Cylista undata and Ascidiella aspersa on infralittoral sandy mud

Summary

UK and Ireland classification

Description

Sheltered sublittoral mud or sandy mud in shallow water with relatively few conspicuous species may be characterised by the anemone Cylista undata in low numbers and the tunicate Ascidiella aspersa. Other taxa may include Carcinus maenasPagurus bernhardus and terebellid polychaetes. The burrowing anemones Cerianthus lloydii may also be found occasionally. The status of this biotope is uncertain at present as it is not known whether it is an impoverished, disturbed or epifaunal variant of other sheltered, shallow mud biotopes such as SS.SMu.IFiMu.PhiVir or if the areas in which it has been recorded have been incompletely surveyed. (Information from JNCC, 2022). 

Depth range

0-5 m, 5-10 m, 10-20 m

Additional information

-

Listed By

Sensitivity reviewHow is sensitivity assessed?

Sensitivity characteristics of the habitat and relevant characteristic species

SS.SMu.ISaMu.SundAasp occurs in sheltered sublittoral mud or sandy mud in shallow water with relatively few conspicuous species.  It is characterized by the anemone Cylista undata in low numbers and the ascidian Ascidiella aspersa.  Other burrowing anemones including Cerianthus lloydii may also be found. Very little information for the characterizing species was found and the assessments are quite general.  Where there was little or no evidence for the characterizing Cylista undata, the assessment was based on similar species, including Cerianthus lloydii. Assessments for the ascidians used evidence for the characterizing Ascidiella aspersa  where possible, and Ciona intesinalis as an example of a large ascidian.  Low confidence scores are ascribed to sensitivity assessments that rely on evidence from these non-chaarcterizing  species. Other species are not important in defining the biotope and are therefore not considered.

Resilience and recovery rates of habitat

Ascidiella aspersa grows to ca 10 cm in height and is usually found in clumps on muddy seabed (Naylor, 2011), although it has also been recorded on algae, stones and artificial substrata.  It is common on all British coasts and is distributed from Norway to the Mediterranean (Hayward & Ryland (1995a).  Ascidiella aspersa is found from the lower shore to 80 m depth and is tolerant of salinities down to 18‰.  In Scotland, larvae settle during summer, with reproduction taking place in the summer following settlement.  Longevity in the British Isles is one to one and a half years (Fish & Fish, 1996).  Ascidiella aspersa is considered an invasive species in the Americas and Asia (Carman et al., 2010; Tatián et al., 2010; Nishikawa et al., 2014).Ciona intestinalis has been reported to spawn more or less year round in temperate conditions  (Yamaguchi, 1975, Caputi et al., 2015, MBA, 1957) with seasonal spawning observed in colder climates from May to June on the Canadian coast (Carver et al., 2006) and in shallower habitats in Sweden (Svane & Havenhand, 1993).  Oviparous solitary ascidians generally spawn both oocytes and sperm into the water column, where the resultant fertilized eggs develop into free swimming, non-feeding larvae.   The eggs are negatively buoyant and slightly adhesive and are either released freely or in mucus strings which are especially adhesive.  These strings have a tendency to settle close to or on the parent ascidian.  In vitro studies conclude that fertilization proceeds normally whether in the water column or attached to the mucus string.  The hatched free-swimming larvae settle nearby, are held by the mucus string until settlement or escape as plankton.  Retention in the mucus string may explain the dense aggregations of adults found (Svane & Havenhand, 1993).  In vitro studies indicate that both spawning and settlement are controlled by light, however Ciona intestinalis in vivo has been observed to spawn and settle at any time of the day (Wittingham, 1967; Svane & Havenhand, 1993 and references therein).  In the Mediterranean, population collapses of Ciona intestinalis were observed, followed by recovery within 1-2 years (Caputi et al., 2015).  The collapses are still poorly understood, although low salinity (Pérès, 1943) and temperature (Sabbadin, 1957) are suggested as possible drivers.  Sebens (1985; 1986) described the recolonization of epifauna on vertical rock walls.  Rapid colonizers such as encrusting corallines, encrusting bryozoans, amphipods and tubeworms recolonized within 1-4 months, but ascidians such as Dendrodoa carnea, Molgula manhattensis and Aplidium spp. achieved significant cover in less than a year and had reached pre-clearance levels of cover after 2 years. A few individuals of Alcyonium digitatum and Metridium senile colonized within four years (Sebens, 1986) and would probably take longer to reach pre-clearance levels (Sebens, 1985;1986).

Little evidence was found to support a resilience assessment for burrowing anemones.  MES (2010) suggested that the genus Cerianthus would be likely to have a low recovery rate following physical disturbance based on long lifespan and slow growth rate.  No specific evidence was cited to support this conclusion.  The MES (2010) review also highlighted that there were gaps in information for this species and that age at sexual maturity and fecundity is unknown although the larvae are pelagic (MES 2010). 

Eggs of Edwardsia timida were observed in a gelatinous matrix at the entrance to a burrow which hatched into ciliated planula larvae and completed development into young anemones within two months (Rawlinson, 1936, cited in Manuel, 1988) although no specific information on longevity, maturity, fecundity or recovery was found for the characterizing Cylista undata.  While burrowing anemones are capable of re-burrowing following disturbance (Manuel, 1988), it is likely that they have limited horizontal mobility and re-colonization via adults is unlikely (Tillin & Tyler-Walters, 2014).  Zostera beds have historically provided suitable substrata for burrowing anemones, however, despite some recovery of eel grass following the mass decline in the 1930s, burrowing anemones have not reappeared in many localities (Manuel, 1988).  There is very little known about community development for this biotope. Almost nothing is known about the life cycle and population dynamics of British burrowing anemones. However, anemones tend to be slow growing, long lived and may have patchy and intermittent recruitment. Sebens (1981) noted that full recovery of anemones may take five years to several decades. 

More generally, anemones may be able to recruit more rapidly in certain circumstances.  Colonization of offshore oil platforms in the North Sea by the anemone Metridium senile during year 3, and had extended down to a depth of 90 m by year 4. Over the following 5 years the anemone zone ascended to a depth of 40 m, out-competing both hydroids and soft corals (Whomersley & Picken, 2003).

Resilience assessment

The ascidians are likely to recover rapidly following decline, Ascidiella aspersa is considered an INIS (invasive non-indigenous species) in the Americas and Asia. Recovery is likely to be rapid folliwng most perturbation events. 

Spawning has been reported as more or less year round in temperate conditions for Ciona intestinalis (Yamaguchi, 1975, Caputi et al., 2015; MBA, 1957).  Ciona intestinalis reaches sexual maturity at a body height of ca 2.5-3.0 cm, with one to two generations per year and longevity of ca 1.5 years.  (Fish & Fish 1996).  Sebens (1985, 1986) found that ascidians such as Dendrodoa carnea, Molgula manhattensis and Aplidium spp. achieved significant cover in less than a year and reached pre-clearance levels of cover after 2 years.

