Biodiversity & Conservation


Explanation of sensitivity and recoverability

Physical Factors

Substratum Loss
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Fucus vesiculosus, Littorina littorea, Semibalanus balanoides and Patella vulgata either permanently attach to, or live upon the hard substratum provided by pebbles and cobbles, whilst Hediste diversicolor and Arenicola marina live infaunally in the sediment beneath. Removal of the substratum would remove species, therefore intolerance has been assessed to be high. Recoverability has been assess to be high (see additional information below).
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A 5 cm layer of sediment or debris on a fucoid dominated shore would reduce photosynthesis in algae that are covered and may cause some plants to rot. Sediment would have an especially adverse effect on young germling algae and on the settlement of larvae and spat. Barnacle feeding may be affected and limpet locomotion and grazing would be impaired. Intolerance has been assessed to be intermediate On sheltered shores there is not likely to be enough wave action to mobilise sediment to alleviate the effects of smothering. Recoverability has been assessed to be high (see additional information below).
Increase in suspended sediment
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Fucus vesiculosus is likely to be not sensitive to an increase in suspended sediment because the species is a primary producer and effects of light attenuation are addressed under turbidity. Moore (1977) reported that Mytilus edulis was relatively tolerant of turbidity and siltation, thriving in areas that would be harmful to other suspension feeders. Mytilus edulis possesses efficient shell cleaning and pseudofaeces expulsion mechanisms to remove silt (Moore, 1977), although it should be noted that pseudofaeces production involves an energetic burden (Navarro & Widdows, 1997). Patella vulgata is found in the lower reaches of turbid estuaries where there is sufficient rock or stone on which it may live, and in such muddy habitats, with abundant silt and detritus, the growth rate is rapid (Fretter & Graham, 1994). Hediste diversicolor and Arenicola marina are unlikely to be perturbed by increased concentrations of suspended sediment since they live infaunally. Intolerance to an increase in suspended sediment for the period of one month has been assessed to be low and recoverability very high.
Decrease in suspended sediment
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Fucus vesiculosus is probably not sensitive to a decrease in suspended sediment because the species is a primary producer. Other species in the biotope, in particular the suspension feeding barnacles and mussels are likely to be more intolerant because a decrease in suspended sediment may also result in a decrease in food supplies so growth may be affected. However, the impact of a decrease, of 100mg/l suspended sediment for a month, on the biotope as a whole will be sublethal effects (i.e. growth, fecundity etc.) so intolerance has been assessed to be low. On return to pre-impact suspended sediment levels feeding of affected species and photosynthetic rates will return to normal very rapidly.
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Fucus vesiculosus can tolerate desiccation until the water content is reduced to 30 %. If desiccation occurs beyond this level, irreversible damage occurs. The plants at the top of the shore probably live at the upper limit of their physiological tolerance and therefore are likely to be unable to tolerate increased desiccation and would be displaced by more physiologically tolerant species. Semibalanus balanoides is prevented from growing higher on the shore due to its desiccation tolerance, therefore an increase in the level of desiccation would cause a depression in the upper limit of the species distribution. Patella vulgata is relatively tolerant of desiccation. During exposure to the air feeding and locomotion, are halted unless conditions are very damp. Patella vulgata creates a home-scar allowing it to clamp tightly to the rock to reduce water loss during periods of emersion. The species is tolerant of long periods (several hours) of exposure to the air and can survive up to 65 % water loss (Davies, 1969). Similarly, feeding and locomotion of Littorina littorea are halted unless conditions are very damp. The species is tolerant of long periods (several hours) of exposure to the air. For longer periods of exposure to desiccating influences, a dried mucus seal forms around the shell aperture reducing evaporation. Intolerance has been assessed to be intermediate as the population of important characterizing species may be reduced by the factor. Recoverability has been assessed to be high (see additional information below).
Increase in emergence regime
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The primary effect of emersion upon algae would be desiccation. Emersion for just four hours on a sunny day can reduce the water content of Fucus vesiculosus to just 30 %. This is the critical water content for the alga and water loss beyond this would cause irreversible damage. The species cannot tolerate increased emersion and it is likely that the species distribution would gradually decline. Intolerance has been assessed to be intermediate as Fucus vesiculosus is the important characterizing species. Faunal species of the biotope were assessed to have a lower intolerance to the benchmark increase in emergence than Fucus vesiculosus. For instance, during exposure to the air, feeding and locomotion of Littorina littorea are halted unless conditions are very damp. Littorina littorea is tolerant of long periods (several hours) of exposure to the air. For longer periods of exposure to desiccating influences, a dried mucus seal forms around the shell aperture reducing evaporation Recoverability has been assessed to be high (see additional information below).
Decrease in emergence regime
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A decrease in the emergence regime would reduce desiccation stress and periods of nutrient deprivation endured by the seaweeds. The upper limit of the biotope may also increase up the shore. However, increased immersion would favour the grazing activity of Littorina littorea whose mobility is hindered by dry conditions (it has to produce extra mucus to move) and hence the grazing pressure exerted by it on the algal species may increase. However, intolerance has been assessed to be low and recoverability high (see additional information below).
