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

The characterizing species Branchiostoma lanceolatum is widely distributed along north-east Atlantic coasts, from northern Norway (67°N) to the Mediterranean Sea and Black Sea (may be absent from the Atlantic Spanish coasts). Branchiostoma lanceolatum entered the Indian Ocean after passage through the Suez Canal; widely distributed in the northern Indian Ocean and tropical south-western Indian Ocean along the east African coast (Poss & Boschung, 1996). Echinocyamus pusillus has a wide distribution and is reported from the north-east Atlantic, Kattegat, Iceland, Norway, Mediterranean, and south and west coasts of Africa among others (WoRMS, 2015). OBIS (2014) report maximum and minimum seawater temperatures as 19.21°C and 6.81°C but the derivation of these temperatures is not clear. Glycera lapidum is found in the north-eastern Atlantic, Mediterranean, North Sea, Skagerrak and Kattegat (Marine Species Identification Portal).

The winter temperatures of the North Sea exert lethal and sub-lethal effects upon the population at Helgoland (Courtney, 1974). There is no growth in the winter months when the temperature is less than 10°C whereas growth is continuous in the Mediterranean populations and the oxygen uptake profiles show that the animal is adapted to temperatures of 10-25°C (Courtney & Newell, 1965). The effects of the cold winter of 1962/63 on Branchiostoma lanceolatum populations was assessed by Courtney & Webb (1964). Water temperatures fell to below zero and remained around this temperature for 8 weeks (minimum temperature recorded at 20 m was -1.3^oC). Based on living Branchiostoma lanceolatum and isolated notochords from deceased individuals, it appeared that an estimated 50% of the population had died, with mortality more severe in younger (smaller) individuals and larger individuals (Courtney & Webb, 1964).

In populations cultivated in aquaria that were collected from Helgoland (Germany), Roscoff or Argele`s-sur-mer (France), lowering the temperature 3°C from the natural range increased survival rates (Benito-Gutiérrez et al., 2013). Branchiostoma lanceolatum is best adapted for life between 10°C and 20°C and can survive in waters up to 27°C and between 10°C and 3°C. Laboratory experiments found that mortality of Branchiostoma lanceolatum occurred at -5°C but short-term exposure 15 minutes to temperatures of -1.7°C (Courtney & Webb, 1964). Failure to clear the mouth at temperatures <3°C may lead to blocking and mortalities, especially as mucus production does not cease and may increase at lower temperatures (Courtney & Webb, 1964). In sediments, the interstitial water may be relatively unmixed with the overlying water column providing some buffering against decreases in temperatures, particularly for deeper buried individuals.

Sensitivity assessment. Overall, short-term acute or long-term chronic changes in temperature at the pressure benchmark are considered unlikely to adversely affect Branchiostoma lanceolatum as the distribution records suggest these species can potentially adapt to a wide range of temperatures experienced in both northern and southern waters. Resistance is therefore assessed as ‘High’ and resilience as ‘High’. This group is therefore considered to be ‘Not sensitive’.  

Temperature decrease (local)

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

Evidence

The characterizing species Branchiostoma lanceolatum is widely distributed along north-east Atlantic coasts, from northern Norway (67°N) to the Mediterranean Sea and Black Sea (may be absent from the Atlantic Spanish coasts). Branchiostoma lanceolatum entered the Indian Ocean after passage through the Suez Canal; widely distributed in the northern Indian Ocean and tropical south-western Indian Ocean along the east African coast (Poss & Boschung, 1996). Echinocyamus pusillus has a wide distribution and is reported from the north-east Atlantic, Kattegat, Iceland, Norway, Mediterranean, and south and west coasts of Africa among others (WoRMS, 2015). OBIS (2014) report maximum and minimum seawater temperatures as 19.21°C and 6.81°C but the derivation of these temperatures is not clear. Glycera lapidum is found in the north-eastern Atlantic, Mediterranean, North Sea, Skagerrak and Kattegat (Marine Species Identification Portal).

