Biodiversity & Conservation

LR.LLR.FVS.Fcer

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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Seaweed species that characterize this biotope are permanently attached to the substratum, species such as barnacles and Littorina littorea are epilithic, all would be removed with the substratum. Intolerance has therefore been assessed to be high. Recoverability has been assessed to be high (see additional information below).
Smothering
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The effects of smothering would depend on the state of the tide when the factor occurred. If smothering happened when the tide was out, the seaweed would be buried under the sediment reducing CO2 diffusion, light penetration and hence photosynthesis. If smothering occurred while the tide was in, some fronds of the seaweed might escape burial allowing the plant continue photosynthesis. Prosobranchs may experience difficulties in regaining the surface, in the case of Littorina littorea death normally occurs within 24 hours. However, if the sediment is well oxygenated and fluid (as with high water, high silt content) snails may be able to move back up through the sediment. Smothering would bury barnacles and prevent feeding. It is likely that barnacles could withstand smothering for some period of time because they are able to respire anaerobically, however no studies have been found to confirm survival under sediment. Intolerance has been assessed to be intermediate as some individuals might die and in general the viability of populations would be reduced. Recovery has been assessed to be high (see additional information below).
Increase in suspended sediment
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The seaweed species of the biotope would not be directly affected by an increase in suspended sediment (effects of light attenuation are addressed under turbidity). Barnacles may experience some clogging of its feeding apparatus, to be cleared at energetic cost, whilst increases in siltation resulting from increased suspended sediment over the period of a year, may in part, have some influence in changing substratum type and clog crevices utilized by prosobranchs, such as Littorina littorea, to avoid desiccation. If habitat type is no longer optimal then the snail population may decrease. Intolerance has been assessed to be low as the viability of some species may be reduced, e.g. prosobranch species. Recoverability has been assessed to be high on return to prior conditions (see additional information below).
Decrease in suspended sediment
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The biotope is likely to be not sensitive to a decrease in suspended sediment because most of the key characterizing species are primary producers and do not require particles for feeding or tube building. Barnacles may be more intolerant because a decrease in suspended sediment may result in a decrease in food availability, so growth may be affected. Intolerance has been assessed to be low as viability of the species may be reduced for the period that the factor operates. On return to prior conditions optimal feeding would probably commence almost immediately.
Desiccation
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Whilst mild desiccation may slightly stimulate photosynthesis of intertidal seaweed, significant drying usually causes a substantial decline. More importantly, the growth rate decreases as a result of even mild desiccation, and repeated exposures are more deleterious than a single, more severe episode (Hodgson, 1984). Furthermore, an increase in the level desiccation at the benchmark level, may result in the upper limit of the Fucus ceranoides distribution on the shore becoming depressed, whilst a decrease in the level of desiccation may allow the species to grow further up the shore. Fucus spiralis can tolerate desiccation until the water content has been reduced to 10-20 % (Lüning, 1990). If water is lost beyond this critical level irreversible damage occurs. During exposure to the air, feeding and locomotion of prosobranchs such as 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. Desiccation tolerance of barnacles varies considerably with the size of the barnacle and its position on the shore. Semibalanus balanoides of 5 mm diameter have a median lethal time (MLT) of 45 hours at 19 °C, whereas barnacles of 11 mm diameter can withstand 92 hours. The median lethal time occurs when 64 % of the water is lost from the body (Foster, 1971a). Desiccation tolerance increases with shore height and increasing body size. The MLT of high shore specimens was reported to be between 48-98 % higher than low shore specimens, depending on size (Ware & Hartnoll, 1996). 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 and increased competition from chthamalid barnacles. The intolerance of the biotope has been assessed to be intermediate owing to a probable reduction in the upper limit of the species and hence reduction in extent of the biotope. Recoverability has been assessed to be high (see additional information below).
