Starlet sea anemone (Nematostella vectensis)

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Summary

Description

A tiny anemone rarely more than 1.5 cm in length. The column is usually between 0.4 and 1.6 cm in length but specimens can occasionally reach 4.1 cm when fully extended. Translucent and colourless in appearance except for variable patterns of opaque white on the column and disk. Tentacles large in proportion to the body, colourless and translucent with pale tips and with faint transverse bars and irregular flecks of white. The 9-16 tentacles are very strongly adhesive and arranged in two cycles, the outer ones longer than the inner.

Recorded distribution in Britain and Ireland

Recorded from the north coast of Norfolk, the east coast of Suffolk, the Blackwater Estuary and Hamford Water in Essex, the Hampshire coast, the south coast of Dorset, Sand Bay in the Bristol Channel, and St' Bees Head, Cumbria.

Global distribution

In North America from Nova Scotia to Georgia on the Atlantic coast, from Florida to Louisiana in the Gulf of Mexico and from California to Washington on the Pacific coast. In Europe, it is restricted to the south and east coast of England.

Habitat

Lives in isolated or semi-isolated brackish pools in saltmarsh and lagoons, in ditches and on mudflats in saltmarshes and shallow estuaries at or above high water, typically in mud, muddy sand and muddy shingle but is also found on vegetation (M. Sheader, pers. comm.; Fincham, 2016a&b).

Depth range

High to low water

Identifying features

  • Column differentiated into physa, scapus and capitulum.
  • No nemathybomes (nematocyst bearing sacs in the column).
  • Unusual, ciliated, spherical bodies called nematosomes, occur in the coelenteron.
  • Tentacles in two cycles, the outer longer than the inner.

Additional information

Nematostella vectensis is a model organism for the study of developmental genetics and evolution, and has a dedicated genomics database (Darling et al., 2005; Sullivan et al., 2006; Tarrant et al., 2015; Layden et al., 2016). However, a discussion of developmental genetics is outside the scope of this review.

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Biology review

Taxonomy

LevelScientific nameCommon name
PhylumCnidaria
ClassAnthozoa
OrderActiniaria
FamilyEdwardsiidae
GenusNematostella
AuthorityStephenson, 1935
Recent Synonyms

Biology

ParameterData
Typical abundanceModerate density
Male size range1-2 cm
Male size at maturity1-2 cm
Female size range1-2 cm
Female size at maturity1-2 cm
Growth formCylindrical
Growth rateSee additional information
Body flexibilityHigh (greater than 45 degrees)
MobilitySedentary, temporary attachment
Characteristic feeding methodPredator
Diet/food sourceCarnivore
Typically feeds onSmall free-living macrofauna e.g. copepods, ostracods, juvenile littorinids, hydrobiids and larvae
SociabilityNot relevant
Environmental positionEpifaunal
DependencyIndependent.
SupportsNone
Is the species harmful?No

Biology information

Nematostella vectensis uses the adhesive rugae on its column to anchor and move in the sediment and to climb on macroalgae (e.g. Chaetomorpha spp.) and macrophytes (e.g. Ruppia spp.). However, less than 5% of the population was observed on macrophytes in the Fleet, Pennington and Gilkicker lagoons (Sheader et al., 1997).

Growth rate and size. The column is usually between 0.4 and 1.6 cm in length but specimens can occasionally reach 4.1 cm when fully extended (Williams, 1975). In the field, they are usually less than 2 cm long, typically with a column diameter of only 0.2 cm, and a crown of tentacles 0.8-1 cm across (Wiliams, 1983; Hand & Uhlinger, 1994). In the laboratory, excessively well-fed specimens can reach over 16 cm in length (Hand & Uhlinger, 1992). Food availability, salinity and temperature probably limit the size, growth rates and abundance of this species under natural conditions (Hand & Uhlinger, 1992, 1994; Sheader et al., 1997). In the laboratory, Hand & Uhlinger (1992) found that young anemones varied in size but could grow to 1 mm long in 10 days, 2 mm in 2 weeks, 4 mm in three weeks and, in the extreme, reach 2.5 cm in a month. The second set of four tentacles arrive after 2-3 weeks and the month-old individuals typically have 12 tentacles and can extend to 1 to 2 cm in length. The anemones approach sexual maturity after two months and are 2 to 5 cm long and have 16 tentacles (Hand & Uhlinger, 1992). Adult spawning can occur in as little as 55-69 days after fertilization, in the laboratory (Hand & Uhlinger, 1992, 1994). However, in the field, individuals tend to be smaller, and once disturbed contract into small white masses rarely more than a few millimetres long, which are easily mistaken for pieces of polychaete or nemerteans (Hand & Uhlinger, 1994). 

Population dynamics. Nematostella vectensis can reach high abundance in favourable conditions. For example, William, unpubl. (cited in Williams, 1983) noted that more than 12,500 /m2 were found in a Norfolk pool in September 1974, and estimated that a single pool could contain over five million individuals. Similarly, Hand & Uhlinger (1994) cite a report of ca 80,000 individuals /m2  in a single isolated pool in Nova Scotia. However, abundance varies with geographic area and time of year (Hand & Uhlinger, 1994; Sheader et al., 1997) and in the field, abundances are typically much lower (Reitzel et al., 2008).

In Pennington Lagoon, Hampshire, winter abundance was low (at <120 /m2), rose slightly in April, with a peak in abundance of up to 2700 individuals /m2 seen from September to October.  In the Fleet, Dorset, the population peaked at around 1500 individuals /m2, in November and December and then fell back to their original spring/summer abundance of 100-400/m2 (Sheader et al., 1997). In the Gilkicker Lagoon, Hampshire, the abundance remained low in 1987 (at <175 /m2 ) with a slight peak in June but the abundance was higher in 1988 (ca 200 /m2) with a peak of (1130 /m2) in October.  In UK lagoons the abundance was low over winter and the beginning of the year and peaked in the later part of the year, although the exact season varied between lagoons (Sheader et al., 1997). Sheader et al. (1997) also noted that the peak abundances in their studied populations coincided with an increase in the proportion of smaller size classes and suggested that the peaks were due to asexual reproduction, especially as no males were found in their samples. The peak in abundance also coincided with peaks in macrofaunal numbers, and hence food availability for Nematostella vectensis. Only females were found in the south coast populations of England (Sheader et al., 1997) and there seems to be only asexual reproduction in the UK (M. Sheader, pers. comm). Unisexual populations are common in this species and recorded from the Pacific and Atlantic coasts of the USA (Hand & Uhlinger, 1994; Reitzel et al., 2008).

Feeding. Nematostella vectensis is a passive predator that captures passing prey. It has been reported to feed on hydrobiid snails, juvenile littorinids, copepods, chironomid larvae, egg masses (probably from copepods), ostracods, nematodes and small polychaetes, corixids, possibly rotifers, and the pediveligers of Macoma, mussels and oysters (Frank & Bleakney, 1978, Posey & Hines, 1991; Hand & Uhlinger, 1992, 1994; Sheader et al., 1997).

Habitat preferences

ParameterData
Physiographic preferencesEstuary, Isolated saline water (Lagoon)
Biological zone preferencesNot relevant
Substratum / habitat preferencesMacroalgae, Mud, Muddy gravel, Muddy sand, Salt marsh
Tidal strength preferencesVery weak (negligible)
Wave exposure preferencesUltra sheltered
Salinity preferencesLow (<18 psu), Variable (18-40 psu)
Depth rangeHigh to low water
Other preferences

No text entered

Migration PatternNon-migratory or resident

Habitat Information

Distribution in Britain and Ireland. Nematostella vectensis is found on the north coast of Norfolk, the east coast of Suffolk, the Blackwater Estuary and Hamford Water in Essex (Carol Reid, English Nature, pers. comm.), the Hampshire coast and on the south coast of Dorset, Sand Bay in the Bristol Channel, and St Bees Head, Cumbria. Nematostella vectensis was first described as a new species from brackish pools on the Isle of Wight (Stephenson, 1935).

