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Information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles

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Saccharina latissima and Chorda filum on sheltered upper infralittoral muddy sediment

Distribution MapBIO Map Legend

Summary

UK and Ireland classification

Description

Shallow kelp community found on sandy mud and gravelly sandy mud, in sheltered or extremely sheltered conditions, with very weak tidal currents. The community is characterized by a reasonable covering of Saccharina latissima and Chorda filum. Beneath the kelp canopy, Ulva lactuca is often frequent and some filamentous and foliose red algae may be present, along with filamentous brown ectocarpoid algae although in much lower abundance than in the SlatR biotopes. At the sediment surface ubiquitous fauna such as Asterias rubens, crabs such as Pagurus bernhardus, Carcinus maenas, and the gastropod Gibbula cineraria may be visible and in some areas, Sabella pavonina may be present. Given the nature of the sediment, it is likely that a wide range of infaunal bivalves and polychaetes are present including Arenicola marina, Mediomastus fragilis and Anaitides mucosa. In more tideswept areas with coarser and generally less muddy sediments SMp.SlatCho may be replaced by one of the sub biotopes of SMp.SlatR. (Information taken from Connor et al., 2004; JNCC, 2015).

Depth range

0-5 m, 5-10 m

Additional information

-

Habitat review

Ecology

Ecological and functional relationships

The species occurring in this biotope appear to be largely independent of each other except that the fronds of Saccharina latissima are likely to be colonized by epibiota, especially solitary ascidians and bryozoans, as well as supporting mobile gastropods such as Steromphala cineraria. Sea urchins Psammechinus miliaris might also feed on the fronds.

Seasonal and longer term change

No information has been found although it would be expected that filamentous red seaweeds especially might be more abundant in spring and summer than autumn and winter.

Habitat structure and complexity

There are a wide range of substrata available for colonization in this biotope and therefore potential for high biodiversity. Sediments are colonized by infauna including conspicuous species such as the burrowing anemone Cerianthus lloydiiand the lugworm Arenicola marina, but also by polychaetes and bivalve molluscs. Pebbles and cobbles will be colonized by attached algae but also by barnacles, tube worms and encrusting bryozoans. Kelp holdfasts provide shelter for a range of mobile species, including amphipods, decapods and echinoderms, whilst the fronds are colonized by the grazing gastropods, Steromphala cineraria and Calliostoma zizyphinum. Sea urchins, Psammechinus miliaris, frequently graze on the kelp fronds.

Productivity

The algae which dominate this biotope are primary producers themselves contributing to the supply of detritus that is used by secondary producers. Sea urchins, Psammechinus miliaris, more directly feed on the fronds of the kelp.

Recruitment processes

Recruitment of characterizing species in the biotope is from planktonic sources. Mobile species such as the shore crab Carcinus maenas and the common starfish Asterias rubens will migrate into the biotope as juveniles and adults. However, other mobile species such as the topshell Steromphala cineraria and the sea urchin Psammechinus miliaris are unlikely to move far once settled.

Time for community to reach maturity

Most of the epibiota species in the biotope are known to be rapid colonizing and fast growing, including the dominant species. However, sediment infauna is probably more slow to colonize and develop. Some species such as Cerianthus lloydiimay be very slow to colonize. Overall, because of the dominance of rapid settling and fast growing species, the biotope develop rapidly but recruitment of a full complement of species may take several years.

Additional information

No biotope specific studies are known to have been undertaken.

Preferences & Distribution

Habitat preferences

Depth Range 0-5 m, 5-10 m
Water clarity preferencesNo information
Limiting Nutrients Nitrogen (nitrates)
Salinity preferences Full (30-40 psu), Variable (18-40 psu)
Physiographic preferences
Biological zone preferences Sublittoral fringe, Upper infralittoral
Substratum/habitat preferences Gravel / shingle, Sandy mud
Tidal strength preferences Very Weak (negligible), Weak < 1 knot (<0.5 m/sec.)
Wave exposure preferences Extremely sheltered, Sheltered, Very sheltered
Other preferences

Additional Information

Species composition

Species found especially in this biotope

    Rare or scarce species associated with this biotope

    -

    Additional information

    Sensitivity review

    Sensitivity characteristics of the habitat and relevant characteristic species

    SS.SMp.KSwSS.SlatR (plus sub-biotopes) and SS.SMp.KSwSS.SlatCho typically occur on a mixture of shallow sediments and rock fractions. The mobility of the sediment and rock fractions allow Saccharina latissima (syn. Laminaria saccharina), Chorda filum and other red and brown seaweeds to grow on small stones and shells. Saccharina latissima and Chorda filum are important canopy-forming species within these biotopes. Four sub-biotopes are present within the SS.SMp.KSwSS.SlatR biotope complex, which are largely distinguished by the degree of tidal flow and wave action. As the degree of wave and/or tidal exposure decreases there is a change in community structure, with the density of Saccharina latissima and the diversity of red algal species increasing. A decrease in tidal flow results in increased sediment stability, which in turn facilitates mature macroalgal communities.

    In undertaking this assessment of sensitivity, an account is taken of knowledge of the biology of all characterizing species in the biotope. For this sensitivity assessment, Saccharina latissima and Chorda filum are the primary foci of research, however, it is recognized that the red seaweed communities of SS.SMp.KSwSS.SlatR also defines these biotopes. Examples of important species groups are mentioned where appropriate.

    Resilience and recovery rates of habitat

    Saccharina latissima (syn. Laminaria saccharina) and Chorda filum are opportunistic seaweeds that have relatively fast growth rates. Saccharina latissima is a perennial kelp that can reach maturity in 15-20 months (Sjøtun, 1993) and has a life expectancy of 2-4 years (Parke, 1948). Chorda filum is an annual seaweed, completing its life cycle in a single season (Novaczek et al., 1986). Saccharina latissima is widely distributed in the north Atlantic from Svalbard to Portugal (Birkett et al., 1998b; Connor et al., 2004; Bekby & Moy 2011; Moy & Christie 2012). Chorda filum is widely distributed across the northern hemisphere (Algae Base, 2015). In the North Atlantic, Chorda filum is recorded from Svalbard (Fredriksen et al., 2014) to Northern Portugal (Araújo et al, 2009).

    Saccharina lattisima and Chorda filum have heteromorphic life strategies (Edwards, 1998). Mature sporophytes broadcast spawn zoospores from reproductive structures known as sori (South & Burrows, 1967; Birkett et al., 1998b). Zoospores settle onto rock and develop into gametophytes, and after fertilization germinate into juvenile sporophytes. Laminarian 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 can be influenced by the proximity of mature kelp beds producing viable zoospores (Kain, 1979; Fredriksen et al., 1995). Saccharina lattisima recruits appear in late winter early spring beyond which is a period of rapid growth, during which sporophytes can reach a total length of 3 m (Werner & Kraan, 2004).  In late summer and autumn growth rates slow and spores are released from autumn to winter (Parke, 1948; Lüning, 1979; Birkett et al., 1998b). The overall length of the sporophyte may not change during the growing season due to marginal erosion, but the growth of the blade has been measured at 1.1 cm/day, with a total length addition of ≥2.25 m per year (Birkett et al., 1998b). Chorda filum recruits appear from February (South & Burrows, 1967) after which is a period of rapid growth during which sporophytes can reach a length of ≤6 m (South & Burrows, 1967). In culture, Chorda filum can reach reproductive maturity and produce zoospores within 186 days (ca 6 months) of settlement, but the time taken to reach maturity may be locally variable (South & Burrows, 1967). In nature, sporophytes growth slows/stops from October and sporophytes may begin to die off (South & Burrows, 1967; Novaczek et al., 1986).

    Saccharina latissima can be quite transient in nature and appears early in algal succession. For example, Leinaas & Christie (1996) removed Strongylocentrotus droebachiensis from “Urchin Barrens” and observed a succession effect. Initially, the substratum was colonized by filamentous algae, after a couple of weeks these were outcompeted, and the habitat dominated by Saccharina latissima.  However, this was subsequently outcompeted by Laminaria hyperborea. In the Isle of Man, 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. Saccharina latissima was an early colonizer, but within 2 years of clearance, the blocks were dominated by Laminaria hyperborea.

    In 2002, a 50.7-83% decline of Saccharina latissima was discovered in the Skaggerak region, South Norway (Moy et al., 2006; Moy & Christie, 2012). Survey results indicated a sustained shift from Saccharina latissima communities to those of ephemeral filamentous algal communities. The reason for the community shift was unknown, but low water movement in wave and tidally sheltered areas combined with the impacts of dense human populations e.g. increased land run-off, was suggested to be responsible for the dominance of ephemeral turf macro-algae. Multiple stressors such as eutrophication, increasing regional temperature, increased siltation and overfishing may also be acting synergistically to cause the observed habitat shift.

    Resilience assessment. Saccharina latissima and Chorda filum have the potential to rapidly recover following disturbance. Saccharina latissima has been shown to be an early colonizer within algal succession, appearing within two weeks of clearance, and can reach sexual maturity within 15-20 months. Chorda filum has rapid growth rates, capable of reaching sexual maturity within a year. Resilience has therefore been assessed as ‘High’.

    Climate Change Pressures

    Use / to open/close text displayedResistanceResilienceSensitivity
    Low Very Low High
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High

    The distribution of kelp is strongly influenced by climatic conditions; therefore, kelp species are extremely sensitive to the ongoing ocean warming (Kain, 1979; Van Den Hoek, 1982; Breeman, 1990; Lüning, 1990; Assis et al., 2016; Smale, 2020). Northern distribution boundaries are set by winter temperatures that are lethal, or summer temperatures too low for growth and/or reproduction, while southern limits are set by high lethal summer temperatures or winter temperatures too high for induction of a crucial step in the life cycle (Breeman, 1990). Kelps have a high dependence on ocean temperatures, which make them highly vulnerable to ocean warming (Assis et al., 2014). As temperatures increase, populations found towards the upper limit of their temperature range may be adversely affected by warming as physiological thresholds are exceeded (Wiens, 2016). Thermal stress can lead to mortality and consequent population-level effects, such as decreased abundance, altered size structure, local extinction and range contractions (Smale, 2020). 