Based on the lack of reappearance of burrowing anemones in some Zostera beds following total loss (Manuel, 1988) and recruitment in other anemones (Sebens, 1981), resilience has been assessed ‘Low’ for events that result in decline of >75 % (resistance of ‘None’).  Resilience has been assessed as ‘Medium’ (2 – 10 years) for other resistance levels in which decline occurs (where resistance is ‘Low’, ‘Medium’). Confidence in this assessment is low, due to the lack of direct evidence for the characterizing species. Resistance assessments of ‘High’ are automatically ascribed a resilience of ‘High’.

Hydrological Pressures

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ResistanceResilienceSensitivity
Temperature increase (local) [Show more]

Temperature increase (local)

Benchmark. A 5°C increase in temperature for one month, or 2°C for one year. Further detail

Evidence

Ascidiella aspersa is common on all British coasts and is distributed from Norway to the Mediterranean (Hayward & Ryland, 1995b).  Cylista undata is found on all coasts of the British Isles and is distributed from Scandinavia to the Mediterranean (Hayward & Ryland, 1995b).

Both characterizing species are found across the British Isles and are not at their southern distribution limit.  Resistance is, therefore, probably ‘High’ and resilience is assessed as ‘High’ and the biotope is probablly ‘Not sensitive’ at the benchmark level.

High
Low
NR
NR
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High
High
High
High
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Not sensitive
Low
Low
Low
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Temperature decrease (local) [Show more]

Temperature decrease (local)

Benchmark. A 5°C decrease in temperature for one month, or 2°C for one year. Further detail

Evidence

Ascidiella aspersa is common on all British coasts and is distributed from Norway to the Mediterranean (Hayward & Ryland, 1995b).  Cylista undata is found on all coasts of the British Isles and is distributed from Scandinavia to the Mediterranean (Hayward & Ryland, 1995b).  Both characterizing species are found across the British Isles and are not at their northern distribution limit.  Resistance is, therefore, probably ‘High’ and resilience is assessed as ‘High’ and the biotope is probablly ‘Not sensitive’ at the benchmark level.

High
Low
NR
NR
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High
High
High
High
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Not sensitive
Low
Low
Low
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Salinity increase (local) [Show more]

Salinity increase (local)

Benchmark. A increase in one MNCR salinity category above the usual range of the biotope or habitat. Further detail

Evidence

The biotope is recorded from full to variable salinity. An increase from full salinity would result in hypersaline conditions.  Naser (2011) described habitats dominated by the burrowing anemone Cerianthus sp. in the areas adjacent to the outlet of the Sitra Power and Water Station, Bahrain.  This desalination outlet is associated with high temperatures, salinities, and a range of chemical and heavy metal pollutants.  Cylista undata has been recorded as occurring in variable to full salinity biotopes (Connor et al., 2004).

No information on Ascidiella aspersa was found. Ciona intestinalis has been classified as euryhaline with a high salinity tolerance range (12-40‰) although it typically occurs in full salinity conditions (>30 ‰) (Tillin & Tyler-Walters, 2014).  Ciona intestinalis has been found in salinities ranging from 11 to 33 psu in Sweden, although the same study found that parent acclimation to salinity (high or low) has an overriding and significant effect on larval metamorphic success, independent of parent origins (Renborg et al., 2014).

Whilst some burrowing anemones have been associated with areas that experience high salinity due to brine effluent from desalination plants, there are is little specie specific information and ‘No evidence’ was found for the characterizing species.

No evidence (NEv)
NR
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Not relevant (NR)
NR
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No evidence (NEv)
NR
NR
NR
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Salinity decrease (local) [Show more]

Salinity decrease (local)

Benchmark. A decrease in one MNCR salinity category above the usual range of the biotope or habitat. Further detail

Evidence

Components of the biotope community are tolerant of variable salinities. Ascidiella aspersa is tolerant of salinities down to 18 psu (ca 18 ‰) and is often common in estuaries, whilst Ciona intestinalis is tolerant of salinities as low as 11 psu (ca 11‰) (Fish & Fish, 1996).  Cylista undata has only been recorded as occurring in variable to full salinity biotopes (Connor et al., 2004).

Sensitivity assessment. A decrease at the benchmark level from variable (18 -35‰) to reduced salinity (18-30‰) is unlikely to result in mortality.  as some of the characterizing species have been recorded in salinities of 18‰ or lower.  Resistance is therefore ‘High’, resilience is ‘High’ and the biotope is probably ‘Not sensitive’ at the benchmark level, although confidence in the assessment is 'Low'.

High
Low
NR
NR
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High
High
High
High
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Not sensitive
Low
Low
Low
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Water flow (tidal current) changes (local) [Show more]

Water flow (tidal current) changes (local)

Benchmark. A change in peak mean spring bed flow velocity of between 0.1 m/s to 0.2 m/s for more than one year. Further detail

Evidence

Increased tidal stream velocity may benefit some passive suspension feeders by increasing the supply of food but may also erode the substratum including removal of species attached to the substratum. The long-lived members of the community, the burrowing anemones, are firmly anchored into the sediment and therefore are unlikely to be lost.   SS.SMu.ISaMu.SundAasp occurs from negligible to moderately strong water flow (0 - 1.5 m/sec). sothat a change of 0.1-0.2 m/s is unlikely to be significant. The burrowing anemones are afforded some protection from the direct effects of water flow, however, prolonged increase in water flow could result in restructuring of the substrata.  However, a decrease in water flow is not relevant as the biotope occurs in very weak flow.

Resistance is, therefore, assessed as ‘High’, resilience as ‘High’ and the biotope is ‘Not sensitive’ at the benchmark level.

High
Low
NR
NR
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High
High
High
High
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Not sensitive
Low
Low
Low
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Emergence regime changes [Show more]

Emergence regime changes

Benchmark.  1) A change in the time covered or not covered by the sea for a period of ≥1 year or 2) an increase in relative sea level or decrease in high water level for ≥1 year. Further detail

Evidence

This biotope can occur at 0-5 m depth.  The burrowing nature of the anemones would probably confer some resistance in the event of one hour of emergence.  The ascidians, however, are limited to the sublittoral.  Exposure to an emergence regime is likely to cause the population to die.  Therefore, resistance is assessed as ‘Low’, resilience as ‘Medium’ and sensitivity as ‘Medium’. 