Habitat preferences. Nematostella vectensis is regarded as a eurythermal and euryhaline species. In the UK, Nematostella vectensis is recorded from coastal brackish ponds or lagoons. The species is usually found in water less than 1 m deep, a few live down to 2 m water depth (M. Sheader, pers. comm.). It has a wider distribution in North America where it is recorded from permanent brackish/saline ponds, salt marsh creeks and subtidally in certain estuaries (Hand & Uhlinger, 1994; Sheader et al., 1997). Recent records from Norfolk and Suffolk estuaries and lagoons suggest that its habitat in the UK is probably very similar to that in the USA, as it has been recorded from pools, ditches and mudlfats in salt marsh and estuaries (Fincham, 2016a). 

In English populations of Nematostella vectensis, the salinity in the vast majority of sites ranged between 2-42 ppt with the greatest abundance in ponds with seasonally varying salinity between 16-32 ppt. (Sheader et al., 1997). Williams (1983; cited by Hand & Uhlinger, 1992,1994) noted that it was usually found in brackish marsh pools of between 10 and 25 ppt but that it was recorded in salinities between 8.96 ppt and 51.54 ppt. Hand & Uhlinger (1992, 1994) noted asexual division at salinities of 7 to 42 ppt and sexual reproduction in salinities of 12 to 34 ppt. Nematostella vectensis was also recorded in pools in Nova Scotia at -1.5°C and 28°C where the low temperature coincided with the pool thickly covered with ice, and in Georgia (USA) in pools at 32.5°C (Hand & Uhinger, 1994). Reitzel et al. (2013) concluded that, while eurythermal, Nematostella vectensis occupied sites (on the western Atlantic coast of the USA) close to their physiological limit. Specimens survived at experimental temperatures up to 39°C but almost all life stages died at 41°C. Temperature also had a significant effect on growth and regeneration rates, which also varied between specimens from higher or lower latitudes at 29°C (Reitzel et al. 2013).  Hand & Uhlinger (1994) and Posey & Hines (1991) also noted that Nematostella vectensis was never found where the salinity is permanently high, and suggested that predation (e.g. by shrimp or nudibranchs) prevented their survival at full salinity.  Sheader et al. (1997) noted that Nematostella vectensis occupied pools with very low or negligible water flow.  They noted that it could be abundant below 0.1 cm/s (0.01 m/s) but was absent above ca 0.18 cm/s (0.018 m/s). Nematostella vectensis can also use macrophytes (e.g. Ruppia sp. or Chaetomorpha sp.) as substrata (Williams, 1991; Sheader et al., 1997).

Non-native status. The restricted distribution of Nematostella vectensis in the UK led Sheader et al. (1997) to suggest that it was introduced from the USA. Subsequent genetic studies using a range of genetic markers have concluded that Nematostella vectensis was probably introduced from the southeastern coast of the USA (Pearson et al., 2002; Darling et al., 2004, 2009; Reitzel et al., 2008). Darling et al. (2004, 2009) concluded that anthropogenic transport was most likely, rather than rafting (i.e. on floating debris or macrophytes), probably via the transport of gear and as fouling communities on watercraft, rather than ballast water. Sheader et al. (1997) suggested that it may have been introduced by accidental transfer with imported North American shellfish (e.g. Crassostrea spp. and Mercenaria mercenaria) into the area of the Solent in the 20th century, and Reitzel et al. (2008) note that it was first recorded on the Isle of Wight in the 1930s.

Life history

Adult characteristics

ParameterData
Reproductive typeAsexual, Budding, Fission, Gonochoristic (dioecious), Sexual
Reproductive frequency Annual episodic
Fecundity (number of eggs)100-1,000
Generation time<1 year
Age at maturity>10 weeks
SeasonNot relevant
Life spanInsufficient information

Larval characteristics

ParameterData
Larval/propagule typePlanula
Larval/juvenile development See additional information
Duration of larval stage2-10 days
Larval dispersal potential Very limited (<1 m)
Larval settlement periodInsufficient information

Life history information

Nematostella vectensis is able to reproduce both sexually and asexually. In the USA, it is easy to collect in the wild and easy to culture under laboratory conditions so that its development is well documented and it is suited to studies of developmental genetics and genomics (Williams, 1975; Frank & Bleakney, 1978; Hand & Uhlinger, 1992, 1994, 1995; Darling et al., 2005; Sullivan et al., 2006; Reitzel et al., 2007; Reitzel et al., 2013; Tarrant et al., 2015; Layden et al., 2016). 

Sexual reproduction. Key points are summarised below.

  • In the laboratory, Nematostella vectensis became sexually mature at 3-4 months old and at column lengths of between 1.5-3.5 cm. Gametes were found to be produced at all times of the year (Hand & Uhlinger, 1992, 1994).
  • Fritzenwanker & Technau (2002) found that, in the laboratory, a combination of feeding regime, dark-light cycle and temperature shift synergistically induced gametogenesis in adult polyps from the Rhode River in America. They concluded that the combination of 4 days of feeding in the dark at 18°C followed by illumination at 24 °C produced the highest number of eggs.
  • The number of eggs is dependent on adult size. Large individuals reared in the laboratory can produce up to 2000 eggs (Hand & Uhlinger, 1992,1994).
  • Eggs are 170-240 µm in diameter and are released embedded in a gelatinous mucoid mass that sticks to the bottom (Hand & Uhlinger, 1992).
  • In the laboratory, spherical ciliated planula larvae (200-250 µm in length) emerge from the egg masses between 3-4 days after fertilization. They bear an apical tuft of cilia at the oral end, which is lost as they develop and become pear-shaped. Planulae are active swimmers from the age of about 3 days old but spend periods of inactivity on the bottom of culture dishes unless disturbed (Hand & Uhlinger, 1992; Darling et al., 2005; Reitzel et al., 2007). Planulae and juveniles 'glide' over the surface of the substratum (in the laboratory) but most cease gliding before they are 1 mm long (Hand & Uhlinger, 1992).
  • They develop four tentacle buds in 4-5 days and settle as 250-500 µm juveniles with four tentacles within 7 to 10 days of fertilization (Hand & Uhlinger, 1992; Darling et al., 2005; Reitzel et al., 2007).   However, settlement and metamorphosis into the juvenile can take at least two weeks or be prolonged for up to 135 days (Hand & Uhlinger, 1994)
  • In the laboratory, Hand & Uhlinger (1992) found that young anemones varied in size but could grow to 1 mm long in 10 days, 2 mm in 2 weeks, 4 mm in three weeks and, in the extreme, reach 2.5 cm in a month. The second set of four tentacles arrives after 2-3 weeks and the month-old individuals typically have 12 tentacles and can extend to 1-2 cm in length.
  • The anemones approach sexual maturity after two months and are 2-5 cm long and have 16 tentacles (Hand & Uhlinger, 1992).
  • Adult spawning can occur in as little as 55-69 days after fertilization, in the laboratory (Hand & Uhlinger, 1992, 1994). Hand & Uhlinger (1992) suggested that pulses of food and/or changes in water stimulated spawning.

In the laboratory, Nematostella vectensis was able to spawn repeatably and predictably at ca seven-day intervals up to Hand & Uhlinger (1992, 1994). The ease of growth and rapid generation time (2-3 months) in the laboratory allow classic genetic studies to be undertaken (Darling et al., 2005). Hand & Uhlinger (1992) also noted that it underwent its full range of development at a wide range of salinities but that growth was inhibited and sexual reproduction and metamorphosis stopped at salinities greater than 34 ppt.