Increase in water flow rate
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Increase in water flow rate may cause algae to be torn off the substratum or the smaller pebbles with plants attached to be mobilized. For example, in sheltered locations Fucus vesiculosus has numerous air bladders in its fronds, the presence of which would increase the drag making Fucus vesiculosus more vulnerable to being removed. A change in two categories in water flow rate from weak and negligible to moderately strong and strong would entrain and maintain particles in suspension increasing scour. Scour by particulate matter may affect the settlement and survival of algal germlings and faunal spat. Intolerance has been assessed to be intermediate and recoverability high.
Decrease in water flow rate
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The effect of a decrease in water flow rate is likely to be low because the biotope is typically found in location with weak water flow. However, a certain degree of water flow is required to supply nutrients and remove waste products so a further reduction in the water flow may affect species viability e.g. reduced growth rate. Such effects are sub-lethal and intolerance has been assessed to be low. Recoverability has been assessed to be very high on return to prior conditions as species would either remain in situ or migrate in to the biotope.
Increase in temperature
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Fucus vesiculosus can withstand a wide range of temperatures. The seaweed tolerated temperatures as high as 30 °C (Lüning, 1990). The species is well within its temperature range in the British Isles so would not be affected by a long term chronic change of 2 °C. The species showed no sign of damage during the extremely hot summer of 1983, when the average temperature was 8 °C hotter than normal (Hawkins & Hartnoll, 1985). Reproduction in Semibalanus balanoides is inhibited by temperatures greater than 10 °C (Barnes, 1989). Cirral beating rate reaches a maximum at 18 °C in the British Isles (Southward, 1955) This rate declines until all spontaneous activity ceases at 31 °C and at a temperature of 37 °C a coma is induced (Southward, 1955). However, such high temperature are unlikely in waters around Britain and Ireland. Fretter & Graham (1994) showed that adult Patella vulgata could survive temperatures of up to 42 °C and 60 % water loss. Infaunal species would be largely protected from the direct effects of a temperature increase. Intolerance has been assessed to be low as species viability may be affected. Recoverability is likely to be very high on return to prior conditions (see additional information below).
Decrease in temperature
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The distribution of species within the biotope extends to the north of the British Isles so the biotope is probably relatively tolerant of a long term chronic decrease of 2 °C. Fucus vesiculosus tolerated -30 °C in Maine for several weeks (Lüning, 1990).Littorina littorea is tolerant of sub-zero temperatures and the freezing of over 50 % of their extracellular body fluids. In colder conditions an active migration may occur down the shore to a zone where exposure time to the air (and hence time in freezing temperatures) is less. The snails are able to tolerate these low temperatures by drastically reducing their metabolic rate (down to 20 % of normal). A long term chronic temperature decrease, however, may slow down growth. Semibalanus balanoides was not affected during the severe winter of 1962-63 in most areas, except the south east coast which suffered 20-100 % mortality. (Crisp, 1964). However, recovery was rapid in this instance due to heavy settlement the following June (Crisp, 1964). However, the lower lethal temperature varies seasonally and regionally. An exceptional tolerance to cold is acquired in December and January and is lost between February and April. The median lethal temperature in January was -17.6 °C in air for 18 hours, whereas animals in June could only withstand -6.0 °C (Crisp & Ritz, 1967). Adults are also largely unaffected by short periods of extreme cold. Ekaratne & Crisp (1984) found adult limpets continuing to grow over winter when temperatures fell to -6 °C, and stopped only by still more severe weather. However, loss of adhesion after exposure to -13 °C has been observed with limpets falling off rocks and therefore becoming easy prey to crabs or birds (Fretter & Graham, 1994). Intolerance has been assessed to be low because acute temperature decreases reported to cause mortality were greater than that of the benchmark level. Acute temperature decreases in temperature may affect growth and therefore species viability. Recoverability has been assessed to be high on return to prior conditions (see additional information below).
Increase in turbidity
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Increased turbidity may reduce seaweed growth rates by reducing light available for photosynthesis. Faunal species are not directly intolerant of the light attenuation effects of an increase in turbidity. On return to prior conditions the rate of photosynthesis is likely to be stimulated by increased light availability and therefore recovery rapid.
Decrease in turbidity
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A reduction in turbidity would be beneficial to seaweed species in the biotopes, as increased light penetration of the water column would enhance photosynthesis. An assessment of not sensitive* has been made.
Increase in wave exposure
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Fucus vesiculosus can tolerate conditions of moderate wave exposure. However, specimens from exposed locations usually have no air bladders and are known as Fucus vesiculosus forma linearis. The loss of airbladders is thought to be because they increase a plants drag, making them more vulnerable to being torn off by waves. However the intolerance of the SLR.FvesX biotope to increased wave exposure has been assessed to be high as cobbles and pebbles are likely to be rolled over, possibly several times, as a result of wave oscillation. Epilithic species would probably accrue damage. Intolerance has been assessed to be high and recoverability also high (see additional information below).

