Mixed Laminaria hyperborea and Saccharina latissima forest on sheltered upper infralittoral rock

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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, Kelsey Lloyd & Megan Mardle

Refereed by

This information is not refereed

Researched by
Thomas Stamp, Kelsey Lloyd & Megan Mardle

Refereed by
This information is not refereed

Summary

UK and Ireland classification

Standard	Classification	Description
EUNIS 2008	A3.3121	Mixed Laminaria hyperborea and Laminaria saccharina forest on sheltered upper infralittoral rock
JNCC 2022	IR.LIR.K.LhypSlat.Ft	Mixed Laminaria hyperborea and Saccharina latissima forest on sheltered upper infralittoral rock
JNCC 2015	IR.LIR.K.LhypLsac.Ft	Mixed Laminaria hyperborea and Laminaria saccharina forest on sheltered upper infralittoral rock
JNCC 2004	IR.LIR.K.LhypLsac.Ft	Mixed Laminaria hyperborea and Laminaria saccharina forest on sheltered upper infralittoral rock
1997 Biotope	IR.SIR.K.LhypLsac.Ft	Mixed Laminaria hyperborea and Laminaria saccharina forest on sheltered upper infralittoral rock

EUNIS 2008 A3.3121 - Mixed Laminaria hyperborea and Laminaria saccharina forest on sheltered upper infralittoral rock
JNCC 2015 IR.LIR.K.LhypLsac.Ft - Mixed Laminaria hyperborea and Laminaria saccharina forest on sheltered upper infralittoral rock
JNCC 2004 IR.LIR.K.LhypLsac.Ft - Mixed Laminaria hyperborea and Laminaria saccharina forest on sheltered upper infralittoral rock
1997 Biotope IR.SIR.K.LhypLsac.Ft - Mixed Laminaria hyperborea and Laminaria saccharina forest on sheltered upper infralittoral rock

Description

Sheltered, often silted upper infralittoral bedrock and boulder slopes with mixed kelps Laminaria hyperborea and Saccharina latissima beneath which red seaweeds such as Plocamium cartilagineum, Bonnemaisonia asparagoides, Delesseria sanguinea and Cryptopleura ramosa occur on top of encrusting coralline algae. The stipes of L. hyperborea are generally densely covered with seaweeds such as Phycodrys rubens, Membranoptera alata and Plocamium cartilagineum, as well as solitary ascidians, while the fronds are often epiphytised by Obelia geniculata and Membranipora membranacea. Beneath the often cape-form kelp canopy, the faunal component is generally less diverse than the more exposed kelp forests.

Depth range

0-5 m, 5-10 m

Additional information

Listed By

Annex 1

Sensitivity reviewHow is sensitivity assessed?

Sensitivity characteristics of the habitat and relevant characteristic species

IR.LIR.K.LhypSlat plus sub-biotopes are characterized by mixed canopies of Laminaria hyperborea with Saccharina latissima (syn. Laminaria saccharina). IR.LIR.K.LhypSlat is predominantly found in Scottish sea lochs, however is also found at sheltered locations around the UK. Although both species can occur in equal abundance (common) Laminaria hyperborea usually dominates the biotope. Underneath the kelp canopy and on kelp stipes there is a community of red seaweeds which includes; Delesseria sanguinea, Plocamium cartilagineum, Cryptopleura ramosa and Metacallophyllis laciniata. Echinus esculentus also defines IR.LIR.K.LhypSlat.Gz, in which intensive grazing diminishes the understorey community.

In wave exposed locations other laminarian kelps (e.g. Laminaria hyperborea) can out-compete Saccharina lattisma or form mixed canopies as in IR.LIR.K.LhypSlat. IR.LIR.K.LhypSlat is typically recorded in sheltered sea lochs of Scotland, however is also recorded in other sheltered locations around the UK. IR.LIR.K.LhypSlat represents an intermediate biotope between a suite of exposed-moderately wave exposed Laminaria hyperborea dominated biotopes and the Saccharina latissima dominated IR.LIR.K.Slat biotopes found predominantly from sheltered-ultra wave sheltered environments (Connor et al., 2004). Observations from Norwegian fjords have also recorded IR.LIR.K.LhypSlat forming a thin band above IR.LIR.K.Slat (Svendsen & Kain, 1971).

Kelp beds increase the three dimensional complexity of unvegetated rock (Norderhaug, 2004, Norderhaug et al., 2007, Norderhaug & Christie, 2011, Gorman et al., 2012; Moy & Christie, 2012; Smale et al., 2013), support high local diversity, abundance and biomass of epibenthic species (Smale et al., 2013), and serve as nursery grounds for a number of commercial important species, e.g. Atlantic cod and pollock (Rinde et al., 1992).

In undertaking this assessment of sensitivity, account is taken of knowledge of the biology of all characterizing species in the biotope. There is an abundance of literature for regeneration of mono-specific Laminaria hyperborea beds, however at the time of writing there is limited research for the recovery of mixed kelp canopies. For this sensitivity assessment Laminaria hyperborea and Saccharina latissima are the primary foci of research, however it is recognized that the understorey red seaweed communities also define the biotope. Examples of important species groups are mentioned where appropriate.

