Laminaria hyperborea on tide-swept, infralittoral mixed substrata.

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Map Key

Orange points: Core Records
Pale Blue points: Non-core, certain determination
Black points: Non-core, uncertain determination
Yellow areas: Predicted habitat extent

Biotope distribution data provided by the JNCC (mhc.jncc.gov.uk)

Researched by

Thomas Stamp, Ellie Burdett, Dr Harvey Tyler-Walters & Kelsey Lloyd

Refereed by

This information is not refereed

Researched by
Thomas Stamp, Ellie Burdett, Dr Harvey Tyler-Walters & Kelsey Lloyd

Refereed by
This information is not refereed

Summary

UK and Ireland classification

Standard	Classification	Description
EUNIS 2008	A3.213	Laminaria hyperborea on tide-swept infralittoral mixed substrata
JNCC 2022	IR.MIR.KR.LhypTX	Laminaria hyperborea on tide-swept infralittoral mixed substrata
JNCC 2015	IR.MIR.KR.LhypTX	Laminaria hyperborea on tide-swept infralittoral mixed substrata
JNCC 2004	IR.MIR.KR.LhypTX	Laminaria hyperborea on tide-swept, infralittoral mixed substrata.
1997 Biotope

EUNIS 2008 A3.213 - Laminaria hyperborea on tide-swept infralittoral mixed substrata
JNCC 2015 IR.MIR.KR.LhypTX - Laminaria hyperborea on tide-swept infralittoral mixed substrata
JNCC 2004 IR.MIR.KR.LhypTX - Laminaria hyperborea on tide-swept, infralittoral mixed substrata.
1997 Biotope -

Description

Wave-exposed through to wave-sheltered, tide-swept infralittoral mixed substrata with Laminaria hyperborea forest/park and other kelp species such as Saccharina latissima. The rich under-storey and stipe flora is characterized by foliose seaweeds including the brown algae Dictyota dichotoma. The kelp stipes support epiphytes such as Cryptopleura ramosa, Metacallophyllis laciniata and Phycodrys rubens. At some sites, instead of being covered by red seaweeds, the kelp stipes are heavily encrusted by the ascidians Botryllus schlosseri and the bryozoan Alcyonidium diaphanum. Epilithic seaweeds such as Desmerestia aculeata, Odonthalia dentate, Delesseria sanguinea, Plocamium cartilagineum, Metacallophyllis laciniata, and crustose seaweeds commonly occur beneath the kelp. The kelp fronds are often covered with growths of the hydroid Obelia geniculata or the bryozoan Membranipora membranacea. On the rock surface, a rich fauna comprising anthozoans such as Alcyonium digitatum and Urticina felina, colonial ascidians such as Clavelina lepadiformis and the calcareous tubeworm Spirobranchus triqueter occurs. More mobile species include the gastropods Gibulla cineria and Calliostoma zizyphinum, the crab Cancer pagurus and the echinoderms Crossaster papposus, Henricia oculata, Asterias rubens and Echinus esculentus. Two variants are described; tide-swept kelp forest on upper infralittoral mixed substrata (LhypTX.Ft) and tide-swept kelp park on lower infralittoral mixed substrata (LhypTX.Pk). (Information taken from JNCC, 2022).

Depth range

0-5 m, 5-10 m, 10-20 m, 20-30 m

Additional information

Listed By

Sensitivity reviewHow is sensitivity assessed?

Sensitivity characteristics of the habitat and relevant characteristic species

At high densities, Laminaria hyperborea forms a canopy over infralittoral rock and mixed substrata. Beneath the canopy an understorey community grows, defined by a mixed red seaweed and faunal (filter feeding) turf. The abundance of Laminaria hyperborea is determined by light availability, which decreases with an increase in water depth. Therefore, depth and water clarity determine the density of Laminaria hyperborea and hence the distribution of kelp forest (high density kelp) and park (low density kelp) variants. What distinguishes IR.MIR.KR.LhypT & IR.MIR.KR.LhypTX biotopes from another Laminaria hyperborea biotopes (e.g. IR.HIR.KFaR.LhypR) is exposure to strong (1.5-3 m/s)-moderately strong (0.5-1.5 m/s) tidal streams, which encourages the abundant growth of filter feeding fauna within the kelp understorey. Laminaria hyperborea stipes can be dominated by dense Botryllus schlosseri rather than the red seaweed communities of IR.HIR.KFaR.LhypR, and species such as Balanus crenatus and can be more abundant. Red seaweeds are also an important component of the understorey and stipe communities, however within IR.MIR.KR.LhypT & IR.MIR.KR.LhypTX biotopes fauna are more predominant within the understorey than in other Laminaria hyperborea biotopes (except in IR.HIR.KFaR.LhypFa).

Kelp biotopes are a major source of primary productivity, and support magnified secondary productivity within North Atlantic coastal waters (Smale et al., 2013; Brodie et al., 2014). In Scotland alone, kelp biotopes are estimated to cover 8000km² (Walker, 1953), and account for ca 45% of primary production in UK coastal waters (Smale et al., 2013). Therefore kelp biotopes, of which Laminaria hyperborea is dominant within UK subtidal rocky reefs (Birkett et al., 1998), make a substantial contribution to coastal primary production in the UK (Smale et al., 2013). Laminaria hyperborea is grazed directly by species such as Patella pellucid, however approximately 80% of primary production is consumed as detritus or dissolved organic material (Krumhansl, 2012) which is both retained within and transported out of the parent kelp forest, providing valuable nutrition to potentially low productivity habitats such as sandy beaches (Smale et al., 2013).

Laminaria hyperborea acts as an ecosystem engineer (Jones et al., 1994; Smale et al., 2013) by altering; light levels (Sjøtun et al., 2006), physical disturbance (Connell, 2003), sedimentation rates (Eckman et al., 1989) and water flow (Smale et al., 2013), profoundly altering the physical environment for fauna and flora in close proximity. Laminaria hyperborea biotopes increase the three-dimensional complexity of unvegetated rock (Norderhaug, 2004; Norderhaug et al., 2007; Norderhaug & Christie, 2011; Gorman et al., 2012; Smale et al., 2013), and support high local diversity, abundance and biomass of epi/benthic species (Smale et al., 2013), and serve as a nursery ground for a number of commercial important species, e.g. Gadidae (The taxonomic family that contains many commercially important marine fish species, including the Atlantic Cod and Pollack) (Rinde et al., 1992).

In undertaking this assessment of sensitivity, an account is taken of knowledge of the biology of all characterizing species/taxa in the biotope. However, 'indicative species' are particularly important in undertaking the assessment because they have been subject to detailed research. For this sensitivity assessment Laminaria hyperborea is the primary focus of research, however, it is recognized that the understorey community also defines the biotope. Examples of important species groups are mentioned where appropriate.

Resilience and recovery rates of habitat

A number of review and experimental publications have assessed the recovery of Laminaria hyperborea kelp beds and the associated community. If environmental conditions are favourable Laminaria hyperborea can recover following disturbance events reaching comparable plant densities and size to pristine Laminaria hyperborea beds within 2-6 years (Kain, 1979; Birkett et al., 1998; Christie et al., 1998). Holdfast communities may recover in 6 years (Birkett et al., 1998). Full epiphytic community and stipe habitat complexity regeneration required over 6 years (possibly 10 years). These recovery rates were based on discrete kelp harvesting events. Recurrent disturbance occurring frequently within 2-6 years of the initial disturbance is likely to lengthen recovery time (Birkett et al., 1998; Burrows et al., 2014). Kain (1975) cleared sublittoral blocks of Laminaria hyperborea at different times of the year for several years. The first colonizers and succession community differed between blocks and at what time of year the blocks were cleared, however within 2 years of clearance the blocks were dominated by Laminaria hyperborea.

