Biodiversity & Conservation

CR.HCR.XFa.FluCoAs

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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Removal of the substratum will result in removal of all the sessile attached species, together with most of the slow mobile species (crustaceans, sea urchins and starfish) and an intolerance of high has been recorded. Recoverability will depend on recruitment from neighbouring communities and subsequent recovery of the original abundance of species, which may take many years, especially in slow growing sponges, anthozoans and Flustra foliacea. Therefore, a recoverability of high has been recorded (see additional information below).
Smothering
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This biotope is characteristic of areas subject to sediment scour and siltation. Holme & Wilson (1985) reported Flustra foliacea dominated communities that were subject to periodic smothering by thin layers of sand, up to ca 5cm in the central English Channel. Flustra foliacea and hydroids such as Nemertesiaspp. and Tubularia sp., the bryozoan Vesicularia spinosa, the ascidians Ascidia mentula and Dendrodoa grossularia and the anemone Urticina felina were noted in their sand scoured communities. Smothering with a layer of sediment will prevent or reduce feeding and hence growth and reproduction.

Although the biotope will probably survive smothering at the benchmark level, the species richness of the biotope will probably decline due to the loss of more intolerant species such as the bryozoan Bugula spp., sponges (e.g. Halichondria panicea) some ascidians (e.g. Clavelina lepadiformis) and reduced abundance of Alcyonium digitatum and the ascidian Molgula manhattensis, due to clogging of their filtration apparatus, interrupted feeding and hence reduced growth, and potential short term anoxia under the sediment layer. Also, associated small species such as prosobranchs, amphipods and worms may be intolerant. Therefore, an intolerance of intermediate is suggested to reflect the reduced species richness. Recoverability is likely to be high (see additional information below).

