Biodiversity & Conservation

LR.SLR.FX.FserX.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 moderately strong currents. Recoverability is likely to be high (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 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 moderately strong 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. In contrast, an increase in suspended sediment may increase the amount of available food for the suspension feeders, especially if the organic fraction of the particulate material increased. On balance, the biotope has been assessed to be of low intolerance to an increase in suspended sediment and recoverability is expected to be very high.
Decrease in suspended sediment
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A decrease in suspended sediment could be of detriment to the suspension feeding community as available food is likely to be reduced. Over the course of one month, a reduction in total ingestion is likely to result in a reduced scope for growth and reproductive success. For short lived species such as the bryozoans and sea squirts, this may prove to be fatal. 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.
Desiccation
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Due to the fact that SLR.FserX.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.

The tissue of the breadcrumb sponge Halichondria panicea holds some water and is tolerant of a certain degree of desiccation. However, at the benchmark level, bleaching and tissue death are likely to occur. The sea squirt Ascidiella aspersa 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.

Other important species associated with this biotope have mechanisms for reducing the effects of desiccation, for example, the common periwinkle Littorina littorea (see MarLIN) review. Two other molluscs frequently associated with this biotope, namely the common mussel Mytilus edulis and slipper limpet Crepidula fornicata, are considered to be of low intolerance to desiccation and Mytilus edulis can be found in the upper eulittoral. Although muddy sediments associated with this biotope will hold some water and protect the infauna and epibenthic fauna to some extent, it is likely that overall, all of the important characterizing species will experience some decline in abundance and consequently, the recognizable biotope may be lost. An intolerance of high has therefore been recorded. Recovery is likely to be high (see additional information).

Increase in emergence regime
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SLR.FserX.T 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 whom 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 including Halichondria panicea and Crepidula fornicata, 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, Ascophyllum nodosum or Mastocarpus stellatus. In terms of infauna, the sand mason Lanice conchilega and peacock work Sabella pavonina will be protected from desiccation to some extent by their burrows. However, they may also experience greater predation from shore birds.

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, desiccation and temperature stresses for all flora and fauna will be reduced as will predation from birds. The recognizable biotope may extend further up the shore (if suitable substrata are present) 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, for example, may become more dominant on the larger boulders than the green and brown algal species. 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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An increase in water flow rate from moderately strong to very strong is likely to adversely affect this biotope. The mixed nature of the substratum means that suspended sediment of various sizes will be re-suspended and cobbles and pebbles are likely to move across the seabed. Fine sediments are likely to be lost. Re-suspended sediment is likely to interfere with the suspension feeders feeding apparatus and respiratory currents to their detriment (see suspended sediment above). In wave sheltered areas such as this biotope, the breadcrumb sponge Halichondria panicea grows in massive forms. Poorly attached massive forms may be ripped off by an increase in water flow rate leading to the death of large colonies. The sand may scour the fronds of Fucus serratus, Chondrus crispus and other algae and sand tolerant algae may prevail. Additionally, an increase to 'very strong' flows may inhibit settlement of spores. The movement of pebbles, cobbles and boulders across the sea floor may scour epilithic sponges, bryozoans and hydroids off the rocks and clumps of algae may become dislodged. Overall, it is likely that many of the associated species will be adversely affected and therefore this biotope is considered to be highly intolerant to an increase in water flow rate at the benchmark level although recovery is expected to be high.
Decrease in water flow rate
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The rich community of suspension feeders in this biotope is, in part, due to the moderately strong tidal streams with which it is associated. It provides 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. In addition, the clumps of Crepidula fornicata and Mytilus edulis have the capacity to produce and accumulate biodeposits including pseudofaeces. Such deposits would accumulate causing the substratum to become highly silted.

Annual species, including the star ascidian Botryllus schlosseri, are likely to experience some mortality. 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 moderately 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.