In south Norway, Laminaria hyperborea forests are harvested, which results in large scale removal of the canopy-forming kelps. Cristie et al. (1998) found that in south Norwegian Laminaria hyperborea beds a pool of small (<25 cm) understorey, Laminaria hyperborea plants persist beneath the kelp canopy for several years. The understorey Laminaria hyperborea sporophytes had fully re-established the canopy at a height of 1 m within 2-6 years after kelp harvesting. Within 1 year following harvesting, and each successive year thereafter, a pool of Laminaria hyperborea recruits had re-established within the understorey beneath the kelp canopy. Cristie et al. (1998) suggested that Laminaria hyperborea bed re-establishment from understorey recruits (see above) inhibits the colonization of other kelps species and furthers the dominance of Laminaria hyperborea within suitable habitats, stating that Laminaria hyperborea habitats are relatively resilient to disturbance events.

Laminaria hyperborea has a heteromorphic life strategy. A vast number of zoospores (mobile asexual spores) are released into the water column between October-April (Kain & Jones, 1964). Zoospores settle onto rock substrata and develop into dioecious gametophytes (Kain, 1979) which, following fertilization, develop into sporophytes and mature within 1-6 years (Kain, 1979; Fredriksen et al., 1995; Christie et al., 1998). Laminaria hyperborea zoospores have a recorded dispersal range of ca 200 m (Fredriksen et al., 1995). However zoospore dispersal is greatly influenced by water movements, and zoospore density and the rate of successful fertilization decreases exponentially with distance from the parental source (Fredriksen et al., 1995). Hence, recruitment following disturbance can be influenced by the proximity of mature kelp beds producing viable zoospores to the disturbed area. (Kain, 1979, Fredriksen et al., 1995).

Laminaria hyperborea biotopes are partially reliant on low (or no) populations of sea urchins, primarily the species; Echinus esculentus, Paracentrotus lividus and Strongylocentrotus droebachiensis, which graze directly on macroalgae, epiphytes and the understorey community. Multiple authors (Steneck et al., 2002; Steneck et al., 2004; Rinde & Sjøtun, 2005; Norderhaug & Christie, 2009; Smale et al., 2013) have reported dense aggregations of sea urchins to be a principal threat to Laminaria hyperborea biotopes of the North Atlantic. Intense urchin grazing creates expansive areas known as ‘urchin barrens’, in which a shift can occur from Laminaria hyperborea dominated biotopes to those characterized by coralline encrusting algae, with a resultant reduction in biodiversity (Leinaas & Christie, 1996; Steneck et al., 2002, Norderhaug & Christie, 2009). Continued intensive urchin grazing pressure on Laminaria hyperborea biotopes can inhibit the Laminaria hyperborea recruitment (Sjøtun et al., 2006) and cause urchin barrens to persist for decades (Cristie et al., 1998; Stenneck et al., 2004; Rinde & Sjøtun, 2005). The mechanisms that control sea urchin aggregations are poorly understood but have been attributed to anthropogenic pressure on top down urchin predators (e.g. cod or lobsters). While these theories are largely unproven a number of studies have shown that removal of urchins from grazed areas coincide with kelp re-colonization (Leinaas & Christie, 1996; Norderhaug & Christie, 2009). Leinaas & Christie, (1996) removed Strongylocentrotus droebachiensis from ‘urchin barrens’ and observed a succession effect, in which the substratum was initially colonized by filamentous macroalgae and Saccharina latissima. However after 2-4 years Laminaria hyperborea dominated the community.

Reports of large scale urchin barrens within the North East Atlantic are generally limited to regions of the North Norwegian and Russian Coast (Rinde & Sjøtun, 2005, Norderhaug & Christie, 2009). Within the UK, urchin grazed biotopes (IR.MIR.KR.Lhyp.GzFt/Pk, IR.HIR.KFaR.LhypPar, IR.LIR.K.LhypSlat.Gz & IR.LIR.K.Slat.Gz) are generally localised to a few regions in North Scotland and Ireland (Smale et al., 2013; Stenneck et al., 2002; Norderhaug & Christie 2009; Connor et al., 2004). IR.MIR.KR.Lhyp.GzFt/Pk, IR.HIR.KFaR.LhypPar, IR.LIR.K.LhypSlat.Gz & IR.LIR.K.Slat.Gz are characterized by a canopy forming kelp. However, urchin grazing decreases the abundance and diversity of understorey species. In the Isle of Man. Jones & Kain (1967) observed that low Echinus esculentus grazing pressure could control the lower limit of Laminaria hyperborea and remove Laminaria hyperborea sporelings and juveniles. Urchin abundances in ‘urchin barrens’ have been reported as high as 100 individuals/m2 (Lang & Mann, 1976). Kain (1967) reported urchin abundances of 1-4/m2 within experimental plots of the Isle of Man. Therefore, while ‘urchin barrens’ are not presently an issue within the UK, relatively low urchin grazing has been found to control the depth distribution of Laminaria hyperborea, negatively impact on Laminaria hyperborea recruitment and reduce the understorey community abundance and diversity.

Other factors that are likely to influence the recovery of Laminaria hyperborea biotopes is competitive interactions with Invasive Non Indigenous Species (INIS), e.g. Undaria pinnatifida (Smale et al., 2013; Brodie et al., 2014; Heiser et al., 2014), and/or the Lusitanian kelp Laminaria ochroleuca (Brodie et al., 2014; Smale et al., 2014). A predicted sea temperature rise in the North and Celtic seas of between 1.5-5 °C over the next century (Philippart et al., 2011) is likely to create northward range shifts in many macroalgal species, including Laminaria hyperborea. Laminaria hyperborea is a northern (Boreal) kelp species, thus increases in seawater temperature is likely to affect the resilience and recoverability of Laminaria hyperborea biotopes with southerly distributions in the UK (Smale et al., 2013; Stenneck et al., 2002). Evidence suggests that the Lustanian kelp Laminaria ochroleuca (Smale et al., 2014), and the INIS Undaria pinnatifida (Heiser et al., 2014) are competing with Laminaria hyperborea along the UK south coast and may displace Laminaria hyperborea from some sub-tidal rocky reef habitats. The wider ecological consequences of Laminaria hyperborea’ competition with Laminaria ochroleuca and Undaria pinnatifida are however as of yet unknown.

Resilience assessment. The evidence suggests that beds of mature Laminaria hyperborea can regenerate from disturbance within a period of 1-6 years, and the associated community within 7-10 years. However, other factors such as competitive interactions with Laminaria ochroleuca and Undaria pinnatifida may limit recovery of Laminaria hyperborea biotopes following disturbance. Also, urchin grazing pressure is shown to limit Laminaria hyperborea recruitment and reduce the diversity and abundance of the understorey community and may limit habitat recovery following disturbance. The recovery of Laminaria hyperborea biotopes to disturbance from commercial harvesting in south Norway suggests that Laminaria hyperborea beds and the associated community could recover from a significant loss of canopy cover within 10 years, resilience has therefore been assessed as Medium.

Please note* as in Northern Norway urchin grazing pressure could extend recovery/resilience of the Laminaria hyperborea biotopes >25 years, If intensive urchin grazing (as seen in Northern Norway) occurs in the UK resilience would be re-assessed as Very Low. However, because of the limited/localised incidence of urchin grazing within the UK, urchin grazing on large scales (as in Northern Norway) has not been included in this general resilience assessment. Introduction of Invasive Non Indigenous Species (INIS) will also inhibit the recovery of Laminaria hyperborea biotopes for an indeterminate amount of time, in these cases resilience would need to be re-assessed as Very Low. Another factor that is beyond the scope of this sensitivity assessment is the presence of multiple concurrent synergistic or cumulative effects, which Smale et al. (2013) suggests could be a more damaging than the individual pressures.

