Biodiversity & Conservation

IR.SIR.Lag.PolFur

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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The majority of species in the biotope live permanently attached to the substratum or to algae growing on the substratum. Substratum loss would result in loss of these populations and therefore intolerance is assessed as high. Recoverability is recorded as moderate (see additional information below). Substratum loss would result in the eradication of entire populations and hence, it is expected that there would be a major decline in species richness in the biotope.
Smothering
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Furcellaria lumbricalis is an erect species which grows up to 300mm in length and is often found with the holdfast buried in coarse sediment (Dixon & Irvine, 1977). Furthermore, Johansson et al. (1998) reported that Furcellaria lumbricalis persisted in areas of the Baltic Sea where eutrophication resulted in high sediment loads. It is likely therefore that mature individuals would be tolerant of smothering with 5 cm of sediment. However, recently settled propagules and small developing plants would be buried by 5cm of sediment and be unable to photosynthesize. For example, Vadas et al. (1992) stated that algal spores and propagules are adversely affected by a layer of sediment, which can exclude up to 98% of light. There is therefore likely to be mortality of some portion of the population. The same is likely to apply to the majority of other algal species in the biotope. Encrusting coralline forms are frequently covered by sediment and appear to be relatively tolerant.
The turf forming suspension feeding fauna are likely to be more intolerant of smothering. The feeding and respiration structures of low growing species such as the ascidian, Clavelina lepadiformis, and the sponge, Halichondria panicea, are likely to become clogged by sediment and kill the species. However, these species colonize and grow rapidly.
In view of the intolerance of the turf forming fauna, biotope intolerance is assessed as high and there is likely to be a decline in species richness. Biotope recoverability is recorded as moderate (see additional information below).
Increase in suspended sediment
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The algae in the biotope, including Furcellaria lumbricalis, are not likely to be affected directly by an increase in suspended sediment. However, increased suspended sediment will have knock on effects in terms of light attenuation (considered in 'turbidity') and siltation. As discussed above in 'smothering', increased rate of siltation may inhibit development of algal spores and propagules resulting in some mortality.
Increased suspended sediment may also result in mortality of ascidians through clogging of respiratory organs (Bakus, 1968). Although Clavelina lepadiformis has relatively wide apertures which help prevent clogging from particles (Naranjo et al., 1996), the structure of its branchial sac is in its simplest form; a gill sheet is formed by a single screen with slits (Fiala-Medioni, 1978). This means that they are less efficient in expelling particles, and more likely to suffer from clogging of feeding apparatus than larger ascidians, such as Ciona intestinalis.
An increase in suspended sediment is therefore likely to cause some mortality of the perennial red algae and the smaller ascidian species so intolerance is assessed as intermediate. In view of the likelihood that some mature individuals of the characteristic algal species would remain in the damaged biotope, a recoverability of high is recorded (but, see additional information below for evidence of slow recovery of Furcellaria lumbricalis). There is not likely to be a change in species richness.
Decrease in suspended sediment
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The suspension feeding fauna in the biotope, including the ascidians and sponges, rely on a supply of nutrients in the water column. A decrease in the suspended sediment would result in decreased food availability for suspension feeders and would be likely to impair growth and reproduction. The benchmark states that this change would occur for one month and therefore would be unlikely to cause mortality. Biotope intolerance is therefore assessed as low. As soon as suspended sediment levels increased, growth would quickly return to normal and hence recovery is recorded as very high.
The red algal turf species Furcellaria lumbricalis and Polyides rotundus are not likely to be affected directly by a decrease in suspended sediment and the consequent decrease in siltation. However, both species are tolerant of a certain amount of siltation as demonstrated by the fact that they are often found with their holdfasts buried in coarse sediment. If siltation decreased, the species may become open to competition from algal species which are less sediment tolerant and would otherwise be excluded, therefore altering the structure of the algal community. However, it is not expected that there would be any change in species richness.
Desiccation
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The biotope occurs sublittorally and is characterized by a number of algal species which are intolerant of emersion. Gessner & Schramm (1971) (reviewed by Bird et al., 1991) recorded that at 18-20°C, the critical saturation deficit for Furcellaria lumbricalis was 60-70% of total water content, as contrasted with 10% for the intertidal species Fucus vesiculosus. On desiccation to 65% total water content, photosynthetic rate was depressed to 60% of the norm and recovery following reimmersion took 7 hours. Desiccation to 42% resulted in only 50% recovery in 7 hours and there was no recovery of photosynthesis in thalli dried to 7% of their original water content. Growth experiments by Indergaard et al. (1986) revealed that growth of Furcellaria lumbricalis in a continuous spray regime was over 3 times faster (227µm/day Vs 61µm/day) than growth in an intermittent spray regime. The benchmark level of desiccation is exposure to air and sun for one hour. It is difficult to determine how this level relates to the recorded reactions, but it is likely that desiccation would cause mass mortality. The ascidians, Clavelina lepadiformis and Ciona intestinalis, are subtidal species with thin tests, which are also likely to be highly intolerant of desiccation. Biotope intolerance is therefore assessed as high and there is likely to be major decline in species richness. Recoverability is recorded as moderate (see additional information below).
Some of the species which occur in the biotope also occur in the littoral zone and are therefore likely to be relatively tolerant of desiccation. These include the red alga, Chondrus crispus, the sponge, Halichondria panicea, and the gastropod, Littorina littorea.
Increase in emergence regime
