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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

Alaria esculenta on exposed sublittoral fringe bedrock

14-07-2000
Researched byThomas Stamp and Dr Harvey Tyler-Walters Refereed byDr Tim Hill
EUNIS CodeA3.111 EUNIS NameAlaria esculenta on exposed sublittoral fringe bedrock

Summary

UK and Ireland classification

EUNIS 2008A3.111Alaria esculenta on exposed sublittoral fringe bedrock
EUNIS 2006A3.111Alaria esculenta on exposed sublittoral fringe bedrock
JNCC 2004IR.HIR.KFaR.AlaAlaria esculenta on exposed sublittoral fringe bedrock
1997 BiotopeIR.EIR.KFaR.AlaAlaria esculenta on sublittoral fringe bedrock

Description

Alaria esculenta forest on exposed sublittoral fringe bedrock with an encrusting fauna of mussels and barnacles. The rock surface is covered with encrusting coralline red algae. Two variants of this biotope are described. The more wave exposed of the two lacks Laminaria digitata and is also characterized by patches of mussels (EIR.Ala.Myt). The other variant is slightly less exposed and is characterized by a mixture of Alaria esculenta and Laminaria digitata (EIR.Ala.Ldig). (Information from the Marine Biotope Classification for Britain and Ireland, Version 97.06: Connor et al., 1997a, b).

Recorded distribution in Britain and Ireland

Found on wave exposed coasts in the Shetland Isles and Orkney, south east Scotland, north east England, Cornwall, Devon and the Isles of Scilly, Pembrokeshire, Ceredigionshire, north Wales, the Isle of Man, the west coasts of Ireland and Scotland including the Hebrides, St Kilda and Rockall.

Depth range

0-5 m, Lower shore

Additional information

This review of IR.HIR.KFaR.Ala represents the sensitivity of the sub-biotope and similar biotopes IR.HIR.KFaR.Ala.Myt, IR.HIR.KFaR.Ala.Ldig, IR.HIR.KFaR.AlaAnCrSp.

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JNCC

Habitat review

Ecology

Ecological and functional relationships

  • Alaria esculenta is able to out compete other Laminarians in wave exposed sublittoral fringe due to its rapid growth rate and ability to withstand wave exposed conditions. It is particularly successful in exposed areas due to its flexible stipe and narrow, streamlined, blade.
  • Grazers are relatively rare in the sublittoral fringe and canopy interactions may be the most important structuring agency (Hawkins & Hartnoll 1985). The sweeping action of Laminaria digitata, and presumably Alaria esculenta, in wave exposed conditions prevents colonization by ephemeral algae by abrasion (Hawkins & Hartnoll 1985).
  • The understory is dominated by encrusting corallines and Corallina officinalis turf. In wave exposed sites the erect coralline turf grows very compactly reducing the interstitial space (exacerbated by presence of small Mytilids) and affecting the interstitial fauna. Dommanses (1968) showed that the coralline turf fauna varied with wave exposure. Wave exposed sites were dominated by amphipods and short legged isopods capable of grasping the fronds firmly. Interstitial fauna consists of grazers and suspension feeders (Dommaneses 1968) that probably remove ephemeral algae and epiphytes from Corallina officinalis.
  • On Rockall, the extreme wave exposure results in Alaria esculenta forest dominating both the sublittoral and infralittoral zone in the deeper areas. In the Rockall Alaria forest the holdfasts of Alaria esculenta become covered in a thick layer of encrusting coralline algae and, after the death of the alga, the holdfast rots leaving a space under the coralline crust that is a habitat for several mobile species that would most likely not survive on the open rock in such a wave exposed situation (K. Hiscock, pers. comm.).
  • Barnacle species are suspension feeders, that probably take algal spores and larvae that would otherwise settle within the community. Birkett et al. (1998b) point out that active suspension feeding by Mytilus edulis probably removes large numbers of settling algal spores and also compete for space. However in the wave exposed sublittoral fringe, the small size of individual mytilids suggests that larger individuals are removed by wave action.
  • Patellids are active grazers, however, they lack the necessary enzymes to digest Laminarian tissue (Birkett et al. 1998b) and probably do not graze Alaria esculenta extensively. However, they probably graze other algae and are important in keeping coralline turf and encrusting corallines free of ephemeral algae. Grazing activity of patellids probably remove Alaria esculenta and other kelp germlings as the limpets pass over them; a bulldozing effect (T. Hill pers. comm.).
  • Helcion pellucidum may graze Alaria esculenta but prefers Laminaria digitata when present.
  • Chitons were reported to be an important controlling agency in Alaria sp. populations allowing a otherwise weaker competitor to dominate in the north east Pacific (Paine 1980).

Seasonal and longer term change

Alaria esculenta is quite ephemeral in nature and will settle on bare surfaces, including mobile boulders and in deeper water than the infralittoral fringe. Alaria esculenta releases spores between November and March with new sporophytes appearing in early spring (Birkett et al.1998b). Growth of Alaria esculenta slows in June and July and the lamina becomes eroded and torn in the following months. In extremely wave exposed conditions, especially in winter months, the blade may be reduced to just the midrib. Similarly, in wave exposed areas Laminaria digitata is stunted and may be removed by storms and appears tattered in the winter months.

Habitat structure and complexity

Alaria esculenta dominates the sublittoral fringe in areas exposed to severe wave action or where water surges along the sides of gullies (Lewis, 1964). Such wave exposed shores are also characterized by pink encrusting and erect corallines, including Corallina officinalis. This biotope (EIR.Ala) can be divided into two sub-biotopes depending on the degree of wave exposure EIR.Ala.Myt and EIR.Ala.Ldig. Alaria esculenta support few epizoics (e.g. Audouinella alariae on older specimens) and holdfasts yield few species (Lewis 1964; Birkett et al. 1998b). In areas of extreme wave exposure, on steeply sloping rock, exposed to oceanic swell EIR.Ala may extend up to 3 m above and below chart datum (Hiscock 1983).
In EIR.Ala.Myt

As the wave exposure decreases the width of the Alaria esculenta zone narrows and Laminaria digitata is able to invade the sublittoral fringe resulting in a mixed macroalgal stand and increased species richness, characteristic of EIR.Ala.Ldig.

EIR.Ala.Ldig usually occurs above Laminaria hyperborea forest although a narrow zone of Laminaria digitata (MIR.Ldig) may intervene. EIR.Ala.Ldig biotopes probably represents and intermediate community between very wave exposed shores dominated by EIR.Ala.Myt and more wave sheltered shores dominated by MIR.Ldig. On the extremely wave exposed steep and vertical rock faces of Rockall Alaria esculenta replaces Laminaria hyperboreaas the dominant kelp and extends to down to 35m in depth. Above 13m the biotope resembles EIR.Ala.Myt. However, from 14 - 35 m the understory is covered by a dense turf of anemones and encrusting sponges. Cryptopleura ramosa dominates horizontal surfaces. Between 30 -35m the Alaria esculenta thins and the rock surface bears a dense red algal turf.