    Saccharina latissima is a polar to temperate macroalgae distributed from Greenland to the coast of Portugal, and in the NW Atlantic is found as far south as New York State, USA. At its southern distribution in New York, temperatures can regularly reach ≥20°C for six weeks or more during summer months (Gerard & Du Bois, 1988). In the UK, sea surface temperatures range between 6-19°C (Huthnance, 2010), and Saccharina latissima is in the middle of its biogeographic range.

    Saccharina latissima has an optimal growth temperature between 10-15°C, with growth reducing by 50-70% at 20°C, and all experimental specimens disintegrating after seven days at 23°C (Bolton & Lüning, 1982). The temperature isotherm of 19-20°C has been reported as limiting Saccharina latissima growth (Müller et al., 2009). Temperature is an environmental factor controlling the development of the microscopic stages of Saccharina latissima, with crucial changes in survival, growth, and gametogenesis occurring within a few degrees of its upper thermal limits (Redmond, 2013). The optimal germination temperature for Saccharina latissima is between 2°C and 12°C, with gametophyte survival between 23-25°C (Müller et al., 2009). Germination rates drop at 22°C, with surviving gametophytes smaller than those grown at lower temperatures (Redmond, 2013). Park et al. (2017) observed reductions in the percentage of sporophytes produced at 15°C when compared to values produced at 5°C and 10°C. 

    In the field, Saccharina latissima has shown significant regional variation in its acclimation response to changing environmental conditions.  For example, Gerard & Dubois (1988) observed sporophytes of Saccharina latissima that were regularly exposed to ≥20°C tolerated these high temperatures, whereas sporophytes from other populations which rarely experience ≥17°C showed 100% mortality after 3 weeks of exposure to 20°C.

    Saccharina latissima has suffered a dramatic decline in the Skagerrak region, Norway, where community structure has shifted from Saccharina latissima forests to communities dominated by filamentous macroalgae (Moy & Christie, 2012). In 2006, Andersen et al. (2011) transplanted Saccharina latissima into areas from where this species had been lost previously to determine whether the kelp could grow and mature. High mortality occurred from August-November each year. In 2008, only six of the seventeen original transplanted Saccharina latissima sporophytes survived (approx. 65% mortality rate). All surviving sporophytes were heavily fouled by epiphytic organisms (estimated cover of 80 & 100%). Between 1960 and 2009, sea surface temperatures in the region had regularly exceeded 20°C and so had the duration at which temperatures remain above 20°C. High sea temperatures have been linked to the slow growth of Saccharina latissima, which is likely due to a decrease in the photosynthetic ability of Saccharina latissima, and an increase in vulnerability to epiphytic loading, bacterial and viral attacks (Anderson et al., 2011).

    Assis et al. (2018) predicted that, under the highest emission scenario (RCP 8.5), the range of Saccharina latissima would move northwards, retreating from the coast of Portugal, France and the southwest coast of the UK. The authors projected that, under RCP 2.6, 13% suitable Laminaria hyperborea habitat would be lost from the Western English Channel, while under the RCP 8.5 emission, 87 % of suitable habitat was expected to be lost.

    Chorda filum is a cold boreal species, with a wide geographical distribution along the Arctic, Atlantic and Pacific coasts (www.obis.org).  Chorda filum has been reported to have relatively good growth between the temperatures of 5-15°C. However, a temperature of 20°C can reduce or inhibited growth (Kawai et al., 2000). Chorda filum has an upper temperature tolerance of 26-28°C (Tom, 1993). Although, Lüning (1980) observed that Chorda filum could not reproduce between the temperatures of 15-20°C but found that sporophytes could tolerate ≤26 °C. In addition, Lüning (1990) reported that gametogenesis occurred at temperatures between 5°C and 10°C in the autumn months. 

    Wilson et al. (2015) reported that an increase in sea surface temperature from 1974 to 2010 has resulted in biogeographical changes, with declines in the abundance of Chorda filum, particularly in the English Channel. Wilson et al. (2015) suggested the declines of Chorda filum could be because the summer temperatures in those southern regions are too high for gametogenesis.

    Ulva sp. are distributed globally (Guiry & Guiry, 2015) and occur in warmer waters than those surrounding the UK suggesting that they can withstand increases in temperature at the pressure benchmark.  Ulva sp. are characteristic of upper shore rock pools, where water and air temperatures are greatly elevated on hot days.  Empirical evidence for thermal tolerance to anthropogenic increases in temperature is provided by the effects of heated effluents on rocky shore communities in Maine, USA. Ascophyllum and Fucus were eliminated from a rocky shore heated to 27-30°C by a power station whilst Ulva intestinalis (as Enteromorpha intestinalis) increased significantly near the outfall (Vadas et al., 1976).

    Sensitivity Assessment. UK populations of Saccharina latissima are found in the middle of the species distribution and are known to be able to survive at higher temperatures than currently experienced around the UK. The ability to tolerate summer seawater temperatures of >20°C in populations at their southern geographic limit is thought to be a genetic adaptation (Gerard & Du Bois, 1988), and maybe crucial in the persistence of this species around the UK, as seawater temperatures rise.

    With sea surface temperature around the UK of between 6-19°C (Huthnance, 2010), populations of Saccharina latissima, Chorda filum and the understorey community of mixed red seaweeds may be able to adapt to cope with a gradual rise in ocean temperatures of 3°C (middle emission scenario) by the end of this century, leading to maximum summer high temperatures in the south of the UK of 22°C.  However, increasing temperatures are likely to lead to decreased growth, some mortality and could reduce the reproduction and recruitment of Chorda filum. Therefore, resistance is assessed as ‘Medium’, and resilience is assessed as ‘Very Low’, as the loss is likely to be a long-term decline, due to the long-term nature of ocean warming. Therefore, this biotope is assessed as ‘Medium’ sensitivity to ocean warming in the middle emission scenario.

    For the high emission scenario and extreme scenario, whereby sea temperatures rise by 4-5°C to potential southern summer temperatures of 23-24°C by the end of this century Saccharina latissima is likely to be lost from southern England, as gametophytes are not thought to be able to survive at temperatures ≥23°C. In addition, Chorda filum is also likely to be lost from southern England as reproduction is inhibited between 15-20°C. This assessment corresponds with the results of ecological niche modelling by Assis et al. (2018), who predicted that Saccharina latissima would be lost from the southwest coast of the UK, because of climate change and the observed reduction in the abundance of Chorda filum from the south coast of the UK (Wilson et al., 2015). Therefore, resistance is assessed as ‘Low’, and resilience is assessed as ‘Very low’. This biotope is assessed as having ‘High’ sensitivity to ocean warming in the high and extreme emission scenarios.  

    Low Very Low High
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High

    The distribution of kelp is strongly influenced by climatic conditions; therefore, kelp species are extremely sensitive to the ongoing ocean warming (Kain, 1979; Van Den Hoek, 1982; Breeman, 1990; Lüning, 1990; Assis et al., 2016; Smale, 2020). Northern distribution boundaries are set by winter temperatures that are lethal, or summer temperatures too low for growth and/or reproduction, while southern limits are set by high lethal summer temperatures or winter temperatures too high for induction of a crucial step in the life cycle (Breeman, 1990). Kelps have a high dependence on ocean temperatures, which make them highly vulnerable to ocean warming (Assis et al., 2014). As temperatures increase, populations found towards the upper limit of their temperature range may be adversely affected by warming as physiological thresholds are exceeded (Wiens, 2016). Thermal stress can lead to mortality and consequent population-level effects, such as decreased abundance, altered size structure, local extinction and range contractions (Smale, 2020). 

    Saccharina latissima is a polar to temperate macroalgae distributed from Greenland to the coast of Portugal, and in the NW Atlantic is found as far south as New York State, USA. At its southern distribution in New York, temperatures can regularly reach ≥20°C for six weeks or more during summer months (Gerard & Du Bois, 1988). In the UK, sea surface temperatures range between 6-19°C (Huthnance, 2010), and Saccharina latissima is in the middle of its biogeographic range.

    Saccharina latissima has an optimal growth temperature between 10-15°C, with growth reducing by 50-70% at 20°C, and all experimental specimens disintegrating after seven days at 23°C (Bolton & Lüning, 1982). The temperature isotherm of 19-20°C has been reported as limiting Saccharina latissima growth (Müller et al., 2009). Temperature is an environmental factor controlling the development of the microscopic stages of Saccharina latissima, with crucial changes in survival, growth, and gametogenesis occurring within a few degrees of its upper thermal limits (Redmond, 2013). The optimal germination temperature for Saccharina latissima is between 2°C and 12°C, with gametophyte survival between 23-25°C (Müller et al., 2009). Germination rates drop at 22°C, with surviving gametophytes smaller than those grown at lower temperatures (Redmond, 2013). Park et al. (2017) observed reductions in the percentage of sporophytes produced at 15°C when compared to values produced at 5°C and 10°C. 

    In the field, Saccharina latissima has shown significant regional variation in its acclimation response to changing environmental conditions.  For example, Gerard & Dubois (1988) observed sporophytes of Saccharina latissima that were regularly exposed to ≥20°C tolerated these high temperatures, whereas sporophytes from other populations which rarely experience ≥17°C showed 100% mortality after 3 weeks of exposure to 20°C.

    Saccharina latissima has suffered a dramatic decline in the Skagerrak region, Norway, where community structure has shifted from Saccharina latissima forests to communities dominated by filamentous macroalgae (Moy & Christie, 2012). In 2006, Andersen et al. (2011) transplanted Saccharina latissima into areas from where this species had been lost previously to determine whether the kelp could grow and mature. High mortality occurred from August-November each year. In 2008, only six of the seventeen original transplanted Saccharina latissima sporophytes survived (approx. 65% mortality rate). All surviving sporophytes were heavily fouled by epiphytic organisms (estimated cover of 80 & 100%). Between 1960 and 2009, sea surface temperatures in the region had regularly exceeded 20°C and so had the duration at which temperatures remain above 20°C. High sea temperatures have been linked to the slow growth of Saccharina latissima, which is likely due to a decrease in the photosynthetic ability of Saccharina latissima, and an increase in vulnerability to epiphytic loading, bacterial and viral attacks (Anderson et al., 2011).