Resilience and recovery rates of habitat

Saccharina lattisma is a perennial kelp characteristic of wave sheltered sites of the North East Atlantic, distributed from northern Portugal to Spitzbergen, Svalbard (Birkett et al., 1998; Conor et al., 2004; Bekby & Moy, 2011; Moy & Christie, 2012). Saccharina lattisma is capable of reaching maturity within 15-20 months (Sjøtun, 1993) and has a life expectancy of 2-4 years (Parke, 1948). Maximum growth has been recorded in late winter early spring, in late summer and autumn growth rates slow (Parke, 1948; Lüning, 1979; Birkett et al., 1998). The overall length of the sporophyte may not change during the growth season due to marginal (distal) erosion of the blade, but extension growth of the blade has been measured at 1.1 cm/day, with total length addition of over 2.25m of tissue per year (Birkett et al., 1998). Saccharina latissima has a heteromorphic life strategy. Vast numbers of zoospores are released from sori located centrally on the blade between autumn and winter. Zoospores settle onto rock substrata and develop into dioecious gametophytes (Kain, 1979) which, following fertilization, germinate into juvenile sporophytes from winter-spring. Kelp zoospores are expected to have a large dispersal range, however 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).

The temperature isotherm of 19-20°C has been reported as limiting Saccharina lattisma growth (Müller et al., 2009). Gametophytes can develop in ≤23°C (Lüning, 1990). However, Bolton & Lüning (1982) reported an experimental optimal temperature of 10-15°C for growth of the Saccharina latissima sporophyte. Growth was inhibited by 50-70% at 20°C and, all experimental specimens completely disintegrated after 7 days at 23°C . In the field Saccharina latissima has however shown significant regional variation in its acclimation response to changing environmental conditions. For example, Gerard & Dubois (1988) observed sporophytes of Saccharina latissima which were regularly exposed to ≥20°C could tolerate these high temperatures, whereas sporophytes from other populations which rarely experience ≥17°C showed 100% mortality after 3 weeks of exposure to 20°C. Therefore, the response of Saccharina latissima to a change in temperatures is likely to be locally variable.

In 2002 a large scale decline of Saccharina latissima was discovered on the Norwegian coast (Moy & Christie, 2012). A subsequent large survey was undertaken between 2004-2009 of 660 sites covering 34,000km of south and west Norway to assess the decline of Saccharina latissima abundance and distribution (Moy & Christie, 2012). The survey indicated an 83% reduction of Saccharina latissima forests across the south Norwegian region of Skagerrak. The west Norwegian coast was less affected, but Saccharina latissima was either absent or very sparse at 38% of sites where it was expected to be abundant. At all sites where Saccharina latissima was sparse a community of ephemeral macro-algae species was dominant and persisted throughout the study period (2004-2009). Bekby & Moy (2011) modelled the regional decline which indicated a decline of 50.7% of Saccharina latissima from Skagerrak, Norway. Approximately 50% of Europe’s Saccharina latissima is found in Norway (Moy et al., 2006), therefore, despite large discrepancies between the two estimates of Saccharina latissima decline (50.7-83%) the results indicated a significant decline in Saccharina latissima across the region. Moy & Christie (2012) suggested the ephemeral filamentous macroalgae communities represented a stable state shift that had persisted throughout the study period (2004-2009). Although no measurements were made, they suggested that the decline was due to low tidal movement and wave action in the worst affected areas combined with the impacts of dense human populations and increased land run-off a Multiple stressors such as eutrophication, increasing regional temperature, increased siltation and overfishing may also be acting synergistically to cause the observed habitat shift.

Kelp 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 & Sjotum, 2005; Norderhaug & Christie, 2009; Smale et al., 2013) have reported dense aggregations of sea urchins to be a principal threat to kelp biotopes of the North Atlantic. In northern Norway intense urchin grazing create expansive areas known as ‘urchin barrens’, in which a shift can occur from kelp 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). Leinaas & Christie (1996) removed Strongylocentrotus droebachiensis from ‘urchin barrens’ and observed a succession effect. The substratum was colonized initially by filamentous algae and,after a couple of weeks, these were out-competed by Saccharina latissima. However after 2-4 years, Laminaria hyperborea dominated the community. These results demonstrate that Saccharina latissima will re-establish quickly in optimal conditions; however in moderately wave exposed conditions will be out-competed by Laminaria hyperborea.

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 low Echinus esculentus grazing pressure can control the lower limit of Laminaria hyperborea in the and remove Laminaria hyperborea sporelings and juveniles. Urchin abundances in ‘urchin barrens’ have been reported as high as 100 individuals/m² (Lang & Mann, 1978). Kain (1967) reported urchin abundances of 1-4/m²within experimental plots of the Isle of Man. Therefore while ‘urchin barrens’ are not presently a large scale 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.

Infavourable conditions 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 requires over 6 years to recover (possibly 10 years). These recovery rates were based on discrete kelp harvesting events and 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.

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 approximately 200m (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).