Low
Low
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Medium
Medium
Medium
Medium
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Medium
Low
Low
Low
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Wave exposure changes (local) [Show more]

Wave exposure changes (local)

Benchmark. A change in near shore significant wave height of >3% but <5% for more than one year. Further detail

Evidence

SS.SMu.ISaMu.SundAasp occurs in wave sheltered to extremely wave sheltered conditions.  Wood (2005) described the characterizing Cylista undata as typically found in sheltered locations.  Ciona intestinalis is often dominant in highly sheltered areas such as harbours (Carver et al., 2006). Decreases in wave exposure are unlikely to have any effect.  High energy wave action can be detrimental to ascidian populations, mainly through physical damage to the sea squirts and through the abrasive action of suspended sediment (Jackson, 2008).  If dislodged, juvenile and adult Ciona intestinalis have a limited capability to re-attach, given calm conditions and prolonged contact with the new substratum (Carver et al., 2006; Jackson 2008; Millar 1971) but increases in wave exposure above moderately exposed are likely to remove a proportion of the population, especially in the shallower examples of the biotope.

Sensitivity assessment. The ascidians and Cylista undata are likely to be damaged by significant increases in wave exposure, particularly in the shallow examples of this biotope. However, a change at the benchmark level is unlikely to result in mortality and resistance is, therefore, ‘High’, resilience is ‘High’ and the biotope is assessed as ‘Not sensitive’.

High
Low
NR
NR
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High
High
High
High
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Not sensitive
Low
Low
Low
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Chemical Pressures

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ResistanceResilienceSensitivity
Transition elements & organo-metal contamination [Show more]

Transition elements & organo-metal contamination

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

No information was found on effects of contaminants on the characterizing burrowing anemone Cylista undata. Therefore, examples of anemone response to contaminants is presented.

Mercier et al. (1998) exposed Metridium senile to tri-butyl tin contamination in surrounding water and in contaminated food. The species produced mucus 48 hours after exposure to contaminated seawater. TBT was metabolised but the species accumulated levels of butyl tins leading the authors to suggest that Metridium senile seemed vulnerable to TBT contamination. However, Mercier et al., (1998) did 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 has been assessed to be low specifically to TBT. No other information has been found on effects of contaminants on other species of the biotopes, so confidence is very low.

Ascidians may be intolerant of synthetic chemicals such as tri-butyl-tin anti-foulants. Rees et al. (2001), working in the Crouch estuary, observed that six ascidian species were recorded at one station in 1997 compared with only two at the same station in 1987, shortly following the banning of TBT in antifouling paints. Also, there was a marked increase in the abundance of ascidians especially Ascidiella aspersa and Ascidia conchilega in the estuary after the ban on TBT was introduced.

However, this pressure is Not assessed but evidence is presented where available.

Not Assessed (NA)
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Not assessed (NA)
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Not assessed (NA)
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Hydrocarbon & PAH contamination [Show more]

Hydrocarbon & PAH contamination

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

This pressure is Not assessed but evidence is presented where available.

No information was found on effects of contaminants on the characterizing burrowing anemone Cylista undata. Therefore, examples of anemone response to contaminants is presented. 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). Ignatiades & Becacos-Kontos (1970) found that Ciona intestinalis can resist oil polluted water and ascidians are frequently found in polluted habitats such as marinas and harbours (Carver et al., 2006; Aneiros et al., 2015).

Not Assessed (NA)
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Not assessed (NA)
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Not assessed (NA)
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Synthetic compound contamination [Show more]

Synthetic compound contamination

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

This pressure is Not assessed. No information was found on effects of contaminants on the characterizing burrowing anemone Cylista undata.

Hoare & Hiscock (1974) reported that the anemone Urticina felina survived near to an acidified halogenated effluent discharge in a 'transition' zone where many other species were unable to survive, suggesting a tolerance to chemical contamination. However, Urticina felina was absent from stations closest to the effluent which were dominated by pollution tolerant species (such as polychaetes). Those specimens closest to the effluent discharge appeared generally unhealthy.

However, this pressure is Not assessed but evidence is presented where available.

Not Assessed (NA)
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Not assessed (NA)
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Not assessed (NA)
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Radionuclide contamination [Show more]

Radionuclide contamination

Benchmark. An increase in 10µGy/h above background levels. Further detail

Evidence

‘No evidence’ was found to support an assessment.

No evidence (NEv)
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Not relevant (NR)
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No evidence (NEv)
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Introduction of other substances [Show more]

Introduction of other substances

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

This pressure is Not assessed.

Not Assessed (NA)
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Not assessed (NA)
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Not assessed (NA)
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De-oxygenation [Show more]

De-oxygenation

Benchmark. Exposure to dissolved oxygen concentration of less than or equal to 2 mg/l for one week (a change from WFD poor status to bad status). Further detail

Evidence

In general, respiration in most marine invertebrates does not appear to be significantly affected until extremely low concentrations are reached. For many benthic invertebrates this concentration is about 2 ml/l (Herreid, 1980; Rosenberg et al., 1991; Diaz & Rosenberg, 1995). Cole et al. (1999) suggest possible adverse effects on marine species below 4 mg/l and probable adverse effects below 2 mg/l.

The ability of solitary ascidians to withstand decreasing oxygen levels has not been well documented. Mazouni et al. (2001) noted that the biofouling community in Thau Lagoon, France (dominated by Ciona intestinali) suffered mortality when exposed to short-term periods of anoxia.  It should be noted, however, that this species is frequently found in areas with restricted water renewal where oxygen concentrations may drop (Carver et al., 2006). While adverse conditions could affect health, feeding, reproductive capability and could eventually lead to mortality, recovery should be rapid. 

The burrowing anemones most likely spend significant periods of time in burrows where water movement is likely to be more restricted. Stachowitsch  & Avcin (1988) reported that in two eutrophication events, anemones where relatively resistant to oxygen depletion.   In the Limfjorden, oxygen concentrations fell to below 1 mg/l in the summer of 1975, with the anemones described as the most resistant group to the event (Jeirgensen, 1980).  Stachowitsch (1984) observed mass mortality in the Gulf of Trieste over two weeks apparently due to oxygen deficiency (although no oxygen concentrations were given).  The majority of species perished within a week, with only several types of anemones and certain infaunal forms surviving into the second week, although Cerianthus sp. died after one week (Stachowitsch  & Avcin, 1988).

Sensitivity assessment.

Both the ascidians and anemones have been reported as being relatively resistant to oxygen depletion (Carver et al., 2006; Stachowitsch  & Avcin, 1988).  However, mortality at the benchmark level cannot be ruled out and resistance is, therefore, ‘Medium’, resilience as ‘Medium’ and sensitivity as ‘Medium’ at the benchmark level.

Medium
Low
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Medium
Medium
Medium
Medium
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Medium
Medium
Low
Medium
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Nutrient enrichment [Show more]

Nutrient enrichment

Benchmark. Compliance with WFD criteria for good status. Further detail

Evidence

There is some suggestion that there are possible benefits to ascidians from increased organic content of water; 'ascidian richness’ in Algeciras Bay was found to increase in higher concentrations of suspended organic matter (Naranjo et al. 1996).  No information was available on the effect of nutrient enrichment on the burrowing anemones. 

