Biodiversity & Conservation

IR.MIR.SedK.LsacChoR

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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The community will be removed with the substratum and so intolerance is high. For recoverability, see Additional Information.
Smothering
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The time of year at which smothering occurred would be important. Smothering at the time spores of colonizing species were settling might reduce their abundance significantly. However, once grown, the algae would protrude above silt. Other species such as encrusting seaweeds, tube worms and barnacles would be likely to survive under silt for the benchmark of three weeks although if de-oxygenation occurred it would cause mortality. For recoverability, see Additional Information.
Increase in suspended sediment
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Increase in the level of suspended sediment mainly affects suspension feeding animal species. It might also be that feeding in suspension feeding animals will be adversely affected. Light penetration will also be affected (see 'Turbidity) and siltation is more likely to occur. Silt falling onto algal fronds is likely to reduce photosynthesis but not cause mortality. An increase in the level of suspended sediment was found to reduce growth rate of Saccharina latissima (studied as Laminaria saccharina) by 20% (Lyngby & Mortensen, 1996). Adults appear to tolerate silt because they are found in areas of siltation (Birkett et al., 1998). Norton (1978) observed that silt settling out on already attached spores prevented the formation of gametophytes in Saccorhiza polyschides sporophytes so that some damaging effects might occur.
Decrease in suspended sediment
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Decrease in siltation is likely to improve growth of the dominant members of the community (algae) as lack of silt on fronds will enable more efficient photosynthesis. Suspension feeding animal species rely on plankton not silt and so are unlikely to be affected.
Desiccation
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Although the biotope might be exposed to air on extreme low water spring tides, the component species, especially algae, are generally subtidal and likely to be damaged by desiccation. For instance, Norton (1970) observed that when sporophytes of Saccorhiza polyschides were exposed to air by an extreme low water springs on a hot summers day, they rapidly dried out and died. However, some components will be protected by overlying algae and some such as tube worms and barnacles are resistant to desiccation. For recoverability, see Additional Information.
Increase in emergence regime
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Increased emergence will result in increased risk of desiccation (see desiccation) and exposure to greater extremes of temperature. In the part of the biotope subject to increased emergence, characterizing species will most likely die and an intolerance of High is therefore given. For recoverability, see Additional Information
Decrease in emergence regime
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The biotope is subtidal except when exposed at extreme low water of spring tides when desiccation might have an unfavourable effect. Therefore, any decrease in emergence is likely to be favourable.
Increase in water flow rate
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The main water movement factor important for this biotope is wave action. However, increased tidal flow may cause drag on large seaweeds which in turn may dislodge the substratum to which they are attached. Plants may be lost from the biotope and be displaced to less favourable situations.
Decrease in water flow rate
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Tidal flow is important in the absence of strong wave action for keeping the biotope clean of silt. Decrease in water flow is likely to facilitate siltation which will reduce photosynthesis in plants and may cause smothering.
Increase in temperature
