) and seaweed (e.g. Saccharina latissima) can act to stabilise the underlying sediment and maerl bed (Birkett et al., 1998). Maerl beds typically develop where there is some tidal flow, such as in the narrows and rapids of sea lochs, or the straits and sounds between islands (BIOMAERL team, 1999). Beds may also develop in more open areas where wave action is sufficient to remove fine sediments, but not strong enough to break the brittle maerl branches. Maerl beds have been recorded from a variety of depths, ranging from the lower shore to 30m depth (OSPAR, 2008). As maerl requires light to photosynthesize, the depth at which it grows is determined by water turbidity. As a result of this, it is mainly found on coarse clean sands and gravels either on the open coast or in tide swept channels to a depth of about 20m, although occasional records from muddier sediments exist, e.g. in 1-5m of water at the head of Loch Torridon (Moore & Atkinson, 2012). Ecological variation across Scottish waters The maerl species present varies depending on sediment type, water movement and salinity. In fully marine conditions the dominant maerl is typically Phymatolithon calcareum, which is found on coarse sand and gravel, such as in Wyre and Rousay Sounds (Hirst et al. 2013). Under variable salinity conditions, for example in some sea lochs such as Loch Sween and Loch Ewe, beds of Lithothamnion glaciale have developed (Moore et al. 2011; Moore & Harries 2013) . Lithothamnion coralloides is generally found in sheltered conditions on silty sediments (Jackson, 2007a). The associated communities of maerl beds also vary with sediment type, water movement, depth of bed and salinity (Davies & Hall-Spencer, 1996; Connor et al., 2004; Moore et al., 2004). On coarse sediments, in shallow conditions, .Pcal maerl beds are generally characterised by epiphytic red algae (SMp.Mrl.Pcal.R) while deeper examples have more echinoderms, e.g. Neopentadactyla mixta (SMp.Mrl.Pcal.Nmix). Thicker maerl beds occur in areas of high water movement (from waves or currents), while sheltered beds tend to be thinner with more epiphytes. Within the North MPA region at Sullom Voe, Shetland, small patches of maerl (Phymatolithon calcareum) have been recorded in clean deep infralittoral gravel and coarse sand with an associated community dominated by hydroids and echinoderms (SS.SMp.Mrl.Pcal.Nmix; Mair et al., 2010). In contrast, in the West MPA region, in Loch na Droghniche, the Sound of Handa and Tob Valasay (Outer Hebrides), shallow maerl beds were found, associated with a significant cover of a variety of algal species (up to 65% cover in the Sound of Handa; James, 2004; BMT 7 Cordah Ltd, 2004). Species included Dictyota dichotoma, Enteromorpha sp., Ectocarpus sp., Halidrys siliquosa, Saccharina latissima, Laminaria hyperborea and other filamentous and foliose red algae, and coralline crusts. Associated fauna included Asterias rubens, Echinus esculentus, Cerianthus lloydii, and Luidia ciliaris (James, 2004; BMT Cordah Ltd, 2004). Further south in Loch Sunart, there are areas of maerl and maerl gravel. Here, beds were found associated with scattered algae and large numbers the anemone Cerianthus lloydii bordering stands of dense S. latissima (Mercer et al., 2007) Moore et al., (2004) found variation in the maerl species and associated communities in a study of the Sound of Arisaig SAC on the west coast. Lithothamnion corallioides and L. glaciale were present in the inner region of Loch Ailort on silty sediments, along with the echinoderm Psammechinus miliaris. This is possibly a reflection of the reduced salinity in this area. However, in the outer region of Loch Ailort, where there are stronger currents, P. calcareum was the dominant species and beds here had the highest number of infaunal taxa, and densest algal cover of all the maerl habitats in the study. In Loch Moidart P. calcareum was the only maerl species found. All three of these aforementioned sites also contained the anemones C. lloydii, A. viridis, Metridium senile and S. elegans. However, the most exposed sites in Loch Ceann Traigh and the mouth of the Loch Moidart North Channel had lower levels of fauna, a lack of anemones and contained P. calcareum and L. glaciale. More L. glaciale was present in the more exposed area, i.e. in the mouth of the Loch Moidart North Channel. In Loch Ceann Traigh the community was dominated by the algae Desmarestia aculeate, whilst in the Loch Moidart North Channel tubeworms and barnacles were the most dominant