Prolonged smothering, however, is likely to favour biotopes dominated by Urticina felina (e.g. £MCR.Urt.Urt£).
Increase in suspended sediment
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This biotope is characteristic of areas subject to sediment scour and suspended sediment. In areas of high suspended sediment and siltation along the Northumberland coast, the MCR.Flu biotope is represented by a relatively species poor sub-biotope £MCR.Flu.Flu£, characterized by the presence of Thuiaria thuja and Sabellaria spinulosa. While an increase in suspended sediment at the benchmark level for a month is likely to reduce the efficiency of filter feeding in some species (e.g. bryozoans, hydroids and soft corals), most species are likely to survive for a month. If there is an associated increase in siltation, it is likely to interfere with larval growth and settlement if it coincided with the reproductive season. Therefore, an intolerance of low has been recorded. If siltation was prolonged then species richness may decrease, especially in more intolerant ascidians and bryozoans.
Decrease in suspended sediment
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This biotope is characteristic of areas subject to sediment scour and suspended sediment. The relatively species poor sub-biotope £MCR.Flu.Flu£ is characteristic of high levels of suspended sediment. Therefore, with decreasing suspended sediment levels, species richness is likely to increase, to something like that of the other sub-biotopes (£MCR.Flu.Hocu£, £MCR.Flu.HByS£, and £MCR.Flu.SerHyd£). A decrease in suspended sediment may decrease food availability for the duration of the benchmark (one month) but otherwise not adversely affect the biotope in such a short period of time. Therefore, an intolerance of low has been recorded. Prolonged decreases in suspended sediment, and consequent reduced scour may allow other species to colonize the habitat and out-compete characterizing species, perhaps increasing dominance by ascidians, sponges or anemones, and their biotopes.
Desiccation
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Bryozoans, hydroids, sponges, and soft corals, are probably highly intolerance of desiccation. However, this biotope is circalittoral, occurring below 5-10m depth and possibly to great depths (e.g. ca 200m) (see Flustra foliacea review) and unlikely to be exposed to the air and desiccation.
Increase in emergence regime
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An increase or decrease in tidal emergence is unlikely to affect circalittoral habitats, except that the influence of wave action may be increased (see wave action below).
Decrease in emergence regime
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An increase or decrease in tidal emergence is unlikely to affect circalittoral habitats, except that the influence of wave action may be decreased (see wave action below).
Increase in water flow rate
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This biotope is characterized by species that are tolerant of moderately strong to strong tidal streams and associated sediment scour. Flustra foliacea colonies are flexible, robust and reach high abundances in areas subject to strong tidal streams (Stebbing, 1971a; Eggleston, 1972b; Knight-Jones & Nelson-Smith, 1977; Hiscock, 1983, 1985; Holme & Wilson, 1985) and occur in areas subject to very strong tidal streams. While Flustra foliacea may not be adversely affected by an increase in water flow to very strong, other species in the biotope such as hydroids and erect bryozoans may be adversely affected by the physical drag caused by very strong water flow, e.g. Bugula species or Molgula manhattensis. Increased water flow is likely to reduce predation by Asterias rubens and large sea urchins, e.g. Echinus esculentus was observed to be rolled along the substratum by currents of 2.6 knots or above (Comely & Ansell, 1988). But the increased sediment scour likely to accompany increased water flow rates may be more damaging, resulting in an increase in the extent of biotopes found in higher scour, such as found at the sediment /rock interface, e.g. Urticina felina dominated £MCR.Urt.Urt£. In severe scour, the community may become impoverished, consisting of Pomatoceros spp., encrusting bryozoans, encrusting coralline algae and Balanus crenatus, e.g. £ECR.PomByC£. Where the biotopes occur on stones or boulders, increased water flow may result in movement or rolling of the stones and boulders, and hence severe scour and abrasion. The likely associated scour and displacement of some species in the biotope over the year (see benchmark), is likely to change the biotope to a different one. Therefore, an intolerance of high has been recorded. Recoverability is likely to be high (see additional information below).
Decrease in water flow rate
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This biotope is characterized by species that are tolerant of moderately strong to strong tidal streams and associated sediment scour. A decrease in water flow rates will decrease sediment scour, however, in the proximity of sediment is likely to result in greater siltation. Water movement is essential for suspension feeders such as hydroids, bryozoans, sponges, amphipods and ascidians to supply adequate food, remove metabolic waste products, prevent accumulation of sediment and disperse larvae or medusae. In addition, water flow was shown to be important for the supply of suitable hard substrata for colonization, and hence the development of bryozoan communities (Eggleston, 1972b; Ryland, 1976). Hydroids are also expected to be abundant where water movement is sufficient to supply adequate food but not cause damage (Hiscock, 1983; Gili & Hughes, 1995). For example, Sertularia operculata was observed to die within a few months when transplanted from Lough Ine rapids to sheltered water, due to the build up of a layer of silt (Round, et al., 1961). Therefore, a decrease in water flow from e.g. moderately strong to very weak is likely to encourage colonization by other species of hydroids, ascidians, sponges and anemones, and may increase the risk of sea urchin predation, resulting in significant changes in the community and possibly the loss of the dominant hydroid/ bryozoans turf. Therefore, an intolerance of high has been recorded. Recoverability is likely to take up to 5 years (see additional information below).
Increase in temperature
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Growth rates were reported to increase with temperature in several bryozoan species, however, zooid size decreased, which may be due to increased metabolic costs at higher temperature (Menon, 1972; Ryland, 1976; Hunter & Hughes, 1994). Temperature is also a critical factor stimulating or inhibiting reproduction in hydroids, most of which have an optimum temperature range for reproduction (Gili & Hughes, 1995). Most of the hydroid and bryozoan species within the biotope are recorded to the north or south of the British Isles and are unlikely to be adversely affected by long term increases in temperature at the benchmark level. Similarly, sponges of the species Polymastia occurs from the Arctic to Gibraltar, and Haliclona oculata is widespread. However, the hydroid Thuiaria thuja is a primarily northern species and likely to be lost due to long term changes in temperature (Hiscock et al., 2001). Similarly, while not likely to be adversely affected by long term change, Urticina felina and Echinus esculentus are probably intolerance of short term increases in temperature at the benchmark level. However, circalittoral habitats are probably protected from extreme changes in temperature by their depth. Whilst the northern hydroid Thuiaria thuja may be lost from the biotope, southern species may take its place and, in view of the likely favourable effects on growth rates in other species, an overall rank of not sensitive has been recorded.
Decrease in temperature
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The majority of the dominant or characterizing species in the biotope are boreal or have a wide distribution to the north or south of British and Ireland and the biotope is unlikely to be adversely affected by long term changes in temperature at the benchmark level. Short term acute change may adversely affect some species, e.g. Echinus esculentus and Urticina felina, resulting in reduced extent or abundance. In addition, temperature influences growth and reproduction in many species of hydroids, bryozoans and ascidians (see above and species reviews). Therefore, an intolerance of low has been recorded.
Increase in turbidity
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An increase in turbidity is likely to result in a decrease in phytoplankton and macroalgal primary production, which may reduce food available to the suspension feeders within the community. As a result , growth rates and reproduction may be decreased, and some species may not be able to keep up with predation (e.g. see Gaulin et al., 1986). However, slow growing species such as Flustra foliacea can probably survive reductions in food availability for a year. Therefore, an intolerance of low has been recorded.
Decrease in turbidity
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A decrease in turbidity may increase phytoplankton and hence zooplankton productivity and potentially increase food availability. Increased light penetration may allow macroalgae to colonize deeper water. Macroalgae effectively compete for space and grow over and may smother fauna. Therefore, decreased turbidity may allow macroalgae to colonize the more shallow examples of this biotope, resulting in loss of a proportion of the biotope, although some members of the community are likely to survive even in the presence of macroalgae. The favourable effects of a potential increase in food supply are probably more important than overgrowth by macroalgae at shallow depths. Therefore a rank of not sensitive has been recorded.
Increase in wave exposure
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This biotope occurs in moderately wave exposed habitats. The sub-biotope £MCR.Flu.HByS£ is also found in wave exposed habitats and includes robust hydroids (e.g. Nemertesia antennina, and Abietinaria abietina) and sponges such as Dysidea fragilis, Polymastia boletiformis and Cliona celata (Conner et al., 1997a).

