The Marine Life Information Network

Temperature increase (local)

Benchmark. A 5°C increase in temperature for one month, or 2°C for one year. Further detail

Evidence

Kain (1964) stated that Laminaria hyperborea sporophyte growth and reproduction could occur within a temperature range of 0-20°C. Upper and lower lethal temperatures have been estimated at between 1 -2°C above or below the extremes of this range (Birkett et al., 1988). However, above 17°C gamete survival is reduced (Kain, 1964; 1971) and gametogenesis is inhibited at 21°C (Dieck, 1992). It is therefore likely that Laminaria hyperborea recruitment will be impaired at a sustained temperature increase of above 17°C. Sporophytes however can tolerate slightly higher temperatures of 20°C. Temperature tolerances for Laminaria hyperborea are also seasonally variable and temperature changes are less tolerated in winter months than summer months (Birkett et al., 1998).

Subtidal red algae are less tolerant of temperature extremes than intertidal red algae, surviving between -2°C and 18-23°C (Lüning 1990; Kain & Norton, 1990). Temperature increase may affect growth, recruitment or interfere with reproduction processes. For example, there is some evidence to suggest that blade growth in Delesseria sanguinea is delayed until ambient sea temperatures fall below 13°C. Blade growth is also likely to be intrinsically linked to gametangia development (Kain, 1987), maintenance of sea temperatures above 13°C may affect recruitment success.

IR.LIR.K.LhypCape is distributed along the west coast of the UK from Orkney to South West Ireland; however records are concentrated in the North West of Scotland (Connor et al., 2004). Northern to southern Sea Surface Temperature (SST) ranges from 8-16°C in summer and 6-13°C in winter (Beszczynska-Möller & Dye, 2013).

The available evidence suggests that combined with southern sea temperatures an increase of temperature of 5°C over a period of 1 month would not inhibit recruitment, however may be outside of the optimal range for spore production and/or settlement as well as negatively affect sporophyte growth. An increase in 2°C over a period of a year may similarly negatively affect Laminaria hyperborea recruitment processes in southern biotopes. Northern examples of IR.LIR.K.LhypCape (where most records are concentrated) are unlikely to be affected at the benchmark level.

Sensitivity assessment. Overall, a chronic change (2°C for a year) outside normal range for a year may reduce recruitment and growth, resulting in a minor loss in the population of kelp, especially in winter months or in southern examples of the biotope. However, an acute change (5°C for a month; e.g. from thermal effluent) may result in loss of abundance of kelp or extent of the bed, especially in winter. Therefore, resistance to the pressure is considered ‘Medium’, and resilience ‘Medium’. The sensitivity of this biotope to increases in temperature has been assessed as ‘Medium’.

Temperature decrease (local)

Benchmark. A 5°C decrease in temperature for one month, or 2°C for one year. Further detail

Evidence

Kain (1964) stated that Laminaria hyperborea sporophyte growth and reproduction could occur within a temperature range of 0 -20°C. Upper and lower lethal temperatures have been estimated at between 1-2°C above or below the extremes of this range (Birkett et al., 1988). Subtidal red algae can survive at temperatures between -2°C and 18-23°C (Lüning, 1990; Kain & Norton, 1990).

Laminaria hyperborea is a boreal/northern species with a geographic range from mid Portugal to northern Norway (Birket et al., 1998), and a mid range within southern Norway (60°-65° North) (Kain, 1971). The average seawater temperature for southern Norway in October is 12-13°C (Miller et al., 2009), and average annual sea temperature, from 1970-2014, is 8°C (Beszczynska-Möller & Dye, 2013). The available information suggests that Laminaria hyperborea and habitat structure would not be affected, and may benefit from a water temperature decrease of 5°C over a month or 2°C for one year.

Sensitivity assessment. Resistance to the pressure is considered ‘High’, and resilience ‘High’. The sensitivity of this biotope to decreases in temperature has been assessed as ‘Not Sensitive’.

Salinity increase (local)

Benchmark. A increase in one MNCR salinity category above the usual range of the biotope or habitat. Further detail

Evidence

Lüning (1990) suggest that ‘kelps’ are stenohaline, their general tolerance to salinity as a phenotypic group covering 16 -50 psu over a 24 hr period. Optimal growth probably occurs between 30 -35 psu (MNCR category ‘Full’ salinity) and growth rates are likely to be affected by periodic salinity stress. Birkett et al. (1998) suggests that long-term increases in salinity may affect Laminaria hyperborea growth and may result in loss of affected kelp, and therefore loss of the biotope.

Sensitivity assessment. Resistance to the pressure is considered ‘Low’, and resilience ‘Medium’. The sensitivity of this biotope to an increase in salinity has been assessed as ‘Medium’.

Salinity decrease (local)

Benchmark. A decrease in one MNCR salinity category above the usual range of the biotope or habitat. Further detail

Evidence

Lüning (1990) suggest that ‘kelps’ are stenohaline, their general tolerance to salinity as a phenotypic group covering 16 - 50 psu over a 24 hr period. Optimal growth probably occurs between 30-35 psu (MNCR category-Full Salinity) and growth rates are likely to be affected by periodic salinity stress. Birkett et al,. (1998) suggest that long-term changes in salinity may result in loss of affected kelp and, therefore loss of this biotope.

Hopkin & Kain (1978) tested Laminaria hyperborea sporophyte growth at various low salinity treatments. The results showed that Laminaria hyperborea sporophytes could grow ‘normally’ at 19 psu, growth was reduced at 16 psu and did not grow at 7 psu. A decrease in one MNCR salinity scale from Full Salinity (30-40psu) to Reduced Salinity (18-30 psu) would result in a decrease of Laminaria hyperborea sporophyte growth.

If salinity was returned to Full Salinity (30-40 psu) Laminaria hyperborea could out-compete Saccharina latissma and re-establish community dominance in 2-4 years (Kain, 1975; Leinaas & Christie, 1996), however full habitat structure may take over 10 years to recover (Birkett et al., 1998; Cristie et al., 1998). The ability of Laminaria hyperborea to out-compete Undaria pinnatifida within the UK is however unknown (Heiser et al., 2014), and as such interspecific interaction between Laminaria hyperborea and Undaria pinnatifida is not included within this sensitivity assessment.

Sensitivity assessment. Resistance to the pressure is considered ‘Low’, and resilience ‘Medium’. The sensitivity of this biotope to decreases in salinity has been assessed as ‘Medium’.

