Biodiversity & Conservation


Explanation of sensitivity and recoverability

Physical Factors

Substratum Loss
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Key and characteristic species are mainly attached to the substratum and are therefore highly intolerant of substratum loss. Most of the species in the biotope, including the sea urchins would probably recolonize within 5 years (see additional information below). However, removal of the bedrock or boulders will remove the kelp species and their gametophytes. Therefore, it is likely that, although the kelps themselves may recolonize within 3-4 years, the community as a whole will take at least 10 years to return due to successional changes especially (see Kain, 1979; Birkett et al., 1998b).
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Smothering by sediment e.g. 5 cm material for a month, is unlikely to damage Laminaria hyperborea plants but is likely to affect sporeling and gametophyte survival as well as holdfast fauna. A layer of sediment will interfere with zoospore settlement. Given the microscopic size of the gametophyte 5 cm of sediment could be expected to significantly inhibit growth. However, laboratory studies showed that gametophytes can survive in darkness for between 6 -16 months at 8 °C and would probably survive smothering for 1 month. Once returned to normal conditions the gametophytes resumed growth or maturation within 1 month (very high recoverability) (see Dieck, 1993). Intolerance to this factor is likely to be higher during the peak periods of sporulation or germling settlement. Understorey epifauna/flora may be adversely effected, especially suspension or filter feeding species and the settlement of larvae or spores may be impaired. Encrusting corallines and encrusting bryozoans are unlikely to be affected since they were reported to survive being overgrown by other species and hence smothering (Gordon, 1972; Sebens, 1985; Todd & Turner, 1988). Similarly both Delesseria sanguinea and Echinus esculentus were assessed as of intermediate intolerance to smothering. Therefore, an overall biotope intolerance of intermediate has been recorded. Recoverability is likely to be high (see additional information below).
Increase in suspended sediment
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Increased siltation resulting from an increase in suspended sediment may interfere with spore attachment, larval settlement and recruitment, smothering germlings and gametophytes (see above), reduce photosynthetic activity if deposited on lamina, and increase sediment scour of surfaces settled by algal spores or larvae (Fletcher, 1996). Fletcher (1996) reports that siltation in the vicinity of outfalls restricts the distribution of Laminaria spp. and result in the general absence or impoverishment of algae leaving only a few selected species. It also increased the quantity of mussels which competed for space with benthic algae in heavily polluted sites. Studies of cooling water discharge in southern California Macrocystis forest suggested that turbidity and siltation significantly reduced the density of snails, sea urchins and starfish whereas two filter feeding species, a gorgonian coral and a sponge increased in relative density (Birkett et al., 1998b). Exposed Laminaria hyperborea biotopes are likely to be free of silt and exhibits more foliose red algae than moderately exposed Laminaria hyperborea biotopes. Increased siltation may adversely affect recruitment in Helcion pellucidum and other grazing gastropods, and could result in decreases in population density resulting in increased abundance of epiphytes on stipes. However, Alcyonium digitatum has been shown to be tolerant of high levels of suspended sediment. Hill et al. (1997) demonstrated that Alcyonium digitatum sloughed off settled particles with a large amount of mucus, although mucus production incurs an energetic cost. Suspension feeding organisms may be adversely affected by increases in suspended sediment, due to clogging of their feeding apparatus. Animal dominated communities develop preferentially on steep surfaces and under overhangs, e.g. bryozoan larvae preferentially