Haloa japonica - Japanese bubble snail

The species is native to the Indo-West Pacific region, in Korean and Japanese marine areas ^[2].

First observation in Belgium

On April 2, 2024, the Japanese bubble snail was observed for the first time in the Sluice dock in Ostend ^[3]. It is possible that the species had already been present there for some time and was only noticed now because the animals, likely similar to the related species Haminella solitaria, temporarily moved to shallow waters to reproduce ^[3].
 

Distribution in Belgium

At this moment, the species has only been observed in the Sluice dock in Ostend.
 

Distribution in neighbouring countries

In June 2018, the Japanese bubble snail was found for the first time in the Netherlands, in the Veerse Meer, which also marked the first observation in Northwestern Europe ^[4]. Between 2020 and 2022, reports in the Netherlands expanded to the Grevelingenmeer, where the species is now abundant ^[4]. The spread in Southern Europe began much earlier via the Mediterranean Sea and the southern Atlantic coasts of Europe ^[2]. In 1991, the species was first found in the Mediterranean region near Naples (Italy), in the brackish Lago Fusaro ^[5]. In 1992, specimens were also found in the Venice Lagoon (Italy). That same year, the species was also observed for the first time along the Atlantic coast of Northwestern Spain, in the Arosa and Eo estuaries ^[6]. In France, the species has been recorded both along the Mediterranean coast and the Atlantic coast (Northern Brittany) ^[7]. However, the observations in Europe were not the first outside the species' natural range, as it had already been reported in the early 1980s along the west coast of North America in the state of Washington ^[8], and later (1999) in the San Francisco area ^[9].

The Japanese bubble snail can colonise new areas through the introduction of commercial bivalves, such as the Philippine carpet clam Ruditapes philippinarum or the Japanese oyster Crassostrea/Magallana gigas ^[2,3,9].

The species has a high tolerance for various environmental conditions, which increases its potential for further spread ^[10]. The snail is found in waters with salinity levels ranging from 18 to 40 psu ^[11] and inhabits cold-temperate to warm-temperate regions with water temperatures between 5 and 30°C ^[12].

The snail typically lays its egg masses on seaweed, meaning detached seaweed could potentially facilitate further spread. However, this is considered an unlikely pathway for the expansion in the Netherlands from the Veerse Meer to the Grevelingenmeer. Additionally, the spread may possibly be aided by the deposition of eggs on the hulls of recreational vessels or via waterfowl ^[4].

In California (USA), it was found that the Japanese bubble snail is a carrier of a parasitic trematode worm. This worm likely cannot proliferate in mammals during its life cycle, requiring a bird as its final host. However, infections in humans were reported, causing skin inflammation (dermatitis) (impact on human health), which led to beach closures (economic impact) ^[2,10,11,13]. In Europe, the parasite has not yet been found in specimens of the Japanese bubble snail to date ^[2].

The Japanese bubble snail is a herbivore, feeding on diatoms. Adult snails grow to about 20-25 mm in size and have a dark coloration with light speckles ^[9]. The shell is much smaller, measuring around 15 x 11 mm, making it impossible for the animal to fully retract into it ^[14]. The snail has two flaps that extend along its back, referred to as ‘rabbit ears’ ^[9]. The shell is covered by a mantle, and in some individuals, the internal shell is visible through the mantle ^[3].

The snail reproduces in the spring ^[3]. Its egg masses are banana-shaped gelatinous structures filled with yellow eggs, each approximately 1 mm in diameter. In the Ostend Sluice dock, these eggs were found among the non-native Japanese wireweed Sargassum muticum, initially high on the concrete embankment and later spread across the area ^[3]. The species' development is unusual, as crawling juveniles, rather than swimming, non-feeding veliger larvae, emerge from the egg masses ^[3].

The snail is primarily found in sheltered water systems, often inhabiting soft (sandy-muddy) substrates. It is also reported on hard (artificial) structures or among green and red algae ^[4,10]. The species occurs from the low-tide line to a depth of about 15 meters but can also be found up to half a meter above the low-tide line during calm weather ^[4].

The species can easily be confused with Haminella solitaria, a species from the east coast of the United States, which also has ‘rabbit ears’. This species has been observed in recent years in Germany, Denmark, and the Baltic states. Haminella solitaria differs from the Japanese bubble snail in that it has spherical egg masses, reproduces in the fall, and has a more rounded shell ^[3]. The two species can be definitively distinguished through microscopic examination of the radula. The rachidian (central) teeth of the radula of the Japanese bubble snail are three-pointed (toothed in Haminella solitaria) and have a second pointed knob on the first lateral teeth (versus a single knob in Haminella solitaria) ^[6,9,15].

Additionally, the snail can be mistaken for the European species Haminoea hydatis. The shells and live animals are very similar, but the cephalic lobes of Haminoea hydatis are shorter and do not overlap ^[16]. In case of doubt, microscopic examination of Hancock's organ (a chemo-sensory structure) provides a definitive identification ^[3].

