Nematostella vectensis
Sea anemones are generally thought of as occurring on rocky sea beds but the Starlet Sea Anemone’s habitat is fine mud in brackish pools. This is not a common habitat and in Britain it is found only in Hampshire, Suffolk, Essex and at Cley on the Norfolk coast. When a pool in which it occurred there was threatened by coastal erosion, a translocation programme transferred it to pools on NWT Cley Marshes where several populations are now thriving. The extended ‘arms’ of the anemone measure less than 2cm across and at the slightest disturbance they, and the anemone’s tubular body, contract into the mud.
Text: Tony Leech
Classified as a Priority Species in the UK Biodiversity Action Plan.
Species of principal importance for the purpose of conservation of biodiversity under the Natural Environment and Rural Communities Act 2006.
Listed as Vulnerable on the IUCN Red List.
The coastal lagoons in which the starlet anemones can be found are a UKBAP priority habitat and are listed in Annex I of the Habitats Directive.
Protected under Schedule 5 of the Wildlife and Countryside Act 1981.
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. Although the column rarely exceeds 15 mm in length, exceptionally large individuals may reach 60 mm long when fully extended.
Nematostella vectensis is 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. Nematostella vectensis was first described as a new species from brackish pools on the Isle of Wight.
Lives in isolated or semi-isolated brackish lagoons at or above high water, typically in mud, muddy sand and muddy shingle but is also found on vegetation. Although the species is usually found in water less than 1 m deep, a few live down to 2 m water depth. 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.
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. 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. 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.
Nematostella vectensis is known to reproduce both sexually and asexually. In the UK there seems to be only female asexual reproduction. Males are absent from populations of Nematostella vectensis on the south coast of England suggesting that these populations produce all their offspring asexually. Furthermore, it is likely that all the females are from one clone.