Increase in emergence regime
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Illuminated intertidal Fucus plants grow significantly only when submerged; irradiating them while emersed (but unstressed) is ineffective (Schonbeck & Norton, 1979). Removal from water also deprives seaweeds from their source of nutrients, including most of the inorganic carbon. As soon as seaweed is removed from water its photosynthesis rate drops sharply. Semibalanus balanoides and Littorina littorea would experience reduced feeding opportunities, as the balances would remain closed and the snails would need to seek refuge in damp areas to avoid desiccation or migrate to other habitats where feeding activity is not hindered. Intolerance has been assessed to be low owing to effects on species viability (e.g. reduced growth). Recoverability on return to prior conditions has been assessed to be immediate.
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.
Increase in water flow rate
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Tidal flow in the biotope is typically very low in the biotope, therefore it is reasonable to expect that the biotope would be intolerant of an increase in water flow rate from negligible to moderately strong (0.5 -1.5 m/sec). Fronds of the seaweed would generally conform to the flow, but may be torn or damaged. Littorina littorea is found in areas with water flow rates from negligible to strong. Increases in water flow rates above 6 knots may cause Littorina littorea in less protected locations (e.g. not in crevices etc) to be continually displaced into unsuitable habitat but in this biotope such displacement is unlikely to occur. Barnacles can tolerate very high flow rates so would not be affected. Intolerance has been assessed to be intermediate as dominant species within the biotope may be damaged. Recoverability has been assessed to be high (see additional information below).
Decrease in water flow rate
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A water flow is important in gas exchange for photosynthesis, respiration and consequently growth of seaweed. Water flow rate in the biotope is typically weak/negligible so an additional decrease in water flow may cause stagnation of the surrounding water, with consequential effects on growth. However, nutrients would be replenished by the flood tide, so on balance effects are unlikely to be significant and an assessment of not sensitive has been made.
Increase in temperature
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Algal symptoms of thermal stress include frond hardening, bleaching or darkening, and cell plasmolysis. Fucus spiralis can tolerate temperatures up to 28 °C and a chronic long-term increase in temperature may be beneficial because the optimum temperature for growth of the species is 15 °C (Lüning, 1990). However the species showed some damage during the unusually hot summer of 1983 when temperatures were on average 8.3 °C higher than normal (Hawkins & Hartnoll, 1985). Littorina littorea survives in upper shore rockpools where temperature may exceed 30 °C. However, at water temperatures above about 20 °C growth rate is reduced. 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). Intolerance has been assessed to be low as species within the biotope seem relatively tolerant of temperature increases above that of the benchmark.
Decrease in temperature
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The distribution of fucoid species within the biotope extends to the north of the British Isles, so would probably be tolerant of a long-term chronic decreases in temperature. Of the other species in the biotope, adult Littorina littorea can tolerate 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). However, long-term chronic temperature decreases may slow down growth. Semibalanus balanoides acquires an exceptional tolerance to cold in December and January which 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). 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). The mean monthly sea temperature must fall below 7.2 °C for the gametes to mature (Barnes, 1958). Intolerance has been assessed to be low as temperature decreases may affect species viability rather cause mortalities at the benchmark level. On return to prior conditions recovery is likely to be immediate.
Increase in turbidity
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Changes in turbidity would alter the light available for photosynthesis during immersion. In laboratory experiments, Strömgren & Nielsen (1986) observed that there was a strong correlation between the total radiant energy during the day and the average daily growth rates whilst Ramus et al. (1977) observed reduced growth rates of fucoid algae with depth. Thus, increased turbidity has the potential to cause local reduction in fucoid biomass. Intolerance has been assessed to be low owing to effects on the viability of seaweed species that this factor would have. On return to prior conditions recovery is likely to be rapid as increased light penetration would favour photosynthesis and hence growth.
Decrease in turbidity
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Decreased turbidity and the concomitant increase in light penetration of the water column would favour photosynthesis by the dominant fucoid species and Enteromorpha with enhanced growth. The biotope has therefore been assessed not to be sensitive*.
