Biodiversity & Conservation

LR.LR.Rkp.G

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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Removal of the substratum will result in the removal and loss of the biotope. Therefore, an intolerance of high has been recorded. The macroalgae within this biotope can rapidly colonize new substratum and grow rapidly, probably within a few months therefore a recoverability of very high has been recorded (see additional information below).
Smothering
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Ulva intestinalis is a filamentous seaweed without structural support for its thalli, therefore it is likely that entire plants would be smothered by an additional covering of 5 cm of sediment. Cladophora rupestris is a stout shrub like seaweed, whose fronds may grow up to 20 cm in height. A covering of sediment to a depth of 5 cm is likely to partially cover the seaweed, and at low tide the whole plant may be covered whilst lying limply on the rock or in shallow pools. Unless the sediment is removed by the incoming tide (which may be some time on the high shore where pools may be isolated from the main body of the sea for several days in succession), photosynthesis would be inhibited and fronds of macroalgae may begin to decay over the duration of one month. Spores, germlings and juveniles are likely to be highly intolerant of smothering by sediment (Vadas et al. 1992). An intolerance assessment of intermediate has been made to reflect the probable impact of smothering on germlings, thereby preventing recruitment for that period, and the inhibitory effects upon more mature specimens. On return to prior conditions, the macroalgae is likely to recover, either new growth will arise from the resistant multicellular branching rhizoids in the case of Cladophora rupestris (van den Hoek, 1982) that may remain in situ, or macroalgal species will recruit to cleared substrata via spores dispersed in the plankton. Smothering by impermeable material such as oil is likely to have a more severe and long lasting impact.
Increase in suspended sediment
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The effects of increased suspended sediment on macroalgae are likely to be indirect but include settlement of silt although, at the level of the benchmark, that is unlikely to cause smothering. Increased turbidity reduces light availability (see below). At the benchmark level an assessment of not relevant has been made and the effects of smothering and turbidity addressed elsewhere.
Decrease in suspended sediment
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The community is unlikely to be intolerant of a decrease in suspended sediment. The effects of increased light penetration owing to reduced turbidity are addressed elsewhere.
Desiccation
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Ulva intestinalis is often very abundant on the high shore where desiccation stress is the primary factor controlling seaweed distribution, and may even be found above the tidal limits of the shore. Ulva intestinalis can survive several weeks of living in completely dried out rock pools, while becoming completely bleached on the uppermost layers, but remaining moist underneath the bleached fronds. Its ability to survive out of water for so long makes Ulva intestinalis an ideal refuge for copepods in supralittoral rockpools (McAllen, 1999). However, marine communities occurring at the highest level on the shore are living at the extreme of their physiological tolerance limits and so would not be likely to tolerate a further increase in desiccation, unless adequate refuge is available locally, e.g. in the case of littorinids, crevices in the rock, or, for other species, within pools. Increased desiccation would therefore result in the upper extent of species distributions being depressed. An intolerance assessment of intermediate has been made. On return to prior conditions, the community is likely to recover rapidly.
Increase in emergence regime
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The biotope is isolated from the main body of the sea for considerable and varying periods of time owing to its position high on the shore. At the benchmark level, it is unlikely that the community will demonstrate any significant additional stress attributable to an extra hour of emersion. An assessment of not sensitive has been made.
Decrease in emergence regime
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A greater period of immersion will lessen the physico-chemical extremes that prevent the colonization of the upper shore by species more typical of the lower shore. Desiccation stress will be lessened and temperature and salinity changes less severe. Thus the LR.G community has been assessed to have a high intolerance to decreased emergence as it will allow the 'up-lift' of lower shore species into the biotope and will begin to change to another. On return to prior conditions, it is likely that species which entered the biotope would be lost owing to intolerance, and recoverability has been assessed to be high to indicate that colonizing species may persist for a period but disappear as the biotope community re-stabilizes.
