Starlet sea anemone (Nematostella vectensis)

NBN Interactive19-04-2007

Map accurate at time of writing. Visit NBN or OBIS to view current distribution

Researched byCharlotte Marshall & Angus Jackson Refereed byDr Simon Davy & Dr Martin Sheader
AuthorityStephenson, 1935
Other common names- Synonyms-

Summary

Description

A tiny anemone, with the column rarely more than 15 mm in length. Translucent and colourless in appearance except for variable patterns of opaque white on the column and disk. Tentacles large in proportion to body, colourless and translucent with pale tips and with faint transverse bars and irregular flecks of white. The tentacles (9 - 18) are very strongly adhesive.

Recorded distribution in Britain and Ireland

Found on north coast of Norfolk, the east coast of Suffolk, the Blackwater Estuary and Hamford Water in Essex, the Hampshire coast and on the south coast of Dorset.

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. Also found on the South and East coast of England.

Habitat

Lives in isolated or semi-isolated brackish lagoons at or above high water, typically in mud, muddy sand and muddy shingle (M. Sheader, pers. comm.) but is also found on vegetation.

Depth range

<1

Identifying features

  • Very small.
  • 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

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Biology review

Taxonomy

PhylumCnidariaSea anemones, corals, sea firs & jellyfish
ClassAnthozoaSea anemones, soft & cup corals, sea pens & sea pansies
OrderActiniaria
FamilyEdwardsiidae
GenusNematostella
AuthorityStephenson, 1935
Recent Synonyms

Biology

Typical abundanceHigh density
Male size rangeSee additional informationMale size at maturity
Female size rangeSmall(1-2cm)Female size at maturity
Growth formCylindricalGrowth rateNo information found
Body flexibilityMobilityNot relevant
Characteristic feeding methodNot relevant, Predator
Diet/food source
Typically feeds onHydrobia, Chironomid and Littorina juveniles.
SociabilityNo information Environmental positionEpifaunal
DependencyIndependent.
SupportsNone
Is the species harmful?Data deficient

Biology information

Although the column rarely exceeds 15 mm in length, exceptionally large individuals may reach 60 mm long when fully extended. Furthermore, food availability probably limits size in this species.
Only females are 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), therefore male size at maturity is not relevant. See reproduction for further information.

Abundance
Abundance generally varies with geographic area and time of year. In Pennington Lagoon, Hampshire, a peak in abundance of up to 2700 individuals / m is seen from September to October whilst in the Fleet, Dorset, the population peaks at around 1500 individuals / m, in November and December (Sheader et al., 1997). In September 1974, more than 12500 / m were found in a Norfolk pool and an estimate of over 5 million individuals in a single pool has even been made (William, unpubl., cited in Williams, R.B., 1983). On the south coast of England, individual population numbers tend to peak in late summer, the considerable increase probably being the result of asexual reproduction (Sheader et al., 1997).

Habitat preferences

Physiographic preferencesIsolated saline water (Lagoon)
Biological zone preferencesNot relevant
Substratum / habitat preferencesMacroalgae, Mud
Tidal strength preferencesVery Weak (negligible)
Wave exposure preferencesUltra sheltered
Salinity preferencesLow (<18 psu), Variable (18-40 psu)
Depth range<1
Other preferencesNo text entered
Migration PatternNon-migratory / resident

Habital Information

The populations of this species in Britain may either be:
1) relicts from a larger earlier distribution,
2) have arrived in Britain from North America by natural mean or
3) have been introduced by human agency.
Dispersal between lagoons may be via floating mats of Chaetomorpha sp. thus extending their dispersal potential. Biological zone is not relevant because this species lives in lagoons, generally not exposed to tidal action.
Posey & Hines (1991) suggested that in the Rhode River, America, the distribution outside lagoons may be limited through predation by shrimps.

Nematostella vectensis is often found using Ruppia sp. or Chaetomorpha sp. as substrata (Williams, 1991).

Depth
Although 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.).