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SIR.PolFur occurs at the level of extreme low water spring tides and in the shallow subtidal. An increase in emergence of 1 hour every tidal cycle for a year would place the portion of the biotope furthest up the shore in a zone where it would be vulnerable to desiccation. The effects of desiccation are detailed in the relevant section above. Mortality of the intolerant species in the emersed portion of the biotope would be likely so intolerance is assessed as intermediate. In view of the likelihood that some mature individuals of the characteristic algal species would remain in the damaged biotope, a recoverability of high is recorded (but, see additional information below for evidence of slow recovery of Furcellaria lumbricalis). There is not likely to be any change in species richness as the lower portion of the biotope would remain immersed.
Decrease in emergence regime
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SIR.PolFur occurs in the subtidal zone and therefore would not be intolerant of a decreased emergence regime. It is possible that decreased emergence would allow the biotope to colonize further up the shore and extend its range.
Increase in water flow rate
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The biotope typically occurs in areas of "very weak" water flow (Connor et al., 1997a) and is therefore likely to be intolerant of increases in water flow in some way, especially being swept away if only loosely attached. Moderate water movement is beneficial to seaweeds as it carries a supply of nutrients and gases to the plants, removes waste products, and prevents settling of silt. However, if flow becomes too strong, plants may be damaged and growth stunted. For example, Austin (1960b) recorded loss of fronds and restricted growth in Furcellaria lumbricalis specimens from a wave exposed shore in Wales. Additionally, an increase in water flow may inhibit settlement of spores and may remove adults or germlings. The benchmark increase in water flow rate would place the biotope in "moderately strong" flows for a year. Although the increase would not be expected to cause mortality directly, the algal community might become open to competition from species that are more tolerant of high flow conditions, with a consequent decline in the previously dominant species such as Furcellaria lumbricalis.
Suspension feeders generally require some degree of water flow in order to replenish the nutrient supply. However, in strong water flow, delicate feeding and respiration structures may be damaged or individuals may be dislodged (Hiscock, 1983). Feeding and respiration may be inhibited in delicate fauna such as ascidians, but generally they are considered to be tolerant of increases in water flow.
Because of the likely intolerance of the algal community, biotope intolerance is assessed as intermediate. In view of the likelihood that some mature individuals of the characteristic algal species would remain in the damaged biotope, a recoverability of high is recorded (but, see additional information below for evidence of slow recovery of Furcellaria lumbricalis). The species most intolerant of competition may be out-competed resulting in a minor decline in species richness.
Decrease in water flow rate
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The biotope typically occurs in areas of "very weak" water flow, the lowest category on the water flow scale (Connor et al., 1997a) and therefore would be not sensitive to decreases in water flow rate. The characterizing species in the biotope are tolerant of low water flow. For example, Gessner (1955) (cited in Schwenke, 1971) stated that deeper growing species of the benthos near Helgoland, including Furcellaria lumbricalis, had a smaller stagnation-caused respiratory inhibition than surface living species, which enabled them to thrive in low flow conditions.
Increase in temperature
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The important species in the biotope have wide geographic ranges and are likely to be tolerant of higher temperatures than those experienced in the British Isles. The European range of Furcellaria lumbricalis, for example, is from northern Norway to the Bay of Biscay. Novaczek & Breeman (1990) recorded that specimens of Furcellaria lumbricalis grew well in the laboratory from 0-25°C with optimal growth between 10 and 15°C. Growth ceased at 25°C and 100% mortality resulted after 3 months exposure to 27°C. Similarly, Bird et al. (1979) recorded optimum growth at 15°C and cessation of growth at 25°C with associated necrosis of apical segments. Considering that maximum sea surface temperatures around the British Isles rarely exceed 20°C (Hiscock, 1998), it is unlikely that Furcellaria lumbricalis would suffer mortality due to the benchmark increase in temperature. However, elevated temperatures would probably result in inhibition of growth, particularly if the change was acute.
Ciona intestinalis occurs in the Mediterranean Sea, where growth is optimal between 15 and 20°C, and Clavelina lepadiformis occurs in the Adriatic Sea (Hayward et al., 1996). Both these species are also likely to be tolerant of chronic temperature increases but acute changes may inhibit growth.
Biotope intolerance is assessed as low. Growth rates should quickly return to normal when temperatures return to their original levels so recoverability is assessed as very high. None of the species which characterize the biotope are expected to experience mortality due to temperature increases so species richness is not likely to change.
Decrease in temperature
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Furcellaria lumbricalis is a northern species whose range extends to northern Norway. Novaczek & Breeman (1990) recorded that specimens of Furcellaria lumbricalis grew well in the laboratory from 0-25°C with optimal growth between 10 and 15°C. The species tolerated -5°C for 3 months with no mortality. Minimum surface seawater temperatures rarely fall below 5°C around the British Isles (Hiscock, 1998) so Furcellaria lumbricalis is unlikely to be intolerant of the benchmark decrease in temperature.
The ascidians which characterize the biotope also have ranges which extend north of the British Isles, Ciona intestinalis occurring in Sweden and Clavelina lepadiformis in Norway (Hayward et al., 1996). However, Ciona intestinalis appears to be quite intolerant of decreases in temperature. Populations acclimated to Mediterranean temperatures suffered mortality of adults below 10°C while the more resistant young survived, and Swedish populations do not reproduce below 8°C. Crisp et al. (1964) reported late development and possible mortality of ascidians on the Welsh coast during the harsh winter of 1962/3. It is likely that some mortality of ascidians would occur and growth and reproduction would be compromised. Biotope intolerance is therefore assessed as intermediate. Some species may be eliminated from the biotope following a chronic temperature decrease. Halichondria panicea, for example, suffered mass mortality in the harsh winter of 1962/3 (Crisp et al., 1964), so species richness may decline. The biotope recoverability will be determined by the recoverability of the ascidians and is therefore assessed as high.