Productivity

Kelp biotopes are highly productive and contribute up to 90 percent of their primary productivity to the detrital food webs of coastal areas in the form of drift algae, particulate and dissolved organic matter. For example primary productivity of Laminaria hyperborea kelp beds were estimated at 1225 gC/sq. meter/year (Mann 1982 cited in Raffaelli & Hawkins 1999). However, no estimates were found for Alaria esculenta biotopes, though figures are likely to be similar for all kelps (Tim Hill pers. comm.).

Recruitment processes

Laminarians, such as Alaria esculenta, exhibit alternation of generations. The sporophytes releases meiotic haploid spores from sori located on sporophylls (born at the top of the short stipe) between November and March. Laminarian spores need to settle at high density so that the resultant gametophytes are close enough to cross fertilise. Laminarians produce vast numbers of spores and are expected to disperse over considerable distances. However, Sundene (1962) noted that germlings colonized within 10 m of adults in a Norwegian fjord, and Norton (1992) suggested that Alaria esculenta would exhibit less dispersal than other kelp species due to the basal location of the sporophylls. Experiments on algal re-colonization in kelp beds (Kain 1975; Hawkins & Harkin 1985; Hill 1993) show that Alaria esculenta is an opportunistic colonizing species, appearing early in the algal succession (c. 3 months after clearance of dominant algae; especially in areas cleared in the winter months) before being out competed by other kelp species (on moderately exposed shores). Corallina officinalis produces spores over a protracted period and can colonize artificial substratum within one week in the intertidal (Harkin & Lindbergh 1977; Littler & Kauker 1984). The crustose base enables Corallina officinalis to survive extreme exposure and damage (loss of fronds), and to take advantage (colonize) of space left after winter storms have removed competing macroalgae (Littler & Kauker 1984). The mobile interstitial fauna of the coralline turf is reduced by trampling (Brown & Taylor 1989) but is likely to recruit to or recolonize the turf from the surrounding communities. Encrusting and erect corallines are also known to stimulate the settlement of a variety of marine invertebrate larvae and algal spores (e.g. Helcion pellucidum).

Time for community to reach maturity

Alaria esculenta is an opportunistic and rapidly colonizing species (see above) capable of growing 20 cm/month in optimal conditions. In canopy removal experiments in the Isle of Man, Hawkins & Harkin (1985) found that areas cleared of Laminaria digitata (moderately exposed) Alaria esculenta became the dominant canopy algae within 9 months (October - June). Corallina officinalis is capable of colonizing new substratum rapidly. In experimental plots 15 percent cover of fronds returned within 3 months (Littler & Kauker 1985) and Brown & Taylor (1999) noted that the articulated coralline algal turf community on a New Zealand shore returned to normal levels within 3 months of trampling events, although they suggested that a return to its previous cover may take longer.

Additional information

Little information on the sublittoral fringe communities was available. Therefore the material presented in based on the general ecology of the key and important characterizing species.

Preferences & Distribution

Recorded distribution in Britain and IrelandFound on wave exposed coasts in the Shetland Isles and Orkney, south east Scotland, north east England, Cornwall, Devon and the Isles of Scilly, Pembrokeshire, Ceredigionshire, north Wales, the Isle of Man, the west coasts of Ireland and Scotland including the Hebrides, St Kilda and Rockall.

Habitat preferences

Depth Range 0-5 m, Lower shore
Water clarity preferences
Limiting Nutrients Nitrogen (nitrates), Phosphorus (phosphates)
Salinity Full (30-40 psu)
Physiographic Open coast
Biological Zone Sublittoral fringe
Substratum Bedrock, Large to very large boulders
Tidal Moderately Strong 1 to 3 knots (0.5-1.5 m/sec.), Weak < 1 knot (<0.5 m/sec.)
Wave Exposed, Extremely exposed, Very exposed
Other preferences No text entered.

Additional Information

No text entered.

Species composition

Species found especially in this biotope

    Rare or scarce species associated with this biotope

    -

    Additional information

    No text entered

    Sensitivity reviewHow is sensitivity assessed?

    Sensitivity characteristics of the habitat and relevant characteristic species

    IR.HIR.KFaR.Ala and IR.HIR.KFaR.AlaAnCrSp (plus associated sub-biotopes) are characterized by the northern/boreal kelp Alaria esculenta and are indicative of very wave exposed sublittoral bedrock. IR.HIR.KFaR.Ala occurs predominantly on sublittoral fringe bedrock to a depth of 1-2 m. However, at extremely exposed sites wave action can prevent competition from Laminaria hyperborea in the infralittoral zone and the Alaria esculenta defined biotopes IR.HIR.KFaR.Ala.Myt and IR.HIR.KFaR.AlaAnCrSp can extend to a depth of 15-35 m. In slightly less wave exposed conditions Laminaria digitata can compete with Alaria esculenta and in the sub-biotope; IR.HIR.KFaR.Ala.Ldig, the two species form a mixed canopy.

    The understory community beneath Alaria esculenta canopies is defined by the degree of wave exposure at the site.  Common understory species across Alaria esculenta biotopes are encrusting coralline algae and Corallina officinalis turf. IR.HIR.KFaR.AlaAnCrSp has only been recorded on steep/vertical bedrock at Rockall, Scotland. Extreme wave exposure at Rockall excludes Laminaria hyperborea and IR.HIR.KFaR.AlaAnCrSp extends from 14-35 m, and the rock surface is covered by a dense turf of anthozoans such as Sagartia elegans, Phellia gausapata and Corynactis viridis, encrusting sponges and coralline algae.  In the sub-biotope IR.HIR.KFaR.Ala.Myt, Mytillus edulis is an abundant component of the understory, while patches of anthozoans and the hydroid Tubularia spp. occur in more wave-surged areas.  In the mixed Alaria esculenta & Laminaria digitata biotope IR.HIR.KFaR.Ala.Ldig, the red seaweeds; Palmaria palmata, Mastocarpus stellatus and Chondrus crispus are predominant features of the understory.

    In undertaking this assessment of sensitivity, an account is taken of knowledge of the biology of all characterizing species/taxa in the biotope. In this sensitivity assessment, Alaria esculenta is the primary focus of research, as in the dominant characteristic species, without which the biotope would not be recognized.  However, Laminaria digitata, plus understory species Corallina officinalis, encrusting algae, Mytilus edulis and red seaweeds also define IR.HIR.KFaR.AlaAnCrSp & IR.HIR.KFaR.Ala plus their associated sub-biotopes. Examples of important species groups are mentioned where appropriate.

    Resilience and recovery rates of habitat

    Alaria esculenta is a perennial kelp found in the North Atlantic (Birkett et al., 1998b) which dominates the sublittoral fringe in areas exposed to severe wave action or where water surges along the sides of gullies or steep/vertical bedrock (Lewis, 1964; Connor et al., 2004). In extreme wave action Laminaria digitata & Laminaria hyperborea are likely to become damaged and die back, whereas morphological features and high growth rates allow Alaria esculenta to survive in such conditions (Birkett et al., 1998b). Alaria esculenta has a compact holdfast, a flexible “short” stipe and a flexible frond with a conspicuous reinforcing midrib (Birkett et al., 1998). Maximum growth rates are recorded in April-May which can exceed 20 cm/month (Birkett et al., 1998b). From June-July growth rates slow and continual erosion along the frond margins can reduce the sporophyte to a holdfast, stipe and short length of the blade, in which state the sporophyte over winters. In extremely wave exposed conditions, especially in winter months, the blade may be reduced to just the midrib. The sporophyte can reach a total length of 4m (Werner & Kraan, 2004), fronds can reach a total length of 2m, however, growth rates are locally variable and are more typically 30-90 cm in length (Birkett et al., 1998b). Alaria esculenta can reach maturity rapidly in 10-14 months and lives for 4-7 years (Birkett et al., 1998b; Baardseth, 1956).