Increase in water flow rate
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The community exists for the great majority of time in still water conditions. Upper shore rockpools may only flood with water due to wave action and would be unaffected by changes in tidal stream velocity that occur away from the shore. An assessment of not sensitive has been suggested.
Decrease in water flow rate
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The community exists for the great majority of time in still water conditions. Upper shore rockpools may only flood with water due to wave action and would be unaffected by changes in tidal stream velocity that occur away from the shore. An assessment of not sensitive has been suggested.
Increase in temperature
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At the benchmark level the community has been assessed not to be intolerant of increased temperature.
In general, the water temperature of rockpools follows that of the air more closely than that of the sea, and throughout any 24 hour period, dramatic changes in temperature may be observed. For instance, Pyefinch (1943) plotted diurnal changes in a pool lying above mean high water during July. When the pool was out of contact with the sea, water temperature increased by 5°C from 14 to 19°C over a three hour period and decreased suddenly to 14 °C within 1.5 hours when the incoming tide reached it. Hence, the community that inhabits such environments needs to be especially tolerant of acute temperature changes. For example, the copepod Tigriopus fulvus is more tolerant of high temperatures at higher salinities (see ecological relationships). At a salinity of 34 psu, the death point of Tigriopus fulvus is reached at 32°C (Goss-Custard et al.,1979). Clark (1992) reviewed the influence of cooling water effluent on shore communities. Effects are usually restricted to the immediate vicinity of the outfall, but brown seaweeds were eliminated from a rocky shore heated to 27-30°C by a power station in Maine, whilst Ulva intestinalis increased significantly near the outfall (Vadas et al., 1976). Fortes & Lüning (1980) and Lüning (1984) reported that Cladophora rupestris could survive exposure to temperatures in the range 0 - 28°C for at least a week.
Decrease in temperature
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At the benchmark level the community has been assessed not to be intolerant of decreased temperature.
In general, the water temperature of rockpools follows that of the air more closely than that of the sea and dramatic temporal changes in temperature may be observed. For instance, Pyefinch (1943) plotted diurnal changes in a pool lying above mean high water during July. When the pool was out of contact with the sea, water temperature increased by 5°C from 14 to 19°C over a three hour period and decreased suddenly to 14 °C within 1.5 hours when the incoming tide reached it. Hence, the community that inhabits such environments needs to be especially tolerant of acute temperature changes. Under extremely low temperatures, components of the community demonstrate tolerance. For instance, Kylin (1917) reported Ulva(as Enteromorpha species to be tolerant of a temperature of -20°C, whilst growth measurements of Cladophora rupestris led Cambridge et al. (1984) to conclude that the species was tolerant of temperatures of below -5°C. The copepod fauna may be less tolerant of near freezing temperatures. For instance, Davenport et al. (1997) stated that unlike other species of Tigriopus, Tigriopus fulvus could not withstand freezing temperatures, whilst Tigriopus brevicornis appears to be able to withstand exposure to low temperature (and to severe hypoxia) by entering a quiescent/dormant state during which its metabolic rate is significantly reduce (McAllen et al., 1999). At extremes of temperature some mortality would be expected.
Increase in turbidity
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The light attenuating effects of increased turbidity are likely to impact on the photosynthetic efficiency of macroalgal species and the microalgal film in the short term, but owing to the relative stillness of water in rockpools, suspended sediment causing increased turbidity is likely to settle out. At the benchmark level an intolerance assessment of low has been made. Optimal photosynthesis is likely is resume rapidly.
Decrease in turbidity
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As photoautotrophs, macroalgae and microalgal films are likely to benefit from reduced turbidity, as the light attenuating effects of turbid water reduce photosynthesis. An assessment of not sensitive* has been made.
