Diadumene lineata - Striped sea anemone

The orange-striped anemone is an anemone, a type of anthozoan, native to the Asian Pacific Ocean. The original distribution range includes China, Japan and Hong Kong ^[2-4].

First observation in Belgium

The first observation of the orange-stripped anemone in Belgium dates back to 1998. The first individual was seen in the Sluice Dock of Ostend ^[5].

Spreading in Belgium

In 2003, the orange-striped anemone was abundantly present at different places in the Sluice Dock of Ostend ^[6]. It seems that the species has permanently established itself at this location. There are no reports of the species from other areas along our coast.

Spreading in neighbouring countries

Most likely, the orange-striped anemone got introduced to Europe at the end of the 19^th century. The species was first observed in Plymouth (England) in 1896 ^[7]. Today, the species is common in the brackish waters of Great Britain ^[3].

In the Netherlands, the species was first observed in 1912-1913 near the harbour of Den Helder. There, the species was observed until the 1930s ^[8]. In 1968 and 1969, it was (possibly) observed in Lake Veerse, near the Eastern Scheldt. On the 12^th of June 1981, this alien species was observed again in the Netherlands, this time on the Wadden Island Texel. Later, the species was found on the nearby island Vlieland ^[9-11]. Currently, the species is widespread in the province of Zeeland ^[12] and the Western Scheldt almost to the Drowned Land of Saeftinghe ^[13].

In Germany, an established population was observed only once between 1920 and 1924 in Büsum, north of the Elbe estuary. This busy and heavily trafficked region could never be recolonized, due to the low salinity in the area. The orange-striped anemone cannot survive in water with a salinity of 12 PSU. By comparison, the North Sea has a salinity of 35 PSU. Another reason might be the introduction of the non-native sea anemone Diadumene cincta in the German coastal waters during the 1920s. D. cincta occupies a similar niche as the orange-striped anemone and can complicate the establishment of other anemone species because of its aggressive behaviour ^[14]

At the end of the 19^th century, transport by attachment to ship hulls or via aquaculture of Japanese oysters introduced the orange-striped anemone to Europe ^[15]. This sea anemone finds it difficult to attach itself directly to ship hulls. However, they can easily attach themselves to and in between oysters, even if these are attached to a hull. Between these shells, they are relatively protected and can rapidly reproduce asexually. A single individual, attached to shells present on ship hulls, can colonize several areas along the route of the ship ^[14].

The orange-stripped anemone moves by crawling rather slowly using its basal disk. In some cases – e.g. when the water is suddenly polluted – these animals can completely detach themselves and float in search of a more suitable habitat. While floating in the water, they can encounter ship hulls, which help them to distribute even further ^{[16, 17]}.

The species is resistant to varying environmental factors (including salinity and temperature) and can rapidly reproduce sexually and asexually. Asexual reproduction occurs by longitudinal fission ^[16].

The distribution of marine organisms depends on their physiological features, environmental factors, distribution potential and ecological interactions ^[18]. Low salinities (less than 12 PSU) inhibit the development of this non-native anemone and limit its distribution to estuarine and marine areas ^{[9, 16]}. In some marine areas, this species can occur quite high in the tidal zone in large numbers. In brackish waters, the anemone can sustain itself even in the areas where the water gets fresher during low tide ^[13].

As one moves away from the North Sea, a salinity gradient (from 15 to 3 PSU) is present in the Baltic Sea ^[19]. This salinity gradient forms a barrier for the anemone, which prefers salt water (24-34 PSU). At a salinity of 7 PSU, it can no longer reproduce asexually. The species could disperse to Skagerrak and Kattegat but not further to the east ^[18]. In theory, the North Sea (with a salinity of 35 PSU) could be completely colonized by this anemone.

The orange-striped anemone attaches itself to mussels and oysters. In aquacultures, molluscs can be affected by the presence of the anemone and, as a result, have lower productivity. Possibly, this non-native anthozoan affects native anemones, although there is no proof to support this hypothesis ^[20].

The orange-striped anemone consists – in the open state – of a column that is usually dark green with orange longitudinal stripes at the base. These longitudinal stripes can be absent, white or in some individuals occur together with white stripes. The upper part of the body is light green and merges into tentacles. The tentacles are longer than the column and have a light grey-greenish to white colour, and sometimes even light dots spread all over. These animals can grow up to 4 cm, but rarely reach these sizes in our areas ^{[10, 16]}.

[1]          World Register of Marine Species (WoRMS) (2020). Diadumene lineata (Verrill, 1869). [http://www.marinespecies.org/aphia.php?p=taxdetails&id=395099] (2020-11-17).

[2]          Stephenson, T.A. (2003). The British sea anemones [CD-ROM]. Pisces Conservation Ltd: Lymington. ISBN 1-904690-10-6. 1 cr-rom (text, plates). [http://www.vliz.be/en/imis?module=ref&refid=73215]

[3]          Eno, N.C.; Clark, R.A.; Sanderson, W.G. (Ed.) (1997). Non-native marine species in British waters: a review and directory. Joint Nature Conservation Committee: Peterborough. ISBN 1-86107-442-5. 152 pp. [http://www.vliz.be/nl/imis?module=ref&refid=24400]

[4]          Cohen, A.N. (2011). The Exotics Guide: Non-native Marine Species of the North American Pacific Coast. Center for Research on Aquatic Bioinvasions, Richmond, CA, and San Francisco Estuary Institute, Oakland, CA. [www.exoticsguide.org] (2018-08-08).

