Biodiversity & Conservation

LR.SLR.F.Fserr.T

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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Loss of the substratum will result in the loss of the entire biotope and therefore intolerance has been assessed as high. Some species may survive as epiphytes on the Fucus serratus, Chondrus crispus and other algae but these plants will soon be washed away in the strong currents. Recoverability is likely to be moderate (see additional information).
Smothering
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Smothering by a 5 cm layer of sediment is unlikely to adversely affect this biotope given that it is associated with areas of moderately strong to very strong water flow. The sediment layer will be washed away and 'normal' conditions will resume rapidly. The suspension feeders may experience some short-lived interference with feeding but, at the level of the benchmark, this is not likely to adversely affect their viability. Therefore, the biotope has been assessed as being tolerant to smothering.
Increase in suspended sediment
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An increase in suspended sediment, in combination with the strong water flow with which this biotope is associated, may be of detriment to the important characterizing species. Sand scour may damage the fronds of the Fucus serratus, Chondrus crispus and other algae in the biotope and reduce available light for photosynthesis (see turbidity). The feeding apparatus of suspension feeders may become bombarded with particles and interfere with their feeding and respiratory currents. Over the course of the benchmark this may lead to a reduction in total ingestion and a reduced scope for growth, especially since cleaning the feeding apparatus is likely to be energetically expensive. For short lived species such as the bryozoans and sea squirts, this may prove fatal. Robbins (1985b) undertook experiments to establish the possible effects of high inorganic particulate concentrations on the sea squirt Ascidiella scabra. He concluded that growth rate was likely to be reduced and mortality was possible in high levels of suspended sediment. On balance, a decline in faunal species diversity is expected and accordingly, intolerance has been assessed as intermediate. Recovery is likely to be high due to the fact that most of the intolerant species produce planktonic larvae and are therefore likely to be able to recolonize quickly from surrounding areas.
Decrease in suspended sediment
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A decrease in suspended sediment could be beneficial to both the algae and the suspension feeding community in SLR.Fserr.T. Sand scour will be reduced and so will any interference with the feeding apparatus of the suspension feeders. Over the course of one month, a reduction in total suspended sediment may result in an increased scope for growth, especially for short lived species such as the bryozoans and sea squirts. Overall, tolerant* has been suggested.
Desiccation
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Due to the fact that SLR.Fserr.T is an intertidal biotope, the benchmark level for desiccation is equivalent to a change in position of one biological vertical zone on the shore for one year. In this case, that would mean a transition from the lower eulittoral to the mid eulittoral.

The toothed wrack Fucus serratus and carrageen Chondrus crispus are both intertidal species that will be adapted to a degree of periodic desiccation. However, seaweeds have a critical water content and for Fucus serratus, it is 40%. Two hours of sunshine can result in this critical water content being exceeded and therefore this species will probably be of intermediate intolerance to desiccation at the benchmark level. Mathieson & Burns (1971) measured the photosynthetic rate of Chondrus crispus at varying degrees of desiccation and found that after loss of 65% of its water content, the rate of photosynthesis was only 55% of the control rate (see MarLIN review). In Palmaria palmata, 50% of the plant's water content can be lost in less than 4 hours in dry air at 25 °C (Kain & Norton, 1990). This scenario can reasonably be expected at low tide in summer in Britain, although the Fucus canopy is likely to protect the underlying red algae to some extent.

