The Marine Life Information Network

Temperature increase (local)

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

Evidence

Cerianthus lloydii adults are locally abundant in many localities on all coasts of the British Isles and in some areas are common on the shore.  This species occurs on all western coasts of Europe from Greenland and Spitzbergen south to Biscay.  Larvae, but not adults, have been recorded from the Mediterranean.  There is no further information available on the temperature tolerance of Cerianthus lloydii.

In a review of the ecology of hydroids, Gili & Hughes, (1995) report that temperature is a critical factor stimulating or preventing reproduction and that most species have an optimal temperature for reproduction.  However, limited evidence for thermal thresholds and thermal ranges were available for the characterizing species recorded in this biotope.  Berrill (1949) reported that growth in Obelia commissularis (syn. dichotoma) was temperature dependant but ceased at 27°C.  Hydranths did not start to develop unless the temperature was less than 20°C and any hydranths under development would complete their development and rapidly regress at ca 25°C. Berrill (1948) reported that Obelia species were absent from a buoy in July and August during excessively high summer temperatures in Booth Bay Harbour, Maine, USA.  Berrill (1948) reported that the abundance of Obelia species and other hydroids fluctuated greatly, disappearing and reappearing as temperatures rose and fell markedly above and below 20°C during this period.  The upwelling of cold water (8-10°C colder than surface water) allowed colonies of Obelia sp. to form in large numbers.  Cantero et al. (2002) describe the presence and year-round fertility of Obelia dichotoma, Kirchenpaureria pinnata, Nemertesia ramosa and Halecium spp.in the Mediterranean, indicating probable tolerance to temperature increases at the benchmark level.

Sensitivity assessment.  At the level of the benchmark, a change in temperature is unlikely to have a negative impact on the biotope. Therefore, both the resistance and resilience are assessed as ‘High’, and sensitivity is assessed as ‘Not sensitive’ at the benchmark level.

Temperature decrease (local)

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

Evidence

Cerianthus lloydii adults are locally abundant in many localities on all coasts of the British Isles and in some areas are common on the shore. This species occurs on all western coasts of Europe from Greenland and Spitzbergen south to Biscay.  No further information is available on the temperature tolerance of Cerianthus lloydii.

Orejas et al. (2012) describe the feeding ecology of Obelia dichotoma in an Arctic environment (Kongsfjorden, Svalbard) which experiences temperatures of 1-5°C (Beszczynska-Möller & Dye, 2013).  Palerud et al. (2004) also describe the presence of Obelia dichotoma, Halecium Halecinum and Nemertesia sp. in Svalbard.  This suggests that the characterizing hydroids are probably tolerant of the lowest temperatures they are likely to encounter in Britain and Ireland of ca 4°C (Beszczynska-Möller & Dye, 2013).  It should be noted that growth rates are reduced at low temperatures.  Berrill (1949) reported that for Obelia, stolons grew, under optimal nutritive conditions, at less than 1 mm in 24 hrs at 10-12°C, 10 mm in 24 hrs at 16-17°C, and as much as 15-20 mm in 24 hrs at 20°C.

Sensitivity assessment. All species assessed are present in northern/boreal habitats and are unlikely to be affected at the benchmark level.  Resistance has been assessed as ‘High’, and resilience as ‘High’.  Therefore, sensitivity has been assessed as ‘Not sensitive’ at the benchmark level.

Salinity increase (local)

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

Evidence

No evidence was found for osmoregulation by Cerianthus lloydii.  Cerianthus lloydii is recorded in biotopes with variable salinity regimes (18-40 psu) such as SS.SMx.CMx.ClloModHo but most records occur in full salinity. Studies on hydroids, in general, have found that prey capture rates may be affected by salinity and temperature (Gili & Hughes, 1995) although no evidence was found for Nemertesia antennina. However, due to the lack of evidence for the characterizing species within this biotope an assessment of ‘No evidence’ has been given. 

Salinity decrease (local)

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

Evidence

No evidence was found for osmoregulation by Cerianthus lloydii.  Cerianthus lloydii is recorded in biotopes with variable salinity regimes (18-40 psu) such as SS.SMx.CMx.ClloModHo but most records occur in full salinity. Due to the lack of evidence for the characterizing species within this biotope an assessment of ‘No evidence’ has been given.