Increase in wave exposure
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Wave action is a major cause of seaweed mortality at all stages of growth, especially for settling spores. Increases in wave exposure would probably result in plants and germlings of Fucus ceranoides being torn off the substratum or mobilisation of the substratum with the plants attached, especially so in the SLR.FcerX biotope where the substratum may consist largely of mobile cobbles and rocks. The biotope contains other fucoids, despite reduced salinity, although Fucus ceranoides always dominates. For instance, Ascophyllum nodosum cannot resist very heavy wave action and wave action is an important factor controlling the distribution of this 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). On wave exposed shores prosobranchs may be dislodged or damaged. Littorina littorea regularly have to abandon optimal feeding sites in order to avoid wave-induced dislodgement which may result in a decreased growth rate (Mouritsen et al., 1999). Increases in wave exposure will probably cause a decrease in population size. Intolerance to increased wave action has been assessed to be intermediate, as some individuals may be lost or damaged. Recoverability of fucoid species, with the exception of Ascophyllum nodosum, and faunal species is likely to be high (see additional information below).
Decrease in wave exposure
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The biotope typically occurs in locations that are very/extremely sheltered from wave action, therefore an intolerance assessment of a further decrease in this factor was not considered relevant.
Noise
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The biological community was considered to be not sensitive to noise.
Visual Presence
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The biological community either lacks visual perception, is unlikely to have the visual acuity to detect objects not normally found in the marine environment.
Abrasion & physical disturbance
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Abrasive forces can damage and remove fronds and germlings of Fucus ceranoides and other algae. Abrasion caused by human trampling can significantly reduce the cover of fucoid algae on a shore (Holt et al., 1997) and may be the most relevant source of abrasion and physical disturbance to the SLR.Fcer biotope. Therefore, intolerance has been assessed to be intermediate. Recoverability of fucoid species (except Ascophyllum nodosum) and faunal species is likely to be high (see additional information below).
Displacement
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Fucoid species and barnacles are permanently attached to the substratum and would be unable to attach to the substratum once displaced. Similarly, barnacles are permanently attached to the substratum and cannot survive if detached. Mobile species, such as Littorina littorea, would be able to re-attach so would probably recover immediately, given an appropriate substratum. Intolerance has been assessed to be high as fucoid species characterize the biotope. Whilst individual plants or sessile animals that had been displaced may not recover, recoverability of the biotope has been assessed to be high (see additional information below).

Chemical Factors

Synthetic compound contamination
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Synthetic chemicals may be used directly in or vicinity of the marine environment or enter estuarine areas through river discharge and runoff. Assessment of effects have largely been conducted within the laboratory. Moss & Woodhead (1975) tested the effects of Paraquat and Amitrole (3-amino-1, 2, 4-triazole) on the settlement, germination and growth of Ulva. Zygotes were able to develop into filaments in the presence of Paraquat at 7 mg/L but germination was deferred at higher concentrations. Ulva (as Enteromorpha) was more intolerant of amitole than Paraquat. Littorina littorea was tolerant of high TBT levels (Oehlmann et al., 1998) and is often present in areas where the very TBT intolerant dog whelk Nucella lapillus has disappeared. Although imposex is rare in Littorina littorea strong TBT-toxication may affect a population significantly by reducing reproductive ability, through the development of intersex (Deutsch & Fioroni, 1996). Intersex is defined as a change in the female pallial oviduct towards a male morphological structure (Bauer et al., 1995). However, only sexually immature and juvenile individuals of Littorina littorea are able to develop intersex. Also, owing to the reproductive strategy of Littorina littorea, which reproduces by means of pelagic larvae, populations do not necessarily become extinct as a result of intersex (Casey et al., 1998) and so recoverability is likely to be good. Holt et al. (1995) concluded that barnacles are fairly sensitive to chemical pollution. Most Semibalanus balanoides were killed in areas treated with dispersants after the Torrey Canyon oil tanker spill (Smith, 1968). Insufficient information was found concerning synthetic chemicals and the intolerance of fucoid species. Intolerance has been assessed to be intermediate owing to potential effects on species viability and/or loss of a species from the community. Recoverability has been assessed to be high (see additional information below), assuming deterioration of toxicants from the system.