Many of the invertebrates will also be protected from extreme levels of desiccation by the canopy.
  • The tissue of the breadcrumb sponge Halichondria panicea holds some water and it is tolerant of a certain degree of desiccation anyway. However, at the benchmark level, bleaching and tissue death in colonies at the upper shore extent of the population are likely to occur.
  • The sea squirt Ascidiella scabra has a soft body and is therefore vulnerable to desiccation. It is afforded some protection to desiccation by its location under seaweed and in damp crevices. However, some individuals at the highest point on the shore may dry out and die at the benchmark level.
  • Some colonies of Dynamena pumila occur on rock and survive exposure to air on every low tide (pers. obs. in Gili & Hughes, 1995).
  • Other important species associated with this biotope have mechanisms for reducing the effects of desiccation, for example, the common limpet Patella vulgata. This limpet has a 'home scar' in the bedrock. The 'home scar' is a shallow depression in the rock which fits closely the shape of the limpet's shell thereby reducing water loss from the soft tissues during emersion. Furthermore, Patella vulgata occurs higher up the shore and so is clearly able to survive desiccation. Pomatoceros triqueter combats desiccation by closing the operculum of the tube thus reducing water loss. However, the amount of time available for feeding and respiration will be reduced as a result, and therefore the population's viability may be reduced. Some individuals may die.
Overall it is likely that some individuals from several species will experience some mortality, including some sponges and ascidians that give the biotope its name. Accordingly, intolerance has been assessed as intermediate with a high recoverability (see additional information).
Increase in emergence regime
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This biotope is found in the intertidal and the associated species are likely to be adapted to cyclical immersion and emersion. However, at the level in the benchmark, an increase in emergence is likely to adversely affect the dominant trophic group (suspension feeders) within this biotope. It will greatly reduce feeding opportunities for the suspension feeders, for which immersion is a prerequisite to feeding. Over the course of a year, this decrease is likely to prove fatal for short lived species such as the bryozoans and ascidians. The longer lived species such as Halichondria panicea and Pomatoceros triqueter, although unlikely to die, will probably experience reduced growth and reproductive potential and abundance of these species may decline. The upper shore extent of the Fucus serratus and Chondrus crispus populations may be replaced by species more tolerant of desiccation and more characteristic of the mid-eulittoral such as Fucus vesiculosus or Ascophyllum nodosum. False Irish moss, Mastocarpus stellatus, is also likely to increase in abundance as this species is capable of out-competing Chondrus crispus at higher levels on the shore due to its ability to tolerate greater extremes of temperature, for instance, (Dudgeon et al., 1999).
Although the biotope is unlikely to disappear completely, its extent on the shore is likely to be reduced and accordingly, intolerance has been assessed as intermediate. Recoverability is likely to be high (see additional information).
Decrease in emergence regime
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A decrease in emergence is likely to benefit this biotope. Feeding opportunity for suspension feeders will increase, and desiccation and temperature stresses for all flora and fauna will be reduced. The recognizable biotope may extend further up the shore but this extension is likely to be counteracted by a reduction in the lower shore extent of the biotope that is likely to be taken over by seaweeds more characteristic of the sublittoral fringe. Encrusting red algae and kelp species, for example, may become more dominant. Furthermore, predation by the common shore crab Carcinus maenas is likely to increase.