The winter temperatures of the North Sea exert lethal and sub-lethal effects upon the population at Helgoland (Courtney, 1974). There is no growth in the winter months when the temperature is less than 10°C whereas growth is continuous in the Mediterranean populations and the oxygen uptake profiles show that the animal is adapted to temperatures of 10-25°C (Courtney & Newell, 1965). The effects of the cold winter of 1962/63 on Branchiostoma lanceolatum populations was assessed by Courtney & Webb (1964). Water temperatures fell to below zero and remained around this temperature for 8 weeks (minimum temperature recorded at 20 m was -1.3°C). Based on living Branchiostoma lanceolatum and isolated notochords from deceased individuals, it appeared that an estimated 50% of the population had died, with mortality more severe in younger (smaller) individuals and larger individuals (Courtney & Webb, 1964).

In populations cultivated in aquaria that were collected from Helgoland (Germany), Roscoff or Argele`s-sur-mer (France), lowering the temperature 3°C from the natural range increased survival rates (Benito-Gutiérrez et al., 2013). Branchiostoma lanceolatum is best adapted for life between 10°C and 20°C and can survive in waters up to 27°C and between 10°C and 3°C. Laboratory experiments found that mortality of Branchiostoma lanceolatum occurred at -5°C but short-term exposure 15 minutes to temperatures of -1.7°C (Courtney & Webb, 1964). Failure to clear the mouth at temperatures <3°C may lead to blocking and mortalities, especially as mucus production does not cease and may increase at lower temperatures (Courtney & Webb, 1964). In sediments the interstitial water may be relatively unmixed with the overlying water column providing some buffering against decreases in temperatures, particularly for deeper buried individuals.

Sensitivity assessment. Overall, long-term chronic changes in temperature at the pressure benchmark are considered unlikely to adversely affect Branchiostoma lanceolatum as the distribution records suggest these species can potentially adapt to a wide range of temperatures experienced in both northern and southern waters, and laboratory experiments suggest a change at the pressure benchmark would fall within the tolerated range. An acute change in temeprature during winter when water temperatures are coldest may lead to mortalities. Resistance is therefore assessed as ‘Low’ and resilience as ‘High’. Sensitivity is therefore 'Low'. 

Salinity increase (local)

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

Evidence

This biotope is found in full salinity (30-35 psu) (JNCC, 2015). Binyon (1979) suggested that Branchiostoma lanceolatum was a stenohaline invertebrate capable of withstanding limited dilution of its environment, but being unable to control the osmotic pressure of its body fluids. Salinity profiles of Mediterranean seawater from sites where Branchiostoma lanceolatum is found fluctuate from 36.5-38.5 psu (Somorjai et al., 2008), indicating some tolerance for small fluctuations in salinity.

A study from the Canary Islands indicates that exposure to high salinity effluents (47-50 psu) from desalination plants alter the structure of biological assemblages, reducing species richness and abundance (Riera et al., 2012). Bivalves and amphipods appear to be less tolerant of increased salinity than polychaetes and were largely absent at the point of discharge. Polychaetes, including species or genera that may occur infaunally in this biotope, such as Spio filicornis, Glycera spp. and Lumbrineris sp., were present at the discharge point (Riera et al., 2012).

Sensitivity assessment. Based on the  inability of Branchiostoma lanceolatum to osmoregulate this species is considered to be restricted to fully marine environments and are judged to have ‘No’ resistance to an increase in salinity at the pressure benchmark. Resilience (following restoration to full salinity) is assessed as ‘Medium’ (2-10 years) as recruitment may be episodic or slow. Sensitivity is therefore assessed as ‘Medium’. Polychaete species may be more tolerant than bivalves so that an increase in salinity may lead to a shift in community composition in the infaunal species associated with this biotope, so that the biotope may alter to resemble the polychaete dominated SS.SCS.CCS.MedLumVen that occurs in similar conditions.