Increase in turbidity
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In general, an increase in turbidity and therefore decreased light penetration would be expected to negatively affect growth of photoautotrophs. However, the biotope occurs in relatively turbid conditions and is characterized by species tolerant of high turbidity. For example, laboratory experiments by Bird et al. (1979) revealed that Furcellaria lumbricalis was growth saturated at very low light levels (ca 20µE/m²/s) compared to other algae such as Chondrus crispus (50-60µE/m²/s) and Fucus serratus (100µE/m²/s). They suggest that this may explain why Furcellaria lumbricalis is able to proliferate in relatively deep and turbid waters. Similarly, in their review, Bird et al. (1991) comment that in all studies, saturation and inhibition radiances were low for Furcellaria lumbricalis compared to other macroalgae indicating good competitive ability in the attenuated light of deeper or more turbid waters. The turf of Furcellaria lumbricalis and Polyides rotundus which characterizes the biotope is therefore not expected to be sensitive to increases in turbidity. Other algal species in the biotope which are less tolerant of turbidity, e.g. Chondrus crispus and fast growing ephemeral species, are likely to decline due to the decreased light attenuation, and therefore the Furcellaria/Polyides turf may proliferate further due to release from competition.
The characterizing ascidian species are also tolerant of high turbidity. Ciona intestinalis and Clavelina lepadiformis are frequently dominant in areas such as harbours with high levels of suspended solids and low light penetration. Naranjo et al. (1996) found that the Clavelina lepadiformis was dominant in a low rate of water renewal, excess silting and high suspended solid concentrations. The biotope is therefore assessed as not sensitive, although changes in community composition may occur. Grazers, such as Littorina littorea, will probably be impacted by the decrease in availability of the ephemeral algae, Ulva sp. and Ulva sp.
Decrease in turbidity
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Furcellaria lumbricalis is growth saturated at very low light levels compared to other macroalgae (Bird et al., 1979; Bird et al., 1991) and will not be affected directly by increased light availability. However, species which are normally light limited have the potential to proliferate, potentially at the expense of the Polyides/Furcellaria turf. It is possible therefore that the Polyides/Furcellaria turf will no longer dominate the biotope and there will be some mortality of these species. Biotope intolerance is therefore recorded as intermediate, but it should be noted that this assessment is made with very low confidence. In view of the likelihood that some mature individuals of the characteristic algal species would remain in the damaged biotope, a recoverability of high is recorded (but, see additional information below for evidence of slow recovery of Furcellaria lumbricalis).
Increase in wave exposure
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The biotope typically occurs in "very sheltered" or "extremely sheltered" areas (Connor et al., 1997a) and is therefore likely to be intolerant of increases in wave exposure to some degree. The reaction of algae to increases in wave exposure may include compromised growth and damage to or removal of the plants due to physical abrasion by sediments mobilized by wave action. Austin (1960b) noted that Furcellaria lumbricalis from extremely exposed sites have smaller dimensions than individuals from semi-exposed sites and that fronds may be lost due to storm action. Furthermore, Sharp et al. (1993) reported Furcellaria lumbricalis found cast ashore following storms. The majority of algal species in the biotope are likely to be capable of tolerating the benchmark increase of 2 categories on the wave exposure scale, but there may be significant changes in the structure of the community and the dominant species. For instance, a move away from the Polyides/Furcellaria turf to a community dominated by fucoids and laminarians.
Increased wave exposure is likely to have a varied effect on the fauna of the biotope. Large, delicate species such as Ciona intestinalis, which are typical of sheltered habitats such as harbours, may suffer some mortality due to abrasion or detachment, while smaller, more compact species, such as Clavelina lepadiformis, which is most abundant in moderately exposed habitats (Picton, 1997) are likely to thrive.
Because of the likely intolerance of the important characterizing algae, biotope intolerance is assessed as intermediate. In view of the likelihood that some mature individuals of the characteristic algal species would remain in the damaged biotope, a recoverability of high is recorded (but, see additional information below for evidence of slow recovery of Furcellaria lumbricalis).
Decrease in wave exposure
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The biotope typically occurs in "very sheltered" or "extremely sheltered" areas (Connor et al., 1997a) and is therefore not likely to be intolerant of a further decrease in wave exposure. The characterizing species are tolerant of low water movement. Gessner (1955) (cited in Schwenke, 1971) noted Furcellaria lumbricalis had a relatively high tolerance of stagnation, whereas Austin (1960b) commented that Furcellaria lumbricalis from extremely sheltered habitats achieved smaller dimensions than individuals from moderately exposed habitats. Ciona intestinalis is dominant in highly sheltered areas such as harbours.
Noise
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The characterizing species in the biotope have no auditory mechanisms and therefore are not likely to be intolerant of noise.
Visual Presence
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The majority of the species in the biotope have little or no visual acuity and would therefore not be intolerant of visual disturbance. There may be some behavioural disturbance, for instance, mysid shrimps seeking cover, but this will not affect the functioning of the biotope.
Abrasion & physical disturbance
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The species most likely to be affected by physical disturbance are the soft bodied fauna such as the ascidians. They are permanently attached and therefore would be unable to avoid a disturbance such as a dragging anchor or mobile fishing gear

