Megabalanus coccopoma - Titan acorn barnacle

Originally, the titan acorn barnacle occurred along the Central and South American coasts of the tropical Pacific Ocean ^[2]. This barnacle is native to the coasts of Baja California to those of Peru ^[3]. This barnacle is an opportunistic species that can settle best in recently disturbed areas on ship hulls, buoys and large crustaceans in the low intertidal zone, down to depths of up to 100 metres ^[4].

First observation in Belgium

In 1997, during a study of the fouling community on buoys off the Belgian coast, a dozen individuals of this barnacle were found for the first time on a buoy off the Kwintebank, about 10 kilometres from the coast of Nieuwpoort ^[2].

Spreading in Belgium

Since 1997, individuals of the titan acorn barnacle have been reported in Belgian waters, both on buoys and floating objects ^{[2, 5-7]}.

In the study area, loose and empty individuals were found in 2006 in a cooling water intake of the Borssele Nuclear Power Station, in the Dutch Western Scheldt. These individuals probably died due to the low temperatures ^[8].

Spreading in neighbouring countries

The first sighting in Europe dates back to 1851 when this barnacle was found on the hull of a ship in Le Havre (Northwest France) ^[9].

In the Netherlands, the first sighting of the titan acorn barnacle dates back to 1976. The species was found on buoys off the coast of Terschelling, in the north of the Netherlands. A dozen or so specimens were then collected. However, the identification did not go smoothly. Originally, these living barnacles were identified as Perforatus perforatus ^[10]. When this material was re-examined a few years later, it was suspected to be Megabalanus tintinnabulum ^[11]. Later this also turned out to be incorrect and – after a third examination – it was concluded that the species was the titan acorn barnacle Megabalanus coccopoma ^[2].

A subsequent observation in the Netherlands occurred in 2004. Then, a dead specimen was found on a washed-up plastic barrel near Domburg, in the southwest of the Netherlands ^[8]. In 2007, another individual washed ashore at Ter Heijde, near The Hague. It is not clear whether the individual was dead or alive ^[7]. In 2009, this exotic species was spotted – alive – in the Eastern Scheldt, near the town of Bruinisse ^[12].

Besides those from France and the Netherlands, there are no reported cases of this barnacle from other neighbouring countries ^[13]. The species is regularly found in the fouling community on ships but is often misidentified as another barnacle species ^[14]. The barnacle can be found in various locations worldwide, such as the eastern United States, North Africa, Japan and Australia ^[15]

The literature mentions two possible ways of introduction. Adult individuals can be transported by attaching themselves to ship hulls. At different locations, larvae can be released into the water column. On the other hand, larvae may be directly transported in ballast water ^[2]. However, the latter possibility is questioned because the larvae of this non-indigenous species are less tolerant to the generally harsh ballast water conditions ^[4].

In the United States, the larvae can also spread northwards through the Gulf Stream ^[16].

The titan acorn barnacle is an opportunistic species that settles on all types of hard substrates but has a clear preference for disturbed and bare substrates ^[4]. This quick-growing barnacle can grow up to 5 cm in height and diameter. This non-native barnacle competes with other species for space and food ^[17].

Settled on ships’ hulls, this barnacle can release its larvae into the water column at various locations. Like all barnacles, its larvae are free-swimming ^[17]. They can live in the water column for up to three weeks, during which they are dispersed by the prevailing currents. In this way, they spread to new habitats, where they can settle themselves in case of a favourable environment ^[4].

Although the titan acorn barnacle is a tropical species, it can adapt to a new, colder environment ^[18]. The larvae of the titan acorn barnacle can undergo metamorphosis at 16 °C which is a much lower temperature than in its natural range. Therefore, it is likely that lower temperatures will not be a barrier to the barnacle. Probably, it will continue its spread to the north in the future ^[3].

Salinity is even less important in regards to determining whether or not Megabalanus coccopoma can establish itself. Although the species thrives best in saltwater, it can survive periods of relatively low salinity without too much trouble and can cope with conditions of fluctuating salt concentrations ^[18].

Settlement and growth on structures such as hulls, buoys and various other (fishing) materials can cause problems. The increased resistance that ships encounter in gliding through the water results in less efficient fuel consumption. Attachment of barnacles can be solved by cleaning the hull or can be avoided 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); the use of which has already been banned since 2003 ^[20].

