Biodiversity & Conservation

LR.FLR.Eph.Ent

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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The biotope is characterized by algal species that adhere to the surface of the substratum and would therefore have a high intolerance to substratum loss. A recoverability of very high has been recorded (see additional information below).
Smothering
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The biotope is characterized by Ulva and Porphyra species that do not have structural support for their thalli, therefore it is likely that entire plants would be smothered by an additional covering of 5 cm of sediment. Smothering would interfere with photosynthesis and over the period of one month the seaweed may begin to rot. At the benchmark level, intolerance of smothering has been assessed to be high. However, on return to prior conditions the species is likely to rapidly recolonize the available substratum (see additional information below) and recoverability has been assessed to be very high.
Increase in suspended sediment
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Increased suspended sediment is unlikely to directly adversely affect the community that is dominated by ephemeral algae. The light attenuating effects of an increase in suspended sediment are addressed under turbidity (see below). However, increased concentrations of suspended sediment in combination with tidal flow may have an adverse effect through scouring, but has been considered under 'increased water flow rate' below.
Decrease in suspended sediment
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The increased light penetration of the water column following a reduction in suspended sediment have been assessed under 'reduced turbidity', below. The biotope is unlikely to be adversely affected by a decrease in suspended sediment. An assessment of not sensitive has been made.
Desiccation
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Intertidal algae grow best when permanently submerged, irrespective of how high on the shore they normally grow. Porphyra is a remarkably desiccation tolerant seaweed being able to lose almost all fluid from its thalli, drying out to a crisp, paper thin film. About 75% of water is lost from the thalli after six hours of exposure (Boney, 1969). While many other seaweeds would die if they lost this much turgidity, Porphyra readily recovers once re-hydrated. Thin seaweeds like Ulva also lose their water content very fast, but overcome the problem by growing in dense populations where they can cover and shade each other to some extent when exposed, 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, several studies have indicated that stress from aerial exposure can cause high mortality to algal propagules. Hruby & Norton (1979) found that 7-14 day old germlings of Ulva were more tolerant of desiccation than earlier stages, so an increase in desiccation stress may impact more adversely on newly settled germlings than more mature plants. An intolerance assessment of low has been made to the benchmark change in desiccation to reflect the intolerance of algal propagules, and recoverability has been assessed to be very high (see additional information below).
Increase in emergence regime
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The characterizing macroalgae of the biotope are often very abundant on the high shore where desiccation stress is the primary factor controlling seaweed distribution. Above Mean High Water Springs (MHWS) level, Ulva intestinalis tends to preferentially inhabit rock pools or is associated with trickles of freshwater that cross the shore, and in such positions the risk of desiccation is reduced. Also as a result of increased emergence, the species that graze on Ulva intestinalis are likely to be less active, e.g. Littorina littorea, owing to risk of desiccation, and the seaweed may benefit from reduced grazing pressure. The distribution of both characterizing seaweed species, Ulva and Porphyra is likely to change in response to a change in the emergence regime and their band of cover on the shore retreat seawards unless freshwater flow across the shore or the presence of rockpools mitigates the effect. An intolerance assessment of low has been made to reflect changes in abundance. On return to prior conditions, recoverability has been assessed to be very high (see additional information, below).
Decrease in emergence regime
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A decrease in the emergence regime, would create conditions equivalent to those of a region lower on the shore. Although, Ulva and Porphyra are likely to remain present, other species of seaweed and fauna are likely to be competitively superior and dominate the shore and influence algal growth. The biotope would begin to change to another so an intolerance of high has been recorded. On return to prior conditions, recoverability has been assessed to be high reflecting the probability that other seaweed species would persist for some time before the MLR.Ent biotope re-stabilized.
Increase in water flow rate
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Moderate water movement is beneficial to seaweeds. It carries a supply of nutrients and gases to the plants, removes waste products and prevents the settling of silt (Kain & Norton, 1990). Seaweeds in still water rapidly deplete the nutrients in their immediate vicinity because the coefficient of molecular diffusion in seawater is very low (Sverdrup et al., 1942). Damage sustained by Ulva and Porphyra spp. by increased water flow is likely to be initially minimised by the fact that the thalli of both species conform to the direction of flow, this also serves to bring the thalli close to the slower moving water near the substratum and minimises the chance of being ripped from the substratum. However, increased water flow in combination with elevated levels of suspended sediment is likely to increase scour. Germlings may be especially susceptible to scour and recruitment may therefore be adversely affected during that period. At the benchmark level an intolerance assessment of low has been made.