However this biotope is considered to be 'Not sensitive' at the pressure benchmark, that assumes compliance with good status as defined by the WFD.

Not relevant (NR)
NR
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Not relevant (NR)
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Not sensitive
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Organic enrichment [Show more]

Organic enrichment

Benchmark. A deposit of 100 gC/m2/yr. Further detail

Evidence

There is some suggestion that there are possible benefits to the ascidians from increased organic content of water; Ascidian ‘richness’ in Algeciras Bay was found to increase in higher concentrations of suspended organic matter (Naranjo et al. 1996).  Kocak & Kucuksezgin (2000) noted that Ciona intestinalis was one of the rapid breeding opportunistic species that tended to be dominant in Turkish harbours enriched by organic pollutants and was frequently found in polluted environments (Carver et al., 2006). Gittenberger & Van Loon (2011) assessed Cylista undata (studied as Sagartiogeton undatus) as Group II (indifferent to enrichment, always present in low densities with non-significant variations with time).  But the basis for their assessment and relation to the pressure benchmark is not clear (Tillin & Tyler-Walters, 2014).

Sensitivity assessment. Both ascidians and Cylista undata may be tolerant of organic enrichment and resistance is, therefore, assessed as ‘High’, but with 'Low' confidence.  Resilience is assessed as ‘High’ and the biotope is assessed as ‘Not sensitive’.

High
Low
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High
High
High
High
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Not sensitive
Low
Low
Low
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Physical Pressures

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ResistanceResilienceSensitivity
Physical loss (to land or freshwater habitat) [Show more]

Physical loss (to land or freshwater habitat)

Benchmark. A permanent loss of existing saline habitat within the site. Further detail

Evidence

All marine habitats and benthic species are considered to have a resistance of ‘None’ to this pressure and to be unable to recover from a permanent loss of habitat (resilience is ‘Very low’). Sensitivity within the direct spatial footprint of this pressure is therefore ‘High’. Although no specific evidence is described, confidence in this assessment is ‘High’ due to the incontrovertible nature of this pressure.

None
High
High
High
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Very Low
High
High
High
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High
High
High
High
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Physical change (to another seabed type) [Show more]

Physical change (to another seabed type)

Benchmark. Permanent change from sedimentary or soft rock substrata to hard rock or artificial substrata or vice-versa. Further detail

Evidence

If sediment were replaced with rock or artificial substrata, this would represent a fundamental change to the biotope with reclassification necessary. Change from a mixed sediment substrata to rock would also result in loss of the infaunal component. 

Sensitivity assessment

Resistance to the pressure is considered ‘None’, and resilience ‘Very low’. Sensitivity has been assessed as ‘High

None
High
High
High
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Very Low
High
High
High
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High
High
High
High
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Physical change (to another sediment type) [Show more]

Physical change (to another sediment type)

Benchmark. Permanent change in one Folk class (based on UK SeaMap simplified classification). Further detail

Evidence

SS.SMu.ISaMu.SundAasp is characterized as occurring on sandy mud (Connor et al., 2004).  The characterizing species of may tolerate a change in one Folk class (based on the Long, 2006 simplification), as similar species have been noted to inhabit muddy sand and fine shell breccia (see Shäfer, 1972). However, this shift in substrata would necessitate a re-classification of the biotope. Resistance is, therefore, assessed as None based on a change from sandy mud or mud to muddy sand or gravelly mud. As this is a permanent change, resilience is ‘Very low’ and sensitivity is therefore ‘High’.

None
High
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High
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Very Low
High
High
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High
High
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High
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Habitat structure changes - removal of substratum (extraction) [Show more]

Habitat structure changes - removal of substratum (extraction)

Benchmark. The extraction of substratum to 30 cm (where substratum includes sediments and soft rock but excludes hard bedrock). Further detail

Evidence

Sedimentary communities are likely to be highly intolerant of substratum removal, which will lead to partial or complete defaunation, expose underlying sediment which may be anoxic and/or of a different character and lead to changes in the topography of the area (Dernie et al., 2003). Any remaining species, given their new position at the sediment / water interface, may be exposed to unsuitable conditions.

Shäfer (1972) conducted a review of locomotion of the Ceriantharia. The burrowing anemones require open tubes as they breathe with their entire body surface (Shäfer, 1972).  Cylista undata can be found 10-15 cm into the sediment (Manuel, 1988). Extraction of 30cm would probably result in total loss of the burrowing anemones as they would be unlikely to escape rapidly. 

Recovery of the sedimentary habitat would occur via infilling, although some recovery of the biological assemblage may take place before the original topography is restored, if the exposed, underlying sediments are similar to those that were removed. Newell et al. (1998) indicate that local hydrodynamics (currents and wave action) and sediment characteristics (mobility and supply) strongly influence the recovery of soft sediment habitats.

Sensitivity assessment. Extraction of 30 cm of sediment will remove the characterizing biological component of the biotope.  Assuming that the revealed substratum is not altered (in terms of the Folk scale), resistance is assessed as ‘None’ and biotope resilience is assessed as ‘Low’.   Sensitivity is therefore assessed as ‘High’.

None
Medium
Low
Medium
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Low
Medium
Medium
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High
Medium
Low
Medium
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Abrasion / disturbance of the surface of the substratum or seabed [Show more]

Abrasion / disturbance of the surface of the substratum or seabed

Benchmark. Damage to surface features (e.g. species and physical structures within the habitat). Further detail

Evidence

No specific evidence for the characterizing burrowing anemone Cylista undata was found, however it was noted that Cerianthus lloydii is rarely caught by fishing boats since it retreats into the burrow as the trawl net approaches (Grzimek, 1972). While Langton & Robinson (1990) reported a 25-27 % decline in abundance of cerianthids following a marked increase in scallop dredging in the Gulf of Maine, this decrease could be down to penetrative disturbance (see below).

Ascidiella aspersa and Ciona intestinalis are large, emergent, sessile ascidians, and physical disturbance is likely to cause damage with mortality likely.  Emergent epifauna are generally very intolerant of disturbance from fishing gear (Jennings & Kaiser, 1998).  However, studies have shown some ascidians become more abundant following disturbance events (Bradshaw et al., 2000), presumably due to high resilience and a reduction in spatial competition.

Sensitivity assessment 

Given the ability to retract into the sediment, the burrowing anemones would be quite resistant to surface abrasion events.  However, given the sessile, emerged nature of Ascidiella aspersa, damage and mortality following a physical disturbance effect are likely to be significant.  Resistance has been assessed as ‘Low’, resilience as ‘Medium’ and sensitivity as ‘Medium’.

