Biodiversity & Conservation

LR.LLR.FVS.Ascmac

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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Although the mackaii ecad of Ascophyllum nodosum is unattached the species is likely to be removed along with substratum removal. Other key or characterizing species in the biotope will also be removed and so intolerance is considered to be high. For recoverability see additional information.
Smothering
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The key species, Ascophyllum nodosum ecad mackaii, is likely to be intolerant of smothering by 5 cm of sediment because photosynthesis would not be possible and plants would also be likely to rot underneath the smothering material. The habitats in which the ecad is found are very sheltered from wave exposure and tidal streams so sediment is unlikely to be removed by water movement. However, some component species such as amphipods and snails may excavate out of the sediment. Thus, because the key characterizing species is lost the biotope will also be lost if smothered and so is considered to be highly intolerant. The small embayments and inlets, often enclosed by rocky headlands, the typical habitat for Ascophyllum nodosum ecad mackaii, are vulnerable to infilling for land-based deposits for marine industries such as fish and shellfish farms, slipways, car parks and other developments (Anonymous, 1999(t)). For recoverability see additional information.
Increase in suspended sediment
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Ascophyllum nodosum ecad mackaii is not likely to be directly intolerant of an increase in suspended sediment because although turbidity will increase, photosynthesis can still occur when the tide is out (see turbidity). However, settlement out of the sediment may cover some surfaces of the plant, reducing photosynthesis rates which may reduce growth. Other species in the biotope, in particular the suspension feeders, such as Lanice conchilega, 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, the impact on the biotope as a whole will be negligible so intolerance has been assessed as low. On return to pre-impact suspended sediment levels feeding rates of affected species and photosynthetic rates will return to normal very rapidly.
Decrease in suspended sediment
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Ascophyllum nodosum ecad mackaii is not likely to be directly intolerant of a decrease in suspended sediment because the species is a primary producer. Other species in the biotope, in particular the suspension feeders, such as Lanice conchilega, 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 negligible 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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Ascophyllum nodosum ecad mackaii is found at upper or mid-tide levels where it regularly becomes exposed to air during tidal cycles and so is tolerant of some desiccation. An increase in desiccation at the level of the benchmark, equivalent to a change in position of one vertical biological zone on the shore, will kill a large proportion of plants at the upper end of the populations range depressing the upper limit and so intolerance is assessed as intermediate. Macrofauna, such as the gammarid amphipod Hyale prevostii, that use the algae as a sheltered and humid habitat are also intolerant of increased desiccation and will be likely to move down the shore to avoid the factor. Other species such as the periwinkle Littorina littorea are able to tolerate some increase in desiccation and will be little affected. Where present, the ecad can proliferate itself vegetatively from its own broken fragments which continue to divide forming new plants. Therefore, recovery should be possible within five years although it may take longer for plants to return to original density and biomass so a rank of moderate of reported.
Increase in emergence regime
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Ascophyllum nodosum is normally exposed to air for no more than a few hours (Lüning, 1990). An increase in the period of emersion would subject the species to greater desiccation and nutrient stress, leading to a depression in the upper limit of the species distribution on the shore. Other species are also likely to be affected in a similar way so intolerance of the biotope is considered to be intermediate. Where present the ecad can proliferate itself vegetatively from its own broken fragments which continue to divide forming new plants. Therefore, recovery should be possible within five years although it may take longer for plants to return to original density and biomass so a rank of moderate of reported.
Decrease in emergence regime
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Ascophyllum nodosum ecad mackaii and its component species are all likely to survive increased or full immersion. However, a reduction in the period of emersion may result in the species being competitively displaced by faster growing species and may allow the upper limit of the population of Ascophyllum nodosum to extend up the shore.
Increase in water flow rate
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The biotope occurs in very sheltered locations with weak or very weak tidal streams because the mackaii ecad is unattached. Therefore, the biotope is likely to be highly intolerant of an increase in water flow rate because plants of the characterizing species will be washed away. The attached form and the other fucoid algal species in the biotope are able to tolerate higher water flow rates than the unattached ecad. For recovery see additional information.
Decrease in water flow rate
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The biotope occurs in very sheltered locations where water flow rates may be negligible so a decrease is not relevant.
Increase in temperature