Water flow (tidal current) changes (local)

Benchmark. A change in peak mean spring bed flow velocity of between 0.1 m/s to 0.2 m/s for more than one year. Further detail

Evidence

Cape-form Laminaria hyperborea (Laminaria hyperborea f. cucullata) is a growth form of Laminaria hyperborea found in extremely sheltered habitats, such as sea lochs. At a sheltered location in southern Norway, Svendsen & Kain (1971) transplanted six cape-form Laminaria hyperborea from 15 m Below Chart Datum (BCD) to 0.5 m BCD. After six months none of the cape-form Laminaria hyperborea had survived at 0.5m and only their holdfasts were still present. Svendsen & Kain (1971) noted whilst transporting the six cape-form Laminaria hyperborea, the cape-form fronds were very fragile and often ruptured under their own weight. Svendsen & Kain (1971) suggested increased wave action at 0.5 m was the reason why none of the cape-form Laminaria hyperborea survived beyond six months. Although the wave exposure at the site was not formally tested, this evidence suggests that cape-form Laminaria hyperborea is highly sensitive to physical disturbance e.g. from water movement (wave action and/or tidal movement).

Sensitivity assessment. IR.LIR.K.LhypCape occurs exclusively in tidal streams of <0.5 m/s. An increase in tidal streams >0.5 m may lead to significant mortality of cape-from Laminaria hyperborea and resultant loss of the characteristic species which defines this biotope.  Laminaria hyperborea can however recover within a period of 2-4 years. Resistance to the pressure is considered ‘None’, and resilience ‘Medium’. The sensitivity of this biotope to changes in peak mean spring bed velocity has been assessed as ‘Medium’.

Emergence regime changes

Benchmark.  1) A change in the time covered or not covered by the sea for a period of ≥1 year or 2) an increase in relative sea level or decrease in high water level for ≥1 year. Further detail

Evidence

The upper limit of the Laminaria hyperborea bed is determined by wave action and water flow, desiccation, and competition from the emergence resistant Laminaria digitata. Laminaria hyperborea exposed at extreme low water are very intolerant of desiccation, the most noticeable effect being bleaching of the frond and subsequent death of the meristem and loss of the plant.

Cape-form Laminaria hyperborea (Laminaria hyperborea f. cucullata) is found from ca 4-25 m BCD (Svendsen & Kain, 1971; Connor et al., 2004). Svendsen & Kain (1971) conducted a transplantation experiment to observe if cape-form fronds (of cape-form Laminaria hyperborea) were a phenotypic response of Laminaria hyperborea to low water movement. At a sheltered location in southern Norway, six cape-form Laminaria hyperborea were transplanted from 15 m Below Chart Datum (BCD) to 0.5 m BCD and ten Laminaria hyperborea vice versa. After six months none of the cape-form Laminaria hyperborea had survived at 0.5 m and only their holdfasts were still present. Of the ten Laminaria hyperborea transplanted to 15 m BCD, four survived and produced cape-form fronds. Svendsen & Kain (1971) noted whilst transporting the six cape-form Laminaria hyperborea, the cape-form fronds were very fragile and often ruptured under their own weight. Svendsen & Kain (1971) suggested increased wave action at 0.5 m was the reason why none of the cape-form Laminaria hyperborea survived beyond six months. Although the wave exposure at the site was not formally tested, this evidence suggests that cape-form Laminaria hyperborea is highly sensitive to physical disturbance e.g. from water movement (wave action and/or tidal movement).

Sensitivity assessment. Increased emergence is likely to lead to high mortality of Laminaria hyperborea through desiccation. Increased wave action in shallow water (0.5 m BCD) may also cause high mortality of shallow water example of the cape-form Laminaria hyperborea biotope. Resistance to the pressure is considered ‘None’, and resilience ‘Medium’. The sensitivity of this biotope to changes in tidal emergence has been assessed as ‘Medium’.

Wave exposure changes (local)

Benchmark. A change in near shore significant wave height of >3% but <5% for more than one year. Further detail

Evidence

Cape-form Laminaria hyperborea (Laminaria hyperborea f. cucullata) is a growth form of Laminaria hyperborea found in extremely sheltered habitats, such as Scottish sea lochs or Irish sea loughs. Cape-form Laminaria hyperborea (Laminaria hyperborea f. cucullata) is a growth form of Laminaria hyperborea found in extremely sheltered habitats, such as sea lochs. At a sheltered location in southern Norway, Svendsen & Kain (1971) transplanted six cape-form Laminaria hyperborea from 15 m Below Chart Datum (BCD) to 0.5 m BCD. After six months none of the cape-form Laminaria hyperborea had survived at 0.5 m and only their holdfasts were still present. Svendsen & Kain (1971) noted whilst transporting the six cape-form Laminaria hyperborea, the cape-form fronds were very fragile and often ruptured under their own weight. Svendsen & Kain (1971) suggested increased wave action at 0.5 m was the reason why none of the cape-form Laminaria hyperborea survived beyond six months. Although the wave exposure at the site was not formally tested, this evidence suggests that cape-form Laminaria hyperborea is highly sensitive to physical disturbance e.g. from water movement (wave action and/or tidal movement).

Svendsen & Kain (1971) suggested that the cape-form Laminaria hyperborea was highly sensitive to physical disturbance, e.g. from water movement. IR.LIR.K.LhypCape occurs exclusively within sheltered-extremely wave sheltered sites. Sheltered sites have a maximum wind fetch of 20 km, and typically experience negligible wave exposure (Connor et al., 2004). At sheltered sites, which experience higher wave exposure than extremely sheltered sites, cape-form Laminaria hyperborea can still persist but not in shallow water (<6 m, Svendsen & Kain 1971). An increase in nearshore significant wave height may therefore lead to significant mortality of cape-from Laminaria hyperborea in shallow water (0-5 m BCD) and therefore dramatically change the biotope structure of IR.LIR.K.LhypCape.

Sensitivity assessment. Resilience of IR.LIR.K.LhypCape to changes in wave height is based on Laminaria hyperborea recovery following commercial harvesting and information on life history traits (see resilience section for evidence base). Resistance to the pressure is considered ‘None’, and resilience ‘Medium’. The sensitivity of this biotope to changes in peak mean spring bed velocity has been assessed as ‘Medium’.

Transition elements & organo-metal contamination

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

This pressure is Not assessed but evidence is presented where available.