Overall, it is possible that the biotope will just shift further up the shore and not necessarily increase or decrease in its extent on the shore. Therefore this biotope has been assessed to be tolerant of a decrease in emergence.
Increase in water flow rate
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This biotope is associated with areas of moderately strong to very strong water flow rates (>6 knots, the highest flow rate in the benchmark). In the Menai Strait, where this biotope was recorded, water flow rates can exceed 8 knots during spring tides. Therefore, an increase in water flow rate is not considered to be relevant.
Decrease in water flow rate
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The rich community of suspension feeders in this biotope is, in part, due to the strong tidal streams with which it is associated. Strong currents provide the suspension feeders with a continual supply of food and removes sediment that would otherwise interfere with their feeding apparatus. A decrease in water flow rate at the level in the benchmark could result in a negligible water flow rate. This would lead to siltation, to the detriment of the filter feeders. Some filter feeders have the ability to cope with siltation and excess suspended material. For example, Ascidiella scabra can extend its siphons, to a small extent, above silt and can also most likely maintain a passage through the silt to the siphons. It also attaches to other erect biota and, in such situations, may escape smothering effects. The breadcrumb sponge Halichondria panicea has a mechanism for sloughing off its complete outer tissue layer together with any debris (Barthel & Wolfrath, 1989). However, there is an energetic cost in cleaning, and this species, together with other filter feeders, would probably experience reduced growth over the benchmark. For annual species, including the star ascidian Botryllus schlosseri, reduced growth could prove fatal. The hydroid Dynamena pumila experienced marked decline in areas with increased silt content in Strangford Lough, Northern Ireland (Seed et al., 1983). The toothed wrack Fucus serratus and red seaweeds including Ceramium sp. and Chondrus crispus, although tolerant of low flow rates, are likely to suffer from the reduced light caused by siltation. Rates of photosynthesis are likely to decrease and, over the course of one year, the plants may experience some negative growth. Furthermore, grazers unable to cope with the strong flow rates normally associated with this biotope may be able to graze more efficiently, resulting in the loss of a greater number of plants. Therefore, on balance, this biotope is likely to be of intermediate intolerance to a decrease in water flow rates although recovery is expected to be high.
Increase in temperature
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The distribution of various important species associated with this biotope, including Halichondria panicea, Fucus serratus, Chondrus crispus, Patella vulgata, Ascidiella scabra and Pomatoceros triqueter, is such that it is likely that they will be tolerant of a 2 °C increase in temperature over one year. However, it is possible that acute changes in temperature may adversely affect some of the species and accordingly, an intolerance of low has been suggested. Recoverability is expected to be very high.
Decrease in temperature
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The distribution of various important species associated with this biotope, including Halichondria panicea, Fucus serratus, Chondrus crispus, Patella vulgata and Ascidiella scabra, is such that it is likely that they will be tolerant of a 2 °C decrease in temperature over one year. However, it is possible that acute temperature reductions may be more harmful. Below a temperature of 7 °C, Pomatoceros triqueter is unable to build calcareous tubes (Thomas, 1940). This means that, although adults may be able to survive a decrease in temperature, larvae would not be able to attach to the substratum. However, due to the fact that this species is not actually characteristic of the biotope but more a representative of annelid suspension feeders, the biotope as a whole has been assessed as being of low intolerance. Recovery is expected to be very high.
Increase in turbidity