Salinity decrease (local)

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

Evidence

Binyon (1979) suggested that Branchiostoma lanceolatum was a stenohaline invertebrate capable of withstanding limited dilution of its environment, but being unable to control the osmotic pressure of its body fluids. Further experimental work, found that flagella and gill cilia activity decreases ‘abruptly’ around 18 ‰. Adults could survive exposure to 24 ‰ for two weeks although the exposed animals became opaque and were less able to burrow but would swim if gently stroked  (Binyon, 1981). Branchiostoma lanceolatum has been recorded from at least two habitats recorded as ‘brackish’: Amvrakikos Gulf, western Greece (Kehayias, 2015), and Pulicat lake area, Tamil Nadu, India (Raveen et al., 2016). Salinity profiles were not provided for these habitats and the population at Pulicat lake has disappeared, possibly due to declines in water quality (Raveen et al., 2016).

The pea urchin Echinocyamus pusillus was reported to occur in environments at 14.8 ‰ in the Sado estuary, Portugal (Russell, 2013). 

Sensitivity assessment. Based on the inability of Branchiostoma lanceolatum to osmoregulate, these species are considered to be restricted to fully marine environments and are judged to have ‘No’ resistance to a decrease in salinity at the pressure benchmark. Resilience (following restoration to full salinity) is assessed is ‘Medium’ (2-10 years) as recruitment may be episodic or slow. Sensitivity is therefore assessed as ‘Medium’.  

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

No information on tidal streams was presented in the biotope description from JNCC (2015). This biotope occurs in clean sands and gravels. Sands are less cohesive than mud sediments and a change in water flow at the pressure benchmark may alter sediment transport patterns within the biotope. Hjulström (1939) concluded that fine sand (particle diameter of 0.3-0.6 mm) was easiest to erode and required a mean velocity of 0.2 m/s. Erosion and deposition of particles greater than 0.5 mm require a velocity >0.2 m/s to alter the habitat. The topography of this habitat is shaped by currents and wave action that influence the formation of ripples in the sediment. Specific fauna may be associated with troughs and crests of these bedforms which may form following an increase in water flow, or disappear following a reduction in flow.

Sensitivity assessment. This biotope probably occurs in areas subject to moderately strong water flows that are a key factor maintaining the clean sand habitat. Changes in water flow may alter the topography of the habitat and may cause some shifts in abundance. However, a change at the pressure benchmark (increase or decrease) is unlikely to affect biotopes that occur in mid-range flows and biotope resistance is therefore assessed as ‘High’, resilience is assessed as ‘High’, and the biotope is considered to be ‘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

'Not relevant' to subtidal biotopes.

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

This biotope occurs in habitats that are moderately exposed or sheltered from wave action (JNCC, 2015). As this biotope occurs in infralittoral habitats, it is not directly exposed to the action of breaking waves. Associated polychaete species that burrow are protected within the sediment but bivalves would be exposed to oscillatory water flows at the seabed. They and other associated species may be indirectly affected by changes in water movement where these impact the supply of food or larvae or other processes. No specific evidence was found to assess this pressure.

Sensitivity assessment. The range of wave exposures experienced by the biotope is considered to indicate, by proxy, that the biotope would have ‘High’ resistance and by default ‘High’ resilience to a change in significant wave height at the pressure benchmark. The biotope is therefore classed as ‘Not sensitive’.

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

A 12-month zooplankton survey (September 2008 to August 2009) in the hypoxic, stratified and seasonally eutrophic Amvrakikos Gulf (western Greece) revealed that the vertical and horizontal distribution of Branchiostoma lanceolatum larvae in the water column was strongly related to oxygen levels. The lower limit of the oxygen concentration for the survival of the larvae seems to have been the hypoxia threshold (2 mg/l) (Kehayias, 2015).

Riedel et al. (2012) assessed the response of benthic macrofauna to hypoxia advancing to anoxia in the Mediterranean. The hypoxic and anoxic conditions were created for 3-4 days in a box that enclosed in-situ sediments. In general, molluscs were more resistant than polychaetes, with 90% surviving hypoxia and anoxia, whereas only 10% of polychaetes survived. Exposed Glycera spp. died. In general, epifauna were more sensitive than infauna, mobile species more sensitive than sedentary species and predatory species more sensitive than suspension and deposit feeders.