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

Evidence for the effect of changes in water flow on Cerianthus lloydii is unavailable.  This species is recorded from biotopes with a wide range of water flow regimes, from very weak to strong flow (Connor et al., 1997b).  Therefore, it is likely to have a high tolerance to changes in water flow regimes.

The characteristic hydroids are typically found in places of low to moderate water movement, although Hayward & Ryland (1995a) note that the abundant communities occur in narrow straits and headlands that may experience high levels of water flow. Hydroids can bend passively with water flow to reduce drag forces to prevent detachment and enhance feeding (Gili & Hughes, 1995). Hydroid growth form also varies to adapt to prevailing conditions, allowing species to occur in a variety of habitats (Gili & Hughes, 1995).  Flow rates are an important factor for feeding in hydroids, and prey capture rates are higher in areas of greater turbulence (Gili & Hughes, 1995).  The capture rate of zooplankton by hydroids is correlated with prey abundance (Gili & Hughes, 1995), thus prey availability can compensate for sub-optimal flow rates. Water movements are also important to hydroids to prevent siltation, which can cause death (Round et al., 1961). Tillin & Tyler-Walters (2014) suggest that the range of flow speeds experienced by biotopes in which hydroids are found indicate that a change (increase or decrease) in the maximum water flow experienced by mid-range populations for the short periods of peak spring tide flow would not have negative effects on this ecological group.

Sensitivity assessment. This biotope is recorded from moderately strong to very weak flow and wave exposed to very wave sheltered conditions from 5 m to 30 m depth.  The biotope probably experiences wave mediated flow in its more shallow examples while tidal flow is more important in its deeper examples.  The biotope probably would not occur in areas subject to both strong flow and wave action, nor in areas subject to very weak flow and shelter from wave action. Therefore, the biotope probably experiences a range of water flow and/or wave mediated flow between the extremes cited above.  Therefore, a change in the flow of 01.-0.2 m/s is probably not significant and a resistance and resilience are assessed as ‘High’ so that sensitivity is assessed as ‘Not sensitive’.

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 does not occur in the intertidal, and consequently an increase in emergence is considered 'Not relevant' to this biotope.

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

No evidence for the effect of changes in wave exposure on Cerianthus lloydii was available.  However, it is recorded from extremely wave sheltered to wave exposed sites (Connor et al., 1997b). Jackson (2004) reported that Nemertesia ramosa was intolerant of high wave exposure and only found in sheltered areas.  Faucci & Boero (2000) recorded hydroid communities at two sites of different wave exposure and recorded the presence of Obelia dichotoma and Halecium spp. in both the exposed and sheltered sites, but only found Kirchenpaueria sp. in the sheltered site.

Sensitivity assessment.  This biotope is recorded from moderately strong to very weak flow and wave exposed to very wave sheltered conditions from 5 m to 30 m depth.  The biotope probably experiences wave mediated flow in its more shallow examples while tidal flow is more important in its deeper examples.  The biotope probably would not occur in areas suggest to both strong flow and wave action, nor in areas subject to very weak flow and shelter from wave action. Therefore, the biotope probably experiences a range of water flow and/or wave mediated flow between the extremes cited above. Storms may mobilise the surface of the substratum and may explain the sparse fauna.  Nevertheless, 3-5% change in significant wave height is unlikely to be significant within this biotope.  Therefore, resistance has been assessed as ‘High’, resilience as ‘High’ and the biotope is probably ‘Not sensitive’ at the benchmark level.

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

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

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.

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 but evidence is presented where available.

Radionuclide contamination

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

Evidence

No evidence.

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.

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 2mg/l.

Hydroids mainly inhabit environments in which the oxygen concentration exceeds 5 ml/l (Gili & Hughes, 1995).  Diaz & Rosenberg (1995) noted that anemones include species that were reported to be particularly tolerant of hypoxia (e.g. Cerianthus sp and Epizoanthus erinaceus). A major hypoxic event due a pyncocline in the Gulf of Trieste resulted in a mass mortality of benthos between 12 and 26^th September 1983 (Stachowitsch, 1992), during which the oxygen levels fell below 4.2 mg/l, became anoxic, and hydrogen sulphide and ammonia were released (Faganeli et al., 1985). Amongst the epifauna, the even hypoxia resistant polychaetes and bivalves died after 4-5 days and the only organism to survive after one week were the anemones Cerianthus sp and Epizoanthus erinaceus, the gastropods Aporrhais pespelecani and Trunculariopsis trunculus and the sphinuculid Sipunculus nudis (Stachowitsch, 1992).

