Biodiversity & Conservation

IR.SIR.Lag.AscSAs

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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The biotope is an algal biotope with attached epiphytes so all species are attached directly or indirectly to the substratum and will be lost if substratum is removed. Any mobile species that are present, such as crabs and fish, will be indirectly affected by the loss of algal cover through increased risk of desiccation and predation and will probably move away. The overall effect of substratum loss is the loss of the biotope therefore, intolerance is reported to be high. Recovery is low - see additional information for rationale.
Smothering
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A 5cm layer of sediment or debris in a dense Ascophyllum nodosum lagoonal habitat will reduce photosynthesis of algae and may cause some plants to rot. Sediment will have an especially adverse effect on young germling algae. The suspension feeding structures of sponges and ascidians are likely to become clogged and may be killed by smothering and in the extremely sheltered conditions found in the SIR.AscSAs lagoonal habitat, there is not likely to be enough wave action to mobilise sediment and alleviate the effects of smothering. However, most of the Ascophyllum nodosum, with its associated epiphytes, will probably be able to float above the layer of silt and so most of the plants and many of the epiphytes are likely to survive. Therefore, intolerance is reported to be low. Recovery will be very high as affected fauna that have survived self-clean. For example, the sponge Halichondria panicea has a mechanism for sloughing off the complete outer tissue layer together with any debris (Bartel & Wolfrath, 1989).
Increase in suspended sediment
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Ascophyllum nodosum, and the other macroalgal species in the biotope, are likely to be relatively tolerant of an increase in suspended sediment because they are primary producers. Settlement out of the sediment may cover some surfaces of the plants, reducing photosynthesis rates which may reduce growth and in the sheltered conditions in which the biotope is found will probably not be removed by wave action. However, the direct effects of increased suspended sediment (see turbidity for indirect effects of light attenuation) on photosynthesising plants are not expected to be significant. Other species in the biotope, such as suspension feeding sponges and tunicates (sea squirts), are likely to be more intolerant because an increase in suspended sediment may interfere with feeding, increase cleaning costs and result in lower growth rates. However, both Halichondria panicea and Ciona intestinalis are reported to have low intolerance to an increase in suspended sediment. Halichondria panicea, for example, has a mechanism for sloughing off the complete outer tissue layer together with any debris (Bartel & Wolfrath, 1989). Therefore, the impact on the biotope as a whole is likely to be sublethal impacts on growth etc. so intolerance has been assessed as low. There may be a loss of a few very intolerant species. On return to pre-impact suspended sediment levels feeding rates of affected species and photosynthetic rates will return to normal very rapidly and so recovery is very high.
Decrease in suspended sediment
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Ascophyllum nodosum is likely to be relatively tolerant of a decrease in suspended sediment because the species is a primary producer. Other species in the biotope, in particular the suspension feeding sponges, such as Halichondria panicea and tunicates, are likely to be more intolerant because a decrease in suspended sediment may also result in a decrease in food supplies so growth may be affected. However, the impact on the biotope as a whole will be sublethal effects (i.e. growth, fecundity etc.) so intolerance has been assessed as low. On return to pre-impact suspended sediment levels feeding of affected species and photosynthetic rates will return to normal very rapidly.
Desiccation
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The biotope is predominantly subtidal but probably extends to the shore becoming exposed at low water. Ascophyllum nodosum is an upper shore intertidal algae and so is likely to be able to tolerate an increase in desiccation. Some of the sponges and ascidians may be more intolerant and could be lost. However, the moist environment found within the centre of the dense beds of fucoids during exposure to air is likely to provide protection for many individuals and colonies. Thus, Ascophyllum nodosum and many of the epiphytes will survive and so the overall nature of the biotope is not likely to be significantly different. Intolerance is therefore considered to be low. Recovery is high as epiphytic species are likely to be able to regrow and recolonize algal plants very rapidly. Halichondria panicea, for example, increases in size by about 5% per week (Barthel, 1988).
Increase in emergence regime
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The biotope is predominantly subtidal but probably extends to the shore becoming exposed at low water. Ascophyllum nodosum is an upper shore intertidal algae and so is likely to be able to tolerate an increase in emergence. However, some of the epiphytic sponges and ascidians may be subtidal species and could be intolerant of increased emergence. However, the dense beds of algae will provide some protection from the effects of increased emergence so some individuals and colonies are expected to survive a benchmark increase (1 additional hour emergence per tidal cycle). Therefore, although epiphytic biomass and diversity may decline the overall nature of the biotope will not be significantly changed and intolerance is assessed as low. Recolonization and regrowth of epiphytic species should be rapid and so recovery is set to high.
Decrease in emergence regime
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The biotope is predominantly subtidal so a decrease in emergence is not relevant.
Increase in water flow rate
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Significant increases in water flow rate may cause some of the macroalgal populations to be torn off the substratum. However, Ascophyllum nodosum and many of the other algae in the biotope are also found in strong tidal streams so most should survive the benchmark increase. Increased water movement also favours filter feeding faunal groups so the richness of sponges and ascidians may increase. Because some algae may be lost, intolerance is considered to be low. However, the richness of the biotope may increase and so enhanced water flow may therefore be considered favourable.