    Assis et al. (2018) predicted that, under the highest emission scenario (RCP 8.5), the range of Saccharina latissima would move northwards, retreating from the coast of Portugal, France and the southwest coast of the UK. The authors projected that, under RCP 2.6, 13% suitable Laminaria hyperborea habitat would be lost from the Western English Channel, while under the RCP 8.5 emission, 87 % of suitable habitat was expected to be lost.

    Chorda filum is a cold boreal species, with a wide geographical distribution along the Arctic, Atlantic and Pacific coasts (www.obis.org).  Chorda filum has been reported to have relatively good growth between the temperatures of 5-15°C. However, a temperature of 20°C can reduce or inhibited growth (Kawai et al., 2000). Chorda filum has an upper temperature tolerance of 26-28°C (Tom, 1993). Although, Lüning (1980) observed that Chorda filum could not reproduce between the temperatures of 15-20°C but found that sporophytes could tolerate ≤26 °C. In addition, Lüning (1990) reported that gametogenesis occurred at temperatures between 5°C and 10°C in the autumn months. 

    Wilson et al. (2015) reported that an increase in sea surface temperature from 1974 to 2010 has resulted in biogeographical changes, with declines in the abundance of Chorda filum, particularly in the English Channel. Wilson et al. (2015) suggested the declines of Chorda filum could be because the summer temperatures in those southern regions are too high for gametogenesis.

    Ulva sp. are distributed globally (Guiry & Guiry, 2015) and occur in warmer waters than those surrounding the UK suggesting that they can withstand increases in temperature at the pressure benchmark.  Ulva sp. are characteristic of upper shore rock pools, where water and air temperatures are greatly elevated on hot days.  Empirical evidence for thermal tolerance to anthropogenic increases in temperature is provided by the effects of heated effluents on rocky shore communities in Maine, USA. Ascophyllum and Fucus were eliminated from a rocky shore heated to 27-30°C by a power station whilst Ulva intestinalis (as Enteromorpha intestinalis) increased significantly near the outfall (Vadas et al., 1976).

    Sensitivity Assessment. UK populations of Saccharina latissima are found in the middle of the species distribution and are known to be able to survive at higher temperatures than currently experienced around the UK. The ability to tolerate summer seawater temperatures of >20°C in populations at their southern geographic limit is thought to be a genetic adaptation (Gerard & Du Bois, 1988), and maybe crucial in the persistence of this species around the UK, as seawater temperatures rise.

    With sea surface temperature around the UK of between 6-19°C (Huthnance, 2010), populations of Saccharina latissima, Chorda filum and the understorey community of mixed red seaweeds may be able to adapt to cope with a gradual rise in ocean temperatures of 3°C (middle emission scenario) by the end of this century, leading to maximum summer high temperatures in the south of the UK of 22°C.  However, increasing temperatures are likely to lead to decreased growth, some mortality and could reduce the reproduction and recruitment of Chorda filum. Therefore, resistance is assessed as ‘Medium’, and resilience is assessed as ‘Very Low’, as the loss is likely to be a long-term decline, due to the long-term nature of ocean warming. Therefore, this biotope is assessed as ‘Medium’ sensitivity to ocean warming in the middle emission scenario.

    For the high emission scenario and extreme scenario, whereby sea temperatures rise by 4-5°C to potential southern summer temperatures of 23-24°C by the end of this century Saccharina latissima is likely to be lost from southern England, as gametophytes are not thought to be able to survive at temperatures ≥23°C. In addition, Chorda filum is also likely to be lost from southern England as reproduction is inhibited between 15-20°C. This assessment corresponds with the results of ecological niche modelling by Assis et al. (2018), who predicted that Saccharina latissima would be lost from the southwest coast of the UK, because of climate change and the observed reduction in the abundance of Chorda filum from the south coast of the UK (Wilson et al., 2015). Therefore, resistance is assessed as ‘Low’, and resilience is assessed as ‘Very low’. This biotope is assessed as having ‘High’ sensitivity to ocean warming in the high and extreme emission scenarios.  

    Medium Very Low Medium
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High

    The distribution of kelp is strongly influenced by climatic conditions; therefore, kelp species are extremely sensitive to the ongoing ocean warming (Kain, 1979; Van Den Hoek, 1982; Breeman, 1990; Lüning, 1990; Assis et al., 2016; Smale, 2020). Northern distribution boundaries are set by winter temperatures that are lethal, or summer temperatures too low for growth and/or reproduction, while southern limits are set by high lethal summer temperatures or winter temperatures too high for induction of a crucial step in the life cycle (Breeman, 1990). Kelps have a high dependence on ocean temperatures, which make them highly vulnerable to ocean warming (Assis et al., 2014). As temperatures increase, populations found towards the upper limit of their temperature range may be adversely affected by warming as physiological thresholds are exceeded (Wiens, 2016). Thermal stress can lead to mortality and consequent population-level effects, such as decreased abundance, altered size structure, local extinction and range contractions (Smale, 2020). 

    Saccharina latissima is a polar to temperate macroalgae distributed from Greenland to the coast of Portugal, and in the NW Atlantic is found as far south as New York State, USA. At its southern distribution in New York, temperatures can regularly reach ≥20°C for six weeks or more during summer months (Gerard & Du Bois, 1988). In the UK, sea surface temperatures range between 6-19°C (Huthnance, 2010), and Saccharina latissima is in the middle of its biogeographic range.

    Saccharina latissima has an optimal growth temperature between 10-15°C, with growth reducing by 50-70% at 20°C, and all experimental specimens disintegrating after seven days at 23°C (Bolton & Lüning, 1982). The temperature isotherm of 19-20°C has been reported as limiting Saccharina latissima growth (Müller et al., 2009). Temperature is an environmental factor controlling the development of the microscopic stages of Saccharina latissima, with crucial changes in survival, growth, and gametogenesis occurring within a few degrees of its upper thermal limits (Redmond, 2013). The optimal germination temperature for Saccharina latissima is between 2°C and 12°C, with gametophyte survival between 23-25°C (Müller et al., 2009). Germination rates drop at 22°C, with surviving gametophytes smaller than those grown at lower temperatures (Redmond, 2013). Park et al. (2017) observed reductions in the percentage of sporophytes produced at 15°C when compared to values produced at 5°C and 10°C. 

    In the field, Saccharina latissima has shown significant regional variation in its acclimation response to changing environmental conditions.  For example, Gerard & Dubois (1988) observed sporophytes of Saccharina latissima that were regularly exposed to ≥20°C tolerated these high temperatures, whereas sporophytes from other populations which rarely experience ≥17°C showed 100% mortality after 3 weeks of exposure to 20°C.

    Saccharina latissima has suffered a dramatic decline in the Skagerrak region, Norway, where community structure has shifted from Saccharina latissima forests to communities dominated by filamentous macroalgae (Moy & Christie, 2012). In 2006, Andersen et al. (2011) transplanted Saccharina latissima into areas from where this species had been lost previously to determine whether the kelp could grow and mature. High mortality occurred from August-November each year. In 2008, only six of the seventeen original transplanted Saccharina latissima sporophytes survived (approx. 65% mortality rate). All surviving sporophytes were heavily fouled by epiphytic organisms (estimated cover of 80 & 100%). Between 1960 and 2009, sea surface temperatures in the region had regularly exceeded 20°C and so had the duration at which temperatures remain above 20°C. High sea temperatures have been linked to the slow growth of Saccharina latissima, which is likely due to a decrease in the photosynthetic ability of Saccharina latissima, and an increase in vulnerability to epiphytic loading, bacterial and viral attacks (Anderson et al., 2011).

    Assis et al. (2018) predicted that, under the highest emission scenario (RCP 8.5), the range of Saccharina latissima would move northwards, retreating from the coast of Portugal, France and the southwest coast of the UK. The authors projected that, under RCP 2.6, 13% suitable Laminaria hyperborea habitat would be lost from the Western English Channel, while under the RCP 8.5 emission, 87 % of suitable habitat was expected to be lost.

    Chorda filum is a cold boreal species, with a wide geographical distribution along the Arctic, Atlantic and Pacific coasts (www.obis.org).  Chorda filum has been reported to have relatively good growth between the temperatures of 5-15°C. However, a temperature of 20°C can reduce or inhibited growth (Kawai et al., 2000). Chorda filum has an upper temperature tolerance of 26-28°C (Tom, 1993). Although, Lüning (1980) observed that Chorda filum could not reproduce between the temperatures of 15-20°C but found that sporophytes could tolerate ≤26 °C. In addition, Lüning (1990) reported that gametogenesis occurred at temperatures between 5°C and 10°C in the autumn months. 

    Wilson et al. (2015) reported that an increase in sea surface temperature from 1974 to 2010 has resulted in biogeographical changes, with declines in the abundance of Chorda filum, particularly in the English Channel. Wilson et al. (2015) suggested the declines of Chorda filum could be because the summer temperatures in those southern regions are too high for gametogenesis.

    Ulva sp. are distributed globally (Guiry & Guiry, 2015) and occur in warmer waters than those surrounding the UK suggesting that they can withstand increases in temperature at the pressure benchmark.  Ulva sp. are characteristic of upper shore rock pools, where water and air temperatures are greatly elevated on hot days.  Empirical evidence for thermal tolerance to anthropogenic increases in temperature is provided by the effects of heated effluents on rocky shore communities in Maine, USA. Ascophyllum and Fucus were eliminated from a rocky shore heated to 27-30°C by a power station whilst Ulva intestinalis (as Enteromorpha intestinalis) increased significantly near the outfall (Vadas et al., 1976).

    Sensitivity Assessment. UK populations of Saccharina latissima are found in the middle of the species distribution and are known to be able to survive at higher temperatures than currently experienced around the UK. The ability to tolerate summer seawater temperatures of >20°C in populations at their southern geographic limit is thought to be a genetic adaptation (Gerard & Du Bois, 1988), and maybe crucial in the persistence of this species around the UK, as seawater temperatures rise.