    Alaria esculenta has a heteromorphic life history (Fredersorf et al., 2009). Between November to March a vast number of meiotic haploid zoospores are released from sori located on sporophylls (found at the top of the stipe).  Zoospore dispersal is greatly influenced by local water movements and zoospore densities. Laminarian spores also need to settle in high density so that the resultant gametophytes are close enough to cross-fertilize (Fredriksen et al., 1995). Recruitment of Alaria escuolenta may, therefore, be influenced by the proximity of mature sporophytes producing viable zoospores (Kain, 1979; Fredriksen et al., 1995). Laminarians are expected to disperse zoospores over considerable distances. However, Alaria esculenta may have a lower dispersal capacity than other Laminarins due to the basal location of the sporophylls Norton (1992). Sundene (1962) agreed with Norton (1992), and observed that Alaria esculenta germlings were restricted to within 10 m of the parental source in an Alaria esculenta translocation experiment conducted in a Norwegian fjord.

    Alaria esculenta is an opportunistic colonizing species (Kain 1975; Hawkins & Harkin 1985; Hill 1993; Engelen, 2010). Alaria esculenta can settle on bare surfaces, including mobile boulders and in deeper water than the infralittoral fringe Alaria esculenta often appears early in the algal succession (ca 3 months after clearance of dominant algae) before being out-competed by other kelp species (in moderately wave exposed shores). During kelp canopy removal experiments in the Isle of Man, Hawkins & Harkin (1985) found that in moderately wave exposed areas cleared of Laminaria digitata (the dominant canopy forming species). Alaria esculenta became the dominant canopy algae within 9 months (October - June) and Laminaria digitata did not re-establish dominance within the study period (15 months). In areas of moderate to sheltered wave exposure Alaria esculenta colonized the blocks within 1 month of clearance and reached 25% coverage within 5 months but within 7 months Laminaria digitata had outcompeted Alaria esculenta and re-established dominance within the community reaching ~90-95% coverage.  Kain (1975) conducted a similar experiment to Hawkins & Harkin (1985), however over a longer time period (>2 years).  Laminaria digitata was cleared from moderately wave exposed concrete blocks at Port Erin, Isle of Man, and the subsequent “succession” of algae communities was documented. Following clearance Laminaria digitata was considered re-established two years after removal, while the understory red seaweed species returned one year later. Engelen (2010) observed a similar recovery time in Britany, France.  Patches of Laminaria digitata (0.25m2 ) were removed.. Laminaria digitata returned to conditions prior to removal within 18-24 months, although competition for space by Saccorhiza polyschides reduced recovery rates in the first year of recolonization. Engelen (2010) stated that Laminaria digitata forest recovery rates varied between seasons, with autumn recovery being more rapid than spring (taking a minimum of 12 months).

    The dispersal of Laminaria digitata’s spores and subsequent successful recruitment has been recorded 600 m from reproductive individuals (Chapman, 1981). The growth rate of Laminaria digitata changes with the seasons. Growth is rapid from February to July, slower in August to January, and occurs diffusely in the Lamina (blade; Kain, 1979). Zoospores are produced at temperatures lower than 18°C with a minimum of 10 weeks a year between 5-18°C needed to ensure spore formation (Bartsch, 2013).  Thus, temperature and by default season impacts the level of reproductive activity. Furthermore, experimental clearance experiments of Laminaria digitata (Kain 1975; Hawkins & Harkin 1985; Hill 1993; Engelen, 2010) found that following clearance Laminaria digitata re-colonization takes 12-24 months. Interspecific competition from ephemeral algae was also found to slow recovery times (Engelen, 2010).

    Corallina officinalis produces spores over a protracted period and can colonize artificial substratum within one week in the intertidal (Harkin & Lindbergh 1977; Littler & Kauker 1984). The crustose base enables Corallina officinalis to survive extreme wave exposure and damage (loss of fronds), and to take advantage (colonize) of space left after winter storms have removed competing macroalgae (Littler & Kauker 1984). The mobile interstitial fauna of the coralline turf is reduced by trampling (Brown & Taylor 1989) but is likely to recruit to or recolonize the turf from the surrounding communities. Encrusting and erect corallines are also known to stimulate the settlement of a variety of marine invertebrate larvae and algal spores. Corallina officinalis is capable of colonizing new substratum rapidly. In experimental plots, 15 percent cover of fronds returned within 3 months (Littler & Kauker 1985) and Brown & Taylor (1999) noted that the articulated coralline algal turf community on a New Zealand shore returned to normal levels within 3 months of trampling events, although they suggested that a return to its previous cover may take longer.

    Resilience assessment. Alaria esculenta is an opportunistic and rapidly colonizing species (see above) capable of growing 20 cm/month in optimal conditions, reaching maturity within 10-14 months, and  often appearing early in the algal succession (c. 3 months after clearance of dominant algae). In canopy removal experiments in the Isle of Man, Hawkins & Harkin (1985) found that areas cleared of Laminaria digitata (moderately exposed) Alaria esculenta became the dominant canopy algae within 9 months (October - June). Corallina officinalis is capable of colonizing new substratum rapidly. In experimental plots 15 percent cover of fronds returned within 3 months (Littler & Kauker, 1985) and Brown & Taylor (1999) noted that the articulated coralline algal turf community on a New Zealand shore returned to normal levels within 3 months of trampling events, although they suggested that a return to its previous cover may take longer. Therefore general resilience of IR.HIR.KFaR.AlaAnCrSp & IR.HIR.KFaR.Ala plus associated sub-biotopes has been assessed as High.

    The resilience and the ability to recover from human induced pressures is a combination of the environmental conditions of the site, the frequency (repeated disturbances versus a one-off event) and the intensity of the disturbance.  Recovery of impacted populations will always be mediated by stochastic events and processes acting over different scales including, but not limited to, local habitat conditions, further impacts and processes such as larval supply and recruitment between populations. Full recovery is defined as the return to the state of the habitat that existed prior to impact.  This does not necessarily mean that every component species has returned to its prior condition, abundance or extent but that the relevant functional components are present and the habitat is structurally and functionally recognizable as the initial habitat of interest. It should be noted that the recovery rates are only indicative of the recovery potential.

    Hydrological Pressures

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

    Alaria esculenta is a northern/boreal species that has been recorded from Brittany, France to Northern Norway (Birkett et al., 1998). Sea temperature regulates metabolism and reproduction and defines the regional distribution of Alaria esculenta (Fredersdorf et al., 2009).  The southern limit of Alaria esculenta has been defined at the 20°C isotherm (Munda & Lüning, 1977; Fredersdorf et al., 2009), however, it is common north of the 16°C isotherm (Munda & Lüning, 1977). As a result of this upper temperature threshold, Alaria esculenta is largely absent from the southern North Sea and English channel where summer temperatures can exceed 16°C.