The oscillatory flow generated by wave action is potentially more damaging than unidirectional flow but is attenuated with depth (Hiscock, 1983). Many of the species in the biotope are likely to be able to tolerate an increase in wave exposure from moderately exposed to very exposed, for example, Alcyonium digitatum, Urticina felina, Bugula species, the sponges Halichondria panicea and Esperiopsis fucorum, and probably the hydroids Nemertesia antennina and Sertularia argentea Abietinaria abietina. Flustra foliacea is found in very wave exposed site, although probably in deeper waters. However, less flexible or weaker hydroids and bryozoans may be removed, e.g. Nemertesia ramosa. Increased wave action may decrease sea urchin and starfish predation, perhaps allowing larger, massive species (e.g. sponges, anemones and ascidians) increase in dominance. Therefore, it is likely that some species within the biotope, especially hydroids may be lost, and some of the Flustra foliacea turf may also be damaged and an intolerance of intermediate has been recorded. Recoverability is likely to be high (see additional information below).

Decrease in wave exposure
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The strong tidal streams that typify this biotope are probably more important as water movement than wave induced oscillatory flow. Therefore, a decrease in wave action may allow more delicate species, such as Nemertesia ramosa, ascidians and sponges to increase in abundance. Decreased wave action may allow the biotope to extend into shallower water (e.g. £MCR.Flu.Hocu£). But reduced wave action may result in an increase in sea urchin predation and hence increased patchiness and species richness (Sebens, 1985; Hartnoll, 1998).