    With sea surface temperature around the UK of between 6-19°C (Huthnance, 2010), populations of Saccharina latissima, Chorda filum and the understorey community of mixed red seaweeds may be able to adapt to cope with a gradual rise in ocean temperatures of 3°C (middle emission scenario) by the end of this century, leading to maximum summer high temperatures in the south of the UK of 22°C.  However, increasing temperatures are likely to lead to decreased growth, some mortality and could reduce the reproduction and recruitment of Chorda filum. Therefore, resistance is assessed as ‘Medium’, and resilience is assessed as ‘Very Low’, as the loss is likely to be a long-term decline, due to the long-term nature of ocean warming. Therefore, this biotope is assessed as ‘Medium’ sensitivity to ocean warming in the middle emission scenario.

    For the high emission scenario and extreme scenario, whereby sea temperatures rise by 4-5°C to potential southern summer temperatures of 23-24°C by the end of this century Saccharina latissima is likely to be lost from southern England, as gametophytes are not thought to be able to survive at temperatures ≥23°C. In addition, Chorda filum is also likely to be lost from southern England as reproduction is inhibited between 15-20°C. This assessment corresponds with the results of ecological niche modelling by Assis et al. (2018), who predicted that Saccharina latissima would be lost from the southwest coast of the UK, because of climate change and the observed reduction in the abundance of Chorda filum from the south coast of the UK (Wilson et al., 2015). Therefore, resistance is assessed as ‘Low’, and resilience is assessed as ‘Very low’. This biotope is assessed as having ‘High’ sensitivity to ocean warming in the high and extreme emission scenarios.  

    None Very Low High
    Q: High
    A: High
    C: Medium
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: Medium

    Marine heatwaves are extreme weather events defined as periods of extreme sea surface temperature that persists for days to months (Frölicher et al., 2018). Marine heatwaves are predicted to occur more frequently, last for longer and at increased intensity by the end of this century under both middle and high emission scenarios (Frölicher et al., 2018). Marine heatwaves are known to cause significant impacts to kelp forests, particularly if a population is found towards the edge of its southern limit (Smale et al., 2019). 

    Saccharina latissima has disappeared almost completely from the Danish estuary Limfjorden, where maximum surface temperatures in summer have increased by 0.7°C per decade over the last 40 years while the number of days with temperatures above 20°C has increased dramatically from 1-2 days year to >25 days year (Pedersen, 2015). Similarly, Saccharina latissima has been lost from the Skagerrak coast of Norway, which is thought to be due to an increase in summer temperatures, coupled with eutrophication (Moy & Christie, 2012).

    Under experimental conditions, Nepper-Davidson et al.(2019) exposed a northern (Denmark) population of Saccharina latissima to a simulated three-week heatwave of three different intensities; 18, 21 and 24°C. When exposed to heatwaves of 18 and 21°C there was a decrease in photosynthesis and growth. When a 24°C was simulated, 91% of sporophytes were dead within a week, and the fronds of the few survivors were disintegrating, so the experiment was terminated (Nepper-Davidsen et al., 2019). These results suggest that this species is unlikely to survive heatwaves of the length and magnitude predicted by the end of this century for both the middle and high emission scenarios.

    Simonson et al. (2015) investigated the impacts of four temperature treatments (11°C, 14°C, 18°C & 21°C) on Saccharina latissima tissue over three weeksHistological analysis showed temperature mediated tissue damage, including holes, splitting of the medulla, damage to the meristoderm and loss of differentiation between tissue layers at temperatures between 14-21°C. 

    Chorda filum has been reported to have an upper temperature tolerance of 26-28°C (Dieck, 1993), however, temperatures of >20°C can reduce or inhibited growth (Kawai et al., 2001), and temperatures of >15°C can inhibit reproduction (Lüning, 1980). Therefore, marine heatwaves could potentially have an impact on the growth and survival of Chorda filum. In addition, marine heatwaves are highly likely to inhibit reproduction and reduce recruitment of the species, depending on the timing of the heatwave. However, no evidence of the effects of marine heatwaves on Chorda filum was found.

    Sensitivity Assessment. Under the middle emission scenario, if heatwaves occurred every three years, with a maximum intensity of 2°C for 80 days by the end of this century, this could lead to summer sea temperatures reaching up to 24°C in southern England. A heatwave of this magnitude is likely to cause mass mortality of Saccharina latissima. Therefore, resistance has been assessed as ‘None’. As widespread mortality may lead to a lack of viable sporophytes for recruitment, resilience has been assessed as ‘Very low.’ This biotope is assessed as having ‘High’ sensitivity to marine heatwaves under the middle emission scenario.

    Under the high emission scenario, if heatwaves occur every two years by the end of this century, reaching a maximum intensity of 3.5°C for 120 days, this could lead to the heatwave lasting the entire summer with temperatures reaching up to 26.5°C. Under this scenario, Saccharina latissima is likely to be already lost from this biotope as a result of rising temperatures (see Global warming) although mortality of any surviving specimens would occur as a result of this projected heatwave. Therefore, resistance has been assessed as ‘None’. As widespread mortality may lead to a lack of viable sporophytes for recruitment, resilience has been assessed as ‘Very low.’ Therefore, this biotope is assessed as having ‘High’ sensitivity to marine heatwaves under the high emission scenario.

    None Very Low High
    Q: High
    A: High
    C: Medium
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: Medium

    Marine heatwaves are extreme weather events defined as periods of extreme sea surface temperature that persists for days to months (Frölicher et al., 2018). Marine heatwaves are predicted to occur more frequently, last for longer and at increased intensity by the end of this century under both middle and high emission scenarios (Frölicher et al., 2018). Marine heatwaves are known to cause significant impacts to kelp forests, particularly if a population is found towards the edge of its southern limit (Smale et al., 2019). 

    Saccharina latissima has disappeared almost completely from the Danish estuary Limfjorden, where maximum surface temperatures in summer have increased by 0.7°C per decade over the last 40 years while the number of days with temperatures above 20°C has increased dramatically from 1-2 days year to >25 days year (Pedersen, 2015). Similarly, Saccharina latissima has been lost from the Skagerrak coast of Norway, which is thought to be due to an increase in summer temperatures, coupled with eutrophication (Moy & Christie, 2012).

    Under experimental conditions, Nepper-Davidson et al.(2019) exposed a northern (Denmark) population of Saccharina latissima to a simulated three-week heatwave of three different intensities; 18, 21 and 24°C. When exposed to heatwaves of 18 and 21°C there was a decrease in photosynthesis and growth. When a 24°C was simulated, 91% of sporophytes were dead within a week, and the fronds of the few survivors were disintegrating, so the experiment was terminated (Nepper-Davidsen et al., 2019). These results suggest that this species is unlikely to survive heatwaves of the length and magnitude predicted by the end of this century for both the middle and high emission scenarios.

    Simonson et al. (2015) investigated the impacts of four temperature treatments (11°C, 14°C, 18°C & 21°C) on Saccharina latissima tissue over three weeksHistological analysis showed temperature mediated tissue damage, including holes, splitting of the medulla, damage to the meristoderm and loss of differentiation between tissue layers at temperatures between 14-21°C. 

    Chorda filum has been reported to have an upper temperature tolerance of 26-28°C (Dieck, 1993), however, temperatures of >20°C can reduce or inhibited growth (Kawai et al., 2001), and temperatures of >15°C can inhibit reproduction (Lüning, 1980). Therefore, marine heatwaves could potentially have an impact on the growth and survival of Chorda filum. In addition, marine heatwaves are highly likely to inhibit reproduction and reduce recruitment of the species, depending on the timing of the heatwave. However, no evidence of the effects of marine heatwaves on Chorda filum was found.

    Sensitivity Assessment. Under the middle emission scenario, if heatwaves occurred every three years, with a maximum intensity of 2°C for 80 days by the end of this century, this could lead to summer sea temperatures reaching up to 24°C in southern England. A heatwave of this magnitude is likely to cause mass mortality of Saccharina latissima. Therefore, resistance has been assessed as ‘None’. As widespread mortality may lead to a lack of viable sporophytes for recruitment, resilience has been assessed as ‘Very low.’ This biotope is assessed as having ‘High’ sensitivity to marine heatwaves under the middle emission scenario.

    Under the high emission scenario, if heatwaves occur every two years by the end of this century, reaching a maximum intensity of 3.5°C for 120 days, this could lead to the heatwave lasting the entire summer with temperatures reaching up to 26.5°C. Under this scenario, Saccharina latissima is likely to be already lost from this biotope as a result of rising temperatures (see Global warming) although mortality of any surviving specimens would occur as a result of this projected heatwave. Therefore, resistance has been assessed as ‘None’. As widespread mortality may lead to a lack of viable sporophytes for recruitment, resilience has been assessed as ‘Very low.’ Therefore, this biotope is assessed as having ‘High’ sensitivity to marine heatwaves under the high emission scenario.

    High High Not sensitive
    Q: High
    A: Medium
    C: Medium
    Q: High
    A: High
    C: High
    Q: High
    A: Medium
    C: Medium

    Increasing levels of CO2 in the atmosphere have led to the average pH of sea surface waters dropping from 8.25 in the 1700s to 8.14 in the 1990s (Jacobson, 2005), with it expected to drop up to a further 0.35 units by the end of this century, dependent on emission scenario. Marine autotrophs will generally benefit from ocean acidification, through an increase in the availability of aqueous COfor photosynthesis (Koch et al., 2013). 

    Research on most kelp species has revealed a positive or neutral effect of ocean acidification (Roleda et al., 2012, Fernández et al., 2015, Nunes et al., 2015, Iñiguez et al., 2016b, a), except for one study, which found that ocean acidification negatively impacted photosynthesis and growth in the southern hemisphere species, Ecklonia radiata (Britton et al., 2016).

    Under experimental COenrichment at levels expected by the end of this century, germination rates in Saccharina latissima were the same as control samples but gametophyte size increased, suggesting a benefit for juvenile stages of this species (Roleda et al., 2012). Nunes et al. (2015) found that experimental exposure of adult Saccharina latissima to enhanced CO2 led to an increase in net primary production, while Gordillo et al. (2015) found that enhanced CO2 led to increased photosynthesis and growth. In contrast, Iñiguez et al. (2016) found no increase in carbon fixation under elevated CO2 conditions. Although contrasting in findings, these studies show that ocean acidification will not negatively impact Saccharina latissima. No evidence on the effects of ocean acidification on Chorda filum was found.