    Munda & Lüning (1977) observed temperatures of 16-17°C sustained over 2 weeks in Helgoland, Germany, were lethal to resident Alaria esculenta. Experimental observations showed that acute exposure to ≥21°C is lethal to Alaria esculenta causing bleaching and disintegration (Sundene, 1962; Fredersdorf et al., 2009). At its northern range edge (Svalbard) it is a prominent macroalga on sublittoral fringe bedrock.  At these latitudes, average summer temperature can reach 5°C, with an average annual sea temperature of 3°C (1980-2014, Beszczynska-Möller & Dye, 2013). Experimental observations conducted by Fredersdorf et al., (2009) found the optimal temperature for sporophyte photosynthesis was within the range of 13-17°C, however, the optimal temperatures for Alaria esculenta germination is 2-12°C (Fredersdorf et al., 2009).

    Alaria esculenta has an approximate mid-range within southern Norway (60 deg to 65 deg North) (Birket et al., 1998), and as such IR.HIR.KFaR.Ala and IR.HIR.KFaR.AlaAnCrSp (plus associated sub-biotopes) have a southerly distribution when considering the geographic distribution of Alaria esculenta. Throughout the UK 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 the effects of an increase in temperature would be seasonally variable, with higher impacts during periods of spore release (Nov-march) and germination. A 5°C increase in temperature for one month may cause high mortality, limit photosynthetic ability plus germination rates.  A 2°C increase in temperature for one year may limit germination; however sporophyte photosynthetic ability may not be dramatically affected. Temperature increases of 2/5°C at the southern extreme of Alaria esculenta’ range (Brittany, France) is likely to cause high mortality.

    Corallina officinalis may tolerate between minus 4 to 28°C (Lüning, 1990). Abrupt temperature changes (10°C in California, Seapy & Littler 1984; 4.8 to 8.5°C, Hawkins & Hartnoll, 1985) resulted in dramatic declines. However, in both cases recovery was rapid, suggesting that the crustose bases survived. Therefore, both Alaria esculenta and Corallina officinalis are probably intolerant of acute short term temperature change of 5°C for a month. Long term change of 2°C may reduce the southern limit of the population of Alaria esculenta.

    Sensitivity assessment. Resistance to the pressure is considered ’None‘, and resilience ’High‘. The sensitivity of this biotope to an increase in temperature has been assessed as ’Medium‘. This sensitivity assessment takes into account a temperature increase of 5°C for one month. The effects of a 2°C increase in temperature for one year is likely to have less of an impact. In the later scenario, resistance would be assessed as “Medium”, and resilience “High”. Sensitivity would be assessed as “Low”.

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

    Alaria esculenta is a northern/boreal species that has been recorded from Brittany, France to Northern Norway (Birkett et al., 1998). Sea temperature has been cited as an influential abiotic stressor; responsible for regulating metabolism and reproduction, plus defining the regional distribution of Alaria esculenta (Fredersdorf et al., 2009). At Alaria’snorthern range edge (Svalbard) it is a prominent macro-algae on sub-littoral fringe bedrock. At these latitudes, average summer temperature can reach 5°C, and average annual sea temperature 3°C (1980-2014, Beszczynska-Möller & Dye, 2013). Experimental observations conducted by Fredersdorf et al., (2009) found the optimal temperature for sporophyte photosynthesis was within the range of 13-17°C, however, the optimal temperatures for Alaria esculenta germination is 2-12°C (Fredersdorf et al., 2009).

    Alaria esculenta has an approximate mid-range within southern Norway (60 deg to 65 deg North) (Birket et al., 1998), and as such IR.HIR.KFaR.Ala and IR.HIR.KFaR.AlaAnCrSp (plus associated sub-biotopes) have a southerly distribution when considering the geographic distribution of Alaria esculenta. Throughout the UK northern to southern Sea Surface Temperature (SST) ranges from 8-16°C in summer and 6-13°C in winter (Beszczynska-Möller & Dye, 2013). A 5°C decrease in temperature for one month at Alaria esculenta’ approximate mid-range may affect the photosynthetic ability of sporophytes, however not impact germination and hence recruitment. A 2 deg C increase in temperature for one year at Alaria esculenta’ approximate mid-range is not likely to significantly affect Alaria esculenta.

    Sensitivity assessment. Resistance to the pressure is considered ’High‘, and resilience ’High‘. The sensitivity of this biotope to an increase in temperature 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

    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.

    Karsten (2007) tested the photosynthetic ability of Alaria esculenta under acute 2 & 5 day exposure to salinity treatments ranging from 5-60 psu. A control experiment was also carried at 34 PSU. Between 10-50 psu Alaria esculenta showed high photosynthetic ability at 83-94% of the control. Hypersaline treatments with 55-60 psu led to a 30% reduction in photosynthetic ability, ~70% of the control level. At 5 psu Alaria esculenta showed a low photosynthetic ability at 15.8% of the control. After 5 days at 5 psu all Alaria esculenta specimens were bleached and none survived. Karsten (2007) suggested that Alaria esculenta photosynthetic ability is highly affected by acute exposure to hyposaline conditions (<10 psu). The effect of long term salinity changes (>5 days) or the effect of salinity >60 psu on Alaria esculenta’ photosynthetic ability was not tested. The experiment was conducted in the Arctic, and the authors suggest that at extremely low water temperatures (1-5 deg C) macro-algal acclimation to rapid salinity changes could be slower than at temperate latitudes. It is therefore possible that Alaria esculenta maybe be able to acclimate to salinity changes more effectively and quicker in UK waters, however evidence for this is limited.

    Corallina officinalis is restricted to full salinity waters in the Baltic and grows maximally between 33 and 38 psu in Texan lagoons (Kinne 1971). This biotope is likely to be exposed to short term freshwater runoff at low tide but is likely to be intolerant of long term changes in salinity, which are likely to depress its upper limit and reduce the extent of the population.

    Sensitivity assessment. IR.HIR.KFaR.AlaAnCrSp & IR.HIR.KFaR.Ala plus associated sub-biotopes have been recorded exclusively in full salinity (30-40‰) (Connor et al., 2004). Karsten (2007) suggests that at salinities ranging from 10-50 psu Alaria esculenta photosynthetic ability was high. At salinities >50 psu, photosynthetic ability was reduced by 30% but no mortality of the specimens was recorded. Resistance to the pressure is considered ’Medium‘, as other characterizing species (e.g. sponges, ascidians) are likely to be more sensitive to hypersaline conditions and resilience ’High’. The sensitivity of this biotope to an increase in salinity has been assessed as ’Low’.

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

    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.