Salinity
In English populations of Nematostella vectensis, the salinity in the vast majority of sites ranges between 2-42 ppt with the greatest abundance in ponds with seasonally varying salinity between 16-32 ppt. (Sheader et al., 1997).

Distribution in Britain and Ireland
Nematostella vectensis is found on 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. Nematostella vectensis was first described as a new species from brackish pools on the Isle of Wight.

Life history

Adult characteristics

Reproductive type Budding Reproductive frequency Annual episodic
Fecundity (number of eggs) Not relevant Generation time Not relevant
Age at maturity >10 weeks Season Not relevant
Life span Insufficient information

Larval characteristics

Larval/propagule type - Larval/juvenile development See additional information
Duration of larval stage Not relevant Larval dispersal potential Not relevant
Larval settlement period Insufficient information

Life history information

Nematostella vectensis is known to reproduce both sexually and asexually. In the UK there seems to be only female asexual reproduction (M. Sheader, pers. comm.). Males are absent from populations of Nematostella vectensis on the south coast of England suggesting that these populations produce all their offspring asexually (Sheader et al., 1997). Furthermore, it is likely that all the females are from one clone (M. Sheader, pers. comm.). Studies from American sexually reproducing populations have produced valuable information concerning gametes and larvae and some of this information is provided below. Unless otherwise stated, all the information in the asexual reproduction and sexual reproduction sections below are taken from Hand & Uhlinger (1995) and Hand & Uhlinger (1992) respectively.

Asexual reproduction
Transverse fission Asexual reproduction is achieved through transverse fission. Transverse fission is known in only four other sea anemones (Shick, 1991, cited in Hand & Uhlinger, 1994). In the laboratory, most fissions were 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. From the time of fission to the time of the first successful food capture, some fragments regenerated within three days. 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, 1995).
Budding
Anemones with multiple oral-crowns are common in both natural and laboratory reared populations of Nematostella vectensis. Fission by such individuals produces normal single-crowned anemones. This is known as budding and is extremely rare in anemones.

Sexual reproduction
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. 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 summarized by saying 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. Eggs are 170-240 µm in diameter and are released embedded in a gelatinous mucoid mass. In the laboratory, spherical ciliated planula larvae emerge from the egg masses between 36-48 hours after fertilization. These larvae are active swimmers from the age of about 3 days old but spend periods of inactivity on the bottom. After a week they settle by which point they are between 250-500 µm long and have four tentacles. By the time they are two months old they are approaching sexual maturity, are 2-5 cm long and have up to 16 tentacles.

Sensitivity reviewHow is sensitivity assessed?