The Polyides/Furcellaria red algal turf is likely to be tolerant of abrasion as the fronds are flexible and cartilaginous. The plants' point of attachment to the substratum, the holdfast, is a potential point of weakness. For example, Taylor (1970) (cited in Sharp et al., 1993) stated that clumps of fronds of Furcellaria lumbricalis were easily removed from the substratum by drag raking but only where the plant had a sufficient number of dichotomies (usually more than 3) to snag in the rake. It is likely therefore that the benchmark level of abrasion would cause some detachment and/or damage. Sharp et al. (1993) noted that, following detachment, Furcellaria lumbricalis plants were capable of reattachment. Growth and reproduction may therefore be compromised by physical abrasion but mortality is not expected to result.

In view of the likely intolerance of the fauna, biotope intolerance is assessed as intermediate. The biotope recoverability will be determined by the recoverability of the ascidians and is therefore assessed as high.
Displacement
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Sharp et al. (1993) noted that, following detachment, Furcellaria lumbricalis plants were capable of reattachment. During this process, growth may be compromised as energy would need to be diverted to the reattachment process.
The ascidian species are not likely to be able to reattach to the substratum quickly enough to settle in a suitable habitat and avoid being washed around and damaged. Biotope intolerance is therefore assessed as high. The biotope recoverability will be determined by the recoverability of the ascidians and is therefore assessed as high.