Hydrological Pressures

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	Resistance	Resilience	Sensitivity
Temperature increase (local) [Show more] Temperature increase (local) Benchmark. A 5°C increase in temperature for one month, or 2°C for one year. Further detail Evidence Kain (1964) stated that Laminaria hyperborea sporophyte growth and reproduction could occur within a temperature range of 0 - 20°C. Upper and lower lethal temperatures have been estimated at between 1-2°C above or below the extremes of this range (Birkett et al., 1988). Above 17°C gamete survival is reduced (Kain, 1964 & 1971) and gametogenesis is inhibited at 21°C (Dieck, 1992). It is, therefore, likely that Laminaria hyperborea recruitment will be impaired at a sustained temperature increase of above 17°C. Sporophytes, however, can tolerate slightly higher temperatures of 20°C. Temperature tolerances for Laminaria hyperborea are also seasonally variable and temperature changes are less tolerated in winter months than summer months (Birkett et al., 1998). Subtidal red algae are less tolerant of temperature extremes than intertidal red algae, surviving between -2°C and 18-23 °C (Lüning 1990; Kain & Norton, 1990). Temperature increase may affect growth, recruitment or interfere with reproduction processes. For example, there is some evidence to suggest that blade growth in Delesseria sanguinea is delayed until ambient sea temperatures fall below 13 °C. Blade growth is also likely to be intrinsically linked to gametangia development (Kain, 1987), and maintenance of sea temperatures above 13 °C may affect recruitment success. Laminaria hyperborea has a geographic range from mid Portugal to Northern Norway (Birket et al., 1998), and a mid range within southern Norway (60°-65° North)(Kain, 1971). The average seawater temperature for southern Norway in October is 12-13°C (Miller et al., 2009), and average annual sea temperature, from 1970-2014, is 8°C (Beszczynska-Möller & Dye, 2013). Against the pressure benchmark the available information suggests that Laminaria hyperborea recruitment processes may be affected and associated red algae communities may decline. Sensitivity assessment. Overall, a chronic change (2°C for a year) outside the normal range for a year may reduce recruitment and growth, resulting in a minor loss in the population of kelp, especially in winter months or in southern examples of the biotope. However, an acute change (5°C for a month; e.g. from thermal effluent) may result in loss of abundance of kelp or extent of the bed, especially in winter. Therefore, resistance to the pressure is considered ‘Medium’, and resilience ‘Medium’. The sensitivity of this biotope to increases in temperature has been assessed as ‘Medium’.	Medium High High High Help	Medium High High High Help	Medium High High High Help
Temperature decrease (local) [Show more] Temperature decrease (local) Benchmark. A 5°C decrease in temperature for one month, or 2°C for one year. Further detail Evidence Kain (1964) stated that Laminaria hyperborea sporophyte growth and reproduction could occur within a temperature range of 0 - 20°C. Upper and lower lethal temperatures have been estimated at between 1-2 °C above or below the extremes of this range (Birkett et al., 1988). Subtidal red algae can survive at temperatures between -2 °C and 18-23 °C (Lüning, 1990; Kain & Norton, 1990). Laminaria hyperborea is a boreal northern species with a geographic range from mid-Portugal to Northern Norway (Birket et al., 1998), and a mid range within southern Norway (60°-65° North)(Kain, 1971). The average seawater temperature for southern Norway in October is 12-13°C (Miller et al., 2009), and average annual sea temperature, from 1970-2014, is 8°C (Beszczynska-Möller & Dye, 2013). The available information suggests that Laminaria hyperborea and biotope structure would not be affected by a change in sea temperature at the benchmark level. Sensitivity assessment. Resistance to the pressure is considered ‘High’, and resilience ‘High’. The sensitivity of this biotope to decreases in temperature has been assessed as ‘Not Sensitive’.	High High High High Help	High High High High Help	Not sensitive High High High Help
Salinity increase (local) [Show more] Salinity increase (local) Benchmark. A increase in one MNCR salinity category above the usual range of the biotope or habitat. Further detail Evidence Lüning (1990) suggest that “kelps” are stenohaline, their general tolerance to salinity as a phenotypic group covering 16 - 50 PSU over a 24 hr period. Optimal growth probably occurs between 30-35 PSU (MNCR category- 'Full' salinity) and growth rates are likely to be affected by periodic salinity stress. Birkett et al, (1998) suggested that long-term increases in salinity may affect Laminaria hyperborea growth and may result in loss of affected kelp, and, therefore, loss of the biotope. Sensitivity assessment. Resistance to the pressure is considered ‘Low’, and resilience ‘Medium’. The sensitivity of this biotope to an increase in salinity has been assessed as ‘Medium’.	Low Low NR NR Help	Medium High Medium High Help	Medium Low NR NR Help
Salinity decrease (local) [Show more] Salinity decrease (local) Benchmark. A decrease in one MNCR salinity category above the usual range of the biotope or habitat. Further detail Evidence Lüning (1990) suggest that ‘kelps’ are stenohaline, their general tolerance to salinity as a phenotypic group covering 16 - 50 PSU over a 24 hr period. Optimal growth probably occurs between 30-35 PSU (MNCR category-Full Salinity) and growth rates are likely to be affected by periodic salinity stress. Birkett et al. (1998b) suggest that long-term changes in salinity may result in loss of affected kelp and, therefore, loss of this biotope. Hopkin & Kain (1978) tested Laminaria hyperborea sporophyte growth at various low salinity treatments. The results showed that Laminaria hyperborea sporophytes could grow ‘normally’ at 19 PSU, growth was reduced at 16 PSU and did not grow at 7 PSU. A decrease in one MNCR salinity scale from Full Salinity (30-40psu) to Reduced Salinity (18-30 PSU) would result in a decrease of Laminaria hyperborea sporophyte growth. Laminaria hyperborea may also be out-competed by low salinity tolerant species e.g. Saccharina latissima (Karsten, 2007), or invasive kelp species, e.g. Undaria pinnatifida (Burrows et al., 2014). If salinity was returned to Full Salinity (30-40 psu) Laminaria hyperborea could out-compete Saccharina latissma and re-establish community dominance in 2-4 years (Leinaas & Christie, 1996), however, full habitat structure may take over 10 years to recover (Birkett et al., 1998; Cristie et al., 1998). The ability of Laminaria hyperborea to out-compete Undaria pinnatifida within the UK is, however, unknown (Heiser et al., 2014), and as such interspecific interaction between Laminaria hyperborea and Undaria pinnatifida is not included within this sensitivity assessment. Sensitivity assessment. Resistance to the pressure is considered ‘Low’, and resilience ‘Medium’. The sensitivity of this biotope to decreases in salinity has been assessed as ‘Medium’.	Low Medium Medium Medium Help	Medium High Medium High Help	Medium Medium Medium Medium Help
Water flow (tidal current) changes (local) [Show more] Water flow (tidal current) changes (local) Benchmark. A change in peak mean spring bed flow velocity of between 0.1 m/s to 0.2 m/s for more than one year. Further detail Evidence Kregting et al. (2013) measured Laminaria hyperborea blade growth and stipe elongation from an exposed and a sheltered site in Strangford Lough, Northern Ireland, from March 2009-April 2010. Maximal significant wave height (Hm0) was 3.67 & 2m at the exposed and sheltered sites, and maximal water velocity (Velrms) was 0.6 & 0.3m/s at the exposed and sheltered sites respectively. Despite the differences in wave exposure and water velocity, there was no significant difference in Laminaria hyperborea growth between the exposed and sheltered sites. Therefore water flow was found to have no significant effect on Laminaria hyperborea growth at the observed range of water velocities. Biotope structure is, however, different between wave exposed and sheltered sites. Pedersen et al. (2012) observed Laminaria hyperborea biomass, productivity and density increased with an increase in wave exposure. At low wave exposure, Laminaria hyperborea canopy forming plants were smaller, had lower densities and had higher mortality rates than at exposed sites. At low wave exposure Pedersen et al. (2012) suggested that high epiphytic loading on Laminaria hyperborea impaired light conditions, nutrient uptake, and increased the drag on the host Laminaria hyperborea during extreme storm events. The morphology of the stipe and blade of kelps vary with water flow. In wave exposed areas, for example, Laminaria hyperborea develops a long and flexible stipe and this is probably a functional adaptation to strong water movement (Sjøtun, et al.,1998). In addition, the lamina becomes narrower and thinner in strong currents (Sjøtun & Fredriksen, 1995). However, the stipe of Laminaria hyperborea is relatively stiff and can snap in strong currents. Laminaria hyperborea is usually absent from areas of high wave action or strong currents, although it is found in the Menai Strait, Wales, where tidal velocities can exceed 4 m/s (NBN, 2015) and in tidal rapids in Norway (J. Jones, pers. comm.) Laminaria hyperborea growth can persist in very strong tidal streams (>3 m/s). Increase water flow rate may also remove or inhibit grazers including Patella pellucida and Echinus esculentus, therefore reducing grazing in the understorey and on stipes. The associated algal flora and suspension feeding faunal populations change significantly with different water flow regimes. Decreased water flow rates may reduce the suspension feeding understorey epifauna, to be replaced by an epiflora dominated community as in the biotope IR.HIR.KFaR.LhypR. The composition of the holdfast fauna may also change, e.g. energetic or sheltered water movements favour different species of amphipods (Moore, 1985). IR.MIR.KR.LhypT, IR.MIR.KR.LhypTX and their associated sub-biotopes are predominantly found within strong (1.5-3 m/s)-moderate (0.5-1.5 m/s) tidal streams. The prominent understorey filter feeding community within IR.MIR.KR.LhypT/TX is reliant on strong tidal flow. It is the abundance of filter feeding organisms that separates the tide swept Laminaria hyperborea biotopes from the not tide-swept biotopes within the same wave exposure (e.g. IR.HIR.KFaR.LhypR). A change in peak mean spring bed flow velocity within the tidal streams 0.5-3 m/s is not likely to significantly affect the abundance of Laminaria hyperborea. A decrease in tidal streams may result in a decline of filter feeding fauna and an increase in red seaweeds within the understorey community. A decrease in tidal flow within this range may also decrease urchin dislodgment and increase urchin grazing. An increase in urchin grazing may cause a decline in the understorey community abundance and diversity (as in IR.MIR.KR.Lhyp.GzFt/Pk). Large increases in water movement (e.g. >3 m/s) may increase the dislodgement/loss of Laminaria hyperborea from the biotope (Birkett et al., 1988), and may cause an increase in the abundance of the ephemeral kelp: Saccharina latissima or Alaria esculenta, which are both fast growing species and tolerant of fast water movement (Birkett et al., 1998). Sensitivity assessment. Water movement is a key environmental characteristic of IR.MIR.KR.LhypT and IR.MIR.KR.LhypTX, however, these biotopes are found within a broad range of tidal streams (0.5-3 m/s). A change in peak mean spring bed flow velocity of between 0.1m/s to 0.2m/s for more than 1 year is however observed as a small change in water movement, and is not likely to significantly affect the community Resistance to the pressure is therefore considered ‘High’, and resilience ‘High’. The sensitivity of this biotope to changes in peak mean spring bed velocity has been assessed as ‘Not Sensitive’ at the benchmark level. Large and dramatic changes in tidal streams (>3 m/sec) may increase the abundance/dominance of ephemeral kelp species Alaria esculenta and Saccharina latissima, and may result in loss of the biotope. Changes of this dramatic nature are however outside of the scope of this habitat sensitivity assessment.	High High High High Help	High High High High Help	Not sensitive High High High Help
Emergence regime changes [Show more] Emergence regime changes Benchmark. 1) A change in the time covered or not covered by the sea for a period of ≥1 year or 2) an increase in relative sea level or decrease in high water level for ≥1 year. Further detail Evidence The upper limit of the Laminaria hyperborea bed is determined by wave action and water flow, desiccation, and competition from the more emergence resistant Laminaria digitata. Laminaria hyperborea exposed at extreme low water are very intolerant of desiccation, the most noticeable effect being bleaching of the frond and subsequent death of the meristem and loss of the plant. An increase in wave exposure (See below- water flow), as a result of increased emergence, has been found to exclude Laminaria hyperborea from shallow waters due to dislodgement of the sporophyte or snapping of the stipe (Birkett et al., 1998). Hence, an increase in emergence is likely to lead to mortality of exposed Laminaria hyperborea and the associated habitat. An increase in water depth/decreased emergence (at the benchmark level) may increase the upper depth restriction of Laminaria hyperborea forest variants within this biotope group. However, limited light availability at depth will decrease the lower extent of Laminaria hyperborea, and may, therefore, result in a shift from forest to park biotope variants at depth. Further increases in depth will cause a community shift to that characterized by circalittoral faunal species, however, this is beyond the scope of the benchmark. Sensitivity assessment. Resistance to the pressure is considered ‘Low’, and resilience ‘Medium’. The sensitivity of this biotope to changes in tidal emergence has been assessed as ‘Medium’.	Low Low NR NR Help	Medium High Low High Help	Medium Low NR NR Help
Wave exposure changes (local) [Show more] Wave exposure changes (local) Benchmark. A change in near shore significant wave height of >3% but <5% for more than one year. Further detail Evidence Kregting et al. (2013) measured Laminaria hyperborea blade growth and stipe elongation from an exposed and a sheltered site in Strangford Lough, Northern Ireland from March 2009-April 2010. Wave exposure was found to be between 1.1. to 1.6 times greater between the exposed and sheltered sites. Maximal significant wave height (Hm0) was 3.67 & 2 m at the exposed and sheltered sites. Maximal water velocity (Velrms) was 0.6 & 0.3 m/s at the exposed and sheltered sites. Despite the differences in wave exposure and water velocity, there was no significant difference in Laminaria hyperborea growth between the exposed and sheltered site. Biotope structure is, however, different between wave exposed and sheltered sites. Pedersen et al. (2012) observed Laminaria hyperborea biomass, productivity and density increased with an increase in wave exposure. At low wave exposure, Laminaria hyperborea canopy forming plants were smaller, had lower densities and had higher mortality rates than at exposed sites. At low wave exposure high epiphytic loading on Laminaria hyperborea was theorised to impair light conditions, nutrient uptake, and increase the drag of the host Laminaria hyperborea during extreme storm events. The morphology of the stipe and blade of kelps vary with water flow. In wave exposed areas, for example, Laminaria hyperborea develops a long and flexible stipe and this is probably a functional adaptation to strong water movement (Sjøtun, 1998). In addition, the lamina becomes narrower and thinner in strong currents (Sjøtun & Fredriksen, 1995). However, the stipe of Laminaria hyperborea is relatively stiff and can snap in strong currents. Lamiaria hyperborea is usually absent from areas of extreme wave action and can be replaced by Alaria esculenta. In extreme wave exposures, Alaria esculenta can dominate the shallow sub-littoral to a depth of 15m, where Laminaria hyperboea dominates the infralittoral (Birket et al., 1998). Increase water flow may also remove or inhibit grazers including Patella pellucida and Echinus esculentus, therefore reducing grazing in the understorey and on stipes. The associated algal flora and suspension feeding faunal populations change significantly with different water flow regimes. Increased water flow rates may reduce the understorey epiflora, to be replaced by an epifauna dominated community (e.g. sponges, anemones and polyclinid ascidians) as in the biotope IR.HIR.KFaR.LhypFa. The composition of the holdfast fauna may also change, e.g. energetic or sheltered water movements favour different species of amphipods (Moore, 1985). IR.MIR.KR.LhypT, IR.MIR.KR.LhypTX and their associated sub-biotopes are found between extremely exposed to sheltered wave exposure but experience elevated tidal streams. Changes in local wave height above or below that experienced in extremely exposed to sheltered exposed sites will affect the dominance of Laminaria hyperborea. Smaller changes in local wave height have the potential to cause changes to the understorey community. The prominent understorey filter feeding community within IR.MIR.KR.LhypT/TX is reliant on high water movement. A decrease in wave surge may result in a decline of filter feeding fauna and an increase in red seaweeds within the understorey community or vice versa. A decrease in local wave height may also decrease the chance of urchins being dislodged (removed) from biotopes found at sites with traditionally high wave exposure and may, therefore, increase urchin grazing. An increase in urchin grazing may cause a decline in the understorey community abundance and diversity (as in IR.MIR.KR.Lhyp.GzFt/Pk and IR.MIR.KR.LhypPar). Sensitivity assessment. A change in nearshore significant wave height >3% but <5% is, however, unlikely to have a significant effect. Resistance to the pressure is considered ’High‘, and resilience ‘High‘. Hence, the sensitivity of this biotope to changes in local wave height has been assessed as ’Not Sensitive’. Large and dramatic changes in near shore wave height may increase the abundance/dominance of the ephemeral kelp species Alaria esculenta, increase the dominance of IR.HIR.KFaR.Ala and may result in loss of the biotope. Changes of this dramatic nature are however outside of the scope of this habitat sensitivity assessment.	High High High High Help	High High High High Help	Not sensitive High High High Help