Some filter feeders have the ability to cope with siltation and excess suspended material. For example, the breadcrumb sponge Halichondria panicea has a mechanism for sloughing off their complete outer tissue layer together with any debris (Barthel & Wolfrath, 1989). Mytilus edulis possesses efficient shell cleaning and pseudofaeces expulsion mechanisms to remove silt (Moore, 1977), although it should be noted that pseudofaeces production involves an energetic burden (Navarro & Widdows, 1997). However, over the course of one year, the majority of the sponges and ascidians are likely to be lost and accordingly SLR.FserX.T has been assessed as being of high 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 Halichondria panicea, Fucus serratus and Chondrus crispus in Britain is towards the centre of their distribution in the north east Atlantic and the two species are therefore likely to be tolerant of an increase in temperature at the benchmark level (see MarLIN reviews). The sea squirt Ascidiella scabra (of the same genus as the important characterizing species Ascidiella aspersa) has also been assessed as being tolerant of an increase in temperature. Other important species associated with this biotope including Mytilus edulis, Littorina littorea and Lanice conchilega are thought be of low tolerance to an increase in temperature. However, due to the fact that these are not actually characteristic of the biotope but more a representative of various different phyla, the biotope as a whole has been assessed as tolerant.
Decrease in temperature
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The distribution of Halichondria panicea, Fucus serratus and Chondrus crispus in Britain is towards the centre of their distribution in the north east Atlantic and the two species are therefore likely to be tolerant of a decrease in temperature at the benchmark level (see MarLIN reviews). The sea squirt Ascidiella scabra (of the same genus as the important characterizing species Ascidiella aspersa) has also been assessed as being tolerant of a decrease in temperature. However, the sand mason Lanice conchilega was assessed as being highly intolerant of low temperatures and other important species associated with this biotope including Mytilus edulis and Littorina littorea are thought to have a low tolerance (see MarLIN reviews). Due to the fact that these are not actually characteristic of the biotope but more a representative of various different phyla, 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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An increase in turbidity is unlikely to 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. 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 Ceramium sp. and Chondrus crispus, for example, may be observed as they out-compete green and brown seaweed. However, the patches of Fucus serratus 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. The proportion of ephemeral green algae may increase and accordingly, tolerant* has been suggested.
Increase in wave exposure
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This biotope occurs in sheltered to extremely wave sheltered habitats. An increase in exposure of two ranks of the wave exposure scale would mean that the biotope could become wave exposed. Due to the shallow water depth in which this biotope is found (lower eulittoral), a wave exposed habitat could be catastrophic for the biotope. The silt / mud and finer sediments and gravels would be continually re-suspended and the habitat for the sand mason Lanice conchilega and peacock worm Sabella pavonina would probably be lost. The increase in suspended sediment would most likely interfere with the feeding apparatus of the suspension feeders (see suspended sediment above) thus reducing total ingestion over the year or incurring energetic costs in cleaning. Short lived species such as the star ascidian Botryllus schlosseri would probably die. Aside from the suspended sediment, the cobbles and pebbles would probably move around too. This could serve to dislodge plants from the cobbles and boulders, break the tubes of the peacock worms and scour colonies of sponges, hydroids and ascidians from the rocks and plants. In addition, some algal species are known to change morphologically according to the degree of exposure. Gutierrez & Fernandez (1992) described morphological variability of Chondrus crispus according to wave exposure and emersion (see MarLIN review). 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 high 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 important characterizing species are unlikely to have mechanisms for detecting noise. Furthermore, the biotope may indirectly benefit from noise disturbance because the birds and crabs that represent the main predators on the associated fauna may be scared off by the noise.
Visual Presence
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The important characterizing species are unlikely to have mechanisms for detecting visual presence. Furthermore, the biotope may indirectly benefit from visual disturbance because the birds and crabs that represent the main predators on the associated fauna may be scared off by the presence of, for example, humans on the shore.
Abrasion & physical disturbance
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At the benchmark level of abrasion, a scallop dredge but more likely lower shore sediment scour or ship grounding, many of the associated species would be adversely affected. The fronds of the toothed wrack Fucus serratus and carrageen Chondrus crispus and parts of these plants, in addition to those of 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. 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 mussels, limpets and periwinkles may be crushed by the weight and force of the abrasion, as will the tubes of the peacock worm. Intolerance to trampling, given the soft nature of much of the substratum, is likely to be lower than to the effects of a passing scallop dredge although 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.
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 ultimately result in the death of some species including Fucus serratus, Chondrus crispus, Halichondria panicea, Ascidiella scabra, Botryllus schlosseri and Crepidula fornicata. Due to the fact that Crepidula fornicata lives in chains of up to 12 individuals, only the individual attached to the substratum would be likely to die, due to increased risk of predation, and Johnson (1972) demonstrated that transplanted individuals continue to grow normally. Young (1985) reported that detached Mytilus edulis produced 8 byssal threads within 24 hours once detached. Although these two species are probably of intermediate intolerance to displacement, the three important characterizing species are highly intolerant 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) (see MarLIN review).
  • 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 the ban.
  • Insufficient information was available on the specific effects of synthetic chemicals on the breadcrumb sponge.
  • The effects of contaminants, including synthetic chemicals, on the common mussel Mytilus edulis has been the focus of a large amount of research (see MarLIN review) and overall, this species has been assessed as being of intermediate intolerance to synthetic chemicals.
  • Oehlmann et al. (1998) reported that the gastropod Littorina littorea was found to be able to tolerate high levels of TBT.
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 mixed nature of the substratum and moderately strong water flow, 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 µg/l over 10 days (Strömgren, 1979b). Zinc, lead, cadmium & mercury significantly reduce growth rate at 1400 µg/l, 810 µg/l, 450 µg/l and 5 µg/l respectively (Strömgren, 1980a, b).
  • No information was found concerning the specific effects of heavy metals on the other three characterizing species, Chondrus crispus, Halichondria panicea and Ascidiella aspersa.
  • The effects of contaminants, including heavy metals, on the common mussel Mytilus edulis has been the focus of a large amount of research (see MarLIN review) and overall, this species has been assessed as being of intermediate intolerance to heavy metals.
  • Sub-lethal concentrations of mercury were shown to impair growth and condition of young adult Crepidula fornicata and impair reproductive capacity at 0.25 µg/l. Nelson et al. (1983) investigated the effects of exposure to silver. Reproductive output was found to be impaired following exposure to the highest concentration of silver nitrate (10 µg/l) for 24 months. The evidence suggests that high concentrations of heavy metals will cause mortality in Crepidula fornicata and lower concentrations could impair growth, condition and reproductive output and will therefore affect the long term health of the population.
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 mixed nature of the substratum and moderately strong water flow, recoverability is expected to be high, although recovery from the effects of highly persistent contaminants may take significantly longer.
Hydrocarbon contamination
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Soft sediment communities are particularly affected by oil pollution (Suchanek, 1993), although the mixed nature of the substratum within this biotope and the moderately strong water flow with which it is associated mean that the extent of hydrocarbon contamination may be reduced.
  • 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 micrograms/ml for 96 hours) interferes with adhesion during settling and (at 0.1 micrograms/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.
  • A 20 year study investigating community effects after the Amoco Cadiz oil spill of 1978 (Dauvin, 2000) found that a population of Lanice conchilega was established between 1978-84 but disappeared after 1985.
No information was found concerning the effects of hydrocarbon contamination in the other characterizing 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 neither of the four important characterizing species nor most of the other important species. However, Greenberber et al. (1986) exposed larval Crepidula fornicata to doses of X-ray radiation between 500 and 20,000 rads in total and found that, after 20 days, there was a dose dependent decrease in larval shell growth rate and a significant increase in larval mortality following doses above 2000 rads. These levels of radiation are extremely high compared to background levels in the environment but lower levels may have sub-lethal effects on growth and reproduction.