Sensitivity assessment.  The above evidence suggests that Cerianthus lloydii would probably survive for a week at or below 2 mg O₂/l while the hydroids would probably be reduced to just resting stages. Therefore, a resistance of 'Low' is recorded to represent the probable significant mortality of hydroids in the community. However, the hydroids would recover rapidly, so that resilience is likely to be 'High' and sensitivity 'Low'.

Nutrient enrichment

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

Evidence

No information was available on the effect of nutrient enrichment on Cerianthus lloydii. Witt et al. (2004) found that the hydroid Obelia sp. was more abundant in a sewage disposal area in the Weser estuary (Germany), which experienced sedimentation of 1 cm for more than 25 days.  It should be noted that another hydroid (Sertularia cupressina) was reduced in abundance when compared with unimpacted reference areas.  As suspension feeders, an increase in organic content at the benchmark is likely to be of benefit to the characterizing hydroids.  However, there is no direct evidence for the characterizing hydroid species Nemertesia anteninna.

Sensitivity assessment.  Little evidence was found on which to base an assessment.  However, the biotope is assessed as ‘Not sensitive' at the pressure benchmark of compliance with good status as defined by the WFD. 

Organic enrichment

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

Evidence

Borja et al., (2000) and Gittenberger & van Loon (2011) in the development of the AZTI Marine Biotic Index (AMBI) index to assess disturbance (including organic enrichment) both assigned Cerianthus lloydii to their Ecological Group I, ‘species very sensitive to organic enrichment and present under unpolluted conditions (initial state)’.  The basis for their assessment and relation to the pressure benchmark is not clear (Tillin & Tyler-Walters, 2014).

Witt et al. (2004) found that the hydroid Obelia spp. was more abundant in a sewage disposal area in the Weser estuary (Germany) which experienced sedimentation of 1 cm for more than 25 days.  It should be noted that another hydroid (Sertularia cupressina) was reduced in abundance when compared with unimpacted reference areas.  As suspension feeders, an increase in organic content at the benchmark is likely to be of benefit to the characterizing hydroids.

Sensitivity assessment.  At the pressure benchmark, which refers to enrichment rather than gross organic pollution, this biotope is considered to have a 'Low' resistance and hence, 'Medium' resilience. Therefore, sensitivity is assessed as 'Medium'.

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.

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 rock was replaced with sediment, this would represent a fundamental change to the physical character of the biotope and the species would be unlikely to recover. The biotope would be lost.

Sensitivity assessment.  The resistance to this change is ‘None’, and the resilience is assessed as ‘Very low’ due to the permanent nature of a change in the substratum.  The biotope is assessed to have a ‘High’ sensitivity to this pressure at the benchmark.

Physical change (to another sediment type)

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

Evidence

Cerianthus lloydii is found in a very wide range of substrata (Tillin & Tyler-Walters, 2014), but only dominates the fauna in the mixed substrata biotope described in this biotope  A change in Folk class from mixed to coarse or sandy mud substrata would result in loss of the biotope, even though population of Cerianthus lloydii could remain. Nemertesia antennina and other hydroids are only found attached to large pebbles and cobbles within SS.SMx.CMx.ClloMx.Nem. A reduction in the presence of cobbles and pebbles due to a change in sediment type would also reduce the abundance of the characteristic hydroids.

Sensitivity assessment.  A change in the substratum by one Folk class would result in the loss of the biotope. Therefore, a resistance of ‘None’ is recorded.  As resilience is 'Very low' (the pressure is a permanent change), sensitivity is, therefore, 'High'. 

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

Resistance is assessed as ‘None’ based on expert judgment but supported by the literature relating to the position of these species on or within the seabed.  At the pressure benchmark, the exposed sediments are considered suitable for recolonization almost immediately following extraction.  Recovery will be mediated by the scale of the disturbance and the suitability of the sedimentary habitat.  Recovery is most likely to occur via larval recolonization.  Resilience is probably ‘Low’, so that sensitivity is assessed as ‘High’.