[1]          World Register of Marine Species (WoRMS) (2024). Haloa japonica (Pilsbry, 1895). https://www.marinespecies.org/aphia.php?p=taxdetails&id=1374250 (2024-10-18). 

[2]          Hanson, D.; Cooke, S.; Hirano, Y.; Malaquias, M.A.E.; Crocetta, F.; Valdés, Á. (2013). Slipping through the cracks: the taxonomic impediment conceals the origin and dispersal of Haminoea japonica, an invasive species with impacts to human health. PLoS One 8(10): e77457. [https://www.vliz.be/en/imis?module=ref&refid=291814] 

[3]          Annys, A.; Laforce, W.; Kerckhof, F. (2024). Een nieuwe slakkensoort voor België: De Japanse zeepbelslak Haloa japonica (Pilsbry, 1895). De Strandvlo 44(2): 52-58. [https://www.vliz.be/en/imis?module=ref&refid=394067] 

[4]          Faasse, M.; Gittenberger, A. (2023). De uitbreiding van de Japanse zeepbelslak Haloa japonica. Het Zeepaard 83(2): 65-72. [https://www.vliz.be/en/imis?module=ref&refid=392227] 

[5]          Alvarez, L.A.; Garcia, F.J.; Villani, G. (1993). A new Mediterranean species of Haminea Leach, 1820 (Gastropoda: Opisthobranchia: Cephalaspidea). J. Moll. Stud. 59: 339-345. [https://www.vliz.be/en/imis?module=ref&refid=395090]  

[6]          Alvarez, L.A.; Martinez, E.; Cigarria, J.; Rolán, E.; Villani, G. (1993). Haminaea callidegenita Gibson and Chia, 1989 (Opisthobranchia: Cephalaspidea), a Pacific species introduced in European coasts = Haminaea callidegenita Gibson y Chia, 1989 (Opisthobranchia: Cephalaspidea), una especie pacífica introducida en las costas de Europa. Iberus 11(2): 59-65. [https://www.vliz.be/en/imis?module=ref&refid=250449]  

[7]          GBIF. Haloa japonica (Pilsbry, 1895). (2024-09-02)

[8]          Gibson, G.D.; Chia, F.-S. (1989). Description of a new species of Haminoea, Haminoea callidegenita (Mollusca: Opisthobranchia), with a comparison with two other Haminoea species found in the northeast Pacific. Can. J. Zool. 67(4): 914-922. [https://www.vliz.be/en/imis?module=ref&refid=395092] 

[9]          Gosliner, T.M.; Behrens, D.W. (2006). Anatomy of an invasion: Systematics and distribution of the introduced opisthobranch snail, Haminoea japonica Pilsbry, 1895 (Gastropoda: Opisthobranchia: Haminoeidae). Proc. Calif. Acad. Sci. 57(37): 1003-1010 [https://www.vliz.be/en/imis?module=ref&refid=395088] 

[10]        Hanson, D.; Hirano, Y.; Valdés, A. (2012). Population genetics of Haminoea (Haloa) japonica Pilsbry, 1895, a widespread non-indigenous sea slug (Mollusca: Opisthobranchia) in North America and Europe. Biological Invasions 15(2): 395-406. [https://www.vliz.be/en/imis?module=ref&refid=395104] 

[11]        Nemesis. Haloa japonica. https://invasions.si.edu/nemesis/species_summary/567649 (2024-09-02)

[12]        OBIS. Haloa japonica (Pilsbry, 1895). https://www.obis.org/taxon/1374250 (2024-09-02)

[13]        Brant, S.V.; Cohen, A.N.; James, D.; Hui, L.; Hom, A.; Loker, E.S. (2010). Cercarial dermatitis transmitted by exotic marine snail. Emerging Infectious Diseases 16(9): 1357-1365. [https://www.vliz.be/en/imis?module=ref&refid=395102] 

[14]        ANEMOON Verspreidingsatlas Weekdieren. Haloa japonica (Pilsbry, 1895). https://www.verspreidingsatlas.nl/S1374250 (2024-09-02)

[15]        du Bois-Reymond Marcus, E. (1972). Notes on some opisthobranch gastropods from the Chesapeake Bay. Chesapeake Science 13(4): 300-317. [https://www.vliz.be/en/imis?module=ref&refid=395096] 

[16]        Malaquias, M.A.E.; Cervera, J.L. (2005). The genus Haminoea (Gastropoda: Cephalaspidea) in Portugal, with a review of the European species. J. Moll. Stud. 72(1): 89-103. [https://www.vliz.be/en/imis?module=ref&refid=395100] 

VLIZ Alien Species Consortium (2024). Haloa japonica – Japanse bubble snail. Introduced alien species of the Belgian part of the North Sea and adjacent estuaries anno 2024. Flanders Marine Institute (VLIZ). 5 pp.