Pacificincola perforata -

Pacificincola perforata naturally occurs in the Indo-West Pacific region around Japan, Hong Kong, and southern China (South and East China Seas) ^[4].

First observation in Belgium

Pacificincola perforata was observed for the first time in the Sluice Dock in Ostend on 14 July 2016 ^[2].
 

Distribution in Belgium

After the initial observations in 2016, the species was repeatedly found in the Ostend Sluice Dock ^[2]. Initially, Pacificincola perforata was observed on hard substrates (e.g., the inner side of mussel shells), and later (from 2021 onward) on the non-native Japanese wireweed, Sargassum muticum ^[2]. However, the colony morphology on Japanese wireweed and the spines on some brood chambers were unusual for Pacificincola (sometimes five spines per brood chamber and often unusually branched) ^[3], raising doubts about the species identification (see also Specific features). DNA analysis has since confirmed that it is indeed the same species ^[3].
 

Distribution in neighbouring countries

The first observation of Pacificincola perforata occurred in 2001 in the Bay of Arcachon (France) ^[4]. Three years later, in 2004, the first colony on Dutch territory was recorded in the Eastern Scheldt, found on empty mussel shells ^[4]. By 2006, it had already become the most common species on rocks near Yerseke and subsequently spread throughout the entire Eastern Scheldt, Veerse Meer, and Grevelingenmeer ^[5,6]. Up to that point, all colonies were found attached to hard substrates (shells, stones), and no spines on brood chambers were reported. It was only in 2016 that the bryozoans were first observed on Japanese wireweed (Sargassum muticum), washed up on the beach.

It is notable that observations of Pacificincola perforata in Europe consistently occur near aquaculture activities, suggesting that introduction (both primary and secondary) via the import of Japanese oysters (Crassostrea/Magallana gigas) is the most plausible explanation ^[4]. Furthermore, Escharella hozawai (Okada, 1929), possibly the same species as Pacificincola perforata (see also Specific features), was found near Hawaii and the west coast of North America on marine debris (plastic, fiberglass) resulting from the tsunami in Japan on 11 March 2011 ^[7].

Based on the environmental conditions in the regions where the species has established itself, it can be concluded that Pacificincola perforata can thrive in surface water temperatures ranging from 1 to 30°C and salinities between 22 and 35.6 psu ^[10-13]. The tolerance range may extend further, but this has not yet been thoroughly investigated.

As the species can attach to various types of substrate and is a known fouling organism in its native region ^[8], combined with its tolerance for diverse environmental conditions, it is expected that Pacificincola perforata will spread rapidly along the Atlantic coast of Europe ^[4].

In the coastal waters of the South China Sea, Pacificincola perforata is one of the most common fouling bryozoans (Bryozoa) ^[8]. The colonies settle on 'bare' substrates (e.g., shells, stones, buoys, and fishing nets) and algae covered with a biofilm of bacteria. They can rapidly expand across the surface and thus compete with other bryozoans and sessile organisms for space ^[4,9]. To date, no economic impact has been established or is expected ^[9].

Pacificincola perforata forms encrusting colonies. The species is capable of developing upright growth. The colonies are grey-white, yellow-white, or yellow in color. The zooids are elongated oval or angular and measure about 0.62 x 0.28 mm ^[4]. For a detailed description, reference is made to the specialised literature ^[4].

Pacificincola perforata differs from Escharella hozawai (Okada, 1929) by the absence of spines on the brood chambers (in Escharella hozawai, three distinctive spines are present). However, in Belgium and the Netherlands, colonies on Japanese wireweed are found that have brood chambers both with and without spines within the same colony. DNA analysis revealed that both types are identical and that the brood chambers exhibit considerable morphological variation within the same species ^[3]. If this is confirmed by further research, the names of both species should be changed to Pacificincola hozawai (Okada, 1929), as the oldest name should be used ^[3]. The function of the spines is currently unknown. It is possible that the growth of spines is related to the limited surface area on algae where the encrusting colonies can attach, after which the colony forms upright, folded, two-layered plates, with the spines possibly keeping the other layer at a distance to allow enough space for extending their tentacle crown ^[3].