settle under overhangs, presumably to avoid smothering and siltation (Ryland, 1977; Hartnoll, 1983). Wendt (1998) noted that Bugula neritina grew faster on downward facing surfaces than upward facing surfaces, presumably due to siltation and reduced feeding efficiency on upward facing surfaces. But where water flow is sufficient to prevent siltation, Bugula turbinata may colonize upward facing surfaces (Hiscock & Mitchell, 1980). Large massive sponges tend to favour fast flowing waters that are free of silt while encrusting species can tolerate more turbid conditions, (e.g. Halichondria panicea), although the response to suspended sediment loads varies with species (Moore, 1977; Morton & Miller, 1968). The tolerance of ascidians to suspended sediment varies with species, e.g. Clavelina lepadiformis and Morchellium argus are probably relatively tolerant (see species reviews) whereas Aplidium pallidum and Botrylloides leachi may be more intolerant. Given the effect on settlement and recruitment, increased siltation may change the age structure of the algal population, reduce understorey flora/fauna species richness, and decrease gastropod grazing. Increased siltation may affect holdfast fauna, encouraging suspension feeders and silt tolerant communities whereas decreased siltation is likely to encourage species associated with clearer waters (Moore 1973a&b; Edwards 1980). Sheppard et al. (1980) noted that increased suspended sediment (measured as clarity) reduced holdfast species diversity due to increased dominance of suspension feeders. Therefore an intolerance of intermediate has been recorded. Recoverability is probably high (see additional information below).
Decrease in suspended sediment
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Decrease in suspended sediment is likely to have a favourable effect on the biotope as light penetration will increase and siltation decrease. However, suspended sediment may hold organic material that is important for some suspension feeding species so that, on balance, not sensitive is suggested.
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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. Increased desiccation will probably remove more adult plants and their associated communities and red algae from the upper limit of its distribution. Most species associated with this biotope are intolerant of increased emergence and would be adversely affected. However, the majority of the kelp bed is subtidal and unlikely to be affected. Therefore, an intolerance of intermediate has been recorded. Recoverability is probably high.
Increase in emergence regime
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An increase in emergence of about 1 hour for a year will decrease the upper limit of the kelp beds, due to the increased insolation and risk of desiccation, with a concomitant decrease in species richness. The biotope may be replaced by sublittoral fringe biotopes, such as £EIR.Ala£. Therefore, an intolerance of high has been recorded. The kelp park biotope (EIR.LhypR.Pk) is unlikely to be exposed to this factor due to its depth. Recoverability is probably moderate (se additional information below).
Decrease in emergence regime
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The biotope is sublittoral and so increase in emergence may expand the area of rock available for development of the biotope. However, as the biotope occurs deeper than the sublittoral fringe, an intolerance of not relevant is most appropriate.
Increase in water flow rate
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Stronger tidal currents may lead to removal of kelps through detachment of holdfasts. Increased water flow rate may remove or inhibit grazers including Echinus esculentus, therefore reducing grazing in the understorey and especially on stipes. The associated foliose algal flora may increase and suspension feeding faunal populations expand. Therefore, an increase in water flow from weak to strong, or moderately strong to very strong (see benchmark) would probably result in removal of a proportion of the Echinus esculentus population and significantly reduce grazing intensity.

