Biodiversity & Conservation

SS.SMp.KSwSS.LsacCho

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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Substratum removal will remove the biotope including the attached species that mainly characterize it. Recoverability is likely to be rapid for the majority of species (see Additional information below).
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, algae would protrude above silt. The biotope is significantly characterized by mobile species that would burrow out of a covering of silt or other material. However, some species will be covered and if de-oxygenation occurred it would cause mortality. Recoverability is likely to be rapid for the majority of species (see Additional information below).
Increase in suspended sediment
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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). It might also be that feeding in suspension feeding animals, such as Ascidiella aspersa, might be adversely affected. However, most animals characterizing the biotope are grazers, predators and scavengers.
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 are generally subtidal and likely to be damaged by desiccation. Some components will be protected by their burrowing habit. Recoverability is likely to be rapid for the majority of species (see Additional information below).
Increase in emergence regime
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Increased emergence will result in desiccation (see desiccation).
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 and allow the biotope to increase in extent.
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, especially likely in Saccharina latissima. Plants may be lost from the biotope and be displaced to less favourable situations. It is unlikely that the mobile and burrowing species in the biotope will be adversely affected. Since some of the key characterizing species are likely to be lost, intolerance is indicated as Intermediate. Although some Saccharina latissima might be lost and some mobile species migrate away temporarily, some plants are likely to remain and animals migrate back so recoverability is likely to be very high (see Additional information below).
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 of some attached benthic species.
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. Some minor mortality may occur. For instance, 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). The response of Asterias rubens to prolonged exposure to unusually high temperatures is arm shedding (autotomy) then death (Schäfer, 1972). Starfish have also been found dead in isolated rock pools during prolonged emersion in calm hot weather, the suspected cause of death being increased water temperature (references in Lawrence, 1995). For Arenicola marina, Wilde & Berghuis (1979) reported 50% mortality of juveniles reared at 20 °C and 90% at 25 °C. Sommer et al. (1997) examined sub-lethal effects of temperature and suggested a critical upper and lower temperature of 20 °C and 5 °C respectively in North Sea specimens. However, in subtidal populations of all species, effects of temperature increase are likely to be reduced compared with intertidal areas. Recoverability is likely to be rapid for the majority of species (see Additional information below).
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. Some species may be affected although not those characteristic of or visually dominant in the community. Following the cold winter of 1962-63, of the characteristic animal species in the biotope, only Lanice conchilega and Carcinus maenas were noted as having been adversely affected (Crisp, 1964). Recoverability is likely to be rapid for the majority of species (see Additional information below).
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.
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. However, higher algal cover may exclude some animal species although species richness is unlikely too be adversely affected.
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 abrasion. It may also winnow away finer sediments creating a different substratum. Recoverability is likely to be rapid for the majority of species (see Additional information below).
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 (see Smothering, although depth of silt would not be expected to be as high as the benchmark).
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 intolerant 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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Some species, especially attached algae, are likely to be removed by physical disturbanceequivalent to a passing scallop dredge. However, many characteristic animal species are mobile or infaunal and so are likely to avoid most effects of surface disturbance. Therefore, an intolerance of intermediate has been recorded. Recoverability is likely to be rapid for the majority of species (see additional information below).
Displacement
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Displacement is most likely to be the result of substratum movement with attached organisms or of displacement of infauna that are able to re-burrow. However, for the characterizing large algal species, reattachment to the substratum will not be possible if detached from their substratum and, in that case, an intolerance of high is indicated. In practice, the algae will most likely be displaced with the stone or pebble to which they are attached and therefore re-establishment can occur. An intolerance of Intermediate is therefore assessed. Mobile species will survive. Since re-establishment and survival of attached, infaunal and mobile species is likely, adverse impacts are likely to be low and the biotope is likely to re-establish rapidly (see Additional information below).