    Sensitivity Assessment. Kelp forests live in a naturally variable pH habitat, with diel fluctuations of 0.3 - 0.45 pH units (Krause-Jensen et al., 2015, Britton et al., 2016), and boundary layer pH fluctuation of up to 0.8 units (Krause-Jensen et al., 2015). Saccharina latissima is not expected to exhibit negative effects from ocean acidification at levels expected for the end of this century. Due to the disturbed nature of the biotope the understorey community can vary locally, therefore impacts to the understory community has not been included in the assessment. Under both the middle and high emission scenario resistance is assessed as ‘High’, and resilience is assessed as ‘High’ so that sensitivity is assessed as ‘Not sensitive’.

    High High Not sensitive
    Q: High
    A: Medium
    C: Medium
    Q: High
    A: High
    C: High
    Q: High
    A: Medium
    C: Medium

    Increasing levels of CO2 in the atmosphere have led to the average pH of sea surface waters dropping from 8.25 in the 1700s to 8.14 in the 1990s (Jacobson, 2005), with it expected to drop up to a further 0.35 units by the end of this century, dependent on emission scenario. Marine autotrophs will generally benefit from ocean acidification, through an increase in the availability of aqueous COfor photosynthesis (Koch et al., 2013). 

    Research on most kelp species has revealed a positive or neutral effect of ocean acidification (Roleda et al., 2012, Fernández et al., 2015, Nunes et al., 2015, Iñiguez et al., 2016b, a), except for one study, which found that ocean acidification negatively impacted photosynthesis and growth in the southern hemisphere species, Ecklonia radiata (Britton et al., 2016).

    Under experimental COenrichment at levels expected by the end of this century, germination rates in Saccharina latissima were the same as control samples but gametophyte size increased, suggesting a benefit for juvenile stages of this species (Roleda et al., 2012). Nunes et al. (2015) found that experimental exposure of adult Saccharina latissima to enhanced CO2 led to an increase in net primary production, while Gordillo et al. (2015) found that enhanced CO2 led to increased photosynthesis and growth. In contrast, Iñiguez et al. (2016) found no increase in carbon fixation under elevated CO2 conditions. Although contrasting in findings, these studies show that ocean acidification will not negatively impact Saccharina latissima. No evidence on the effects of ocean acidification on Chorda filum was found.

    Sensitivity Assessment. Kelp forests live in a naturally variable pH habitat, with diel fluctuations of 0.3 - 0.45 pH units (Krause-Jensen et al., 2015, Britton et al., 2016), and boundary layer pH fluctuation of up to 0.8 units (Krause-Jensen et al., 2015). Saccharina latissima is not expected to exhibit negative effects from ocean acidification at levels expected for the end of this century. Due to the disturbed nature of the biotope the understorey community can vary locally, therefore impacts to the understory community has not been included in the assessment. Under both the middle and high emission scenario resistance is assessed as ‘High’, and resilience is assessed as ‘High’ so that sensitivity is assessed as ‘Not sensitive’.

    Medium Very Low Medium
    Q: Low
    A: NR
    C: NR
    Q: High
    A: High
    C: High
    Q: Low
    A: Low
    C: Low

    Sea-level rise is occurring through a combination of thermal expansion and ice melt.  Sea levels have risen 1-3 mm/yr. in the last century (Cazenave & Nerem, 2004, Church et al., 2004, Church & White, 2006). Sea-level rise is expected to lead to substantial loss of intertidal habitats. Rocky shores backed by cliffs constitute about 80% of oceanic coastlines globally and in Britain, 42% of the coastline is hard rock, with many areas having cliffs behind the shore (Jackson & McIlvenny, 2011).

    Light availability and water turbidity are principal factors in determining kelp depth range (Birkett et al. 1998b), with laminarians being reported to be able to withstand light levels of up to 1% surface irradiance. In Maine, USA, Saccharina latissima is abundant at both turbid and deep sites where surface irradiance averages 2.5% surface irradiance and have adapted to low-light conditions (Gerard, 1990).

    This biotope (SS.SMp.KSwSS.SlatCho) occurs on sheltered, very sheltered and extremely sheltered infralittoral sediments from 0-10m (JNCC, 2015). Understanding how sea-level rise will affect tidal energy is fraught with uncertainty, although evidence appears to suggest that any alterations will be non-linear (Pickering et al., 2012, Li et al., 2016). Modelling potential outcomes of sea-level rise on the tidal and residual currents in the Bohai Sea, China showed effects were site-dependent, with energy either increasing or decreasing (Li et al., 2016). Similarly, Pickering et al. (2012) found a similar pattern around the UK for tidal amplitude. 

    Saccharina latissima occurs in a wide range of water flow rates, from strong tidal currents to areas with low wave exposure (Birkett et al., 1998b). Therefore, Saccharina latissima is unlikely to be affected by a change in water flow. 

    Chorda filum sporophytes often grow on unstable objects, such as pebbles and shell. Owing to the typically unstable substratum on which Chorda filum grows, whole populations can be moved during storms and deposited in more sheltered locations where development will continue (South & Burrows, 1967). A large increase in near-shore wave height is likely to significantly influence biotope structure. As highlighted by Connor et al. (2004), sub-biotopes within SS.SMp.KSwSS.SlatR are largely distinguished by wave exposure

    Sensitivity assessment.  The biotope is recorded from 0 to 10 m in depth (JNCC, 2015). This biotope may be able to expand its range and migrate landwards to compensate for sea-level rise, if not constrained by lack of tide-swept rock, or human-modified shorelines (IPCC, 2019). If landward migration is not possible, it is expected that depth distribution of this biotope will shrink substantially in response to a 50, 70 or 107 cm sea-level rise, without the possibility of recovery, due to the increased depth, leading to a reduction in light availability for photosynthesis. 

    There is likely to be considerable variation between sites, the relative contribution of wave surge and exposure to habitat suitability, and the depth range occupied by the biotope. Hence, it is difficult to assess the effect of the different sea-level rise scenarios. However, as the biotope can occur from 0-10 m in depth, it is assumed at a sea-level rise of 50 cm, or 70 cm (middle to high emission scenarios) would have limited effect but that a 107 cm rise (the extreme emission scenario) might result in loss of some of the deeper extent of the biotope in some sites. Therefore, resistance is assessed as ‘High’ under the middle and high emission scenarios so that resilience is ‘High’ and sensitivity assessed as ‘Not sensitive’. But resistance may be ‘Medium’ under the extreme emission scenario so that resilience is ‘Very low’ and sensitivity assessed as ‘Medium’, albeit with ‘Low’ confidence.

    High High Not sensitive
    Q: Low
    A: NR
    C: NR
    Q: High
    A: High
    C: High
    Q: Low
    A: Low
    C: Low

    Sea-level rise is occurring through a combination of thermal expansion and ice melt.  Sea levels have risen 1-3 mm/yr. in the last century (Cazenave & Nerem, 2004, Church et al., 2004, Church & White, 2006). Sea-level rise is expected to lead to substantial loss of intertidal habitats. Rocky shores backed by cliffs constitute about 80% of oceanic coastlines globally and in Britain, 42% of the coastline is hard rock, with many areas having cliffs behind the shore (Jackson & McIlvenny, 2011).

    Light availability and water turbidity are principal factors in determining kelp depth range (Birkett et al. 1998b), with laminarians being reported to be able to withstand light levels of up to 1% surface irradiance. In Maine, USA, Saccharina latissima is abundant at both turbid and deep sites where surface irradiance averages 2.5% surface irradiance and have adapted to low-light conditions (Gerard, 1990).

    This biotope (SS.SMp.KSwSS.SlatCho) occurs on sheltered, very sheltered and extremely sheltered infralittoral sediments from 0-10m (JNCC, 2015). Understanding how sea-level rise will affect tidal energy is fraught with uncertainty, although evidence appears to suggest that any alterations will be non-linear (Pickering et al., 2012, Li et al., 2016). Modelling potential outcomes of sea-level rise on the tidal and residual currents in the Bohai Sea, China showed effects were site-dependent, with energy either increasing or decreasing (Li et al., 2016). Similarly, Pickering et al. (2012) found a similar pattern around the UK for tidal amplitude. 

    Saccharina latissima occurs in a wide range of water flow rates, from strong tidal currents to areas with low wave exposure (Birkett et al., 1998b). Therefore, Saccharina latissima is unlikely to be affected by a change in water flow. 

    Chorda filum sporophytes often grow on unstable objects, such as pebbles and shell. Owing to the typically unstable substratum on which Chorda filum grows, whole populations can be moved during storms and deposited in more sheltered locations where development will continue (South & Burrows, 1967). A large increase in near-shore wave height is likely to significantly influence biotope structure. As highlighted by Connor et al. (2004), sub-biotopes within SS.SMp.KSwSS.SlatR are largely distinguished by wave exposure

    Sensitivity assessment.  The biotope is recorded from 0 to 10 m in depth (JNCC, 2015). This biotope may be able to expand its range and migrate landwards to compensate for sea-level rise, if not constrained by lack of tide-swept rock, or human-modified shorelines (IPCC, 2019). If landward migration is not possible, it is expected that depth distribution of this biotope will shrink substantially in response to a 50, 70 or 107 cm sea-level rise, without the possibility of recovery, due to the increased depth, leading to a reduction in light availability for photosynthesis. 

    There is likely to be considerable variation between sites, the relative contribution of wave surge and exposure to habitat suitability, and the depth range occupied by the biotope. Hence, it is difficult to assess the effect of the different sea-level rise scenarios. However, as the biotope can occur from 0-10 m in depth, it is assumed at a sea-level rise of 50 cm, or 70 cm (middle to high emission scenarios) would have limited effect but that a 107 cm rise (the extreme emission scenario) might result in loss of some of the deeper extent of the biotope in some sites. Therefore, resistance is assessed as ‘High’ under the middle and high emission scenarios so that resilience is ‘High’ and sensitivity assessed as ‘Not sensitive’. But resistance may be ‘Medium’ under the extreme emission scenario so that resilience is ‘Very low’ and sensitivity assessed as ‘Medium’, albeit with ‘Low’ confidence.