Decrease in water flow rate
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Moderate water movement is beneficial to seaweeds. It carries a supply of nutrients and gases to the plants, removes waste products and prevents the settling of silt (Kain & Norton, 1990). Seaweeds in still water rapidly deplete the nutrients in their immediate vicinity because the coefficient of molecular diffusion in seawater is very low (Sverdrup et al., 1942). Reduced water flow may therefore affect the viability of the characterizing seaweed through reduced growth. An intolerance assessment of low has been made. On return to prior conditions, optimal growth is likely to resume rapidly, and recoverability has been assessed to be immediate.
Increase in temperature
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Ulva intestinalis and Porphyra species occur to the south of the British Isles, so are likely to be tolerant of a chronic increase in temperature of 2°C. Also, they are characteristic of the upper shore where water and air temperatures may be greatly elevated on hot days. 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 of the genus, Ascophyllum and Fucus 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). At the benchmark level, an assessment of not sensitive* has been made because the characterizing species may benefit from loss of other algal species.
Decrease in temperature
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Ulva intestinalis and Porphyra species occur to the north of the British Isles, so are likely to be tolerant of a chronic decrease in temperature of 2°C. Ulva species were reported to be tolerant of a temperature of -20C (Kylin, 1917). Porphyra species are also reported to be tolerant of subzero temperatures (Lobban & Harrison, 1997), so are unlikely to be adversely affected by the benchmark acute decrease in temperature. At the benchmark level, an assessment of not sensitive has been made.
Increase in turbidity
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The light attenuating effects of an increase in turbidity are likely to affect the characterizing algae of the biotope. Reduced photosynthesis may result and growth may be affected. Intolerance has been assessed to be low to reflect the possible impact on the viability of important characterizing species. Upon return to conditions of greater water clarity, recovery is likely to be immediate as optimal photosynthesis resumes.
Decrease in turbidity
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A decrease in turbidity is likely to be beneficial to the macroalgae characteristic of the biotope as a greater percentage of light is transmitted through the water column. An assessment of not sensitive* has been made.
Increase in wave exposure
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The recorded distribution of the biotope includes wave exposed shores, and wave action as a disturbance is an important factor in determining presence of the community. The ephemeral algae that colonize the biotope are able to exploit fresh surfaces on unstable substrata owing to rapid recruitment. Furthermore, the morphology of the species offers a degree of tolerance to wave exposure. For instance, Porphyra species are considered to be wave tolerant (Kain & Norton, 1990). The thalli give no impression of strength, rather, they are delicate and flimsy and yield to the wave. Thalli deflect downstream and conform with the flow, this also serves to bring the thalli close to the slower moving water near the substratum and minimises the chance of being ripped from the substratum. At the benchmark level an intolerance assessment of low has been made, as although a few individual specimens may be damaged by increased wave exposure, the factor creates conditions that favour the development of the biotope, e.g. through clearance of substrata / turning of boulders. Recoverability has been assessed to be very high (see additional information below).
Decrease in wave exposure
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Disturbance is a factor determining the community composition of the biotope. Wave exposure is important in determining the stability of the substratum. The species that characterize the biotope are especially able to exploit unstable substrata owing to rapid recruitment. With increased stability, following a reduction in wave exposure, species of adjacent biotopes may be able to colonize, e.g. lichens or fucoids, and the biotope begin to change to another, in the absence of other factors of disturbance such as freshwater flow. Intolerance has been assessed to be high. On return to prior conditions, recoverability has been assessed to be very high (see additional information below)
Noise
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The biotope is characterized by algae. Algae are not known to have mechanisms for noise reception. An assessment of not sensitive has been made.
Visual Presence
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The biotope is characterized by algae. Algae are not known to have mechanisms for visual perception. An assessment of not sensitive has been made.
Abrasion & physical disturbance
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Ulva intestinalis and Porphyra species 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. Intolerance has been assessed to be high. However, both 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 and Porphyra species typically form a permanent attachment to suitable substrata, suggesting that they would be intolerance of displacement. These algal species characterize the biotope and, in their absence, the biotope would not be recognized. Intolerance to displacement has been assessed to be high. The species are able to recruit rapidly to cleared substrata and recoverability has been assessed to be very high (see additional information below).
In some circumstances, Enteromorpha intestinalis may become 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). The thalli of the seaweed tend to loose their tubular shape, spread, and formed unattached monostromatic sheets.