Water movement is essential for suspension feeders such as hydroids, bryozoans, sponges, amphipods and ascidians to supply adequate food, remove metabolic waste products, prevent accumulation of sediment (siltation) and disperse larvae or medusae. Most hydroids utilize a narrow range of water flow rates for effective feeding, and feeding efficiency decreases at high water flow rates (Gili & Hughes, 1995). Similarly, water flow rates affect filter feeding efficiency in bryozoans, the preferred ranges depending on species. An increase in water flow from weak to strong (see benchmark), whilst bringing a greater supply of food for suspension feeders, is likely to adversely affect some members of the community due to drag. For example, species tolerant of strong water flow, e.g. Tubularia indivisa, Halichondria panicea, Alcyonium digitatum and Flustra foliacea may increase in abundance, while species that are less tolerant of strong water flow, e.g. Nemertesia spp., Caryophyllia smithii, Ophiothrix fragilis and Ascidia mentula may be excluded (see Hiscock, 1983). In addition, very strong water flow may interfere with larval settlement and recruitment.

Overall, a significant reduction in grazing intensity or increase in the abundance of suspension feeders is likely to result in major changes in the community and loss of the biotope as described. Therefore, an intolerance of high has been recorded. The biotope may become one that is characteristic of moderately exposed kelp biotopes. The composition of the holdfast fauna may also change, e.g. energetic or sheltered water movements favour different species of amphipods (Moore, 1985). Because the biotope may change to a different one, intolerance is high. However, on return of grazing pressure and reduction in supply of food to suspension feeders, the grazed biotope would be expected to reappear within one or two years.
Decrease in water flow rate
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The biotope and its sub-biotopes mainly occur in areas subject to weak tidal streams and where wave action most likely contributes the main water movement that keeps rocks clear of silt and brings suspended food. Decrease in water flow rate is therefore considered not relevant.
Increase in temperature
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The key structuring species Laminaria hyperborea is stenothermal, with upper and lower lethal temperatures between 1-2 °C above or below the normal temperature tolerances of between 0 and 20 °C (depending on season) (Birkett et al., 1998b). Hoek (1982) suggests that Laminaria hyperborea can tolerate an annual temperature span of 17 °C with an upper and lower lethal temperatures of 19 °C and 2 °C. It is likely that the biotope as a whole will be damaged by temperatures outside the temperature tolerance of Laminaria hyperborea. Subtidal red algae are less tolerant of temperature extremes than intertidal Rhodophyceae, surviving between -2 °C (in seawater) and 18-23 °C (Lüning, 1990; Kain & Norton, 1990). Temperature increase may affect growth, recruitment or interfere with the reproductive cycle in some species, e.g. temperatures below 13 °C are required for new blade growth in Delesseria sanguinea. Increases in temperature of e.g. 2 °C for a year or 5 °C for one week may raise ambient temperatures outside the tolerable range for the species within the biotope, causing changes in recruitment, growth rates and perhaps loss of red algae and changes in grazing patterns. It should be noted that increases in temperature tolerances by kelp species is less well tolerated in winter months than summer months (Birkett et al., 1998b). Laminaria ochroleuca, which is restricted to Devon, Cornwall and the Isles of Scilly but common on the coasts of Brittany may, in the case of long term increases of 1 -3 °C in temperature, spread northwards (Birkett et al. 1998b). At the level of the benchmark, some organisms in the biotope may be subject to stress but mortality is unlikely and an intolerance of low is suggested with a recovery of very high.
Decrease in temperature
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The key structuring species Laminaria hyperborea is stenothermal, with upper and lower lethal temperatures between 1-2 °C above or below the normal temperature tolerances of between 0 and 20 °C (depending on season) (Birkett et al., 1998b). Hoek (1982) suggests that Laminaria hyperborea can tolerate an annual temperature span of 17 °C with an upper and lower lethal temperatures of 19 °C and 2 °C. Cold temperatures have been associated with high recruitment of sea urchins overseas (Birkett et al., 1998b). Echinus esculentus, a key functional species, is recorded from the north and south of the British Isles, experiencing for example temperatures between 0 -18 °C in the Limfjord, Denmark (Ursin, 1960), and it is unlikely that this species will be adversely affected by a long term temperature change in British waters. Similarly, Alcyonium digitatum occurs from Iceland in the North, to Portugal and was also reported to be apparently unaffected by the severe winter of 1962-1963 (Crisp, 1964).

Most of the hydroid and bryozoan species within the biotope are recorded to the north or south of the British Isles and are unlikely to be adversely affected by long term increases in temperature at the benchmark level. Temperature is a critical factor stimulating or inhibiting reproduction in hydroids, most of which have an optimum temperature range for reproduction (Gili & Hughes, 1995). Sebens (1986) reported that growth rates of most species were higher in the warmer months, except in Alcyonium spp. and Spirorbis spp. which showed little seasonal differences.