    Karsten (2007) tested the photosynthetic ability of Alaria esculenta under acute 2 & 5 day exposures to salinity treatments ranging from 5-60 psu. A control experiment was also carried at 34 PSU. Between 10-50 psu Alaria esculenta showed high photosynthetic ability at 83-94% of the control. Hypersaline treatments with 55-60 psu led to a 30% reduction in photosynthetic ability, ~70% of the control level. At 5 psu Alaria esculenta showed a low photosynthetic ability at 15.8% of the control. After 5 days at 5 psu all Alaria esculenta specimens were bleached and none survived. Karsten (2007) suggested that Alaria esculenta photosynthetic ability is highly affected by acute exposure to hyposaline conditions (<10 psu). The effect of long term salinity changes (>5 days) or the effect of salinity >60 psu on Alaria esculenta’ photosynthetic ability was not tested. The experiment was conducted in the Arctic, and the authors suggest that at extremely low water temperatures (1-5 deg C) macro-algal acclimation to rapid salinity changes could be slower than at temperate latitudes. It is therefore possible that Alaria esculenta maybe be able to acclimate to salinity changes more effectively and quicker in UK waters, however evidence for this is limited.

    Corallina officinalis is restricted to full salinity waters in the Baltic and grows maximally between 33 and 38 psu in Texan lagoons (Kinne 1971). This biotope is likely to be exposed to short term freshwater runoff at low tide but is likely to be intolerant of long term changes in salinity, which are likely to depress its upper limit and reduce the extent of the population.

    Sensitivity assessment. IR.HIR.KFaR.AlaAnCrSp & IR.HIR.KFaR.Ala plus associated sub-biotopes have been recorded exclusively in full salinity (30-40‰) (Connor et al., 2004). Karsten (2007) suggests that at salinities ranging from 10-50 PSU Alaria esculenta photosynthetic ability was high. At 5 PSU Alaria esculenta showed a dramatic decline in photosynthetic ability and after 5 days specimens bleached and did not survive. Sundene (1962) also noted that Alaria esculenta sporophytes grew poorly below 25 PSU. A decrease of 1 MNCR salinity scale to “Reduced Salinity” (18-30‰) may reduce growth rates, however not cause high mortality of Alaria esculenta. Resistance to the pressure is therefore considered ’Medium‘, as other characterizing species (e.g. sponges, ascidians) are likely to be more sensitive to hyposaline conditions, and resilience ’High‘.  The sensitivity of this biotope to an increase in salinity has been assessed as ’Low’.

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

    Alaria esculenta dominates the sublittoral fringe in areas exposed to severe wave action or where water surges along the sides of gullies/steep bedrock faces (Lewis, 1964; Connor et al., 2004). The high wave exposure that defines IR.HIR.KFaR.AlaAnCrSp & IR.HIR.KFaR.Ala plus associated sub-biotopes damages other laminarians, and generally excludes them.  In less wave exposed locations Alaria esculenta is outcompeted by other Laminarians, e.g. Laminaria digitata and Laminaria hyperborea (Connor et al., 2004).IR.HIR.KFaR.AlaAnCrSp and IR.HIR.KFaR.Ala plus associated sub-biotopes are recorded within moderately strong (0.5-1.5 m/sec)-weak (<0.5m/sec) tidal streams, but have been recorded in very strong (>3 m/sec) tidal streams. Therefore, while elevated tidal flows (>3 m/sec) may increase Alaria esculenta dislodgment (Birket et al., 1998).

    Increased tidal flow may remove fronds of Corallina officinalis however calcification is thought to be an adaptation to mechanical damage (Littler & Kauker 1984). Increases in water flow rate may facilitate the colonization of filter feeding organisms within the understory and IR.HIR.KFaR.Ala.Myt may dominate over IR.HIR.KFaR.Ala.Ldig. Decreases in water flow are likely to have the opposite effect (Connor et al. 2004). Changes in the water flow regimes under kelp canopies can modify larval supply and settlement (Eckman, 1983), and affect the growth and survival of Mytillus edulis (Eckman & Duggins, 1991). Mytillus edulis settlement has been found significantly higher in close proximity to Alaria esculenta and is thought to increase beneath the canopy (Bégin et al., 2004). Therefore any loss of Alaria esculenta, as a result of changes to local water movements, may affect Mytilus edulis recruitment.

    Sensitivity assessment. IR.HIR.KFaR.AlaAnCrSp & IR.HIR.KFaR.Ala plus associated sub-biotopes are found in a wide range of tidal flows but exclusively in wave disturbed areas, which generally exclude other laminarians. Changes in tidal flow are not likely to independently affect the dominance of Alaria esculenta, however, may affect the understory community.  Nevertheless, wave exposure is the dominant source of water movement in theses biotope, and a change in water flow of 0.1-0.2 m/s is unlikely to be significant. Therefore, resistance has been assessed as ’High‘ and resilience ’High‘. Sensitivity has been assessed as ’Not Sensitive‘ at the benchmark level.

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

    An increase in emergence will result in an increased risk of desiccation. Increased immersion may allow IR.HIR.KFaR.Ala biotopes to extend higher up the shore. However, Alaria esculenta forest will come under increased competition from Laminaria hyperborea in the shallow infralittoral. In this scenario IR.HIR.KFaR.Ala biotope distribution may shift on the shore, however, biotope structure will remain.

    Alaria esculenta may extend into the lower eulittoral in extremely wave exposed conditions. However, these marginal populations have a reduced age range in comparison to subtidal populations due to desiccation increasing mortality of Alaria esculenta at low tide. An increase in desiccation is likely to remove Alaria esculenta. The resultant loss of canopy would expose Corallina officinalis turf and macrofaunal crust to desiccation and/or damage by high light intensity (bleaching). Hawkins & Harkin (1985) noted that encrusting corallines and Corallina officinalis often die when their protective algal canopy is removed. Severe damage was noted in Corallina officinalis as a result of unusually hot and sunny weather in the UK summer 1983 (Hawkins & Hartnoll, 1985). Laminaria digitata is likely to be intolerant of desiccation and destruction of its meristem (base of the blade), caused by increased wave action at low tide, will kill the sporophyte. Therefore, both IR.HIR.KFaR.Ala.Myt and IR.HIR.KFaR.Ala.Ldig are likely to be highly intolerant of increases in desiccation and the upper limit of the population would be depressed. Desiccation is unlikely to be relevant in IR.HIR.KFaR.AlaAnCrSp due to its depth (15-35m BCD) (Connor et al., 2004).

    Sensitivity assessment. Resistance to this pressure is considered ’Low‘, and resilience ’High‘. The sensitivity of this biotope to a change in emergence is considered as ’Low‘.  

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

    Alaria esculenta dominates the sublittoral fringe in areas exposed to severe wave action or where water surges along the sides of gullies (Lewis, 1964). A decrease in local wave height will increase spatial competition from other laminarians (Connor et al., 2004). Increased wave exposure may remove fronds of Corallina officinalis however calcification is thought to an adaptation to mechanical damage (Little & Kauker 1984) and the fronds grow as a compact (short) turf in wave exposed conditions.

    IR.HIR.KFaR.AlaAnCrSp occurs at one site, Rockall, Scotland where extreme oceanic swell excludes Laminaria hyperborea in the infralittoral from 14-35 m. IR.HIR.KFaR.Ala.Myt occurs predominantly on sub-littoral fringe bedrock in very exposed to exposed wave exposure.  Extremely wave exposed variants of IR.HIR.KFaR.Ala.Myt can extend to 15 m BCD where Alaria esculenta replaces Laminaria hyperborea as the assemblage dominant, and Mytillus edulis is a common understory species in the sublittoral fringe variant (Bégin et al., 2004, Connor et al., 2004) but as depth increases Tubularia spp. becomes more abundant. IR.HIR.KFaR.Ala.Ldig occurs predominately at exposed-moderately wave exposed sites, where Laminaria digitata can spatially compete with Alaria esculenta (Connor et al., 2004).