Low
Medium
Medium
Medium
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Medium
Medium
Medium
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Medium
Medium
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Medium
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Penetration or disturbance of the substratum subsurface [Show more]

Penetration or disturbance of the substratum subsurface

Benchmark. Damage to sub-surface features (e.g. species and physical structures within the habitat). Further detail

Evidence

No specific evidence for the characterizing Cylista undata was found, however it was noted that the similar Cerianthus lloydii is rarely caught by fishing boats since it retreats into the burrow as the trawl net approaches (Grzimek, 1972).  Langton & Robinson (1990) reported a 25-27 % decline in abundance of cerianthids following a marked increase in scallop dredging in the Gulf of Maine.  Cylista undata grows to a length of ca 12 cm (Manuel, 1988) and burrows 10-15 cm into the sediment (Manuel, 1988).  The ascidians are epifaunal and disturbance effects are likely to be analogous to the surface abrasion pressure (see above). However, Cylista undata may be more affected.

Sensitivity assessment. Based on monitoring of cerianthid populations exposed to scallop dredging by Langton & Robinson (1990), resistance is likely to be ‘Low’, resilience ‘Medium’ and sensitivity ‘Medium’.

Low
Medium
Medium
Medium
Help
Medium
Medium
Medium
Medium
Help
Medium
Medium
Medium
Medium
Help
Changes in suspended solids (water clarity) [Show more]

Changes in suspended solids (water clarity)

Benchmark. A change in one rank on the WFD (Water Framework Directive) scale e.g. from clear to intermediate for one year. Further detail

Evidence

A significant increase in suspended sediment may have a deleterious effect on the suspension feeding community.  It may clog feeding apparatus, which would result in a reduced ingestion over the benchmark period and, subsequently, a decrease in growth rate (Jackson, 2004).  A decrease in suspended sediment is likely to benefit the community associated with this biotope. The suspension feeders may be able to feed more efficiently due to a reduction in time and energy spent cleaning feeding apparatus.

For examples, Ciona intestinalis frequently occurs in habitats close to harbours and marinas with high levels of silt and suspended matter (Carver et al., 2006; Kocak & Kucuksezgin, 2000). Naranjo et al. (1996) described Ciona intestinalis as having a large body and siphons that have wide apertures that helps prevent blocking. Increased suspended sediment may potentially have some detrimental effects in clogging up feeding filtration mechanisms. However, there are possible benefits from increased suspended sediment as ascidian ‘richness’ in Algeciras Bay was found to increase in higher concentrations of suspended organic matter (Naranjo et al. 1996). In high (up to 300 mg/l of inorganic and 2.5 x107 cells/l) suspended particulate concentrations, the active rejection mechanism (squirting) is increased in Ciona intestinalis with no discrimination between organic and inorganic particulates observed in any of the ascidians observed (Robbins, 1984a).

Despite these observations, the turbidity tolerance level for this species is not well established. Robbins (1985b) found that continual exposure to elevated levels of inorganic particulates (>25 mg/l) arrested the growth rate of Ciona intestinalis and exposure to 600 mg/l resulted in 50% mortality after 12-15 days and 100% mortality after 3 weeks.  It was suggested that because this species can only “squirt” to clear the branchial sac, it may be vulnerable to clogging under heavy sediment loads.  Specific data on the characterizing Ascidiella aspersa was not found. 

No evidence on the effect of a change in suspended solids was found for the burrowing anemones Cylista undata  or Cerianthus lloydii

Sensitivity assessment. Resistance to this pressure is assessed as 'High', but with 'Low' confidence.  Resilience is assessed as 'High' by default and the biotope is probably 'Not Sensitive' at the benchmark level.

High
Low
NR
NR
Help
High
High
High
High
Help
Not sensitive
Low
Low
Low
Help
Smothering and siltation rate changes (light) [Show more]

Smothering and siltation rate changes (light)

Benchmark. ‘Light’ deposition of up to 5 cm of fine material added to the seabed in a single discrete event. Further detail

Evidence

The solitary ascidians considered in this report are permanently attached to the substratum and are active suspension feeders. Ciona intestinalis and Ascidiella aspersa grow up to 15 cm and 10 cm in length respectively (Hayward & Ryland, 1995b; Fish & Fish, 1996).  Smothering with 5 cm of sediment is likely to only affect a small proportion of the population.

Whilst no information for the characterizing Cylista undata was found, cerianthids require open tubes as they breathe with their entire body surface (Schäfer, 1972).  In the event of gradual sedimentation, the burrowing anemone compensates by upward construction of its tube.  In the event of rapid sedimentation resulting in burial, cerianthids abandon their burrow, pushing vertically to the surface of the sediment (Schäfer, 1972).  Cylista undata is up to 12 cm long (Wood, 2005).  It is probable that the majority of the anemones would tolerate the deposition by burrow extension and those unable would likely escape burial by abandoning their burrow. 

Resistance is, therefore, assessed as ‘High’, with ‘High’ resilience, and the biotope is probably ‘Not sensitive’ at the benchamrk level.

High
Low
NR
NR
Help
High
High
High
High
Help
Not sensitive
Low
Low
Low
Help
Smothering and siltation rate changes (heavy) [Show more]

Smothering and siltation rate changes (heavy)

Benchmark. ‘Heavy’ deposition of up to 30 cm of fine material added to the seabed in a single discrete event. Further detail

Evidence

The solitary ascidians considered in this report are permanently attached to the substratum and are active suspension feeders. Ciona intestinalis and Ascidiella aspersa grow up to 15 cm and 10 cm in length respectively (Hayward & Ryland, 1995b; Fish & Fish, 1996).  When considering that his biotope occurs on sandy mud, smothering with 30 cm of sediment would likely result in significant mortality of the population, unless the sediment is rapidly removed.

Whilst no information for the characterizing anemones was found, cerianthids require open tubes as they breathe with their entire body surface (Schäfer, 1972).  In the event of gradual sedimentation, the burrowing anemone compensates by upward construction of its tube.  In the event of rapid sedimentation resulting in burial, cerianthids abandon their burrow, pushing vertically to the surface of the sediment (Schäfer, 1972). 

Cylista undata is up to 12 cm long (Wood, 2005).  Whilst it is unlikely that the characterizing species would be able to extend their burrows in the event of burial by 30 cm in a single event, the majority of anemones would probably escape by abandoning their burrows.  

It should be noted that permanent addition of sediment could result in a change in substrata, and therefore reclassification of the biotope would be necessary,  as SS.SMu.ISaMu.SundAasp occurs in negligible and weak water flow and the sediment might not be removed.

Sensitivity assessment. While a propotion of the burrowing anemones would likely escape a burial event, addition of 30 cm of fine sediment would smother the ascidians.  As SS.SMu.ISaMu.SundAasp can occur in areas that experience negligible water flow, the deposited sediment could be a permanent addition and necessitate a reclassification, given that the biotope is characterized as occurring on ‘sandy mud’.  Assuming that the sediment was removed, resistance is, therefore, assessed as ‘Low’, resilience is ‘Medium’ and sensitivity is ‘Medium’.