Asexual reproduction. Nematostella vectensis is able to reproduce by transverse fission and budding (Hand & Uhlinger, 1992, 1994, 1995; Frank & Bleakney, 1978; Reitzel et al., 2007). The vegetative asexual reproduction results in genetically identical clones; for example, a single isolated male individual gave rise to 96 individuals, and an isolated female gave rise to 38 individuals in the laboratory. The male and female clones were then able to breed successfully (Hand & Uhlinger (1992).

Transverse fission. Transverse fission is known in only four other sea anemones (Shick, 1991, cited in Hand & Uhlinger, 1994). In the laboratory, most transverse fission (across the column) was found to take place at night and only in well-expanded individuals. The fragment produced by fission is usually shorter than the oral piece and sometimes multiple fission occurs, producing two or three fragments. Some fragments regenerated and were able to feed within three days and, if well fed, completed growth to the adult spawning stage within a few more weeks (Hand & Uhlinger, 1995). Although asexual division becomes common at about 10 weeks, it has been noted as early as seven weeks. Increased food intake leads to an increase in the frequency of fission and starvation can suppress the process (Hand & Uhlinger, 1992, 1995; Reitzel et al., 2007).

Budding. Anemones with multiple oral crowns are common in both natural and laboratory-reared populations of Nematostella vectensis (Williams, 1975; Frank & Beakney, 1978; Hand & Uhlinger, 1995; Reitzel et al., 2007). This is caused by polarity reversal, in which a new oral crown develops at the aboral end of the column (physa) (Reitzel et al., 2007).  Fission (within weeks or months) by such individuals produces normal single-crowned anemones. This is known as budding and is extremely rare in anemones (Hand & Uhlinger, 1995; Reitzel et al., 2007).

Regeneration. Hand & Uhlinger (1995) and Reitzel et al. (2007) note that Nematostella vectensis has good regeneration capability. Complete bisection of the column normally results in two complete adults (Reitzel et al., 2007). However, injuries and anomalous fission can result in a range of anomalous individuals, e.g. with multiple crowns and Y-shaped individuals (Hand & Uhlinger, 1995; Reitzel et al., 2007).

Population structure. The relative proportion of sexual and asexual reproduction in natural populations is uncertain but sexual reproduction rates are probably much lower in nature than in the laboratory (Hand & Uhlinger, 1992, 1994). This is borne out by the number of single-sex populations and high levels of genetic differentiation between populations. For example, Hand & Uhlinger (1994) noted that 6 of the 21 populations they studied contained both sexes while the other 15 were single sexed. In the UK, only female populations were recorded (Hand & Uhlinger, 1994; Sheader et al., 1997). Darling et al. (2004) found that five or nine populations studied were asexual.

Genetic studies have shown that Nematostella vectensis populations show a mixture of sexual and asexual reproduction, with numerous asexual only populations, and extraordinarily high levels of genetic differentiation, sometimes over the space of less than 100 m, which is consistent with low gene flow, poor dispersal and/or bottlenecks (where few individuals survive environmental perturbation, e.g., the drying up of pools), and sporadic, discontinuous dispersal by random events and anthropogenic transport (Sheader et al., 1997; Pearson et al., 2002; Darling et al., 2004, 2009; Reitzel et al., 2008). In the UK, Pearson et al. (2002) found that the English population was dominated (61% of individuals) by a single genotype (RAPD (random amplified polymorphic DNA) haplotype). DNA fingerprinting and mitochondrial DNA (mtDNA) studies of populations from the Atlantic and Pacific coasts of the USA and the UK (Darling et al., 2004, 2009; Reitzel et al., 2008) revealed higher genetic diversity on the Atlantic coasts of the USA than of the Pacific coast or in England and concluded that populations on both the Pacific and English coasts were introduced from the Atlantic coasts, most probably by human activity. The English population probably originated in the southeastern USA (Reitzel et al., 2008), possibly by a single individual, or a few individuals and subsequent bottlenecks (Pearson et al., 2002; Darling et al., 2004). Genetic differentiation was extremely high.  In rare cases, individuals were significantly genetically distinct from members of the same population, or any other population (Reitzel et al., 2008). Similarly, significant genetic differentiation was observed between subpopulations separated by <100 m at a single site, e.g. in Sippewssett Marsh (Darling et al., 2004). Reitzel et al. (2008) also noted that males may exist in low numbers in populations previously thought to be all female.

Sensitivity reviewHow is sensitivity assessed?

Resilience and recovery rates

Nematostella vectensis is a very small sea anemone that lives in the surface of muddy sediments in very sheltered conditions. It is able to reproduce both sexually and asexually. It grows rapidly in the laboratory and has a short generation time (2-3 months), although sexual reproduction in the wild is probably less frequent, probably annual, and does not occur in all populations (Hand & Uhlinger, 1992, 1994, 1995; Darling et al., 2005). Asexual reproduction allows this species to generate clones that can rapidly colonize a suitable habitat.  The rapid seasonal increases in abundance reported in UK lagoons are probably due to rapid asexual proliferation in response to food availability (Sheader et al., 1997). But while it can occur in huge numbers its normal abundance is probably low (Hand & Uhlinger, 1994; Sheader et al., 1997; Reitzel et al., 2008). Sexual reproduction, coupled with asexual proliferation provides this species with the ability to develop genetic clonal lines that are highly adapted to the local conditions (Darling et al., 2004, 2009; Reitzel et al., 2008). Local adaptation with varied levels of asexual reproduction and founder effects (bottlenecks due to die back in populations) partly explain the high levels of genetic differentiation seen between populations. However, numerous studies (Sheader et al., 1997; Person et al., 2002; Darling et al., 2004, 2009; Reitzel et al., 2008) concluded that the extraordinarily high levels of genetic differentiation was explained by low gene flow due to poor dispersal and/or bottlenecks and sporadic, discontinuous dispersal by random events and anthropogenic transport. 

Effective dispersal is probably extremely poor. Darling et al. (2004) noted high levels of genetic differentiation between isolated pools separated by less than 100 m. Although the planulae are able to swim, in the laboratory, they spend most of their time stationary unless disturbed (Hand & Uhlinger, 1992; Reitzel et al., 2007, 2008). Stocks & Grassle (2001) recorded that very few Nematostella vectensis colonized experimental salt marsh pond mesocosms in their 60-day study, even though it was found in the surrounding sediment. Thomas & Thorp (1994) also noted that Nematostella vectensis was lost from the Emsworth millpond complex (a brackish lagoon is south-east England) in 1987, probably due the poor summer of 1985 and extreme winter of 1985/86, and had not returned by 1991.

Adults bear sticky rugae and sticky tentacles (Williams, 1975; Hand & Uhlinger, 1994) so may be dispersed passively. It is also eurythermal, euryhaline, and capable of surviving long periods of starvation, for example, Williams (1976) starved adults for 80 days without ill effects, and Hand & Uhlinger (1994) reported that individuals survived 6 months without food, although they became smaller. In UK lagoons, a small percentage of the population was recorded from vegetation (Sheader et al., 1997) so that it is possible that they could raft on floating vegetation or debris. However, Darling et al. (2004, 2009) concluded that anthropogenic transport was most likely, rather than rafting (i.e. on floating debris or macrophytes), because rafting in other species resulted in lower levels of genetic differentiation than observed in this species and did not explain the high levels of genetic differences (lack of shared genotypes) between neighbouring locations in the USA. Darling et al. (2004, 2009) and Reitzel et al. (2008) concluded that dispersal was an episodic and idiosyncratic process probably via the transport of gear and as fouling communities on watercraft, rather than ballast water. Sheader et al. (1997) suggested that it may have been introduced to England by accidental transfer with imported North American shellfish (e.g. Crassostrea spp. and Mercenaria mercenaria) into the area of the Solent in the 20th century.