Bryan (1984) suggested that the general order for heavy metal toxicity in seaweeds is: Organic Hg > inorganic Hg > Cu > Ag > Zn > Cd > Pb. Cole et a,. (1999) reported that Hg was very toxic to macrophytes. Similarly, Hopkin & Kain (1978) demonstrated sub-lethal effects of heavy metals on Laminaria hyperborea gametophytes and sporophytes, including reduced growth and respiration. Sheppard et al., (1980) noted that increasing levels of heavy metal contamination along the west coast of Britain reduced species number and richness in holdfast fauna, except for suspension feeders which became increasingly dominant. Gastropods may be relatively tolerant of heavy metal pollution (Bryan, 1984). Echinus esculentus recruitment is likely to be impaired by heavy metal contamination due to the intolerance of its larvae. Echinus esculentus are long-lived and poor recruitment may not reduce grazing pressure in the short-term. Although macroalgae species may not be killed, except by high levels of contamination, reduced growth rates may impair the ability of the biotope to recover from other environmental disturbances.

Hydrocarbon & PAH contamination

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

This pressure is Not assessed but evidence is presented where available

Laminaria hyperborea fronds, being almost exclusively subtidal, would not come into contact with freshly released oil, but only to sinking emulsified oil and oil adsorbed onto particles (Birket et al., 1998). The mucilaginous slime layer coating of laminarians may protect them from smothering by oil. Hydrocarbons in solution reduce photosynthesis and may be algicidal. However, Holt et al,. (1995) reported that oil spills in the USA and from the Torrey Canyon had little effect on kelp forest. Similarly, surveys of subtidal communities at a number sites between 1 -22.5 m below chart datum, including Laminaria hyperborea communities, showed no noticeable impacts of the Sea Empress oil spill and clean up (Rostron & Bunker, 1997). An assessment of holdfast fauna in Laminaria showed that although species richness and diversity decreased with increasing proximity to the Sea Empress oil spill, overall the holdfasts contained a reasonably rich and diverse fauna, even though oil was present in most samples (Sommerfield & Warwick, 1999). Laboratory studies of the effects of oil and dispersants on several red algae species, including Delesseria sanguinea (Grandy 1984; cited in Holt et al., 1995) concluded that they were all sensitive to oil/ dispersant mixtures, with little differences between adults, sporelings, diploid or haploid life stages. Holt et al., (1995) concluded that Delesseria sanguinea is probably generally sensitive of chemical contamination. Overall the red algae are likely to be highly intolerant to hydrocarbon contamination. Loss of red algae is likely to reduce the species richness and diversity of the biotope and the understorey may become dominated by encrusting corallines; however, red algae are likely to recover relatively quickly.

Synthetic compound contamination

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

This pressure is Not assessed but evidence is presented where available

O'Brien & Dixon (1976) suggested that red algae were the most sensitive group of macrophytes to oil and dispersant contamination (see Smith, 1968). Although Laminaria hyperborea sporelings and gametophytes are intolerant of atrazine (and probably other herbicides) overall they may be relatively tolerant of synthetic chemicals (Holt et al., 1995). Laminaria hyperborea survived within >55 m from the acidified halogenated effluent discharge polluting Amlwch Bay, Anglesey, albeit at low density. These specimens were greater than 5 years of age, suggesting that spores and/or early stages were more intolerant (Hoare & Hiscock, 1974). Patella pellucida was excluded from Amlwch Bay by the pollution and the species richness of the holdfast fauna decreased with proximity to the effluent discharge; amphipods were particularly intolerant although polychaetes were the least affected (Hoare & Hiscock, 1974). The richness of epifauna/flora decreased near the source of the effluent and epiphytes were absent from Laminaria hyperborea stipes within Amlwch Bay. The red alga Phyllophora membranifolia was also tolerant of the effluent in Amlwch Bay. Smith (1968) also noted that epiphytic and benthic red algae were intolerant of dispersant or oil contamination due to the Torrey Canyon oil spill; only the epiphytes Crytopleura ramosa and Spermothamnion repens and some tufts of Jania rubens survived together with Osmundea pinnatifida, Gigartina pistillata and Phyllophora crispa from the sublittoral fringe. Delesseria sanguinea was probably to most intolerant since it was damaged at depths of 6m (Smith, 1968). Holt et al., (1995) suggested that Delesseria sanguinea is probably generally sensitive of chemical contamination. Although Laminaria hyperborea may be relatively insensitive to synthetic chemical pollution, evidence suggests that grazing gastropods, amphipods and red algae are sensitive. Loss of red algae is likely to reduce the species richness and diversity of the biotope and the understorey may become dominated by encrusting corallines; however, red algae are likely to recover relatively quickly.

Radionuclide contamination

Benchmark. An increase in 10µGy/h above background levels. Further detail

Evidence

No evidence

Introduction of other substances

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

This pressure is Not assessed.

De-oxygenation

Benchmark. Exposure to dissolved oxygen concentration of less than or equal to 2 mg/l for one week (a change from WFD poor status to bad status). Further detail

Evidence

Reduced oxygen concentrations have been shown to inhibit both photosynthesis and respiration in macroalgae (Kinne, 1977). Despite this, macroalgae are thought to buffer the environmental conditions of low oxygen, thereby acting as a refuge for organisms in oxygen depleted regions especially if the oxygen depletion is short-term (Frieder et al., 2012).  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. However, small invertebrate epifauna may be lost, causing a reduction in species richness. Therefore a resistance of ‘High’ is recorded. Resilience is likely to be ‘High’, and the biotopes is probably ‘Not sensitive’ at the benchmark level.

Nutrient enrichment

Benchmark. Compliance with WFD criteria for good status. Further detail

Evidence

This biotope is considered to be 'Not sensitive' at the pressure benchmark, that assumes compliance with good status as defined by the WFD.

Holt et al. (1995) suggest that Laminaria hyperborea may be tolerant of nutrient enrichment since healthy populations are found at ends of sublittoral untreated sewage outfalls in the Isle of Man. Increased nutrient levels e.g. from sewage outfalls, has been associated with increases in abundance, primary biomass and Laminaria hyperborea stipe production but with concomitant decreases in species numbers and diversity (Fletcher, 1996).

Increased nutrients may result in phytoplankton blooms that increase turbidity (see above). Increased nutrients may favour sea urchins, e.g. Echinus esculentus, due their ability to absorb dissolved organics, and result in increased grazing pressure leading to loss of understorey epiflora/fauna, decreased kelp recruitment and possibly 'urchin barrens'. Therefore, although nutrients may not affect kelps directly, indirect effects such as turbidity, siltation and competition may significantly affect the structure of the biotope.