Overall, a decrease in wave action may not adversely affect the biotope while strong tidal flow maintains adequate water exchange and, although some species in the biotope may change, Flustra foliacea and the biotope will probably survive. Therefore, an intolerance of low has been recorded.

Noise
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Hydroids, bryozoans, sponges and ascidians are unlikely to be sensitive to noise or vibration at the benchmark level. Mobile fish species may be temporarily scared away from the areas but few if any adverse effects on the biotope are likely to result.
Visual Presence
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Hydroid and bryozoan polyps or barnacle cirri may retract when shaded by potential predators, however the community is unlikely to be affected by visual presence. Mobile fish species may be temporarily scared away from the areas but few if any adverse effects on the biotope are likely to result.
Abrasion & physical disturbance
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The species that characterize this biotope are tolerant of sediment scour and unlikely to be damaged by abrasion. However, physical disturbance by an anchor or mobile fishing gear may be more damaging.

Erect epifaunal species are particularly vulnerable to physical disturbance. Hydroids and bryozoans are likely to be detached or damaged by bottom trawling or dredging (Holt et al., 1995). Veale et al. (2000) reported that the abundance, biomass and production of epifaunal assemblages decreased with increasing fishing effort. Hydroid and bryozoan matrices were reported to be greatly reduced in fished areas (Jennings & Kaiser, 1998 and references therein). Mobile gears also result in modification of the substratum, including removal of shell debris, cobbles and rocks, and the movement of boulders (Bullimore, 1985; Jennings & Kaiser, 1998). The removal of rocks or boulders to which species are attached results in substratum loss (see above). Magorrian & Service (1998) reported that queen scallop trawling flattened horse mussel beds and removed emergent epifauna in Strangford Lough. They suggested that the emergent epifauna such as Alcyonium digitatum, a frequent component of this biotope, were more intolerant than the horse mussels themselves and reflected early signs of damage. However, Alcyonium digitatum is more abundant on high fishing effort grounds, which suggests that this seemingly fragile species is more resistant to abrasive disturbance than might be assumed (Bradshaw et al., 2000), presumably owing to good recovery due to its ability to replace senescent cells and regenerate damaged tissue, together with early larval colonization of available substrata. Species with fragile tests such as Echinus esculentus and the brittlestar Ophiocomina nigra and edible crabs Cancer pagurus were reported to suffer badly from the impact of a passing scallop dredge (Bradshaw et al., 2000). Scavengers such as Asterias rubens and Buccinum undatum were reported to be fairly robust to encounters with trawls (Kaiser & Spencer, 1995) may benefit in the short term, feeding on species damaged or killed by passing dredges. However, Veale et al. (2000) did not detect any net benefit at the population level.

Overall, physical disturbance by an anchor or mobile fishing gear is likely to remove a proportion of all groups within the community and attract scavengers to the community in the short term. Therefore, an intolerance of intermediate has been recorded. Recoverability is likely to be high due to repair and regrowth of hydroids and bryozoans (e.g. Flustra foliacea), and recruitment within the community from surviving colonies and individuals (see additional information below).
Displacement
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Most permanently fixed, sessile species, such as bryozoans (e.g. Flustra foliacea and Bugula species), sponges (e.g. Halichondria panicea), ascidians (e.g. Molgula manhattensis) and hydroids (e.g. Nemertesia species) cannot reattach to the substratum if removed, and may be damaged or destroyed in the process. Hydroids and sponges may be able to grow from fragments, aiding recovery. Mobile species, such as amphipods, gastropods, small crustaceans, crabs and fish are likely to survive displacement. Anemones (e.g. Urticina felina) are strongly but not permanently attached and will probably reattach to suitable substrata. However, the dominant bryozoans and hydroids are likely to be lost and an intolerance of high has been recorded. Recovery of the Flustra foliacea abundance is likely to take many years and a recoverability of high has been recorded (see additional information below).