Chemical Pressures

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	Resistance	Resilience	Sensitivity
Transition elements & organo-metal contamination [Show more] Transition elements & organo-metal contamination Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail Evidence This pressure is Not assessed but evidence is presented where available. Bryan (1984) suggested that the general order for heavy metal toxicity in seaweeds is: Organic Hg > inorganic Hg > Cu > Ag > Zn > Cd > Pb. Cole et a,. (1999) reported that Hg was very toxic to macrophytes. Similarly, Hopkin & Kain (1978) demonstrated sub-lethal effects of heavy metals on Laminaria hyperborea gametophytes and sporophytes, including reduced growth and respiration. Sheppard et al., (1980) noted that increasing levels of heavy metal contamination along the west coast of Britain reduced species number and richness in holdfast fauna, except for suspension feeders which became increasingly dominant. Gastropods may be relatively tolerant of heavy metal pollution (Bryan, 1984). Echinus esculentus recruitment is likely to be impaired by heavy metal contamination due to the intolerance of its larvae. Echinus esculentus are long-lived and poor recruitment may not reduce grazing pressure in the short-term. Although macroalgae species may not be killed, except by high levels of contamination, reduced growth rates may impair the ability of the biotope to recover from other environmental disturbances.	Not Assessed (NA) NR NR NR Help	Not assessed (NA) NR NR NR Help	Not assessed (NA) NR NR NR Help
Hydrocarbon & PAH contamination [Show more] Hydrocarbon & PAH contamination Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail Evidence This pressure is Not assessed but evidence is presented where available. Laminaria hyperborea fronds, being almost exclusively subtidal, would not come into contact with freshly released oil, but only to sinking emulsified oil and oil adsorbed onto particles (Birkett et al., 1998). The mucilaginous slime layer coating of laminarians may protect them from smothering by oil. Hydrocarbons in solution reduce photosynthesis and may be algicidal. However, Holt et al. (1995) reported that oil spills in the USA and from the 'Torrey Canyon' had little effect on kelp forests. Similarly, surveys of subtidal communities at a number sites between 1-22.5 m below chart datum, including Laminaria hyperbora communities, showed no noticeable impacts of the Sea Empress oil spill and clean up (Rostron & Bunker, 1997). An assessment of holdfast fauna in Laminaria showed that although species richness and diversity decreased with increasing proximity to the Sea Empress oil spill, overall the holdfasts contained a reasonably rich and diverse fauna, even though oil was present in most samples (Sommerfield & Warwick, 1999). Laboratory studies of the effects of oil and dispersants on several red algae species, including Delesseria sanguinea (Grandy 1984; cited in Holt et al., 1995) concluded that they were all sensitive to oil/ dispersant mixtures, with little differences between adults, sporelings, diploid or haploid life stages. Holt et al., (1995) concluded that Delesseria sanguinea is probably generally sensitive of chemical contamination. Overall the red algae are likely to be highly intolerant to hydrocarbon contamination. Loss of red algae is likely to reduce the species richness and diversity of the biotope and the understorey may become dominated by encrusting corallines; however, red algae are likely to recover relatively quickly.	Not Assessed (NA) NR NR NR Help	Not assessed (NA) NR NR NR Help	Not assessed (NA) NR NR NR Help
Synthetic compound contamination [Show more] Synthetic compound contamination Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail Evidence This pressure is Not assessed but evidence is presented where available. O'Brian & Dixon (1976) suggested that red algae were the most sensitive group of macrophytes to oil and dispersant contamination (see Smith, 1968). Although Laminaria hyperborea sporelings and gametophytes are intolerant of atrazine (and probably other herbicides) overall they may be relatively tolerant of synthetic chemicals (Holt et al., 1995). Laminaria hyperborea survived within >55 m from the acidified halogenated effluent discharge polluting Amlwch Bay, Anglesey, albeit at low density. These specimens were greater than 5 years of age, suggesting that spores and/or early stages were more intolerant (Hoare & Hiscock, 1974). Patella pellucida was excluded from Amlwch Bay by the pollution and the species richness of the holdfast fauna decreased with proximity to the effluent discharge; amphipods were particularly intolerant although polychaetes were the least affected (Hoare & Hiscock, 1974). The richness of epifauna/flora decreased near the source of the effluent and epiphytes were absent from Laminaria hyperborea stipes within Amlwch Bay. The red alga Phyllophora membranifolia was also tolerant of the effluent in Amlwch Bay. Smith (1968) also noted that epiphytic and benthic red algae were intolerant of dispersant or oil contamination due to the Torrey Canyon oil spill; only the epiphytes Crytopleura ramosa and Spermothamnion repens and some tufts of Jania rubens survived together with Osmundea pinnatifida, Gigartina pistillata and Phyllophora crispa from the sublittoral fringe. Delesseria sanguinea was probably to most intolerant since it was damaged at depths of 6 m (Smith, 1968). Holt et al., (1995) suggested that Delesseria sanguinea is probably generally sensitive of chemical contamination. Although Laminaria hyperborea may be relatively insensitive to synthetic chemical pollution, evidence suggests that grazing gastropods, amphipods and red algae are sensitive. Loss of red algae is likely to reduce the species richness and diversity of the biotope and the understorey may become dominated by encrusting corallines; however, red algae are likely to recover relatively quickly.	Not Assessed (NA) NR NR NR Help	Not assessed (NA) NR NR NR Help	Not assessed (NA) NR NR NR Help
Radionuclide contamination [Show more] Radionuclide contamination Benchmark. An increase in 10µGy/h above background levels. Further detail Evidence No evidence	Not relevant (NR) NR NR NR Help	Not relevant (NR) NR NR NR Help	No evidence (NEv) NR NR NR Help
Introduction of other substances [Show more] Introduction of other substances Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail Evidence This pressure is Not assessed.	Not Assessed (NA) NR NR NR Help	Not assessed (NA) NR NR NR Help	Not assessed (NA) NR NR NR Help
De-oxygenation [Show more] De-oxygenation Benchmark. Exposure to dissolved oxygen concentration of less than or equal to 2 mg/l for one week (a change from WFD poor status to bad status). Further detail Evidence Reduced oxygen concentrations have been shown to inhibit both photosynthesis and respiration in macroalgae (Kinne, 1977). Despite this, macroalgae are thought to buffer the environmental conditions of low oxygen, thereby acting as a refuge for organisms in oxygen depleted regions especially if the oxygen depletion is short-term (Frieder et al., 2012). In addition, the biotope occurs in areas of moderate to extreme wave action, so is likely to be continuously aerated. A rapid recovery from a state of low oxygen is expected if the environmental conditions are transient. If levels do drop below 4 mg/l negative effects on these organisms can be expected with adverse effects occurring below 2mg/l (Cole et al., 1999). Sensitivity Assessment. Reduced oxygen levels are likely to inhibit photosynthesis and respiration but not cause a loss of the macroalgae population directly. Furthermore wave exposure is likely to constantly aerate the affected area. While de-oxygenation may not directly affect Laminaria hyperborea, small invertebrate epifauna may be lost, causing a reduction in species richness. Therefore resistance has been assessed as ‘Medium’ is recorded. Resilience is likely to be ‘High’, and the biotopes is probably ‘Low’ at the benchmark level.	Medium High Medium High Help	High High Medium High Help	Low High Medium High Help
Nutrient enrichment [Show more] Nutrient enrichment Benchmark. Compliance with WFD criteria for good status. Further detail Evidence Holt et al. (1995) suggest that Laminaria hyperborea may be tolerant of nutrient enrichment since healthy populations are found at ends of sublittoral untreated sewage outfalls in the Isle of Man. Increased nutrient levels e.g. from sewage outfalls, has been associated with increases in abundance, primary biomass and Laminaria hyperborea stipe production but with concomitant decreases in species numbers and diversity (Fletcher, 1996). Increased nutrients may result in phytoplankton blooms that increase turbidity (see above). Increased nutrients may favour sea urchins, e.g. Echinus esculentus, due their ability to absorb dissolved organics, and result in increased grazing pressure leading to loss of understorey epiflora/fauna, decreased kelp recruitment and possibly 'urchin barrens'. Therefore, although nutrients may not affect kelps directly, indirect effects such as turbidity, siltation and competition may significantly affect the structure of the biotope. However, this biotope is considered to be 'Not sensitive' at the pressure benchmark, that assumes compliance with good status as defined by the WFD.	Not relevant (NR) NR NR NR Help	Not relevant (NR) NR NR NR Help	Not sensitive NR NR NR Help
Organic enrichment [Show more] Organic enrichment Benchmark. A deposit of 100 gC/m²/yr. Further detail Evidence Holt et al. (1995) suggest that Laminaria hyperborea may be tolerant of organic enrichment since healthy populations are found at ends of sublittoral untreated sewage outfalls in the Isle of Man. Increased nutrient levels e.g. from sewage outfalls, has been associated with increases in abundance, primary biomass and Laminaria hyperborea stipe production, but with concomitant decreases in species numbers and diversity (Fletcher, 1996). Increase organic enrichment has also been found to increase the abundance and dominance of suspension feeding fauna within Laminaria hyperborea holdfasts (Sheppard et al., 1980). Increase in ephemeral and opportunistic algae are associated with reduced numbers of perennial macrophytes (Fletcher, 1996). Increased nutrients may also result in phytoplankton blooms that increase turbidity. Therefore, although nutrients may not affect kelps directly, indirect effects such as turbidity and the increased abundance of suspension feeding fauna may affect the structure of Laminaria hyperborea biotopes (see water clarity above). Sensitivity assessment. While organic enrichment may not have any direct effects on Laminaria hyperborea, increased turbidity and abundance of suspension feeding fauna may have significant effects on the biotope structure. Resistance to the pressure has therefore been considered ‘Medium’, and resilience ‘High’. The sensitivity of this biotope to organic enrichment is assessed as ‘Low’.	Medium Medium Medium Medium Help	High High Medium High Help	Low Medium Medium Medium Help