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This biotope has been recorded in the Menai Strait where turbidity levels are known to be very high and an increase in turbidity is unlikely to adversely affect the suspension feeders within this biotope. Indeed, if the turbidity were associated with an increase in organic particulate concentration, they may benefit actually from it. Ascidiella scabra, for example, lives in estuaries and other enclosed areas where turbidity may increase to high levels. The height of colonies of the hydroid Dynamena pumila fell to almost half their original height less than 6 weeks after the Fucus serratus plants on which they were attached were transferred from a relatively clean, fast flowing site to a turbid site in Strangford Lough (Seed & Boaden, 1977, cited in Seed et al., 1981). However, this may be related to the associated decrease in flow rate and in any case, this hydroid is not a characterizing species and occurred in less than half the records of this biotope. The algal component of the biotope may suffer due to the associated reduction in light. Over the course of one year, Fucus serratus may experience a reduction in total growth. Red algae can tolerate a wider range of light levels than any other group of photosynthetic plants (Kain & Norton, 1990) and an increase in the abundance of Mastocarpus stellatus and Chondrus crispus, for example, may be observed as they out-compete finer green and brown algal species. However, the Fucus serratus canopy will still remain and a large change in the recognizable biotope is unlikely. Therefore, tolerant has been assessed.
Decrease in turbidity
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The algal component of this biotope would benefit from a decrease in turbidity and they may experience enhanced photosynthesis and increased total growth over the benchmark period. The proportion of ephemeral green algae, in particular, may increase.
Increase in wave exposure
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This biotope occurs in sheltered to extremely sheltered habitats. An increase in exposure of two ranks of the wave exposure scale would mean that the biotope could become wave exposed. Hiscock (1983) noted that strong wave action may damage delicate feeding apparatus or lead to its retraction which would, ultimately, result in a reduction in total ingestion over the year. If the increase in wave exposure was coupled with the resuspension of sediments, energetic costs in cleaning the feeding apparatus would also need to be considered. The tubeworm Pomatoceros triqueter can tolerate very wave exposed habitats although the ascidian Ascidiella scabra would be outside its preferred habitat in moderately exposed habitats. Furthermore, short lived species such as the star ascidian Botryllus schlosseri would probably die. The boulders and cobbles in the biotope are likely to move around which could serve to dislodge plants from the cobbles, boulders and bedrock, and crush the tubes of serpulid and spirorbid worms and colonies of sponges, hydroids and ascidians. In addition, some algal species are known to change morphologically according to the degree of exposure. Fucus serratus would be outside its zone of preference, in terms of wave exposure and, over the course of the year the recognizable biotope is likely to be lost and replaced with opportunistic species and those species better adapted to high energy environments. Intolerance has been assessed as high with a moderate recovery.
Decrease in wave exposure
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This biotope occurs in sheltered to extremely sheltered habitats and therefore a decrease in wave exposure is not relevant.
Noise
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The key structural and important characterizing species are unlikely to have mechanisms for detecting noise. Some of the other important species, including Patella vulgata and Pomatoceros triqueter, may respond to the vibrations caused by noise by clamping down on the rock and withdrawing into the tube respectively. This would temporarily reduce feeding opportunity although at the benchmark level this is not likely to aversely affect the biotope. Therefore tolerant has been recorded.
Visual Presence
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The key structural and important characterizing species are unlikely to have mechanisms for detecting visual presence. Shadows detected by the photoreceptive surface of serpulid polychaetes may result in withdrawal of the worm back into its tube (Kinne, 1970). This would temporarily reduce feeding opportunity although at the benchmark level this is not likely to aversely affect the biotope. Therefore tolerant has been recorded.
Abrasion & physical disturbance
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At the benchmark level of abrasion, many of the associated species would be adversely affected. The fronds of the toothed wrack Fucus serratus, carrageen Chondrus crispus and other algal species, are likely to be torn off thus decreasing their photosynthetic capabilities. The holdfasts of Chondrus crispus are likely to escape unscathed and, due to the fact that the species is capable of regenerating from its holdfasts (e.g. Dudgeon & Johnson, 1992), no mortality is expected for this species. However, Dudgeon et al. (1999) reported that, on the coast of Maine, Chondrus crispus was more susceptible than Mastocarpus stellatus to dislodgement.