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The species present in the biotope are widely distributed in the north-east Atlantic and are therefore well-within their limits of tolerance in the British Isles. Mature sporophytes of Saccharina latissima (studied as Laminaria saccharina) from the Isle of Man have been found to have an upper temperature tolerance of 17°C (Kain 1979). In the unusually hot summer of 1983, when temperatures were 8.3°C higher than normal, Saccharina latissima (studied as Laminaria saccharina) showed signs of bleaching (Hawkins & Hartnoll, 1985). However, in subtidal populations, effects are likely to be reduced compared with intertidal areas.
Decrease in temperature
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The species present in the biotope are widely distributed in the north-east Atlantic and are well-within their limits of tolerance in the British Isles. For instance, the minimum temperature required for growth and reproduction of Saccorhiza polyschides is 5°C. The 'northern lethal boundary' of the species occurs where the temperature falls below 4°C for a period of 2 months (Hoek van den, 1982). Some species may be affected although not those characteristic of or visually dominant in the community.
Increase in turbidity
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High turbidity at the time of year when settlement of algal spores and growth mostly occurs will depress the amount of algal cover present although not necessarily species richness. The overall effect will be a lower cover particularly of ephemeral algal species.
Decrease in turbidity
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Low turbidity will enable the biotope to establish a greater depths than in higher turbidity regimes so that, in a year with low turbidity, the biotope may be more extensive than in a year with high turbidity. Since algae from normally shallow well-lit depths will be able to grow in deeper water, the species diversity in that deeper water is likely to be higher.
Increase in wave exposure
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The substratum type in the biotope is determined mainly by wave exposure regime. Increase in wave exposure is likely to disturb the substratum destroying some attached species through breakage or abrasion. It may also winnow away finer sediments creating a different substratum. For recoverability, see Additional Information.
Decrease in wave exposure
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Wave action is important for keeping the biotope clean of silt. Decrease in wave action is likely to facilitate siltation which will reduce photosynthesis in plants and may cause smothering.
Noise
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The characteristic and dominant species in this biotope are seaweeds and are not sensitive to noise. Some fish that inhabit the biotope may be sensitive and may seek shelter but will not be affected in the long term.
Visual Presence
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The characteristic and dominant species in this biotope are seaweeds and are not sensitive to visual presence. Some fish that inhabit the biotope may be intolerant and may seek shelter but will not be affected in the long term.
Abrasion & physical disturbance
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This is a biotope that exists because of physical disturbance of mobile substrata. The community is likely to be destroyed by severe storms but will regenerate the following spring when conditions of wave action usually settle down. It might be that the biotope develops in a largely undisturbed way until the next sever storm, perhaps after several years. If disturbance occurs 'out-of-season', the biotope will be adversely affected for the remainder of the year. '
Displacement
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The majority of species that characterize this biotope are sessile and their displacement through detachment from substratum will result in death. Some other species such as gastropods and infaunal species can re-settle and survive. For recoverability, see Additional Information.