Low
Low
NR
NR
Help
Medium
Medium
Medium
Medium
Help
Medium
Low
Low
Low
Help
Litter [Show more]

Litter

Benchmark. The introduction of man-made objects able to cause physical harm (surface, water column, seafloor or strandline). Further detail

Evidence

Not assessed.

Not Assessed (NA)
NR
NR
NR
Help
Not assessed (NA)
NR
NR
NR
Help
Not assessed (NA)
NR
NR
NR
Help
Electromagnetic changes [Show more]

Electromagnetic changes

Benchmark. A local electric field of 1 V/m or a local magnetic field of 10 µT. Further detail

Evidence

‘No evidence’ was found.

No evidence (NEv)
NR
NR
NR
Help
Not relevant (NR)
NR
NR
NR
Help
No evidence (NEv)
NR
NR
NR
Help
Underwater noise changes [Show more]

Underwater noise changes

Benchmark. MSFD indicator levels (SEL or peak SPL) exceeded for 20% of days in a calendar year. Further detail

Evidence

McDonald (2014) studied the effect of generator noise on fouling of four vessels by Ciona intestinalis and found that fouling was highest at locations closest to the generators and lowest furthest away from the generators.  Subsequent in vitro experiments demonstrated that larvae settled much faster in the presence of noise (2 h- 20 h compared with 6 h-26 h for control), underwent metamorphosis more rapidly (between 10 and 20 h compared with ca 22h) and had a markedly increased survival rate to maturity (90-100% compared with 66%).  Other studies also reported that noise emissions from vessels promoted fouling by organisms including ascidians (Stanley et al., 2016).  No evidence for burrowing anemones was found.

Sensitivity assessment. Resistance to this pressure is assessed as 'High' and resilience as 'High'. This biotope is therefore considered to be 'Not sensitive'.  Confidence is assessed as ‘Low’ given the lack of literature for anemones.

High
Low
NR
NR
Help
High
High
High
High
Help
Not sensitive
Low
Low
Low
Help
Introduction of light or shading [Show more]

Introduction of light or shading

Benchmark. A change in incident light via anthropogenic means. Further detail

Evidence

The biotope is recorded in the infra and circalittoral and no algae were included in the recorded species list (Connor et al., 2004).  Whilst an increase in light could stimulate algal colonization, growth ceases for a number of red algae (including Chrondrus crispus)  below ca 1.0 μmol m-2l-1 (ca 50 Lux), and 2 μmol m-2l-1 (ca 100 Lux) for green algae (Leukart & Lüning, 1994) .  A change at the benchmark level (0.1 Lux) is therefore unlikely to be significant.  Resistance to this pressure is assessed as 'High' and resilience as 'High'. This biotope is, therefore, considered to be 'Not sensitive' at the benchmark level.

High
Low
NR
NR
Help
High
High
High
High
Help
Not sensitive
Low
Low
Low
Help
Barrier to species movement [Show more]

Barrier to species movement

Benchmark. A permanent or temporary barrier to species movement over ≥50% of water body width or a 10% change in tidal excursion. Further detail

Evidence

'Not relevant' as barriers and changes in tidal excursion are not relevant to biotopes restricted to open waters.

Not relevant (NR)
NR
NR
NR
Help
Not relevant (NR)
NR
NR
NR
Help
Not relevant (NR)
NR
NR
NR
Help
Death or injury by collision [Show more]

Death or injury by collision

Benchmark. Injury or mortality from collisions of biota with both static or moving structures due to 0.1% of tidal volume on an average tide, passing through an artificial structure. Further detail

Evidence

'Not relevant' to seabed habitats.  NB. Collision by grounding vessels is addressed under ‘surface abrasion’.

Not relevant (NR)
NR
NR
NR
Help
Not relevant (NR)
NR
NR
NR
Help
Not relevant (NR)
NR
NR
NR
Help
Visual disturbance [Show more]

Visual disturbance

Benchmark. The daily duration of transient visual cues exceeds 10% of the period of site occupancy by the feature. Further detail

Evidence

'Not relevant'

Not relevant (NR)
NR
NR
NR
Help
Not relevant (NR)
NR
NR
NR
Help
Not relevant (NR)
NR
NR
NR
Help

Biological Pressures

Use [show more] / [show less] to open/close text displayed

ResistanceResilienceSensitivity
Genetic modification & translocation of indigenous species [Show more]

Genetic modification & translocation of indigenous species

Benchmark. Translocation of indigenous species or the introduction of genetically modified or genetically different populations of indigenous species that may result in changes in the genetic structure of local populations, hybridization, or change in community structure. Further detail

Evidence

‘No evidence’ was found to assess this pressure.

No evidence (NEv)
NR
NR
NR
Help
Not relevant (NR)
NR
NR
NR
Help
No evidence (NEv)
NR
NR
NR
Help
Introduction or spread of invasive non-indigenous species [Show more]

Introduction or spread of invasive non-indigenous species

Benchmark. The introduction of one or more invasive non-indigenous species (INIS). Further detail

Evidence

The American slipper limpet Crepidula fornicata was introduced to the UK and Europe in the 1870s from the Atlantic coasts of North America with imports of the eastern oyster Crassostrea virginica. It was recorded in Liverpool in 1870 and the Essex coast in 1887-1890. It has spread through expansion and introductions along the full extent of the English Channel and into the European mainland (Blanchard, 1997, 2009; Bohn et al., 2012, 2013a, 2013b, 2015; De Montaudouin et al., 2018; Helmer et al., 2019; Hinz et al., 2011; McNeill et al., 2010; Powell-Jennings & Calloway, 2018; Preston et al., 2020; Stiger-Pouvreau & Thouzeau, 2015).

Crepidula fornicata is recorded from shallow, sheltered bays, lagoons and estuaries or the sheltered sides of islands, in variable salinity (18 to 40) although it prefers ca 30 (Tillin et al., 2020). Larvae require hard substrata for settlement. It prefers muddy gravelly, shell-rich, substrata that include gravel, or shells of other Crepidula, or other species e.g., oysters, and mussels. It is highly gregarious and seeks out adult shells for settlement, forming characteristic ‘stacks’ of adults. But it also recorded in a wide variety of habitats including clean sands, artificial substrata, Sabellaria alveolata reefs and areas subject to moderately strong tidal streams (Blanchard, 1997, 2009; Bohn et al., 2012, 2013a, 2013b, 2015; De Montaudouin et al., 2018; Hinz et al., 2011; Powell-Jennings & Calloway, 2018; Preston et al., 2020; Stiger-Pouvreau & Thouzeau, 2015; Tillin et al., 2020). 