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 direct evidence was found to assess the sensitivity Cerianthus lloydii to surface abrasion.  The burrowing life habit of the species specifically assessed would confer some protection from surface disturbance although individuals would be more exposed when close to the surface feeding. Cerianthus lloydii inhabits a soft tube, which can be up to 40 cm long and is permanently buried. The anemone can move freely within the tube and can retract swiftly if required (Tillin & Tyler-Walters, 2014).

The available evidence indicates that hydroids can be entangled and removed by abrasion.  Drop down video surveys of Scottish reefs exposed to trawling showed that visual evidence of damage to bryozoans and hydroids on rock surfaces was generally limited and restricted to scrape scars on boulders (Boulcott & Howell, 2011).  The study showed that damage is incremental with damage increasing with the frequency of trawls rather than a blanket effect occurring on the pass of the first trawls.

Re-sampling of grounds that were historically studied (from the 1930s) indicates that some species have increased in areas subject to scallop fishing (Bradshaw et al., 2002).  This study also found (unquantified) increase in abundance of tough stemmed hydroids including Nemertesia spp.; its morphology may have prevented excessive damage. Bradshaw et al. (2002) suggested that as well as having high resistance to abrasion pressures, Nemertesia spp. have benthic larvae that could rapidly colonize disturbed areas with newly exposed substrata close to the adult.  Hydroids may also recover rapidly as the surface covering of hydrorhizae may remain largely intact, from which new uprights are likely to grow. In addition, the resultant fragments of colonies may be able to develop into new colonies.

Hydroid colonies were still present in the heavily fished area, albeit at lower densities than in the closed area. This may largely be because the Isle of Man scallop fishery is closed from 1^st June to 31^st October (Andrews et al., 2011), so at the time the samples were taken for the study in question, the seabed had been undredged for at least 3.5 months. The summer period is also the peak growing/breeding season for many marine species. (Bradshaw, 2003)

Sensitivity assessment.  Abrasion at the surface only is considered likely to damage and remove epiphytic species.  Cerianthus lloydii has the ability to retract into its tube.  However, there is the possibility of the tube being damaged, which could affect the health of the organism.  The resistance of the biotope is assessed as ‘Medium’, although the significance of the impact for the bed will depend on the spatial scale of the pressure footprint.  Resilience is assessed as ‘Medium’ (2-10 years), and sensitivity is assessed as ‘Medium’.

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

Penetration and or disturbance of the substratum would result in similar results as abrasion or removal of this biotope.  Damage to Cerianthus lloydii would be greater within this pressure, as their ability to retract within their tubes would be limited.

Sensitivity assessment.  The resistance of the biotope is assessed as ‘Low’, although the significance of the impact for the bed will depend on the spatial scale of the pressure footprint.  Resilience is assessed as ‘Medium’, and sensitivity is assessed as ‘Medium’.

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

An increase in suspended sediment may have a deleterious effect on the suspension feeding community.  It is likely to clog their feeding apparatus to some degree, resulting in a reduced ingestion over the benchmark period and, subsequently, a decrease in growth rate (Jackson, 2004).  As the hydroids capture small prey in suspension (Gili & Hughes, 1995), a reduction in feeding efficiency could potentially lead to a reduction in overall biomass.

No evidence on the effect of a change in turbidity on Cerianthus lloydii could be found. Nemertesia ramosa is a passive suspension feeder, extracting seston from the water column. Increased siltation may clog up the feeding apparatus, requiring energetic expenditure to clear.  Recovery is likely to take only a few days. (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. Over the course of the benchmark, the hydroids may increase in abundance.

Sensitivity assessment.  No directly relevant evidence was found to assess the effect of pressure.  Resistance to this pressure is assessed as 'High' as an increase in turbidity may influence feeding and growth rates but not result in mortality of adults.  Resilience is assessed as 'High' (by default) and the biotope is assessed as 'Not sensitive' to changes in turbidity at the benchmark level.

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

In normal accretion, Cerianthus lloydii keeps pace with the accretion and, as a result, develops burrows much larger than the animal itself (Schäfer, 1972; Bromley, 2012). Schäfer (1972) reported that an increase in depositional rate led to an avoidance behaviour in Cerianthus lloydii.  The organism ceases tube building activity and instead the animal bunches its tentacles and intrudes its way up to the new surface, where it establishes a new burrow. However, no information on the depth of material through which is can burrow was given.