Sensitivity assessment. The larval observations and the mortalities of Glycera spp. suggest that de-oxygenation at the pressure benchmark may be relevant to larval supply and survival of adults. Biotope resistance is assessed as ‘Low’ and resilience as ‘High’, so sensitivity is assessed as ‘Low’.

Nutrient enrichment

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

Evidence

This pressure relates to increased levels of nitrogen, phosphorus and silicon in the marine environment compared to background concentrations. The pressure benchmark is set at compliance with Water Framework Directive (WFD) criteria for good status, based on nitrogen concentration (UKTAG, 2014).  

Declines in the abundance of Branchiostoma lanceolatum have been linked to eutrophication and organic pollution, although separating direct and indirect effects such as change in sediment type has not been possible. Declines have been recorded along the north-eastern Atlantic coast and Mediterranean  (Konsulova, 1992 cited from Kehayias, 2015; Antoniadou et al., 2004; Rota et al., 2009) and in lake populations in India (Raveen et al., 2016).

Sensitivity assessment. As this biotope is structured by the sediments and water flow rather than nutrient enrichment and is not characterized by macroalgae (although some may be present), the biotope is considered to have ‘High’ resistance to this pressure and ‘High’ resilience, (by default) and is assessed as ‘Not sensitive’.

Organic enrichment

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

Evidence

The biotope occurs in mobile sand sediments where sediment disturbance leads to particle sorting and in-situ primary production is restricted to microphytobenthos. An input of organic matter could provide a food subsidy to the deposit feeding polychaetes. Borja et al. (2000) and Gittenberger & Van Loon (2011) assigned Glycera alba and Glycera lapidum to their AMBI Group III, defined as: ‘Species tolerant to excess organic matter enrichment. These species may occur under normal conditions, but their populations are stimulated by organic enrichment (slight unbalance situations)’ (Borja et al., 2000; Gittenberger & Van Loon, 2011). 

No direct evidence was found for Echinocyamus pusillus. However, this species lives in areas of high water movement and wave action, so that excess matter silted on the surface is considered to be rapidly removed.  Borja et al. (2000) and Gittenberger & Van Loon (2011) in the development of an AMBI index to assess disturbance (including organic enrichment) both assigned Echinocyamus pusillus to their Ecological Group I: ‘Species very sensitive to organic enrichment and present under unpolluted conditions (initial state)’ (Borja et al., 2000; Gittenberger & Van Loon, 2011).

Declines in the abundance of Branchiostoma lanceolatum have been linked to eutrophication and organic pollution, although separating direct and indirect effects such as change in sediment type has not been possible. Declines have been recorded along the north-eastern Atlantic coast and Mediterranean  (Konsulova, 1992 cited from Kehayias, 2015; Antoniadou et al., 2004; Rota et al., 2009) and in lake populations in India (Raveen et al., 2016).

Branchiostoma lanceolatum traps particles on a mucous filter (Riisgård & Svane 1999). Riisgård & Svane (1999) observed that while filter-feeding Branchiostoma lanceolatum ‘coughs’ periodically by closing the excurrent opening and contracting the body to dislodge excess detritus clogging its filter and force it back out of the mouth. Coughing may allow this species to tolerate inputs of organic matter. Gross pollution (at levels greater than the pressure nbenchmark) is likely to reduce habitat suitability, resulting in the loss of Branchiostoma lanceolatum.

Sensitivity assessment.  At the pressure benchmark, organic inputs are likely to represent a food subsidy for the associated deposit feeding species such as Glycera spp. and are unlikely to significantly affect the structure of the biological assemblage or impact the physical habitat. An increase greater than the pressure benchmark is likely to reduce habitat suitability for Branchiostoma lanceolatum and Echinocyamus pusillus. Biotope sensitivity is assessed as ‘High’ and resilience as ‘High’ (by default), and the biotope is therefore considered to be ‘Not sensitive’ (at the pressure benchmark).