Heavy metal contamination
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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). Fucus ceranoides accumulates heavy metals in its tissues (Barreiro et al., 1993), but information regarding the effects that such accumulation might have was not available. Information available suggests that adult gastropod molluscs are rather tolerant of heavy-metal toxicity (Bryan, 1984). Winkles may absorb metals from the surrounding water by absorption across the gills or from the diet, and evidence from experimental studies on Littorina littorea suggest that the diet is the most important source (Bryan et al., 1987). Clarke (1947) investigated the intolerance of Semibalanus balanoides to copper, mercury, zinc and silver. He found that 90 % of barnacles died when held in 0.35 mg/l Cu carbonate for two days. Zinc, mercury and silver killed 90 % of barnacles in two days at concentrations of 32 mg/l, 1 mg/l and 0.4 mg/l respectively. Pyefinch & Mott (1948) recorded median lethal concentrations of 0.32 mg/l copper and 0.36 mg/l mercury over 24 hours for this species. However, barnacles may tolerate fairly high level of heavy metals in nature, for example they are found in Dulas Bay, Anglesey, where copper reaches concentrations of 24.5 µg/l, due to acid mine waste (Foster et al., 1978). Intolerance has been assessed to be intermediate owing to the possible loss of barnacles and probable reduction in viability of other species within the community. Recoverability has been assessed to be high (see additional information below).
Hydrocarbon contamination
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Experience gained from incidents such as the Torrey Canyon and Exxon Valdiz oil spills suggests that adult intertidal fucoids are not generally very intolerant of oil, though blanketing effects can be severe in very badly affected areas (see smothering) (Holt et al., 1997). However, Fucus spiralis disappeared from heavily oiled shores some months after the Amoco Cadiz oil spill. The species suffered less than fucoids further down the shore, probably due to its position high on the shore, which meant that oil was present on the algae for a long time before being washed off (Floc'h & Diouris, 1980). Prosobranchs, such as Littorina littorea, are reported to be highly intolerant of hydrocarbon pollution. Significant reductions in densities of Semibalanus balanoides were observed after the Exxon Valdez oil spill (1989) , especially at high and mid shore (Highsmith et al., 1996). Although barnacles survived on most shores, up to 98 % reduction in barnacle cover resulted primarily from treatment by hot-water washing. However, recovery on most rocky shores was reported to have progressed considerably by July 1992 (Houghton et al., 1996). Experimentally, Semibalanus balanoides has been found to tolerate exposure to the water-accommodated fraction of diesel oil at 129.4 µg/l for two years (Bokn et al., 1993). Intolerance has been assessed to be intermediate as Littorina littorea and Semibalanus balanoides may be lost from the biotope as a result of hydrocarbon contamination. Recoverability has been assessed to be moderate following the loss of grazing species. The opportunistic species Ulva is likely to be the first macrophyte to colonize the shore after a disturbance that removes herbivorous grazers (Smith, 1968; Southward & Southward, 1978; Hawkins & Southward, 1992). Small-scale spatial and temporal patterns of both flora and fauna are likely remain disrupted for a period longer than five years.
Radionuclide contamination
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Insufficient information.
Changes in nutrient levels
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When in high densities, seaweeds compete for space, light and nutrients. Nutrient availability is the most important factor controlling germling growth. Nitrogen most frequently limits the growth of seaweeds, phosphorus being the second most limiting (Lobban & Harrison, 1997). Plants under low nutrient regimes achieve smaller sizes and may be out competed. A 50% reduction in the annual average concentration of the limiting nutrients would probably affect viability of seaweed species within the biotope and subsequently grazing species, such as Littorina littorea. Therefore intolerance to nutrient reduction has been assessed to be low. Recovery has been assessed to be high on return to prior conditions, as nutrient limitation in combination with reduced salinity would probably ensure that the substratum remained relatively bare and thus readily available for colonization.