Increase in wave exposure
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The biotope may occur on the upper shore in locations with varying wave exposures (exposed to sheltered) (Connor et al., 1997b). The effects of wave exposure upon rockpool communities high on the shore are likely to depend on tidal amplitude as within a shore, and where the tidal amplitude is significant, the time for which organisms are subjected to wave action will vary along the intertidal gradient. For instance, during neap tide periods, high shore rockpools may remain isolated from the main body of the sea for several days or weeks in concession. During such times wave action is unlikely to be of direct influence other than generating a spray, whilst during periods of tidal immersion wave action may directly affect the community. The changes in community composition that occur with increased wave exposure are accompanied by striking changes in the vertical levels of zones on the shore. In north-west Europe, all the zones become greater in vertical extent as wave exposure increases, and thus are found at greater heights above chart datum (Little & Kitching, 1996). The upper limit of littorinids and Verrucaria may rise dramatically, so that the vertical extent of the shore may increase from a few metres in shelter to 30 m or more in extreme exposures. Hence over a year the upward extent of the LR.G biotope may increase following an increase of two ranks on the MNCR wave exposure scale. More frequent renewal of seawater at the lower extent of the biotope may allow other species less tolerant of temperature and salinity variation to establish and begin to change the biotope to another. An intolerance assessment of low has been suggested as increased competition for space and resources may occur. On return to prior conditions, recovery is likely to be very high as intolerant species decline.
Decrease in wave exposure
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The biotope may occur on the upper shore of locations with varying wave exposure (exposed to sheltered) (Connor et al., 1997b). As elevated wave exposure serves to 'up-lift' zones of animal and plant communities up the shore (see increased wave exposure), decreased wave exposure will presumably cause a reversal to some extent and the upward extent of species characteristic of the biotope dominate become lower. However, providing suitable habitats are available the LR.G biotope may develop in pools further down the shore no longer subject to frequent renewal of seawater. Therefore an assessment of not sensitive has been suggested.
Noise
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The biotope is characterized by macroalgae and small crustaceans and molluscs unlikely to be disturbed by noise at the benchmark level. An assessment of not sensitive has been made.
Visual Presence
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The biotope is characterized by macroalgae and small crustaceans and molluscs unlikely to be disturbed by the visual presence of objects not normally found in the marine environment. An assessment of not sensitive has been made.
Abrasion & physical disturbance
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Ulva intestinalis and Cladophora rupestris are likely to be susceptible to abrasion as they are not of a resilient growth form and would easily be scraped from the substratum by dragging objects. Littorinids may be knocked from rocks by physical disturbance and unless damaged are likely to reattach. Small copepods would probably be able to avoid abrasive agents by seeking refuge. Intolerance has been assessed to be high. Ulva intestinalis and Cladophora rupestris are cosmopolitan species that reproduce rapidly enabling them to colonize available substrata, so recoverability has been assessed to be very high (see additional information below).
Displacement
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Ulva intestinalis typically forms a permanent attachment to suitable substrata. However, in some circumstances, the algae may becomes detached from the substratum, and buoyed-up by gas, it floats up to the surface and continues to grow in mats (e.g. Baeck et al., 2000) but in which case it would be lost from the biotope. Cladophora rupestris forms a permanent attachment to solid substrata. It is likely to be intolerant of displacement as once removed, mature plants are unable to reattach. Faunal species associated with the biotope are mobile. The intolerance of the biotope to displacement has been assessed to be high as the key structuring seaweed species, Ulva and Cladophora, would not be able to reattach. However, recoverability has been assessed to be very high (see additional information below).