In general, it appears that hydroids are sensitive to silting (Boero, 1984; Gili & Hughes, 1995) and the decline of beds in the Wadden Sea have been linked to environmental changes including siltation.  Round et al., 1961 reported that the hydroid Sertularia (now Amphisbetia) operculata died when covered with a layer of silt after being transplanted to sheltered conditions.  Boero (1984) suggested that deepwater hydroid species develop upright, thin colonies that accumulate little sediment, while species in turbulent water movement were adequately cleaned of silt by water movement.  Hughes (1977) found that maturing hydroids that had been smothered with detritus and silt lost most of the hydrocladia and hydranths. After one month, the hydroids were seen to have recovered but although neither the growth rate nor the reproductive potential appeared to have been affected, the viability of the planulae may have been affected.  Nemertesia ramosa is an upright hydroid with a height of up to 15 cm. The colony structure is fairly tough and flexible. Smothering with 5 cm of sediment may cover over some individuals; others may just have the lower section of the main stem covered (Hayward & Ryland, 1994).

Sensitivity assessment. Cerianthus lloydii will actively burrow up through sediment that has smothered the entrance to its burrow.  The thickness of sediment through which Cerianthus lloydii is able to burrow is not known.  Smothering by 5 cm of sediment is likely to cause some mortality of Cerianthus lloydii.  It may be possible for fully grown adults to burrow through the sediment, however, the confidence in this assessment is low.  This pressure will also influence the hydroid species within SS.SMx.CMx.ClloMx.Nem.  Given the information available, the resistance to this pressure is considered to be ‘Medium’, as is the resilience, and sensitivity is assessed as ‘Medium’ at the benchmark.

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

In normal accretion, Cerianthus lloydii keeps pace with the accretion and, as a result, develops burrows much larger than the animal itself (Schäfer, 1972; Bromley, 2012). Schäfer (1972) reported that an increase in depositional rate led to an avoidance behaviour in Cerianthus lloydii.  The organism ceases tube building activity and instead the animal bunches its tentacles and intrudes its way up to the new surface, where it establishes a new burrow. However, no information on the depth of material through which it can burrow was given.

In general, it appears that hydroids are sensitive to silting (Boero, 1984; Gili & Hughes, 1995) and the decline of beds in the Wadden Sea have been linked to environmental changes including siltation.  Round et al. (1961) reported that the hydroid Sertularia (now Amphisbetia) operculata died when covered with a layer of silt after being transplanted to sheltered conditions.  Boero (1984) suggested that deepwater hydroid species develop upright, thin colonies that accumulate little sediment, while species in turbulent water movement were adequately cleaned of silt by water movement.  Hughes (1977) found that maturing hydroids that had been smothered with detritus and silt lost most of the hydrocladia and hydranths. After one month, the hydroids were seen to have recovered but although neither the growth rate nor the reproductive potential appeared to have been affected, the viability of the planulae may have been affected.  Nemertesia ramosa is an upright hydroid with a height of up to 15 cm and Nemertesia antennina grows up to 25 cm (Hayward & Ryland, 1994). The colony structure is fairly tough and flexible. Smothering with 30 cm of sediment will completely cover all individuals.

Sensitivity assessment. Cerianthus lloydii will actively burrow up through sediment that has smothered the entrance to its burrow.  The thickness of sediment through which Cerianthus lloydii is able to burrow is not known.  However, at a maximum body length of 15 cm, a deposit of 30 cm is a considerable amount of sediment to burrow through.  The level of energy expenditure needed to burrow through this amount of sediment may be too much for some individuals, and there will be a higher change of asphyxia due to the amount of time the organisms are buried. For these reasons smothering by 30 cm of sediment is likely to cause mortality of a large proportion of Cerianthus lloydii.  At this pressure benchmark, the hydroid species within SS.SMx.CMx.ClloMx.Nem will all be totally smothered, which will result in their death.  Given the information available, the resistance to this pressure is considered to be ‘Low’, the resilience is probably 'Medium', and sensitivity is assessed as ‘Medium’ at the benchmark.

Litter

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

Evidence

Not assessed.

Electromagnetic changes

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

Evidence

No evidence.

Underwater noise changes

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

Evidence

Species characterizing this habitat do not have hearing perception but vibrations may cause a response. However, noise, as defined by the pressure, is probably 'Not relevant'.

Introduction of light or shading

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

Evidence

No evidence.