Chemical Factors

Synthetic compound contamination
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Bryozoans are common members of the fouling community, and amongst those organisms most resistant to antifouling measures, such as copper containing anti-fouling paints (Soule & Soule, 1979; Holt et al., 1995). However, Hoare & Hiscock (1974) suggested that Polyzoa (Bryozoa) were amongst the most intolerant species to acidified halogenated effluents in Amlwch Bay, Anglesey and reported that Flustra foliacea did not occur less than 165m from the effluent source and noted that Bugula flabellata did not occur within the bay. Urticina felina survived near to the acidified halogenated effluent discharge in a 'transition' zone where many other species were unable to survive, suggesting a tolerance to chemical contamination but did not survive closer to the effluent source (Hoare & Hiscock, 1974). Moran & Grant (1993) reported that settlement of marine fouling species, including Bugula neritina was significantly reduced in Port Kembla Harbour, Australia, exposed to high levels of cyanide, ammonia and phenolics.

The species richness of hydroid communities decreases with increasing pollution (Boero, 1984; Gili & Hughes, 1995). Stebbing (1981) reported that Cu, Cd, and tributyl tin fluoride affected growth regulators in Laomedea (as Campanularia) flexuosa resulting in increased growth.

Alcyonium digitatum at a depth of 16m in the locality of Sennen Cove (Pedu-men-du, Cornwall) died resulting from the offshore spread and toxic effect of detergents e.g. BP 1002 sprayed along the shoreline to disperse oil from the Torrey Canyon tanker spill (Smith, 1986). Possible sub-lethal effects of exposure to synthetic chemicals, may result in a change in morphology, growth rate or disruption of reproductive cycle. Smith (1968) also noted that large numbers of dead Echinus esculentus were found between 5.5 and 14.5 m in the vicinity of Sennen, presumably due to a combination of wave exposure and heavy spraying of dispersants in that area (Smith, 1968). Smith (1968) also demonstrated that 0.5 -1ppm of the detergent BP1002 resulted in developmental abnormalities in echinopluteus larvae of Echinus esculentus.

Tri-butyl tin (TBT) has a marked effect on numerous marine organisms (Bryan & Gibbs, 1991). The encrusting bryozoan Schizoporella errata suffered 50% mortality when exposed for 63 days to 100ng/l TBT. Bryan & Gibbs (1991) reported that virtually no hydroids were present on hard bottom communities in TBT contaminated sites and suggested that some hydroids were intolerant of TBT levels between 100 and 500 ng/l. Copepod and mysid crustaceans were particularly intolerant of TBT while crabs were more resistant (Bryan & Gibbs, 1991), although recent evidence suggests some sublethal endocrine disruption in crabs. The effect of TBT on Nucella lapillus and other neogastropods is well known (see review), and similar effects on reproduction may occur in other gastropod molluscs, including nudibranchs. Rees et al. (2001) reported that the abundance of epifauna had increased in the Crouch estuary in the five years since TBT was banned from use on small vessels. Rees et al. (2001) suggested that TBT inhibited settlement in ascidian larvae. This report suggests that epifaunal species (including, bryozoan, hydroids and ascidians) may be at least inhibited by the presence of TBT.

Therefore, hydroids crustaceans, gastropods, and ascidians are probably intolerant of TBT contamination while bryozoans are probably intolerant of other chemical pollution and an intolerance of intermediate has been recorded, albeit at low confidence. A recoverability of moderate has been recorded (see additional information below).
Heavy metal contamination
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Various heavy metals have been show to have sublethal effects on growth in the few hydroids studied experimentally (Stebbing, 1981; Bryan, 1984; Ringelband, 2001). Bryozoans are common members of the fouling community and amongst those organisms most resistant to anti-fouling measures, such as copper containing anti-fouling paints.