Overall, 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 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. However, as long as some red seaweeds remained, the recognizable biotope would be unaffected per se. Accordingly, an intolerance of low has been assessed with a very high recoverability.
Increase in salinity
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SLR.FserX.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 muddy sediment 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.FserX.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 of low salinity, Ascidiella scabra (in the same genus as Ascidiella aspersa) is found in reduced salinity conditions, the star ascidian Botryllus schlosseri is found in brackish water and Crepidula fornicata is described as euryhaline (Blanchard, 1997). However, 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 and therefore intolerance has been assessed as low but with a very high recovery.

Changes in oxygenation
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No specific information was found concerning the effects of reduced oxygenation on the important 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. Littorina littorea, for example, can endure long periods of oxygen deprivation by drastically reducing their metabolic rate (MacDonald & Storey, 1999). However, this reduces feeding rate and thus the viability of a population may be reduced. In general, it is likely that, at the benchmark level, some of important characterizing fauna may be of low intolerance to reduced oxygenation although recoverability is expected to be very high on return to 'normal' conditions.

Biological Factors

Introduction of microbial pathogens/parasites
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Some of the important species, for example Mytilus edulis and Chondrus crispus are known to be adversely affected by infestation by microbial pathogens (See MarLIN reviews). However, even if microbial infestation resulted in the loss of these two species from the biotope, the recognizable biotope per se would not be affected. The actual occurrence of and effects of pathogens on most of the species associated with this biotope are not known and therefore, insufficient information was available to assess sensitivity.
Introduction of non-native species
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Crepidula fornicata is an introduced species that has spread widely since its introduction to the United Kingdom at the end of the 19th century. It has the ability to recover rapidly from environmental perturbation and colonize new areas. Crepidula fornicata can form large mats in some areas and the boulders and cobbles within SLR.FserX.T could potentially become infested with them, although it is not known under what circumstances this species would change from being an important component of the biotope to a dominant species.

