Megabalanus tintinnabulum -

The giant purple barnacle is a cosmopolite in warm seas ^[2]. It is unknown where this barnacle originates from ^[3]. Some publications refer to the West Coast of Africa and the Indo-Pacific region as its area of origin ^[4]. This animal is a typical biofouling species on hard surfaces ^[5] and is mainly found in the sublittoral area, i.e. the zone just below the low water line ^[6]. Very occasionally, this barnacle can also be found in the low intertidal zone ^[7].

First observation in Belgium

During a study of the biofouling community on buoys off the Belgian coast, specimens of the giant purple barnacle were found for the first time in 1998 at three different locations. These buoys were temporarily deployed and were located at different distances from the coast ^[5].

This exotic species was already reported in 1881, but then it concerned some individuals washed ashore ^[8]. Because it is uncertain that these washed-up specimens originated from the Belgian part of the North Sea, this is not considered the first sighting of this species.

Spreading in Belgium

Since 1998, individuals are regularly found on buoys off our coast ^{[2, 9]}. Washed-up individuals are also regularly found on the beach and along the Dutch Western Scheldt. These consider individuals originating from ship hulls and fossils from the Pliocene that have washed ashore ^{[10, 11]}. In 2005, an individual was observed in De Panne, among the rubbish on the beach ^[12].

Spreading in neighbouring countries

This first European record of the giant purple barnacle dates from 1764 in North Holland (the Netherlands). The individual was found on a moored ship coming from Ghana ^[10]. After 1764, this barnacle was regularly spotted along the west coast of the Netherlands, between Schouwen-Duiveland (Zeeland) and Schiermonnikoog (Wadden Sea) ^{[10, 11]}. When studying washed-up giant purple barnacles, sometimes the origin of the specimen can be determined. For example, traces of rust were found on the underside of specimens washed ashore in the Netherlands ^[4]. This led to the conclusion that these individuals were probably detached from the hulls of ships.

The giant purple barnacle can be found along the French coast ^[3], as in the United Kingdom ^[13] and the Mediterranean ^[14]. However, there are no known permanent populations of this species in either the UK or the Mediterranean ^{[13, 14]}.

Mainly the larvae of the giant purple barnacle are responsible for its spread. The free-swimming larvae can be transported to new areas via the ballast water of ships. On the other hand, sessile adult individuals of the barnacle (e.g. on ship hulls) release their larvae into the environment where they are present ^[5]. The larvae swim around in the water column and settle after only four days ^[15].

The giant purple barnacle can grow to a considerable size: up to 7.5 centimetres, both in diameter and in height. These dimensions ensure that this non-native species can outcompete other sessile organisms, such as sea squirts, sponges, mussels or even other barnacles and compete with them for food and space ^[16].

The species is mainly found in the sublittoral. Closer to the coast – in the tidal zone – the larvae do not succeed in establishing themselves due to, among other things, the swell. In addition, the presence of light also plays an important role: in the intertidal zone, the intensity of the light is too strong, whereas deeper in the sea there is insufficient light for the giant purple barnacle ^{[17, 18]}.

Temperature and salinity are less important for the survival of the species, although it is a typical marine species ^[6]. The giant purple barnacle can tolerate temperatures up to 35 °C ^[7].

The giant purple barnacle is a sessile species that can establish itself on various substrates, including ship hulls. This increases the resistance of ships when sailing and results in less efficient fuel consumption. Attachment of barnacles can be prevented by treatment with antifouling paint, which is an expensive undertaking ^[19]. In addition, many of these paints damage the ecosystem. Some paints cause environmental damage long after they have been withdrawn from circulation, such as tributyltin (TBT), which use has been banned since 2003 ^[20].

If the species were to establish itself permanently, it could compete with indigenous species. The two closely related non-indigenous barnacles Megabalanus tintinnabulum (giant purple barnacle) and Megabalanus coccopoma (titan acorn barnacle) compete not only with our indigenous species but also with each other. A study in southern Brazil shows that when the two species compete, the titan acorn barnacle increases in number at the expense of the giant purple barnacle ^[21].