[1]          World Register of Marine Species (WoRMS) (2024). Pacificincola perforata (Okada & Mawatari, 1937). https://www.marinespecies.org/aphia.php?p=taxdetails&id=408260 (2024-10-18). 

[2]          Jonckheere, I.; Kerckhof, F. (2024). Waarnemingen gedaan tijdens de SWG-excursie naar de Spuikom van Oostende op 9 juli 2023 met vondsten van verschillende nieuwe geïntroduceerde soorten voor de Belgische fauna. De Strandvlo 44(2): 33-41. [https://www.vliz.be/en/imis?module=ref&refid=394050] 

[3]          De Blauwe, H.; Gittenberger, A.; Kerckhof, F. (2024). Zijn Pacificincola perforata (Okada & Mawatari, 1937) en Escharella hozawai (Okada, 1929) (Bryozoa, Cheilostomatidae) dezelfde soort? De Strandvlo 44(2): 44-51. [https://www.vliz.be/en/imis?module=ref&refid=394066] 

[4]          De Blauwe, H. (2006). On the taxonomy and distribution of the family Pacificincolidae Liu & Liu, 1999 (Bryozoa, Cheilostomata), with the description of a new genus. Bull. Kon. Belg. Inst. Natuurwet. Biologie 76: 139-145. [https://www.vliz.be/en/imis?module=ref&refid=110685] 

[5]          Faasse, M.A.; van Moorsel, G.W.N.M.; Tempelman, D. (2013). Moss animals of the Dutch part of the North Sea and coastal waters of the Netherlands (Bryozoa). Ned. Faunist. Meded. 41: 1-14. [https://www.vliz.be/en/imis?module=ref&refid=302003] 

[6]          Gittenberger, A.; Rensing, M.; Niemantsverdriet, P.; Schrieken, N.; D’Hont, A.; Stegenga, H. (2015). Soorteninventarisatie oesterputten en oesterpercelen. GiMaRIS Rapport, 2015(19). GiMaRIS: Leiden. 23 pp. [https://www.vliz.be/en/imis?module=ref&refid=395106] 

[7]          McCuller, M.I.; Carlton, J. (2018). Transoceanic rafting of Bryozoa (Cyclostomata, Cheilostomata, and Ctenostomata) across the North Pacific Ocean on Japanese tsunami marine debris. Aquat. Invasions 13(1): 137-162. [https://www.vliz.be/en/imis?module=ref&refid=395108] 

[8]          Liu, H.; Liu, H. (1999). Systematic position of Mucronella perforata Okada et Mawatari 1937. Chin. J. Oceanol. Limnol. 17(4): 338-343. [https://www.vliz.be/en/imis?module=ref&refid=79941]  

[9]          Nederlands soortenregister – Overzicht van de Nederlandse biodiversiteit. Pacifisch mosdiertje Pacificincola perforata. https://www.nederlandsesoorten.nl/linnaeus_ng/app/views/species/nsr_taxon.php?id=173010&cat=162 (2024-09-03)

[10]        Deborde, J.; Anschutz, P.; Auby, I.; Glé, C.; Commarieu, M.-V.; Maurer, D.; Lecroart, P.; Abril, G. (2008). Role of tidal pumping on nutrient cycling in a temperate lagoon (Arcachon Bay, France). Mar. Chem. 109(1-2): 98-114. [https://www.vliz.be/en/imis?module=ref&refid=395111] 

[11]        Maarse, M.; Kleissen, F.; Nolte, A. (2021). Klimaatrobuustheid van het waterbeheer van het Verse Meer: Houdbaarheid in het licht van klimaatverandering. Rijkswaterstaat Water Verkeer en Leefomgeving: Utrecht. 81 pp. [https://www.vliz.be/en/imis?module=ref&refid=395115] 

[12]        https://www.vliz.be/spuikom/metingen (2024-09-03)

[13]        Nemesis. Pacificincola perforata. https://invasions.si.edu/nemesis/jtmd/species_summary/Pacificincola%20perforata (2024-09-03)

VLIZ Alien Species Consortium (2024). Pacificincola perforata. Introduced alien species of the Belgian part of the North Sea and adjacent estuaries anno 2024. Flanders Marine Institute (VLIZ). 5 pp.