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

The biotope is characterized by the sedimentary habitat (JNCC, 2015), so a change to an artificial or rock substratum would alter the character of the biotope leading to reclassification and the loss of the sedimentary community including the characterizing species that live buried within the sediment.

Sensitivity assessment. Based on the loss of the biotope, resistance is assessed as ‘None’, recovery is assessed as ‘Very Low’ (as the change at the pressure benchmark is permanent and sensitivity is assessed as ‘High’.

Physical change (to another sediment type)

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

Evidence

The biotope description from JNCC (2015) defines this biotope as occurring in coarse sand habitats. A change in sediment type would alter the biotope from the classification. The key characterizing species and the associated biological assemblage have narrow sediment preferences and would also be lost if the sediment change.

Branchiostoma lanceolatum prefer coarse sand with fairly fast water flow and do not inhabit silty sediments (Berrill, 1987). Antoniadou et al. (2004) studied ‘Amphioxus’ sands from the eastern Mediterranean. The amphioxus (Branchiostoma lanceolatum) assemblage was usually found on gravel and coarse sands with shell fragments. The expansion of muddy sediments following eutrophication and organic pollution led to reductions in Branchiostoma lanceolatum density and changes in community structure. Similarly, Desprez (2000) reported on the loss of Branchiostoma lanceolatum  dominated communities following aggregate extraction that resulted in a change from gravels and gravelly sands to a fine sand habitat. The habitat had declined in extent from the 1970’s. In Racou beach (southern France), Branchiostoma lanceolatum preferred sandy sites (Desdevises et al., 2011).

Telford et al. (1983) report that in the Firth of Lorne, Scotland, Echinocyamus pusillus was found most abundantly in highly variable, poorly sorted substrata but absent in fine sediments in sheltered areas. Wolff (1968, cited in Telford et al., 1983) reported that Echinocyamus pusillus was abundant in the North Sea in relatively coarse sands with a median grain size of 210-460 µm.

Sensitivity assessment. Branchiostoma lanceolatum appears to occur in a relatively restricted range of sediment types, related to burrowing, feeding and other characteristics and is therefore considered to have ‘No’ resistance to a change in sediment. Resilience is assessed as ‘Very Low’ as a change at the benchmark is permanent and sensitivity is assessed as ‘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

This biotope is characterized by shallowly buried species. The lancelet, Branchiostoma lanceolatum is usually partially or fully buried in the sand filtering microscopic food particles from the water (Riisgard & Svane, 1999).   

Recovery of sediments will be site-specific and will be influenced by currents, wave action and sediment availability (Desprez, 2000). Except in areas of mobile sands, the process tends to be slow (Kenny & Rees, 1996; Desprez, 2000 and references therein).  Boyd et al. (2005) found that in a site subject to long-term extraction (25 years), extraction scars were still visible after six years and sediment characteristics were still altered in comparison with reference areas with ongoing effects on the biota. The strongest currents are unable to transport gravel. A further implication of the formation of these depressions is a local drop in current strength associated with the increased water depth, resulting in deposition of finer sediments than those of the surrounding substrate (Desprez et al., 2000 and references therein).

Sensitivity assessment. Within the extraction footprint all individuals would be removed and hence resistance is assessed as ‘None’. Resilience is predicted to be ‘Medium’ (within 2-10 years) and to occur largely through larval recolonisation. Sensitivity is, therefore, assessed as ‘Medium’.  

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

The lancelet, Branchiostoma lanceolatum is usually partially buried in the sand filtering microscopic food particles from the water (Riisgard & Svane, 1999). When disturbed they quickly leave their burrow and swim fast a short distance, then rapidly burrow again posterior end first into the sand (Lambert, 2005). Where sediments are coarse and permeable Branchiostoma lanceolatum may live buried several centimetres and rarely come to the surface (Courtney & Webb, 1964). Depth of burial depends on ability to displace sediment grains and the ability of Branchiostoma lanceolatum to set up a current through the pharynx in the interstitial water (Courtney & Webb, 1964). Smaller and larger individuals may be buried closer to the surface, due to sediment sorting by lancelet activity, so that a fine sand layer limits depth of penetration for small lancelets and requirements for large ciliary currents by larger lancelets (Courtney & Webb, 1964).