Resilience assessment. Nematostella vectensis can reproduce asexually and sexually, depending on location and, where present, can reach high densities seasonally, probably due to asexual reproduction. Therefore, where an existing population suffered some mortality (i.e. Medium resistance) it could probably recover within the next season (several months). Similarly, if an existing population experienced significant mortality (i.e. Low resistance) then the survivors could repopulate within two years. For example, Pearson et al. (2002) and Reitzel et al. (2008) suggested that the introduction of Nematostella vectensis could have been due to a single individual, or few individuals followed by subsequent bottlenecks. Hence, as long as members of the population survive, resilience is probably 'High'. However, if a population is removed or lost (i.e. resistance is 'None') then recolonization would depend on either human transportation (or intervention) or random, unpredictable, events and take anywhere from a few years to never. In this instance, a resilience of 'Very low' (negligible or prolonged recovery) is recorded.

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

Nematostella vectensis is very tolerant to temperature change. It has been recorded at temperatures ranging from -1 to 28°C (Williams, 1983, 1991). Nematostella vectensis was also recorded in pools in Nova Scotia at -1.5°C and 28°C where the low temperature coincided with the pool thickly covered with ice, and in Georgia (USA) in pools at 32.5°C (Hand & Uhinger, 1994). The species has reportedly survived freezing at -5 °C for 48 hours (M. Sheader, pers. comm.).

Temperatures above 28°C were found to adversely affect the animals in the laboratory (Fritzenwanker & Technau, 2002), although no further information was given. Reitzel et al. (2013) noted that Nematostella vectensis occupied habitats that experienced large daily (> 20°C) and seasonal (>25°C) fluctuations in temperature.  For example, the high marsh pools occupied by this species in Great Sippewisset Marsh, Massachusetts, varied in temperature from 1.3°C at the end of October to 43.7°C in mid-July. Reitzel et al. (2013) concluded that, while eurythermal, Nematostella vectensis occupied sites (on the western Atlantic coast of the USA) close to their physiological limit. Specimens survived at experimental temperatures up top 39°C but almost all life stages died at 41°C (measured at exposures of 0.5 to 6 hr). Embryos and larval stages exhibited the same response but were significantly lower than juveniles by 1°C.  In the field, four high temperature events exceeded the LT50 for developmental stages one site in July.  Temperature also had a significant effect on growth and regeneration rates at 29°C (but not at 13°C or 21°C). Clones from the north regenerated slower than clones from the south at 29°C, which indicated a level of latitudinal adaptation to temperature (Reitzel et al. 2013). Reitzel et al. (2013) suggested that climate change might threaten southern USA populations.

Sensitivity assessment.  Nematostella vectensis is a eurythermal species adapted to extreme fluctuations in temperature. Therefore, a short-term change in temperatures of 5°C or a change in 2°C for a year is unlikely to adversely affect populations of this species in UK waters.  Therefore, a resistance of ‘High’ is suggested so that resilience is also ‘High’ and the species is assessed as ‘Not sensitive’ at the benchmark level.

High
High
Medium
Medium
Help		High
High
High
High
Help		Not sensitive
High
Medium
Medium
Help
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

Nematostella vectensis is very tolerant to temperature change. It has been recorded at temperatures ranging from -1 to 28°C (Williams, 1983, 1991). Nematostella vectensis was also recorded in pools in Nova Scotia at -1.5°C and 28°C where the low temperature coincided with the pool thickly covered with ice, and in Georgia (USA) in pools at 32.5°C (Hand & Uhinger, 1994). The species has reportedly survived freezing at -5°C for 48 hours (M. Sheader, pers. comm.).

Temperatures above 28°C were found to adversely affect the animals in the laboratory (Fritzenwanker & Technau, 2002), although no further information was given. Reitzel et al. (2013) noted that Nematostella vectensis occupied habitats that experienced large daily (> 20°C) and seasonal (>25°C) fluctuations in temperature.  For example, the high marsh pools occupied by this species in Great Sippewisset Marsh, Massachusetts, varied in temperature from 1.3°C at the end of October to 43.7°C in mid-July. Reitzel et al. (2013) concluded that, while eurythermal, Nematostella vectensis occupied sites (on the western Atlantic coast of the USA) close to their physiological limit. Specimens survived at experimental temperatures up top 39°C but almost all life stages died at 41°C (measured at exposures of 0.5 to 6 hr). Embryos and larval stages exhibited the same response but were significantly lower than juveniles by 1°C.  In the field, four high temperature events exceeded the LT50 for developmental stages one site in July.  Temperature also had a significant effect on growth and regeneration rates at 29°C (but not at 13°C or 21°C). Clones from the north regenerated slower than clones from the south at 29°C, which indicated a level of latitudinal adaptation to temperature (Reitzel et al. 2013). Reitzel et al. (2013) suggested that climate change might threaten southern USA populations.

Sensitivity assessment.  Nematostella vectensis is a eurythermal species adapted to extreme fluctuations in temperature. Therefore, a short-term change in temperatures of 5°C or a change in 2°C for a year is unlikely to adversely affect populations of this species in UK waters.  Therefore, a resistance of ‘High’ is suggested so that resilience is also ‘High’ and the species is assessed as ‘Not sensitive’ at the benchmark level.

High
High
Medium
Medium
Help		High
High
High
High
Help		Not sensitive
High
Medium
Medium
Help
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

Nematostella vectensis is a euryhaline species and, in England, has been recorded from 8.96 to 51.54 ppt (Williams, 1991), although the greatest abundances have been found in ponds varying seasonally between 16-36 ppt (Sheader et al., 1997). In laboratory cultures from American specimens, salinity had a pronounced effect on both reproduction and the health of the animal itself (Hand & Uhlinger, 1992). For example, up to 20% of anemones in 10 and 20% (ca 3.5 and 7 ppt) seawater were deflated and had their mesenteries everted through their mouths within 5 weeks. At the other extreme, anemones in 125% (ca 43.7 ppt) seawater had decreased in size after 4 months and only spawned once, although asexual reproduction was not markedly less effective than at 33% (ca 11.5 ppt) seawater. Overall, the American studies found that asexual division was recorded, albeit at varying levels of success, at salinities between 7-42‰ and sexual reproduction between 12-34 ‰ (Hand & Uhlinger, 1992). Hand & Uhlinger (1994) noted that Nematostella vectensis was never found where salinities were permanently high (i.e. fully marine) and suggested that their restriction to estuaries (and by implication other variable salinity habitats) was due to predation by marine species, e.g. shrimp and nudibranchs.

Salinity varies depending on the geographical location of each population. At Keyhaven-Pennington in Hampshire, for example, salinity varies from 2-25 ppt whereas, at the Fleet in Dorset, salinity varies between 18-32 ppt.  Field observations indicate that above 40 ppt, tentacles are retracted and feeding ceases (Sheader et al., 1997). In the laboratory, Sheader et al. (1997) noted that feeding ceased (i.e. tentacles were withdrawn) at 10-12 ppt (at 15°C). Sheader et al. (1997) suggested that low and high salinity interfered with feeding and hence long-term fitness, which explained their higher abundance between 16-36 ppt.  Sheader et al. (1997) also noted that, while the salinity of brackish pools and lagoons in the UK vary, salinity was generally higher in summer and lower in winter.