Overall, this predominantly northern biotope would be expected to be unaffected by decrease in temperature.
Increase in turbidity
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Turbidity will primarily affect Laminaria hyperborea and the depth to which it is likely to grow. In the sub-biotope MIR.LhypGz.Pk Laminaria hyperborea occurs at low density, due mainly to limiting light levels. Red algae are shade tolerant extending to greater depths and probably not as intolerant of increases in turbidity as kelp species. Encrusting coralline algae are amongst the deepest water species of macroalgae occurring in the circalittoral, at great depths, and a light levels as low as 0.05 -0.001% of surface incident light (Lüning, 1990). A reduction in light intensity may reduce their growth rates, especially in the deepest examples of the biotope. However, their extremely slow growth rates mean that the corallines will probably not be adversely affected for the duration of the benchmark. Suspended material in the vicinity of outfalls has been reported to result in reduced depth range and fewer new plants under the canopy (Fletcher, 1996) (see 'siltation' above). Within the time frame of the benchmark, changes in the extent of the biotope are unlikely as species are sufficiently long-lived that they will survive albeit is sub-optimal conditions. An intolerance of low is therefore suggested and a recoverability of very high. However, a prolonged increase (greater than a year) in turbidity will most likely result in a reduction in vertical extent of the biotope.
Decrease in turbidity
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Turbidity will primarily affect Laminaria hyperborea and the depth to which it is likely to grow. In the sub-biotope MIR.LhypGz.Pk Laminaria hyperborea occurs at low density, due mainly to limiting light levels. Red algae are shade tolerant extending to greater depths and probably not as intolerant of increases in turbidity as kelp species. Suspended material in the vicinity of outfalls has been reported to result in reduced depth range and fewer new plants under the canopy (Fletcher, 1996) (see 'siltation' above). Within the time frame of the benchmark, some recruitment of kelp sporelings may occur deeper than the existing downward limit of the biotope and so a increase in extent is possible and the biotope may benefit so that an assessment of not sensitive* is appropriate although no associated increase or decrease in species richness is expected.
Increase in wave exposure
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The biotope occurs in exposed or moderately wave exposed situations. Increased wave exposure is likely to remove older kelp plants, especially from the upper extent of the kelp forest, where Laminaria hyperborea may become replaced by kelps tolerant of stronger wave action such as Laminaria digitata and Alaria esculenta. However, Echinus esculentus has been observed to occur as shallow as 15 m depth off the most wave-exposed rock (Rockall) in Britain (K. Hiscock, own obs.) suggesting high tolerance of wave action and continued grazing. Nevertheless, movement and feeding in Echinus esculentus may be reduced allowing more foliose red algae and epifauna to survive, perhaps progressing the biotope towards EIR.LhypR. Also, increased water movement is likely to favour the growth of suspension feeding species such as erect Bryozoa and hydroids. In view of the possibility of a change in biotope, intolerance is assessed as high. Following a return to previous conditions of wave exposure, nearby populations of sea urchins would rapidly return to intense grazing although may not affect established plants so that a recoverability of high is suggested.
Decrease in wave exposure
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The biotope occurs in exposed or moderately wave exposed situations. Decreased wave exposure may allow settlement of increased amounts of silt and will decrease supply of food for suspension feeders, especially as the biotope occurs in areas sheltered from strong tidal flow. In very sheltered situations Laminaria hyperborea is replaced by Saccharina latissima and the biotope may change significantly should the wave exposure drop from moderately exposed to very sheltered, perhaps to £SIR.LsacRS.Psa£ where Psammechinus miliaris becomes the dominant grazer. In view of the possibility of a change in biotope, intolerance is assessed as high. Following a return to previous conditions of wave exposure, settlements of Saccharina latissima would be removed, Laminaria hyperborea would re-establish and Echinus esculentus migrate back or settle from the plankton. Assuming that the switch to a different biotope had not occurred completely within the time scale of change (see benchmark) a recoverability of high is suggested.
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Hydroids, bryozoans, sponges, sea urchins and ascidians are unlikely to be sensitive to noise or vibration at the benchmark level. Fish species using the kelp beds as a nursery or feeding ground may be disturbed by underwater noise or vibration. Fish species may be temporarily scared away from the areas but few if any adverse effects on the biotope are likely to result.
Visual Presence
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Fish species using the kelp beds as a nursery or feeding ground and crustaceans may be affected or disturbed by visual presence of seals or scuba divers but it is unlikely that the disturbance will adversely affect feeding or residence. Other species in the biotope are likely to be not sensitive to visual presence.
Abrasion & physical disturbance
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Laminarians and red algae are likely to suffer some damage from physical disturbance such as anchor impact, mobile fishing gear, and sand or cobble scour. Therefore, the community as a whole is likely to be of intermediate intolerance to abrasion. This biotope may be more intolerant of higher levels or frequency of abrasion e.g. routine or numerous anchorages or a ship grounding. However, at the level of the benchmark, an intolerance of intermediate is suggested. Recoverability is likely to be high.
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Laminaria hyperborea and other algae cannot reattach once removed and will be lost. Cleared areas are likely to be colonized by opportunistic species such as Alaria esculenta, Saccorhiza polyschides, and Desmarestia spp. but these species were out-competed by Laminaria hyperborea within 3 years (Kain, 1975; Kain, 1979). Norwegian studies suggest that kelp communities take at least 10 years to recover from harvesting (Svendsen, 1972, cited in Birkett et al., 1998b). Similarly many species of epifauna have a permanent attachment and would be lost if displaced. However, Echinus esculentus is relatively insensitive to displacement and would return rapidly to the area. Overall, an intolerance of high is likely. In view of evidence from kelp harvesting, a recoverability of moderate is suggested.