Decrease in water flow rate
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The biotope is found in areas of very weak tidal streams so a decrease is not relevant.
Increase in temperature
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The algal species in the biotope are also found in the intertidal, where they are exposed to wide fluctuations in temperature. Most species occur to the south of Britain and Ireland and so are well within the upper temperature range and would probably not be significantly affected by an increase of 5°C. Growth and reproductive output may change in response to a temperature increase. Halichondria panicea and Ciona intestinalis are both distributed to the south of British waters and so are likely to be able to tolerate an increase in temperature. Some of the other epiphytic sponges and ascidians may have narrower temperature preferences and may not tolerate an increase in temperature. However, if some species are lost this will not affect the overall nature of the biotope and so intolerance is reported to be low. On return to normal conditions algal growth and fecundity will return to pre-impact levels and recovery of lost epiphytes should be possible within a few years and so recoverability of the biotope is considered to be high.
Decrease in temperature
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The algal species in the biotope are also found in the intertidal, where they are exposed to wide fluctuations in temperature. The key species, Most species occur to the north of Britain and Ireland and so are well within the lower temperature range and would probably not be significantly affected by a decrease of 5°C. Growth and reproductive output may change in response to a temperature decrease. Some sponges and ascidians may have narrower temperature preferences and may not tolerate a decrease in temperature. However, if some species are lost this will not affect the overall nature of the biotope and so intolerance is reported to be low. On return to normal conditions algal growth and fecundity will return to pre-impact levels and recovery of lost epiphytes should be possible within a few years and so recoverability of the biotope is considered to be high.
Increase in turbidity
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An increase in turbidity would reduce the light available for photosynthesis during immersion which could result in reduced biomass of plants and may reduce the depth to which the algae can grow. However, an increase in turbidity, at the benchmark level, is not likely to threaten the survival of algal species, and the faunal organisms will not be affected by the light attenuation effects, so intolerance of the biotope is reported to be low. Upon return to previous turbidity levels the photosynthesis rate would return immediately to normal.
Decrease in turbidity
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A decrease in turbidity would increase the light available for photosynthesis during immersion which may increase growth rates of all the algae in the biotope. Upon return to previous turbidity levels the photosynthesis rate would return immediately to normal.
Increase in wave exposure
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The dense Ascophyllum nodosum stands of the SIR.AscSAs biotope can only develop in extremely sheltered conditions. The species cannot resist very heavy wave action so exposure is an important factor controlling distribution. 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). Work in New England has suggested that the distribution of Ascophyllum nodosum may be directly set by wave action preventing settlement of propagules (Vadas et al., 1990). Thus, the species is only present in sheltered or moderately exposed locations and increased wave exposure causes plants to be torn off the substratum and replaced by Fucus vesiculosus. Fucus serratus is also reported to be intolerant of wave exposure, only occurring in locations with moderate exposure. Ascidians and sponges can be damaged by wave exposure and species like Ciona intestinalis are often more abundant in sheltered locations. Thus, an increase in wave exposure of two ranks on the exposure scale, e.g. from sheltered to exposed, is likely to result in the removal of many plants from the substratum and the loss of the biotope and so intolerance is considered to be high. On return to normal conditions recovery is likely to be low because of poor recruitment and slow growth of Ascophyllum nodosum - see additional information for full rationale.
Decrease in wave exposure
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Dense subtidal canopies of Ascophyllum nodosum in lagoons can only develop in extremely sheltered conditions where wave exposure is negligible so a decrease in wave exposure at the level of the benchmark is not relevant to the SIR.AscSAs.
Noise
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Algae, sponges and ascidians have no known noise perception so the biotope is likely to be not sensitive to noise disturbance.
Visual Presence
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Algae, sponges and ascidians have no visual perception so the biotope is likely to be not sensitive to visual disturbance.
Abrasion & physical disturbance
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In the intertidal fucoid algae including Ascophyllum nodosum are very sensitive to abrasion caused by trampling. In the subtidal an abrasive force equivalent to a scallop dredge is likely to damage some plants and remove others and their epiphytic sponges and ascidians. A single event is likely to remove a proportion of egg wrack cover, and intolerance is reported to be intermediate. With the exception of Ascophyllum nodosum, recovery of most damaged flora or fauna by regrowth will be rapid. Ascophyllum nodosum, has poor recruitment rates and is slow growing, limiting recovery (Holt et al., 1997). The lack of recovery of Ascophyllum nodosum from harvesting is well documented. For example, in their work on fucoid recolonization of cleared areas at Port Erin, Knight and Parke (1950) observed that even eight years after the original clearance there was still no sign of the establishment of an Ascophyllum nodosum population. Therefore, recovery is likely to be low.
Displacement
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intolerance to displacement is high because most species are permanently attached, either to the rock or the algae, and cannot re-establish themselves if detached. Loss of the key species, Ascophyllum nodosum results in loss of the biotope. Recovery is low - see additional information for rationale.