Sensitivity assessment. Nematostella vectensis is a euryhaline species recorded from low, reduced and variable salinity habitats. An increase in salinity (>40 psu) is likely to reduce feeding, although this species can survive starvation for up to 6 months (Hand & Uhlinger, 1994; Sheader, et al., 1997). Nevertheless, is most abundant in the UK lagoons and pools between 16-36 ppt (Sheader, et al., 1997). Therefore, it may be reduced in abundance by hypersaline conditions and resistance is recorded as ‘Medium’. Resilience is probably ‘High’ so that sensitivity is assessed as ‘Low’.

Medium
High
Medium
Medium
Help		High
High
Medium
Medium
Help		Low
High
Medium
Medium
Help
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

Nematostella vectensis is a euryhaline species and, in England, has been recorded from 8.96 to 51.54 ppt (Williams, 1991), although the greatest abundances have been found in ponds varying seasonally between 16-36 ppt (Sheader et al., 1997). In laboratory cultures from American specimens, salinity had a pronounced effect on both reproduction and the health of the animal itself (Hand & Uhlinger, 1992). For example, up to 20% of anemones in 10 and 20% (ca 3.5 and 7 ppt) seawater were deflated and had their mesenteries everted through their mouths within 5 weeks. At the other extreme, anemones in 125% (ca 43.7 ppt) seawater had decreased in size after 4 months and only spawned once, although asexual reproduction was not markedly less effective than at 33% (ca 11.5 ppt) seawater. Overall, the American studies found that asexual division was recorded, albeit at varying levels of success, at salinities between 7 and 42‰ and sexual reproduction between 12-34 ‰ (Hand & Uhlinger, 1992). Hand & Uhlinger (1994) noted that Nematostella vectensis was never found where salinities were permanently high (i.e. fully marine) and suggested that their restriction to estuaries (and by implication other variable salinity habitats) was due to predation by marine species, e.g. shrimp and nudibranchs.

Salinity varies depending on the geographical location of each population. At Keyhaven-Pennington in Hampshire, for example, salinity varies from 2-25 ppt whereas, at the Fleet in Dorset, salinity varies between 18-32 ppt.  Field observations indicate that above 40 ppt, tentacles are retracted and feeding ceases (Sheader et al., 1997). In the laboratory, Sheader et al. (1997) noted that feeding ceased (i.e. tentacles were withdrawn) at 10-12 ppt (at 15°C). Sheader et al. (1997) suggested that low and high salinity interfered with feeding and hence long-term fitness, which explained their higher abundance between 16-36 ppt.  Sheader et al. (1997) also noted that, while the salinity of brackish pools and lagoons in the UK vary, salinity was generally higher in summer and lower in winter.

Sensitivity assessment. Nematostella vectensis is a euryhaline species recorded from low (<18 psu), reduced (18-30 psu) and variable (18-40 psu) salinity habitats. It is adapted to habitats with fluctuating salinities and may be excluded from areas that experience stable and full salinity conditions, i.e. fully marine conditions. Therefore, a reduction in salinity from variable to reduced or from reduced to low is unlikely to have an effect on the population.  However, populations that occur in low salinity will be more sensitive, as a reduction in salinity from low to freshwater for a year may result in loss of the population. Therefore, a resistance of ‘Low’ is suggested. Resilience is probably ‘High’ and sensitivity is assessed as ‘Low’.

Low
High
Medium
Medium
Help		High
High
Medium
Medium
Help		Low
High
Medium
Medium
Help
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

All English populations of Nematostella vectensis are found in brackish and saline lagoons and ponds at or above high water (Sheader et al., 1997). It has a wider distribution in North America where it is recorded from permanent brackish/saline ponds, salt marsh creeks and subtidally in certain estuaries (Hand & Uhlinger, 1994; Sheader et al., 1997). In the English sites, the saline lagoons are usually shallow (less than 1 m deep), in fine sand and muds with a mixture or overlay of shingle, with a high organic content, and very low near-bottom water flow rates. Extreme shelter is needed as it allows a layer of fine mud to build up, in which the animal burrows (Williams, 1983). Nematostella vectensis populations remain submerged at all times (Sheader et al., 1997). Nematostella vectensis is usually found in water less than 1 m deep, although a few live down to 2 m water depth (M. Sheader, pers. comm.).

Sheader et al. (1997) examined the effect of water flow on the abundance of Nematostella vectensis at five sites of the south coast of England. They noted that it could be abundant below 0.1 cm/s (0.01 m/s) but was absent above ca 0.18 cm/s (0.018 m/s).  The rates were measured during the maximum flood on spring tides at a height of 2 cm above the sediment surface, so probably represent the upper limit of the range of water flow at those sites. Sheader et al. (1997) noted that water flow was dependent on tidal exchange, riverine input and wind driven currents. 

Sensitivity assessment. The lagoonal habitat is dependent on very low to negligible water flow. An increase in water flow of 0.1-0.2 m/s (the benchmark) for a year is a significant (order of magnitude) change and likely to result in the removal of the surface of the sediment, the population of Nematostella vectensis, the removal or reworking of the lagoonal pool habitat. Therefore, a resistance of 'None' is suggested. Resilience is probably 'Very low' so that sensitivity is assessed as 'High'.

None
High
High
Medium
Help		Very Low
High
Medium
Medium
Help		High
High
Medium
Medium
Help
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

All English populations of Nematostella vectensis are found in brackish and saline lagoons and ponds at or above high water (Sheader et al., 1997). It has a wider distribution in North America where it is recorded from permanent brackish/saline ponds, salt marsh creeks and subtidally in certain estuaries (Hand & Uhlinger, 1994; Sheader et al., 1997). In the English sites, the saline lagoons are usually shallow (less than 1 m deep), in fine sand and muds with a mixture or overlay of shingle, with a high organic content, and very low near-bottom water flow rates. Nematostella vectensis populations remain submerged at all times (Sheader et al., 1997). Nematostella vectensis is usually found in water less than 1 m deep, although a few live down to 2 m water depth (M. Sheader, pers. comm.).

Williams (1991) suggested that desiccation was likely to be a limiting factor in the distribution of this species. In the laboratory, Williams (1976) found that the animals had contracted their tentacles after eight hours without water and after 31 hours, had withdrawn into their burrow. After 4 days without water, 70% of the animals were still alive but trapped in the dried sediment and by 6 days, none had survived (Williams, 1976). Therefore, the drying up of the pools or lagoons in which the species live is likely to destroy the population.

Sensitivity assessment.  Nematostella vectensis is found in shallow lagoons pools, where it is permanently submerged. Changes in emergence that result in the lowering of the water table and increase the risk of drying out of the pools will probably result in loss of the population. Therefore, a resistance of 'None' is recorded and, as resilience is probably 'Very low', sensitivity is assessed as 'High'.

None
High
Medium
Medium
Help		Very Low
High
Medium
Medium
Help		High
High
Medium
Medium
Help
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

All English populations of Nematostella vectensis are found in brackish and saline lagoons and ponds at or above high water (Sheader et al., 1997). It has a wider distribution in North America where it is recorded from permanent brackish/saline ponds, salt marsh creeks and subtidally in certain estuaries (Hand & Uhlinger, 1994; Sheader et al., 1997). In the English sites, the saline lagoons are usually shallow (less than 1 m deep), in fine sand and muds with a mixture or overlay of shingle, with a high organic content, and very low near-bottom water flow rates. Extreme shelter is needed as it allows a layer of fine mud to build up, in which the animal burrows (Williams, 1983) and wave action is probably a limiting factor in the distribution of the species (Williams, 1991).  Nematostella vectensis populations remain submerged at all times (Sheader et al., 1997). Nematostella vectensis is usually found in water less than 1 m deep, although a few live down to 2 m water depth (M. Sheader, pers. comm.).

