Aplidium glabrum -

The exact origin of A. glabrum is unknown ^[2]. Since it was observed near Russia and Japan before 1906, the species is assumed to be native to the northwestern part of the Pacific Ocean ^[3]. This species has also been observed off the coasts of the Northwest Atlantic Ocean ^[4] and is considered native there ^[5].

In general, A. glabrum is described as a species originating from cold to Arctic regions. It occurs at depths of 0 to 400 metres ^[6] and attaches itself to all kinds of hard substrates, such as stones and shells ^[7].

First observation in Belgium

In June 2000, A. glabrum was observed for the first time in the fishing port (marina) of Zeebrugge ^[8].

Spreading in Belgium

Since the first report, this species gets observed annually on pontoons in the marina of Zeebrugge ^{[2, 8]}. There are no known observations at other locations.

Spreading in neighbouring countries

A. glabrum occurs in the Northeast Atlantic Ocean, from northern Scotland to the Arctic Ocean. Since 1977, it lives also more to the south, in the Netherlands and Belgium ^[9].

In the Netherlands, the species was first reported in 1977 in Yerseke. Later, more observations followed in the Eastern Scheldt ^{[10, 11]}. Nowadays, A. glabrum is widespread in the Eastern Scheldt and Lake Grevelingen ^[12]. The species was first observed in the Wadden Sea in 2009, in the port of Terschelling ^[13]. More recently, it was observed on the West Frisian islands Vlieland and Schiermonnikoog ^[14].

Today, this exotic species is present along the Irish and English west coast ^[9]

It remains unclear how this species covered the large distances between the northwestern part of the Pacific and North Atlantic coasts. It is suspected that the introduction of A. glabrum in the Netherlands took place via the import of oysters ^[11]. This sea squirt can, like many other species, attach itself to shells, e.g. mussels and oysters. By attaching to oysters, imported from the Northwest Pacific to Europe, these sea squirts could have reached Europe. The relocation of oysters within Europe subsequently caused a rapid spread throughout our continent ^[15].

A. glabrum attaches itself to all kinds of hard substrates, particularly pontoons, ropes and poles ^[7].  Harbours – with their many artificial substrates – provide for an ideal environment for successful colonisation.

This sea squirt is found exclusively in cold to Arctic regions in the Pacific and the Atlantic Ocean ^{[4, 6, 12, 16]}. This indicates that the spread of the species is likely limited to colder environments.

Effects on the natural environment are unknown. This species is part of the biofouling community. Fouling can affect various substrates and even cause economic damage. Preventing their attachment to ship hulls via cleaning and treatment with antifouling paint is very expensive ^[17]. Additionally, many of these paints cause damage to the ecosystem.

In 2007, a control measure got introduced in the Netherlands that banned the import of mussels from Ireland. This measure was taken after the discovery that mussel shells host a high diversity of non-native species, including A. glabrum. After less than one year, in December 2008, this measure was repealed under the pressure of the European Commission, who challenged the Netherlands to the European Court for violating the European Free Trade Agreement ^[15]. From 2012, a strict shellfish transport policy got introduced ^[18] with continuous intensive monitoring in potential export areas and upon arrival in the Netherlands. This policy focuses specifically on minimizing the risk of problem species (i.e. species that are expected to have a significant negative impact on the Natura 2000 values of the Eastern Scheldt) being imported on/with shellfish.

A colony of A. glabrum forms crusty lumps of up to three centimetres high. The colour is often yellow to orange with a translucent white haze at the top. They can also have a uniformly off-white colour. The colony consists of one or more flattened lobes on the upper side. The lateral sides are often covered with sand and sediment. Individuals (zooids) sit close together in an irregular pattern ^[10]. The colonies are relatively dense and considerably firmer than colonies of other colony-forming sea squirts found in Belgium and neighbouring countries.

Sea squirts are filter-feeders. Water, carrying numerous small food particles, flows through their oral siphon to the inside of the sea squirt. These particles get caught in mucus produced by a gland called the endostyle. Their waste flows out of their body via the atrial siphon ^[10].

A. glabrum produces a substance called ‘3-demethylubiquinone Q2’, used to extract energy from its food. Recent research suggests that this substance has a cancer-preventive effect ^[19].

[1]          World Register of Marine Species (WoRMS) (2020). Aplidium glabrum (Verrill, 1871). [http://www.marinespecies.org/aphia.php?p=taxdetails&id=103647] (2020-11-17).

[2]          De Blauwe, H.; Dumoulin, E. (2009). De zeefauna en -flora uit de jachthaven van Zeebrugge, in het bijzonder de fouling-organismen van drijvende pontons. De Strandvlo 29(2): 41-63. [http://www.vliz.be/imis/imis.php?module=ref&refid=139489]

[3]          Tokioka, T. (1967). Pacific Tunicata of the United States National Museum. Bulletin. United States National Museum, 251. Institution, S.: Washington D.C., USA. 247 pp. [http://www.vliz.be/en/imis?module=ref&refid=98352]

[4]          Costello, M.J.; Bouchet, P.; Boxshall, G.; Arvanitidis, C.; Appeltans, W. (2018). European Register of Marine Species. Aplidium glabrum (Verrill, 1871). [http://www.vliz.be/vmdcdata/narms/narms.php?p=taxdetails&id=103647#distributions] (2018-07-19).