Epifaunal species have been found to be particularly adversely affected by trawling or dredging activities, either due to direct damage or modification of the substratum (Jennings & Kaiser, 1998). However, some epifaunal species have been reported to exhibit increased abundances on high fishing effort areas, probably due to their ability to colonize and grow rapidly (Bradshaw et al., 2000). In a study of the long term effects of scallop dredging, Bradshaw et al. (2002) reported that Ascidiella species had become more abundant and suggested that they were probably able to survive by regeneration of damage and budding. Individuals are easily ripped from the substratum and are unlikely to re-attach and will die. Patches of hydroids and bryozoans and encrusting fauna such as colonial ascidians and sponges are likely to be scraped off the rock although a proportion of the colonies are likely to remain. The shells of limpets, tubeworms and periwinkles may be crushed by the weight and force of the abrasion. However, Hiscock (1983) noted that a community, under conditions of scour and abrasion from stones and boulders moved by storms, developed into a community consisting of fast growing species such as Pomatoceros triqueter. Scour and abrasion will probably remove a proportion of the population although it demonstrates rapid growth and recruitment. The abundance of Pomatoceros triqueter may increase due to decreased competition from other species.

However, Pomatoceros triqueter is not a characterizing species and, on balance, intolerance has been assessed as intermediate due to the fact that after a single event, a proportion of all of the species is likely to remain. This in turn will favour recoverability and accordingly, recoverability has been assessed as high. Intolerance to trampling is likely to be lower than to the effects of a passing scallop dredge.
Displacement
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All of the important characterizing species and the majority of 'important other' species in this biotope are sessile and permanently attached to the hard substrata. Displacement would probably result in the death of some species including Fucus serratus, Chondrus crispus, Halichondria panicea, Ascidiella scabra, Alcyonidium gelatinosum and Patella vulgata. Thomas (1940) found that if Pomatoceros triqueter is removed from its tube, it will start to make a new one in a few hours. Therefore, it is likely that the worm will be able to leave the old tube to start constructing another. However, this would involve considerable energetic cost and, furthermore, this is not a characterizing species. The displacement of the key and important species is likely to have a similar effect to substratum loss on the biotope and therefore, an intolerance of high has been recorded.