    High High Not sensitive
    Q: Low
    A: NR
    C: NR
    Q: High
    A: High
    C: High
    Q: Low
    A: Low
    C: Low

    Sea-level rise is occurring through a combination of thermal expansion and ice melt.  Sea levels have risen 1-3 mm/yr. in the last century (Cazenave & Nerem, 2004, Church et al., 2004, Church & White, 2006). Sea-level rise is expected to lead to substantial loss of intertidal habitats. Rocky shores backed by cliffs constitute about 80% of oceanic coastlines globally and in Britain, 42% of the coastline is hard rock, with many areas having cliffs behind the shore (Jackson & McIlvenny, 2011).

    Light availability and water turbidity are principal factors in determining kelp depth range (Birkett et al. 1998b), with laminarians being reported to be able to withstand light levels of up to 1% surface irradiance. In Maine, USA, Saccharina latissima is abundant at both turbid and deep sites where surface irradiance averages 2.5% surface irradiance and have adapted to low-light conditions (Gerard, 1990).

    This biotope (SS.SMp.KSwSS.SlatCho) occurs on sheltered, very sheltered and extremely sheltered infralittoral sediments from 0-10m (JNCC, 2015). Understanding how sea-level rise will affect tidal energy is fraught with uncertainty, although evidence appears to suggest that any alterations will be non-linear (Pickering et al., 2012, Li et al., 2016). Modelling potential outcomes of sea-level rise on the tidal and residual currents in the Bohai Sea, China showed effects were site-dependent, with energy either increasing or decreasing (Li et al., 2016). Similarly, Pickering et al. (2012) found a similar pattern around the UK for tidal amplitude. 

    Saccharina latissima occurs in a wide range of water flow rates, from strong tidal currents to areas with low wave exposure (Birkett et al., 1998b). Therefore, Saccharina latissima is unlikely to be affected by a change in water flow. 

    Chorda filum sporophytes often grow on unstable objects, such as pebbles and shell. Owing to the typically unstable substratum on which Chorda filum grows, whole populations can be moved during storms and deposited in more sheltered locations where development will continue (South & Burrows, 1967). A large increase in near-shore wave height is likely to significantly influence biotope structure. As highlighted by Connor et al. (2004), sub-biotopes within SS.SMp.KSwSS.SlatR are largely distinguished by wave exposure

    Sensitivity assessment.  The biotope is recorded from 0 to 10 m in depth (JNCC, 2015). This biotope may be able to expand its range and migrate landwards to compensate for sea-level rise, if not constrained by lack of tide-swept rock, or human-modified shorelines (IPCC, 2019). If landward migration is not possible, it is expected that depth distribution of this biotope will shrink substantially in response to a 50, 70 or 107 cm sea-level rise, without the possibility of recovery, due to the increased depth, leading to a reduction in light availability for photosynthesis. 

    There is likely to be considerable variation between sites, the relative contribution of wave surge and exposure to habitat suitability, and the depth range occupied by the biotope. Hence, it is difficult to assess the effect of the different sea-level rise scenarios. However, as the biotope can occur from 0-10 m in depth, it is assumed at a sea-level rise of 50 cm, or 70 cm (middle to high emission scenarios) would have limited effect but that a 107 cm rise (the extreme emission scenario) might result in loss of some of the deeper extent of the biotope in some sites. Therefore, resistance is assessed as ‘High’ under the middle and high emission scenarios so that resilience is ‘High’ and sensitivity assessed as ‘Not sensitive’. But resistance may be ‘Medium’ under the extreme emission scenario so that resilience is ‘Very low’ and sensitivity assessed as ‘Medium’, albeit with ‘Low’ confidence.

    Hydrological Pressures

    Use / to open/close text displayedResistanceResilienceSensitivity
    None High Medium
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High

    The temperature isotherm of 19-20 °C has been reported as limiting Saccharina latissima geographic distribution (Müller et al., 2009). Gametophytes can develop in ≤23°C (Lüning, 1990) however the optimal temperature range for sporophyte growth is 10-15 °C (Bolton & Lüning, 1982). Bolton & Lüning (1982) experimentally observed that sporophyte growth was inhibited by 50-70% at 20 °C and following 7 days at 23 °C all specimens completely disintegrated. In the field Saccharina latissima has shown significant regional variation in its acclimation to temperature changes, for example Gerard & Dubois (1988) observed sporophytes of Saccharina latissima which were regularly exposed to ≥20 °C could tolerate these 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 experiments, Lüning (1980) observed that Chorda filum could not reproduce at 15-20 °C but found that sporophytes could tolerate ≤26 °C.

    Northern to southern Sea Surface Temperature (SST) ranges from 8-16 °C in summer and 6-13 °C in winter in the UK (Beszczynska-Möller & Dye, 2013). The effect of this pressure is likely to be regionally variable.

    Sensitivity assessment. Ecotypes of Saccharina lattisma have been shown to have different temperature optimums (Dubois, 1988). Both a 2 & 5 °C increase in temperature when combined with high UK summer temperatures in the south of the UK could cause large scale mortality of Saccharina lattisma and inhibit Chorda filum reproduction. Resistance has been assessed as ‘None’, Resilience as ‘High’. Sensitivity has been assessed as ‘Medium’.

    High High Not sensitive
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High

    Saccharina lattissima and Chorda filum are widespread throughout the arctic. Saccharina lattissima has a lower temperature threshold for sporophyte growth at 0 °C (Lüning, 1990). Chorda filum sporophytes can also tolerate 0 °C, Novaczek et al., (1986) observed that 99% of newly settled zoospores died at 0 °C but sporophytes transferred from 5 °C to 0 °C remained healthy and continued to grow for a period of 2 months. Novaczek et al., (1986) therefore demonstrated that sporophytes could tolerate exposure to low (≥0°C) temperatures, but that exposure could have negative effects on larval survival and recruitment processes. Subtidal red algae can survive at -2°C (Lüning, 1990; Kain & Norton, 1990). The distribution and temperature tolerances of these species suggests they likely be unaffected by temperature decreases assessed within this pressure.

    Sensitivity assessment. Resistance has been assessed as ‘High’, resilience as ‘High’”. Sensitivity has been assessed as ‘Not Sensitive’.

    Medium High Low
    Q: Low
    A: NR
    C: NR
    Q: High
    A: High
    C: High
    Q: Low
    A: Low
    C: Low

    Karsten (2007) tested the photosynthetic ability of Saccharina latissima under acute 2 and 5 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. However, Birkett et al. (1998) suggested that kelps are stenohaline and therefore long-term increases in salinity may be detrimental.

    Chorda filum can be found in rock pools (South & Burrows, 1967). High air temperatures cause surface evaporation of water from rock pools, so that salinity steadily increases. The extent of temperature and salinity change is affected by the frequency and time of day at which tidal inundation occurs. If high tide occurs in early morning and evening the diurnal temperature follows that of the air, whilst high water at midday suddenly returns the temperature to that of the sea (Pyefinch, 1943). It should be noted however that local populations may be acclimated to the prevailing salinity regime and may therefore exhibit different tolerances to other populations subject to different salinity conditions and therefore caution should be used when inferring tolerances. However, it is likely that Chorda filum is tolerant of short-term salinity increases.

    Sensitivity assessment. The evidence suggests that Saccharina latissima and Chorda filum can tolerate short-term exposure to hypersaline conditions (≥40‰-MNCR full salinity). An increase in salinity to ≥40‰ may however be above the optima for characterizing species and cause a decline in growth, and possibly loss of red algae and a reduction in species diversity.  Resistance has been assessed as ‘Medium’, resilience as ‘High’. The sensitivity of this biotope to an increase in salinity has been assessed as ‘Low’.

    Medium High Low
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High

    Karsten (2007) tested the photosynthetic ability of Saccharina latissima under acute 2 and 5 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 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.

    Chorda filum is tolerant of low salinities (Wilce, 1959; Hayren, I940; Norton & South, 1969), and has been recorded at Björnholm, Finland at a salinity as low as 5.15%o (Hayren, I940). Norton & South (1969) observed that Chorda filum could develop sporophytes at ≥5%o under laboratory conditions, however at low salinities the time taken to develop into sporophytes took 65 days at 5%o, or 16 days at 35%o. It was also noted that below 9%o sporophytes did not grow above 2 mm in length.

    Sensitivity assessment.  A decrease in one MNCR salinity scale from “Full Salinity” (30-40psu) to “Reduced Salinity” (18-30 psu) would inhibit Saccharina lattissima photosynthesis and hence growth. Chorda filum is highly tolerant of low salinity and is unlikely to be affected at the bench mark level. However, a shift to reduced salinity conditions is likely to result in a change in the infauna community and an overall reduction in species diversity. Therefore, resistance has been assessed as ‘Medium’ resilience as ‘High’. Sensitivity of this biotope to a decrease in salinity has been assessed as ‘Low’.

    High High Not sensitive
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High

    Peteiro & Freire (2013) measured Saccharina latissima growth from 2 sites, the 1st had maximal water velocities of 0.3 m/sec and the 2nd 0.1 m/sec. At site 1 Saccharina latissima had significantly larger biomass than at site 2 (16 kg/m to 12 kg/m respectively). Peteiro & Freire (2013) suggested that faster water velocities were beneficial to Saccharina latissima growth. However, Gerard & Mann (1979) measured Saccharina latissima productivity at greater water velocities and found Saccharina latissima productivity is reduced in moderately strong tidal streams (≤1 m/sec) when compared to weak tidal streams (<0.5 m/sec).

    Chorda filum sporophytes often grow on unstable objects, such as pebbles and shell. Owing to the typically unstable substratum which Chorda filum grows on, whole populations can be moved during storms and deposited in more sheltered locations where development will continue (South & Burrows, 1967). The survival of Chorda filum sporophytes following transport of their attached substrata indicates the species is relatively tolerant to changes in water flow or wave action.

    As highlighted by Connor et al., (2004) large increases in tidal flow (>0.5 m/s) are likely to influence biotope structure and smaller changes in tidal flow (e.g. 0.1-0.2m/s) are not likely to have a significant effect on the characterizing species. A change in tidal flow of 0.1-0.2 m/sec in low energy biotopes e.g. SS.SMp.KSwSS.SlatR.Mu, may however remove finer sediment fractions (e.g. mud) and may therefore change the biotope. However, evidence is lacking and a change in tidal velocities is not likely to result in a significant change to the dominant species.