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Chock & Mathieson (1979) found no major physiological difference between the attached form of Ascophyllum nodosum and its ecad scorpioides so it seems likely that the mackaii ecad will also be physiologically similar to the attached form. Ascophyllum nodosum and the mackaii ecad are intertidal and so are regularly exposed to rapid and short-term variations in temperature. Both exposure at low tide or rising tide on a sun-heated shore may involve considerable temperature increases. Growth has been measured between 2.5 and 35°C with an optimum between 10 and 17°C (Strömgren, 1977). In the North Sea Ascophyllum nodosum can tolerate a maximum temperature of 28°C and the optimum growth rate is at 15°C (Lüning, 1990). Laboratory experiments in New Hampshire showed that Ascophyllum nodosum exhibits a eurythermal response to temperature with a more pronounced optimum occurring during the summer than the winter (Chock & Mathieson, 1979). Overall, summer plants showed a higher rate of net photosynthesis than winter specimens. Therefore, the species is likely to be quite tolerant of a long term change in temperature of 2°C. The species is unlikely to be affected by a short term change of 5°C, as it was not damaged during the unusually hot summer of 1983 when the average temperature was 8.3°C higher than normal (Hawkins & Hartnoll, 1985). Although some of the associated macrofauna may be more intolerant of increases in temperature they are not key to the structure and function of the biotope. Therefore, the biotope is considered to have low intolerance to increases in temperature. However, the species has been found to be damaged by thermal pollution if the water temperature is above 24°C for several weeks (Lobban & Harrison, 1997) and the southern limit of the species distribution is controlled by the maximum summer temperature of about 22°C (Baardseth, 1970).
Decrease in temperature
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In Newfoundland populations of Ascophyllum nodosum ecad mackaii are subjected to low temperatures and ice conditions probably seldom encountered in the Scottish and Irish habitats studied by Gibb (1957). In January 1970, some populations were encased in ice, a phenomenon enhanced by the "layering" effect of fresh and salt water in these habitats (South & Hill, 1970). Judging from the age of some of the globular tufts at some of these sites, the authors suggest the plants can presumably withstand a number of successive winters of ice encasement without undue harm. Such conditions during the particularly stormy months of the year could possibly ensure the survival of mackaii in these localities. The extreme sheltered conditions occupied by the ecad, and its free-living habit would preclude it, however, from the severest action of pack ice frequently occurring on the open coast in Newfoundland. Although some other species, such as the gammarid amphipod Hyale prevostii, will be more intolerant of long and short term changes in temperature the key species, the ecad, is likely to tolerate such changes and so intolerance is assessed as low. Metabolic and reproductive processes which may be affected by a drop in temperature are likely to return to normal very quickly.
Increase in turbidity
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An increase in turbidity would reduce the light available for photosynthesis during immersion. However, the species is found at the upper and mid-tide levels and so is subject to long periods of emersion during which time it can continue to photosynthesize as long as the plant has a sufficiently high water content. Therefore, photosynthesis and consequently growth will be unaffected during this period and so intolerance of the species, and hence the biotope, is considered 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 biotope is likely to be highly intolerant of increases in wave exposure because the free living mackaii ecad of Ascophyllum nodosum only develops in locations of extreme shelter. Increased wave action could also result in the displacement of plants from ideal conditions. In addition the fauna that shelter in plants are also likely to be displaced if wave action increases. Therefore, the intolerance of the biotope is considered to be high. Recoverability is assessed as low because it is not known if lost beds can recover - see additional information.
Decrease in wave exposure
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Ascophyllum nodosum ecad mackaii only develops in areas of extreme shelter where wave exposure in negligible so a decrease in wave exposure at the level of the benchmark is not relevant.
Noise
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Macroalgae have no known sound or vibration sensors so the biotope will not be intolerant of noise disturbance such as boat traffic. The response of macroinvertebrates is not known.
Visual Presence
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Macrophytes have no known visual sensors. Most macroinvertebrates have poor or short range perception and are unlikely to be affected by visual disturbance such as boat traffic or walkers on the shore.
Abrasion & physical disturbance
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Frond injury in the mackaii ecad is common and often severe and plays an important part in the life of plants (Gibb, 1957). Injury influences the branching of the plant by acting as a stimulus for the development of lateral branches. Therefore, the plants are likely to have low intolerance to abrasion. However, a passing scallop dredge, or similar impact, is likely to physically remove a number of the plants themselves, similar to but not as extensive as substratum loss above. Therefore, an intolerance of intermediate has been recorded. Where present, the ecad can proliferate itself vegetatively from its own broken fragments which continue to divide forming new plants. Therefore, recovery should be possible within five years although it may take longer for plants to return to original density and biomass so a score of moderate of reported.
Displacement
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Ascophyllum nodosum ecad mackaii is unattached and so should not be intolerant of displacement to another suitable location.