Sensitivity assessment.   Sheader et al. (1997) noted that wind-driven currents were one source of water flow in lagoons but that their magnitude depended on local topography, shelter by terrestrial vegetation and submerged macrophytes. Increased storminess may result in increased wind-driven wave generation and storm-driven waves may also damage the lagoons seaward extent or breach retaining structures (e.g. spit or wall). Nevertheless Nematostella vectensis is abundant is extremely wave sheltered habitats with very low near bottom water flow rates.  Therefore, an increase in wave action as low as the benchmark (3-5% of significant wave height) is probably enough to remove the population of this species, rework the sediment and destroy the pools in which it lives. Hence a resistance of 'None' is recorded. Resilience is probably 'Very low' so that sensitivity is assessed as 'High'.

None
Medium
Medium
Medium
Help		Very Low
High
Medium
Medium
Help		High
Medium
Medium
Medium
Help

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

This pressure is Not assessed.

Not Assessed (NA)
NR
NR
NR
Help		Not assessed (NA)
NR
NR
NR
Help		Not assessed (NA)
NR
NR
NR
Help
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.

Not Assessed (NA)
NR
NR
NR
Help		Not assessed (NA)
NR
NR
NR
Help		Not assessed (NA)
NR
NR
NR
Help
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.

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

Radionuclide contamination

Benchmark. An increase in 10µGy/h above background levels. 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
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)
NR
NR
NR
Help		Not assessed (NA)
NR
NR
NR
Help		Not assessed (NA)
NR
NR
NR
Help
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

Fluctuation in oxygen levels in shallow lagoonal pools is normal. however, lagoon environments frequently have a high macroalgal production which can result in anoxic conditions on the sediment - water interface. Sheader et al. (1997) noted that the sediment and near-bottom water of pools occupied by Nematostella vectensis may occasionally become anoxic but that the oxygen concentration in the water column was usually high. This species, along with several other lagoon species, can move up onto the algal mats to avoid the anoxic conditions. Maas et al. (2016) examined respiration and circadian rhythms in Nematostella vectensis.  They noted that respiration rates were highest in the light part of the light: dark or dark: light cycles in the laboratory. They reported that Nematostella vectensis maintained a constant respiration rate down to 25% oxygen saturation (2.5 mg/l). Williams (1991) suggested that extreme hypoxia is likely to be a limiting factor in the distribution of this species. Furthermore, anemones recovered from anoxic mud in the field were 'very sick' (Williams, 1976).

Sensitivity assessment. Nematostella vectensis is probably adapted to fluctuating oxygen levels and experiences periods of anoxia in the organic-rich sediment. It is unclear at what level of hypoxia mortality, if any, may occur, although anoxia may be detrimental. Therefore, a precautionary resistance of 'Medium' is recorded but with 'Low' confidence. As resilience is probably 'High' a sensitivity of 'Low' is recorded.

Medium
Low
NR
NR
Help		High
High
Medium
Medium
Help		Low
Low
Low
Low
Help
Nutrient enrichment [Show more]

Nutrient enrichment

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

Evidence

Nutrient enrichment may result in increased macrophyte growth and, hence, increase food for this species, or may result in algal mats that smother the benthos, and algal blooms, that on death result in increased hypoxia and anoxia, to the detriment of the species.  However, no evidence on the direct effect on this species was found. Nevertheless, this species is probably 'Not sensitive' at the benchmark level (resistance and resilience are 'High') set at compliance with Water Framework Directive (WFD) criteria for good status, based on nitrogen concentration (UKTAG, 2014).

High
Low
NR
NR
Help		High
High
High
High
Help		Not sensitive
Low
Low
Low
Help
Organic enrichment [Show more]

Organic enrichment

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

Evidence

Nematostella vectensis occurs in organic-rich muddy sediments in saline or brackish pools (Sheader et al., 1997). Further organic enrichment may increase the frequency and extent of anoxic events but no direct evidence about this species was found. Nematostella vectensis is probably adapted to fluctuating oxygen levels and experiences periods of anoxia in the organic-rich sediment. It is unclear at what level of hypoxia mortality, if any, may occur, although anoxia may be detrimental. Therefore, a precautionary resistance of 'Medium' is recorded but with 'Low' confidence. As resilience is probably 'High' a sensitivity of 'Low' is recorded.

Medium
Low
NR
NR
Help		High
High
Medium
Medium
Help		Low
Low
Low
Low
Help

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
Help		Very Low
High
High
High
Help		High
High
High
High
Help
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

A change from sediment to hard rock substratum would result in loss of the habitat for this species.  Therefore, resistance is assessed as ‘None’.  The change is defined as permanent so that resilience is assessed as ‘Very low’ and sensitivity is assessed as ‘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
Help		Very Low
High
High
High
Help		High
High
High
High
Help
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

Nematostella vectensis is recorded from muddy sedients (mud, muddy sand and muddy gravel). A chagne in sediment type, e.g. to clean sands and gravels) would result in loss of its habitat. Therefore, resistance is assessed as ‘None’.  The change is defined as permanent so that resilience is assessed as ‘Very low’ and sensitivity is assessed as ‘High’.

None
High
High
High
Help		Very Low
High
High
High
Help		High
High
High
High
Help
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

Nematostella vectensis is a small burrowing anemone that lives in the surface of the sediment. Removal of the sediment to a depth of 30 cm (the benchmark) would remove the entire population of this species within the affected area. Therefore, a resistance of 'None' is recorded'. This species has very poor active dispersal capability and its ability to recolonize an area is dependent on unpredictable events (storms, human transport etc), and lagoonal habitats are often isolated. Hence, resilience is likely to be 'Very low' and sensitivity is assessed as 'High'.

None
Low
NR
NR
Help		Very Low
High
Medium
Medium
Help		High
Low
Low
Low
Help
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

Nematostella vectensis is a small (1-2 cm in length) burrowing anemone that lives in the surface of the sediment. When disturbed, the anemone shrinks down to a small white mass seldom more than a few millimetres in length (Hand & Uhlinger, 1994). Therefore, disturbance of the sediment surface (e.g. by trampling or vehicle access, or fishing gear) has the potential to kill a proportion of this soft-bodied species, depending on the extent, frequency and duration of the impact. Therefore, a resistance of 'Medium' is suggested. As a proportion of the population will probably survive, and its preferred habitat remains, resilience is probably 'High' and sensitivity is assessed as 'Low'. 

Medium
Low
NR
NR
Help		High
High
Medium
Medium
Help		Low
Low
Low
Low
Help
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

Nematostella vectensis is a small (1-2 cm in length) burrowing anemone that lives in the surface of the sediment. When disturbed, the anemone shrinks down to a small white mass seldom more than a few millimetres in length (Hand & Uhlinger, 1994). Therefore physical disturbance that penetrates the surface of the sediment (e.g. fishing gear, tractor towed rakes or dredges) has the potential to kill a proportion of this soft-bodied species, depending on the extent, frequency and duration of the impact. Therefore, a resistance of 'Medium' is suggested. As a proportion of the population will probably survive, and its preferred habitat remains, resilience is probably 'High' and sensitivity is assessed as 'Low'. 

Medium
Low
NR
NR
Help		High
High
Medium
Medium
Help		Low
Low
Low
Low
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

Nematostella vectensis lives in the surface of muddy sediments. It is probably adapted to the localised resuspension of sediment by the tide and occurs in depositional habitats with very low near bottom flow rates. As a predator it is not dependent on light, however, Sheader et al. (1997) noted suggested that its seasonal abundance was linked with the growth of macroalgae and, hence, the grazers which form part of its food chain. Increases in suspended sediment may affect its food supply, although it can survive for months without food (Hand & Uhlinger, 1992, 1994).  Therefore, a precautionary resistance of 'Medium' is suggested, although resilience is probably 'High' and sensitivity is 'Low'.