The Portuguese oyster Crassostrea gigas is another introduced species that has established itself in the wild after being introduced in England in 1926 for cultivation purposes. The species can form dense beds e.g. in the Netherlands, and, together with Crepidula fornicata, have the potential to cover large patches on the shore. Although Crassostrea gigas was not recorded in this biotope (JNCC, 1999), in areas where SLR.FserX.T presently coincides with the distribution of Crassostrea gigas, i.e. the south coast of Devon and coast of Essex, the oyster could become dominant.

On balance, it is suggested that SLR.FserX.T is of intermediate intolerance to the introduction of alien species since both Crassostrea gigas and Crepidula fornicata have the potential to alter the recognizable biotope. If these two species came to dominate the biotope, recoverability would only be possible if the majority of the two species were removed (through either natural or unnatural process) to allow the re-establishment of other species. Therefore, recoverability has not been assessed.
Extraction
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Several of the species indicative of sensitivity are known to be targeted for extraction, namely, Fucus serratus, Chondrus crispus, Mytilus edulis and Littorina littorea (see individual reviews). The extraction of Fucus serratus would lead to a reduction in the extent of the recognizable biotope, as the plant gives the biotope its name. In addition to the loss of either of the two algal species, many epiphytic species would be lost including proportions of bryozoan species such as Dynamena pumila (found especially on fucoid species), the star ascidian Botryllus schlosseri, and the breadcrumb sponge Halichondria panicea. Furthermore, the larvae of Dynamena pumila are thought to settle and metamorphose in response to the microbial films on the surface of this algae and subsequent recruitment of this hydroid will also be affected. Overall, each of the species indicative of sensitivity mentioned above may experiences some loss. However, the eulittoral position of this biotope and the fact that the algae and mussels are unlikely to grow in particularly large patches will mean that they are unlikely to be heavily exploited and intolerance has been assessed as intermediate.
Recovery has been assessed as high as it will probably have occurred after one year (see additional information).

Additional information icon Additional information

Recoverability in the four important characterizing species, and indeed most of the other important species, is considered to be high and therefore, the recoverability of this biotope from factors to which it is considered highly tolerant is also likely to be high.

Fucus serratus is 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 of from other populations and, providing that some of the population remains, it is unlikely that other species will come to dominate. Recovery will probably have occurred after one year.

Chondrus crispus has an extended reproductive period (e.g. Pybus, 1977; Fernandez & Menendez, 1991; Scrosati et al., 1994) and produces large numbers of spores (Fernandez & Menendez, 1991). Recovery of a population of Chondrus crispus following a perturbation is likely to be largely dependent on whether holdfasts remain, from which new thalli can regenerate (Holt et al., 1995). In addition, the spores of red algae are non-motile (Norton, 1992) and therefore entirely reliant on the hydrographic regime for dispersal. Hence, it is expected that Chondrus crispus would normally only recruit from local populations and that recovery of remote populations would be much more protracted.
Minchinton et al. (1997) documented the recovery of Chondrus crispus after a rocky shore in Nova Scotia, Canada, was totally denuded by an ice scouring event. Initial recolonization was dominated by diatoms and ephemeral macroalgae, followed by fucoids and then perennial red seaweeds. After 2 years, Chondrus crispus had re-established approximately 50% cover on the lower shore and after 5 years it was the dominant macroalga at this height, with approximately 100% cover. The authors pointed out that although Chondrus crispus was a poor colonizer, it was the best competitor. Therefore, recovery by Chondrus crispus will be relatively rapid (approximately 18 months) in situations where intolerance to a factor is intermediate and some holdfasts remain for regeneration of fronds. In situations of high intolerance, where the entire population of Chondrus crispus is removed, recovery will be limited by recruitment from a remote population and would be likely to take up to 5 years.

The settlement of new colonies of the breadcrumb sponge Halichondria panicea is likely within one year and growth rate is rapid.

The larvae of the sea squirt Ascidiella aspersa have a short free-swimming planktonic stage. Time taken from fertilization until settlement and metamorphosis is only about 24 hours at 20 °C (Niermann-Kerkenberg & Hofmann, 1989). However, due to the moderately strong flow rates with which this biotope is associated, there is still the possibility for this species to disperse over considerable distances. The sea squirt Ascidiella scabra (of the same genus as Ascidiella aspersa) has a high fecundity and settles readily, probably for an extended period from spring to autumn. Svane (1988) describes it as "an annual ascidian" and demonstrated recruitment onto artificial and scraped natural substrata. 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 about 2 months. However, if mortality and the consequent establishment of free space available occurs at a time when larvae are not being produced, other species may settle and dominate.

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.


This review can be cited as follows:

Marshall, C.E. 2006. Fucus serratus with sponges, ascidians and red seaweeds on tide-swept lower 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 25/04/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=221&code=1997>