[5]          Locke, A. (2009). A screening procedure for potential tunicate invaders of Atlantic Canada. Aquat. Invasions 4(1): 71-79. [http://www.vliz.be/en/imis?module=ref&refid=197743]

[6]          Hayward, P.J.; Ryland, J.S. (Ed.) (1990). The marine fauna of the British Isles and North-West Europe: 2. Molluscs to chordates. Clarendon Press: Oxford, UK. ISBN 0-19-857515-7. xvi, 628-996 pp. [http://www.vliz.be/en/imis?module=ref&refid=4891]

[7]          Gittenberger, A. (2007). Recent population expansion of non-native ascidians in The Netherlands. J.Exp. Mar. Biol. Ecol. 342(1): 122-126. [http://www.vliz.be/en/imis?module=ref&refid=206037]

[8]          Waarnemingen afkomstig van Waarnemingen.be: een initiatief van Natuurpunt Studie vzw en de Stichting Natuurinformatie (2018). Glanzende Bolzakpijp - Aplidium glabrum. [https://waarnemingen.be/soort/view/27531?from=2007-08-13&to=2009-08-13&species=27531&prov=0&akt=0&from=1974-08-22&to=2009-08-13&prov=0] (2018-07-06).

[9]          Global Biodiversity Information Facility (GBIF) (2018). Aplidium glabrum (Verrill, 1871). [https://www.gbif.org/species/2330928] (2018-07-19).

[10]        Buizer, D.A.G. (1983). De Nederlandse zakpijpen (Manteldieren) en Mantelvisjes: Tunicata, Ascidiacea en Appendicularia. Wetenschappelijke Mededelingen van de Koninklijke Nederlandse Natuurhistorische Vereniging, 158. Koninklijke Nederlandse Natuurhistorische Vereniging (KNNV). Hoogwoud, The Netherlands. 42 pp. [www.vliz.be/en/imis?module=ref&refid=8883]

[11]        Buizer, B. (1989). De zakpijp Aplidium glabrum en de sponzen Haliclona rosea, Prosuberites epiphytum en Hymeniacidon perlevis succesvol in de Oosterschelde. Het Zeepaard 49(6): 156-159. [http://www.vliz.be/en/imis?module=ref&refid=197745]

[12]        Wolff, W.J. (2005). Non-indigenous marine and estuarine species in the Netherlands. Zool. Meded. 79(1): 3-116. [http://www.vliz.be/en/imis?module=ref&refid=101200]

[13]        Gittenberger, A.; Rensing, M.; Stegenga, H.; Hoeksema, B. (2010). Native and non-native species of hard substrata in the Dutch Wadden Sea. Ned. Faunist. Meded. 33: 21-76. [http://www.vliz.be/en/imis?module=ref&refid=206549]

[14]        Gittenberger, A.; Rensing, M.; Dekker, R.; Niemantsverdriet, P.; Schrieken, N.; Stegenga, H. (2015). Native and non-native species of the Dutch Wadden Sea in 2014. GiMaRIS rapport 2015_08. Office for Risk Assessment and Research, The Netherlands Food and Customer Product Safety Authority of the Ministry of Economical Affairs. Leiden. 94 pp. [http://www.vliz.be/nl/catalogus?module=ref&refid=312571]

[15]        Gittenberger, A. (2009). Invasive tunicates on Zeeland and Prince Edward Island mussels, and management practices in The Netherlands. Aquat. Invasions 4(1): 279-281. [http://www.vliz.be/en/imis?module=ref&refid=197746]

[16]        Sanamyan, K.E. (2000). Three related Aplidium species from the southern Kurile Islands (Ascidiacea: Polyclinidae). Zoosyst. Ross. 8(2): 211-216. [http://www.vliz.be/en/imis?module=ref&refid=197749]

[17]        Schultz, M.P.; Bendick, J.A.; Holm, E.R.; Hertel, W.M. (2010). Economic impact of biofouling on a naval surface ship. Biofouling 27(1): 87-98. [http://www.vliz.be/en/imis?module=ref&refid=206434]

[18]        Bleker, H. (2012). Beleidsregels van de Staatssecretaris van Economische Zaken, Landbouw en Innovatie van 6 juni 2012, nr. 267278, houdende vaststelling van beleidsregels inzake schelpdierverplaatsingen. Staatscourant, 2012 (12068). Koninkrijk der Nederlanden. 4 pp. [http://www.vliz.be/nl/catalogus?module=ref&refid=312605]

[19]        Fedorov, S.N.; Radchenko, O.S.; Shubins, L.K.; Balaneva, N.N.; Bode, A.M.; Stonik, V.A.; Dong, Z. (2006). Evaluation of cancer-preventive activity and structure-activity relationships of 3-demethylubiquinone Q2, isolated from the ascidian Aplidium glabrum, and its synthetic analogues. Pharm. Res. 23(1): 70-81. [http://www.vliz.be/nl/catalogus?module=ref&refid=297886]

VLIZ Alien Species Consortium (2020). Aplidium glabrum. Non-indigenous species in the Belgian part of the North Sea and adjacent estuaries anno 2020. Flanders Marine Institute (VLIZ). 5 pp.