Other factors that are likely to influence the recovery of kelp biotopes is competitive interactions with the Invasive Non Indigenous Species (INIS) Undaria pinnatifida (Smale et al., 2013; Brodie et al., 2014; Heiser et al., 2014). Undaria pinnatifida has received a large amount of research attention as an INIS which could out-compete UK kelp habitats (see Farrell & Fletcher, 2006; Thompson & Schiel, 2012, Brodie et al., 2014; Hieser et al., 2014). Undaria pinnatifida was first recorded in Plymouth Sound, UK in 2003 (NBN, 2015) subsequent surveys in 2011 have reported that Undaria pinnatifida is widespread throughout Plymouth Sound, colonizing rocky reef habitats. Where Undaria pinnatifida is present there was a significant decrease in the abundance of other Laminaria species, including Laminaria hyperborea (Heiser et al., 2014). In new Zealand, Thompson & Schiel (2012) observed that native fucoids could out-compete Undaria pinnatifida and re-dominate the substratum. However, Thompson & Schiel (2012) suggested the fucoid recovery of the substratum was partially due to an annual Undaria pinnatifida die back, which as noted by Heiser et al. (2014) did not occur in Plymouth sound, UK. It is unknown whether Undaria pinnatifida will out-compete native macro-algae in the UK. However from 2003-2011 Undaria pinnatifida had spread throughout Plymouth sound, UK, becoming a visually dominant species at some locations within summer months (Hieser et al., 2014). At the time of writing there is limited evidence available to assess the ecological impacts of Undaria pinnatifida on Laminaria hyperborea associated communities. Undaria pinnatifida was successfully eradicated on a sunken ship in Clatham Islands, New Zealand, by applying a heat treatment of 70°C (see Wotton et al., 2004) however numerous other eradication attempts have failed, and as noted by Farrell & Fletcher (2006) once established Undaria pinadifida resists most attempts of long-term removal. Kelp biotopes are unlikely to fully recover until Undaria pinnatifida is fully removed from the habitat, which as stated above is unlikely to occur.

Resilience assessment. Of the 2 kelp species (Laminaria hyperborea and Saccharina latissima) that characterize IR.LIR.K.LhypSlat plus associated sub-biotopes, Laminaria hyperborea is the slowest to recover following disturbance. Laminaria hyperborea can regenerate from disturbance within a period of 1-6 years, and the associated community within 7-10 years. Saccharina latissima has reportedly a rapid recovery rate or re-generation time, following clearance of Strongylocentrotus droebachiensis from ‘urchin Barrens’ Saccharina latissima was a rapid colonizer appearing after a few weeks, and can reach maturity within 15-20 months (Birkett et al., 1998). Due to comparatively slow growth rates resilience estimates are largely based on Laminaria hyperborea, however the recovery of Saccharina latissima and the understorey red seaweed is accounted for where relevant. Resilience has therefore been assessed as ‘Medium’.