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 – this pressure is considered applicable to mobile species, e.g. fish and marine mammals rather than seabed habitats. Physical and hydrographic barriers may limit propagule dispersal.  But propagule dispersal is not considered under the pressure definition and benchmark.

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 – this pressure is considered applicable to mobile species, e.g. fish and marine mammals rather than seabed habitats. Physical and hydrographic barriers may limit propagule dispersal.  But propagule dispersal is not considered under the pressure definition and benchmark.

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.

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

Habitat restoration projects may translocate stock to re-populate areas of suitable habitat (Elsäßer et al., 2013).  No evidence was found for detrimental effects arising from this practice in this habitat, although there is potential for the movement of pathogens and non-indigenous, invasive species.

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). 

King scallop (Pecten maximus) and Queen scallop (Aequipecten opercularis) in the Bay of Brest, have been reported to decrease in the presence of Crepidula, largely due to silting and biodeposition that changes the habitat (Stiger Pouvreau & Thouzeau, 2015; Thouzeau et al., 2000). The scallop post larvae are unable to settle and survive on muddy Crepidula substrata. Crepidula could potentially be the main competitor for Pecten maximus, especially creating competition for space (Menesguen & Gregoris, 2018; Ragueneau et al., 2018). However, no direct competition for food was observed between Crepidula and the scallops (Thouzeau et al., 2000, Chauvaud et al. 2000) and scallop shell growth rates did not decrease with increasing Crepidula populations. Therefore, although Crepidula populations will likely impact scallop post-larvae settlement, it does not affect shell growth rates or adult survivorship (Thouzeau et al., 2000). Models show that competition for space between the species does not impact the abundance of Crepidula, but does lower the abundance of Pecten sp. (Menesguen & Gregoris, 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. However, the above evidence suggests that Crepidula could colonize mixed sediment habitats in the subtidal, typical of this biotope, due to the presence of gravel, shells, cobbles, or any other hard substrata embedded in the substratum that can be used for larvae settlement (Tillin et al., 2020). Bohn et al. (2015) demonstrated that Crepidula had a preference for gravelly habitats, while De Montaudouin & Sauriau (1999) and Bohn et al. (2015) noted that Crepidula densities were low in intertidal coarse sediments. Therefore, Crepidula has the potential to colonize, and modify the habitat and its associated community due to the introduction of Crepidula shell biomass, silt, pseudofaeces and faeces (Blanchard, 2009; Tillin et al., 2020), as occurs in maerl gravels (Grall & Hall-Spencer, 2003), resulting in the loss of the biotope. This is a moderately exposed to very sheltered habitat, so storms may mobilise the sediment (JNCC, 2022), which may also mitigate or prevent colonization by Crepidula at high densities, although it has been recorded from areas of strong tidal streams (Hinz et al., 2011). Therefore, the habitat may be more suitable for Crepidula in wave sheltered areas of the biotope and where water movement is mediated by tidal flow rather than wave action, e.g., the deeper examples of the biotope. 

Therefore, resistance is assessed as 'Medium' in examples where wave action is high and subject to storms but 'Low' in wave sheltered areas dominated by tidal flow. Resilience is assessed as 'Very low' as it would require the removal of Crepidula, probably by artificial means. Hence, sensitivity is assessed as 'High' based on the worst-case scenario. Crepidula has not yet been reported to occur in this biotope so the confidence in the assessment is 'Low' and further evidence is required.

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

No evidence was available on the effect of microbial pathogens on Cerianthus lloydii.  Hydroids exhibit astonishing regeneration and rapid recovery from injury (Sparks, 1972) and the only inflammatory response is active phagocytosis (Tokin & Yaricheva, 1959; 1961, as cited in Sparks, 1972).  No record of diseases in the characterizing hydroids could be found.

Sensitivity assessment.  There was insufficient information to assess the effect of this pressure on the biotope.  Therefore, an assessment of ‘No evidence’ has been given. 

Removal of target species

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

Evidence

Sensitivity assessment.  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’.

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 easily 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.

Sensitivity assessment. Removal of a large percentage of the characterizing species would alter the character of the biotope.  The resistance to removal is ‘Low’ due to the easy accessibility of the biotopes location and the inability of these species to evade collection. The resilience is ‘Medium’ with recovery only being able to begin when the harvesting pressure is removed altogether. This gives an overall sensitivity score of ‘Medium’.