    Sensitivity assessment. The abundance of Alaria esculenta is highly affected by the degree of wave exposure at a site. Within IR.HIR.KFaR.Ala, increasing wave exposure may favour IR.HIR.KFaR.Ala.Myt over IR.HIR.KFaR.Ala.Ldig (Connor et al. 2004). Further increases in wave exposure may cause damage to Laminaria hyperborea, allowing Alaria esculenta to dominate the infralittoral. Kelp clearance experiments have shown that at moderate or lower wave exposure sites Laminaria digitata can out-compete Alaria esculenta so that a decrease in wave exposure is likely to result in loss of the Alaria dominated biotopes. Alaria dominated biotopes are therefore, sensitive to any activity or event that reduces incident wave energy.  However, a change of 3-5% in significant wave height (the benchmark) is unlikely to be significant in the wave exposed conditions favoured by theses biotopes.  Therefore, resistance is recorded as ‘High’, with a ‘High’ resilience, resulting is an assessment of ‘Not sensitive’ at the benchmark level.

    Chemical Pressures

     ResistanceResilienceSensitivity
    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

    Johnston & Roberts (2009) conducted a meta-analysis, which reviewed 216 papers to assess how a variety of contaminants (including metal contamination) affected six marine habitats (including intertidal and subtidal reefs). A 30-50% reduction in species diversity and richness was identified from all habitats exposed to the contaminant types. Johnston & Roberts (2009) also highlighted that macroalgal communities are relatively tolerant to contamination but that metal and nutrient impacted intertidal communities can have low diversity assemblages which are dominated by opportunistic and fast growing species (Johnston & Roberts, 2009 and references therein).

    Mercury (organic > inorganic) is highly toxic to macrophytes (Bryan 1984; Cole et al. 1999).  Mercury and copper were lethal at 0.05 mg/l and 0.1 mg/l respectively and toxic at 0.05 mg/l and 0.01 mg/l respectively in Laminaria hyperborea.  Zinc and Cadmium were lethal at 5 mg/l and 10 mg/l respectively. The presence of alginates in kelp tissue is thought to sequester heavy metals in a biologically unavailable form. It is likely that laminarians such as Alaria esculenta are relatively tolerant of heavy metals except at high concentrations at high levels.  Little information on heavy metal tolerance of corallines was found.

    However this biotope is considered to be 'Not sensitive' at the pressure benchmark, that assumes compliance with all relevant environmental protection standards.

    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

    The mucilaginous coating on kelp fronds is thought to protect them from coatings of oil. Hydrocarbons in solution reduce photosynthesis and may be algicidal. Reduction in photosynthesis is dependent on the type of oil, its concentration and length of exposure, oil-water mixture and irradiance in experimental trials (Lobban & Harrison, 1994). Subtidal populations are only exposed to oil emulsions or oil adsorbed particles. Kelps are relatively insensitive to dispersants (Birkett et al. 1998) e.g. Laminaria digitata exposed to diesel oil at 0.130 mg/l reduced growth by 50% in a 2 year experiment. No growth inhibition was noted at 0.03 mg/l and the plants recovered completely in oil free conditions. Coraliina officinalis, however, exhibited dramatic bleaching after the Sea Empress oil spill and died after the Torrey Canyon spill (Crump et al. 1999; Smith 1968). Encrusting corallines and Coraliina officinalis recovered from the Sea Empress spill quickly, bleaching only affecting the fronds or surface of crustose forms. Grazing gastropods, e.g. limpets are highly intolerant of oil spillage and if not killed are narcotinized and washed offshore and/or consumed by predators. The lower littoral populations are likely to be most vulnerable to oil spill and sublittoral fringe would be particularly affected at low tide. Although Alara esculenta may not be affected severely, the articulated coralline turf may be lost but recover quickly although the red algae may be intolerant. Grazers such as limpets, barnacles and meiofaunal crustaceans may also be lost from the community.

    Sensitivity assessment. IR.HIR.KFaR.AlaAnCrSp & IR.HIR.KFaR.Ala plus associated sub-biotopes are however considered “Not Sensitive” at the benchmark level, which assumes compliance with all relevant environmental protection standards.

    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

    Cole et al. 1999 suggest that macrophytes are generally intolerant of herbicides such as atrazine, simazine, diuron and linuron e.g. atrazine was lethal to Laminaria hyperborea sporophytes at 1mg/l and suppressed growth at 0.01 mg/l (Hopkin & Kain, 1978). Smith (1968) noted that Corallina officinalis was killed in areas of heavy spraying after the Torrey Canyon oil spill and affected at 6 m depth in areas of high wave action. High water specimens were more affected than low water specimens, presumably because they are emmersed for longer and had more contact with oil and dispersants. Gastropods are known to be highly sensitive to endocrine disrupters such as TBT. Crustaceans (e.g. amphipods, isopods, ostracods, copepods and barnacles) are also susceptible to endocrine disruption by synthetic chemicals. It is, therefore, likely that some taxa within IR.HIR.KFaR.AlaAnCrSp & IR.HIR.KFaR.Ala plus associated sub-biotopes, especially grazing invertebrates and meiofauna will be intolerant of synthetic chemical contamination.

    However, this biotope is considered to be 'Not sensitive' at the pressure benchmark, that assumes compliance with all relevant environmental protection standards.

    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 sensitive
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR
    Q: NR
    A: NR
    C: NR

    Not sensitive at the pressure benchmark that assumes compliance with all relevant environmental protection standards.

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

    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 conditions are transient, which is likely given the wave exposed distribution of defines IR.HIR.KFaR.AlaAnCrSp & IR.HIR.KFaR.Ala plus associated sub-biotopes. If levels do drop below 4 mg/l negative effects on these organisms can be expected with adverse effects occurring below 2mg/l (Cole et al., 1999). 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.

    Sensitivity assessment.  Due to the mixing experienced in strongly wave exposed environment, resistance has been assessed as “High” resilience as “High”. Sensitivity has been assessed as “Not Sensitive” at the pressure 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

    Organic enrichment is associated with eutrophication, increased siltation and turbidity (Fletcher 1996). Eutrophication is associated with loss of perennial algae and replacement by mussels or opportunistic algae (Fletcher 1996). Johnston & Roberts (2009) conducted a meta-analysis that reviewed 216 papers to assess how a variety of contaminants (including sewage and nutrient loading) affected 6 marine habitats (including intertidal and subtidal reefs). A 30-50% reduction in species diversity and richness was identified from all habitats exposed to the contaminant types. Johnston & Roberts (2009) also highlighted that macroalgal communities are relative

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

    Organic enrichment is associated with eutrophication, increased siltation and turbidity (Fletcher 1996). Eutrophication is associated with loss of perennial algae and replacement by mussels or opportunistic algae (Fletcher 1996). Johnston & Roberts (2009) conducted a meta-analysis that reviewed 216 papers to assess how a variety of contaminants (including sewage and nutrient loading) affected six marine habitats (including intertidal and subtidal reefs).  A 30-50% reduction in species diversity and richness was identified from all habitats exposed to the contaminant types. Johnston & Roberts (2009) also highlighted that macroalgal communities are relatively tolerant to contamination, but that contaminated intertidal communities can have low diversity assemblages which are dominated by opportunistic and fast growing species (Johnston & Roberts, 2009 and references therein). Due to the high wave exposure that defines IR.HIR.KFaR.AlaAnCrSp & IR.HIR.KFaR.Ala plus associated sub-biotopes, it is likely that additional organic input to the system may be dispersed out of the biotope’s local vicinity (Johnston & Roberts, 2009). Increased nutrients may favour Mytilus edulis in IR.HIR.KFaR.Ala.Myt which may increase in cover and abundance. Corallina officinalis is also tolerant of polluted waters (Kindig & Littler, 1980).