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 Laminaria hyperborea 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). The temperature isotherm of 19-20°C has been reported as limiting Saccharina lattisma growth (Müller et al., 2009). Gametophytes can develop in ≤23°C (Lüning, 1990). Optimal temperature for Saccharina latissima sporophyte growth was 10-15°C (Bolton & Lüning, 1982), while reported growth was inhibited by 50-70% at 20°C and all experimental specimens completely disintegrated after 7 days at 23°C. In the field, Saccharina latissima has however shown significant regional variation in its acclimation response to changing environmental conditions. For example Gerard & Dubois (1988) found Saccharina latissima sporophytes which were regularly exposed to ≥20°C could tolerate these high temperatures, whereas sporophytes from other populations which rarely experience ≥17°C showed 100% mortality after 3 weeks of exposure to 20°C. Therefore, the response Saccharina latissima to a change in temperatures is likely to be locally variable. Andersen et al. (2011) transplanted Saccharina latissima in the Skagerrak region, Norway and from 2006-2009. There was annual variation however high mortality occurred from August-November within each year of the experiment. In 2008 of the original 17 sporophytes 6 survived from March-September (approx. 65% mortality rate). All surviving sporophytes were heavily fouled by epiphytic organisms (estimated cover of 80 & 100%). Between 1960-2009, sea surface temperatures in the region have regularly exceeded 20°C and so has the duration which temperatures remain above 20°C. High sea temperatures has been linked to slow growth of Saccharina latissima which is likely to decrease the photosynthetic ability of, and increase the vulnerability of Saccharina latissima to epiphytic loading, bacterial and viral attacks (Anderson et al., 2011). These factors combined with establishment of annual filamentous algae in Skegerrak, Norway are likely to prevent the establishment of self sustaining populations in the area (Anderson et al., 2011; Moy & Christie, 2012). IR.LIR.K.LhypSlat is distributed throughout the UK (Connor et al., 2004). Northern to southern Sea Surface Temperature (SST) ranges from 8-16°C in summer and 6-13°C in winter (Beszczynska-Möller & Dye, 2013) Sensitivity assessment. A 2°C increase for one year may impair Laminaria hyperborea recruitment processes and Saccharina latissima sporophyte growth but otherwise not affect the characterizing species. A 5°C increase for one month combined with high UK summer temperatures is likely to affect Laminaria hyperborea sporophyte growth. Saccharina latissima populations that are not acclimated to >20°C may incur mass mortality within 3 weeks of exposure. Resistance has been assessed as ‘None’, to reflect the potential mass mortality effect of sudden temperature increases on Saccharina latissima, and resilience as ‘High’. Sensitivity has been assessed as ‘Medium’.	None High High High Help	High 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 these ranges (Birkett et al., 1988). Saccharina lattissima has a lower temperature threshold for sporophyte growth at 0°C (Lüning, 1990). Subtidal red algae can survive at temperatures between -2 °C and 18-23 °C (Lüning, 1990; Kain & Norton, 1990). Sensitivity assessment. Both Laminaria hyperborea and Saccharina latissima have northern distributions (Birkett et al., 1998). An acute or long-term decrease in temperature within the UK, at the benchmark level, is not likely to have any dramatic effect on biotope structure. Resistance has been assessed as ‘High’, resilience as ‘High’ and sensitivity 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 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. Karsten (2007) tested the photosynthetic ability of Saccharina latissima under acute 2 and5 day exposure to salinity treatments ranging from 5-60 psu. A control experiment was also carried at 34 psu . Saccharina latissima showed high photosynthetic ability at >80% of the control levels between 25-55 psu. Hyposaline treatment of 10-20 psu led to a gradual decline of photosynthetic ability. After 2 days at 5 psu Saccharina latissima showed a significant decline in photosynthetic ability at approx.. 30% of control. After 5 days at 5 psu Saccharina latissima specimens became bleached and showed signs of severe damage. The affect of long-term salinity changes (>5 days) or salinity >60 PSU on Saccharina latissima’ photosynthetic ability was not tested. The experiment was conducted on Saccharina latissima from the Arctic, and the authors suggest that at extremely low water temperatures (1-5°C) macroalgae acclimation to rapid salinity changes could be slower than at temperate latitudes. It is therefore possible that resident Saccharina latissima of the UK maybe be able to acclimate to salinity changes more effectively and quicker. Sensitivity assessment. The evidence suggests that Saccharina latissima can tolerate exposure to hypersaline conditions of ≥40‰. However, optimal salinities for Laminaria hyperborea growth are assumed to be 30-35 psu . Hence, an increases in salinity may cause mortality for Laminaria hyperborea. Resistance has been assessed as ‘Low’, resilience as ‘Medium’. The sensitivity of this biotope to an increase in salinity has been assessed as ‘Medium’.	Low High High High Help	Medium High Low High Help	Medium High Low High 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 and growth rates are likely to be affected by periodic salinity stress. Birkett et al,. (1998) suggest that long-term changes in salinity may result in loss of affected kelp. 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. Karsten (2007) tested the photosynthetic ability of Saccharina latissima under acute 2 and5 day exposure to salinity treatments ranging from 5-60 psu. A control experiment was also carried at 34 psu . Saccharina latissima showed high photosynthetic ability at >80% of the control levels between 25-55 psu. Hyposaline treatment of 10-20 psu led to a gradual decline of photosynthetic ability. After 2 days at 5 psu Saccharina latissima showed a significant decline in photosynthetic ability at approx. 30% of control. After 5 days at 5 psu Saccharina latissima specimens became bleached and showed signs of severe damage. The affect of long-term salinity changes (>5 days) or salinity >60 PSU on Saccharina latissima’ photosynthetic ability was not tested. The experiment was conducted on Saccharina latissima from the Arctic, and the authors suggest that at extremely low water temperatures (1-5°C) macroalgae acclimation to rapid salinity changes could be slower than at temperate latitudes. It is therefore possible that resident Saccharina latissima of the UK maybe be able to acclimate to salinity changes more effectively and quicker. Sensitivity assessment. A decrease in one MNCR salinity scale from ‘Full Salinity’ (30-40psu) to ‘Reduced Salinity’ (18-30 psu) may result in a decrease of Laminaria hyperborea sporophyte growth and Saccharina latissima. Resistance has been assessed as ‘Low’ and resilience as ‘Medium’. Therefore, sensitivity of this biotope to a decrease in salinity has been assessed as ‘Medium’.	