The giant purple barnacle is large in comparison to other barnacles. This species reaches a diameter and height of up to 7.5 centimetres and has a pink to purple colour. The robust ‘shell’ consists of six calcareous plates. The overlap between the plates is recognisable by the horizontal stripes in these areas. Where there is no overlap, the shell is not ribbed but smooth. Young individuals are conical, while adults become more cylindrical by widening the aperture ^[13]. Barnacles only feed when they are submerged. While feeding, they stick out their six pairs of long and hairy feeding legs or cirri to filter small particles from the water column. The giant purple barnacle can be distinguished in the field from the tropical barnacle Megabalanus coccopoma by its cylindrical shell, a less rounded opening and a pinkish-purple colour. Megabalanus coccopoma has a conical shell, a circular to oval central opening and pinkish-red colour ^{[22, 23]}. The giant purple barnacle often has a diamond-shaped opening. Finally, the plates of the operculum are also a good feature for identifying the species ^{[11, 13]}.

Furthermore, barnacles are hermaphrodites, which means that they are both male and female at the same time. Therefore, they can engage in self-fertilisation, but this gets avoided as much as possible. They have a long penis to fertilise a neighbouring barnacle ^[7]

[1]          World Register of Marine Species (WoRMS) (2020). Megabalanus tintinnabulum (Linnaeus, 1758). [http://www.marinespecies.org/aphia.php?p=taxdetails&id=106225] (2020-11-17).

[2]          Kerckhof, F. (2002). Barnacles (Cirripedia, Balanomorpha) in Belgian waters, an overview of the species and recent evolutions, with emphasis on exotic species. Bull. Kon. Belg. Inst. Natuurwet. Biologie 72(Suppl.): 93-104. [http://www.vliz.be/en/imis?module=ref&refid=66768]

[3]          Goulletquer, P.; Bachelet, G.; Sauriau, P.G.; Noel, P. (2002). Open Atlantic coast of Europe: a century of introduced species, in: Leppäkoski, E. et al. Invasive aquatic species of Europe: Distribution, impacts and management. Kluwer Academic: Dordrecht: pp. 276-290. [http://www.vliz.be/en/imis?module=ref&refid=40609]

[4]          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]

[5]          Kerckhof, F.; Cattrijsse, A. (2001). Exotic Cirripedia (Balanomorpha) from buoys off the Belgian coast. Senckenb. Marit. 31(2): 245-254. [http://www.vliz.be/en/imis?module=ref&refid=25318]

[6]          Fernando, S.A. (1999). Reproductive biology of tropical barnacles., in: Thompson, M.-F. et al. Barnacles: the biofoulers. Regency Publications: New Delhi: pp. 51-67. [www.vliz.be/en/imis?module=ref&refid=35437]

[7]          National Introduced Marine Pest Information System (NIMPIS) (2018). Megabalanus tintinnabulum general information. National Introduced Marine Pest Information System. [http://www.marinepests.gov.au/nimpis] (2018-07-24).

[8]          Pelseneer, P. (1881). Etudes sur la faune littorale de la Belgique: Tuniciers, crustacés, vers, échinodermes et coelentérés recueillis en 1881 sur la côte belge. Bull. Soc. Malac. Belgique 16: 168-173. [http://www.vliz.be/en/imis?module=ref&refid=122081]

[9]          ICES Advisory Committee on the Marine Environment (2006). Report of the Working Group on Introductions and Transfers of Marine Organisms (WGITMO) 16-17 March 2006 Oostende, Belgium. CM Documents - ICES. CM 2006(ACME:05). ICES: Copenhagen. 330 pp. [http://www.vliz.be/en/imis?module=ref&refid=111237]

[10]        Holthuis, L.B.; Heerebout, G.R. (1972). Vondsten van de zeepok Balanus tintinnabulum (Linnaeus, 1758) in Nederland. Zoologische Bijdragen 13: 24-31. [http://www.vliz.be/en/imis?module=ref&refid=195971]