Organic enrichment

Benchmark. A deposit of 100 gC/m²/yr. Further detail

Evidence

Holt et al. (1995) suggest that Laminaria hyperborea may tolerate organic enrichment since healthy populations are found at the ends of sublittoral untreated sewage outfalls in the Isle of Man. Increased nutrient levels e.g. from sewage outfalls, have been associated with increases in abundance, primary biomass and Laminaria hyperborea stipe production but with concomitant decreases in species numbers and diversity (Fletcher, 1996). Increased ephemeral and opportunistic algae are associated with reduced numbers of perennial macrophytes (Fletcher, 1996). Increased nutrients may also result in phytoplankton blooms that increase turbidity. Therefore, although nutrients may not affect kelps directly, indirect effects such as turbidity may significantly affect the structure of Laminaria hyperborea biotopes.

Sensitivity assessment. Resistance to the pressure is considered ‘Medium’, and resilience ‘High’. The sensitivity of this biotope to organic enrichment is assessed as ‘Low’.

Physical loss (to land or freshwater habitat)

Benchmark. A permanent loss of existing saline habitat within the site. Further detail

Evidence

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.

Physical change (to another seabed type)

Benchmark. Permanent change from sedimentary or soft rock substrata to hard rock or artificial substrata or vice-versa. Further detail

Evidence

If rock substrata were replaced with sedimentary substrata this would represent a fundamental change in habitat type, which Laminaria hyperborea would not be able to tolerate (Birket et al., 1998). The biotope would be lost.

Sensitivity assessment. Resistance to the pressure is considered ‘None’, and resilience ‘Very Low’ or None. The sensitivity of this biotope to change from sedimentary or soft rock substrata to hard rock or artificial substrata or vice-versa is assessed as ‘High’.

Physical change (to another sediment type)

Benchmark. Permanent change in one Folk class (based on UK SeaMap simplified classification). Further detail

Evidence

Not relevant to bedrock biotopes.

Habitat structure changes - removal of substratum (extraction)

Benchmark. The extraction of substratum to 30 cm (where substratum includes sediments and soft rock but excludes hard bedrock). Further detail

Evidence

The species characterizing this biotope are epifauna or epiflora occurring on rock and would be sensitive to the removal of the habitat. However, extraction of rock substratum is considered unlikely and this pressure is considered to be ‘Not relevant’ to hard substratum habitats.

Abrasion / disturbance of the surface of the substratum or seabed

Benchmark. Damage to surface features (e.g. species and physical structures within the habitat). Further detail

Evidence

Svendsen & Kain (1971) conducted a transplantation experiment to observe if cape-form fronds (of cape-form Laminaria hyperborea) were a phenotypic response of Laminaria hyperborea to low water movement. At a sheltered location in southern Norway, six cape-form Laminaria hyperborea were transplanted from 15 m below Chart Datum (BCD) to 0.5 m BCD and ten Laminaria hyperborea vice versa. After six months none of the cape-form Laminaria hyperborea had survived at 0.5 m and only their holdfasts were still present. Of the ten Laminaria hyperborea transplanted to 15 m BCD, four survived and produced cape-form fronds. Svendsen & Kain (1971) noted whilst transporting the six cape-form Laminaria hyperborea, the cape-form fronds were very fragile and often ruptured under their own weight. Svendsen & Kain (1971) therefore indicates that cape-form Laminaria hyperborea would be highly sensitive to abrasion.

Resilience of IR.LIR.K.LhypCape to abrasion is based on Laminaria hyperborea recovery following commercial harvesting and information on life history traits (see resilience section for evidence base).

Sensitivity assessment. The cape form of Laminaria hyperborea is particularly fragile and susceptible to physical disturbance (Svendsen & Kain, 1971). Loss of this distinctive characterizing species would result in loss of the biotope. Therefore resistance to the pressure is considered ‘None’, and resilience ‘Medium’. The sensitivity of this biotope to damage to seabed surface features is assessed as ‘Medium’.

Penetration or disturbance of the substratum subsurface

Benchmark. Damage to sub-surface features (e.g. species and physical structures within the habitat). Further detail

Evidence

Not relevant, please refer to pressure ‘Abrasion/disturbance of the substratum on the surface of the seabed’.

Changes in suspended solids (water clarity)

Benchmark. A change in one rank on the WFD (Water Framework Directive) scale e.g. from clear to intermediate for one year. Further detail

Evidence

Suspended Particle Matter (SPM) concentration has a linear relationship with sub-surface light attenuation (Kd) (Devlin et al., 2008). An increase in SPM results in a decrease in sub-surface light attenuation. Light availability and water turbidity are principal factors in determining kelp depth range (Birkett et al., 1998). Light penetration influences the maximum depth at which kelp species can grow and it has been reported that laminarians grow down to 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 6-7 m 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 Laminaria hyperborea 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 (Birkett et al. 1998b; Lüning, 1990).

Laminaria spp. 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). An increase in water turbidity will likely affect the photosynthetic ability of Laminaria hyperborea and Laminaria ochroleuca and decrease Laminaria hyperborea abundance and density (see sub-biotope- IR.MIR.KR.Lhyp.Pk). Kain (1964) suggested that early Laminaria hyperborea gametophyte development could occur in the absence of light. Furthermore, observations from south Norway found that a pool of Laminaria hyperborea recruits could persist growing beneath Laminaria hyperborea canopies for several years, indicating that sporophyte growth can occur in light-limited environments (Christe et al., 1998). However in habitats exposed to high levels of suspended silts Laminaria hyperborea is out-competed by Saccharina latissima, a silt tolerant species, and thus, a decrease in water clarity is likely to decrease the abundance of Laminaria hyperborea in the affected area (Norton, 1978).

Sensitivity Assessment. Changes in water clarity are likely to affect photosynthetic rates and enable Saccharina latissima to compete more successfully with Laminaria hyperborea.  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 clarity from clear to intermediate (10-100 mg/l) represents a change in light attenuation of ca 0.67-6.7 Kd/m, and is likely to result in a greater than 50% reduction in photosynthesis of Laminaria spp. Therefore, as this biotope occurs in the vicinty of sediments and is already silted, the dominant kelp species will probably suffer a significant decline and resistance to this pressure is assessed as ‘None’. Resilience to this pressure is probably ‘Medium’ at the benchmark.  Hence, this biotope is assessed as having a sensitivity of ‘Medium ‘to this pressure.