The important characterizing seaweed of the SLR.Asc.X biotope, Ascophyllum nodosum cannot resist very heavy wave action and wave action is an important factor controlling the distribution of the species. In moving from protected sites to the open sea the number of plants become progressively reduced, and individual plants become increasingly short and stumpy (Baardseth, 1970) and with a higher percentage of injured tissue (Levin & Mathieson, 1991). Thus, the species is only present in sheltered or moderately exposed locations and increased wave exposure causes plants to be torn off the substratum and replaced by Fucus vesiculosus. The intolerance of the SLR.AscX biotope is therefore high. Recoverability of the SLR.FvesX biotope would take an extensive length of time and has been assessed to be low (see additional information below).
Decrease in wave exposure
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The biotopes represented by this review may normally occur in locations that are extremely sheltered from wave action an assessment of a further decrease was considered not to be relevant.
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Faunal species within the biotope may detect noise vibrations but are not known to be intolerant of noise at the benchmark level. An assessment of not sensitive has been made.
Visual Presence
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Faunal species within the biotope lack the visual acuity to be affected by visual presence at the benchmark level. An assessment of not sensitive has been made.
Abrasion & physical disturbance
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Abrasion may damage fronds of established seaweed and crush germlings and faunal species. However, Patella vulgata, for instance has a tough shell that offers protection from any abrading factors and any near vibration causes the shell muscles to contract vigorously, clamping the animal to the rock. However, a short, sharp knock may dislodge an individual leaving it vulnerable to predation. In the intertidal zone, abrasion caused by human trampling may be the most relevant source of abrasion and physical disturbance in the biotope. Trampling has been shown to reduce algal cover on shores (Holt et al., 1997). At the benchmark level intolerance has been assessed to be intermediate as some plants would be removed and some animals crushed. Recoverability has been assessed to be high as a population would remain in situ (see additional information below).
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Fucus vesiculosus and Semibalanus balanoides permanently attach to hard substratum. If removed from the substratum these species are unable to reattach and will probably die. However, if pebbles to which the algae are attached are moved from the biotope, the species would probably survive in maintained in suitable conditions. Intolerance has been assessed to be high (assuming physical removal from the substratum) as Fucus vesiculosus is an important characterizing species. Recoverability has been assessed to be high (see additional information below).