However, the alternative scenario of a 50 % increase in nutrient availability may favour excessive growth of opportunistic species such as Ulva. For example, Ulva (as Enteromorpha) species were observed to overgrow germlings of fucoid species in experimental recolonization plots situated near a sewage outfall (Rueness, 1973). Species diversity would decline and the biotope would not be recognized in the absence of its characterizing fucoid species. Intolerance has therefore been reported to be high following nutrient enrichment. The higher intolerance of the two scenarios has been recorded in the intolerance matrix. On return to prior conditions recoverability is likely to be high. Littorina littorea feeds on Ulva and the population may increase as a consequence of abundant food, resultant grazing pressure may serve to control ephemeral algal growth.
Increase in salinity
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Fucus ceranoides is physiologically adapted to brackish conditions. It is thought to be absent from fully saline sites due to an inability to compete with the faster growing fucoids, such as Fucus vesiculosus and a physiological intolerance of fully saline conditions. When cultured in high salinity, Suryono & Hardy (1997) found that plant tissue decayed within 5 to 6 weeks. Khjafi & Norton (1979) recorded similar results, but, Baeck et al. (1992) found that Fucus ceranoides grew at full salinity for 11 weeks. The biotope is likely to have a high intolerance to a chronic long-term increase in salinity as the key characterizing species Fucus ceranoides would be replaced by fucoid species that thrive in marine conditions. In the absence of Fucus ceranoides the biotope would not be recognized. Species richness may rise as the substratum would probably to colonized by marine species which were previously excluded by an intolerance to reduced salinity. On return to prior conditions, reduced salinity would exert a physiological stress upon colonizing species, probably reducing their abundance and allowing Fucus ceranoides to become established and dominate again. Therefore recoverability has been assessed to be high.
Decrease in salinity
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SLR.Fcer is a reduced (18-30 psu) salinity biotope. Species that are present in saline waters of the open coast may be present, but are probably close to the lowest salinity regime tolerable. Fucus ceranoides is physiologically adapted to brackish water conditions and it is always dominant in this biotope, but experiences reduced growth in freshwater. Other fucoid species such as Fucus spiralis, Fucus vesiculosus and Ascophyllum nodosum may be present, but are already competitively inferior in brackish waters and may further decline in abundance following a further decline in salinity. For instance, Fucus spiralis and Fucus vesiculosus are both replaced by Fucus ceranoides below 11 psu. Littorina littorea may be found in waters of full, variable and reduced salinities. It is also an intertidal species where precipitation can cause exposure to low salinity water. Short periods of reduced salinity are unlikely to have adverse effect. Furthermore, it would probably migrate to avoid conditions that it could not tolerate. Semibalanus balanoides can tolerate salinities as low as 12 psu, but below which cirral activity ceases (Foster, 1970). However, barnacles can survive periodic emersion in freshwater, e.g. from rainfall or fresh water run off, by closing their opercular valves (Foster, 1971b). They can also withstand large changes in salinity over moderately long periods of time by falling into a "salt sleep". In this state motor activity ceases and respiration falls, enabling animals to survive in freshwater for three weeks (Barnes, 1953). The non-native barnacle, Elminius modestus, competes with Semibalanus balanoides (Crisp, 1958). If salinity declined and became persistently low (< 18 psu) for a period of one year, the barnacle population may become dominated by Elminius modestus which can tolerate salinities much lower than Semibalanus balanoides. Furthermore, Elminius modestus produces several broods in a year, compared to the one brood of Semibalanus balanoides, enhancing its competitive superiority in low salinity environments. Intolerance has been assessed to be low. The community is resilient and likely to tolerate short periods of reduced salinity, whilst in the long-term some species may experience reduced growth and decline in abundance as a consequence of displacement by other species. However, such species would be replaced by those of a similar if not identical functional group, so the biotope would not change dramatically. On return to prior conditions, increased salinity would exert a physiological stress upon colonizing species, probably reducing their abundance and allowing species to become established again. Therefore recoverability has been assessed to be high.