Chemical Factors

Synthetic compound contamination
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Ulva intestinalis was assessed to have an intermediate intolerance to synthetic chemicals owing to evidence of adverse effects on the species viability and damage causing mortality (Moss & Woodhead, 1975; Scarlett et al., 1997; Smith 1968). Smith (1968) reported Cladophora rupestris to be amongst algae of unhealthy appearance following exposure to oil dispersants. The intolerance of the biotope has been assessed to be high as key structural species may be adversely affected. Assuming deterioration of contaminants, recovery of the key structuring species has been assessed to be very high (see additional information below).
Heavy metal contamination
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The order of metal toxicity to algae varies, with the algal species and environmental conditions, but generally the order is Hg>Cu>Cd> Ag>Pb>Zn (Rice et al., 1973; Rai et al., 1981). Available evidence suggested that Ulva intestinalis was relatively tolerant of heavy metal exposure, only experiencing reduced growth (see full MarLIN review). Most of the information available suggests that adult gastropod molluscs are rather tolerant of heavy-metal toxicity (Bryan, 1984). Winkles may absorb metals from the surrounding water by absorption across the gills or from the diet, and evidence from experimental studies suggest that the diet is the most important source, e.g. Bryan et al., 1983). The intolerance of the community to heavy metal pollution has been assessed to be low as available evidence suggests effects upon species viability. Recoverability has been assessed to be high. Whilst the key structuring algal species may recolonize rapidly within six months, the littorinids associated with this biotope are likely to take longer to recover should the population become depleted owing to the fact that they have very localized recruitment with live young rather than a dispersive larval stage (see recruitment processes).
Hydrocarbon contamination
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Bokn et al. (1993) examined 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 µ/mg/L and Low = 30.1µ/mg/L of WAF of diesel oil were delivered via sea water to established rocky shore mesocosms over a two year period, however there were no demonstrable effects in the abundance patterns of Cladophora rupestris, Ulva lactuca in the oil contaminated compared with the control mesocosms at the end of that period.

However, direct contact with viscous oil is likely to have a greater impact on the community. The toxic effects of oil on algae may be categorized as those associated with the coating of the fronds, e.g. coating by oil is likely to reduce CO2diffusion and light penetration to the plant, and those attributable to the uptake of hydrocarbons and subsequent disruption of cellular metabolism (Lobban & Harrison, 1997). For instance, Cullinane et al. (1975) summarised the damage caused to Cladophora rupestris following the crude oil spill in 1974 in Bantry Bay, Ireland. No damage was immediately apparent to Cladophora rupestris, but microscopic examination of material from rock pools at League Point showed complete bleaching of the terminal cells (only). Burrows (1991) indicated that following damage to the apical cells of fronds, that regeneration was possible. Ulva intestinalis also tends to recover very rapidly from oil pollution incidents. For instance, after the Torrey Canyon oil in 1967, grazing littorinid species were killed, and a dense flush of ephemeral green algae (Ulva and Blidingia) appeared on the rocky shore within a few weeks and persisted for up to one year (Smith, 1968).
Experience of and observations from oil spills such as the Sea Empress and Amoco Cadiz suggest that gastropod molluscs are highly intolerant of hydrocarbon pollution and it is likely that littorinid species would suffer mortality following oil contamination of this biotope. However, they are not very characteristic of the biotope and in the absence of their grazing pressure the green algae characteristic of the biotope may extend in distribution. Intolerance has been assessed to be intermediate. Recoverability has been assessed to be very high.
Radionuclide contamination
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Insufficient information.
Changes in nutrient levels
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Nutrient enrichment of the water column, e.g. resulting from sewage discharge, can stimulate blooms of opportunistic algae, especially by those of the Chlorophyceae,Ulva, Cladophora and Ulva species (Knox, 1986). An assessment of not sensitive* has been made, as the species experience increased growth rates as a result of nutrient enrichment. Grazers in the biotope would benefit from a more abundance food supply.
Increase in salinity
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Conditions within rockpools are the consequence of prolonged separation from the main body of the sea, and physico-chemical parameters within them fluctuate dramatically (Huggett & Griffiths, 1986). Small and shallow pools are especially influenced by insolation, air temperature and rainfall, the effects of which become more significant towards the high shore, where pools may be isolated from the sea for a number of days or weeks (Lewis, 1964). Rockpools in the supralittoral, littoral fringe and upper eulittoral are liable to gradually changing salinities followed by days of fully marine or fluctuating salinity at times of spring tide (Lewis, 1964). The community has been assessed not to be intolerant of increased salinity at the benchmark level because it represents a lesser change in salinity than the community might normally be expected to experience and the community persists owing to the tolerance of species to short-term acute changes.
Decrease in salinity
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Conditions within rockpools are the consequence of prolonged separation from the main body of the sea, and physico-chemical parameters within them fluctuate dramatically (Huggett & Griffiths, 1986). Small and shallow pools are especially influenced by insolation, air temperature and rainfall, the effects of which become more significant towards the high shore, where pools may be isolated from the sea for a number of days or weeks (Lewis, 1964). Rockpools in the supralittoral, littoral fringe and upper eulittoral are liable to gradually changing salinities followed by days of fully marine or fluctuating salinity at times of spring tide (Lewis, 1964). Values ranging from 5-30 psu have been recorded in a period of 24 hours (Ranade, 1957). The community has been assessed to be tolerant of increased salinity at the benchmark level because it represents a lesser change in salinity than the community might normally be expected to experience and the community persists owing to the tolerance of species to short-term acute changes.
Changes in oxygenation
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During the day, algae within rockpools produce oxygen by photosynthesis, and oxygen concentrations may rise to three times the saturation value, so that it is actually released as bubbles. The effect of which is to increase the pH of water in the pool owing to utilization of carbon dioxide. At night, when photosynthesis has ceased, algal respiration may utilize much of the available oxygen and minimum values of 1-5 % saturation have been recorded (Morris & Taylor, 1983). Algae in this biotope are unlikely to be adversely affected by decreased oxygen as they produce their own. The effect of oxygen saturation resulting from algal photosynthesis is lesser in high shore pools as they tend to contain fewer algae. The effect of severe hypoxia on the copepod Tigriopus brevicornis is for it to enter a quiescent/dormant state during which its metabolic rate is significantly reduced. It recovers on return to optimal conditions (McAllen et al., 1999). As inhabitants of littoral rockpools are subjected and therefore likely to be highly adapted to dramatic changes in physico-chemical conditions such as oxygen concentration, the community has been assessed not to be sensitive at the benchmark level.