Bryozoans were also shown to bioaccumulate heavy metals to a certain extent (Soule & Soule, 1979; Holt et al., 1995). However, Bugula neritina was reported to survive but not grow exposed to ionic Cu concentrations of 0.2-0.3 ppm (larvae died above 0.3ppm) but die where the surface leaching rate of Cu exceeded 10µg Cu/cm²/day (Ryland, 1967; Soule & Soule, 1979). Ryland (1967) also noted that Bugula neritina was less intolerant of Hg than Cu.

Echinus esculentus populations in the vicinity of an oil terminal in A Coruna Bay, Spain, showed developmental abnormalities in the skeleton and their tissues contained high levels of aliphatic hydrocarbons, naphthalenes, pesticides and heavy metals (Zn, Hg, Cd, Pb, and Cu) (Gomez & Miguez-Rodriguez 1999). Waters containing 25 µg / l Cu caused developmental disturbances in Echinus esculentus (Kinne, 1984) and heavy metals caused reproductive anomalies in the starfish Asterias rubens (Besten, et al., 1989, 1991). Sea urchin larvae have been used in toxicity testing and as a sensitive assay for water quality (reviewed by Dinnel et al. 1988), so that echinoderms are probably intolerant of a heavy metal contamination. Gastropod molluscs have been reported to relatively tolerant of heavy metals while a wide range of sublethal and lethal effects have been observed in larval and adult crustaceans (Bryan, 1984).

Overall, the dominant bryozoans may be tolerant and hydroids manifest only sublethal effects. The sea urchin Echinus esculentus is probably highly intolerant of heavy metal contamination. Heavy metals contamination may, therefore, reduce reproduction and recruitment in starfish and sea urchins, potentially reducing predation pressure in the biotope. Therefore, an intolerance of low has been recorded to represent the sublethal effects on dominant bryozoans and hydroids. Loss of predatory sea urchins, may result in an increased dominance by some species and a slight decrease in species richness.

