The Marine Life Information Network

Substratum loss

Benchmark. All of the substratum occupied by the species or biotope under consideration is removed. A single event is assumed for sensitivity assessment. Once the activity or event has stopped (or between regular events) suitable substratum remains or is deposited. Species or community recovery assumes that the substratum within the habitat preferences of the original species or community is present. Further details

Evidence

Removal of the substratum would result in the removal of the Flustra foliacea population and its associated fauna. Recovery will depend on recruitment from other populations and is assessed as high (see additional information below).

Smothering

Benchmark. All of the population of a species or an area of a biotope is smothered by sediment to a depth of 5 cm above the substratum for one month. Impermeable materials, such as concrete, oil, or tar, are likely to have a greater effect. Further details.

Evidence

Holme & Wilson (1985) examined the bottom fauna in a tide-swept region of the central English Channel. Flustra foliacea dominated communities were reported to form in, and hence tolerate, areas subject to sediment transport (mainly sand) and periodic, temporary, submergence by thin layers of sand (ca <5 cm). In some cases, Flustra foliacea was seen to be partially buried by sand. It is likely that Flustra foliacea would withstand smothering by 5cm of sediment for a month. Large colonies are likely to be >6cm in height and exposed autozooids, will be able to feed, providing food for the rest of the colony. Therefore, not sensitive has been recorded. However, smothering for protracted periods or by impermeable materials may have a greater impact.

Increase in suspended sediment

Benchmark. An arbitrary short-term, acute change in background suspended sediment concentration e.g., a change of 100 mg/l for one month. The resultant light attenuation effects are addressed under turbidity, and the effects of rapid settling out of suspended sediment are addressed under smothering. Further details

Evidence

Suspended sediment is likely to cause abrasion and effect suspension feeding physically. But Flustra foliacea dominated communities have been reported from areas subject to sediment abrasion due to strong tidal streams, either by mainly sand (Holme & Wilson, 1985) or by gravel (Knight-Jones & Nelson-Smith, 1977; Hartnoll, 1983). Their toughness and erect form, coupled with their flexibility probably confers tolerance (Knight-Jones & Nelson-Smith, 1977; Holme & Wilson, 1985). Hyman (1959) noted that erect forms were more calcified than encrusting forms, e.g. Flustra foliacea was reported to have a calcareous content of 97-99%. In addition, Flustra foliacea was reported to be abundant in turbid, fast flowing waters of the Menai Straits (Moore, 1977). Therefore, together with evidence of periodic partial burial by sediment (see smothering above) Flustra foliacea is likely to tolerate increased suspended sediment. Bryozoan larvae are reported to avoid areas affected by siltation (Eggleston, 1972b; Ryland, 1976), however, the abundance of Flustra foliacea in areas subject to sediment abrasion and suspended sediment loads subjects that the some of its larvae are also able to settle and survive. An increase in siltation and associated scour may remove competitors and provide additional space for colonization, therefore, 'tolerant*' has been recorded.

Decrease in suspended sediment

Benchmark. An arbitrary short-term, acute change in background suspended sediment concentration e.g., a change of 100 mg/l for one month. The resultant light attenuation effects are addressed under turbidity, and the effects of rapid settling out of suspended sediment are addressed under smothering. Further details

Evidence

A significant reduction in suspended sediment load for a month (see benchmark) is unlikely to adversely affect Flustra foliacea. Therefore, a rank of tolerant has been recorded. However, the longer term reduction may allow other species to colonize available substratum and increase competition for space with Flustra foliacea.

Desiccation

1. A normally subtidal, demersal or pelagic species including intertidal migratory or under-boulder species is continuously exposed to air and sunshine for one hour.
2. A normally intertidal species or community is exposed to a change in desiccation equivalent to a change in position of one vertical biological zone on the shore, e.g., from upper eulittoral to the mid eulittoral or from sublittoral fringe to lower eulittoral for a period of one year. Further details.