Low High High High Help	Medium High Low High Help	Medium High Low High 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 Peteiro & Freire (2013) measured Saccharina latissima growth from 2 sites, the first had maximal water velocities of 0.3m/sec and the second 0.1m/sec. At site 1 Saccharina latissima had significantly larger biomass than at site 2 (16kg /m to 12 kg /m respectively). Peteiro & Freire (2013) suggested that faster water velocities were beneficial to Saccharina latissima growth. However, Gerard & Mann (1979) found Saccharina latissima productivity is reduced in moderately strong tidal streams (≤1m/sec) when compared to weak tidal streams (<0.5m/sec). Despite the results published in Gerard & Mann (1979) Saccharina latissima can characterize or be a dominant in the tide swept biotopes IR.MIR.KT.XKTX & IR.MIR.KT.SlatT, which have been recorded from very strong (>3m/sec) to moderately strong tidal streams (≤1m/sec) (Connor et al., 2004), indicating Saccharina latissima can tolerate greater tidal streams than <1m/sec. Kregting et al. (2013) measured Laminaria hyperborea blade growth and stipe elongation from an exposed and a sheltered site in Strangford Lough, 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. Sensitivity assessment. IR.LIR.K.LhypSlat plus sub-biotopes are classed as low energy biotopes, found predominantly in weak tidal streams (<0.5m/sec). Large scale changes tidal velocities (~>1 m/sec) may increase the predominance of tide swept biotopes (e.g. IR.MIR.KR.LhypT/X, IR.MIR.KT.XKTX or IR.MIR.KT.SlatT) and replace IR.LIR.K.LhypSlat. However the available evidence suggests that a change in flow velocities of between 0.1-0.2 m/sec would have little effect on Laminaria hyperborea or Saccharina latissima growth or productivity. Resistance has been assessed as ‘High’, resilience as ‘High’. Sensitivity has been assessed as ‘Not Sensitive’ at the benchmark level.	High Medium High High Help	High High High High Help	Not sensitive Medium 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 IR.LIR.K.LhypSlat plus associated sub-biotopes are recorded predominantly in the sublittoral. An increase in emergence will result in an increased risk of desiccation and mortality of the dominant kelp species (Laminaria hyperborea & Saccharina latissima) in shallow examples of the biotope. Removal of canopy forming kelps has also been shown to increase desiccation and mortality of the understorey macro-algae (Hawkins & Harkin, 1985). Several mobile species such as sea urchins, brittle stars and feather stars are likely to move away. However, providing that suitable substrata are present, the biotope is likely to re-establish further down the shore within a similar emergence regime to that which existed previously. Sensitivity assessment. Resilience has been assessed as ‘Low’. Resistance as ‘Medium’. The sensitivity of this biotope to a change in emergence is considered 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 IR.LIR.K.LhypSlat represents an intermediate biotope between a suite of exposed-moderately wave exposed Laminaria hyperborea dominated biotopes and the Saccharina latissima characterized IR.LIR.K.Slat biotopes found in very wave sheltered environments (Connor et al., 2004). Large changes in local wave height may affect the proportion/dominance of Laminaria hyperborea and Saccharina latissima and change the biotope structure. Changes in local wave height also have the potential to increase urchin dislodgement from IR.LIR.K.LhypSlat.Gz, and potentially decrease urchin grazing. Kregting et al. (2013) measured Laminaria hyperborea blade growth and stipe elongation from an exposed and a sheltered site in Strangford Lough, 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 & 2m at the exposed and sheltered sites. Maximal water velocity (Velrms) was 0.6 & 0.3m/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. However, Pedersen et al. (2012) observed Laminaria hyperborea biomass, productivity and density increased with greater wave exposure. At low wave exposure Laminaria hyperborea canopy forming plants were smaller, had lower densities and had higher mortality rates. At low wave exposure, high epiphytic loading on Laminaria hyperborea was suggested to impair photosynthesis, nutrient uptake, and increase the drag of the host Laminaria hyperborea during extreme storm events. The morphology of kelp stipe and blades vary in different water flows and wave exposures 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). Saccharina latissima is rarely found at wave exposed sites (Birkett et al., 1998). Saccharina latissima, if present, develops a short thick stipe and a short, narrow and tightly wrinkled blade (Birkett et al., 1998). Sensitivity assessment. Wave exposure is one of the principal defining features of kelp biotopes, and changes in wave exposure are likely to alter the relative abundance of the kelp species, grazing and understorey community, and hence, the biotope. However a change in near shore significant wave height of 3-5% is unlikely to have any significant effect on IR.LIR.K.LhypSlat or associated sub-biotopes. Resistance has been assessed as ‘High', resilience as ‘High’ and sensitivity as ‘Not Sensitive’ at the benchmark level.	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 the 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 al. (1999) reported that Hg was very toxic to macrophytes. Similarly, Hopkin & Kain (1978) demonstrated the 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 is 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. Sporophytes of Saccharina latissima have a low intolerance to heavy metals, but the early life stages are more intolerant. The effects of copper, zinc and mercury on Saccharina latissima have been investigated by Thompson & Burrows (1984). They observed that the growth of sporophytes was significantly inhibited at 50 µg Cu /l, 1000 µg Zn/l and 50 µg Hg/l. Zoospores were found to be more intolerant and significant reductions in survival rates were observed at 25 µg Cu/l, 1000 µg Zn/l and 5 µg/l. Little is known about the effects of heavy metals on echinoderms. Bryan (1984) reported that early work had shown that echinoderm larvae were intolerant of heavy metals, e.g. the intolerance of larvae of Paracentrotus lividus to copper (Cu) had been used to develop a water quality assessment. Kinne (1984) reported developmental disturbances in Echinus esculentus exposed to waters containing 25 µg / l of copper (Cu). Sea-urchins, especially the eggs and larvae, are used for toxicity testing and environmental monitoring (reviewed by Dinnel et al. 1988). Taken together with the findings of Gomez & Miguez-Rodriguez (1999) above it is likely that echinoderms are intolerant of heavy metal contamination.	