Chemical Factors

Synthetic compound contamination
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Little information was found specific to the biotope. However, Ulva intestinalis has been assessed to have an intermediate intolerance to synthetic chemical pollution as available evidence highlights adverse effects upon the species viability and damage leading to death (Smith 1968; Moss & Woodhead, 1975; Scarlet et al., 1997) (refer to full MarLIN review). Intolerance has been assessed to be intermediate, because Ulva intestinalis is an important characterizing species of the biotope.
Heavy metal contamination
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intolerance of the biotope has been assessed to be low, as important characterizing species seem to be relatively resistant to heavy metal pollution. Species of the genus Ulva seem to be especially suitable for monitoring heavy metals in coastal areas (e.g. Leal et al., 1997). For instance, laboratory experiments have shown that the accumulation of Cu, Zn, Cd and Pb by four different species of Ulva was sufficiently similar to justify pooling samples of the genus for field monitoring (Say et al., 1990). The effects of copper on macrophytes have been more extensively studied than the effects of any other metal owing to its use in antifouling paints. Lewis et al. (1998) investigated the influence of copper exposure and heat shock on the physiology and cellular stress response of Ulva intestinalis (as Enteromorpha). Heat shock proteins (HSPs) are known to be expressed in response to a variety of stress conditions, including heavy metals (Lewis et al., 1999). Ulva intestinalis was exposed to a range of copper concentrations (0-500 µg -1 for 5 days, to assess the effect of copper exposure on stress proteins (Stress-70 levels) and physiology of the seaweed. Stress-70 was induced by copper exposure, but was found to be no better an indicator of copper exposure than measurement of growth, which was inhibited by copper.
Hydrocarbon contamination
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The intolerance of the biotope to hydrocarbon contamination has been assessed to be high. The biotope occurs on the upper shore where oil originating from a spill is likely to be thickly deposited on the ebb tide. Following the Torrey Canyon oil spill in mid-March 1967, both Ulva and Porphyra species were adversely affected by oil. The oil bleached filamentous algae such as Ulva and adhered to the thin fronds of Porphyra, which after a few weeks became brittle and were washed away. However, regeneration of Porphyra and Ulva was noted by the end of April at Marazion, Cornwall. Similarly, at Sennen Cove where rocks had completely lost their cover of Porphyra and Ulva during April by mid-May had occasional blade-shaped fronds of Porphyra up to 15 cm long. These had either regenerated from basal parts of the 'Porphyra' phase or from the 'conchocelis' phase on the rocks (see recruitment processes). By mid-August these regenerated specimens were common and well grown but darkly pigmented and reproductively immature. Besides the Porphyra, a very thick coating of Ulva was recorded in mid-August (Smith 1968). Such evidence suggests that the community would reach maturity relatively rapidly and probably be considered mature in terms of species present and ability to reproduce well within six months. Recoverability has been assessed to be very high.
Radionuclide contamination
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Levels of radioactivity in seaweeds in some areas may be higher than average because of fallout from the atmosphere or from wastes discharged to the sea from the nuclear recycling industry. In the vicinity of Selafield on the Irish Sea, the additional radioactivity emanating from the reprocessing plant results in contamination of Porphyra, especially with 106Ru, with its levels of radioactivity ranging up to 12 kBq per kg (35 time normal). For residents of South Wales, 'laver bread' made from Porphyra is a speciality food, and through regular consumption people can expose themselves to considerable levels of radiation (up to about 20% of permissible dosage of radioactivity) (Hetherington, 1976). Information concerning effects of radionuclides on seaweed was not found.
Changes in nutrient levels
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Nitrogen enrichment enhances growth of Ulva intestinalis (as Enteromorpha intestinalis) (Kamer & Fong, 2001), making the species a useful indicator of nutrient enrichment, although it also thrives in 'un-enriched' water. An assessment of not sensitive* has been made as the abundance of an important characterizing species is likely to increase as a result of the factor.
Increase in salinity
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The biotope typically experiences conditions of full (30-40 psu) or variable (reduced, owing to freshwater runoff) salinity. Whilst Ulva no doubt survives hypersaline conditions in supralittoral rockpools subjected to evaporation Salinities greater than that of seawater are unlikely to occur in this biotope, as it occurs on open rock. An assessment of not relevant has been made.
Decrease in salinity
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This biotope may be associated with the course of freshwater seeps across the intertidal zone, so it is unlikely to be adversely affected by reduced salinity. Reed et al. (1980) noted that when transferred from full to slightly reduced salinity water, the photosynthetic rate of Porphyra purpurea was temporarily lowered, so reduced salinity may affect the species viability over a longer period of time. However, overall an assessment of not sensitive has been made as the biotope is favoured by disturbance events, especially reduced salinity, as other species find survival harder and species such as Ulva and Porphyra are more tolerant of the conditions.
Changes in oxygenation
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Insufficient information is available to assess the impact of reduced oxygen concentration in the water column upon the biotope. The effects of deoxygenation on macroalgae are poorly studied. At the benchmark level an assessment of not relevant has been made because the biotope is only intermittently covered by water.