Medium
Low
NR
NR
Help		High
High
Medium
Medium
Help		Low
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

Nematostella vectensis lives in the surface of muddy sediments. It is probably adapted to the localised resuspension of sediment by the tide and occurs in depositional habitats with very low near bottom flow rates. It probably routinely readjusts its position in the sediment as sediment is moved and deposited at each tidal cycle.  However, the sudden deposition of 5 cm of sediment (the benchmark) will smother the population, and the sediment will remain in the isolated, wave sheltered habitats occupied by this species. No information on its ability to burrow was found. Therefore, smothering has the potential to remove a significant proportion of the population (especially smaller juveniles) and a resistance of 'Low' is suggested but with 'Low' confidence. Resilience is probably 'High' and sensitivity is assessed as 'Low'.

Low
Low
NR
NR
Help		High
High
Medium
Medium
Help		Low
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

Nematostella vectensis lives in the surface of muddy sediments. It is probably adapted to the localised resuspension of sediment by the tide and occurs in depositional habitats with very low near bottom flow rates. It probably routinely readjusts its position in the sediment as sediment is moved and deposited at each tidal cycle.  However, the sudden deposition of 30 cm of sediment (the benchmark) will smother the population, and the sediment will remain in the isolated, wave sheltered habitats occupied by this species. No information on its ability to burrow was found. Therefore, smothering has the potential to remove a significant proportion of the population (especially smaller juveniles) and a resistance of 'Low' is suggested but with 'Low' confidence. Resilience is probably 'High' and sensitivity is assessed as 'Low'.

Low
Low
NR
NR
Help		High
High
Medium
Medium
Help		Low
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

Not relevant. Nematostella vectensis probably reacts to localised vibration but is unlikely to react to the noise from passing vessels etc. 

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

As a passive predator, Nematostella vectensis is not dependent on light, however, Sheader et al. (1997) noted suggested that its seasonal abundance was linked with the growth of macroaglae and, hence, the grazers which form part of its food chain.  Shading may the growth of some macroaglae and influence its food supply, however, it can survive for months without food (Hand & Uhlinger, 1992, 1994).  Therefore, a resistance of 'High' is suggested. As resilience is 'High', 'Not sensitive' is recorded.

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

Nematostella vectensis has very poor dispersal capability and occupies isolated habitats. It is thought that its dispersal is due to unpredicted events and human transportation, especially on the Pacific coasts of the USA and in the UK (Pearson et al., 2002; Darling et al., 2004, 2009; Reitzel et al., 2008).  The addition of physical barriers to dispersal is unlikely to change its already high level of isolation. However, the dispersal of larval stages or propagules is not considered under the pressure definition and benchmark.

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 interaction with bottom towed fishing gears and moorings are 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. Nematostella vectensis probably reacts to localised shading but is unlikely to react to the visual disturbance from passing vessels etc. 

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

Biological Pressures

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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

Hand & Uhlinger (1994) noted that viable offspring could be obtained from crosses of specimens of Nematostella vectensis from the UK and USA. Nematostella vectensis is thought to have been introduced (translocated) from the southeastern Atlantic coast of the USA.  But no evidence of further translocation, breeding or hybridization with other species was found.

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

No evidence of the interaction of Nematostella vectensis with other non-native or native species was found. 

No evidence (NEv)
NR
NR
NR
Help		Not relevant (NR)
NR
NR
NR
Help		No evidence (NEv)
NR
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

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
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

Nematostella vectensis has been collected from the wild by scientists in areas where it is readily abundant (see Layden et al., 2016). However, it is readily cultured in the laboratory for experiments in developmental genetics and genomics.  It is not known to be targeted commercially. Therefore, this pressure (as defined by the benchmark) is '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

Incidental removal of the Nematostella vectensis (e.g. from harvesting of other species) could result in loss of a proportion of the population, depending on the nature of the activity. however, the species is very small, so a proportion of the population is likely to remain.  Therefore, a resistance of 'Medium' is suggested. Resilience is probably 'High' so sensitivity is assessed as 'Low'.  It should also be noted that Nematostella vectensis can stick to macrophytes and other substata so that the removal and subsequent transport of sediment, other species, or equipment used in the process may introduce Nematostella vectensis into new areas. 

Medium
Low
NR
NR
Help		High
High
Medium
Medium
Help		Low
Low
Low
Low
Help

Importance review

Policy/legislation

DesignationSupport
Wildlife & Countryside ActSchedule 5, section 9
UK Biodiversity Action Plan PriorityYes
Species of principal importance (England)Yes
IUCN Red ListVulnerable (VU)
Features of Conservation Importance (England & Wales)Yes

Status

Non-native

ParameterData
NativeNon-native
OriginSoutheastern U.S.A.
Date Arrived1930s

Importance information

In England, Nematostella vectensis is under threat because it is recorded from only a few restricted areas and these areas are especially vulnerable (Williams, 1991). If a salt marsh became polluted or dried up, for example, the entire population of Nematostella vectensis could be lost together with the the habitat. At Gilkicker Point in Hampshire, several lagoons have already been infilled (Williams, R.B., 1976). Current threats to this species include:

  • loss and damage to lagoons and other sheltered brackish water habitats caused by factors including pollution, drainage and other activities.
  • isolation of pools leading to fragmentation of populations;
  • coastal defence works and associated infilling (Anonymous, 1999k); and
  • coastal squeeze due to sea-level rise.

Williams (1983) stated that it had been proposed to transfer individuals to unbounded open marshes free from human influence so that the population could spread naturally. However, experimental tranlocation studies in the Cley marsh lagoons, Norfolk proved to be inconclsuive due to the difficulty of establishing a control site within the study area (Fincham, 2016a&b).

Bibliography

  1. Anonymous, 1999k. Starlet sea anemone (Nematostella vectensis). Species Action Plan In UK Biodiversity Group. Tranche 2 Action Plans. English Nature for the UK Biodiversity Group, Peterborough., English Nature for the UK Biodiversity Group, Peterborough.

  2. Carlgren, O., 1949. A survey of the Ptychodactiaria, Corallimorpharia and Actiniaria. Kungliga Svenska Vetenskapsakadamiens Handlingar, Series 4, 1, 16-110.

  3. Darling, J.A., Kuenzi, A. & Reitzel, A.M., 2009. Human-mediated transport determines the non-native distribution of the anemone Nematostella vectensis, a dispersal-limited estuarine invertebrate. Marine Ecology Progress Series, 380, 137-146.

  4. Darling, J.A., Reitzel, A.M. & Finnerty, J.R., 2004. Regional population structure of a widely introduced estuarine invertebrate: Nematostella vectensis Stephenson in New England. Molecular Ecology, 13 (10), 2969-2981.

  5. Darling, J.A., Reitzel, A.R., Burton, P.M., Mazza, M.E., Ryan, J.F., Sullivan, J.C. & Finnerty, J.R., 2005. Rising starlet: the starlet sea anemone, Nematostella vectensis. BioEssays, 27 (2), 211-221.

  6. Fincham, J., 2016a. Norfolk's starlet anemone: a brief popuation update. In Biodiversity News, 73, 28-30. Peterborough: Defra.