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 the evidence is presented where available. Laminaria hyperborea and Saccharina latissima fronds, being predominantly 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 laminariales 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 1-22.5m 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 to chemical contamination. Loss of red algae is likely to reduce the species richness and diversity of IR.LIR.K.LhypSlat.	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 the 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). Saccharina latissima has also been found to be sensitive to antifouling compounds. Johansson (20090 exposed samples of Saccharina latissima to several antifouling compounds, observing chlorothalonil, DCOIT, dichlofluanid and tolylfluanid inhibited photosynthesis. Exposure to Chlorothalonil and tolylfluanid was also found to continue inhibiting oxygen evolution after exposure had finished, and may cause irreversible damage. 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; Johansson, 2009). Laminaria hyperborea survived within >55m 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 6m (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	No evidence (NEv) 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 can 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). 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 2 mg/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. Resistance has been assessed as ‘High’, Resilience as ‘High’. Sensitivity has been assessed as ‘Not sensitive’ at the benchmark level.	High Medium Low Low Help	High High High High Help	Not sensitive Medium Low Low Help
Nutrient enrichment [Show more] Nutrient enrichment Benchmark. Compliance with WFD criteria for good status. Further detail Evidence Conolly & Drew (1985) found Saccharina latissima sporophytes had relatively higher growth rates when in close proximity to a sewage outlet in St Andrews, the UK when compared to other sites along the east coast of Scotland. At St Andrew's, nitrate levels were 20.22 µM, which represents an approx 25% increase when compared to other comparable sites (approx 15.87 µM). Handå et al. (2013) also reported Saccharina latissima sporophytes grew approx 1% faster per day when in close proximity to Salmon farms, where elevated ammonium can be readily absorbed. Read et al. (1983) reported after the installation of a new sewage treatment works which reduced the suspended solid content of liquid effluent by 60% in the Firth of Forth, Saccharina latissima became abundant where previously it had been absent. Bokn et al. (2003) conducted a nutrient loading experiment on intertidal fucoids. No significant effect was observed in the communities within 3 years of the experiment. However, a shift from perennial to ephemeral algae occurred after 4-5 years into the experiment. Although Bokn et al. (2003) focussed on fucoids the results could indicate that long-term (>4 years) nutrient loading can result in community shift to ephemeral algae species. Disparities between the findings of the aforementioned studies are likely to be related to the level of organic enrichment but could also be time dependent. Johnston & Roberts (2009) conducted a meta-analysis, which reviewed 216 papers to assess how a variety of contaminants (including sewage and nutrient loading) affected 6 marine habitats (including subtidal reefs). A 30-50% reduction in species diversity and richness were identified from all habitats exposed to the contaminant types. Johnston & Roberts (2009) however also highlighted that macro-algal communities are relatively tolerant to contamination, but that contaminated communities can have low diversity assemblages which are dominated by opportunistic and fast-growing species (Johnston & Roberts, 2009 and references therein). 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). Increases 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. Sensitivity assessment. Although nutrients may not affect kelps directly, indirect effects such as turbidity may significantly affect photosynthesis. Furthermore, organic enrichment may denude the associated community. However, the biotope is probably ‘Not sensitive’ (resistance is ‘High’ and resilience is ‘High') at the benchmark level (i.e. compliance with WFD criteria).	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 Conolly & Drew (1985) found Saccharina latissima sporophytes had relatively higher growth rates when in close proximity to a sewage outlet in St Andrews, the UK when compared to other sites along the east coast of Scotland. At St Andrews, nitrate levels were 20.22µM, which represents an approx 25% increase when compared to other comparable sites (approx 15.87 µM). Handå et al. (2013) also reported Saccharina latissima sporophytes grew approx 1% faster per day when in close proximity to Salmon farms, where elevated ammonium can be readily absorbed. Read et al. (1983) reported after the installation of a new sewage treatment works which reduced the suspended solid content of liquid effluent by 60% in the Firth of Forth, Saccharina latissima became abundant where previously it had been absent. Bokn et al. (2003) conducted a nutrient loading experiment on intertidal fucoids. No significant effect was observed in the communities within 3 years of the experiment. However, a shift from perennial to ephemeral algae occurred after 4-5 years into the experiment. Although Bokn et al. (2003) focussed on fucoids the results could indicate that long-term (>4 years) nutrient loading can result in community shift to ephemeral algae species. Disparities between the findings of the aforementioned studies are likely to be related to the level of organic enrichment however could also be time dependent. Johnston & Roberts (2009) conducted a meta-analysis, which reviewed 216 papers to assess how a variety of contaminants (including sewage and nutrient loading) affected 6 marine habitats (including subtidal reefs). A 30-50% reduction in species diversity and richness were identified from all habitats exposed to the contaminant types. Johnston & Roberts (2009) however also highlighted that macro-algal communities are relatively tolerant to contamination, but that contaminated communities can have low diversity assemblages which are dominated by opportunistic and fast-growing species (Johnston & Roberts, 2009 and references therein). 