Smothering and siltation rate changes (light)

Benchmark. ‘Light’ deposition of up to 5 cm of fine material added to the seabed in a single discrete event. Further detail

Evidence

Smothering by sediment e.g. 5 cm material during a discrete event, is unlikely to directly damage cape-form Laminaria hyperborea plants but inundation of sediment is likely to provide a barrier which may inhibit zoospore settlement and affect gametophyte survival (Birkett et al., 1998). Given the microscopic size of the gametophyte, 5 cm of sediment could be expected to significantly inhibit growth. Laboratory studies showed that Laminaria hyperborea gametophytes survived darkness for between 6 - 16 months at 8 °C and would probably survive smothering by a discrete event. Once returned to normal conditions the gametophytes resumed growth or maturation within 1 month (Dieck, 1993). IR.LIR.K.LhypCape is generally typified by low water movement (low wave and tidal exposure) and often found in close proximity to silted or muddy biotopes e.g. CR.LCR.BrAs.AmenCio and SS.SMu.CSaMu.VirOphPmax (Connor et al., 2004). Deposited sediments may therefore be retained within the resident habitat for numerous tidal cycles, and could affect kelp recruitment and the survival of the understorey community (Birkett et al., 1998). Laminaria hyperborea can live for greater than 10 years (Pederson et al., 2012) and is therefore likely to persist following ‘Light’ deposition of up to 5 cm of fine material added to the seabed in a single, discrete event, however Laminaria hyperborea recruitment processes may be negatively affected and the understorey community be denuded until the sediment is cleared. Following clearance of deposited sediment Laminaria hyperborea populations and the understorey communities are expected to recover quickly.

Sensitivity assessment. Resistance to the pressure is considered ‘High’, and resilience ‘High’. The sensitivity of this biotope to light deposition of up to 5cm of fine material added to the seabed in a single discreet event is assessed as ‘Low’.

Smothering and siltation rate changes (heavy)

Benchmark. ‘Heavy’ deposition of up to 30 cm of fine material added to the seabed in a single discrete event. Further detail

Evidence

Cape-form Laminaria hyperborea stipe is described as short, normally less than 50cm long (Svendsen & Kain 1971). Smothering by sediment e.g. 30 cm material during a discrete event, may inundate entire plants for extended periods and cause mortality of Laminaria hyperborea. Heavy deposition would also provide a barrier which may inhibit zoospore settlement and affect gametophyte survival (Birkett et al., 1998). Given the microscopic size of the gametophyte, 30 cm of sediment could be expected to significantly inhibit growth. Laboratory studies showed that Laminaria hyperborea gametophytes survived darkness for between 6 - 16 months at 8 °C and would probably survive smothering by a discrete event. Once returned to normal conditions the gametophytes resumed growth or maturation within 1 month (Dieck, 1993). The understorey epifauna/flora may be adversely affected, e.g. suspension or filter feeding fauna and/or algal species. If clearance of deposited sediment occurs rapidly then understorey communities are expected to recover quickly.

Due to the short length of cape-form Laminaria hyperborea stipes (normally <50 cm) a large number of plants may be inundated by a ‘heavy’ deposition of up to 30 cm of fine material added to the seabed in a single discrete event. Inundation is also likely to smother the understorey red seaweed and faunal community plus inhibt Laminaria hyperborea photosynthesis and respiration. IR.LIR.K.LhypCape is a low energy habitat in which deposited sediments are likely to remain within the habitat for numerous tidal cycles. Once the sediment is removed however Laminaria hyperborea has been shown to recover within 2-6 years (Kain, 1975; Leinaas & Christie, 1996). The associated understorey community of red seaweeds is expected to recover relatively quickly.

Sensitivity assessment. Resistance to the pressure is considered ‘Low’, and resilience ‘Medium’. The sensitivity of this biotope to heavy deposition of up to 30 cm of fine material added to the seabed in a single discreet event is assessed as ‘Medium’.

Litter

Benchmark. The introduction of man-made objects able to cause physical harm (surface, water column, seafloor or strandline). Further detail

Evidence

Not assessed. There is no evidence to suggest that litter would affect Laminaria hyperborea or associated habitats.

Electromagnetic changes

Benchmark. A local electric field of 1 V/m or a local magnetic field of 10 µT. Further detail

Evidence

No evidence

Underwater noise changes

Benchmark. MSFD indicator levels (SEL or peak SPL) exceeded for 20% of days in a calendar year. Further detail

Evidence

Macroalgae have no hearing perception but vibrations may cause an impact, however no studies exist to support an assessment. Sensitivity has been assessed as ‘No evidence’.

Introduction of light or shading

Benchmark. A change in incident light via anthropogenic means. Further detail

Evidence

There is no evidence to suggest that anthropogenic light sources would affect Laminaria hyperborea. 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 laminarian abundance from forest to park type biotopes.

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.

Barrier to species movement

Benchmark. A permanent or temporary barrier to species movement over ≥50% of water body width or a 10% change in tidal excursion. Further detail

Evidence

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.

Death or injury by collision

Benchmark. Injury or mortality from collisions of biota with both static or moving structures due to 0.1% of tidal volume on an average tide, passing through an artificial structure. Further detail

Evidence

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

Visual disturbance

Benchmark. The daily duration of transient visual cues exceeds 10% of the period of site occupancy by the feature. Further detail

Evidence

Not relevant

Genetic modification & translocation of indigenous species

Benchmark. Translocation of indigenous species or the introduction of genetically modified or genetically different populations of indigenous species that may result in changes in the genetic structure of local populations, hybridization, or change in community structure. Further detail

Evidence

No evidence regarding the genetic modification or effects of translocation of native populations was found.

Introduction or spread of invasive non-indigenous species

Benchmark. The introduction of one or more invasive non-indigenous species (INIS). Further detail

Evidence

Undaria pinnatifida has received a large amount of research attention as a major Invasive Non-Indigenous Species (INIS) which could out-compete native UK kelp habitats (see Farrell & Fletcher, 2006; Thompson & Schiel, 2012, Brodie et al., 2014; Hieser et al., 2014). Undaria pinnatifida was first recorded in the UK, Hamble Estuary, in June 1994 (Fletcher & Manfredi, 1995) and has since spread to a number of British ports. Undaria pinnatifida is an annual species, sporophytes appear in Autumn and grow rapidly throughout winter and spring during which they can reach a length of 1.65 m (Birkett et al., 1998). Farrell & Fletcher (2006) suggested that native short-lived species that occupy similar ecological niches to Undaria pinnatifida, such as Saccharina latissima, Saccorhiza polyschides or Desmarestia spp., are likely to be worst affected and out-competed by Undaria pinnatifida. Where present an abundance of Undaria pinnatifida has corresponded to a decline in Saccharina lattisima (Farrell & Fletcher, 2006) and Laminaria hyperborea (Hieser et al., 2014).