Changes in oxygenation
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Littorina littoreamay endure long periods of oxygen deprivation. The prosobranch can tolerate anoxia by drastically reducing its metabolic rate (down to 20 % of normal) (MacDonald & Storey, 1999). However, this reduces feeding rate and thus the viability of a population may be reduced. Normal metabolic rate and feeding can be re-established rapidly on return to more hospitable conditions. The barnacle Semibalanus balanoides can respire anaerobically, so it too can tolerate some reduction in oxygen concentration (Newell, 1979). When placed in wet nitrogen, where oxygen stress is maximal and desiccation stress is low, Semibalanus balanoides had a mean survival time of 5 days (Barnes et al., 1963). Intolerance has therefore been assessed to be low at the benchmark level and recovery rapid.

Biological Factors

Introduction of microbial pathogens/parasites
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Barnacles are parasitised by a variety of organisms and, in particular, the cryptoniscid isopod Hemioniscus balani. Heavy infestation can cause castration of the barnacle. Levels of infestation within a population vary. Intolerance has been assessed to be low as viability would be affected. Once infected recovery of an individual barnacle is unlikely, species diversity within the biotope may begin to decline owing to reduced recruitment.
Introduction of non-native species
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The Australasian barnacle Elminius modestus was introduced to British waters on ships during the second world war. As the species withstands reduced salinity and turbid waters it consequently does well in estuaries and bays, where it can displace Semibalanus balanoides and Chthamalus montagui. Balanus improvisus also seems to be retreating where it is in competition with Elminius modestus (Crisp, 1958; Hayward & Ryland, 1990; A. Southward pers. comm. to Eno, 1997) Elminius modestus may therefore be common in this biotope. Whilst the presence of Elminius modestus may affect the viability of a native species, it will not change the structure of the biotope as the two species occupy the same ecological niche. In this instance, the biotope has been assessed to be not sensitive.
Extraction
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Fucus ceranoides and other important species are not targeted for extraction. Littorina littorea is harvested by hand, without regulation, for human consumption. In some areas, notably Ireland, collectors have noted a reduction in the number of large snails available. Littorina littorea preferentially grazes on Ulva over tougher fucoid species, a reduction in grazing pressure might allow Ulva to dominate and smother the fucoid species during early stages of recruitment. The biotope may begin to change into another biotope, therefore intolerance has been assessed to be high. Adults are slow crawlers so active immigration of snails is unlikely. The larvae form the main mode of dispersal. Littorina littorea is an iteroparous breeder with high fecundity that lives for several (at least 4) years. Breeding can occur throughout the year. The planktonic larval stage is long (up to 6 weeks) although larvae do tend to remain in waters close to the shore. Recruitment and recovery rates should therefore be high.

Additional information icon Additional information

Recoverability
Recolonization of cleared Fucus-dominated areas may take between one to three years in British waters, with the exception of Ascophyllum nodosum, and is especially rapid in areas cleared of grazers (Hartnoll & Hawkins, 1985; Hawkins & Hartnoll, 1985), though it may take longer before normal cycles of stability are reached. Ulva spp. is an ephemeral seaweed that is amongst the first to colonize newly available substrate, usually within weeks, depending upon availability of spores.
Prosobranchs are represented by Littorina littorea, which is widespread and often common or abundant. Adults are slow crawlers so active immigration of snails is unlikely. Recolonization may occur through rafting of adults on floating wood or weed. The larvae form the main mode of dispersal. Littorina littorea is an iteroparous breeder with high fecundity that lives for several (at least 4) years. Breeding can occur throughout the year and the planktonic larval stage is long (up to 6 weeks). Bennell (1981) observed that following accidental removal of barnacles at Amlwch, North Wales, the barnacle populations returned to pre-accident levels within 3 years. However, barnacle recruitment can be very variable because it is dependent on a suite of environmental and biological factors, such as wind direction (see reproduction, in MarLIN review of Semibalanus balanoides). Elminius modestus produces several broods each year. With an initial growth rate over 40 days of ca 6 mm, Elminius modestus reaches maturity in its first season (Eno, 1997). Recolonization, recruitment and recovery rates for the majority of species particularly characteristic of the biotope should therefore be high (within five years).

This review can be cited as follows:

Budd, G.C. 2007. Fucus ceranoides on reduced salinity eulittoral rock. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 21/09/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=271&code=2004>