A number of authors describe collecting Branchiostoma lanceolatum for laboratory cultivation by dredging and subsequently sieving sediments (Fuentes et al., 2004; Somorjai et al., 2008). No mortality/damage rates were provided but as this technique successfully captures live individuals it is considered to indicate that the animals are relatively robust.

Sensitivity assessment. As members of this ecological group are generally buried within the sediment this will provide some protection, resistance is assessed as ‘Medium’ (<25 % mortality). Resilience is assessed as ’High’ (based on repair of damaged individuals, inward migration by adults from adjacent populations and recolonization by larvae). Biotope sensitivity is therefore assessed as ‘Low’.  

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 direct evidence for the sensitivity of this ecological group to abrasion and penetration of the seabed below the surface was found. A number of authors describe collecting Branchiostoma lanceolatum for laboratory cultivation by dredging and subsequently sieving sediments (Fuentes et al., 2004; Somorjai et al., 2008). No mortality/damage rates were provided but as this technique successfully captures live individuals it is considered to indicate that the animals are relatively robust.

The fragility of the tests of Echinocyamus pusillus means that these species have little protection from abrasion that is coupled with penetration and disturbance of the seabed. Evidence to assess the sensitivity of this ecological group is provided by studies on by-catch damage, comparisons between areas with different levels of fishing activities and re-sampling of areas after exposure to directly estimate mortality. No evidence was found for impacts on Echinocyamus pusillus. This species may be too small to be retained as by-catch and in-situ assessments have not been carried out.

Sensitivity assessment. Based on expert judgement, resistance is assessed as ‘Low’ (loss of 25-75 % of individuals) and resilience as ‘High’ (recovery within 2-10 years). Sensitivity is therefore 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

No empirical evidence was found regarding the effects of turbidity on Branchiostoma lanceolatum and this biotope. This biotope is not characterized by primary producers and direct effects from changes in light penetration are not relevant. Increases or decreases in organic suspended solids and other particles may affect epifauna through abrasion and affect feeding by filter feeders. Riisgård & Svane (1999) observed that while filter-feeding, Branchiostoma lanceolatum “coughs” periodically by closing the excurrent opening and contracting the body to dislodge excess detritus clogging its filter and force it back out of the mouth.

The sedimentary habitats where Branchiostoma lanceolatum and the associated species are found, may experience periodic high levels of suspended particles. The burrowing habit of infauna may mediate exposure, however, species such as Branchiostoma lanceolatum and Glycymeris glycymeris that depend on inhalant currents from the surface for respiration may be affected where fine particles are deposited in interstitial spaces (see physical change and siltation pressures). Increased organic matter in suspension or that is subsequently deposited may enhance food supply to suspension feeders. The feeding apparatus of Branchiostoma lanceolatum are considered more robust than the more delicate structures of, for example, filter feeding molluscs, although no evidence was found regarding the likelihood of clogging. 

Sensitivity assessment. Resistance is therefore assessed as ‘High’ and resilience as ‘High’ (no effect to recover from). This group is therefore assessed as ‘Not sensitive’.  

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

Little evidence was found to assess the impacts of this pressure on this ecological group. Branchiostoma lanceolatum are not found in silty sediments and as the pressure benchmark refers explicitly to fine sediments, this species may be unsuited to burrowing through the deposited overburden which would be different in composition to its usual habitat.  

Bijkerk (1988, results cited from Essink 1999) indicated that the maximal overburden through which Echinocardium could migrate was approximately 30 cm in sand.  No further information was available on the rates of survivorship or the time taken to reach the surface. No information was found regarding the sensitivity of Echinocyamus pusillus. Glycera alba and Glycera lapidum have been categorized through expert judgement and literature review as AMBI sedimentation Group II: 'Species sensitive to high sedimentation. They prefer to live in areas with some sedimentation, but don’t easily recover from strong fluctuations in sedimentation' (Gittenberger & Van Loon, 2011).