Chemical Factors

Synthetic compound contamination
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Adult fucoids are generally quite tolerant of chemical pollutants. However, Cole et al. (1999) suggested that herbicides such as Simazina and Atrazine were very toxic to macrophytic algae. For instance, Fucus serratus was found to be intolerant of three biocides likely to be found in the marine environment (Scanlan & Wilkinson, 1987). Also, fucoids in general are reported to exhibit high intolerance to chlorate and pulp mill effluents containing chlorate (Kautsky, 1992). The disappearance of Ascophyllum nodosum from Oslofjord has been attributed to the reduced ability of germlings to recruit at highly polluted sites (Sjoetun & Lein, 1993). However, Hoare & Hiscock (1974) observed that Ascophyllum nodosum was found within 100m of an acidified, halogenated effluent discharge, although plants had abnormal and retarded growth. Almost all red algal species and many animal species were also absent from the acidified halogenated effluent at Amlwch Bay in North. Red algae have also been found to be sensitive to oil spill dispersants (O'Brien & Dixon 1976; Grundy quoted in Holt et al. 1995). There was no other information found on the intolerance of sponges or ascidians to chemicals. Intolerance of the biotope is reported to be high. See additional information for recovery.
Heavy metal contamination
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The disappearance of Ascophyllum nodosum from Oslofjord has been attributed to an increase in pollution and copper at concentrations of 1039 nM (66 µg/L) have been found to inhibit the growth of Ascophyllum nodosum (Strömgren, 1979). However, adult plants appear to be fairly robust in the face of heavy metal pollution (Holt et al., 1997). For example, the species penetrates into the metal polluted middle reaches of Restronguet Creek in the Fal estuary system where concentrations of both copper and zinc are in the region of 1000-2000µg/g in the sediment and 10-100µg/l in seawater (Bryan & Gibbs, 1983). Fucoids are able to concentrate heavy metals in their tissues and have been used as bioindicators of heavy metals. The alginate within the fucoids is believed to have a role both in the uptake of the metals, and in storing them in fairly inert terms, so that plants do not seem to be harmed (Holt et al., 1997). Although Ascophyllum nodosum accumulates copper this can be removed because the species naturally sheds its epidermis at regular intervals (Stengel & Dring, 2000). Therefore, because effects are likely to be sub-lethal intolerance of the biotope is reported to be low. There was no information found on the intolerance of sponges or ascidians although it is likely that some of the epiphytic species in the biotope may be more intolerant of heavy metals and in areas of high metal pollution species diversity may decline. However, there was no information found On return to pre-impact levels of heavy metal pollution there should be a return to normal algal growth levels within a year or two and any lost or damaged sponge or ascidian species should recolonized or regrow rapidly. Therefore, recoverability of the biotope is considered to be high.
Hydrocarbon contamination
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Long-term exposure to low levels of diesel have been shown to reduce growth rates in Ascophyllum nodosum (Bokn, 1987). However, growth rates recovered within a season after two years exposure so it appears the species has some tolerance to chronic levels of oil in seawater and so intolerance is assessed as low and recovery will be high. However, other species in the biotope, such as red algae, sponges and ascidians, may be more intolerant and so species diversity is likely to decline. It appears that Halichondria panicea survived in areas affected by the Torrey Canyon oil spill (Smith, 1968) although few observations were made. If mortality occurred, settlement of new colonies is likely within one year and growth rate is rapid. Major impacts will however, result from oil spills. In Norway heavy oil pollution from a grounded ship reduced both fucoid cover and the number of associated species. In sheltered conditions species number had not recovered after 4 years (Hjolman & Lein, 1994 cited in Holt et al., 1997).
Radionuclide contamination
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Insufficient information.
Changes in nutrient levels
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Ascophyllum nodosum, like several other intertidal algae, is able to accumulate nitrogen in its tissues in response to seasonal availability. A reduction in the level of nutrients could reduce growth rates in Ascophyllum nodosum. A slight increase in nutrients may enhance growth rates but very high nutrient concentrations could lead to the overgrowth of the algae by ephemeral green algae. Ascophyllum nodosum plants, when transplanted into sewage-stressed areas have become heavily infested with epiphytes and frequently overgrown by Ulva species and there are reports of a decline in populations of the species in the North Atlantic as a result of increased eutrophication (Fletcher, 1996). There is no information regarding the intolerance of the key faunal species although there is some suggestion that there are possible benefits to the adults from increased organic content of water (Naranjo et al., 1996). Intolerance of the biotope is considered to be intermediate. On return to normal nutrient levels the growth rate would be quickly restored. Lost plants will take longer however to return as Ascophyllum nodosum has poor recruitment and slow growth rates.
Increase in salinity
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The biotope is a variable salinity biotope so all species will be tolerant of some change. In lagoons in the summer months salinity reaches a peak and may become hypersaline. Ascophyllum nodosum is found in fully marine conditions so will be tolerant of an increase. Baardseth (1970) found the species to have a salinity tolerance of between 15 and 37 psu. Growth and fecundity may be affected but the algae should survive and so intolerance of the biotope is reported to be low.
Decrease in salinity
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The biotope is a variable salinity biotope so all species will be tolerant of some change. Ascophyllum nodosum is euryhaline with a salinity tolerance of about 15 to 37 psu (Baardseth, 1970). The species can also withstand periodic emersion in freshwater (Baardseth, 1970) and frequently inhabits estuaries and lagoons where salinity is variable. The other species in the biotope are also subject to varying salinity and so should be fairly tolerant of a decrease. Halichondria panicea occurs from full to low salinity conditions and only prolonged exposure to fresh or almost fresh water is likely to result in mortality. Growth rates and fecundity of some species may be impaired but individuals are expected to survive changes in salinity and so intolerance of the biotope to a decrease in salinity is therefore assessed as low. Once salinity levels have returned to normal the biotope should recover rapidly.
Changes in oxygenation
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The biotope occurs in areas where relatively still water conditions do occur and so some species may be tolerant of a small degree of deoxygenation. The effects of deoxygenation on macroalgae are poorly studied. Kinne (1972) reports that reduced oxygen concentrations inhibit both photosynthesis and respiration although macroalgae may not be very intolerant of slight deoxygenation since they can produce their own oxygen. Cole et al. (1999) suggest possible adverse effects on marine species below 4 mg/l and probable adverse effects below 2 mg/l so some very intolerant species may be affected. Ciona intestinalis is frequently found in areas with restricted water renewal where oxygen concentrations may drop. For a period of a week effects are expected to be minimal so an intolerance rank of intermediate is reported. On return to oxygenated conditions recovery will be rapid.