  7. Fincham, J., 2016b. Starlet sea anemone: Suffolk. In White Admiral, 94, 29-31. Ipswich: Suffolk Naturalists Society.

  8. Frank, P.G. & Bleakney, J.S., 1978. Asexual reproduction, diet, and anomalies of the anemone Nematostella vectensis in Nova Scotia. The Canadian Field-Naturalist, 92, 259-263.

  9. Fritzenwanker, J.H. & Technau, U., 2002. Induction of gametogenesis in the basal cnidarian Nematostella vectensis (Anthozoa). Development Genes and Evolution, 212, 99-103.

  10. Hand, C. & Uhlinger, K.R., 1992. The culture, sexual and asexual reproduction, and growth of the sea anemone,Nematostella vectensis. Biological Bulletin, Marine Biological Laboratory, Woods Hole, 182, 169-176.

  11. Hand, C. & Uhlinger, K.R., 1994. The unique, widely distributed, estuarine sea anemone, Nematostella vectensis, Stephenson: A review, new facts and questions. Estuaries, 17, 501-508.

  12. Hand, C. & Uhlinger, K.R., 1995. Asexual reproduction by transverse fission and some anomalies in the sea anemone Nematostella vectensis. Invertebrate Biology, 114, 9-18.

  13. Howson, C.M. & Picton, B.E., 1997. The species directory of the marine fauna and flora of the British Isles and surrounding seas. Belfast: Ulster Museum. [Ulster Museum publication, no. 276.]

  14. Layden, M.J., Rentzsch, F. & Röttinger, E., 2016. The rise of the starlet sea anemone Nematostella vectensis as a model system to investigate development and regeneration. Wiley Interdisciplinary Reviews: Developmental Biology, 5 (4), 408-428.

  15. Manuel, R.L., 1988. British Anthozoa. Synopses of the British Fauna (New Series) (ed. D.M. Kermack & R.S.K. Barnes). The Linnean Society of London [Synopses of the British Fauna No. 18.]. DOI https://doi.org/10.1002/iroh.19810660505

  16. Pearson, C.V.M., Rogers, A.D. & Sheader, M., 2002. The genetic structure of the rare lagoonal sea anemone, Nematostella vectensis Stephenson (Cnidaria; Anthozoa) in the United Kingdom based on RAPD analysis. Molecular Ecology, 11 (11), 2285-2293.

  17. Posey, M.H. & Hines, A.H., 1991. Complex predator-prey interactions within an estuarine benthic community. Ecology, 72, 2155-2169.

  18. Reitzel, A.M., Burton, P.M., Krone, C. & Finnerty, J.R., 2007. Comparison of developmental trajectories in the starlet sea anemone Nematostella vectensis: embryogenesis, regeneration, and two forms of asexual fission. Invertebrate Biology, 126 (2), 99-112.

  19. Reitzel, A.M., Chu, T., Edquist, S., Genovese, C., Church, C., Tarrant, A.M. & Finnerty, J.R., 2013. Physiological and developmental responses to temperature by the sea anemone Nematostella vectensis. Marine Ecology Progress Series, 484, 115-130.

  20. Reitzel, A.M., Darling, J.A., Sullivan, J.C. & Finnerty, J.R., 2008. Global population genetic structure of the starlet anemone Nematostella vectensis: multiple introductions and implications for conservation policy. Biological Invasions, 10 (8), 1197-1213.

  21. Reitzel, A.M., Sullivan, J.C. & Finnerty, J.R., 2010. Discovering SNPs in protein coding regions with stellasnp: Illustrating the characterization and geographic distribution of polymorphisms in the estuarine anemone Nematostella vectensis. Estuaries and Coasts, 33 (4), 930-943.

  22. Sheader, M., Suwailem, A.M. & Rowe, G.A., 1997. The anemone, Nematostella vectensis, in Britain: considerations for conservation management. Aquatic Conservation: Marine and Freshwater Ecosystems, 7, 13-25.

  23. Stefanik, D.J., Friedman, L.E. & Finnerty, J.R., 2013. Collecting, rearing, spawning and inducing regeneration of the starlet sea anemone, Nematostella vectensis. Nature Protocols, 8 (5), 916-923.

  24. Stephenson, T.A., 1935. The British Sea Anemones, vol. 2. London: Ray Society.

  25. Stocks, K.I. & Grassle, J.F., 2001. Effects of microalgae and food limitation on the recolonization of benthic macrofauna into in situ saltmarsh-pond mesocosms. Marine Ecology Progress Series, 221, 93-104.

  26. Sullivan, J.C., Ryan, J.F., Watson, J.A., Webb, J., Mullikin, J.C., Rokhsar, D. & Finnerty, J.R., 2006. StellaBase: The Nematostella vectensis Genomics Database. Nucleic Acids Research, 34 (suppl 1), D495-D499.

  27. Tarrant, A.M., Gilmore, T.D., Reitzel, A.M., Levy, O., Technau, U. & Martindale, M.Q., 2015. Current directions and future perspectives from the third Nematostella research conference. Zoology, 118 (2), 135-140.

  28. Tarrant, A.M., Reitzel, A.M., Kwok, C.K. & Jenny, M.J., 2014. Activation of the cnidarian oxidative stress response by ultraviolet radiation, polycyclic aromatic hydrocarbons and crude oil. Journal of Experimental Biology, 217 (9), 1444-1453.

  29. Williams, R.B., 1976. Conservation of the sea anemone Nematostella vectensis in Norfolk, England, and its worldwide distribution. Transactions of the Norfolk and Norwich Naturalists Society, 23, 257-266.

  30. Williams, R.B., 1983. Nematostella vectensis. In The IUCN invertebrate red data book (ed. S.M. Wells, R.M. Pyle and N.M. Collins), pp. 43-46. Gland: IUCN.

  31. Williams, R.B., 1991. Nematostella vectensis. In British Red Data Books. III. Invertebrates other than insects (ed. J.H. Bratton), pp. 32-33. Peterborough: Joint Nature Conservation Committee.

Datasets

  1. Bristol Regional Environmental Records Centre, 2017. BRERC species records recorded over 15 years ago. Occurrence dataset: https://doi.org/10.15468/h1ln5p accessed via GBIF.org on 2018-09-25.

  2. Dorset Environmental Records Centre, 2017. Dorset SSSI Species Records 1952 - 2004 (Natural England). Occurrence dataset: https://doi.org/10.15468/vcjzts accessed via GBIF.org on 2018-09-25.

  3. Isle of Wight Local Records Centre, 2017. IOW Natural History & Archaeological Society Marine Invertebrate Records 1853- 2011. Occurrence dataset: https://doi.org/10.15468/d9amhg accessed via GBIF.org on 2018-09-27.

  4. National Trust, 2017. National Trust Species Records. Occurrence dataset: https://doi.org/10.15468/opc6g1 accessed via GBIF.org on 2018-10-01.

  5. NBN (National Biodiversity Network) Atlas. Available from: https://www.nbnatlas.org.

  6. Norfolk Biodiversity Information Service, 2017. NBIS Records to December 2016. Occurrence dataset: https://doi.org/10.15468/jca5lo accessed via GBIF.org on 2018-10-01.

  7. OBIS (Ocean Biodiversity Information System),  2024. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. www.iobis.org. Accessed: 2024-11-02

  8. Suffolk Biodiversity Information Service., 2017. Suffolk Biodiversity Information Service (SBIS) Dataset. Occurrence dataset: https://doi.org/10.15468/ab4vwo accessed via GBIF.org on 2018-10-02.

Citation

This review can be cited as:

Tyler-Walters, H., Marshall, C.E. & Jackson, A. 2017. Nematostella vectensis Starlet sea anemone. 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 02-11-2024]. Available from: https://marlin.ac.uk/species/detail/1136

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Last Updated: 08/03/2017