In New Zealand, Thompson & Schiel (2012) observed that native fucoids could out-compete Undaria pinnatifida and re-dominate the substratum. However, Thompson & Schiel (2012) suggested the fucoid recovery was partially due to an annual Undaria pinnatifida dieback, which as noted by Heiser et al. (2014) does not occur in Plymouth Sound, UK. Undaria pinnatifida was successfully eradicated on a sunken ship in Chatham Islands, New Zealand, by applying a heat treatment of 70°C (Wotton et al., 2004) however numerous other eradication attempts have failed, and as noted by Farrell & Fletcher (1999), once established Undaria pinadifida resists most attempts of long-term removal. The biotope is unlikely to fully recover until Undaria pinnatifida is fully removed from the habitat, which as stated above is unlikely to occur.

The carpet sea squirt Didemnum vexillum (syn. Didemnum vestitum; Didemnum vestum) is a colonial ascidian with rapidly expanding populations that have invaded most temperate coastal regions around the world (Kleeman, 2009; Stefaniak et al., 2012; Tillin et al., 2020). It is an ‘ecosystem engineer’ that can change or modify invaded habitats and alter biodiversity (Griffith et al., 2009; Mercer et al., 2009). Didemnum vexillum has colonized and established populations in the northeast Pacific, Canadian and USA coast; New Zealand; France, Spain, and the Wadden Sea, Netherlands; the Mediterranean Sea and Adriatic Sea (Bullard et al., 2007; Coutts & Forrest, 2007; Dijkstra et al., 2007; Valentine et al., 2007a; Valentine et al., 2007b; Lambert, 2009; Hitchin, 2012; Tagliapietra et al., 2012; Gittenberger et al., 2015; Vercaemer et al., 2015; Mckenzie et al., 2017; Cinar & Ozgul, 2023; Holt, 2024). In the UK, Didemnum vexillum has colonized Holyhead marina and Milford Haven, Wales; the west coast of Scotland (marinas around Largs, Clyde, Loch Creran and Loch Fyne), South Devon (Plymouth, Yealm, and Dartmouth estuaries), the Solent, northern Kent, Essex, and Suffolk coasts (Griffith et al., 2009; Lambert, 2009; Hitchin, 2012; Michin & Nunn, 2013; Bishop et al., 2015; Mckenzie et al., 2017; Tillin et al., 2020, Holt, 2024; NBN, 2024).

Although a widespread invader, Didemnum vexillum has a limited ability for natural dispersal since the pelagic larvae remain in the water column for a short time (up to 36 hours). Therefore, it has a short dispersal phase that can allow the species to build localized populations (Herborg et al., 2009; Vercaemer et al., 2015; Holt, 2024). However, Bullard et al. (2007) suggested that Didemnum vexillum can form new colonies asexually by fragmentation. Colonies can produce long tendrils from an encrusting colony, which can fragment, disperse and settle, attaching to suitable hard substrata elsewhere (Bullard et al., 2007; Lambert, 2009; Stefaniak & Whitlatch, 2014). A fragmented colony can spread naturally for up to three weeks transported by ocean currents, attached to floating seaweed, seagrass or other floating biota, or as free-floating spherical colonies (Bullard et al., 2007; Lengyel et al., 2009; Stefaniak & Whitlatch, 2014; Holt, 2024). Fragments can reattach to suitable substrata within six hours of contact. Fragments have the potential to disperse around 20 km before reattachment (Lengyel et al., 2009). Valentine et al. (2007a) reported that colonies of Didemnum vexillum enlarged by 6 to 11 times by asexual budding after 15 days and enlarged 11 to 19 times after 30 days. Valentine et al. (2007a) concluded fragments could successfully grow, survive, and help to spread Didemnum vexillum.

While natural fragmentation of tendrils is thought to allow Didemnum vexillum to invade longer distances and increase its dispersal potential, Stefaniak & Whitlatch (2014) found that only one tendril out of 80 reattached to the flat, bare substrata used in their study, because tendrils required an extensive (at least eight hour) period of contact to reattach. Stefaniak & Whitlatch (2014) suggested that once fragmented from a colony, the success of tendril reattachment was limited, and reattachment was not a major contributor to the invasive success of Didemnum vexillum. However, Stefaniak & Whitlatch (2014) also found that larvae-packed tendril fragments may increase natural dispersal distance, reproduction, and invasive success of Didemnum vexillum, and increase the distance larvae can travel. Not all colonies produce tendrils at all locations.

Human-meditated transport via aquaculture facilities, boat hulls, commercial fishing vessels, and ballast water is probably the most important vector that has aided the long-distance dispersal of Didemnum vexillum and explains its prevalence in harbours and marinas (Bullard et al., 2007; Dijkstra et al., 2007; Griffith et al., 2009; Herborg et al., 2009). Fragmentation of colonies during transport or human disturbance (such as trawling or dredging) could indirectly disperse the species and enable it to find suitable conditions for establishment (Herborg et al., 2009). For example, in oyster farms in British Columbia, large fragments of Didemnum sp. come off oyster strings when they are pulled out of water and other fragments can be pulled off oysters and mussels and thrown back into the water, which is likely to aid dispersal of the invasive species (Bullard et al., 2007). Dijkstra et al. (2007) hypothesised that Didemnum sp. was introduced to the Gulf of Maine with oyster aquaculture in the Damariscotta River and transported via Pacific oysters.

Didemnum vexillum was likely introduced into the UK from northern Europe or Ireland via poorly maintained or not antifouled vessels, movement of contaminated shellfish stock and aquaculture equipment, or via marine industries such as oil, gas, renewables, and dredging (Holt, 2024). Recent evidence from genetic material suggests that human-mediated dispersal, between marinas and shellfish culture sites, is the most likely pathway for connectivity of Didemnum vexillum populations throughout Ireland and Britain (Prentice et al., 2021; Holt, 2024). Didemnum vexillum can disperse away from artificial substrata, invading and colonizing natural substrata in surrounding areas (Tillin et al., 2020). Holt (2024) noted that Didemnum vexillum had not spread as far as feared in the UK since it was first recorded. The current evidence of Didemnum vexillum’s ability to spread on natural habitats in this area is sparse and often conflicting, complicated by genetics and its apparent variable habitat preferences and tolerances and its variable ability to adapt to ‘new’ conditions (Holt 2024).