taxa, with no hydroids or echinoderms recorded (Moore et al., 2004). Therefore exposure does seem to be an important variable in maerl bed community structure. Findings of Moore et al., (2004) confirm previous work by Davies and Hall-Spencer (1996) who found lower infaunal and epifaunal species richness at the most exposed sites in the same area. A similar pattern was found in Loch nam Madadh where Moore et al., (2006) found the most exposed maerl bed site also had the lowest number of epifaunal and infaunal taxa and there was a significant difference in the species composition between sheltered and exposed maerl beds. Viability The dispersal potential of maerl is thought to be limited from current knowledge of its reproduction and propagation methods. L. glaciale has reproductive conceptacles that produce dispersive spores allowing sexual and asexual reproduction (Jackson, 2007a). The dispersal potential of sexual propagules is unknown because these have not been observed in UK waters and there have been no published studies of the genetic exchange between populations (Hill et al., 2010). L. glaciale can also propagate by vegetative (somatic) growth (Jackson, 2007a). However, for P. calcareum and L. corallioides, vegetative growth is the main form of propagation (Irvine & Chamberlain, 1994; Jackson, 2007b). As the reproduction of Scottish maerl is assumed to be mainly vegetative, the dispersal potential is limited and is probably less than 1 km, based on the dispersal of adults by water movements (Hill et al., 2010). Whilst many of the mapped maerl beds in Scottish waters are less than or around 1 km2 some are larger, up to around 9 km2. Due to the vegetative propagation methods and low dispersal distances of adult plants individual maerl beds could be largely 8 self-sustaining, especially beds of P. calcareum and L. corallioides. In light of the uncertainty around reproduction, viable area size and dispersal of maerl, it is recommended that a precautionary approach should be taken to protect maerl beds (Hill et al., 2010). Therefore, regardless of the size of the maerl bed it is recommended that the whole bed is protected. Longevity Maerl is extremely slow-growing and its growth rates have been recorded in data from Ireland, England, France, Norway, Scotland and Spain. These are of the order of tenths of millimetres to two millimetre per year (Bosence & Wilson, 2003, Jackson 2008; 2007a, b). Adey (1970) estimated the life span of individual plants of L. glaciale to be from 10 to 50 years. However, Jackson (2008; 2007a, b) indicates that the life span of P. calcareum and L. glaciale may be slightly longer from 20 to 100 years. It is thought that maerl beds are able to persist in one location for over 5000 years (Grall & Hall-Spencer, 2003). The various maerl species within a single bed can show periodic dominance and decline over time scales of between 3 and 30 years (Birkett et al., 1998). Fragmentation The proportion of live maerl and level of fragmentation can vary greatly with water movement, depth (light penetration), sediment and salinity. In the Sound of Arisaig a considerable degree of variation was found in the proportion of live maerl to other substrates. From the south channel of Loch Moidart to Rubha Ghead a Leighe, waves of maerl gravel and sand were recorded mosaiced with rocky reefs and coarse sediments with little or no live maerl (Moore et al. 2004). 9 Indicators of Least Damaged/More Natural Up to date information on the sensitivity of Maerl beds to pressures associated with human activities are included in the Feature Activity Sensitivity Tool (FeAST; Marine Scotland, 2013). Below, information on indicators of naturalness and damage are taken from primary literature (where referenced) or from MarLIN sensitivity data (Jackson, 2007b; 2008) (where reference is absent). Table 1. Indicators of damage and naturalness Indicators of Naturalness Indicators of Damage Potential Sources of damage Presence of maerl bed with a lack of smothering sediment Layer of sediment over maerl thalli (which may smother the maerl) Resuspended sediment, altered hydrography, extraction, eutrophication (e.g. from aquaculture (Hall-Spencer et al. 2006) Presence of maerl bed with a low cover of ephemeral algae Increase in ephemeral algae cover Eutrophication (Haskoning UK Ltd, 2006) Intact maerl thalli with few broken. Presence of typical assemblage of associated biota Broken/damaged maerl thalli. Broken fragments of other fragile animals e.g. tests of