Chemical Factors

Synthetic compound contamination
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The species frequently associated with this biotope are known to have varying degrees of tolerance to synthetic chemicals. In general, however, most of the species show at least some intolerance to synthetic chemical contamination.
  • Scanlan & Wilkinson (1987) found that the spermatozoa and newly fertilized eggs of Fucus serratus were the most intolerant of biocides, while adult plants were only just significantly affected at 5 ml/l of the biocides Dodigen v181-1, Dodigen v 2861-1 and ML-910.
  • O'Brien & Dixon (1976) suggested that red algae were the most sensitive group of algae to oil or dispersant contamination, possibly due to the susceptibility of phycoerythrins to destruction. Laboratory studies of the effects of oil and dispersants on several red algal species concluded that they were all sensitive to oil/dispersant mixtures, with little difference between adults, sporelings, diploid or haploid life stages (Grandy, 1984, cited in Holt et al., 1995).
  • Ascidians may be intolerant of synthetic chemicals such as tri-butyl-tin (TBT) anti-foulants. Rees et al. (2001), working in the Crouch estuary, observed that six ascidian species were recorded at one station in 1997 compared with only two at the same station in 1987, shortly following the banning of TBT in antifouling paints. Also, there was a marked increase in the abundance of ascidians especially Ascidiella aspersa and Ascidia conchilega in the estuary after TBT had been banned.
  • Insufficient information was available on the specific effects of synthetic chemicals on the breadcrumb sponge and other important species including the common limpet and tubeworm Pomatoceros triqueter.
On balance, it is likely that many of the species characteristic of this biotope will experience some mortality and accordingly, intolerance has been assessed as intermediate. Due to the strong water flow with which this biotope is associated, recoverability is expected to be high, although recovery from the effects of highly persistent chemicals may take significantly longer.
Heavy metal contamination
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Fucoid algae readily accumulate heavy metals within their tissues. The effect of heavy metals on the growth rate of adult Fucus serratus plants has been studied by Strömgren (1979b; 1980a, b). Copper significantly reduces the growth rate of vegetative apices at 25 g/l over 10 days (Strömgren, 1979b). Zinc, lead, cadmium & mercury significantly reduce growth rate at 1400 g/l , 810 g/l, 450 g/l and 5 g/l respectively (Strömgren, 1980a, b). No information was found concerning the specific effects of heavy metals on the other important and characterizing species although an intolerance of low has been recorded to take account of the sub-lethal effects on Fucus serratus mentioned above. Recovery is likely to be very high although recovery from the effects of highly persistent metal and their compounds may take significantly longer.
Hydrocarbon contamination
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  • Adult Fucus serratus plants are tolerant of exposure to spills of crude oil although very young germlings are intolerant of relatively low concentrations of 'water soluble' extractions of crude oils. Exposure of eggs to these extractions (at 1.5 µg/ml for 96 hours) interferes with adhesion during settling and (at 0.1µg/ml) prevents further development (Johnston, 1977).
  • Observations have shown that filamentous red algae are among the most severely affected by the toxic properties of oil (O'Brien & Dixon, 1976). Effects including bleaching and loss of photosynthetic pigments have been observed in red algal species following contamination with fuel oil (O' Brien & Dixon, 1976). The long term effects on Chondrus crispus of continuous doses of the water accommodated fraction (WAF) of diesel oil were determined in experimental mesocosms (Bokn et al., 1993). Mean hydrocarbon concentrations tested were 30.1 µg/l and 129.4 µg/l. After 2 years, there were no demonstrable differences in the abundance patterns of Chondrus crispus. Furthermore, Kaas (1980, cited in Holt et al., 1995) reported that the reproduction of adult Chondrus crispus plants on the French coast was normal following the Amoco Cadiz oil spill.
  • It appears that Halichondria panicea survived in areas affected by the Torrey Canyon oil spill (Smith, 1968), although few observations were made.
No information was found concerning the effects of hydrocarbon contamination on the other characterizing and important species. However, given the evidence above, an intolerance of low has been suggested with very high recovery.
Radionuclide contamination
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No information was found concerning the effects of radionuclides on any of the four important characterizing species or most of the other important species. Therefore, insufficient information was available in order to assess sensitivity.
Changes in nutrient levels
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An influx of nutrients into the biotope is likely to stimulate phytoplankton production, depending on other environmental conditions. This means that the amount of food potentially available to the suspension feeders will increase. In the long term, a sustained increase in nutrients could lead to the formation of algal blooms. Algal blooms have the potential to block light from underlying plants, thereby reducing their photosynthetic capacity. In addition, the eventual biodegradation of the blooms / mats involves the consumption of a large amount of oxygen, although the moderately strong water flows with which this biotope is associated means are likely to ameliorate this (see oxygenation). It is possible, therefore, that Fucus serratus and other plants may experience some reduced growth over time but it is unlikely that any species will experience mortality. Chondrus crispus may be out-competed by faster growing or ephemeral species. Johansson et al. (1998) investigated the changes in the algal vegetation of the Swedish Skagerrak coast, an area heavily affected by eutrophication, between 1960 and 1997. Slow growing species, including Chondrus crispus declined in abundance, probably due to competition from faster growing red algal species such as Phycodrys rubens and Delesseria sanguinea. Overall, the recognizable biotope would be unaffected per se and accordingly, an intolerance of low has been assessed with a very high recoverability.
Increase in salinity
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SLR.Fserr.T is an intertidal biotope that will most likely experience cyclical periods of hypo- and hyper-salinity. It is found in areas of variable to full salinity and therefore an increase in salinity is not relevant. Short periods of hyper-salinity may occur where patches of surface water on the bedrock evaporate although this is unlikely to continue for periods of time similar to those benchmark and only small areas of substratum will be affected anyway.
Decrease in salinity
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SLR.Fserr.T is an intertidal biotope that will most likely experience cyclical periods of hypo- and hyper-salinity. Fucus serratus is able to compensate for these changes in salinity by adjusting internal ion concentrations. Salinity affects the photosynthetic rate and hence growth rate of seaweed. For Fucus serratus, growth rate is maximal at a salinity of 20 psu and therefore, a decrease in salinity into the 'low' salinity category would be of preference to the plant. Other important / characterizing species associated with this biotope are also likely to be tolerant of a reduction in salinity. The breadcrumb sponge Halichondria panicea and carrageen Chondrus crispus are found in low salinity and Ascidiella scabra and Patella vulgata can be found in reduced salinity conditions. Patella vulgata can survive in salinities down to about 20 psu. However, growth and reproduction may be impaired in reduced salinity. Little et al. (1991), for example, observed reduced levels of activity in limpets after heavy rainfall and in the laboratory activity completely stopped at 12 psu. Patella vulgata can endure periods of low salinity and was found to die only when the salinity was reduced to 3-1psu (Fretter & Graham, 1994). Therefore, a rapid fall in salinity of two categories on the MNCR scale from variable to low salinity could result in more adverse effects on the whole community but over one week, intolerance has been assessed as low. Recovery is expected to be very high.
Changes in oxygenation
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No specific information was found concerning the effects of reduced oxygenation on the key / characterizing species although Cole et al. (1999) suggested possible adverse effects on marine species below 4 mg/l and probably adverse effects below 2 mg/l. Some of the associated fauna may be tolerant of low oxygen environments and the strong water flow rates associated with this biotope are likely to ameliorate any reductions in oxygenation. Overall, an intolerance of low has been suggested although recoverability is expected to be very high on return to 'normal' conditions.