Physical Pressures

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Biological Pressures

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	Resistance	Resilience	Sensitivity
Genetic modification & translocation of indigenous species [Show more] Genetic modification & translocation of indigenous species Benchmark. Translocation of indigenous species or the introduction of genetically modified or genetically different populations of indigenous species that may result in changes in the genetic structure of local populations, hybridization, or change in community structure. Further detail Evidence No evidence regarding the genetic modification or effects of translocation of native populations was found.	Not relevant (NR) NR NR NR Help	Not relevant (NR) NR NR NR Help	No evidence (NEv) NR NR NR Help
Introduction or spread of invasive non-indigenous species [Show more] Introduction or spread of invasive non-indigenous species Benchmark. The introduction of one or more invasive non-indigenous species (INIS). Further detail Evidence Competition with invasive macroalgae may be a potential threat to this biotope. Potential invasives include Undaria pinnatifida and Sargassum muticum. Sargassum muticum is a circumglobal invasive species (Engelen et al., 2015). It is recorded (2015) from Norway to Morocco and into the Mediterranean in the eastern Atlantic and from Alaska to Baja California in the eastern Pacific and from southern Russia to southern China in the western Pacific (Engelen et al., 2015). It colonizes a variety of habitats and can tolerate -1°C to 30°C and survive salinities below 10 ppt. Although fertilization does not occur below 15 ppt and growth of germlings is limited below 10°C it can complete its life cycle as long as temperatures are over 8°C for at least four months of the year (Engelen et al., 2015). However, its distribution is limited by the availability of hard substratum (e.g., stones >10 cm) and light (Staeher et al., 2000; Strong & Dring 2011; Engelen et al., 2015). It is most abundant between 1 and 3 m below mean water. But it has been recorded at 18 m or 30 m in the clear waters of California. However, it is a poor competitor under low light and only develops dense canopies in shallow areas (Engelen et al., 2015). Sargassum muticum was shown to replace and out-compete leathery, canopy-forming macroalgae such as Saccharina latissima, Halidrys siliquosa, and Fucus spp. and, to a lesser degree, understorey species such as Codium fragile, Chondrus crispus and Dictyota dichotoma in Limfjorden, Denmark between 1984 and 1997 (Staehr et al., 2000; Engelen et al., 2015; de Bettignies et al., 2021). The invasion in Limfjorden had stabilized by 2005 although many of the native macroalgal species continued to decline (Engelen et al., 2015). In Limfjorden, the distribution of Sargassum muticum was limited to areas with hard substratum, in particular stones >10 cm in diameter, while smaller stones, gravel and sand were unsuitable. It was most abundant between 1 and 4 m in depth but had low cover at 0 to 0.5 m and 4 to 6 m, in the turbid waters of the Limfjorden. Limfjorden is wave sheltered but wave exposure has been reported to restrict the growth and survival of Sargassum muticum (Staehr et al., 2000). Viejo et al. (1995) reported that Sargassum muticum transplanted to wave exposed shores in Spain experienced >80% breakages within a month and that the growth of undamaged plants was significantly lower than that of plants on sheltered shores. Similarly, Andrew & Viejo (1998) noted that Sargassum muticum was restricted to intertidal rockpools in wave exposed sites in the Bay of Biscay. Strong & Dring (2011) used canopy removal experiments to investigate inter- and intra-species competition between Sargassum muticum and Saccharina latissima in the Dorn, Strangford Lough, N. Ireland. The Dorn consists of tidal pools, very sheltered from wave action but with moderately strong tidal streams (1 - 2 knots). Sargassum muticum grew better in mixed stands with Saccharina latissima than in the highest-density monospecific stands examined. However, the growth of Saccharina was not affected by the proportion of Sargassum in mixed stands. They concluded that Saccharina was not impacted significantly by the alien species while Sargassum benefited from growth in mixed stands. Experimental manipulation of subtidal algal canopies in the San Juan Islands, Washington State, USA, showed that Sargassum muticum reduced the abundance of native macroalgae, including the kelp Laminaria bongardiana due to shading. However, the experimental removal of Sargassum resulted in the recovery of native species within about one year (Britton-Simmons, 2004; Engelen et al., 2015). The negative effects of Sargassum muticum on native macroalgae are mainly due to competition for light, rather than changes in nutrient availability, sedimentation or water flow (Britton-Simmons, 2004; Engelen et al., 2015). Undaria pinnatifida (Wakame or Asian kelp) is a large brown seaweed and an Invasive Non-Indigenous Species (INIS) that could out-compete native UK kelp species (see Farrell & Fletcher, 2006; Thompson & Schiel, 2012; Brodie et al., 2014; Hieser et al., 2014; Arnold et al., 2016; Epstein & Smale, 2017; Epstein & Smale, 2018; Kraan, 2017; Epstein et al., 2019a,b; Tidbury, 2020). Undaria pinnatifida originates from Japan but is established currently on the coastlines of New Zealand, Australia, Northern France, Spain, Italy, the UK, Portugal, Belgium, Holland, Argentina, Mexico, and the USA (De Leij et al., 2017). Undaria pinnatifida was first recorded in the UK in the Hamble Estuary in 1994 (Macleod et al., 2016) and has since proliferated along UK coastlines. One year after its discovery at the Queen Anne Battery marina, Plymouth, it became a major fouling plant on pontoons (Minchin & Nunn, 2014). Although initially restricted to artificial habitats, such as marinas and ports, it is now widespread in natural habitats in several areas, including Plymouth Sound. Undaria pinnatifida seems to settle better on artificial substrata (e.g., floats, marinas or piers) than on natural rocky shores among local kelps (Vaz-Pinto et al., 2014). It is found predominantly in low intertidal to shallow subtidal habitats (Epstein et al., 2019b) and is significantly more abundant on artificial substrata compared to natural rocky substrata (Heiser et al., 2014; Epstein & Smale, 2018). James (2017) suggested that Undaria pinnatifida could out-compete native species on artificial substrata (such as marinas and wharf structures). In Plymouth, UK, De Leij et al. (2017) found