Physical pressures

 IntoleranceRecoverabilitySensitivityEvidence/Confidence
High Very low / none Very High Low
Nematostella vectensis typically lives within the muddy substratum or on algae. Loss of the substratum is, therefore, likely to result in loss of the entire population and accordingly, intolerance has been assessed as high. Dispersal is very limited due to the isolated nature of suitable habitat, the lack of a dispersive phase in UK populations, and preponderance of asexual reproduction. Recovery is therefore likely to be very low.
Intermediate High Low Low
Nematostella vectensis typically burrows in mud and it is likely that most individuals would be able to move up through the smothering material. However, some mortality may be expected due to the small size of the animals and smothering by heavier material such as tar is likely to increase mortality. Intolerance has therefore been assessed as intermediate. Populations should recover relatively rapidly through asexual reproduction.
Low Immediate Not sensitive Low
Increases in siltation may interfere with feeding by clogging up the feeding apparatus. There may be an energetic cost associated with clearing the feeding apparatus. However, this is likely to be slight as the anemone is a sediment burrowing species used to dealing with particulate matter. Over the duration of benchmark some reductions in growth or reproduction may be observed. The amount of available food has been found to be linked to the frequency of fission and starvation can suppress the process (Hand & Uhlinger, 1995). An intolerance of low has been recorded to reflect a reduction in the viability of the population. Recovery is expected to be immediate on resumption of normal levels of suspended sediment.
No information
High Very low / none Very High Low
Nematostella vectensis populations remain submerged throughout the tidal cycle and are therefore likely to be intolerant to desiccation. Williams (1991) suggested that desiccation is likely to be a limiting factor in the distribution of this species. In the laboratory, Williams, R.B. (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 by trapped in the dried sediment and by 6 days, none had survived (Williams, R.B., 1976). The drying up of the pools or lagoons in which the species live is likely to destroy the population. For subtidal species, desiccation at the benchmark level is continual exposure to air and sunshine for one hour. In the natural environment, exposure is likely to have a more deleterious affect than in the laboratory, as sunshine and wind are likely to enhance desiccation. Therefore, an intolerance of high has been recorded. Dispersal is very limited due to the isolated nature of suitable habitat, lack of a dispersive phase in UK populations, and preponderance of asexual reproduction. Recovery is therefore likely to be very low.
High Very High Low
Nematostella vectensis populations remain submerged throughout the tidal cycle and are therefore likely to be intolerant to increased emergence at the benchmark level. Mortality is likely to be high at the upper limit of the population distribution. A decrease in emergence may extend the lower limit of the population providing suitable substratum remained. However, intolerance has been assessed as high to reflect the mortality associated with increased emergence. Dispersal is very limited due to the isolated nature of suitable habitat, lack of a dispersive phase in some populations, and preponderance of asexual reproduction. Recovery is therefore likely to be very low.
No information
High Very High High
Nematostella vectensis only inhabits areas that are ultra sheltered and have very low water flow rates (Sheader et al., 1997). Extreme shelter is needed as it allows a layer of fine mud to build up, in which the animal burrows (Williams, R.B., 1983). In the UK, Nematostella vectensis was found to be absent from areas where water flow exceeded 0.18 cm/s (Sheader et al., 1997) and is likely to be highly intolerant to changes in water flow rate at the benchmark level. Dispersal is very limited due to the isolated nature of suitable habitat, lack of a dispersive phase in UK populations, and preponderance of asexual reproduction. Recovery is therefore likely to be very low.
No information
Intermediate High Low Moderate
Living in eurythermal environments, Nematostella vectensis is very tolerant to temperature change. Nematostella vectensis has been found in temperatures ranging from -1 to 28C (Williams, 1991; Hand & Uhlinger, 1992). Temperatures above 28 °C were found to adversely affect the animals in the laboratory (Fritzenwanker & Technau, 2002), although no further information was given. Furthermore, the species has reportedly survived freezing at -5 °C for 48 hours (M. Sheader, pers. comm.). A short term acute change in temperature may result in the loss of some of the population and intolerance has therefore been assessed as intermediate. Longer term changes will probably have little or no effect. Assuming a portion of the population remains, recoverability should be fairly high through asexual reproduction.
No information
Tolerant Not relevant Not sensitive High
Nematostella vectensis has no visual ability other than to perhaps determine direction of light. Changes in light attenuation through cause by changes in the level of turbidity are, therefore, unlikely to have any effect and accordingly, tolerant has been recorded.
No information
High Very High High
Nematostella vectensis only inhabits areas that are ultra sheltered and have very low water flow rates (Sheader et al., 1997). Extreme shelter is needed as it allows a layer of fine mud to build up, in which the animal burrows (Williams, R.B., 1983). The animal is highly intolerant to increases in water flow rate (see water flow rate) and therefore likely to be highly intolerant to increases in wave exposure for the same reasons. Williams (1991) suggested that heavy wave exposure is likely to be a limiting factor in the distribution of this species. Dispersal is very limited due to the isolated nature of suitable habitat, lack of a dispersive phase in UK populations, and preponderance of asexual reproduction. Recovery is therefore likely to be very low.
No information
Tolerant Not relevant Not sensitive High
Nematostella vectensis is probably responsive to localised vibration, which is likely to cause it to withdraw into the substratum. However, it is unlikely to perceive noise at the benchmark level.
Tolerant Not relevant Not sensitive High
Nematostella vectensis has no visual ability other than to perhaps determine direction of light. This species is therefore likely to be tolerant of visual presence at the benchmark level.
Intermediate High Low Low
Although this species can retract into its burrow on disturbance, its small size and soft bodied nature mean that physical disturbance is likely to adversely affect individuals. A proportion of the population is likely to be killed and, therefore, intolerance has been assessed as intermediate. Given the high local abundance commonly associated with this species (see adult general biology), a proportion of the population is likely to remain and recoverability is likely to be high through asexual reproduction.
Tolerant Not relevant Not sensitive Low
Nematostella vectensis is a burrowing species that can move from a muddy substratum up on to an algal substratum and back again. This species is therefore likely to be tolerant of displacement.