    Sensitivity assessment. Resistance has been assessed as “Medium, (to represent potential changes in species diversity), resilience as “High. Sensitivity has been assessed as “Low”.

    Physical Pressures

     ResistanceResilienceSensitivity
    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 rock substrata were replaced with sedimentary substrata this would represent a fundamental change in habitat type, which Alaria esculenta would not tolerate (Birkett 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 hard rock or artificial substrata to sedimentary or soft rock substrata  is assessed as ’High’.

    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 to hard rock biotopes.

    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 to hard rock biotopes.

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

    The sublittoral fringe is unlikely to be significantly impacted by trampling due to its position of the lower shore but may be prone to abrasion from moorings or low tide landings. Given its resilience to wave action Alaria esculenta is unlikely to be significantly damaged by abrasion although the understory coralline turf may suffer some damage. The coralline turf meiofauna will probably be lost as a result of trampling. Moderate trampling on articulated coralline algal turf in the New Zealand intertidal (Brown & Taylor 1999; Schiel & Taylor 1999) resulted in reduced turf height, declines in turf densities, and loss of crustose bases in some case probably due to loss of the canopy algae and resultant desiccation. Calcification is thought to an adaptation to grazing and sediment scour (Littler & Kauker 1984).

    If exposed to moorings, groundings, or passing fishing gear, the resultant abrasion may result in the physical removal of a proportion of the Alaria esculenta canopy. Depending on the scale of the impact, although no evidence of this impact was found.  However, Alaria esculenta has been shown to be an opportunistic colonizing species, capable of rapid recovery (see resilience section).

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

    Not Relevant to hard rock biotopes.

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

    Suspended Particle Matter (SPM) concentration has a linear relationship with sub surface light attenuation (Kd) (Devlin et al., 2008). Light penetration influences the maximum depth at which kelp species 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 6-7 m in the silt-laden German Bight. In European Atlantic waters, the depth limit is typically 35 m.

    Alaria esculenta is not found in areas of siltation and sediment scour (Birkett et al. 1998). Increased siltation and sediment scour inhibits photosynthesis and algal growth, interfere with spore or larval recruitment plus smother germlings and gametophytes (Fletcher 1996). However, the high degree of wave exposure that typically defines IR.HIR.KFaR.AlaAnCrSp & IR.HIR.KFaR.Ala plus associated sub-biotopes is likely to clear suspended sediments relatively quickly. If low water clarity is persistent and wave exposure decreased then low energy silted kelp biotopes (IR.LIR.K) may proliferate. Once siltation returns to its pre-effect level the biotope is likely to recover its canopy within a year and the rest of the community in no more than five years. Increased siltation will also increase turbidity. Increased sediment may benefit Mytilus edulis and its abundance may increase in IR.HIR.KFaR.Ala.Myt although large individuals are likely to be removed by wave action.

    Increased turbidity is likely to reduce the depth to which Alaria  esculenta can grow. However, an increase of one level in WFD water clarity scale for a period of one year is unlikely to affect the population since Alaria esculenta’s lower limit, is generally determined by competition from other Laminarians rather than light penetration.

    Sensitivity assessment. Resistance has been assessed as Medium, Resilience as High. Sensitivity has been assessed as Low.

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

    Due to their size juvenile sporophytes, germlings, gametophytes and spores are likely to be inundated by deposition of 5cm during a discrete event but the high wave exposure that defines the distribution of IR.HIR.KFaR.AlaAnCrSp & IR.HIR.KFaR.Ala (plus associated sub-biotopes deposited sediments) are likely to be removed rapidly and any effects of inundation are likely to be temporary.

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

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

    Due to their size juvenile sporophytes, germlings, gametophytes and spores are likely to be inundated by deposition of 30cm during a discrete event but the high wave exposure that defines the distribution of IR.HIR.KFaR.AlaAnCrSp & IR.HIR.KFaR.Ala (plus associated sub-biotopes deposited sediments) are likely to be removed rapidly and any effects of inundation are likely to be temporary.

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

    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

    No evidence to suggest that litter would affect IR.HIR.KFaR.AlaAnCrSp & IR.HIR.KFaR.Ala plus associated sub-biotopes was found.

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

    There was no evidence to suggest that anthropogenic light sources would affect IR.HIR.KFaR.AlaAnCrSp & IR.HIR.KFaR.Ala plus associated sub-biotopes. Shading (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 'High' resilience and a sensitivity of 'High', 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 benchmarks, 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

     ResistanceResilienceSensitivity
    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

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

    The Japanese kelp Undaria pinnatifida (wakame) has recently spread to the south coast of England from Brittany where it was introduced for aquaculture.  It may spread in ballast water of commercial or recreational boats and shipping.  Field studies within New Zealand found that the physical structure of coralline turfing algae substantially aided the establishment of Undaria pinnatifida in the intertidal.  The physical structure of coralline turfing algae (e.g. Corallina officinalis) retains moisture, provide a physical barrier to grazers, and create a physically complex habitat on which algal spores can settle (Thompson & Schiel, 2012). Once established Undaria pinnatifida has been associated with declines in native kelp abundance (e.g. Laminaria hyperborea, Heiser et al., 2014).  In the UK Undaria pinnatifida has to date only been recorded from predominantly sheltered locations e.g. harbours (Thompson & Schiel, 2012).  The high wave exposure which defines IR.HIR.KFaR.AlaAnCrSp & IR.HIR.KFaR.Ala plus associated sub-biotopes may inhibit the establishment of Undaria pinnatifida However colonization of Undaria pinnatifida within UK habitats needs further study (Birkett et al. 1998, Heiser et al., 2014).

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

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

    Streblonema sp. is associated with spot disease in kelps and has been found growing on Alaria esculenta (Lein et al. 1991) but no incidence of Alaria esculenta spot disease was found. Corallina officinalis may host several epiphytes of which Titanoderma corallinae is thought to cause tissue damage. Hyperplasia or gall growths are often seen as dark spots on Laminaria digitata and have been associated with endophytic brown filamentous algae. There is no evidence in the literature that infection by microbial pathogens results in the mass death of kelp populations and the kelp themselves are known to regulate bacterial infections through iodine metabolism (Cosse et al., 2009).