that natural habitats with dense native macroalgal canopies, such as Laminaria hyperborea, Laminaria ochroleuca, Laminaria digitata and Saccharina latissima had more resistance to Undaria pinnatifida invasion than disturbed or sparse canopies, due to limited space and light availability for Undaria pinnatifida recruits. However, the dense canopies did not always prevent the invasion of Undaria pinnatifida as sporophytes were still recorded within dense Laminaria canopies, so that canopy disturbance was not always required (De Leij et al., 2017; Epstein & Smale, 2018). Undaria behaves as a winter annual, and recruitment occurs in winter followed by rapid growth through spring, maturity and then senescence through summer, with only the microscopic life stages persisting through autumn. It exhibits multiple dispersal strategies, such as short-range spore dispersal, and long-range dispersal as whole drift plants or fragments. Undaria pinnatifida has spread rapidly across the UK and Europe, resulting in community-wide responses and impacts (Vaz-Pinto et al., 2014; Epstein & Smale, 2017). Its impacts are complex and context-specific, depending on space, time, and taxa present in the introduced location (Epstein & Smale, 2017; Teagle et al., 2017; Tidbury, 2020). Undaria pinnatifida has a wide physiological niche meaning it can occur in both coastal and estuarine environments showing tolerance for varying salinities, turbidity and siltation (Heiser et al., 2014; Epstein & Smale, 2018). Undaria pinnatifida has a greater preference for sites sheltered with low wave exposure and weak tidal streams (Heiser et al., 2014; Epstein & Smale, 2018). In natural habitats, Undaria pinnatifida was not recorded if the wave fetch was greater than 642 km but increased in abundance and cover in very sheltered sites (Epstein & Smale, 2018). In St Malo, France, there was evidence that Undaria pinnatifida co-existed with Laminaria hyperborea under certain conditions (Castric-Fey et al., 1993). Epstein & Smale (2018) also observed that Undaria pinnatifida was relatively common (abundance of >70 individuals per 25 m transect) at three sites in Devon, UK (Jennycliff, Bovisand and Beacon Cove) where Laminaria spp. were abundant (40 - 79%) or superabundant (>80%), which suggested that Undaria pinnatifida could co-exist within refugia amongst areas with dense Laminaria spp.. In Plymouth Sound, UK, Heiser et al. (2014) observed that Laminaria hyperborea was significantly less abundant at sites with the presence of Undaria pinnatifida, with only ca 0.5 Laminaria hyperborea individuals per m² present compared to ca 8 individuals per m² at sites without the presence of Undaria pinnatifida. However, the results from their correlation study only showed that the species were not found together (pers. comm., Epstein 2021). Whereas exclusion and succession experiments on reefs tell us that Laminaria spp. exclude Undaria pinnatifida, not the other way around. Epstein & Smale (2018) reported that in Devon, UK, persistent, dense, and intact Laminaria spp. canopies in rocky reef habitats exerted a strong influence over the presence/absence, abundance, and percentage cover of Undaria pinnatifida. A dense canopy of native kelp restricts the proliferation of Undaria pinnatifida and disturbance of the canopy is often the key to the recruitment of Undaria pinnatifida. Epstein et al. (2019b) reported that Undaria pinnatifida density and biomass were significantly negatively correlated with the sum of all Laminaria spp. in Plymouth, UK. The evidence indicated that native Laminaria spp. canopies in the UK inhibited Undaria pinnatifida and implied that Undaria pinnatifida was opportunistic but competitively inferior (Farrell & Fletcher, 2006; Heiser et al., 2014; Minchin & Nunn, 2014; De Leij et al., 2017; Epstein & Smale, 2018; Epstein et al., 2019b). However, Epstein et al. (2019b) also noted that Laminaria hyperborea had a non-significant positive relationship with Undaria pinnatifida due to low densities of Laminaria hyperborea across the study area, resulting in insufficient data. In Plymouth Sound (UK), Epstein et al. (2019b) found that within its depth range (+1 to –4 m), Undaria pinnatifida co-existed with seven species of canopy-forming brown macroalgae, including Laminaria hyperborea. De Leij et al. (2017) found that natural habitats with dense native macroalgal canopies, such as Laminaria hyperborea had more resistance to Undaria pinnatifida invasion than disturbed or sparse canopies, due to limited space and light availability for Undaria recruits. However, the dense canopies will not prevent the invasion of Undaria, as sporophytes were still recorded within dense Laminaria canopies, and this suggests that canopy disturbance is not always required. Undaria pinnatifida was successfully eradicated on a sunken ship in Chatham Islands, New Zealand, by applying a heat treatment of 70°C (Wotton et al., 2004). However, numerous other eradication attempts have failed and as noted by Fletcher & Farrell (1998), once established Undaria pinnatifida resists most attempts at long-term removal. Sensitivity Assessment. The above evidence suggests that Undaria pinnatifida can co-exist with Laminaria hyperborea where sites are suitable e.g., Laminaria hyperborea in Plymouth Sound, UK. A dense kelp canopy may restrict or slow the proliferation of Undaria pinnatifida, however, there is mixed evidence of its colonization with Laminaria hyperborea beds and in some areas, a lower abundance of Laminaria hyperborea may result in increased Undaria pinnatifida growth. This Laminaria hyperborea dominated biotope (IR.MIR.KR.LhypTX) is found within the infralittoral zone, exposed to or sheltered from wave exposure with strong to weak tidal streams. The evidence above suggests that Sargassum muticum prefers wave sheltered, shallow sites in the sublittoral fringe. It was reported to out-compete and replace Saccharina latissima in the Limfjorden and achieve maximum abundance between 1 and 4 m (Staehr et al., 2000; Engelen et al., 2015). However, no evidence of the effects of Sargassum on Laminaria hyperborea beds was found. Therefore, competition with Sargassum is probably site-specific and dependent on local conditions. It is possible that Sargassum will be able to co-exist with Laminaria hyperborea and survive within this biotope, where the site is shallow and sheltered from wave exposure. Undaria pinnatifida has the potential to colonize and co-exist in refugia within Laminaria sp. dominated habitats, especially in sheltered examples of their biotopes that are within its depth range (+ 1 to – 4 m) but it is competitively inferior to Laminaria sp. and likely reduce in abundance, unless regular disturbance (e.g., from storms) provide gaps in the kelp canopy for it to colonize. Therefore, resistance to Undaria is assessed as ‘Medium’ to represent initial colonization. Hence, resilience is assessed as ‘Medium’ due to the natural recovery of the Laminaria hyperborea bed, and sensitivity is assessed as ‘Medium’. Overall, confidence is assessed as ‘Low’ due to evidence of variation and the site-specific nature of competition between native kelps and Undaria pinnatifida.	Medium Low NR NR Help	Medium High Medium Medium Help	Medium Low NR NR Help