Biological Factors

Introduction of microbial pathogens/parasites
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Insufficient information.
Introduction of non-native species
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No known alien species are reported to adversely affect the biotope. An assessment of not relevant has been made.
Extraction
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It is extremely unlikely that any of the species indicative of sensitivity would be targeted for extraction and we have no evidence for the indirect effects of extraction of other species on this biotope.

Additional information icon Additional information

Recoverability
It is likely that Ulva and Cladophora species will have a considerable capacity for recovery. Both species are widespread around the British Isles and Ireland, and may be found in reproductive condition all year round. Numerous motile swarmers (gametes and spores) are released and in the water column they can be dispersed over considerable distances. In addition to recruitment by swarmers, new growth of Cladophora rupestris may arise from the resistant multicellular branching rhizoids (van den Hoek, 1982) that may remain in situ. Recoverability has therefore been assessed to be very high. For instance, after the Torrey Canyon tanker oil spill in mid March 1967, recolonization by sporelings of Ulva and Cladophora species had occurred by the end of April (Smith, 1968). Recovery of the copepod Tigriopus fulvus would be expected to be rapid (presuming a residual or localized population remained from which to recruit) as the species is in reproductive condition all year round and reaches sexual maturity within two months. It also can produce more than one brood from one fertilization. These aforementioned species are characteristic of the biotope, which would be recognized upon their probably rapid re-establishment. Other components of the community, such as the littorinids and other grazers, are of lower abundance owing to physical conditions and are not considered to be characterizing species. However, in their total absence the biotope would be considered to be impoverished. Owing to recruitment of live young in a localized area without a dispersive larval stage recovery of such species may take longer.

This review can be cited as follows:

Budd, G.C. 2002. Green seaweeds (Ulva spp. and Cladophora spp.) in upper shore rockpools. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 17/09/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=246&code=1997>