Didemnum vexillum has a seasonal growth cycle influenced by temperature (Valentine et al., 2007a). In warmer months (June and July) colonies may be large and well-developed encrusting mats. Populations experience more rapid growth from July to September sometimes continuing into December. Colonies begin to decline in health and ‘die-off’ when temperatures drop below 5°C during winter months from around October to April (Gittenberger, 2007; Valentine et al., 2007a; Herborg et al., 2009). Cold water months cause colonies to regress and reduce in size, yet they often regenerate as temperatures warm (Griffith et al., 2009; Kleeman, 2009, Mercer et al., 2009), although some populations may not survive winter at all (Dijkstra et al., 2007). The early growth phase, from May to July, is initiated by smaller colonies developing from remnants of colonies that survived the cold water (Valentine et al., 2007a). The seasonal growth cycle is also likely influenced by location. For example, the Didemnum sp. growth cycle for colonies in Sandwich tide pool (temperature range from -1 °C to 24 °C, with daily fluctuations), probably does not occur in deep offshore subtidal habitats in Georges Bank (annual temperature range from 4 °C to 15°C, and daily fluctuations are minimal) (Valentine et al., 2007a).  Larval release and recruitment typically occur between 14 to 20°C and slow or cease below 9 to 11°C as summer ends (Griffith et al., 2009; Mckenzie et al., 2017). In New Zealand, recruitment occurs from November to July, where the highest average temperatures were recorded in February (18 to 22°C) and the lowest average temperatures were recorded in July (9 to 10°C) (Fletcher et al., 2013a). In this New Zealand study, higher water temperatures were associated with a higher level of recruitment (Fletcher et al., 2013a).

Didemnum vexillum requires suitable hard substrata for successful settlement and the establishment of colonies. It can grow quickly and establish large colonies of dense encrusting mats on a variety of hard substrata (Valentine et al., 2007a; Griffith et al., 2009; Lambert, 2009; Groner et al., 2011; Cinar & Ozgul, 2023). Gittenberger (2007) stated that invasive Didemnum sp. was a threat to native ecosystems because of its ability to overgrow virtually all hard substrata present. Suitable hard substrata can include rocky substrata such as bedrock gravel, pebble, cobble, or boulders or artificial substrata such as a variety of maritime structures such as pontoons, docks, wood and metal pilings, chains, ropes and moorings, plastic and ship hulls and at aquaculture facilities (Valentine et al., 2007 a&b; Bullard et al., 2007; Griffith et al., 2009; Lambert, 2009; Tagliapietra et al., 2012; Tillin et al., 2020). Didemnum vexillum has been reported colonizing these types of hard substrata in the USA, Canada, northern Kent, and the Solent (Bullard et al., 2007; Valentine et al., 2007a; Valentine et al., 2007b; Hitchin, 2012; Vercaemer et al., 2015; Tillin et al., 2020).

Didemnum vexillum has the ability to rapidly overgrow and displace on other sessile organisms such as other colonial ascidians (Ciona intestinalis, Styela clava, Ascidiella aspera, Botrylloides violaceus, Botryllus schlosseri, Diplosoma listerianium and Aplidium spp.), bryozoan, hydroids, sponges (Clione celata and Halichrondria sp.), anemone (Diadumene cincta), calcareous tube worms, eelgrass (Zostera marina), kelp (Laminaria spp. and Agarum sp.), green algae (Codium fragile subsp. fragile), red algae (Plocamium, Chondrus crispus and bush weed Agardhiella subulata), brown algae (Ascophyllum nodosum, Sargassum, Halidrys, Fucus evanescens and Fucus serratus), calcareous algae (Corallina officinalis), mussels (Mytilus galloprovincialis, Perna canaliculus  and Mytilus edulis), barnacles, oysters (Magallana gigas, Ostrea edulis and Crassostrea virginica), sea scallops (Placopecten magellanicus), or dead shells (Dijkstra et al., 2007; Gittenberger, 2007; Valentine et al., 2007a; Valentine et al., 2007b; Griffith et al., 2009; Carman & Grunden, 2010; Dijkstra & Nolan, 2011; Groner et al., 2011; Hitchin, 2012; Tagliapietra et al., 2012; Minchin & Nunn, 2013; Gittenberger et al., 2015; Long & Groholz, 2015; Vercaemer et al., 2015).

In contrast to Didemnum vexillum’s preference for sheltered conditions, established colonies observed in Georges Bank and Long Island Sound were exposed to moderately strong tidal currents (1 to 2 knots; ca 0.5 to 1 m/s recorded at both sites) that may mobilise sediment (Valentine et al., 2007b; Mercer et al., 2009; Tillin et al., 2020). However, Valentine et al. (2007b) describe the substratum as immobile, presumably consolidated gravel, cobbles and pebbles. Kleeman (2009), stated that the presence of a consistent mild wave action or ‘swash zone’ appears to favour Didemnum sp. establishment in the intertidal. Although some evidence suggests that waves and currents can facilitate the fragmentation and spread of Didemnum vexillum (Mckenzie et al., 2017), the tidal current velocities at some sites where Didemnum vexillum has been reported (for example, New England, where current velocities reach up to around 3 m/s) is lower than the current velocity required for the dislodgement of Didemnum vexillum fragments (around 7.6 m/s) (Reinhardt et al., 2012). This suggests that not all tidal currents are likely to dislodge Didemnum vexillum fragments. When on boat hulls the species can experience higher current velocities which is enough to cause dislodgement (Reinhardt et al., 2012).  

Sensitivity assessment. Resistance to this invasion by Undaria is considered ‘Low’, and resilience ‘Very low’ as the invasive would need to be removed to allow recovery. The sensitivity of this biotope to invasion by Undaria is assessed as ‘High’ but with 'Low' confidence due to the lack of direct evidence. 

There is no evidence of Didmenum vexillum colonizing this biotope in the UK. Didemnum vexillum requires hard substrata for successful colonization, therefore, it could colonize the bedrock and boulders which characterize this biotope. Also, Didemnum vexillum prefers wave-sheltered conditions and has been recorded in the lower intertidal. Didemnum vexillum can overgrow sessile organisms, including kelp species Laminaria sp. and Agarum sp. However, no evidence was found on how Didemnum vexillum affects kelp or if it contributes to kelp mortality. However, Didemnum vexillum may compete for light and space with kelp and epifauna and potentially interfere with recruitment, which could lead to the mortality of some species and a reduction in biodiversity. Therefore, a resistance of 'Medium' (some mortality, <25%) is suggested as a precaution. Resilience is likely to be 'Very low' as Didemnum vexillum would need to be physically removed to allow recovery. Hence, sensitivity to invasion by Didemnum is assessed as 'Medium'.