Evidence

Flustra foliacea is probably highly intolerant of desiccation, and specimens washed ashore are usually dead. However, it is a subtidal species unlikely to be exposed to the air.

Increase in emergence regime

Benchmark. A one hour change in the time covered or not covered by the sea for a period of one year. Further details

Evidence

Flustra foliacea is a subtidal species, and unlikely to be affected by a change in emergence regime at the benchmark level.

Decrease in emergence regime

Benchmark. A one hour change in the time covered or not covered by the sea for a period of one year. Further details

Evidence

Flustra foliacea is a subtidal species, and unlikely to be affected by a change in emergence regime at the benchmark level.

Increase in water flow rate

A change of two categories in water flow rate (view glossary) for 1 year, for example, from moderately strong (1-3 knots) to very weak (negligible). Further details

Evidence

Flustra foliacea colonies are flexible, robust and reach high abundances in areas subject to strong currents and tidal streams (see distribution; Stebbing, 1971; Eggleston, 1972b; Knight-Jones & Nelson-Smith, 1977; Hiscock, 1983, 1985; Holme & Wilson, 1985). Dyrynda (1994) suggested that mature fronded colonies do not occur on unstable substratum due to the drag caused by their fronds, resulting in rafting of colonies on shells or the rolling of pebbles and cobbles, resulting in destruction of the colony. Dyrynda (1994) reported that the distribution of Flustra foliacea in the current swept entrance to Poole Harbour was restricted to circalittoral boulders, on which it dominated as nearly mono-specific stands. Therefore, an increase in water flow from moderately strong to very strong may not adversely affect colonies on stable substrata. However, colonies, especially if large, on coarse grounds, shells, cobble and pebbles are likely to be more intolerant of increase in water flow, and a proportion of the population may be displaced, although the colony may survive as long as it is not crushed in the process. Therefore, tolerant has been recorded.

Decrease in water flow rate

A change of two categories in water flow rate (view glossary) for 1 year, for example, from moderately strong (1-3 knots) to very weak (negligible). Further details

Evidence

Flustra foliacea reaches high abundances in strong currents (see above) but decreases in abundance in weak currents. Decreased water flow may result in increased siltation and accumulation of fine sediments, increased competition from other space occupying species such as sponges, hydroids and other bryozoans, and a decrease in food availability. While, the pumping activity of the lophophores provide the greatest proportion of the colonies food requirements (Hayward & Ryland, 1998), the current generated is probably very localized and the colonies are dependant on water currents to carry food particles to them. Therefore, a decrease in water flow from, e.g. moderately strong to weak, is likely to result in a decrease in the abundance of Flustra foliacea and an intolerance of intermediate has been recorded.

Increase in temperature

1. A short-term, acute change in temperature; e.g., a 5°C change in the temperature range for three consecutive days. This definition includes ‘short-term’ thermal discharges.
2. A long-term, chronic change in temperature; e.g. a 2°C change in the temperature range for a year. This definition includes ‘long term’ thermal discharges.

For intertidal species or communities, the range of temperatures includes the air temperature regime for that species or community. Further details

Evidence

No information concerning temperature tolerance was found. However, Flustra foliacea is an amphiboreal species found in the Arctic Circle and south to the Bay of Biscay, and from the shallow sublittoral to deep circalittoral. Therefore, it is unlikely to be adversely affected by long term changes in temperature within British waters, and a rank of tolerant has been recorded.

Decrease in temperature

1. A short-term, acute change in temperature; e.g., a 5°C change in the temperature range for three consecutive days. This definition includes ‘short-term’ thermal discharges.
2. A long-term, chronic change in temperature; e.g. a 2°C change in the temperature range for a year. This definition includes ‘long term’ thermal discharges.

For intertidal species or communities, the range of temperatures includes the air temperature regime for that species or community. Further details

Evidence

No information concerning temperature tolerance was found. However, Flustra foliacea is an amphiboreal species found in the Arctic Circle and south to the Bay of Biscay, and from the shallow sublittoral to deep circalittoral. Therefore, it is unlikely to be adversely affected by long term changes in temperature within British waters, and a rank of tolerant has been recorded.