Biological Factors

Introduction of microbial pathogens/parasites
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No information was found concerning the effects of and occurrence of microbial pathogen infestations on the key and characterizing species. Therefore, insufficient information was available to assess sensitivity.
Introduction of non-native species
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There are no known alien or invasive species that are likely to compete with or displace the important characterizing species associated with this biotope. The Australasian barnacle Elminius modestus was introduced to British waters on ships during the second world war. The species does well in estuaries and bays, where it can displace Semibalanus balanoides. However, Semibalanus balanoides is not a characterizing species within SLR.Fserr.T and, therefore, not relevant to the sensitivity assessment of the biotope.
Extraction
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Fucus serratus, Chondrus crispus and Mastocarpus stellatus are the only key / characterizing species known to be targeted for extraction (see 'Importance'). The extraction of Fucus serratus would lead to the loss of the recognizable biotope, as the plant gives the biotope its name. In addition to the loss of these plants, many epiphytic species would be lost including proportions of populations of Dynamena pumila (found especially on fucoid species), Halichondria panicea, Ascidiella scabra, Alcyonidium gelatinosum and Spirorbis spirorbis. Intolerance has therefore been assessed as high. Fucus serratus is highly fecund and the eggs are broadcast into the water column allowing a potentially large dispersal distance. Recovery has been assessed as moderate (see additional information).

Additional information icon Additional information

Recoverability (i.e. recruitment) in the key and characterizing species varies in terms of timescales but, in general, recoverability of the individual species is considered to be high. For the majority of other important species within this biotope, reproduction and recruitment is an annual process (see recruitment processes). In addition, many of the species have planktonic larvae thereby facilitating recruitment from local sources.

The settlement of new colonies of the breadcrumb sponge Halichondria panicea is likely within one year and growth rate is rapid. Ascidiella scabra has a high fecundity and settles readily, probably for an extended period from spring to autumn. Eggs and larvae are free-living for only a few hours and so recolonization would have to be from existing individuals no more than a few km away. It is also likely that Ascidiella scabra larvae are attracted by existing populations and settle near to adults (Svane et al., 1987) . Fast growth means that a dense cover could be established within as little as two months. However, if mortality and the consequent establishment of free space available occur at a time when larvae are not being produced, other species may settle and dominate. In this case, recolonization by Ascidiella scabra may take several years.

Fucus serratus is also highly fecund and the eggs are broadcast into the water column allowing a potentially large dispersal distance. The species is found on all British and Irish coasts so there are few mechanisms isolating populations. Recruitment may occur through reproduction of the remaining population or from other populations and, providing that some of the population remains, it is unlikely that other species will come to dominate and recovery will probably have occurred after one or two years. At this point, the available substratum for epiphytic species will increase also, thereby facilitating their colonization of the biotope.

However, the loss of the entire Fucus serratus canopy or loss of the entire biotope would result in a complete disruption in the equilibrium of the community. The understory algal species may become bleached and die if the canopy layer was lost. As a result, the abundance of limpets is likely to increase which would prevent further recruitment of the fucoids. Fucoid abundance would subsequently decrease and it wouldn't be until the level of algae had increased to such a point that there was an insufficient amount to sustain the limpet population that fucoids could start to return. Hawkins & Southward (1992) found that, after the Torrey Canyon oil spill, it took between 10 and 15 years for the Fucus sp. to return to 'normal' levels of spatial and variation in cover on moderately exposed shores. Therefore, for factors which are likely to totally destroy the biotope (i.e. to which SLR.Fserr.T is highly intolerant), recoverability is likely to be moderate.


This review can be cited as follows:

Marshall, C.E. 2005. Fucus serratus, sponges and ascidians on tide-swept lower eulittoral rock. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 16/04/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=42&code=1997>