Chemical Factors

Synthetic compound contamination
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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). Hoare & Hiscock (1974) observed that Ascophyllum nodosum was absent from within 100m of an acidified, halogenated effluent discharge, and that plants nearby had abnormal and retarded growth. Most Ascophyllum nodosum ecad mackaii beds are found in unpolluted sites so the ecad may be intolerant of synthetic chemicals.
Heavy metal contamination
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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).
Hydrocarbon contamination
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Experimental studies have found that long-term exposure to low levels of diesel reduces the growth rate in Ascophyllum nodosum. A limited amount of oil pollution need not be detrimental to a population of the characterizing species with good recruitment (Sjoetun & Lein, 1993). However, other components of the biotope are known to be intolerant of hydrocarbon pollution, especially amphipods.
Radionuclide contamination
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Insufficient information.
Changes in nutrient levels
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There are reports of a decline in populations of Ascophyllum nodosum in the North Atlantic as a result of increased eutrophication (Fletcher, 1996). Most A. nodosum ecad mackaii beds are in unpolluted sites and may be adversely affected by eutrophication of sea lochs which can be caused by fish farm activities.
Increase in salinity
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The development and maintenance of the ecad depends on the frequent alternation of high and low salinity. These conditions occur between high and low water neaps, in places where freshwater streams have an influence but where there is full marine salinity for a period during the tidal cycle. Therefore, it is expected that a long term increase in salinity would be detrimental to the species and hence the biotope and a rank of high is recorded. Information on recovery can be found in 'additional information' below.
Decrease in salinity
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The development and maintenance of the ecad depends on the frequent alternation of high and low salinity. These conditions occur between high and low water neap tide levels, in places where freshwater streams have an influence but where there is full marine salinity for a period during the tidal cycle. Therefore, the ecad can tolerate very short periods of low salinity. However, the longest exposure will only be about 10 hours and so A. nodosum ecad mackaii is not likely to be able to tolerate the benchmark decreases in salinity. When the ecad and the attached plant are frequently submerged for long periods in running fresh water they develop 'freshwater decay' where plants begin to break up. Although this breaking up of plants is important to the life of plants (it influences the branching habit) a long term decrease in salinity would probably cause the death of plants and so the biotope is considered to have high intolerance to decreased salinity. For recovery see additional information.
Changes in oxygenation
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There is insufficient information on the response of the key and other organisms in the biotope to changes in oxygenation to make an assessment. However, an oxygen concentration of 2 mg/l is thought likely to cause effects in marine organisms (Cole et al., 1999) and if experienced for a period of one week is likely to result in the death of some intolerant species.

Biological Factors

Introduction of microbial pathogens/parasites
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Although bacteria and fungi are associated with the attached form of 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 ecad mackaii and so the biotope is assessed as not sensitive. However, as several species have become established in British waters there is always the potential for an adverse effect to occur.
Extraction
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The attached form of Ascophyllum nodosum is still collected on a small scale in western Scotland for the extraction of alginate. The unattached mackaii ecad is very easy to collect as it does not need cutting from the rock and it has been collected along with the attached form in the past. For example, Ascophyllum nodosum ecad mackaii beds and associated communities in the Uists in the Outer Hebrides have been decimated by removal of plants.

Littorina littorea is also harvested by hand, without regulation, for human consumption. In some areas, notably Ireland, collectors have noted a reduction in the number of large snails available.

It is likely that at least part of the population of either of these two species may be lost and accordingly, intolerance has been assessed as intermediate. It is not known if it is possible, or how long it takes, for beds of Ascophyllum nodosum ecad mackaii to recover from harvesting. For example, there was no sign of recovery of a bed two years after its removal at Kyle of Lochalsh (Anonymous, 1999(t)). However, once present the ecad can proliferate itself vegetatively from its own broken fragments which continue to divide forming new plants. Therefore, recovery should be possible within five years although it may take longer for plants to return to original density and biomass so a rank of moderate of reported.

Additional information icon Additional information

Recoverability

On return to normal conditions after a perturbation the sheltered conditions of the biotope should enable fragments of the attached Ascophyllum nodosum to grow and develop into the ecad. However, recovery depends on the supply of Ascophyllum nodosum fragments which may be from distant sources and may therefore take several years to return. For example, during the construction of the Skye Bridge a dense bed at Kyle of Lochalsh was accidentally removed and more than two years later there was still no sign of recovery of this bed so recovery may be unpredictable. The key characterizing species Ascophyllum nodosum ecad mackaii is also very slow growing so recovery to original sized plants and beds could take many years. Recoverability is assessed as low because it is not known if lost beds can recover.

This review can be cited as follows:

Hill, J.M. 2001. Ascophyllum nodosum ecad mackaii beds on extremely sheltered mid eulittoral mixed substrata. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 31/10/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=138&code=2004>