Increase in turbidity

1. A short-term, acute change; e.g., two categories of the water clarity scale (see glossary) for one month, such as from medium to extreme turbidity.
2. A long-term, chronic change; e.g., one category of the water clarity scale (see glossary) for one year, such as from low to medium turbidity. Further details

Evidence

Increased turbidity will reduce light penetration and hence phytoplankton productivity. Small phytoplankton are probably an important food source in the shallow subtidal, although, Flustra foliacea is also found at greater depths, where organic particulates (detritus) are probably more important. Therefore, an increase in turbidity is unlikely to adversely affect Flustra foliacea.

Decrease in turbidity

1. A short-term, acute change; e.g., two categories of the water clarity scale (see glossary) for one month, such as from medium to extreme turbidity.
2. A long-term, chronic change; e.g., one category of the water clarity scale (see glossary) for one year, such as from low to medium turbidity. Further details

Evidence

Decreased turbidity is likely to result in increased primary productivity, and therefore indirectly increase the availability of food (phytoplankton or detritus) for Flustra foliacea, which may, therefore, benefit. Therefore, a rank of tolerant* has been recorded.

Increase in wave exposure

A change of two ranks on the wave exposure scale (view glossary) e.g., from Exposed to Extremely exposed for a period of one year. Further details

Evidence

Flustra foliacea occurs from very wave exposed to sheltered waters, although probably limited to deeper waters in very wave exposed conditions. The oscillatory water flow generated by wave action may be more damaging than constant strong currents, e.g. strong wave action may generate an oscillatory flow of 2m/sec at 20m (Hiscock, 1983, 1985). Flustra foliacea is a common member of the flotsam, having been removed from its substratum by storms. Colonies on unstable substrata or subject to extreme wave exposure and storms are likely to be more intolerant. An increase in wave action from exposed to extremely exposed, or storms (especially in more wave sheltered environments or shallow water populations) are likely to remove a proportion of the population. Therefore, Flustra foliacea is probably of intermediate intolerance to increases in wave action. Recoverability is likely to be high (see additional information below).

Decrease in wave exposure

A change of two ranks on the wave exposure scale (view glossary) e.g., from Exposed to Extremely exposed for a period of one year. Further details

Evidence

Flustra foliacea occurs from very wave exposed to sheltered waters. In wave sheltered habitats water flow rates are probably more important than wave action in determining the occurrence and abundance of Flustra foliacea. Water movement (wave or water flow induced) is important for suspension feeding invertebrates such as Flustra foliacea, to prevent siltation and provide adequate food supplies, oxygenation, nutrients and remove waste products. A decrease in wave action to very sheltered or ultra sheltered, in the absence of adequate water flow, may decrease water movement, leading to an increase in fine sediments, loss of suitable substratum and a reduction in food supply and oxygenation. Predation and competition from space occupying species such as hydroids, and macroalgae are likely to increase.
In very wave exposed sites, however, a decrease in wave exposure may be beneficial by reducing the populations vulnerability to storm damage (see above).

Overall, Flustra foliacea populations are most abundant in areas of high water movement (e.g. Menai Straits), and a decrease in wave action, in the absence of tidal flow or currents, is likely to result in a reduction of the abundance of Flustra foliacea. Therefore, an intolerance of intermediate has been recorded. Recoverability has been assessed as high (see additional information below).

Noise

1. Underwater noise levels e.g., the regular passing of a 30-metre trawler at 100 metres or a working cutter-suction transfer dredge at 100 metres for one month during important feeding or breeding periods.
2. Atmospheric noise levels e.g., the regular passing of a Boeing 737 passenger jet 300 metres overhead for one month during important feeding or breeding periods. Further details

Evidence

Bryozoa probably react to local vibrations, that may herald the attach of predators, interrupting feeding. But they are unlikely to be aware of noise at the benchmark level.