Chemical Factors

Synthetic compound contamination
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Fucoids are generally considered to be quite robust in terms of chemical pollution (Holt et al., 1995). However, Fucus vesiculosus is extraordinarily highly intolerant of chlorate, such as from pulp mill effluents. In the Baltic, the species disappeared in the vicinity of pulp mill discharge points and was also affected even intermediate and remote distances (Kautsky, 1992). Ascophyllum nodosum growing within 100 m of an acidified, halogenated effluent discharge had abnormal and retarded growth (Hoare & Hiscock, 1974). Limpets are extremely intolerant of aromatic solvent based dispersants used in oil spill clean-up. During the clean-up response to the Torrey Canyon oil spill nearly all the limpets were killed in areas close to dispersant spraying. Viscous oil will not be readily drawn in under the edge of the shell by ciliary currents in the mantle cavity, whereas detergent, alone or diluted in sea water, would creep in much more readily and be liable to kill the limpet (Smith, 1968). Barnacles have a low resilience to chemicals such as dispersants, dependant on the concentration and type of chemical involved (Holt et al., 1995), however, they are less sensitive than some species, e.g. Patella vulgata, to dispersants (Southward & Southward, 1978). Most Semibalanus balanoides were killed in areas treated with dispersants (Smith, 1968). However, the barnacle population may suffer indirectly as a result of the mass mortality of grazers. The resultant bloom of algae, and growth of fucoids, within 6 months, grew over and killed surviving barnacles (Hawkins & Southward, 1992). Intolerance to synthetic chemicals has been assessed to be intermediate as populations of some species may be reduced and most species will experience a reduction in some aspect of their viability. On return to prior conditions recoverability of the SLR.FvesX biotope would be expected to be high (see additional information below).
Heavy metal contamination
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Mature fucoids may be particularly robust in terms of chemical pollution. Fucoids may concentrate heavy metals and have been proposed as indicators of heavy metals (Soenko et al., 1976; Luoma & Bryan, 1982; Burt et al., 1992). However uptake of heavy metals from solution by seaweed is influenced by factors such as light, algal nitrogen content, frond age, length of emersion, temperature, salinity, season of the year and presence of other pollutants in the surrounding water (see Lobban & Harrison, 1997) and consequently seaweed may not accurately reflect metal concentrations in the surrounding water. The order of metal toxicity to algae varies with the algal species and the experimental conditions, but generally the order is Hg>Cu>Cd>Ag>Pb>Zn (Rice et al., 1973; Rai et al., 1981), however insufficient information was available to comment further on the particular intolerance of algal species within the biotope. Several faunal species have been assessed to have an intermediate intolerance to heavy metal pollution, e.g. Mytilus edulis, Patella vulgata and Hediste diversicolor (see full information reviews). Intolerance has therefore been assessed to be intermediate and recoverability high assuming deterioration of contaminants.
Hydrocarbon contamination
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Fucus vesiculosus shows limited intolerance to oil. Although, a heavy coating of oil could inhibit light penetration and hence photosynthesis. However, after the Amoco Cadiz oil spill it was observed that Fucus vesiculosus suffered very little (Floc'h & Diouris, 1980).