Hydrocarbon contamination
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Flustra foliacea dominated communities are likely to be protected from the direct effects of oil spills by its subtidal habit but may be exposed to emulsified oil treated with dispersants, especially in areas of turbulence, or exposed to water soluble fractions of oils, PAHs or oil adsorbed onto particulates. For example:
  • Species of the encrusting bryozoan Membranipora and the erect bryozoan Bugula were reported to be lost or excluded from areas subject to oil spills. (Mohammad, 1974; Soule & Soule, 1979). Houghton et al. (1996) also reported a reduction in the abundance of intertidal encrusting bryozoans (no species given) at oiled sites after the Exxon Valdez oil spill.
  • The water soluble fractions of Monterey crude oil and drilling muds were reported to cause polyp shedding and other sublethal effects in the athecate hydroid Tubularia crocea in laboratory tests (Michel & Case, 1984; Michel et al., 1986; Holt et al., 1995).
  • Suchanek (1993) reported that the anemones Anthopleura spp. and Actinia spp. survived in waters exposed to spills and chronic inputs of oils. Similarly, one month after the Torrey Canyon oil spill the dahlia anemone, Urticina felina, was found to be one of the most resistant animals on the shore, being commonly found alive in pools between the tide-marks which appeared to be devoid of all other animals (Smith, 1968).
  • Amphipods, especially ampeliscid amphipods, are regarded as especially sensitive to oil (Suchanek, 1993).
  • Smith (1968) reported dead colonies of Alcyonium digitatum at depth in the locality of Sennen Cove (Pedu-men-du, Cornwall) resulting from the combination of wave exposure and heavy spraying of dispersants sprayed along the shoreline to disperse oil from the Torrey Cannon tanker spill (see synthetic chemicals).
  • Crude oil from the Torrey Canyon and the detergent used to disperse it caused mass mortalities of echinoderms; Asterias rubens, Echinocardium cordatum, Psammechinus miliaris, Echinus esculentus, Marthasterias glacialis and Acrocnida brachiata (Smith, 1968). Echinus esculentus populations in the vicinity of an oil terminal in A Coruna Bay, Spain, showed developmental abnormalities in the skeleton. The tissues contained high levels of aliphatic hydrocarbons, naphthalenes, pesticides and heavy metals (Zn, Hg, Cd, Pb, and Cu) (Gomez & Miguez-Rodriguez 1999).
  • Halichondria panicea survived in areas affected by the Torrey Canyon oil spill, although few observations were made (Smith 1968).
If the physiology within different animals groups can be assumed to be similar, then bryozoans, amphipods, echinoderms and soft corals may be intolerant of hydrocarbon contamination, while hydroids may demonstrate sublethal effects and anemones and some species of sponge are relatively tolerant. Some members of the bryozoan turf and some members of the community may be lost or damaged as a result of acute hydrocarbon contamination, although a recognisable biotope may remain. Therefore, an intolerance of intermediate has been suggested, albeit at very low confidence. Recoverability is likely to be moderate (see additional information below).
Radionuclide contamination
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No information found.
Changes in nutrient levels
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An increase in nutrient levels from e.g. sewage sludge, sewage effluent or riverine flooding, may result in an increase in inorganic and organic suspended particulates (see above), increased turbidity (see above) and increased phytoplankton productivity. Moderate nutrient enrichment may increase the food available to the community in the form of phytoplankton, zooplankton or organic particulates. However, eutrophication may result in deoxygenation (see below) or algal blooms. While the biotope is unlikely to be directly affected by algal blooms, the biotope may be adversely affected by toxins from toxic algae that accumulate in zooplankton, or smothered by dead 'bloom' algae and deoxygenation resulting form their subsequent decay (see below). Death of a bloom of the phytoplankton Gyrodinium aureolum in Mounts Bay, Penzance in 1978 produced a layer of brown slime on the sea bottom. This resulted in the death of invertebrates, including Echinus esculentus, Marthasterias glacialis, while sessile bryozoans, sponges and Alcyonium spp. appeared moribund, presumably due to anoxia caused by the decay of the dead dinoflagellates (Griffiths et al. 1979). This biotope occurs in areas subject to moderately strong to strong tidal streams, so that prolonged deoxygenation is unlikely to occur. However, an intolerance of low has been recorded to represent the potential toxic effects of the algae and the siltation caused by death of an algal bloom.
Increase in salinity
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This biotope occurs in full salinity and is unlikely to encounter increases in salinity.
Decrease in salinity
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Most of the species identified as indicative of intolerance may be of 'intermediate' or 'low' intolerance to a reduction in salinity. Ryland (1970) stated that, with a few exceptions, the Gymnolaemata were fairly stenohaline and restricted to full salinity (ca 35 psu) and noted that reduced salinities result in an impoverished bryozoan fauna but this biotope (MCR.Flu) and those biotopes it has been used to represent, are found in the circalittoral and are unlikely to be exposed to reduced or low salinity.
Changes in oxygenation
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This biotope occurs in areas subject to moderately strong to strong tidal streams, so that deoxygenating conditions are unlikely to develop.

Biological Factors

Introduction of microbial pathogens/parasites
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Stebbing (1971a) reported that encrusting epizoics reduced the growth rate of Flustra foliacea by ca 50% and Stebbing (1971b) described the epizoic fauna of horn wrack in detail. For example, Bugula flabellata produces stolons that grow in and through the zooids of Flustra foliacea, causing "irreversible degeneration of the enclosed polypide" (Stebbing, 1971b). Therefore, given the reduction in growth caused by epizoic infestation an intolerance of low has been recorded. Recovery and repair would probably be rapid (see additional information below).
Introduction of non-native species
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No non-native species are known to occur in this biotope.
Extraction
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Flustra foliacea is not presently known to be subject to extraction. However, many bryozoans have been recently found to contain pharmacologically active substances (Hayward & Ryland, 1998) and, therefore, Flustra foliacea, Bugula spp. and other bryozoans may be subject to harvesting in the future. The use of mobile fishing gear, such as scallop dredges and beam trawls, in the vicinity of the biotope result in physical disturbance to the sediment surface, and an increase in suspended sediment (Hartnoll, 1998). Circalittoral faunal turf biotopes may be subject to fishing for crabs, crawfish and lobster, using pots, creels or fixed bottom-set tangle or gill nets (Hartnoll, 1998). Potting and fixed netting (their placement and collection) probably results in abrasion and physical disturbance (see above). In addition, Echinus esculentus has been collected by diving in the past (Nichols, 1984). Loss of functionally important predators such as sea urchins, and to a lesser extent crabs and lobster may affect community structure (Hartnoll, 1998). Therefore, an intolerance of intermediate and a recoverably of high have been recorded to represent physical disturbance caused by fishing activities (see additional information below).