[5]          Kerckhof, F.; Haelters, J.; Gollasch, S. (2007). Alien species in the marine and brackish ecosystem: the situation in Belgian waters. Aquat. Invasions 2(3): 243-257. [http://www.vliz.be/en/imis?module=ref&refid=114365]

[6]          De Maersschalck, V. (2004). Een inventarisatie van de macrofauna van de Spuikom te Oostende: bijdrage tot een geïntegreerd beheer. MSc Thesis. Universiteit Gent, Vakgroep Biologie: Gent. 71 pp. [http://www.vliz.be/en/imis?module=ref&refid=63805]

[7]          Walton, C.L. (1908). Notes on some Sagartiidae and Zoanthidae from Plymouth. J. Mar. Biol. Ass. U.K. 8: 207-214. [http://www.vliz.be/en/imis?module=ref&refid=128399]

[8]          van Urk, R.M. (1956). Diadumene luciae (Verrill). Het Zeepaard 16(2): 28-29. [http://www.vliz.be/en/imis?module=ref&refid=114451]

[9]          Braber, L.; Broghouts, C.H. (1977). Distribution and ecology of Anthozoa in the estuarine region of the rivers Rhine, Meuse and Scheldt. Hydrobiologia 52(1): 15-21. [www.vliz.be/en/imis?module=ref&refid=108970]

[10]        Dekker, R. (1982). De zeeanemoon, Haliplanella lineata (Verrill), weer in Nederland. Het Zeepaard 42(5): 117-121. [http://www.vliz.be/en/imis?module=ref&refid=117473]

[11]        Faasse, M. (1996). Diadumene luciae (Verrill, 1869) en Balanus amphitrite Darwin, 1854 bij de koelwateruitlaat te Borssele. Het Zeepaard 56: 73-75. [http://www.vliz.be/en/imis?module=ref&refid=138071]

[12]        Faasse, M. (1997). Nieuwe vindplaatsen van de groene golfbrekeranemoon (Diadumene luciae Verrill, 1898). Het Zeepaard 57(4): 76-80. [http://www.vliz.be/nl/catalogus?module=ref&refid=207068]

[13]        Faasse, M. (2019). Persoonlijke mededeling

[14]        Gollasch, S.; Riemann-Zürneck, K. (1996). Transoceanic dispersal of benthic macrofauna: Haliplanella luciae (Verrill, 1898) (Anthozoa, Actiniaria) found on a ship's hull in a shipyard dock in Hamburg Harbour, Germany. Helgol. Meeresunters. 50(2): 253-258. [http://www.vliz.be/en/imis?module=ref&refid=27137]

[15]        Nehring, S.; Leuchs, H. (1999). Neozoa (Makrozoobenthos) an der deutschen Nordseeküste: eine Übersicht. Bericht BfG, 1200. Bundesanstalt für Gewässerkunde = Federal Institute of Hydrology: Koblenz. 131 pp. [http://www.vliz.be/en/imis?module=ref&refid=120661]

[16]        Shick, J.M. (1991). A functional biology of sea anemones. Functional biology series. . Chapman & Hall: London. ISBN 0-412-33150-0. xxi, 395 pp. [http://www.vliz.be/en/imis?module=ref&refid=138245]

[17]        Pax, F. (1920). Die aktinienfauna von Büsum. Schr. zool. Stat. Büsum Meeresk 5: 1-24. [http://www.vliz.be/en/imis?module=ref&refid=128811]

[18]        Podbielski, I.; Bock, C.; Lenz, M.; Melzner, F. (2016). Using the critical salinity (S_crit) concept to predict invasion potential of the anemone Diadumene lineata in the Baltic Sea. Mar. Biol. (Berl.) 163(227): 1-15. [http://www.vliz.be/nl/catalogus?module=ref&refid=300131]

[19]        Sjöqvist, C.; Godhe, A.; Jonsson, P.R.; Sundqvist, L.; Kremp, A. (2015). Local adaptation and oceanographic connectivity patterns explain genetic differentiation of a marine diatom across the North Sea-Baltic Sea salinity gradient. Mol. Ecol. 24(11): 2871-2885. [http://www.vliz.be/nl/catalogus?module=ref&refid=300132]

[20]        Cohen, A.N. (2009). Guide to marine invaders in the Gulf of Maine: Diadumene lineata orange-striped anemone. Salem Sound Coastwatch: Salem. 2 pp. [http://www.vliz.be/en/imis?module=ref&refid=207012]

VLIZ Alien Species Consortium (2020). Diadumene lineata – Orange-striped anemone. Non-indigenous species in the Belgian part of the North Sea and adjacent estuaries anno 2020. Flanders Marine Institute (VLIZ). 5 pp.