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

    None Medium Medium
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High

    Alaria esculenta has recently received commercial interest as a consumable product called “Sea Vegetables” or “Atlantic Wakame Kelp”. However no studies examining the effect of commercial extraction of Alaria esculenta biotopes were found. Removal of the algal canopy would expose the understory fauna and flora to increased desiccation. Experimental macroalgal canopy removal experiments conducted in the Isle of Man (Hawkings & Harkin, 1985) found that following the removal of the macroalgal canopy the understory encrusting red algae became bleached and died within a week. Mytilus edulis settlement has also been found significantly higher in close proximity to Alaria esculenta and is thought to increase beneath Alaria esculenta canopies (Bégin et al., 2004).  Therefore, any loss of Alaria esculenta, as a result of commercial extraction, may dramatically affect the understory community.

    Traditionally Laminaria digitata was added to agricultural lands as fertilizers; now Laminaria species are used in a range of different products, with its alginates used in the cosmetic, pharmaceutical and agri-food industries (Kervarec et al., 1999; McHugh, 2003). Laminaria digitata is harvested with a ‘Scoubidou’ (a curved iron hook which is mechanically operated) in France. This device is considered to be selective- only harvesting individuals older than 2 years (Arzel, 2002). France reportedly harvests 75,000t kelp, mainly consisting of Laminaria digitata annually (FAO, 2007). The loss of Laminaria digitata would represent as significant change to IR.HIR.KFaR.Ala.Ldig.

    Corallina officinalis is collected for medical purposes; the fronds are dried and converted to hydroxyapatite and used as bone forming material (Ewers et al. 1987). It is also sold as a powder for use in the cosmetic industry. Moderate trampling on articulated coralline algal turf in the New Zealand intertidal (Brown & Taylor 1999; Schiel & Taylor 1999) resulted in reduced turf height, declines in turf densities, and loss of crustose bases in some case probably due to loss of the canopy algae and resultant desiccation. Calcification is thought to be an adaptation to grazing and sediment scour (Littler & Kauker 1984). Corallina officinalis produces spores over a protracted period and can colonize artificial substratum within one week in the intertidal (Harkin & Lindbergh 1977; Littler & Kauker 1984). The crustose base enables Corallina officinalis to survive the loss of fronds.

    Sensitivity assessment. There is little evidence for the effects of commercial harvesting of Alaria esculenta. If it is assumed that all canopy forming kelp are removed then resistance would be assessed as ’None‘, resilience would be assessed as ’Medium‘. Sensitivity has been assessed as ’Medium‘. Within IR.HIR.KFaR.AlaAnCrSp and IR.HIR.KFaR.Ala.Myt, monospecific canopies of Alaria esculenta are expected to recover quicker than mixed canopies of Laminaria digitata (as in IR.HIR.KFaR.Ala.Ldig) Sensitivity of the latter would be assessed as follows; resistance ’None‘, resilience as ’High‘, Sensitivity as ’Medium’.

    None Medium Medium
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High
    Q: High
    A: High
    C: High

    Incidental/accidental removal of Alaria esculenta is likely to cause similar effects to that of direct harvesting; hence, the same evidence has been used for both pressure assessments.

    Alaria esculenta has recently received commercial interest as a consumable product called “Sea Vegetables” or “Atlantic Wakame Kelp”. However,  no studies examining the effect of commercial extraction of Alaria esculenta biotopes were found. Removal of the algal canopy would expose the understory fauna and flora to increased desiccation. Experimental macroalgal canopy removal experiments conducted in the Isle of Man (Hawkings & Harkin, 1985) found that following the removal of the macroalgal canopy the understory encrusting red algae became bleached and died within a week. Mytilus edulis settlement has also been found significantly higher in close proximity to Alaria esculenta and is thought to increase beneath Alaria esculenta canopies (Bégin et al., 2004).  Therefore, any loss of Alaria esculenta, as a result of commercial extraction, may dramatically affect the understory community.

    Traditionally Laminaria digitata was added to agricultural lands as fertilizers; now Laminaria species are used in a range of different products, with its alginates used in the cosmetic, pharmaceutical and agri-food industries (Kervarec et al., 1999; McHugh, 2003). Laminaria digitata is harvested with a ‘Scoubidou’ (a curved iron hook which is mechanically operated) in France. This device is considered to be selective- only harvesting individuals older than 2 years (Arzel, 2002). France reportedly harvests 75,000t kelp, mainly consisting of Laminaria digitata annually (FAO, 2007). The loss of Laminaria digitata would represent as a significant change to IR.HIR.KFaR.Ala.Ldig.

    Corallina officinalis is collected for medical purposes; the fronds are dried and converted to hydroxyapatite and used as bone forming material (Ewers et al. 1987). It is also sold as a powder for use in the cosmetic industry. Moderate trampling on articulated coralline algal turf in the New Zealand intertidal (Brown & Taylor 1999; Schiel & Taylor 1999) resulted in reduced turf height, declines in turf densities, and loss of crustose bases in some case probably due to loss of the canopy algae and resultant desiccation. Calcification is thought to be an adaptation to grazing and sediment scour (Littler & Kauker 1984). Corallina officinalis produces spores over a protracted period and can colonize artificial substratum within one week in the intertidal (Harkin & Lindbergh 1977; Littler & Kauker 1984). The crustose base enables Corallina officinalis to survive loss of fronds.

    Sensitivity assessment. There is little evidence for the effects of commercial harvesting of Alaria esculenta. If it is assumed that all canopy-forming kelp are removed then resistance would be assessed as ’None‘, resilience would be assessed as ’Medium‘. Sensitivity has been assessed as ’Medium‘. Within IR.HIR.KFaR.AlaAnCrSp and IR.HIR.KFaR.Ala.Myt, monospecific canopies of Alaria esculenta are expected to recover quicker than mixed canopies of Laminaria digitata (as in IR.HIR.KFaR.Ala.Ldig) Sensitivity of the latter would be assessed as follows; resistance ’None‘, resilience as ’High‘, Sensitivity as ’Medium’.

    Importance review

    Policy/Legislation

    Habitats Directive Annex 1Reefs

    Exploitation

    • Alaria esculenta was farmed by rope culture off the Isle of Man during the 1980s and early 1990s (Guiry & Blunden 1991; Tim Hill pers. comm.).
    • It is eaten fresh or cooked in Greenland, Iceland, Scotland and Ireland.
    • It may be used as a fodder additive and is grazed by sheep in Orkney.
    • It is collected in Ireland and sold as a health food 'Atlantic Wakame'
    • Corallina officinalis was used in Europe as a vermifuge although it no longer seems to be collected for this purpose (Guiry & Blunden 1991).
    • Corallina officinalis is collected for medical purposes; the fronds are dried and converted to hydroxyapatite and used as bone forming material (Ewers et al. 1987). It is also sold as a powder for use in the cosmetic industry.
    • An European research proposal for cultivation of Corallina officinalis is pending (Thomas Wiedemann pers. comm.).

    Additional information

    -

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    Citation

    This review can be cited as:

    Stamp, T.E. & Tyler-Walters, H. 2015. Alaria esculenta on exposed sublittoral fringe bedrock. 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. Available from: http://www.marlin.ac.uk/habitat/detail/165

    Last Updated: 16/12/2015

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