The Marine Life Information Network

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 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.

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.

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.

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.

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.

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

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.

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.

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.

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.

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).

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.

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.

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.

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

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

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.

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.

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.

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

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.

No information has been found.

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.

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.

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.

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).

No information has been found of effects of any microbial pathogens.

No non-native species currently present in Britain and Ireland are known to have any impact on populations of Metridium senile.

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

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.