Introduction of microbial pathogens [Show more] Introduction of microbial pathogens Benchmark. The introduction of relevant microbial pathogens or metazoan disease vectors to an area where they are currently not present (e.g. Martelia refringens and Bonamia, Avian influenza virus, viral Haemorrhagic Septicaemia virus). Further detail Evidence Galls on the blade of Laminaria hyperborea and spot disease are associated with the endophyte Streblonema sp. although the causal agent is unknown (bacteria, virus or endophyte). The resultant damage to the blade and stipe may increase losses in storms. The endophyte inhibits spore production and, therefore, recruitment and recoverability (Lein et al., 1991). Sensitivity assessment. Resistance to the pressure is considered ‘Medium’, and resilience ‘High’. The sensitivity of this biotope to the introduction of microbial pathogens is assessed as ‘Low’.	Medium Low NR NR Help	High Low NR NR Help	Low Low Low Low Help
Removal of target species [Show more] Removal of target species Benchmark. Removal of species targeted by fishery, shellfishery or harvesting at a commercial or recreational scale. Further detail Evidence Christie et al. (1998) observed Laminaria hyperborea habitat regeneration following commercial Laminaria hyperborea trawling in south Norway. Within the study area, trawling removed all large canopy-forming adult Laminaria hyperborea. Within 2-3 years of harvesting, a new canopy had formed 1m off the seabed. The associated holdfast communities recovered in 6 years however the epiphytic stipe community did not fully recover within the same time period. Christie et al. (1998) suggested that kelp habitats were relatively resistant to direct disturbance of Laminaria hyperboreaa canopy. Recurrent disturbance occurring at a smaller time scale than the recovery period of 2-6 years (stated above) could extend recovery time. Kain (1975) cleared sublittoral blocks of Laminaria hyperborea at different times of the year for several years. The first colonizers and succession community differed between blocks and at what time of year the blocks were cleared however within 2 years of clearance the blocks were dominated by Laminaria hyperborea. Leinaas & Christie (1996) also observed Laminaria hyperborea re-colonization of ‘urchin barrens’, following removal of urchins. The substratum was initially colonized by filamentous macroalgae and Saccharina latissima however after 2-4 years Laminaria hyperborea dominated the community. Following disturbance or in areas were recurrent rapid disturbance occurs Laminaria hyperborea recruitment could also be affected by interspecific competitive interactions with Non-Indigenous Invasive Species or ephemeral algal species (Brodie et al., 2014; Smale et al., 2013), however, evidence for this is limited and thus not included in this assessment. Sensitivity assessment. Resistance to the pressure is considered ‘None’, and resilience ‘Medium’. The sensitivity of this biotope to damage to seabed surface features is assessed as ‘Medium’.	None High High High Help	Medium High High High Help	Medium High High High Help
Removal of non-target species [Show more] Removal of non-target species Benchmark. Removal of features or incidental non-targeted catch (by-catch) through targeted fishery, shellfishery or harvesting at a commercial or recreational scale. Further detail Evidence Incidental/accidental removal of Laminaria hyperborea from other fisheries or extraction processes are likely to cause similar effects to that of direct harvesting; as such the same evidence has been used for both pressure assessments. Christie et al. (1998) observed Laminaria hyperborea habitat regeneration following commercial Laminaria hyperborea trawling in south Norway. Within the study area, trawling removed all large canopy-forming adult Laminaria hyperborea. Within 2-3 years of harvesting, a new canopy had formed 1 m off the seabed. The associated holdfast communities recovered in 6 years however the epiphytic stipe community did not fully recover within the same time period. Christie et al. (1998) suggested that kelp habitats were relatively resistant to direct disturbance of Laminaria hyperborea canopy. Recurrent disturbance occurring at a smaller time scale than the recovery period of 2-6 years (stated above) could extend recovery time. Kain (1975) cleared sublittoral blocks of Laminaria hyperborea at different times of the year for several years. The first colonizers and succession community differed between blocks and at what time of year the blocks were cleared however within two years of clearance the blocks were dominated by Laminaria hyperborea. Leinaas & Christie (1996) also observed Laminaria hyperborea re-colonization of ‘urchin barrens’, following removal of urchins. The substratum was initially colonized by filamentous macroalgae and Saccharina latissima however after 2-4 years Laminaria hyperborea dominated the community. Following disturbance or in areas were recurrent rapid disturbance occurs Laminaria hyperborea recruitment could also be affected by interspecific competitive interactions with Non-Indigenous Invasive Species or ephemeral algal species (Brodie et al., 2014; Smale et al., 2013), however, evidence for this is limited and thus not included in this assessment. Sensitivity assessment. Resistance to the pressure is considered ‘Low’, and resilience ‘Medium’. The sensitivity of this biotope to damage to seabed surface features is assessed as ‘Medium’.	Low High High High Help	Medium High High High Help	Medium High High High Help

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Stamp, T.E., Burdett, E.G., Tyler-Walters, H., & Lloyd, K.A., 2023. Laminaria hyperborea on tide-swept, infralittoral mixed substrata.. In Tyler-Walters H. Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 26-12-2024]. Available from: https://marlin.ac.uk/habitat/detail/1045

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