Psammechinus miliaris and the arms of Ophiothrix fragilis. Reduction in number of sessile epifauna such as Modiolus modiolus or Limaria hians, sponges and the anemone Metridium senile (Hall-Spencer & Moore, 2000a). Physical disturbance increased wave action, extraction (HallSpencer & Moore, 2000a, b; De Grave & Whitaker, 1999) Presence of intact, unburied maerl bed, with no mobile fishing gear tracks or creel/anchor damage in bed Mobile fishing gear tracks, creels/pots or anchor damage in bed, broken thalli, or thalli (often dead) buried under sediment (resulting in increased mortality) Physical disturbance (HallSpencer & Moore, 2000a, b). Maintenance of maerl bed area Loss of maerl bed area Extraction (De Grave & Whitaker, 1999) Full assemblage of associated biota Loss of associated high levels of biological diversity Changes in nutrient levels and oxygenation (Willson et al. 2004) Community composition comprising of typical species (see biological diversity section). Few ‘southern species’ present. Increases in abundance of ‘southern species’ and/or declines in characteristic species within the community. Increased ambient water temperature possibly as a result of climate change. (Hiscock et al., 2004) Risk Assessment The details of the assessment of risk for each MPA search feature is addressed in a separate report (Chaniotis et al., 2014). 10 Recovery Potential The impacts of any damage to maerl beds are long lasting because the key habitat structuring species has a very poor regenerative ability due to its extremely slow growth rates (Hall-Spencer & Moore, 2000a; Bosence & Wilson, 2003). Maerl is considered a non-renewable resource (Bosence & Wilson, 2003; OSPAR, 2008). Smothering of maerl thalli Smothering of the maerl thalli can result in a reduction in photosynthesis, with burial under just 2.5 mm of muddy sand for two weeks leading to death (Willson et al. 2004). In a study of the impact of fish-farm deposition on maerl beds, Hall-Spencer et al. (2006) highlighted that even in areas of relatively high currents there was likely to be a build-up of organic material which could lead to death of the maerl thalli. MarLIN’s sensitivity assessment for maerl beds states the recoverability of maerl to smothering as being ‘very low’ or ‘no recovery’ (Jackson, 2007b; 2008). Increase in ephemeral algae Nutrient enrichment can lead to increased suspended sediments and smothering, including by ephemeral epiphytic algae. This may impact the photosynthetic capacity of the maerl. No information was found on recovery of maerl beds from an increase in ephemeral algae. Broken thalli No specific information was found on the recovery potential from broken thalli however, as successful continued growth of thalli after fragmentation is very sporadic and growth rates are very slow (Bosence & Wilson, 2003), recovery rates are also likely to be slow. Physical disturbance Physical damage to the surface layer of a bed can result in living maerl nodules being buried and disrupt the physical integrity of accreted maerl beds (Jackson 2008). Hall-Spencer & Moore (2000a, b) reported that a single pass of a scallop dredge could bury and kill 70% of the living maerl, redistribute coarse sediment and affect the associated community. Recovery was slow, with dredge tracks remaining visible for over two and a half years (Hall-Spencer & Moore, 2000a, b). Hall-Spencer & Moore (2000a, b) suggested that repeated anchorage could create impacts similar to towed fishing gear. Additionally, creels/pots can also cause surface impacts to which maerl beds are sensitive (Tillin et al. 2010). MarLIN’s sensitivity assessment of maerl beds states that this habitat has ‘very low’ or ‘no recovery’ ability from physical disturbance (Jackson, 2007b; 2008). Loss of maerl bed area As maerl is considered a non-renewable resource (OSPAR, 2008) it is unlikely to recover from any extraction activity. Partial removal of a bed and recovery of maerl thalli is very slow and likely to take in the order of several decades to recover, if recovery occurs at all (Jackson, 2008). 