Observations following oil spills indicate that grazing species are particularly intolerant of oil pollution. For example, thick layers of deposited oil would probably interfere with respiration and spoil food supplies for Patella vulgata. Limpets are unable to remain 'closed-off' from the environment for very long, and the adductor muscles relax occasionally, lifting the shell very slightly exposing the animal to contaminants. After the Braer oil spill, in common with many other oil spills, the major impact in the intertidal zone was on the population of limpets and other grazers. In West Angle Bay, where fresh oil from the Sea Empress tanker reached rocky shores within one day of the spill, limpet mortality was 90 % (Glegg et al., 1999). In the case of the Torrey Canyon spill the quantity and toxicity of the oil dispersants applied to the shore caused more mortalities than the oil alone, Patella vulgata being particularly susceptible, although all animals and many algae were killed in areas heavily sprayed (Raffaelli & Hawkins, 1996). In longer term studies into the environmental effects of oil, refinery effluent discharged into Littlewick Bay, Milford Haven, the number of limpets, usually found in substantial numbers, were considerably reduced in abundance in areas close to the discharge (Petpiroon & Dicks, 1982).
Following oil pollution rocky shore communities are highly disturbed owing to the loss of structuring species. The recovery period can be extensive owing to both loss of species and the subsequent extreme fluctuations in abundance. In the Torrey Canyon incident, following the death of grazing species, a dense green flush of ephemeral algae (Blidingia, Ulva) developed and lasted for nearly a year, whilst after six months Fucus vesiculosus and Fucus serratus began to recolonize the shore and persisted in dense stands for between 1 to 3 years. Patella vulgata recolonized affected shores within the year and thrived in damp conditions under the fucoids, its grazing inhibited further extensive fucoid recruitment. Abnormal numbers of limpets accrued and cleared rocky substrata of much of the algae, allowing, after a period of 4 years (in dispersant treated areas), increased barnacle recruitment. Fucoid cover remained abnormal for the first 11 years following the spill and fluctuated for 15 years, whilst the population structure of Patella vulgata remained abnormal for at least 10 years (Smith, 1968; Southward & Southward, 1978; Hawkins & Southward, 1992).
In the SLR.FesX biotope similar effects of oil pollution would probably be witnessed, in terms of species lost and recruitment processes. Intolerance has been assessed to be high as major changes of species composition would probably occur in the biotope. Recoverability has been assessed to be moderate, as whilst species normally found in the biotope may be found within 5 years, full recovery (in terms of establishment of small-scale spatial and temporal fluctuations in the major components of fucoids, barnacles and limpets) is likely to take 10 years or longer.
Radionuclide contamination
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Insufficient information
Changes in nutrient levels
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Nutrients are essential for algal growth and are often a limiting factor. When plants grow in high densities they are usually competing for nutrients. Moderate nutrient enrichment may lead to overgrowth by green algae and reduced oxygen levels. Ascophyllum nodosum was reported to have declined in the North Atlantic as a result of increased eutrophication (Fletcher, 1996). Idotea is a herbivorous isopod that prefers to graze old, eroding thalli of Fucus vesiculosus (Salemma, 1987). A rise in salinity and nutrients in the late 1970s and early 1980s caused a bloom of microalgae on Baltic populations of Fucus vesiculosus. The microalgal bloom in turn supported a population increase in Idotea species, as the juveniles fed upon the microalgal resource. Adults, however, fed on the adult plant itself and the increased numbers exceeded the carrying capacity of the host, rapidly depleting the Fucus vesiculosus population in the Baltic (Kangas et al., 1982). Little data exists on the effects of increased nutrients on barnacles. A slight increase in nutrient levels could be beneficial for barnacles by promoting the growth of phytoplankton levels and therefore increasing zooplankton levels. However, smothering by ephemeral green algae is a possibility under eutrophic conditions. In turn, stimulated algal growth would increase the food available to Patella vulgata. Mytilus edulis may benefit from moderate nutrient enrichment, especially in the form of organic particulates and dissolved organic material. The resultant increased food availability may increase growth rates, reproductive potential and decrease vulnerability to predators. Therefore, Mytilus edulis was assessed to be not sensitive*. However, long term and/or high levels of organic enrichment may result in deoxygenation (see oxygenation below) and algal blooms, which may have adverse effects indirectly on the biotope. Intolerance has been assessed to be intermediate as population of the important characterizing seaweed may be lost from the biotope as a result of overgrowth by ephemeral epiphytic algae. On return to prior conditions recovery of the SLR.FvesX biotope would be expected to occur within five years, recoverability is therefore high.
Increase in salinity
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The biotope is found in conditions of full and variable salinity. Conditions of hypersalinity are unlikely to occur.
Decrease in salinity
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In the British Isles Fucus vesiculosus can tolerates salinity down to 11 psu, below which it is replaced by Fucus ceranoides (Suryono & Hardy, 1997). In the Teign Estuary in South Devon Ascophyllum nodosum inhabits areas subject to salinities as low as 8 psu (Laffoley & Hiscock, 1993). Semibalanus balanoides can tolerate salinities as low as 12 psu, below which cirral activity ceases (Foster, 1970). Some of the other characterizing species in the biotope are, however, more intolerant than Ascophyllum nodosum to a decrease in salinity. The distribution of Patella vulgata, for example, extends into the mouths of estuaries surviving in salinities down to about 20 psu (Fish & Fish, 1996). Over a period of one year (the benchmark period of reduced salinity) Fucus vesiculosus is likely to be displaced by Fucus ceranoides, which is adapted to living in brackish water conditions. Intolerance has therefore been assessed to be high as, in the absence of Fucus vesiculosus, the biotope would not be recognized. Species diversity would decline as intolerant species would be lost. On return to prior conditions, increased salinity would exert a physiological stress upon colonizing species, probably reducing their abundance and allowing Fucus vesiculosus to become established and dominate again. Therefore recoverability has been assessed to be high.
Changes in oxygenation
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The biotope occurs in areas where still water conditions probably do occur and so may experience deoxygenated conditions. The effects of deoxygenation on macroalgae are poorly studied. Kinne (1972) reports that reduced oxygen concentrations inhibit both photosynthesis and respiration. Cole et al. (1999) suggest possible adverse effects on marine species below 4 mg/l and probable adverse effects below 2mg/l. Patella vulgata is an intertidal species and is able to respire in air, so will only be intolerance of low oxygen in the water column intermittently during periods of tidal immersion. Semibalanus balanoides can respire anaerobically, so it can tolerate some reduction in oxygen concentration (Newell, 1979). Mytilus edulis is highly tolerant of hypoxia at the benchmark level (2mg/l O2 for 1 week), although it incurs a metabolic cost and, hence, reduced growth. Intolerance has been assessed to be low at the benchmark level and recoverability on return to prior conditions immediate.