    Sensitivity assessment. Resistance has been assessed as ‘High’, resilience as ‘High’. Sensitivity has been assessed as ‘Not Sensitive’.

    Medium High Low
    Q: Medium
    A: High
    C: High
    Q: High
    A: Low
    C: High
    Q: Medium
    A: Low
    C: High

    SS.SMp.KSwSS.SlatR and SS.SMp.KSwSS.SlatCho are recorded from 0-10m, while SlatR can extend to 20m (Connor et al., 2004). Therefore the upper limit of the biotopes in the sub-littoral fringe (South & Burrows, 1967; White & Marshall, 2007) could be exposed during some low tides.

    An increase in emergence will result in an increased risk of desiccation and mortality of Saccharina latissima and Chorda filum. Removal of macroalgae canopy may also increase desiccation and mortality of the undergrowth red seaweed community (Hawkins & Harkin, 1985). 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. Resistance has been assessed as ‘Medium’. Resilience as ‘High’. The sensitivity of this biotope to a change in emergence is considered as ‘Low’.

    High High Not sensitive
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High

    Birkett et al. (1998b) suggested that Saccharina latissima is rarely present in areas of wave exposure, where it is out-competed by Laminaria hyperborea. Chorda filum sporophytes often grow on unstable objects, such as pebbles and shell. Owing to the typically unstable substratum which Chorda filum grows on, whole populations can be moved during storms and deposited in more sheltered locations where development will continue (South & Burrows, 1967). A large increase in near-shore wave height is likely to significantly influence biotope structure. As highlighted by Connor et al. (2004), sub-biotopes within SS.SMp.KSwSS.SlatR are largely distinguished by wave exposure

    Sensitivity assessment. A large scale increase in local wave height may increase local sediment mobility, potentially increase dislodgment or relocation of the characterizing species (South & Burrows, 1967; Birkett et al., 1998b). However, an increase in nearshore significant wave height of 3-5% is not likely to have a significant effect on biotope structure. Resistance has been assessed as ‘High’, Resilience as ‘High’. Sensitivity has been assessed as ‘Not Sensitive’ at the benchmark level.

    Chemical Pressures

    Use / to open/close text displayedResistanceResilienceSensitivity
    Not Assessed (NA) Not assessed (NA) Not assessed (NA)
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR

    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 al., (1999) reported that Hg was very toxic to macrophytes. Similarly, Hopkin & Kain (1978) demonstrated sub-lethal effects of heavy metals on kelp 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). 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. Thompson & Burrows (1984) observed the growth of Saccharina latissima sporophyte growth 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.

    Not Assessed (NA) Not assessed (NA) Not assessed (NA)
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR

    This pressure is Not assessed but evidence is presented where available

    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 kelps. Similarly, surveys of subtidal communities at a number sites between 1-22.5m below chart datum showed no noticeable impacts of the Sea Empress oil spill and clean up (Rostron & Bunker, 1997) or during experimental release of untreated oil in Baffin Island, Canada (Cross et al., 1987). Laboratory studies of the effects of oil and dispersants on several red algae species (Grandy 1984) concluded that they were all sensitive to oil/ dispersant mixtures, with little differences between adults, sporelings, diploid or haploid life stages.

    Not Assessed (NA) Not assessed (NA) Not assessed (NA)
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR

    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). Saccharina latissima has also been found to be sensitive to antifouling compounds. Johansson (2009) exposed samples of Saccharina latissima to several antifouing 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.

    Smith (1968) observed that epiphytic and benthic red algae were intolerant of dispersant or oil contamination during 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.

    Not relevant (NR) Not relevant (NR) No evidence (NEv)
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR

    No evidence

    Not Assessed (NA) Not assessed (NA) Not assessed (NA)
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR

    This pressure is Not assessed.

    High High Not sensitive
    Q: Medium
    A: High
    C: High
    Q: High
    A: High
    C: High
    Q: Medium
    A: High
    C: High

    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’ and resilience as ‘High’. Sensitivity has been assessed as ‘Not sensitive’ at the benchmark level.

    Not relevant (NR) Not relevant (NR) Not sensitive
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR

    Conolly & Drew (1985) found Saccharina latissima sporophytes had relatively higher growth rates when in close proximity to a sewage outlet in St Andrews, UK, compared to other sites along the east coast of Scotland. At St Andrews nitrate levels were 20.22µM, which represents an approx. 25% increase compared to other 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 Norwegian salmon farms, where elevated ammonium could be readily absorbed by sporophytes.  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. Within 3 years of the experiment no significant effect was observed in the communities, however 4-5 years into the experiment a shift occurred from perennials to ephemeral algae. 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.

    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 was identified from all habitats exposed to the contaminant types. Johnston & Roberts (2009) however also highlighted that macroalgal communities are relative 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).

    Sensitivity assessment. Although short-term exposure (<4 years) to nutrient enrichment may not affect seaweeds directly, indirect effects such as turbidity may significantly affect photosynthesis and result in reduced growth and reproduction and increased competition form fast growing but ephemeral species. However, this biotope is considered to be 'Not sensitive' at the pressure benchmark, that assumes compliance with good status as defined by the WFD.

    Medium High Low
    Q: Medium
    A: High
    C: High
    Q: Medium
    A: High
    C: High
    Q: Medium
    A: Medium
    C: High

    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. Within 3 years of the experiment no significant effect was observed in the communities, however 4-5 years into the experiment a shift occurred from perennials to ephemeral algae. 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.

    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 was identified from all habitats exposed to the contaminant types. Johnston & Roberts (2009) however also highlighted that macroalgal 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). Organic enrichment may also result in phytoplankton blooms that increase turbidity and therefore may negatively impact photosynthesis.

    Sensitivity assessment. Although short-term exposure (<4 years) to organic enrichment may not affect seaweeds directly, indirect effects such as turbidity may significantly affect photosynthesis, and result in reduced growth and reproduction and increased competition form fast growing but ephemeral species Resistance has been assessed as ‘Medium’, resilience as ‘High’. Sensitivity has been assessed as ’Low’.

    Physical Pressures

    Use / to open/close text displayedResistanceResilienceSensitivity
    None Very Low High
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High

    All marine habitats and benthic species are considered to have a resistance of ‘None’ to this pressure and to be unable to recover from a permanent loss of habitat (resilience is ‘Very Low’).  Sensitivity within the direct spatial footprint of this pressure is therefore ‘High’. Although no specific evidence is described confidence in this assessment is ‘High’, due to the incontrovertible nature of this pressure.

    None Very Low High
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High

    If sediment were replaced with rock or artificial substrata, this would represent a fundamental change to the biotope (Macleod et al., 2014). All the characterizing species within this biotope can grow on rock biotopes (Birkett et al., 1998; Connor et al., 2004), however SS.SMp.KSwSS are by definition sediment biotopes and introduction of rock would change them into a rock based habitat complex, and the biotope would be lost

    Sensitivity assessment. Resistance to the pressure is considered ‘None’, and resilience ‘Very low’. Sensitivity has been assessed as ‘High

    None Very Low High
    Q: Low
    A: NR
    C: NR
    Q: High
    A: High
    C: High
    Q: Low
    A: Low
    C: Low

    SS.SMp.KSwSS are sediment based biotopes. Stabilised cobbles, pebbles, gravel and shell fractions provide a substrate for macro-algae to dominate the community (Connor et al., 2004). An increase in the dominance of smaller sediment fractions e.g. sand and/or mud will likely smoother the existing biotope, inhibit successive re-colonisation of macro-algae and/or increase the sediment scour.

    Sensitivity assessment. Resistance has been assessed as ‘None’, resilience as Very low (the pressure is a permanent change), and sensitivity as High. 

    None High Medium
    Q: Low
    A: NR
    C: NR
    Q: High
    A: High
    C: High
    Q: Low
    A: Low
    C: Low

    SS.SMp.KSwSS.SlatR (plus sub-biotopes), SS.SMp.KSwSS.SlatCho can be found on a varied mixture of sediment and rock fractions. Extraction of substratum to 30 cm is likely to remove small sediment fractions (e.g. gravel) and may mobilize the remaining larger rock fractions (e.g. boulders) causing high mortality within the resident community. All characterizing species have rapid growth rates and are likely to recover within 2 years.

    Sensitivity assessment. Resistance has been assessed as ‘None’, Resilience as ‘High’. Sensitivity has been assessed as ‘Medium’.

    None High Medium
    Q: Low
    A: NR
    C: NR
    Q: High
    A: High
    C: High
    Q: Low
    A: Low
    C: Low

    Abrasion of the substratum e.g. from bottom or pot fishing gear, cable laying etc. may cause localised mobility of the substrata and mortality of the resident community. The effect would be situation dependent, however, if bottom fishing gear were towed over a site it may mobilise a high proportion of the rock substrata and cause high mortality in the resident community.

    Sensitivity assessment. Resistance has been assessed as ‘None’, Resilience as ‘High’. Sensitivity has been assessed as ‘Medium’.

    None High Medium
    Q: Low
    A: NR
    C: NR
    Q: High
    A: High
    C: High
    Q: Low
    A: Low
    C: Low

    Penetration and/or disturbance of the substrate below the surface of the seabed, may cause localised mobility of the substrata and mortality of the resident community.

    Sensitivity assessment. Resistance has been assessed as ‘None’, Resilience as ‘High’. Sensitivity has been assessed as ‘Medium’.

    Low High Low
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High

    Suspended Particle Matter (SPM) concentration has a positive linear relationship with subsurface light attenuation (Kd) (Devlin et al., 2008). Light availability and water turbidity are principal factors in determining depth range at which macro-algae can be found (Birkett et al., 1998b). Light penetration influences the maximum depth at which laminarians can grow and it has been reported that laminarians grow at depths at which the light levels are reduced to 1 percent of incident light at the surface. Maximal depth distribution of laminarians, therefore, varies from 100 m in the Mediterranean to only 6-7m in the silt-laden German Bight. In Atlantic European waters, the depth limit is typically 35 m. In very turbid waters the depth at which kelp is found may be reduced, or in some cases excluded completely (e.g. Severn Estuary), because of the alteration in light attenuation by suspended sediment (Lüning, 1990; Birkett et al. 1998b). Laminarians show a decrease of 50% photosynthetic activity when turbidity increases by 0.1/m (light attenuation coefficient =0.1-0.2/m; Staehr & Wernberg, 2009).