Introduction of microbial pathogens

Benchmark. The introduction of relevant microbial pathogens or metazoan disease vectors to an area where they are currently not present (e.g. Martelia refringens and Bonamia, Avian influenza virus, viral Haemorrhagic Septicaemia virus). Further detail

Evidence

Galls on the blade of Laminaria hyperborea and spot disease are associated with the endophyte Streblonema sp. although the causal agent is unknown (bacteria, virus or endophyte). Resultant damage to the blade and stipe may increase losses in storms. The endophyte inhibits spore production and therefore recruitment and recoverability (Lein et al., 1991).

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

Removal of target species

Benchmark. Removal of species targeted by fishery, shellfishery or harvesting at a commercial or recreational scale. Further detail

Evidence

At the time of writing no evidence could be found on harvesting of cape-form Laminaria hyperborea. As noted by Sjøtun et al. (1998) cape form Laminaria hyperborea plants, on average, have a lower biomass than Laminaria hyperborea from exposed habitats (e.g. IR.HIR.Kfra.LhypR), and is therefore unlikely to be of the same commercial value. Svendsen & Kain (1971) conducted a transplantation experiment to observe if cape-form fronds (of cape-form Laminaria hyperborea) were a phenotypic response of Laminaria hyperborea to low water movement. At a sheltered location in southern Norway, six cape-form Laminaria hyperborea were transplanted from 15 m below Chart Datum (BCD) to 0.5 m BCD and ten Laminaria hyperborea vice versa.  After six months none of the cape-form Laminaria hyperborea had survived at 0.5 m and only their holdfasts were still present. Of the ten Laminaria hyperborea transplanted to 15 m BCD, four survived and produced cape-form fronds. Svendsen & Kain (1971) noted whilst transporting the six cape-form Laminaria hyperborea, the cape-form fronds were very fragile and often ruptured under their own weight. Cape-form Laminaria hyperborea is therefore thought to be extremely fragile and brittle, physical disturbance of any nature is likely to result in mortality.

A number of review and experimental publications have assessed the recovery of Laminaria hyperborea beds and the associated community within high energy habitats. If environmental conditions are favourable Laminaria hyperborea can recover following disturbance events reaching comparable plant densities and size to pristine Laminaria hyperborea beds within 2-6 years (Kain, 1979; Birkett et al., 1998; Christie et al., 1998). Holdfast communities may recover in 6 years (Birkett et al., 1998). Full epiphytic community and stipe habitat complexity regeneration requires over 6 years to recover (possibly 10 years). These recovery rates were based on observations of discrete kelp harvesting events, recurrent disturbance occurring frequently within 2-6 years of the initial disturbance is likely to lengthen recovery time (Birkett et al., 1998; Burrows et al., 2014). Kain (1975) cleared sublittoral blocks of Laminaria hyperborea at different times of the year for several years. The first colonizers and succession community differed between blocks and at what time of year the blocks were cleared however within 2 years of clearance the blocks were dominated by Laminaria hyperborea. Leinaas & Christie (1996) also observed Laminaria hyperborea re-colonization of ‘urchin barrens’, following removal of urchins. The substratum was initially colonized by filamentous macroalgae and Saccharina latissima however after 2-4 years Laminaria hyperborea dominated the community.

Sensitivity assessment. Targeted removal of kelp from this biotope is likely to result in loss of the biotope. Resistance to the pressure is considered ‘None’. However, the resilience is assessed as ‘Medium’ and the sensitivity of this biotope is considered to be ‘Medium’.

Removal of non-target species

Benchmark. Removal of features or incidental non-targeted catch (by-catch) through targeted fishery, shellfishery or harvesting at a commercial or recreational scale. Further detail

Evidence

At the time of writing no evidence could be found on harvesting (incidental or intentional trawling) of cape-form Laminaria hyperborea. As noted by Sjøtun et al., (1998) cape form Laminaria hyperborea plants, on average, have a lower biomass than Laminaria hyperborea from exposed habitats (e.g. IR.HIR.Kfra.LhypR), and is therefore unlikely to be of the same value. Laminaria hyperborea cape form is highly sensitive to any physical disturbance. Incidental/accidental removal of cape-form Laminaria hyperborea as a result of other fisheries e.g. Pectin maximus collection within SS.SMu.CSaMu.VirOphPmax which is often in close proximity to IR.LIR.K.LhypCape (Connor et al., 2004),  is likely to cause similar effects to that of direct harvesting; as such the same evidence has been used for both pressure assessments.

Cape-form Laminaria hyperborea (Laminaria hyperborea f. cucullata) is a growth form of Laminaria hyperborea found in extremely sheltered habitats, such as Scottish sea lochs or Irish Sea Loughs. Svendsen & Kain (1971) conducted a transplant experiment between Laminaria hyperborea and cape-form Laminaria hyperborea. 100% mortality of cape-form Laminaria hyperborea was suggested to be a result of increased wave exposure at the transplanted site. Furthermore in transit to the host site, cape-form Laminaria hyperborea was noted to be extremely brittle and fronds often ruptured under their own weight. Cape-form Laminaria hyperborea is therefore thought to be extremely fragile and brittle, physical disturbance of any nature is likely to result in mortality.

A number of review and experimental publications have assessed the recovery of Laminaria hyperborea beds and the associated community within high energy habitats. If environmental conditions are favourable Laminaria hyperborea can recover following disturbance events reaching comparable plant densities and size to pristine Laminaria hyperborea beds within 2-6 years (Kain, 1979; Birkett et al., 1998; Christie et al., 1998). Holdfast communities may recover in 6 years (Birkett et al., 1998). Full epiphytic community and stipe habitat complexity regeneration requires over 6 years to recover (possibly 10 years). These recovery rates were based on observations of discrete kelp harvesting events, recurrent disturbance occurring frequently within 2-6 years of the initial disturbance is likely to lengthen recovery time (Birkett et al., 1998; Burrows et al., 2014). Kain (1975) cleared sublittoral blocks of Laminaria hyperborea at different times of the year for several years. The first colonizers and succession community differed between blocks and at what time of year the blocks were cleared however within 2 years of clearance the blocks were dominated by Laminaria hyperborea. Leinaas & Christie (1996) also observed Laminaria hyperborea re-colonization of ‘urchin barrens’, following removal of urchins. The substratum was initially colinized by filamentous macroalgae and Saccharina latissima however after 2-4 years Laminaria hyperborea dominated the community.

Sensitivity assessment. Resistance to the pressure is considered ‘None’, and resilience ‘Medium’. Sensitivityhas been assessed as ‘Medium’.