Biological Factors

Introduction of microbial pathogens/parasites
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Although bacteria and fungi are associated with Ascophyllum nodosum no information could be found on any disease causing microbes in the biotope and so intolerance is assessed as low. However, there is always the potential for this to change.
Introduction of non-native species
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There are no records of any non-native species invading the biotope that may compete with or graze upon Ascophyllum nodosum. The ascidian Styela clava was first recorded in the UK at Plymouth in 1952 (Eno et al., 2000). Where Styela clava and Ciona intestinalis co-occur they may compete for space and food. However, this is not likely to change the nature of the biotope and so a rank of low is reported. However, as several species have become established in British waters there is always the potential for invasive species to affect the biotope.
Extraction
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The biotope consists of dense stands of Ascophyllum nodosum and other algae such as Fucus serratus which are both extracted commercially (see reviews). Given the infralittoral position of the biotope it is unlikely that large amounts of either species would be collected. Nevertheless some extraction is possible and intolerance has been assessed as intermediate. Given that some of each species is likely to remain, recovery will probably be high (sea additional information).

Additional information icon Additional information

Recoverability
Where Ascophyllum nodosum is lost, recovery would be slow due to the slow growth rate and poor recruitment of this dominant species and so a rank of moderate recovery is reported. The lack of recovery of Ascophyllum nodosum from harvesting is well documented. For example, in their work on fucoid recolonization of cleared areas at Port Erin, Knight and Parke (1950) observed that even eight years after the original clearance there was still no sign of the establishment of an Ascophyllum nodosum population. The species is extremely fertile every year and Printz (1959) suggests it must be assumed that some special combination of climatic or environmental conditions is needed for an effective recolonization. Most of the epiphytic species are likely to have planktonic larvae and rapid growth so that recovery will be rapid. For example, settlement of new colonies of Halichondria panicea within one year is likely and the species increases in size by about 5% per week (Barthel, 1988). Recovery of the sea squirt Ciona intestinalis, is also expected to be rapid as it is thought to reproduce all year and is an initial colonizing species in settlement experiments (K. Hiscock pers. comm.). However, if all local populations are lost recovery may take a little longer because the species probably has limited dispersal as the larval stage is very short (hours or days) and larvae are often retained near the adults by mucus threads. Thus, if Ascophyllum nodosum remains recovery of the biotope will be much more rapid and a rank of high is reported.

This review can be cited as follows:

Hill, J.M. 2001. Ascophyllum nodosum with epiphytic sponges and ascidians on variable 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 21/09/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=328&code=1997>