    Sensitivity Assessment. A decrease in turbidity is likely to support enhanced growth (and possible habitat expansion) and is therefore not considered in this assessment. An increase in water turbidity is likely to primarily affect photosynthesis, therefore, growth and density of the canopy-forming seaweeds. Resistance to this pressure is defined as ‘Low’ and resilience to this pressure is defined as ‘High’ at the benchmark level due to the scale of the impact. Hence, this biotope is regarded as having a sensitivity of ‘Low‘.

    High High Not sensitive
    Q: Low
    A: NR
    C: NR
    Q: High
    A: High
    C: High
    Q: Low
    A: Low
    C: Low

    Smothering by sediment e.g. 5 cm material during a discrete event, is unlikely to damage mature examples of Saccharina latissima and Chorda filum but may provide a physical barrier to zoospore settlement and therefore could negatively impact on recruitment processes (Moy & Christie, 2012). Laboratory studies showed that kelp and gametophytes can survive in darkness for between 6-16 months at 8 °C and would probably survive smothering by a discrete event and once returned to normal conditions gametophytes resumed growth or maturation within 1 month (Dieck, 1993).

    SS.SMp.KSwSS biotopes are all recorded in moderately strong tidal streams to negligible (≤1.5 m/sec) (Connor et al., 2004). In tidally exposed biotopes deposited sediment is unlikely to remain for more than a few tidal cycles (due to water flow or wave action). In sheltered biotopes deposited sediment could remain however are unlikely to remain for longer than a year.

    Sensitivity assessment. Resistance has been assessed as ‘High’, resilience as ‘High’. Sensitivity has been assessed as ‘Not Sensitive’.

    Medium High Low
    Q: Low
    A: NR
    C: NR
    Q: Low
    A: NR
    C: NR
    Q: Low
    A: NR
    C: NR

    Smothering by sediment e.g. 30 cm material during a discrete event, is unlikely to damage mature examples of Saccharina latissima and Chorda filum but may provide a physical barrier to zoospore settlement and therefore could negatively impact on recruitment processes (Moy & Christie, 2012). Laboratory studies showed that kelp and gametophytes can survive in darkness for between 6-16 months at 8°C and would probably survive smothering by a discrete event and once returned to normal conditions gametophytes resumed growth or maturation within 1 month (Dieck, 1993).

    SS.SMp.KSwSS biotopes are all recorded in moderately strong tidal streams to negligible (≤1.5 m/sec) (Connor et al., 2004). In tidally exposed biotopes deposited sediment is unlikely to remain for more than a few tidal cycles (due to water flow or wave action). In sheltered biotopes deposited sediment could remain however are unlikely to remain for longer than a year.

    Sensitivity assessment. Resistance has been assessed as ‘Medium’, resilience as ‘High’. Sensitivity has been assessed as ‘Low’.

    Not Assessed (NA) Not assessed (NA) Not assessed (NA)
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR

    Not assessed.

    Not relevant (NR) Not relevant (NR) No evidence (NEv)
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR

    No evidence

    Not relevant (NR) Not relevant (NR) Not relevant (NR)
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR

    Not relevant

    Low Medium Medium
    Q: Low
    A: NR
    C: NR
    Q: Low
    A: NR
    C: NR
    Q: Low
    A: Low
    C: Low

    There is no evidence to suggest that anthropogenic light sources would affect macro-algae. Shading of the biotope (e.g. by construction of a pontoon, pier etc.) could adversely affect the biotope in areas where the water clarity is also low, and tip the balance to shade tolerant species, resulting in the loss of the biotope directly within the shaded area, or a reduction in seaweed abundance.

    Sensitivity assessment. Resistance is probably 'Low', with a 'Medium' resilience and a sensitivity of 'Medium', albeit with 'low' confidence due to the lack of direct evidence. .

    Not relevant (NR) Not relevant (NR) Not relevant (NR)
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR

    Not relevant. This pressure is considered applicable to mobile species, e.g. fish and marine mammals rather than seabed habitats. Physical and hydrographic barriers may limit the dispersal of spores.  But spore dispersal is not considered under the pressure definition and benchmark.

    Not relevant (NR) Not relevant (NR) Not relevant (NR)
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR

    Not relevant. Collision from grounding vessels is addressed under abrasion above.

    Not relevant (NR) Not relevant (NR) Not relevant (NR)
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR

    Not relevant

    Biological Pressures

    Use / to open/close text displayedResistanceResilienceSensitivity
    Not relevant (NR) Not relevant (NR) No evidence (NEv)
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR

    At the time of writing there is no evidence for translocation of Saccharina latissima, Chorda filum over significant geographic distances.

    Low Very Low High
    Q: Low
    A: NR
    C: NR
    Q: High
    A: High
    C: High
    Q: Low
    A: Low
    C: Low

    Competition with invasive macroalgae may be a potential threat to this biotope (de Bettignies et al., 2021).  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 0-0.5 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 muticumgrew 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).  It 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).  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 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 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 can inhibit a broad range of habitats including reefs; coastal brackish/saline lagoons; large shallow inlets and bays; estuaries; estuarine rocky habitats; natural or near natural estuary; coastal lagoons; and tidal rivers, estuaries, mudflats, sandflats and lagoons (James 2017).  Undaria pinnatifida prefers 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 Plymouth Sound (UK), Epstein et al. (2019b) found that within its depth range (+1 to –4 m), Undaria pinnatifidaco-existed with seven species of canopy-forming brown macroalgae, including Saccharina latissima.  However, they 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 latissimadecreased 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 latissimahad not.

    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.

    The proliferation of Undaria pinnatifida and out-competing of native species may cause a reduction in local biodiversity (Valentine & Johnson, 2003; Vaz-Pinto et al., 2014; Arnold et al., 2016; Teagle, 2017; Tidbury, 2020).  A shift towards Undaria pinnatifida dominated beds could result in diminished epibiotic assemblages and lower local biodiversity compared with assemblages associated with native perennial kelp species, such as Laminaria spp. and Saccharina latissima (Arnold et al., 2016; Teagle et al., 2017).  In Plymouth, UK, Arnold et al. (2016) found that Undaria pinnatifida supported less than half the number of taxa and had no unique epibionts compared to Laminaria ochroleuca and Saccharina latissima (Arnold et al., 2016).

    Sensitivity assessment. 

    The above evidence suggests that both Sargassum muticum and Undaria pinnatifida can compete with and co-exist with Saccharina latissima, depending on local conditions.  For example, Undaria pinnatifida can out-compete Saccharina latissima in artificial habitats, such as in Torquay Marina but 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.  Similarly, Sargassum muticum out-competed Saccharina latissima in the Limfjorden but coexisted in the Dorn in Strangford Lough. 

    This Saccharina latissima biotope (SS.SMp.KSwSS.SlatCho) is found at variable depths (0-10 m; JNCC, 2015) in moderately exposed to wave sheltered environments with moderately strong to weak tidal flow.  The evidence above suggests that Undaria prefers sheltered conditions, with a low tidal flow, in the shallow subtidal and sublittoral fringe (ca +1 to 4 m in depth), while Sargassum also prefers wave sheltered conditions and shallow water (ca 1 to 4 m depth).  Therefore, Undaria pinnatifida and Sargassum muticum are only likely to threaten the most shallow (e.g. 0-5 m) and wave sheltered examples of this biotope, where suitable had substrata is available.  They may either co-exist with or out-compete Saccharina latissima, resulting in a potentially significant (25-75%) reduction in the abundance or extent of the native kelp and a possible decrease in the diversity of other macroalgae.  

    Therefore, resistance is assessed as ‘Low’ for shallow, wave sheltered examples of the biotope, i.e. above ca 5 m in depth, while it is probably ‘Not relevant’ to examples below 10 m.  Recovery after invasion by Sargassum orUndaria, although rapid, would require direct intervention (removal) so that resilience is assessed as ‘Very low’.  Hence, the sensitivity of shallow, sheltered, 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, Sargassum muticum, and Undaria pinnatifida.

    Low High Low
    Q: Low
    A: NR
    C: NR
    Q: High
    A: Low
    C: High
    Q: Low
    A: Low
    C: Low

    Laminarians 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 Infection can reduce growth rates of host algae (Peters & Scaffelke, 1996). The marine fungi Eurychasma spp can also infect early life stages of Laminarians however the effects of infection are unknown (Müller et al., 1999).

    Sensitivity assessment. Resistance to the pressure is considered ‘Low’, and resilience ‘High’. The sensitivity of this biotope to introduction of microbial pathogens is assessed as ‘Low’.

    Not relevant (NR) Not relevant (NR) Not relevant (NR)
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR

    This pressure has been assessed as ‘Not relevant’.

    There has been recent commercial interest in Saccharina lattisma as a consumable called “sea vegetables” (Birket et al., 1998). However, Saccharina lattissima sporophytes are typically matured on ropes (Handå et al 2013) and not directly extracted from the seabed, as with Laminaria hyperborea (Christie et al., 1998). No evidence has been found for commercial extraction of Chorda filum.

    None High Medium
    Q: Low
    A: NR
    C: NR
    Q: High
    A: High
    C: High
    Q: Low
    A: Low
    C: Low

    Low level disturbances (e.g. solitary anchors) are unlikely to cause harm to the biotope as a whole, due to the impact’s small footprint. Thus evidence to assess the resistance of SS.SMp.KSwSS.SlatR (plus sub-biotopes), SS.SMp.KSwSS.SlatCho to non-targeted removal is limited. It is assumed that incidental non-targeted catch (e.g. by trawls or dredges) could mobilise sediment, remove large kelp species, overturn boulders and cobbles and bury smaller seaweeds and cause high mortality within the affected area.

    Sensitivity assessment. Resistance has been assessed as ‘None’, Resilience as ‘High’. Sensitivity has been assessed as ‘Medium’.

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    Citation

    This review can be cited as:

    Stamp, T.E., Hiscock, K. & Williams, E. & Mardle, M.J., 2022. Saccharina latissima and Chorda filum on sheltered upper infralittoral muddy sediment. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 29-01-2023]. Available from: https://marlin.ac.uk/habitat/detail/58

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