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

Adult Metridium senile live attached to the substratum and will be removed with it. Re-colonization is likely to be rapid and occur within two or three years, although full recovery of dominance may take in excess of five years (see additional information below). Larvae of Metridium dianthus settle readily from the plankton and are known to colonize new structures such as wrecks and jetty piles within two to three years (K. Hiscock, own observations). The growth rate is rapid and a large size is reached in well-fed individuals within about nine months (see Bucklin, 1985). It is also possible that migration might occur from nearby adult populations as is believed to occur in re-colonizing previously de-oxygenated areas (Wahl, 1985). Therefore an intolerance of high and a recoverability of high has been recorded.

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

Smothering by sediment is unlikely to occur as the anemone can expand above a layer of silt. Smothering by more impervious material is likely to result in anoxia and Metridium senile is very tolerant of deoxygenated conditions (Wahl, 1884). However, smothering may result in the anemone withdrawing its tentacles and shrinking or expending energy to rise above the sediment so that an intolerance of low is appropriate.

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

Metridium senile can produce mucus to clear itself of silt. The production of mucus may have an energetic consequence and an intolerance of low is 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

Metridium senile does not rely on silt for feeding and may benefit by not having to produce mucus to slough off silt. However, a decrease in siltation may result in decreased turbidity but see 'turbidity' for effects.

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

Metridium senile does not generally occur in the intertidal although may be present under piers and under overhangs, i.e. in shaded locations. They can produce mucus which would provide some protection from desiccation but, on the open shore, are most likely vulnerable and would be adversely affected. At least some may be killed following a one-hour exposure to sunshine whilst, in the case of a longer-term alteration in tidal level (see increase in emergence) migration is likely. An intolerance of intermediate is suggested but with a low confidence. For recoverability, see additional information below.

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

Metridium senile does not generally occur in the intertidal but may be present under piers and under overhangs, i.e. in shaded locations. In the case of an increase in emergence, migration is likely. Metridium senile is capable of detaching and floating away when conditions become undesirable. For instance, Wahl (1984, 1985) noted that in anoxic conditions, anemones detached from the substratum and drifted away. Although individual anemones are therefore unlikely to be killed by an increase in emergence, they will be lost from a particular location and therefore intolerance is described as high. For recoverability, see additional information below.

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

Metridium senile is predominantly a subtidal species and therefore decrease in emergence would provide new habitats for it to settle in.

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

Metridium senile is a passive suspension feeder relying on water currents to bring food. Hiscock (1983) describes the reaction of Metridium dianthus to increasing flow rate (to 90 cm/s) in a flume. The anemones were stimulated to expand tentacles as flow increased and only withdrew them at flow rates in excess of 70 cm/s. They were not swept away. Whilst large Metridium senile thrive in tidal narrows where surface velocity may be in the region of 3-5 knots, they do not appear to occur in very strong tidal flows (exceeding 5 knots) such as in the Gulf of Corryvreckan or Strangford Lough Narrows. An increase in water flow rate to about 5 knots is therefore likely to favour settlement and growth of Metridium senile especially because of increased food supply whilst above 5 knots, adverse effects including the inability to feed and possible displacement occur. As the benchmark is for an increase from moderately strong to very strong (>6 knots) water flow, adverse effects may occur and an intolerance assessment of intermediate is suggested to reflect the possible loss of some individuals.

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

Metridium senile is a passive suspension feeder relying on water currents to bring food. A decrease in water flow rate is likely to significantly reduce opportunities for feeding and the growth rate and expansion of populations by basal laceration may be reduced. Established individuals are likely to survive for the period of decreased flow prescribed in the benchmark and therefore an intolerance of low is suggested. However, in the long-term, the population is likely to decline through predation and detachment and not be replaced so that an intolerance, in that situation, of intermediate or high would be appropriate. For recoverability, see additional information.

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

Metridium senile occurs in the Bay of Biscay south of Britain but also in the Adriatic (Manual, 1988) suggesting that it would be tolerant of long-term increases in temperature in Britain and Ireland. No evidence has been found of adverse effects of short-term temperature increase on anemones occurring, for instance, adjacent to thermal effluents. Therefore an assessment of tolerant is made but with low confidence.

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

Metridium senile occurs in much colder waters than those surrounding Britain and Ireland. Crisp (1964) records (but from only one location) that the anemone was unaffected by the cold winter of 1962-63.

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

Metridium senile may benefit from increase in turbidity as algal growth on hard substrata will be reduced. For instance, Svane & Groendahl (1988) found that, in comparison with records from 1926-29, Metridium senile had colonized areas in the Gullmar Fjord where it had not been recorded and ascribed the reason to a possible increase in turbidity (and tolerance of pollution).

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

Metridium senile may be adversely affected by a decrease in turbidity as algal growth on hard substrata will be increased. Svane & Groendahl (1988) found that, in comparison with records from 1926-29, Metridium senile had colonized areas in the Gullmar Fjord where it had not been recorded and ascribed the reason to a possible increase in turbidity (and tolerance of pollution). However, evidence for an adverse effect on Metridium senile due to a decrease in turbidity is poor and, although an intolerance of intermediate is assigned, confidence is very low. For recoverability, see additional information below.