Sensitivity assessment. Although some individuals may reposition within sediments, resistance is assessed as ‘Low’ (loss of 25-75 % of exposed individuals) at the pressure benchmark due to the depth of the overburden.  Resilience  is assessed as ‘High’ (following sediment restoration). Sensitivity is therefore categorised as ‘Low’.

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

Little evidence was found to assess the impacts of this pressure on this ecological group.  Branchiostoma lanceolatum are not found in silty sediments and as the pressure benchmark refers explicitly to fine sediments, this species may be unsuited to burrowing through the deposited overburden which would be different in composition to its usual habitat.  

Bijkerk (1988, results cited from Essink 1999) indicated that the maximal overburden through which Echinocardium could migrate was approximately 30 cm in sand.  No further information was available on the rates of survivorship or the time taken to reach the surface. No information was found regarding the sensitivity of Echinocyamus pusillus. Glycera alba and Glycera lapidum have been categorized through expert judgement and literature review as AMBI sedimentation Group II: 'Species sensitive to high sedimentation. They prefer to live in areas with some sedimentation, but don’t easily recover from strong fluctuations in sedimentation' (Gittenberger & Van Loon, 2011).

Sensitivity assessment. Although some individuals may reposition within sediments, resistance is assessed as ‘Low’ (loss of 25-75 % of exposed individuals) at the pressure benchmark due to the depth of the overburden.  Resilience  is assessed as ‘High’ (following sediment restoration). Sensitivity is therefore categorised as ‘Low’

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

Not relevant.

Introduction of light or shading

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

Evidence

Amphioxus have photoreceptors along their entire length (Lacalli, 2004) and will move away from light when disturbed (Somorjai et al., 2008; Fuentes et al., 2004). Wild amphioxus populations spawn after sunset, a change in lighting could affect this (Benito-Gutiérrez et al., 2013).

Sensitivity assessment. Changes in light levels may alter spawning cues and behaviour of the characterizing species Branchiostoma lanceolatum. Biotope resistance based on this characterizing species is assessed as 'Low' and resilience is assessed as 'High', following restoration of the usual light environment. Biotope sensitivity is therefore assessed as 'Low'.

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' to biotopes restricted to open waters.

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'.

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

Key characterizing species within this biotope are not cultivated or translocated. This pressure is therefore considered ‘Not relevant’ to this biotope.

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; 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 from rock, artificial substrata, and Sabellaria alveolata reefs (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 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 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.  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 (Tillin et al., 2020). 

Sensitivity assessment. The above evidence suggests that Crepidula fornicata could colonize coarse sediment habitats in the subtidal, typical of this biotope, especially in the wave sheltered and deeper examples of the biotope, which are more liable to be colonized compared to shallower and more wave exposed examples.  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. This is a moderately wave exposed to wave sheltered habitat. Therefore, if Crepidula colonized the habitat it would probably 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 lost of the biotope. Hence, resistance is assessed as 'Low'. Resilience is assessed as 'Very low' as it would require the removal of Crepidula, probably by artificial means. Hence, sensitivity is assessed as 'High'. 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. In aquaria populations the major cause of mortality is bacterial infection (Benito-Gutiérrez et al., 2013). Courtney & Webb (1964) noted that damaged lancelets and animals in poor condition are subject to attack from ciliate protozoa leading to mortality.

Removal of target species

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

Evidence

'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

The loss of the key characterizing species Branchiostoma lanceolatum through unintentional removal would alter the character of the biotope and may lead to reclassification to a similar, infaunal biotope such as SS.SCS.ICS.MoeVen or SS.SCS.CCS.MedLumVen. The ecosystem services such as secondary production provided by this species would be lost.

Sensitivity assessment. Biotope resistance to loss of the characterizing species is assessed as ‘Low’, as the burrowing lifestyle and mobility of Branchiostoma lanceolatum mean that a proportion of the population may escape removal. Resilience is assessed as ‘High’ based on in-situ recovery and migration from adjacent populations, and sensitivity is therefore assessed as ‘Low’.