Heleobia charruana - South American brackish water snail

The South American brackish water snail is native to the eastern coast of South America, specifically in Brazil and Uruguay (and possibly slightly further south ^[2]), with the Brazilian state of São Paulo marking its northernmost occurrence ^[3-6].

First observation in Belgium

The first official report of the species on European soil occurred in Antwerp in May 2017. Initially, the snail was incorrectly identified as Heleobia cf. australis based on shell morphology, but later DNA analysis confirmed that it was indeed Heleobia charruana ^[2,3]. This confirmation also validated earlier detections in the Netherlands and the United Kingdom (see below).
 

Distribution in Belgium

The occurrence of the South American brackish water snail is currently limited to the Antwerp port area ^[3].
 

Distribution in neighbouring countries

During the first two decades of this century, the species (then not yet identified at the species level) was repeatedly found in the intertidal zone of the Thames in southeastern United Kingdom (since 2003). In 2014, the snail was also detected for the first time in the North Sea Canal, near IJmuiden and in the Port of Amsterdam (the Netherlands) ^[2,3]. More recently, the species was found in Schiedam (2019, near the Port of Rotterdam) and the Eastern Scheldt (2020, Bergse Diepsluis) ^[2].

The fact that the species has been repeatedly observed in three northwestern European countries over the past 20 years suggests that established populations are present ^[3]. Given the strong resemblance to the native Peringia ulvae (the Common mud snail), it is possible that the South American brackish water snail has been present in Northeast European estuaries for longer but has gone unnoticed. However, confirming this would require a re-examination of older Peringia ulvae material ^[2,3].

It is suspected that the European population is the result of a single intercontinental introduction into the Thames estuary, after which the species spread further across the Southern North Sea via secondary transport. The most plausible primary introduction vector is likely ballast water transport. This could also be the secondary vector, but other natural pathways are also possible, such as survival through the digestive systems of migratory fish or birds ^[3] (as has been demonstrated for other species ^[7-9]) or attached on floating seaweed ^[3,4]. Hull fouling on (recreational) vessels is considered unlikely ^[3].

The species inhabits brackish water environments with variable salinity, tolerating levels between 0.5 and 34.5 psu ^[3,4]. The snail is found on various substrates, ranging from muddy sediment to stones, primarily in stagnant or slow-flowing water ^[3]. In the sheltered Port of Antwerp, the snail is commonly found at depths between 5 and 12.5 meters. In the side branches of the Dutch North Sea Canal, the species also seeks sheltered areas and is mainly found in shallow water (<1 meter), while in the canal itself, it has been observed at depths up to 19.2 meters, with densities ranging from 10 to over 3,500 individuals per m². In both the ports of Antwerp and Amsterdam, the snail is also found in the dark, underground water systems of the harbor ^[3].

The offspring of the South American brackish water snail do not go through a true larval stage, making further dispersal by drifting with prevailing currents (without a medium to attach to) unlikely ^[3].

Currently, there is no evidence of the impact of the South American brackish water snail on native fauna, although the species is often dominant at its locations, meaning potential effects on native species cannot be ruled out ^[3]. Moreover, the biological community in its current introduction areas is often already dominated by the non-native species Potamopyrgus antipodarum (Jenkins' Spire Snail), which exhibits similar colonisation traits ^[3,10].

The strong shell varies in color from nearly white to dull yellowish-gray to brownish. The growth lines are rather inconspicuous, and the shell has a conical spire. The whorls are separated by a barely incised suture. Shell sizes are variable. The 33 measured specimens in Antwerp ranged from 3.9 and 6.4 mm in length and 2.1 and 3.0 mm in width, with length-to-width ratios between 1.7 and 2.1. No larger shells have been reported from the United Kingdom and the Netherlands. It is important to note that it is impossible to determine whether a shell is fully grown, making the minimum dimensions more reliable than the maximum sizes. For a detailed species description, refer to the literature ^[3].

[1]          World Register of Marine Species (WoRMS) (2024). Heleobia charruana (d’Orbigny, 1841). https://www.marinespecies.org/aphia.php?p=taxdetails&id=760578 (2024-10-18). 

[2]          van Haaren, T.; de Bruyne, R. (2021). Vermomd wadslakje eindelijk ontmaskerd. Nature Today 13 mei: online https://www.naturetoday.com/intl/nl/nature-reports/message/?msg=27705 [https://www.vliz.be/en/imis?module=ref&refid=394074] 

[3]          van Haaren, T.; Worsfold, T.M.; Stelbrink, B.; Collado, G.A.; Gonçalve, I.C.B.; Serra, W.S.; Scarabino, F.; Gittenberger, A.; Gittenberger, E. (2021). Heleobia charruana (Gastropoda, Truncatelloidea, Cochliopidae), a South American brackish water snail in northwest European estuaries. Basteria 85(1): 82-91 [https://www.vliz.be/en/imis?module=ref&refid=394073] 

[4]          Marcus, E. (1963). On Brazilian supralittoral and brackish water snails. Bol. Inst. Oceanogr. Sao Paulo 13(2): 41-52. [https://www.vliz.be/en/imis?module=ref&refid=394072] 

[5]          Cenzano, C.S.S.; Würdig, N.L. (2006). Spatial and temporal variations of the benthic macrofauna in different habitats of a lagoon of the northern coastal system of Rio Grande do Sul State, Brazil. Acta Limnologica Brasiliensia 18(2): 153-163. [https://www.vliz.be/en/imis?module=ref&refid=394071]  

[6]          Ortega, I.; Colling, L.A.; Dumont, L.F.C. (2018). Response of soft-bottom macrobenthic assemblages to artisanal trawling fisheries in a subtropical estuary. Est., Coast. and Shelf Sci. 207: 142-153. [https://www.vliz.be/en/imis?module=ref&refid=394070] 

[7]          Haynes, A.; Taylor, B.J.R.; Varley, M.E. (1985). The influence of the mobility of Potamopyrgus jenkinsi (Smith E. A.) (Prosobranchia : Hydrobiidae) on its spread. Arch. Hydrobiol. 103(4): 497-508. [https://www.vliz.be/en/imis?module=ref&refid=394069] 

[8]          van Leeuwen, C.H.A.; van der Velde, G.; van Lith, B.; Klaassen, M. (2012). Experimental quantification of long distance dispersal potential of aquatic snails in the gut of migratory birds. PLoS One 7(3): e32292. [https://www.vliz.be/en/imis?module=ref&refid=394061] 

[9]          Vinson, M.R.; Baker, M.A. (2008). Poor growth of rainbow trout fed New Zealand mud snails Potamopyrgus antipodarum. N. Am. J. Fish. Manage. 28(3): 701-709. [https://www.vliz.be/en/imis?module=ref&refid=394060] 

[10]        Alonso, A.; Castro-Díez, P. (2008). What explains the invading success of the aquatic mud snail Potamopyrgus antipodarum (Hydrobiidae, Mollusca)? Hydrobiologia 614(1): 107-116 [https://www.vliz.be/nl/imis?module=ref&refid=206637]

VLIZ Alien Species Consortium (2024). Heleobia charruana – South American brackish water snail. Introduced alien species of the Belgian part of the North Sea and adjacent estuaries anno 2024. Flanders Marine Institute (VLIZ). 4 pp.