Biological Factors

Introduction of microbial pathogens/parasites
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Although bacteria and fungi are associated with Ascophyllum nodosum no information could be found on any disease causing microbes. Nematodes have been associated with small, round galls, usually located near the air vesicles in Ascophyllum nodosum (Barton, 1892). Patella vulgata has been reported to be infected by the protozoan Urceolaria patellae at sites sheltered from extreme wave action in Orkney (Brouardel, 1948). Baxter (1984) found shells to be infested with two boring organisms, the polychaete Polydora ciliata and a siliceous sponge Cliona celata. Barnacles are parasitised by a variety of organisms and, in particular, the cryptoniscid isopod Hemioniscus balani. Heavy infestation can cause castration of the barnacle but levels of infestation within a population vary. Although infection by microbial pathogens and infestation have the potential to kill populations of species, insufficient information has been found concerning such effects on populations. Intolerance has therefore been assessed to be low as infestation and disease would affect species viability rather than survival. Recoverability of the SLR.FvesX biotope has been assessed to be very high but with low confidence (see additional information below).
Introduction of non-native species
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The only species identified as potentially threatened by non-native species was the barnacle, Semibalanus balanoides by the Australasian barnacle Elminius modestus which was introduced to British waters on ships during the second world war. Elminius modestus does well in sheltered estuaries and bays (locations where SLR.FvesX is found), where it could potentially displace Semibalanus balanoides and Chthamalus montagui. Semibalanus balanoides and Chthamalus montagui are important species in the biotope, and Elminius modestus occupies the same niche as these species. Elminius modestus seems well adapted to survive in the SLR.FvesX biotope. It withstands variable salinity and turbid waters. It is fast growing and produces several broods per year as opposed to one brood produced by Semibalanus balanoides. Balanus improvisus may have been displaced from the Tamar Estuary, Devon and Cornwall , and become extremely rare in the Dart Estuary, Devon as a result of competition with Elminius modestus (A. Southward pers. comm. to Eno, 1997). However, the overall effect on the dynamics of rocky shores has however, been small as Elminius modestus has been observed to replace some individuals of a group of co-occurring barnacles (Raffaelli & Hawkins, 1996). Intolerance has been assessed to be low as, although the physical appearance of the biotope would not change dramatically, the population of native species may become depressed.
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Fucus vesiculosus is not targeted for extraction. However, species that may be collected from this biotope (but not identified as important structural or functional species) are the infaunal species Hediste diversicolor and Arenicola marina. These species are frequently used by anglers as bait and considering that the biotope is found in enclosed coastal areas in the proximity of harbours bait collectors are likely to visit the biotope. To collect infaunal species the substratum requires digging, consequently pebbles and cobbles would be turned over. Such activity would expose surfaces for colonization but epilithic species on what was the top side of the pebble are likely to be damaged by abrasion and smothered. Whilst mobile species such as Littorina littorea and Patella vulgata may be capable of relocating, species such as Semibalanus balanoides are not. The fronds of Fucus vesiculosus are likely to rot if trapped between the sediment surface and the cobbles and pebbles and photosynthesis would certainly be impaired. Intolerance has therefore been assessed to be intermediate, but recoverability high (see additional information below).

Additional information icon Additional information

Recoverability: Fucus vesiculosus recruits readily to cleared areas of the shore and full recovery takes 1-3 years in British waters (Hartnoll & Hawkins, 1985; Hawkins & Hartnoll, 1985). Faunal species of the biotope are widespread and fecund with a planktonic larval stage so dispersion can occur over some distance.
Recoverability of the SLR.Asc.X biotope will differ from that of the SLR.FvesX and SLR.FserX biotope. Where the whole plant is removed, recovery is slow due to the slow growth rate and poor recruitment of Ascophyllum nodosum. In their work on fucoid recolonization of cleared areas at Port Erin, Knight and Parke (1950) observed that even eight years after the original clearance there was still no sign of the establishment of an Ascophyllum nodosum population. Even in an area where many plants remained after harvesting no repopulation was seen for several years (Printz, 1959). The species is extremely fertile every year and Printz (1959) suggested that some special combination of climatic or environmental conditions is needed for an effective recolonization. Recovery of the population to original abundance and biomass is likely to take a very long time and has been assessed to be typically low.

This review can be cited as follows:

Budd, G.C. 2002. Fucus vesiculosus on mid eulittoral mixed substrata. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 30/11/2015]. Available from: <>