[11]        Huwae, P.H.M. (1985). De Rankpotigen (Crustacea - Cirripedia) van de Nederlandse kust. Tabellenserie van de Strandwerkgemeenschap (SWG), 28. Strandwerkgemeenschap: Leiden. 44 pp. [http://www.vliz.be/en/imis?module=ref&refid=197223]

[12]        Kerckhof, F.; Haelters, J. (2005). Enkele opmerkelijke waarnemingen en strandingen in 2004 en 2005. De Strandvlo 15(3-4): 101-105. [http://www.vliz.be/en/imis?module=ref&refid=78684]

[13]        Southward, A.J. (2008). Barnacles: keys and notes for the identification of British species. Synopses of the British Fauna, N.S. 57. Field Studies Council: Shrewsbury. ISBN 978-1-85153-270-4. viii, 140 pp. [http://www.vliz.be/en/imis?module=ref&refid=119980]

[14]        Zenetos, A.; Cinar, M.E.; Pancucci-Papadopoulou, M.A.; Harmelin, J.G.; Furnari, G.; Andaloro, F.; Bellou, N.; Streftaris, N.; Zibrowius, H. (2005). Annotated list of marine alien species in the Mediterranean with records of the worst invasive species. Mediterr. Mar. Sci. 6(2): 63-118. [http://www.vliz.be/en/imis?module=ref&refid=109742]

[15]        Thiyagarajan, V.; Venugopalan, V.P.; Subramoniam, T.; Nair, K.V.K. (1997). Description of the naupliar stages of Megabalanus tintinnabulum (Cirripedia: Balanidae). J. Crust. Biol. 17(2): 332-342. [http://www.vliz.be/en/imis?module=ref&refid=199607]

[16]        Foster, B.A. (1987). Barnacle ecology and adaptation., in: Southward, A.J. Barnacle biology. Crustacean Issues, 5. pp. 113-133. [http://www.vliz.be/en/imis?module=ref&refid=58983]

[17]        Daniel, A. (1957). Influence of stage of tide on the attachment of barnacle cyprids. J. Bombay Nat. Hist. Soc. 54(4): 866-868. [http://www.vliz.be/en/imis?module=ref&refid=141030]

[18]        Daniel, A. (1957). Illumination and its effects on the settlement of barnacle cyprids. Proc. Zool. Soc. Lond. 129(3): 305-313. [http://www.vliz.be/en/imis?module=ref&refid=141123]

[19]        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]

[20]        Thomas, K.V.; Brooks, S. (2010). The environmental fate and effects of antifouling paint biocides. Biofouling 26(1): 73-88. [http://www.vliz.be/nl/catalogus?module=ref&refid=298933]

[21]        Young, P.S. (1994). The Balanoidea (Cirripedia) from the Brazilian coast. Bolm Mus. nac., N.S., Zool. 356: 1-36. [http://www.vliz.be/en/imis?module=ref&refid=141161]

[22]        Kerckhof, F.; Haelters, J.; Degraer, S. (2010). The barnacles Chirona (Striatobalanus) amaryllis (Darwin 1854) and Megabalanus coccopoma (Darwin 1854) (Crustacea, Cirripedia): two invasive species new to tropical West African waters. Afr. J. Mar. Sci. 32(2): 265-268. [http://www.vliz.be/en/imis?module=ref&refid=199831]

[23]        Power, A.; Rahn, A.; Bliss, T. (2007). Aquatic invasive species: A guide to non-native species in coastal Georgia. University of Georgia: Savannah. 12 pp. [http://www.vliz.be/nl/catalogus?module=ref&refid=296745]

VLIZ Alien Species Consortium (2020). Megabalanus tintinnabulum – Giant purple barnacle. Non-native species of the Belgian part of the North Sea and adjacent estuaries anno 2020. Flemish Institute for the Sea (VLIZ). 6 pp.