Chemical Factors

Synthetic compound contamination
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Several species that occur in the biotope are known to be sensitive to synthetic chemicals. O'Brian & Dixon (1976) suggested that red algae were the most sensitive group of macrophytes to oil and dispersant contamination (see also Smith, 1968). Large numbers of dead Echinus esculentus were found between 5.5 and 14.5 m depth in the vicinity of Sennen following the Torrey Canyon oil spill, presumably due to a combination of wave exposure and heavy spraying of dispersants in that area (Smith, 1968). Smith (1968) also demonstrated that 0.5 -1ppm of the detergent BP1002 resulted in developmental abnormalities in echinopluteus larvae of Echinus esculentus. 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 >55m from the acidified halogenated effluent discharge polluting Amlwch Bay, Anglesey, albeit at low density. These specimens were greater the 5 years of age, suggesting that spores and/or early stages were more intolerant of (Hoare & Hiscock, 1974). Many other species were excluded from Amlwch Bay and the species richness of the holdfast fauna decreased with proximity to the effluent discharge: amphipods were particularly intolerant of although polychaetes were the least affected (Hoare & Hiscock, 1974). 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 Spermothamnium repens and some tufts of Jania rubens survived together with Laurencia pinnatifida, Gigartina pistillata and Phyllophora crispa from the sublittoral fringe. Delesseria sanguinea was probably to most intolerant of 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 loss of Echinus esculentus would result in growth of those species tolerant of synthetic chemicals and the development of an different biotope. The intolerance of the key structuring species Echinus esculentus and the change to a different biotope that would accompany its demise suggests that intolerance is high, although confidence in that conclusion is very low. Red algae and urchins are likely to recover relatively quickly.
Heavy metal contamination
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Bryan (1984) suggested that the general order for heavy metal toxicity in seaweeds is: Organic Hg > inorganic Hg > Cu > Ag > Zn > Cd > Pb. Cole et al. (1999) reported that Hg was very toxic to macrophytes. Similarly, Hopkin & Kain (1978) demonstrated sublethal affects of heavy metals of 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. Adult Echinus esculentus are long-lived and poor recruitment of may not reduce grazing pressure in the short term. Although macrophytes 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. Overall, it is not expected that the benchmark increase would cause significant mortality of species and the biotope would persist. Therefore an intolerance of low is suggested to represent possible adverse effects on growth.
Hydrocarbon contamination
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Oil spills will rarely result in significant hydrocarbon contamination of infralittoral biotopes as oil does not, except when dispersed by wave action or chemicals, penetrate deeply. The mucilaginous slime layer coating laminarians may anyway 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 (Somerfield & Warwick, 1999). Echinus esculentus populations in the vicinity of an oil terminal in A Coruna Bay, Spain showed developmental abnormalities in the skeleton. The tissues contained high levels of aliphatic hydrocarbons, naphthalenes, pesticides and heavy metals (Zn, Hg, Cd, Pb, and Cu) (Gomez & Miguez-Rodriguez, 1999) but survived. 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. For Echinus esculentus, large numbers of were found dead between 5.5 and 14.5 m in the vicinity of Sennen following the Torrey Canyon oil spill, presumably due to a combination of wave exposure and heavy spraying of dispersants in that area (Smith, 1968). Smith (1968) also demonstrated that 0.5 -1 ppm of the detergent BP1002 resulted in developmental abnormalities in echinopluteus larvae of Echinus esculentus. Whilst experimental studies suggest some intolerance of component species in the biotope, there is little evidence from field studies during oil spill s to suggest significant damage. Overall, it is concluded that a small number of intolerant of species may be adversely affected by hydrocarbon contamination but that the biotope is likely to survive. Recovery may take some time as settlement of adversely affected species will be required but should occur within a year or two.