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). Increases 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. Sensitivity assessment. Although nutrients may not affect kelps directly, indirect effects such as turbidity may significantly affect photosynthesis. Furthermore, organic enrichment may denude the associated community. Resistance has therefore been assessed as ‘Medium’, resilience as ‘High’. Sensitivity has been assessed as ’Low’.	Medium High High High Help	High High High High Help	Low High High High 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 Saccharina latissima has shown significant regional acclimation to environmental conditions. Gerard & Dubois (1988) found Saccharina latissima sporophytes which were regularly exposed to ≥20°C could tolerate these high temperatures, whereas sporophytes from other populations which rarely experience ≥17°C showed 100% mortality after 3 weeks of exposure to 20°C. It is therefore possible that transplanted eco-types of Saccharina latissima may react differently to environmental conditions that differ from those of their origin. However, there is little evidence for translocation of Saccharina latissima over significant geographic distances. Nor is there any evidence regarding the genetic modification or effects of translocation of native kelp populations.	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 Mediterranea 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 0-0.5 m or 4-6 m, in the turbid waters of the Limfjorden. Limfjorden is wave sheltered although 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 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, experimental removal of Sargassum resulted in recovery of native species within about one year (Britton-Simmons, 2004; Engelen et al., 2015). The negative effects of Sargassum muticum on native macroalgae is 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 had become 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). De Leij et al. (2017) suggested that in natural substrata, Undaria pinnatifida can be inhibited by the presence of native competitors, such as large perennial species. The dense macroalgae canopies formed by native kelps result in limited space and light availability for Undaria pinnatifida recruits. However, it will not always completely prevent the assimilation of Undaria pinnatifida (De Leij et al., 2017; Epstein & Smale, 2018). Undaria pinnatifida species 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 is 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 Undaria pinnatifida. However, the results from their correlation study only showed that the species were not found together (pers. comm., Epstien 2021). Whereas, exclusion and succession experiments on reefs tell us that Laminaria spp. exclude Undaria pinnatifida, not the other way round. 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 restricted 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. Epstein et al. (2019b) reported that Undaria pinnatifida biomass was negatively related to Saccharina latissima in both intertidal and subtidal habitats. This was only statistically significant in subtidal habitats, which suggested that there was some competition between the two species (Epstein et al., 2019b). Heiser et al. (2014) surveyed 17 sites within Plymouth Sound, UK, and found that Saccharina latissima was significantly more abundant at sites with Undaria pinnatifida with ca 5 Saccharina latissima individuals present per m², compared to ca 0.5 Saccharina latissima individuals per m² present at sites without Undaria pinnatifida. Undaria pinnatifida has been reported to both co-exist with and out-compete Saccharina latissima (Farrell & Fletcher, 2006; Heiser et al., 2014; Epstein et al., 2019b). For example, in Torquay Marina, UK, Farrell & Fletcher (2006) completed a canopy removal experiment between 1996-2002. They reported that Saccharina latissima decreased in both control and treatment plots from ca 3 plants per 0.45 m² in 1996 to ca 1 plant per 0.45 m² in 1997 and had disappeared completely from pontoons by 2002. This coincided with a significant increase in Undaria pinnatifida from zero plants per 0.45 m² in 1996 to ca 6 plants per 0.45 m² in 1997. However, there was a slight decrease in Undaria pinnatifida at both control and treatment plots between 1997 and 1998. By 2002, Undaria pinnatifida had recovered at control and treatment plots to ca 4-6 plants per 0.45 m² whereas Saccharina latissima had not. 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 Saccharina latissima and Laminaria hyperborea. De Leij et al. (2017) found that natural habitats with dense native macroalgal canopies, such as Laminaria hyperborea 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 will not prevent invasion of Undaria pinnatifida as sporophytes were still recorded within dense Laminaria canopies, suggesting that canopy disturbance is not always required. Undaria pinnatifida was successfully eradicated on a sunken ship in Clatham 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 Saccharina latissima and Laminaria hyperborea. For example, within natural habitats, it can co-exist with native kelp species within its depth range (-1 to 4 m), as shown in Plymouth Sound, UK. A dense kelp canopy may restrict or slow the proliferation of Undaria pinnatifida, however, there has been 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. Sargassum muticum also prefers wave sheltered shallow sites in the sublittoral fringe and shallow infralittoral. It was reported to out-compete and replace Saccharina latissima in the Limfjorden, and achieve maximum abundance at 1-4 m (Staehr et al., 2000; Engelen et al., 2015). But Strong & Dring (2011) concluded that Sargassum was not a threat to Saccharina latissima in the Dorn, Strangford Lough where it coexisted and grew better in mixed stands. Therefore, competition with Sargassum is probably site-specific and dependent on local conditions. No evidence of the effects of Sargassum on Laminaria hyperborea beds was found. The biotope IR.LIR.K.LhypSlat.Ft occurs in low energy, silty environments with full salinity, from 0-10 m (JNCC, 2015), which are the preferred habitat conditions for Undaria pinnatifida and Sargassum muticum. The dense canopy of Laminaria hyperborea and Saccharina latissima may inhibit colonization but any disturbance may allow Undaria and/or Sargassum to colonize. Colonization by Sargassum muticum would probably be limited