Additional information icon Additional information

Recoverability
Where local populations exist or remain after disturbance recruitment is likely to be rapid for most species, including Flustra foliacea. Many species, e.g. hydroids, colonial ascidians, sponges and Metridium senile are capable of asexual reproduction and colonize space rapidly. For example, in studies of subtidal epifaunal communities in New England, Sebens (1985, 1986) reported that cleared areas were colonized by erect hydroids, bryozoans, crustose red algae and tube worms within 1-4 months in spring, summer and autumn. Tunicates such as Dendrodoa carnea and Aplidium spp. appeared within a year, Aplidium sp., and Halichondria panicea achieved pre-clearance cover within >2 years, while only a few individuals of Metridium senile and Alcyonium sp. colonized within 4 years.

Flustra foliacea is slow growing, long-lived and new colonies take at least 1 year to develop erect growth and 1-2 years to reach maturity (Stebbing, 1971a; Eggleston, 1972a), depending on environmental conditions. Four years after sinking, the wreck of a small coaster, the M.V. Robert, off Lundy was found to be colonized by erect bryozoans and hydroids, including occasional Flustra foliacea (Hiscock, 1981). The wreck was several hundreds of metres from any significant hard substrata, and hence a considerable distance from potentially parent colonies (Hiscock, 1981 and pers. comm.). Overall, local recruitment is probably good and a damaged or reduced population of Flustra foliacea, other erect bryozoans and hydroids may recover abundance and percentage cover in less than 5 years.

Where the populations are removed or destroyed. recolonization will depend on recruitment of larvae from other communities. The majority of species are widespread but have poor dispersal so that recruitment rates will depend on the proximity of nearby communities and the hydrographic regime. Exceptions include, mobile crustaceans and echinoderms with long-lived planktonic larvae, and Nemertesia antennina and Alcyonium digitatum which can probably disperse up to 50m or over 100km respectively (Hughes, 1977; Hartnoll, 1998). But Sebens (1985) suggested that Alcyonium spp and Metridium senile would probably not recruit to epifaunal communities unless other populations of the species were nearby. Flustra foliacea is evidently capable of dispersing over considerable distance, since it colonized the M.V. Robert and achieved 1-5% (occasional) cover within 4 years (Hiscock, 1981). However, it would probably take many years for Flustra foliacea to recover its original cover. Many other members of the community would probably occupy space rapidly once they colonize the habitat.

Colonization of cleared space from distant populations is probably stochastic, reliant on hydrography and environmental conditions. Overall, encrusting bryozoans, hydroids, and ascidians will probably develop a faunal turf within less than 2 years, and Flustra foliacea can evidently colonize and reach an abundance of occasional (1-5% cover) within 4 years. While the biotope may be recognisable in up to five years, Flustra foliacea may take at least five years to recover its original dominance. Where habitats are isolated by geography (distance) or hydrography, recovery may take longer.

This review can be cited as follows:

Tyler-Walters, H. 2002. Flustra foliacea and other hydroid/bryozoan turf species on slightly scoured circalittoral rock or mixed substrata. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 19/09/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=267&code=2004>