Radionuclide contamination
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Insufficient information.
Changes in nutrient levels
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Holt et al. (1995) suggest that Laminaria hyperborea may be tolerant of eutrophication since healthy populations are found at ends of sublittoral untreated sewage outfalls in the Isle of Man. Nutrients may be added to macrophyte cultures to increase productivity. Increased nutrient levels e.g. from sewage outfalls, has been associated with increases in abundance, primary biomass and Laminaria hyperborea stipe production but with concomitant decreases in species numbers and diversity (Fletcher, 1996). Increase in ephemeral and opportunistic algae are associated with reduced numbers of perennial macrophytes (Fletcher, 1996). Increased nutrients may also result in phytoplankton blooms that increase turbidity (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 decreased kelp recruitment and possibly 'urchin barrens'. So, algal productivity may increase but nutrients may also favour Echinus esculentus so that the dynamic balance is likely to be maintained and not sensitive is suggested but with low confidence.
Increase in salinity
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The biotope occurs in full salinity and this factor is not relevant.
Decrease in salinity
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Kain (1979) states that Laminaria hyperborea grows optimally between 20 -35 psu but did not survive at 6 psu. Echinoderms are generally unable to tolerate low salinity and possess no osmoregulatory organ (Boolootian, 1966). At low salinity, urchins gain weight and the epidermis loses its pigment as patches are destroyed; prolonged exposure is fatal. The coelomic fluid of Echinus esculentus is isotonic with seawater (Stickle & Diehl, 1987). It therefore seems likely that Echinus esculentus would be adversely affected by lowered salinity. The representative species suggested for this biotope are assessed as intermediate intolerance to reduced salinity. It seems likely that, if lowered salinity is prolonged, Laminaria hyperborea and possibly Echinus esculentus will be lost and the biotope will become a different one, perhaps similar to £SIR.LsacRS.Psa£.
Changes in oxygenation
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The effects of deoxygenation in plants has been little studied. Since plants produce oxygen they may be considered relatively insensitive. However, they may be more intolerant of during darkness when they continue to respire. A study of the effects of anaerobiosis (no oxygen) on some marine algae concluded that Delesseria sanguinea was very intolerant of anaerobic conditions; at 15 °C death occurred within 24hrs and no recovery took place although specimens survived at 5 °C (Hammer, 1972). Under hypoxic conditions echinoderms become less mobile and stop feeding. Death of a bloom of the phytoplankton Gyrodinium aureolum in Mounts Bay, Penzance in 1978 produced a layer of brown slime on the sea bottom. This resulted in the death of fish and invertebrates, including Echinus esculentus, presumably due to anoxia caused by the decay of the dead dinoflagellates (Griffiths et al., 1979). Low concentrations of dissolved oxygen may be detrimental, especially to sedentary benthic epifauna and some species of red algae. A reduction in dissolved oxygen levels to 2 mg/l will probably adversely affect several members of the epifauna and holdfast fauna, although this may be a rare occurrence in exposed conditions. It seems that at least some species in the biotope may be adversely affected by hypoxia and an intolerance of intermediate is suggested but with low confidence. Recovery is likely to be high.