Chemical pressures

 IntoleranceRecoverabilitySensitivityEvidence/Confidence
No information No information No information Not relevant
Insufficient
information
Heavy metal contamination
No information No information No information Not relevant
Insufficient
information
Hydrocarbon contamination
No information No information No information Not relevant
Insufficient
information
Radionuclide contamination
No information No information No information Not relevant
Insufficient
information
Changes in nutrient levels
No information No information No information Not relevant
Insufficient
information.
Low Very high Very Low High
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). Field observations indicate that above 40 ppt, tentacles are retracted and feeding ceases (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% seawater were deflated and had mesenteries everted through their mouths within 5 weeks. At the other extreme, anemones in 125% seawater had decreased in size after 4 months and only spawned once, although asexual reproduction was not markedly less effective than at 33% 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 ‰. 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. Changes in salinity, at the benchmark level, are therefore likely to affect different populations in different ways, depending on the salinity regime they are adapted to and, therefore, an intolerance of intermediate has been recorded. Assuming some portion of the population remains, recoverability is likely to be high through asexual reproduction.
No information
Intermediate High Low Low
Lagoon environments frequently have high macroalgal production which can result in anoxic conditions on the sediment - water interface. Williams (1991) suggested that extreme hypoxia is likely to be a limiting factor in the distribution of this species. Further, anemones recovered from anoxic mud in the field were 'very sick' (Williams, R.B., 1976). Nematostella vectensis, along with several other lagoon species can move up onto the algal mats to avoid the anoxic conditions. Intolerance has been recorded as intermediate to reflect some mortality, although populations should recover fairly rapidly through asexual reproduction.

Biological pressures

 IntoleranceRecoverabilitySensitivityEvidence/Confidence
No information No information No information Not relevant
Insufficient
information
No information No information No information Not relevant
Insufficient
information
Not relevant Not relevant Not relevant Not relevant
Targeted extraction of this species is highly unlikely.
Intermediate High Low Very low
During periods of reduced oxygen concentrations, algae may be used as a preferential substratum. Removal of these algae may result in intermediate intolerance in times of low oxygenation. Assuming some portion of the population remains, recoverability should be high through asexual reproduction.

Additional information

Importance review

Policy/legislation

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

Status

National (GB) importanceNot rare/scarceGlobal red list (IUCN) categoryVulnerable (VU)

Non-native

Native-
Origin- Date Arrived-

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 marsh became polluted or dried up, for example, the entire population of Nematostella vectensis would be annihilated. 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).
Williams, R.B. (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.

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

  4. 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.

  5. 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.

  6. 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.

  7. Howson, C.M. & Picton, B.E. (ed.), 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.]

  8. Manuel, R.L., 1988. British Anthozoa. London: Academic Press.[Synopses of the British Fauna, no. 18.]

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

  10. 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.

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

  12. 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.

  13. 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.

  14. 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.

Citation

This review can be cited as:

Marshall, C.E. & Jackson, A. 2007. Nematostella vectensis Starlet sea anemone. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. Available from: http://www.marlin.ac.uk/species/detail/1136

Last Updated: 19/04/2007