Chemical Factors

Synthetic compound contamination
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Very little information is available on the effects of chemicals on dominant and characteristic species in the biotope. However, Hoare & Hiscock (1974) observed that the majority of red algae were excluded from the region of an acidified halogenated effluent. Hopkin & Kain (1978) observed that growth of gametophytes and very young sporophytes of Laminaria hyperborea was inhibited at low levels of atrazine, sodium pentachlorophenate and phenol. For recoverability, see Additional Information.
Heavy metal contamination
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Little information has been found for the range of dominant and characteristic species in the biotope. However, sporophytes of Saccharina latissima have a low intolerance to heavy metals, but the early life stages are more intolerant. The effects of copper, zinc and mercury on Saccharina latissima (studied as Laminaria saccharina) have been investigated by Thompson & Burrows (1984). They observed that the growth of sporophytes was significantly inhibited at 50 µg Cu /l, 1000 µg Zn/l and 50 µg Hg/l. Zoospores were found to be more intolerant and significant reductions in survival rates were observed at 25 µg Cu/l, 1000 µg Zn/l and 5 µg/l. For recoverability, see Additional Information.
Hydrocarbon contamination
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Hydrocarbons, when dispersed into the water column, may cause bleaching in red seaweeds. However, following dispersion of large quantities of oil in Martins Haven West Wales, no damage to red algae could be found even in shallow depths (K. Hiscock, own observations). Saccharina latissima (studied as Laminaria saccharina) has been observed to show no discernible effects from oil spills, largely due to poor dispersion into the water column and high levels of dilution (Holt et al., 1995). Drew et al. (1967) recorded that the kelp forest escaped undamaged after the 'Torrey Canyon' oil spill. Kelp may also be protected by the mucilaginous slime which covers the frond, by preventing damage from coating by oil (Birkett et al., 1998). No studies have been carried out specifically on the impact on Saccorhiza polyschides but the alga is probably tolerant of this factor. Species of gastropods and crustaceans in the biotope may be intolerant of oil pollution and an intolerance of low is therefore given. For recoverability, see Additional Information.
Radionuclide contamination
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No information has been found.
Changes in nutrient levels
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Nutrients are essential for the growth of the alga. A decrease in nutrient levels would reduce growth rates. A slight increase in the level of nutrients may enhance growth, but high levels of nutrients may cause overgrowth of the alga by ephemeral green seaweed (Fletcher, 1996). Also, the growth rate of mature plants of Saccharina latissima (studied as Laminaria saccharina) was lower in water collected near a sewage sludge dumping ground in Liverpool Bay, Irish Sea (Burrows, 1971) and Read et al. (1983), reported that after removal of a major sewage pollution in the Firth of Forth, Saccharina latissima (studied as Laminaria saccharina) became abundant on rocky shores from which it was previously absent. For recoverability, see Additional Information.
Increase in salinity
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The biotope is found in full or nearly full salinity.
Decrease in salinity
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Most of the species present in the biotope are found only in full or slightly reduced salinity. For instance, it has been observed that Saccharina latissima grows fastest at 31 psu, is severely retarded at 16 psu and plants do not survive below 8 psu. Saccorhiza polyschides is not found in areas of reduced salinity. In culture, lowered salinities have been found to reduce growth rate and development is irreversibly inhibited below 9 psu (Norton & South, 1969), so the species is regarded as highly intolerant of this factor. However, Chorda filum is found in low salinity environments such as estuaries and the Baltic and has been successfully cultured at salinities as low as 5 psu (Norton & South, 1969). It is also found in lagoonal habitats with low salinity (for example, see biotope SIR.FChoG). For recoverability, see Additional Information.
Changes in oxygenation
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The effect of low oxygen levels on the main characteristic species in this biotope, seaweeds, is poorly studied. Where local deoxygenation occurs rotten seaweed is characteristic. Animals may be intolerant of reduction in oxygen. However, at the bench mark level of reduction below 2 mg/l, it is not expected that significant adverse effects will occur to the biotope as there is always some water motion (from waves or tides) in this biotope.

Biological Factors

Introduction of microbial pathogens/parasites
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It is not expected that microbial pathogens will significantly affect the biotopes and little information has been found. Saccharina latissima may be infected by the microscopic brown alga Streblonema aecidioides. Infected algae show symptoms of Streblonema disease, i.e. alterations of the blade and stipe ranging from dark spots to heavy deformations and completely crippled thalli (Peters & Scaffelke, 1996). Infection can reduce growth rates of host algae.
Introduction of non-native species
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The biotope is likely to be colonized by wireweed Sargassum muticum which occupies space but not to the exclusion of native species.
Extraction
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Extraction of Saccharina latissima may occur but the plant rapidly colonizes cleared areas of the substratum: Kain (1975) recorded that Saccharina latissima (studied as Laminaria saccharina) was abundant six months after the substratum was cleared so recovery should be rapid. Associated species are unlikely to be affected by removal of Saccharina latissima unless protection from desiccation on the lower shore is important. Little evidence has been found on the impact of extraction of Chorda filum although the species is harvested in Japan. However, if removed, recovery should also be rapid. Intolerance has been assessed as intermediate to reflect some possible loss although recovery is expected to be high.

Additional information icon Additional information

Recoverability
The community is composed of predominantly opportunistic and fast colonizing species. For instance, Kain (1975) recorded that Saccharina latissima (studied as Laminaria saccharina) was abundant six months after substratum was cleared. Although the community might look very similar one year after loss of species, some species such as encrusting coralline algae that survive winter storms will not reach their previous extent on cobbles for some years. Recoverability from impact is therefore described as high.

This review can be cited as follows:

Hiscock, K. 2001. Laminaria saccharina, Chorda filum and dense red seaweeds on shallow unstable infralittoral boulders or cobbles. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 21/12/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=363&code=1997>