High densities of Crepidula fornicata cause ecological impacts on sedimentary habitats. The species can form dense carpets that can smother the seabed in shallow bays, changing and modifying the habitat structure. At high densities, the species physically smothers the sediment, and the resultant build-up of silt, pseudofaeces, and faeces is deposited and trapped within the bed (Tillin et al., 2020, Fitzgerald, 2007, Blanchard, 2009, Stiger-Pouvreau & Thouzeau, 2015). The biodeposition rates of Crepidula are extremely high and once deposited, form an anoxic mud, making the environment suitable for other species, including most infauna (Stiger-Pouvreau & Thouzeau, 2015, Blanchard, 2009). For example, in fine sands, the community is replaced by a reef of slipper limpets, that provide hard substrata for sessile suspension-feeders (e.g., sea squirts, tube worms and fixed shellfish), while mobile carnivorous microfauna occupy species between or within shells, resulting in a homogeneous Crepidula dominated habitat (Blanchard, 2009). Blanchard (2009) suggested the transition occurred and became irreversible at 50% cover of the limpet. De Montaudouin et al. (2018) suggested that homogenization occurred above a threshold of 20-50 Crepidula /m2

Impacts on the structure of benthic communities will depend on the type of habitat that Crepidula colonizes. De Montaudouin & Sauriau (1999) reported that in muddy sediment dominated by deposit-feeders, species richness, abundance and biomass increased in the presence of high densities of Crepidula (ca 562 to 4772 ind./m2), in the Bay of Marennes-Oléron, presumably because the Crepidula bed provided hard substrata in an otherwise sedimentary habitat. In medium sands, Crepidula density was moderate (330-1300 ind./m2) but there was no significant difference between communities in the presence of Crepidula. Intertidal coarse sediment was less suitable for Crepidula with only moderate or low abundances (11 ind./m2) and its presence did not affect the abundance or diversity of macrofauna. However, there was a higher abundance of suspension–feeders and mobile Crustacea in the absence of Crepidula (De Montaudouin & Sauriau, 1999). The presence of Crepidula as an ecosystem engineer has created a range of new niche habitats, reducing biodiversity as it modifies habitats (Fitzgerald, 2007). De Montaudouin et al. (1999) concluded that Crepidula did not influence macroinvertebrate diversity or density significantly under experimental conditions, on fine sands in Arcachon Bay, France. De Montaudouin et al. (2018) noted that the limpet reef increased the species diversity in the bed, but homogenised diversity compared to areas where the limpets were absent. In the Milford Haven Waterway (MHW), the highest densities of Crepidula were found in areas of sediment with hard substrata, e.g., mixed fine sediment with shell or gravel or both (grain sizes 16-256 mm) but, while Crepidula density increased as gravel cover increased in the subtidal, the reverse was found in the intertidal (Bohn et al., 2015). Bohn et al. (2015) suggested that high densities of Crepidula in high-energy environments were possible in the subtidal but not the intertidal, suggesting the availability of this substratum type is beneficial for its establishment. Hinz et al. (2011) reported a substantial increase in the occurrence of Crepidula off the Isle of Wight, between 1958 and 2006, at a depth of ca 60 m, on hard substrata (gravel, cobbles, and boulders), swept by strong tidal streams. Presumably, Crepidula is more tolerant of tidal flow than the oscillatory flow caused by wave action which may be less suitable (Tillin et al., 2020). 

The availability of hard substrata (e.g., gravel) may only restrict initial colonization as higher densities of Crepidula function as substrata for subsequent colonization (Thieltges et al., 2004; Blanchard, 2009). However, Bohn et al. (2015) noted that Crepidula occurred at low density or was absent in areas of homogenous fine sediment and areas dominated by boulders. Bohn et al. (2015) suggested that wave action (exposure) probably prevented the establishment of large numbers of Crepidula in high-energy areas. Blanchard (2009) noted that sandy areas in the Bay of Saint-Mont Michel were not colonized by Crepidula because of surface sand mobility. Thieltges et al. (2003) also noted that storm events removed some clumps of mussels and presumably Crepidula onto tidal flats where they disappeared, which caused their abundance to fluctuate. Similarly, Crepidula was absent from sandy substrata in Swansea Bay but was most abundant in the shelter of the breakwater at the Swansea east site (Powell-Jennings & Calloway, 2018).

Sensitivity assessment. The sediments characterizing this biotope are likely to be too mobile and unsuitable for most of the invasive non-indigenous species currently recorded in the UK. The above evidence suggests that this biotope is unsuitable for the colonization of Crepidula fornicata due to a lack of gravel, shells, or any other hard substrata used for larvae settlement (Tillin et al., 2020), despite the sheltered to very sheltered conditions of the habitat which would be suitable for Crepidula. This biotope may be an impoverished or disturbed version of SS.SMu.IFiMu.PhiVir and if disturbed it may be unsuited for Crepidula. Hence, resistance is assessed as 'High' and resilience as 'High' so that the biotope is assessed as 'Not sensitive', although further evidence is required. 

High
Low
NR
NR
Help
High
High
High
High
Help
Not sensitive
Low
NR
NR
Help
Introduction of microbial pathogens [Show more]

Introduction of microbial pathogens

Benchmark. The introduction of relevant microbial pathogens or metazoan disease vectors to an area where they are currently not present (e.g. Martelia refringens and Bonamia, Avian influenza virus, viral Haemorrhagic Septicaemia virus). Further detail

Evidence

There appears to be little research into ascidian diseases, particularly in the Atlantic.  The parasite Lankesteria ascidiae targets the digestive tubes and can cause ‘long faeces syndrome’ in Ciona intestinalis (although it has also been recorded in other species).  Mortality occurs in severely affected individuals within about a week following first symptoms. (Mita et al., 2012).  No evidence was found on the effect of microbial pathogens on the characterizing burrowing anemones. 

Sensitivity assessment

Whilst there is evidence of disease in Ciona intestinalis, with mortality possible in severe cases, ‘No evidence’ for the characterizing species was found. 

No evidence (NEv)
NR
NR
NR
Help
Not relevant (NR)
NR
NR
NR
Help
No evidence (NEv)
NR
NR
NR
Help
Removal of target species [Show more]

Removal of target species

Benchmark. Removal of species targeted by fishery, shellfishery or harvesting at a commercial or recreational scale. Further detail

Evidence

 None of the characterizing species within this biotope are currently directly targeted in the UK and hence this pressure is considered to be ‘Not relevant’.