Chemical Factors

Synthetic compound contamination
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O'Brien & Dixon (1976) suggested that red algae were the most sensitive group of algae to oil or dispersant contamination, possibly due to the susceptibility of phycoerythrins to destruction. They also report that red algae are effective indicators of detergent damage since they undergo colour changes when exposed to relatively low concentration of detergent. Smith (1968) reported that 10 ppm of the detergent BP 1002 killed the majority of specimens in 24hrs in toxicity tests. Laboratory studies of the effects of oil and dispersants on several red algal species concluded that they were all sensitive to oil/ dispersant mixtures, with little difference between adults, sporelings, diploid or haploid life stages (Grandy, 1984) (cited in Holt et al., 1995). Cole et al. (1999) suggested that herbicides, such as simazine and atrazine were very toxic to macrophytes. Hoare & Hiscock (1974) noted that all red algae except Phyllophora sp. were excluded from Amlwch Bay, Anglesey, by acidified halogenated effluent discharge. The evidence suggests that, in general, red algae are very intolerant of synthetic chemicals.
Brown algae may generally be less intolerant of chemical pollution. Fucoids, for example, are quite robust in terms of tolerance of synthetic chemicals (Holt et al., 1997). However, certain species are highly intolerant of particular chemicals; Fucus vesiculosus is extraordinarily highly intolerant of chlorate (Kautsky, 1992) and Laminaria hyperborea was intolerant of atrazine (Hopkin & Kain, 1978).
No information was found concerning the intolerance of the characterizing ascidians.
In view of the likely intolerance of the red algal turf, biotope intolerance is assessed as high. Recoverability is recorded as moderate (see additional information below).
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. The sub-lethal effects of Hg (organic and inorganic) on the sporelings of an intertidal red algae, Plumaria elegans, were reported by Boney (1971). 100% growth inhibition was caused by 1 ppm Hg.
No information was found concerning the effects of heavy metal contamination on the fauna which characterize the biotope and therefore an intolerance assessment has not been attempted.
Hydrocarbon contamination
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O'Brien & Dixon (1976) suggested that red algae were the most sensitive group of algae to oil or dispersant contamination, possibly due to the susceptibility of phycoerythrins to destruction. Laboratory studies of the effects of oil and dispersants on several red algal species concluded that they were all sensitive to oil/ dispersant mixtures, with little difference between adults, sporelings, diploid or haploid life stages (Grandy, 1984) (cited in Holt et al., 1995). Encrusting calcareous algae are reportedly intolerant to hydrocarbon contamination. For example, Crump et al. (1999) describe "dramatic and extensive bleaching" of Lithothamnia following the Sea Empress oil spill.
No information was found concerning the intolerance of the characterizing fauna to hydrocarbons. In view of the likely intolerance of the red algal turf, biotope intolerance is assessed as high and there is likely to be a decline in species richness. Recoverability is recorded as moderate (see additional information below).
Radionuclide contamination
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No information was found concerning the intolerance of the biotope to radionuclides.
Changes in nutrient levels
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Johansson et al. (1998) suggested that one of the symptoms of large scale eutrophication is the deterioration of benthic algal vegetation in areas not directly affected by land-runoff or a point source of nutrient discharge. Altered depth distributions of algal species caused by decreased light penetration and/or increased sedimentation through higher pelagic production have been reported in the Baltic Sea (Kautsky et al., 1986; Vogt & Schramm, 1991). Johansson et al. (1998) studied changes in the benthic algal community of the Skagerrak coast in the Baltic Sea, an area heavily affected by eutrophication, between 1960 and 1997. They noted the disappearance of the red alga, Polyides rotundus, but commented that problems existed in their sampling method. They also noted the increase of delicate red algae with foliaceous thalli, e.g. Delesseria sanguinea and Phycodrys rubens, and tougher red algae with foliaceous thalli, e.g. Phyllophora sp. Increases in the delicate algae were most pronounced at the more wave exposed sites, while increases in the tougher algae occurred at the more sheltered sites with high sedimentation. They commented that these results