11 Loss of associated high levels of biological diversity No information was found on recoverability of loss of biological diversity associated with a maerl bed. Climate change L. glaciale is a northern species and most UK records are in Scotland, especially in locations with variable or reduced salinity. A decline in this species and therefore the biotope .Lgla in response to warming is likely (Hiscock et al. 2004). L. coralloides, however, is a southern species and seawater warming may enable it to expand its distribution north (Hiscock et al. 2004). P. calcareum is widely distributed from Scotland to France and it is suggested that these maerl beds would persist. Geographic Variation The distribution of live maerl is determined by the physical conditions that favour maerl growth; it cannot withstand desiccation or low light so is restricted to the low intertidal and subtidal, to depths of around 30 m, in the relatively turbid waters of Scotland. Maerl also requires a degree of shelter from wave action, to prevent dispersal into deeper water, but requires sufficient water movement to prevent smothering with silt and provide sufficient gaseous exchange (Hall-Spencer, 1998). Therefore, maerl is usually restricted to places such as the sills of fjords and fjards (sea lochs in Scotland), together with the shores to the leeward of headlands and island archipelagos (Hall-Spencer, 1998; 2001a, b). Maerl beds are found all along the west coasts of the UK, from Shetland to south-west England, but the vast majority of beds are in Scotland (30% of the north-west European resource; HallSpencer, 2001a). Within Scotland, maerl beds are found in the west, north and southwest MPA regions, with the west and north regions having the most records. In the west region all three maerl biotopes (and the two .Pcal sub biotopes) have been recorded. Biotopes .Pcal, .Pcal.R and .Pcal.Nmix are widespread along the region’s coastline, concentrated within sea lochs and inlets on the mainland such as the Sound of Arisaig and Loch Laxford and areas such as Loch nam Madadh and the Sound of Barra in the Outer Hebrides. .Lcor and .Lgla are less widespread in the region and are only recorded in a few locations on the west coast and Outer Hebrides. In the north region there are widespread records of maerl beds in tide-swept areas, especially in Orkney and Shetland (Howson et al. 2009). .Pcal and .Pcal.R are widespread in Shetland, Orkney and Loch Eriboll on the north coast of the Scottish mainland. .Pcal.Nmix has also been recorded in Orkney and Shetland (Scapa Flow, Lunna Ness and Out Skerries) but .Lgla has only been recorded on the west coast of Shetland. In the south-west region there is a single .Lcor record with .Lgla records in the region. .Lgla has been recorded in areas including Loch Fyne, at the northern tip of the Isle of Bute and in the Clyde Sea around Inchmarnock. 12 Geographic context Elsewhere in the UK this habitat is recorded in Southern England at the Fal Estuary (Jackson, 2007a; 2007b), South Wales, the Isle of Man and Lundy. Sparse records exist from north and south-western Ireland (Howson et al., 2009). The abundance of suitable physical habitat conditions for maerl growth in Scotland makes it an important place in Europe for maerl, with the vast majority of maerl beds in the UK situated in Scotland. Maerl is rare in the English Channel, Irish Sea, and North Sea (Jackson, 2007a; 2007b). Outside of the UK, maerl beds are found world-wide. In the northeast Atlantic maerl occurs in discrete areas from the Canaries and Madeira (McMaster & Conover 1966; Cabioch, 1974), north-west Spain (Adey & McKibbin, 1970), Brittany (Cabioch 1970; Grall & Hall-Spencer, 2003), Denmark (King & Schramm, 1982), Russia, the Faeroe Isles, Iceland, the western Baltic (although it is rare in these waters), along the Norwegian shelf (Freiwald & Henrich, 1994) to the Arctic (Kjellmann, 1883; Adey & Adey,1973). Although maerl beds are found in many places across the north-east Atlantic, Scottish maerl beds are of particular importance with 30% of the north-west European maerl resource thought to be in Scotland (Hall-Spencer, 2001a). In the north-west Atlantic, maerl beds are recorded from Cape Cod, north to Arctic Canada and into Greenland and it has also been found in northern Japan and China in the western Pacific (Howson et al., 2009). 13 References Adey, W.H. & Adey, P.J. 1973. Studies on the biosystematics and ecology of the epilithic crustose Corallinaceae of the British Isles. British Phycological Journal, 8, 343–407. Adey, W.H. & McKibbin, D.L. 1970. Studies on the maerl species Phymatolithon calcareum (Pallas) nov.comb. and Lithothamnion corallioides Crouan in the Ria de Vigo. Botanica Marina, 13, 100–106. Birkett, D. A., Maggs, C. A. & Dring, M. J. 1998. Maerl (volume V). An overview of dynamic and sensitivity characteristics for conservation management of marine SACs. 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