Visual presence

Benchmark. The continuous presence for one month of moving objects not naturally found in the marine environment (e.g., boats, machinery, and humans) within the visual envelope of the species or community under consideration. Further details

Evidence

Bryozoa probably react to very local shading effects, interrupting feeding. But their visual acuity is probably extremely poor, and they are unlikely to be affected by visual disturbance.

Abrasion & physical disturbance

Benchmark. Force equivalent to a standard scallop dredge landing on or being dragged across the organism. A single event is assumed for assessment. This factor includes mechanical interference, crushing, physical blows against, or rubbing and erosion of the organism or habitat of interest. Where trampling is relevant, the evidence and trampling intensity will be reported in the rationale. Further details.

Evidence

Flustra foliacea is tolerant of sediment abrasion (see smothering and suspended sediment above) but physical disturbance by fishing gear has been shown to adversely affect emergent epifaunal communities. For example, emergent epifauna were indicative of scallop dredge damage on Modiolus modiolus beds (see species review), and 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).
Although, Flustra foliacea is flexible physical disturbance by a passing scallop dredge (see benchmark) is likely to damage fronds and remove some colonies, suggesting an intolerance of intermediate. Colonies on hard substrata are probably less vulnerable to fishing activity but would probably be damaged or partially removed. Colonies growing on rocks, cobbles and shells on coarse grounds, may be removed by a scallop dredge (see substratum loss above) and therefore, be highly intolerant. Recovery will depend on local recruitment from surviving colonies (depending on where the nearest undamaged colonies are situated) and a recoverability of high has been recorded (see additional information below).

Displacement

Benchmark. Removal of the organism from the substratum and displacement from its original position onto a suitable substratum. A single event is assumed for assessment. Further details

Evidence

Colonies of Flustra foliacea that are displaced while attached to their substratum, e.g. shell debris or rocks will probably survive if moved to a suitable habitat and not crushed in the process. But if removed from its substratum, Flustra foliacea colonies cannot reattach and will probably be washed to deep water or be deposited on the strand line and die. Therefore, an intolerance of high has been recorded, with a recoverability of high (see additional information below).

Synthetic compound contamination

Sensitivity is assessed against the available evidence for the effects of contaminants on the species (or closely related species at low confidence) or community of interest. For example:

• evidence of mass mortality of a population of the species or community of interest (either short or long term) in response to a contaminant will be ranked as high sensitivity;
• evidence of reduced abundance, or extent of a population of the species or community of interest (either short or long term) in response to a contaminant will be ranked as intermediate sensitivity;
• evidence of sub-lethal effects or reduced reproductive potential of a population of the species or community of interest will be assessed as low sensitivity.

The evidence used is stated in the rationale. Where the assessment can be based on a known activity then this is stated. The tolerance to contaminants of species of interest will be included in the rationale when available; together with relevant supporting material. Further details.

Evidence

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). Bryan & Gibbs (1991) reported that there was little evidence regarding TBT toxicity in bryozoa with the exception of the encrusting Schizoporella errata, which suffered 50% mortality when exposed for 63 days to 100ng/l TBT. Rees et al. (2001) reported that the abundance of epifauna (including bryozoans) had increased in the Crouch estuary in the five years since TBT was banned from use on small vessels. This last report suggests that bryozoans may be at least inhibited by the presence of TBT. 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.
Therefore, an intolerance of high has been recorded. A recoverability of high has been recorded (see additional information).

Heavy metal contamination

Evidence

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, 1977; Holt et al., 1995). Bryozoans were shown to bioaccumulate heavy metals to a certain extent (Holt et al., 1995). For example, Bowerbankia gracialis and Nolella pusilla accumulated Cd, exhibiting sublethal effects (reduced sexual reproduction and inhibited resting spore formation) between 10-100 µg Cd /l and fatality above 500 µg Cd/l (Kayser, 1990). However, given the tolerance of bryozoans to copper based anti-fouling treatments, as assuming similar physiology between species, an intolerance of low has been recorded albeit with very low confidence.