Biological Factors

Introduction of microbial pathogens/parasites
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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. Echinus esculentus is susceptible to 'bald-sea-urchin disease', which causes lesions, loss of spines, tube feet, pedicellariae, destruction of the upper layer of skeletal tissue and death. Bald sea-urchin disease was recorded from Echinus esculentus on the Brittany Coast. Although associated with mass mortalities of Strongylocentrotus franciscanus in California and Paracentrotus lividus in the French Mediterranean it is not known if the disease induces mass mortality in Echinus esculentus (Bower, 1996) and no instances of mass moralities of Echinus esculentus associated with disease have been recorded in Britain and Ireland. Alcyonium digitatum acts as the host for the endoparasitic species Enalcyonium forbesi and Enalcyonium rubicundum (Stock, 1988). Parasitization may reduce the viability of a colony but not to the extent of killing them but no further evidence was found to substantiate this suggestion. It therefore seems that microbial pathogens are likely to cause stress in component species and some mortality of individuals is possible but, overall, intolerance is low.
Introduction of non-native species
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The Japanese kelp Undaria pinnatifida(wakame) has recently spread to the south coast of England from northern Brittany and it thought to compete with native kelps. Macrocystis pyrifera was briefly introduced to French waters, for aquaculture, before it was stopped by international pressure. Macrocystis pyrifera is large and rapid growing and could potentially compete with native kelp species (Birkett et al., 1998b) resulting in different biotopes. There is the potential for currently known non-native species to occur in this biotope although it would be expected that they would not displace native species. However, as the biotope occurs in the north of Britain where no colonizing non-native species are known from sublittoral rocky areas, intolerance is assessed as not relevant. Alien species that may become established in the future may have a much more serious impact if, for instance, they were a disease of or predated on sea urchins.
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Laminaria hyperborea and Echinus esculentus are key structural and functional species respectively. Research on harvested populations of Laminaria hyperborea in Norway suggest that epiphytic and understorey fauna and flora were reduced in harvested areas compared to areas 10 years post harvesting (Sivertsen, 1997 and Rinde et al., 1992, cited in Birkett et al., 1998b). Collecting of Echinus esculentus for the curio trade was studied by Nichols (1984). He concluded that the majority of divers collected only large specimens that are seen quickly and often missed individuals covered by seaweed or under rocks, especially if small. As a result, a significant proportion of the population remains. He suggested that exploited populations should not be allowed to fall below 0.2 individuals per square metre. But in this heavily grazed biotope, any reduction in grazing pressure may significantly affect the community, probably allowing increased escapes of erect epifauna, and possibly macroalgae in shallow examples of the biotope. Removal of urchin predators such as lobsters or crawfish has been implicated in increases in urchin populations and therefore 'urchin barrens' and the loss of kelp beds. However, attempts to correlate sea urchin numbers with specific predators are equivocal (Elner & Vadas, 1990; Birkett et al., 1998; Hawkins & Raffaelli, 1999). It is likely that there is a complex interaction between sea urchin numbers, recruitment and predation. Populations of Echinus esculentus, for example, are probably controlled by several predators, parasites, disease and recruitment. However, removal of predators or other grazers may perturb the community, making it more intolerant of natural fluctuations in sea urchin numbers or other perturbations and may result in loss of areas of kelp and 'urchin barrens'. Extraction of Echinus esculentus may encourage dominant macroalgae, including kelps, and reduce the species richness of epiphyte and understorey fauna and flora. Because of the evidence from Norway regarding kelp harvesting, intolerance has been indicated as high and recoverability moderate (see additional information below).