suggest that the increase of delicate species with large growth potential may have been caused by eutrophication, but that the effect is counteracted when eutrophication results in high sedimentation, in which case the tougher Phyllophora sp. thrive. Additionally, Chondrus crispus and Furcellaria lumbricalis, both species with tough thalli, decreased at the wave exposed sites, possibly due to competition from the more vigorous Phycodrys rubens and Delesseria sanguinea, but persisted at the sites with high sedimentation. These findings suggest that the dominant red algal turf which characterizes the biotope is likely to persist following increases in nutrient levels. However, there may be community changes. For instance, the loss of Polyides rotundus and die back of Furcellaria lumbricalis, possibly due to proliferation and overgrowth of filamentous brown and green algae which are usually nutrient limited in the biotope. Biotope intolerance is therefore assessed as intermediate. In view of the likelihood that some mature individuals of the characteristic algal species would remain in the damaged biotope, a recoverability of high is recorded (but, see additional information below for evidence of slow recovery of Furcellaria lumbricalis).
The suspension feeding fauna in the biotope, including the ascidians, may benefit from an increase in nutrients in the water column (Naranjo et al., 1996).
Increase in salinity
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The biotope occurs in the lowest category on the salinity scale (Connor et al., 1997a). The important characterizing alga, Furcellaria lumbricalis, is a euryhaline species which occurs in a wide range of salinity conditions (Bird et al., 1991). In the Kattegat and the Gulf of St Lawrence, it is reported to compete well with other species at salinities ranging from 25-32 psu (see review by Bird et al., 1991). Growth experiments in the laboratory revealed that optimum growth occurred at 20 psu, the species grew well at 10 psu and 30 psu, but that growth declined above 30 psu to negligible levels at 50 psu (Bird et al., 1979). It is expected that the benchmark increase in salinity may cause reduced growth and fecundity, but that mortality is unlikely. The majority of other species in the biotope, including the characterizing fauna are fully marine species that would not be expected to be intolerant of increases in salinity. Biotope intolerance is therefore assessed as low, on the basis of the intolerance of Furcellaria lumbricalis. When salinity returns to original levels, growth should quickly return to normal so recoverability is assessed as very high. There is not likely to be any change in species richness.
Decrease in salinity
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The biotope occurs in the lowest category on the salinity scale (Connor et al., 1997a) and therefore would not be affected by decreases in salinity. The flora and fauna which characterize the biotope are unusual in their tolerance of very reduced salinity conditions. Furcellaria lumbricalis, for example, forms extensive populations in the main basin of the Baltic Sea where salinity is 6-8 psu in the upper 60-70 m, and its extension into the Gulfs of Bothnia and Finland is limited by the 4 psu isohaline (see review by Bird et al., 1991). The reason for the alga's euryhalinity may lie in its betaine content. Although these substances are present in insufficient quantity to act as osmotic solutes, they may have a complementary osmoregulatory function in modifying membrane behaviour or in transporting ions (Blunden et al., 1989).
The ascidians which characterize the biotope are tolerant of low salinities, but not as low as the characterizing algae. Ciona intestinalis is reported to tolerate 11 psu and Clavelina lepadiformis, 14 psu (Fish & Fish, 1996).
Changes in oxygenation
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The physical conditions in which the biotope occurs, very sheltered and very weak tidal streams, place the community at risk of anoxia and suggests that the characterizing species are likely to be relatively tolerant of low oxygen levels. However, the aerobic organisms are certain to be intolerant of anoxia to some degree, and it is expected that, at the very least, growth and reproduction would be compromised by the benchmark decrease in oxygen levels. Biotope intolerance is therefore recorded as low. Growth should quickly return to normal levels when normoxia returns so recoverability is recorded as very high.
The effects of reduced oxygenation on algae are not well studied. Plants require oxygen for respiration, but this may be provided by production of oxygen during periods of photosynthesis. Lack of oxygen may impair both respiration and photosynthesis (see review by Vidaver, 1972).