Not relevant (NR)
NR
NR
NR
Help
Not relevant (NR)
NR
NR
NR
Help
Not relevant (NR)
NR
NR
NR
Help
Removal of non-target species [Show more]

Removal of non-target species

Benchmark. Removal of features or incidental non-targeted catch (by-catch) through targeted fishery, shellfishery or harvesting at a commercial or recreational scale. Further detail

Evidence

Direct, physical impacts from harvesting are assessed through the abrasion and penetration of the seabed pressures.  The characterizing species within this biotope could be incidentally removed from this biotope as by-catch when other species are being targeted.  The loss of these species and other associated species would decrease species richness and negatively impact on the ecosystem function. Langton & Robinson (1990) reported a 25-27 % decline in abundance of cerianthids following a marked increase in scallop dredging in the Gulf of Maine.  Emergent epifauna are generally very intolerant of disturbance from fishing gear (Jennings & Kaiser, 1998).  However, studies have shown some ascidians become more abundant following disturbance events (Bradshaw et al., 2000), presumably due to high resilience and a reduction in spatial competition.

Sensitivity assessment

Removal of a large percentage of the characterizing species would alter the character of the biotope.  The resistance to removal is ‘Low’ based on the effects of scallop dredging on burrowing anemones. Resilience is assessed as ‘Medium’ and overall sensitivity as ‘Medium’.

Low
Medium
Medium
Medium
Help
Medium
Medium
Medium
Medium
Help
Medium
Medium
Medium
Medium
Help

Bibliography

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  2. Blanchard, M., 2009. Recent expansion of the slipper limpet population (Crepidula fornicata) in the Bay of Mont-Saint-Michel (Western Channel, France). Aquatic Living Resources, 22 (1), 11-19. DOI https://doi.org/10.1051/alr/2009004

  3. Blanchard, M., 1997. Spread of the slipper limpet Crepidula fornicata (L.1758) in Europe. Current state and consequences. Scientia Marina, 61, Supplement 9, 109-118. Available from: http://scimar.icm.csic.es/scimar/index.php/secId/6/IdArt/290/

  4. Bohn, K., Richardson, C. & Jenkins, S., 2012. The invasive gastropod Crepidula fornicata: reproduction and recruitment in the intertidal at its northernmost range in Wales, UK, and implications for its secondary spread. Marine Biology, 159 (9), 2091-2103. DOI https://doi.org/10.1007/s00227-012-1997-3

  5. Bohn, K., Richardson, C.A. & Jenkins, S.R., 2015. The distribution of the invasive non-native gastropod Crepidula fornicata in the Milford Haven Waterway, its northernmost population along the west coast of Britain. Helgoland Marine Research, 69 (4), 313.

  6. Bohn, K., Richardson, C.A. & Jenkins, S.R., 2013b. The importance of larval supply, larval habitat selection and post-settlement mortality in determining intertidal adult abundance of the invasive gastropod Crepidula fornicata. Journal of Experimental Marine Biology and Ecology, 440, 132-140. DOI https://doi.org/10.1016/j.jembe.2012.12.008

  7. Bohn, K., Richardson, C.A. & Jenkins, S.R., 2013a. Larval microhabitat associations of the non-native gastropod Crepidula fornicata and effects on recruitment success in the intertidal zone. Journal of Experimental Marine Biology and Ecology, 448, 289-297. DOI https://doi.org/10.1016/j.jembe.2013.07.020

  8. Bradshaw, C., Veale, L.O., Hill, A.S. & Brand, A.R., 2000. The effects of scallop dredging on gravelly seabed communities. In: Effects of fishing on non-target species and habitats (ed. M.J. Kaiser & de S.J. Groot), pp. 83-104. Oxford: Blackwell Science.

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  11. Carver, C., Mallet, A. & Vercaemer, B., 2006. Biological synopsis of the solitary tunicate Ciona intestinalis. Canadian Manuscript Report of Fisheries and Aquatic Science, No. 2746, v + 55 p. Bedford Institute of Oceanography, Dartmouth, Nova Scotia.

  12. Chauvaud, L., Jean, F., Ragueneau, O. & Thouzeau, G., 2000. Long-term variation of the Bay of Brest ecosystem: benthic-pelagic coupling revisited. Marine Ecology Progress Series, 200, 35-48. DOI https://doi.org/10.3354/meps200035

  13. Cole, S., Codling, I.D., Parr, W. & Zabel, T., 1999. Guidelines for managing water quality impacts within UK European Marine sites. Natura 2000 report prepared for the UK Marine SACs Project. 441 pp., Swindon: Water Research Council on behalf of EN, SNH, CCW, JNCC, SAMS and EHS. [UK Marine SACs Project.]. Available from: http://ukmpa.marinebiodiversity.org/uk_sacs/pdfs/water_quality.pdf

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  16. De Montaudouin, X., Andemard, C. & Labourg, P-J., 1999. Does the slipper limpet (Crepidula fornicata L.) impair oyster growth and zoobenthos diversity ? A revisited hypothesis. Journal of Experimental Marine Biology and Ecology, 235, 105-124.

  17. De Montaudouin, X., Blanchet, H. & Hippert, B., 2018. Relationship between the invasive slipper limpet Crepidula fornicata and benthic megafauna structure and diversity, in Arcachon Bay. Journal of the Marine Biological Association of the United Kingdom, 98 (8), 2017-2028. DOI https://doi.org/10.1017/s0025315417001655

  18. Dernie, K.M., Kaiser, M.J., Richardson, E.A. & Warwick, R.M., 2003. Recovery of soft sediment communities and habitats following physical disturbance. Journal of Experimental Marine Biology and Ecology, 285-286, 415-434.

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  22. Gittenberger, A. & Van Loon, W.M.G.M., 2011. Common marine macrozoobenthos species in the Netherlands, their characteristics and sensitivities to environmental pressures. GiMaRIS Report no 2011.08. DOI: https://doi.org/10.13140/RG.2.1.3135.7521

  23. Grzimek, 1972. Animal Life Encyclopedia Volume1: Lower Animals. Litton World Trade Corporation.

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  26. Helmer, L., Farrell, P., Hendy, I., Harding, S., Robertson, M. & Preston, J., 2019. Active management is required to turn the tide for depleted Ostrea edulis stocks from the effects of overfishing, disease and invasive species. Peerj, 7 (2). DOI https://doi.org/10.7717/peerj.6431

  27. Herreid, C.F., 1980. Hypoxia in invertebrates. Comparative Biochemistry and Physiology Part A: Physiology, 67 (3), 311-320. DOI https://doi.org/10.1016/S0300-9629(80)80002-8

  28. Hinz, H., Capasso, E., Lilley, M., Frost, M. & Jenkins, S.R., 2011. Temporal differences across a bio-geographical boundary reveal slow response of sub-littoral benthos to climate change. Marine Ecology Progress Series, 423, 69-82. DOI https://doi.org/10.3354/meps08963

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Citation

This review can be cited as:

Readman, J.A.J., & Watson, A., 2023. Cylista undata and Ascidiella aspersa on infralittoral sandy mud. In Tyler-Walters H. Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 28-03-2024]. Available from: https://www.marlin.ac.uk/habitat/detail/1119

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