Hydrocarbon contamination

Evidence

Little information on the effects of hydrocarbons on bryozoans was found. Flustra foliacea is likely to be protected from the direct effects of oil spills by its subtidal habit but may be exposed to water soluble fractions of oils, PAHs or oil adsorbed onto particulates. In addition, Ryland & Putron (1998) did not detect adverse effects of oil contamination on the bryozoan Alcyonidium spp. in Milford Haven or St. Catherine's Island, south Pembrokeshire although it did alter the breeding period. However, it is difficult to extrapolate between species, and no assessment has been made.

Radionuclide contamination

Evidence

Insufficient
information

Changes in nutrient levels

Evidence

A moderate increase in nutrient levels may increase the food available to Flustra foliacea, either in the form of phytoplankton or detritus. However, no effects of nutrients enrichment on bryozoans were found.

Increase in salinity

1. A short-term, acute change; e.g., a change of two categories from the MNCR salinity scale for one week (view glossary) such as from full to reduced.
2. A long-term, chronic change; e.g., a change of one category from the MNCR salinity scale for one year (view glossary) such as from reduced to low. Further details.

Evidence

Flustra foliacea is unlikely to encounter hypersaline conditions in current swept, subtidal habitats.

Decrease in salinity

1. A short-term, acute change; e.g., a change of two categories from the MNCR salinity scale for one week (view glossary) such as from full to reduced.
2. A long-term, chronic change; e.g., a change of one category from the MNCR salinity scale for one year (view glossary) such as from reduced to low. Further details.

Evidence

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. Similarly, Dyrynda (1994) noted that Flustra foliacea and Alcyonidium diaphanum were probably restricted to the vicinity of the Poole Harbour entrance by their intolerance to reduced salinity. Although, protected from extreme changes in salinity due to their subtidal habitat, the introduction of freshwater, or hyposaline effluents may adversely affect Flustra foliacea colonies. Therefore, an intolerance of high has been recorded, and recoverability assessed as high (see additional information below).

Changes in oxygenation

Benchmark.  Exposure to a dissolved oxygen concentration of 2 mg/l for one week. Further details.

Evidence

No information on the tolerance of Flustra foliacea to changes in oxygenation was found.

Introduction of microbial pathogens/parasites

Benchmark. Sensitivity can only be assessed relative to a known, named disease, likely to cause partial loss of a species population or community. Further details.

Evidence

No information on diseases was found. Stebbing (1971a) reported that encrusting epizoites reduced the growth rate of Flustra foliacea by ca 50% and Stebbing (1971b) described the epizoic fauna of hornwrack in detail. The bryozoan Bugulina 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

Sensitivity assessed against the likely effect of the introduction of alien or non-native species in Britain or Ireland. Further details.

Evidence

No information found.

Extraction of this species

Benchmark. Extraction removes 50% of the species or community from the area under consideration. Sensitivity will be assessed as 'intermediate'. The habitat remains intact or recovers rapidly. Any effects of the extraction process on the habitat itself are addressed under other factors, e.g. displacement, abrasion and physical disturbance, and substratum loss. Further details.

Evidence

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; Lysek et al., 2002; Peters et al., 2003). Therefore, Flustra foliacea may be subject to harvesting in the future.

Extraction of other species

Benchmark. A species that is a required host or prey for the species under consideration (and assuming that no alternative host exists) or a keystone species in a biotope is removed. Any effects of the extraction process on the habitat itself are addressed under other factors, e.g. displacement, abrasion and physical disturbance, and substratum loss. Further details.

Evidence

Flustra foliacea may occur on coarse grounds used for fishing of other marine species, e.g. scallops. Mobile fishing gear, such as scallop dredges and beam trawls result in physical disturbance to the sediment surface. Emergent epifauna have been shown to be particularly intolerant of physical disturbance, depending on intensity (see abrasion) and emergent fauna, together with shells, and rocks form part of by-catch. Therefore, an intolerance of high and a recoverably of high have been recorded (see additional information below).