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, some work has been undertaken on kelps. 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 Arenicola marina, the xenobiotic Ivermectin (used to control parasitic infestations in livestock including sea lice in fish farms), degrades slowly in marine sediments (half life >100 days). Ivermectin was found to produce a 10 day LC50 of 18µg ivermectin /kg of wet sediment in Arenicola marina. Sub-lethal effects were apparent between 5 - 105 µg/kg. Besten et al. (1989) reported that exposure of Asterias rubens to polychlorinated biphenyls (PCBs) resulted in production of defective offspring. However, Asterias rubens was found to be fairly resistant to the oil dispersant used, BP1002. A concentration of BP1002 at 25 ppm was required in toxicity tests to kill 50% of Asterias rubens within 24 hours (Smith, 1968). Therefore several members of the community are likely to be adversely affected by some synthetic contamination and an intolerance of Intermediate has been recorded. Recoverability is likely to be rapid for the majority of species (see Additional information below).
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.
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., 1998b). However, Asterias rubens appears to be intolerant of oil pollution. Bokn et al., (1993) examined of the long term effects of the water-accommodated fraction (WAF) of diesel oil on rocky shore populations. Two doses (average hydrocarbon concentration in diesel oil equivalents; High: = 129.4 µmg l-1, and Low = 30.1 µmg l-1) of WAF of diesel oil were delivered via sea water to established rocky shore mesocosms over a two year period. The numbers of Asterias rubens decreased at all tidal levels (even in the control mesocosms during the study) and Asterias rubens disappeared entirely from upper sublittoral samples in the mesocosm receiving a high dose of WAF diesel oil suggesting a negative effect upon this species caused by the high dose treatment. Crude oil from the Torrey Canyon in 1967 off Land's End of Cornwall, and the detergent used to disperse it caused mass mortalities of Asterias rubens (Smith, 1968). Arenicola marina is less intolerant of oil but still shows adverse effects. Prouse & Gordon (1976) examined the effects of surface fuel oil contamination and fuel oil : sediment mixtures on Arenicola marina in the laboratory. They found that worms were driven out of the sediment by waterborne concentration of >1 mg/l or sediment concentration of >100 µg/g. Worms forced out of sediment may be able to migrate out of affected area but will be exposed to severe predation risk, especially in daylight. Seawater oil concentrations of 0.7 mg oil /l reduced feeding after 5hrs and all worms exposed for 22hrs to 5mg/l oil left the sediment and died after 3 days. Species of gastropods and crustaceans in the biotope may also be intolerant of oil pollution and an intolerance of intermediate is therefore given. Recoverability is likely to be rapid for the majority of species (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 (providing more food for grazing species), 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. The abundance and biomass of Arenicola marina increases with increased organic content in their favoured sediment (Longbottom, 1970; Hayward, 1994). Therefore, moderate nutrient enrichment may be beneficial. However, increasing nutrient enrichment may result in a well studied succession from the typical sediment community, to a community dominated by opportunist species (e.g. capitellids) with increased abundance but reduced species richness and eventually to abiotic anoxic sediments (Pearson & Rosenberg, 1978). Indirect effects may include algal blooms and the growth of algal mats (e.g. of Ulva sp.) on the surface of the intertidal flats. Algal mats smother the sediment, reducing water and oxygen exchange and resulting in localized hypoxia and anoxia when they die. Algal blooms have been implicated in mass mortalities of lugworms, e.g. in South Wales where up to 99% mortality was reported (Holt et al. 1995; Olive & Cadman, 1990; Boalch, 1979). The benchmark level for nutrient enrichment (a 50% change over the annual average) would probably cause some slight increase in productivity (increase in nutrients) or decrease in productivity (decrease in nutrients) but is unlikely to cause mortality or significant loss. Intolerance is assessed as low. Recovery is likely to be very high (see Additional information below).
Increase in salinity
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The biotope is found in full or variable salinity. Increase in salinity above full salinity is not considered likely and so 'not relevant' is indicated.
Decrease in salinity
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Most of the species present in the biotope are found only in full or slightly reduced or variable salinity. For instance, it has been observed that Saccharina latissima (studied as Laminaria saccharina) 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 animal species, echinoderms, which are stenohaline, are likely to be particularly affected by a fall in salinity. For instance, a sudden inflow of river water into an inshore coastal area caused mass mortality of the conspecific species Asterias vulgaris at Prince Edward Island, Canada (Smith, 1940, in Lawrence, 1995). Some species in the biotope may thrive in reduced salinity, for instance the shore crab Carcinus maenas. Overall, since several key characterizing species would be adversely affected, intolerance is indicated as high. Recoverability is likely to be rapid for the majority of species (see Additional information below).
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 4 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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This biotope is likely to be colonized by the non-native wireweed Sargassum muticum. However, in this predominantly subtidal biotope, Sargassum muticum tends to occupy minimal space on the seabed and not displace other species. However, the biotope may also be colonized by the slipper limpet Crepidula fornicata which is likely to significantly change the character of the substratum through production of pseudofaeces and by displacing other species. Therefore, intolerance is ranked as high. The presence of shells of slipper limpets and the increased muddiness of the sediment is likely to change the substratum for some time and the biotope may not return rapidly to its original condition until the substratum reverts to pre-Crepidula character.
Extraction
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Neither Chorda filum nor Saccharina latissima are thought to be currently targeted for extraction in the UK and we have no evidence for the indirect effects of extraction of other species on this biotope.

Additional information icon Additional information

Recoverability
The majority of species that characterize this biotope are likely to colonize within a year of an adverse reaction to a factor as they either have planktonic propagules or are mobile and will migrate into the area. For instance, Kain (1975) recorded that Saccharina latissima (studied as Laminaria saccharina) was abundant six months after substratum was cleared. However, some probably long-lived species, including the burrowing anemone Cerianthus lloydii, may take longer to settle and grow. Nevertheless, because the biotope will have re-established, recovery is ranked high.

This review can be cited as follows:

Hiscock, K. 2001. Laminaria saccharina, Chorda filum and filamentous red seaweeds on sheltered infralittoral sediment. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 24/09/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=58&code=2004>