Competition with other filter-feeding and/or fouling species for food and space may affect the indigenous community ^[21]. The two non-native barnacles Megabalanus tintinnabulum and Megabalanus coccopoma (titan acorn barnacle) are competing not only with our native species but also with each other. A study in southern Brazil shows that when the two species compete, the titan acorn barnacle increases in numbers at the expense of the Megabalanus tintinnabulum ^[22].

The titan acorn barnacle can grow up to 5 centimetres both in width and height, making it one of the larger barnacles. The shell consists of six overlapping calcareous (limestone) plates, with the non-overlapping parts being smooth and pinkish-red and the relatively narrow overlapping parts being purple to white. The central opening is also narrow ^[4]. Barnacles only feed when they are submerged. Then, the central opening is opened and they stick out their six pairs of long and hairy legs or cirri. They filter small food particles from the water column.

In the field, this barnacle can be distinguished relatively easily from the other tropical Megabalanus tintinnabulum. The titan acorn barnacle has a conical shell, a narrow circular to oval central opening and a pinkish-red colour, while Megabalanus tintinnabulum has a more cylindrical shell, a less rounded opening and a pink to purple colour ^[23].

Barnacles are hermaphroditic. They have a long phallus or penis to fertilise a neighbouring barnacle ^[17]. The larvae go through several nauplius stages, after which a transformation takes place into a non-feeding cypris larva. The cypris larvae are completely dependent on the energy stored during previous feeding stages. The available energy that was stored earlier determines their survival success at this juvenile stage ^{[3, 24, 25]}.

The titan acorn barnacle can store metals such as copper (Cu), lead (Pb) or zinc (Zn), which are normally toxic, in its body. By measuring the concentration of these substances in certain tissues of the body, scientists can get an idea of the state and evolution of water quality over time, and how this has affected the present fauna ^[26].

[1]          World Register of Marine Species (WoRMS) (2020). Megabalanus coccopoma (Darwin, 1854). [http://www.marinespecies.org/aphia.php?p=taxdetails&id=149682] (2020-11-17).

[2]          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]

[3]          Crickenberger, S.; Walther, K.; Moran, A.L. (2017). Lower thermal limits to larval development do not predict poleward range limits of the introduced tropical barnacle Megabalanus coccopoma. Invertebr. Biol. 136(1): 37-49. [http://www.vliz.be/nl/catalogus?module=ref&refid=296742]

[4]          Newman, W.A.; McConnaughey, R.R. (1987). A tropical eastern Pacific barnacle, Megabalanus coccopoma (Darwin), in southern California, following El Niño 1982-83. Pacif. Sci. 41: 1-4. [http://www.vliz.be/en/imis?module=ref&refid=204522]

[5]          Kerckhof, F.; Van Outryve, R. (2005). Verslag van de excursie naar Koksijde op 29 november 2003. De Strandvlo 25(1): 19-25. [http://www.vliz.be/en/imis?module=ref&refid=72346]

[6]          ICES Advisory Committee on the Marine Environment (2006). Report of the Working Group on the Assessment of Demersal Stocks in the North Sea and Skagerrak (WGNSSK), 6-15 September 2005, ICES Headquarters, Copenhagen. CM Documents - ICES. CM 2006/ACFM:09. ICES: Copenhagen. 981 pp. [http://www.vliz.be/nl/catalogus?module=ref&refid=302997]

[7]          Waarnemingen afkomstig van Waarnemingen.be: een initiatief van Natuurpunt Studie vzw en de Stichting Natuurinformatie (2018). Grote roze zeepok - Megabalanus coccopoma (Darwin, 1854). [https://waarneming.nl/soort/view/106300] (2018-07-24).