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Kain (1975) examined recolonization by algae of artificially cleared areas in a Laminaria hyperborea forest in Port Erin, Isle of Man. Cleared concrete blocks were colonized by Saccorhiza polyschides, Alaria esculenta, Desmarestia spp., Laminaria hyperborea, Laminaria digitata, Saccharina latissima (studied as Laminaria saccharina) and un-specified Rhodophyceae at 0.8 m depth. Saccorhiza polyschides dominated within 8 months but had virtually disappeared with 77 weeks to be replaced by laminarians, including Alaria esculenta. After about 2.5 years, Laminaria hyperborea standing crop, together with an understorey of red algae (Rhodophyceae), was similar to that of virgin forest. Rhodophyceae were present throughout the succession increasing from 0.04 to 1.5% of the biomass within the first 4 years. Colonizing species varied with time of year, for example blocks cleared in August 1969 were colonized by primarily Saccharina latissima and subsequent colonization by Laminaria hyperborea and other laminarians was faster than blocks colonized by Saccorhiza polyschides; within 1 year the block was occupied by laminarians and Rhodophyceae only. Succession was similar at 4.4m, and Laminaria hyperborea dominated within about 3 years. Blocks cleared in August 1969 at 4.4m were not colonized by Saccorhiza polyschides but were dominated by Rhodophyceae after 41 weeks, e.g. Delesseria sanguineaand Cryptopleura ramosa. Kain (1975) cleared one group of blocks at two monthly intervals and noted that Phaeophyceae were dominant colonists in spring, Chlorophyceae (solely Ulva lactuca) in summer and Rhodophyceae were most important in autumn and winter.

The development of this community is probably dependant on the abundance and density of the sea urchin population. The majority of the epifaunal and algal crust species were shown to re-colonize cleared areas quickly. For example red crustose algae, encrusting bryozoans, tubeworms, tubicolous amphipods and worms, erect hydroids and bryozoans were reported to cover cleared areas within 1-4 months in spring, summer and autumn (Sebens, 1986). Colonial ascidians re-appeared and achieved significant cover within a year. Sponges (e.g. Halichondria panicea) recovered cover within >2 years while only a few individuals of Alcyonium and Balanus balanus established after 4 years, probably requiring longer to achieve prior cover (Sebens, 1985, 1986). Encrusting coralline algae (e.g. Lithothamnion and Phytomatolithon took 1-2 years to recolonize cleared areas (Sebens, 1985, 1986) and with their slow growth rates probably take many years to recover their original abundance.

In the absence of sea urchin grazing the community below the kelp would probably develop into a foliose algal community. Echinus esculentus produces long-lived planktonic larvae with high dispersal potential. Settlement is thought to occur in autumn and winter (Comely & Ansell, 1988). But recruitment is sporadic or variable depending on locality, e.g. Millport populations showed annual recruitment, whereas few recruits were found in Plymouth populations during Nichols studies between 1980-1981 (Nichols, 1984). Lewis & Nichols (1979) found that adults were able to colonize an artificial reef in small numbers within 3 months and the population steadily grew over the following year. Bishop & Earll (1984) suggested that the population of Echinus esculentus at St Abbs had a high density and recruited regularly whereas the Skomer population was sparse, ageing and had probably not successfully recruited larvae in the previous 6 years. But Echinus esculentus is a widespread, mobile species so that recovery is probably improved by migration from neighbouring areas.

Some of the most useful information for assessing rate of recovery from catastrophic damage comes from studies of the impact of kelp harvesting in Norway which suggest that epiphytic and understorey fauna and flora were reduced in harvested areas compared to areas 10 years post harvesting (Sivertsen, 1997 and Rinde et al., 1992, cited in Birkett et al., 1998b). Full recovery of the biotope is therefore likely to take in excess of 5 years.

This review can be cited as follows:

Hiscock, K. 2002. Grazed Laminaria hyperborea with coralline crusts on infralittoral rock. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 28/11/2015]. Available from: <>