Biological Factors

Introduction of microbial pathogens/parasites
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No information was found concerning microbial pathogens and effects upon the biotope in natural conditions. Diseases caused by fungi are known to occur amongst commercially cultivated Porphyra (Lobban & Harrison, 1997).
Introduction of non-native species
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The biotope is not known to be adversely affected by non-native species. An assessment of not relevant has been made.
Extraction
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Porphyra, an important characterizing genus commonly known as 'laver', is a commercially exploited species, especially in the Far East. The main problem of harvesting Porphyra from natural populations is the relatively small amount of naturally occurring plants in one area and the relatively low biomass of individual plants. If 50% of the Porphyra population were removed from a wild area, it is likely that, owing to the presence of localized population remaining in situ, that rapid recruitment would occur and recoverability has been assessed to be very high.

Additional information icon Additional information

Recoverability
The biotope is considered to have a very high recoverability following disturbance. Ulva intestinalis is generally considered to be an opportunistic species, with an 'r-type' strategy for survival. The r-strategists have a high growth rate and high reproductive rate. For instance, the thalli of Ulva intestinalis, which arise from spores and zygotes, grow within a few weeks into thalli that reproduce again, and the majority of the cell contents are converted into reproductive cells. The species is also capable of dispersal over a considerable distance. For instance, Amsler & Searles (1980) showed that 'swarmers' of a coastal population of Ulva (as Enteromorpha) reached exposed artificial substrata on a submarine plateau 35 km away. Ulva species are amongst the first multicellular algae to appear on substrata that have been cleared following a disturbance, e.g. following the Torrey Canyon oil spill in March 1967, species of the genus Ulva rapidly recruited to areas where oil had killed the herbivores that usually grazed on them, so that a rapid greening of the rocks (owing to a thick coating of Ulva) was apparent by mid-May (Smith, 1968). Porphyra is also able to rapidly recruit to cleared substrata, and may regenerate from its discoid shaped holdfast if it remains in situ. After the Torrey Canyon oil spill, its presence was noted on rocks within two months of the disturbance (see 'general biology' time to reach maturity).

This review can be cited as follows:

Budd, G.C. 2004. Ulva spp. on freshwater-influenced or unstable upper eulittoral rock. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 25/04/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=104&code=2004>