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

Metridium senile occurs in greatest abundance in the most wave sheltered situations (but usually with significant tidal flow) and in the most extremely wave exposed conditions where populations are of small individuals in shallow surge situations. The likely impact of increased wave exposure on the large individuals that typically occur in wave sheltered situations is especially considered here. Those wave sheltered situations may, from time to time, be subject to strong wave action when winds blow from a direction that is not prevailing. For instance, on the open east coast of Lundy, Metridium senile occurs on shallow jetty piles and on a wreck at 15 m depth where they persist despite occasional strong wave action during easterly winds. It seems most likely that individuals close and shrink down during strong wave action but survive. Metridium senile is strongly adherent and when closed probably produces little resistance to water flow. Therefore, the impact will be of decreased feeding opportunities and perhaps loss of condition but recovery will be rapid. For situations where wave exposure increases in already wave exposed situations, it might be that abundance of Metridium senile will increase. Bucklin (1987b) found that the small size of intertidal populations was imposed, most likely, by limited food and feeding time and damage from wave action, which stimulates fragmentation. Their reaction to strong wave action seems to be to increase in numbers but remain small.

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

Metridium senile occurs in greatest abundance in the most wave sheltered (but usually with significant tidal flow) situations. Therefore, a decrease in wave exposure may favour colonization by the anemone. However, decreased wave exposure at the sort of extremely exposed locations where populations of small individuals occur may adversely affect the survival of those populations. For the purpose of this review, the most widespread occurrence of Metridium senile (in sheltered locations) is applied and where a decrease in wave exposure might be favourable.

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

Metridium senile is likely to have poor ability for detection of noise vibrations and as such is unlikely to be sensitive to noise.

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

Metridium senile has very limited, if any, ability for visual perception. The anemone is unlikely to be sensitive to visual presence.

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

The anemone is soft, flexible and can reform its attachment to the substratum. Physical impact is likely to cause damage and mortality to exposed individuals but, because the species habitually reproduces by basal laceration, it seems likely that torn individuals will re-grow. Although some individuals will be displaced or killed, at the level of the benchmark, effects will be intermediate and recovery likely to be very high. In more extensive events of physical disturbance, intolerance is likely to be more similar to substratum removal.

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

Wahl (1984) observed that anemones detached from the substratum during the first week of deoxygenation in the Inner Flensburg Fjord and may drift away eventually to resettle. Metridium senile therefore seems able to survive displacement from the substratum but, presumably, may be damaged during the displacement in which case some repair may be needed.

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

Mercier et al. (1998) exposed Metridium senile to tributyltin contamination in surrounding water and in contaminated food. The species produced mucus 48 hours after exposure to contaminated seawater. TBT was metabolized but accumulated lower levels of butyltins leading the authors to suggest that they seemed vulnerable to TBT contamination. However, Mercier et al. (1998) do not indicate any mortality and, since Metridium senile is a major component of jetty pile communities immediately adjacent to large vessels coated with TBT antifouling paints, intolerance is assessed as low specifically to TBT.

Heavy metal contamination

Evidence

No information has been found of accumulation or effects of heavy metals on Metridium senile.

Hydrocarbon contamination

Evidence

Metridium senile is a major component of jetty pile communities immediately adjacent to areas subject, in previous times, to the discharge of oily ballast and also, in Milford Haven, to a refinery effluent containing hydrocarbons (K. Hiscock, own observations). The anemone is able to produce mucus as a protective mechanism should oil settle onto individuals. No records have been found of any mortality of Metridium senile during oil spills or of any experimental studies of effects. Therefore, although an intolerance of low is indicated, it is with low confidence.

Radionuclide contamination

Evidence

No information has been found.

Changes in nutrient levels

Evidence

Metridium senile may benefit from an increase in nutrients. For instance, Svane & Groendahl (1988) found that, in comparison with records from 1926-29, Metridium senile had colonized areas in the Gullmar Fjord where it had not been recorded and ascribed the reason to possible tolerance of pollution from a pulp mill (and increase in turbidity). Therefore tolerant* is indicated.

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

The species occurs in full salinity but seems to thrive in variable salinity conditions (for instance in tidal narrows at the entrance to estuaries and on jetty piles in enclosed areas). It might be that higher salinity conditions would reduce its competitiveness and an intolerance of 'low' is suggested.

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

Although Metridium senile is predominantly marine, the species does penetrate into estuaries. Braber & Borghouts (1977) found that Metridium senile occurred in about 10 ppt Chlorinity (about 19 psu) in the Delta Region of the Netherlands suggesting that it would be tolerant of reduced salinity conditions. Shumway (1978) found that, during exposure to 50% seawater, animals retracted their tentacles whilst animals exposed to fluctuating salinity, contracted their body wall and produced copious mucus. Therefore, the species seems to have a high tolerance to reduction in salinity but may have to retract tentacles, suffer reduced opportunity to feed and expend energy to produce mucus. Intolerance has therefore been assessed as low suggesting that individuals are unlikely to be killed by changes at the level of the benchmark. Recovery is in terms of condition and is therefore very high.

Changes in oxygenation

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

Evidence

Wahl (1984, 1985) noted that the LC₅₀ value for Metridium senile in anoxic conditions is about three weeks and that none survive beyond six weeks. He observed that anemones detached from the substratum during the first week of deoxygenation in the Inner Flensburg Fjord and may drift away. When oxygen is lacking, Metridium senile diminishes the body surface area. At the level of the benchmark, Metridium senile is not sensitive and even in extreme conditions seems able to survive for some time and then detach. Although, at the benchmark level, recoverability is 'Not Relevant', it seems that re-colonization can be very rapid from nearby individuals. However, following a severe effect, it might take several years for re-colonization to the previous cover to occur (see additional information below).

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 has been found of effects of any microbial pathogens.

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 non-native species currently present in Britain and Ireland are known to have any impact on populations of Metridium senile.

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

If the species were to be extracted, mortality would occur. For recoverability, see additional information below.

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

Metridium senile sometimes occur, as small individuals, on kelp (Laminaria hyperborea) stipes. Kelp is extracted in some countries. Where attached individuals are collected, demise is certain. For recoverability, see additional information below.