to the shallow examples of the biotope (ca 0-5m). The presence of the opportunistic Saccharina latissima suggests that the habitat is subject to periodic disturbance, e.g. by siltation. Therefore, both Sargassum muticum and Undaria pinnatifida may be able to colonize this biotope, co-exist with Laminaria hyperborea but out-compete Saccharina latissima resulting in a potentially significant (25-75%) reduction in the abundance or extent of the native sugar kelp. Even if the species co-exist, invasion by Sargassum or Undaria may result in a change in the classification of the biotope and the structure of the under storey macroalgae due to shading (Staehr et al., 2000). Therefore, resistance is assessed as ‘Low’ for the biotope. Recovery after invasion by either species, although rapid, would require direct intervention (removal). Hence, resilience is assessed as ‘Very low’. Hence, the sensitivity of shallow examples of the biotope is assessed as ‘High’. Overall, confidence is assessed as ‘Low’ due to evidence of variation and site-specific nature of competition between native kelps and Undaria pinnatifida.	Low Low NR NR Help	Very Low High High High Help	High Low Low Low 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 Laminaria hyperborea and Saccharina latissima may be infected by the microscopic brown alga Streblonema aecidioides. Infected algae show symptoms of Streblonema disease, i.e. alterations of the blade and stipe ranging from dark spots to heavy deformations and completely crippled thalli (Peters & Scaffelke, 1996). Infection can reduce growth rates of host algae. Echinus esculentus is susceptible to 'Bald-sea-urchin disease', which causes lesions, loss of spines, tube feet, pedicellariae, destruction of the upper layer of skeletal tissue and death. It is thought to be caused by the bacteria Vibrio anguillarum and Aeromonas salmonicida. Bald sea-urchin disease was recorded from Echinus esculentus on the Brittany Coast. Although associated with mass mortalities of Strongylocentrotus franciscanus in California and Paracentrotus lividus in the French Mediterranean it is not known if the disease induces mass mortality (Bower 1996). No evidence of mass mortalities of Echinus esculentus associated with disease have been recorded in Britain and Ireland. Sensitivity assessment. Resistance to the pressure is considered ‘Medium’, and resilience ‘High’. The sensitivity of this biotope to introduction of microbial pathogens is assessed as ‘Low’.	Medium Medium High Medium Help	High Low NR NR Help	Low Low NR NR 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 Incidental/accidental removal of Laminaria hyperborea and Saccharina latissima is likely to cause similar effects to that of direct harvesting; as such the same evidence has been used for both pressure assessments. There has been recent commercial interest in Saccharina latissima as a consumable called ‘sea vegetable’’ (Birkett et al., 1998). Laminaria hyperborea is also extracted on a commercial scale in southern Norway, primarily for alginates (Werner & Kraan, 2004). Commercial Laminaria hyperborea trawling occurs in Norway. Please refer to resilience section for more detail however trawling typically removes all large canopy forming sporophytes but sub-canopy sporophytes and understorey community remain intact (Christie et al., 1998). Saccharina latissima is commercially cultivated, however typically sporophytes are matured on ropes (Handå et al 2013) and not directly extracted from the seabed. Thus evidence to assess the resistance of Saccharina latissima to in/direct harvesting or abrasion is limited. The collection of Echinus esculentus for the curio trade was studied by Nichols (1984). He concluded that the majority of divers collected only large specimens that are seen quickly and often missed individuals covered by seaweed or under rocks, especially if small. As a result, a significant proportion of the population remains. Sensitivity assessment. Commercial extraction removes all large canopy forming kelps (Laminaria hyperborea), but sub-canopy sporophytes and understorey community remain intact. Saccharina latissima can reportedly recover from disturbance and dominate the substrate within a couple of weeks, however Laminaria hyperborea may take up 2-6 years to fully recover, and the associated understorey community 7-10 years. Resistance has been assessed as ‘Low’, resilience as ‘Medium’ and sensitivity as ‘Medium’.	Low 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 There has been recent commercial interest in Saccharina lattisma as a consumable called ‘sea vegetables’ (Birkett et al., 1998). Laminaria hyperborea is also extracted on a commercial scale in southern Norway, primarily for alagnate (Werner & Kraan, 2004). Commercial Laminaria hyperborea trawling occurs in Norway. Please refer to resilience section for more detail however trawling typically removes all large canopy forming sporophytes but sub-canopy sporophytes and understorey community remain intact (Christie et al., 1998). Saccharina latissima is commercially cultivated, however typically sporophytes are matured on ropes (Handå et al 2013) and not directly extracted from the seabed. Thus evidence to assess the resistance of Saccharina latissima to in/direct harvesting or abrasion is limited. The collection of Echinus esculentus for the curio trade was studied by Nichols (1984). He concluded that the majority of divers collected only large specimens that are seen quickly and often missed individuals covered by seaweed or under rocks, especially if small. As a result, a significant proportion of the population remains. An intermediate intolerance has been suggested to reflect the possibility that either of these two species may experience some loss. Sensitivity assessment. Commercial extraction removes all large canopy forming kelps (Laminaria hyperborea), but sub-canopy sporophytes and understorey community remain intact. Saccharina latissima can reportedly recover from disturbance and dominate the substrate within a couple of weeks, however Laminaria hyperborea may take up 2-6 years to fully recover, and the associated understorey community 7-10 years. Resistance has been assessed as ‘None’, Resilience as ‘Medium’. Sensitivity has been assessed as ‘Medium’.	None High High High Help	Medium High High High Help	Medium High High High Help

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Stamp, T.E., Lloyd, K.A., & Mardle, M.J., 2022. Mixed Laminaria hyperborea and Saccharina latissima forest on sheltered upper infralittoral rock. 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 27-12-2024]. Available from: https://marlin.ac.uk/habitat/detail/20

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