Biological Factors

Introduction of microbial pathogens/parasites
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Little evidence exists concerning the infection of the biotope's characterizing species by microbial pathogens. Barton (1901) noted that Furcellaria lumbricalis may become infested with nematode worms and reacts by gall formation. Insufficient information exists to make a biotope intolerance assessment.
Introduction of non-native species
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The brown seaweed Sargassum muticum is a non native species which could potentially invade the biotope. It may proliferate at the expense of the existing flora provided it could tolerate the reduced salinity conditions.
Extraction
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Commercial utilization of Furcellaria lumbricalis is based on the gelling properties of its extracted structural polysaccharide, furcellaran (Bird et al., 1991). Extraction of Furcellaria lumbricalis was reviewed by Guiry & Blunden (1991 - see Importance). Commercial beds of Furcellaria lumbricalis occur in Denmark where the algae are harvested with purpose built trawl nets, whereas in the rest of Europe, the biomass is not sufficient for harvesting. Christensen (1971) (cited in Bird et al., 1991) and Plinski & Florczyk (1984) noted that over-exploitation of Furcellaria lumbricalis has resulted in severe depletion of stocks. A sustainable harvest of Furcellaria lumbricalis occurs in Canada on the shores of the Gulf of St Lawrence where the harvest is sustainable as dredging and raking are prohibited and only storm cast plants may be gathered.

Although not a species indicative of sensitivity, Chondrus crispus may also be collected. Chondrus crispus is harvested commercially in Ireland, Spain, France, Portugal and North America for the extraction of carrageenan (Guiry & Blunden, 1991). In Ireland harvesting has generally remained sustainable through pickers developing an intuitive feel for the annual cycle of local stocks and certain practices which involve pulling only the bushy top half of the frond off leaving the base and holdfast behind (Morrissey et al., 2001).

Although no commercial harvest of Furcellaria lumbricalis as yet occurs in Britain or Ireland, it may be picked on a small scale along with Chondrus crispus and accordingly intolerance has been assessed as intermediate. Various epiphytic species may also experience some loss as a result. Recoverability is recorded as high (see additional information below).

Additional information icon Additional information

Recoverability
The most important factor to consider in assessing the intolerance of the biotope is the intolerance of the important characterizing species. Furcellaria lumbricalis is highly fecund, an average sized gametophyte being able to produce approximately 1 million carpospores, or a tetrasporophyte, up to 2 million tetraspores (Austin, 1960a). However, the species grows very slowly compared to other red algae (Bird et al., 1979) and takes a long time to reach maturity. For example, Austin (1960b) reported that, in Wales, Furcellaria lumbricalis typically takes 5 years to attain fertility. This would mean that, following perturbation, recovery to a mature reproductive community would take at least 5 years. Norton (1992) reviewed dispersal by macroalgae and concluded that dispersal potential is highly variable. Spores of Ulva sp. have been reported to travel 35km, Phycodrys rubens 5km and Sargassum muticum up to 1km. However, the point is made that reach of the furthest propagule and useful dispersal range are not the same thing and recruitment usually occurs on a much more local scale, typically within 10m of the parent plant. Hence, it is expected that Furcellaria lumbricalis would normally only recruit from local populations and hence recovery would be even more protracted in isolated areas. Christensen (1971) (cited in Bird et al., 1991) noted that following harvesting of Furcellaria lumbricalis forma aegagropila in the Baltic Sea, harvestable biomass had not been regained 5 years after the suspension of harvesting. In view of its slow growth, time to maturity and limited dispersal, recoverability of Furcellaria lumbricalis is assessed as moderate.
Of all the algal species in the biotope, Furcellaria lumbricalis probably takes the longest to colonize and mature and therefore is the limiting factor in the recoverability of the algal turf.
The other important species to consider are the ascidians. Clavelina lepadiformis has a life span of approximately 2 years. Each zooid reproduces once during June to September in temperate and cold seas (Picton, 1997; Millar, 1970). Brunetti (1987) recorded up to about 50 embryos present in the atrium at one time. The larval phase is short, and metamorphosis into adults is rapid, so dispersal may be limited. Recolonization following perturbation is likely to be within a year providing that other nearby populations have survived. Rafting by adults attached to floating objects or shipping may form an alternative important mechanism for recolonization.
The limiting factor in the recovery of the biotope is the re-establishment of the red algal turf, governed by the recovery of Furcellaria lumbricalis, and hence biotope recoverability is recorded as moderate.

This review can be cited as follows:

Rayment, W.J. 2001. Polyides rotundus and/or Furcellaria lumbricalis on reduced salinity infralittoral rock. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 27/11/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=316&code=1997>