[8]          Van Nieulande, F.; Raad, H.; Faasse, M. (2006). De exotische zeepok Megabalanus coccopoma (Darwin, 1854) autochtoon voorkomend bij Borssele. Het Zeepaard 66(6): 174-176. [http://www.vliz.be/en/imis?module=ref&refid=106306]

[9]          Nilsson-Cantell, C.A. (1932). Revision der Sammlung rezenter Cirripedien des Naturhistorischen Museums in Basel. Verh. Naturforsch. Ges. Basel. 42: 103-137. [http://www.vliz.be/en/imis?module=ref&refid=196984]

[10]        Buizer, D.A.G. (1978). First autochtonous records of Balanus perforatus Bruguière (Cirripedia Balanomorpha) and Conchoderma auritum (L;) (Cirripedia Lepadomorpha) in the coastal waters of the Netherlands. Zoöl. Bijdr. 23: 34-37. [http://www.vliz.be/en/imis?module=ref&refid=141154]

[11]        Buizer, D.A.G. (1980). Balanus tintinnabulum (L., 1758) autochtonous in the Netherlands with notes on size and growth of other operculate barnacles (Cirripedia, Balanomorpha). Bull. Zool. Mus. Univ. Amsterdam 7(15): 149-154. [http://www.vliz.be/en/imis?module=ref&refid=197092]

[12]        Lengkeek, W.; Kerckhof, F. (2009). Eerste melding van exotische zeepok in Nederland. [https://www.naturetoday.com/intl/nl/nature-reports/message/?msg=15766] (2018-07-24).

[13]        DAISIE (Delivering Alien Invasive Species Inventories for Europe) (2018). Species Factsheet: Megabalanus coccopoma. [http://www.europe-aliens.org/speciesFactsheet.do?speciesId=53378] (2018-07-24).

[14]        Kerckhof, F. (2019). Persoonlijke mededeling

[15]        Crickenberger, S. (2014). Range limits, range shifts, and lower thermal tolerance in the tropical barnacle Megabalanus coccopoma. PhD Thesis. Clemson University: Clemson, South Carolina. 135 pp. [http://www.vliz.be/nl/catalogus?module=ref&refid=299219]

[16]        Hare, J.A.; Govoni, J.J. (2005). Comparison of average larval fish vertical distributions among species exhibiting different transport pathways on the southeast United States continental shelf. Fish. Bull. 103: 728-736. [http://www.vliz.be/nl/catalogus?module=ref&refid=70403]

[17]        Smithsonian Marine Station at Fort Pierce (2018). Indian River Lagoon Species Inventory: Megabalanus coccopoma Darwin, 1854. [http://www.sms.si.edu/irlspec/Megabalanus_coccopoma.htm] (2018-07-24).

[18]        Spinuzzi, S.; Schneider, K.R.; Walters, L.J.; Yuan, W.S.; Hoffman, E.A. (2013). Tracking the distribution of non-native marine invertebrates (Mytella charruana, Perna viridis and Megabalanus coccopoma) along the south-eastern USA. Marine Biodiversity Records 6: 55. [http://www.vliz.be/nl/catalogus?module=ref&refid=296743]

[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]        Perreault, R.T. (2004). An exotic tropical barnacle, Megabalanus coccopoma (Darwin 1854), in Louisiana: its probable arrival and environmental implications. Proc. La. Acad. Sci. 66: 13-16. [http://www.vliz.be/nl/catalogus?module=ref&refid=204521]

[22]        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]

[23]        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]

[24]        Pechenik, J. (2006). Larval experience and latent effects–metamorphosis is not a new beginning. Integr. Comp. Biol. 46: 323-333. [http://www.vliz.be/nl/catalogus?module=ref&refid=66898]

[25]        Tremblay, R.; Olivier, F.; Bourget, E.; Rittschof, D. (2007). Physiological condition of Balanus amphitrite cyprid larvae determines habitat selection success. Mar. Ecol. Prog. Ser. 340: 1-8. [http://www.vliz.be/nl/catalogus?module=ref&refid=261478]

[26]        Reis, P.A.; Salgado, M.A.; Vasconcelos, V. (2011). Barnacles as biomonitors of metal contamination in coastal waters. Est., Coast. and Shelf Sci. 93(4): 269-278. [http://www.vliz.be/nl/catalogus?module=ref&refid=296694]

VLIZ Alien Species Consortium (2020). Megabalanus coccopoma – Titan acorn barnacle. Non-native species of the Belgian part of the North Sea and bordering estuaries anno 2020. Flemish Institute for the Sea (VLIZ). 6 pp.