Prosthiostomum wagurensis -
This polyclad flatworm is native to the northwestern Pacific Ocean [2,3].
First observation in Belgium
The indistinguishable morphology between the specimens found in the port of Zeebrugge in 2019 and those found in 2020 in the Veerse Meer, which were confirmed through DNA analysis, suggests that 2019 represents the first observation of this species in Belgian territory [2].
Distribution in Belgium
To date, there have been no confirmed observations outside the port of Zeebrugge.
Verspreiding in onze buurlandenDistribution in neighbouring countries
This flatworm was officially first recorded in the Netherlands in 2020, in the Veerse Meer. Molecular analyses have made the identification of these species possible, as closely related flatworm species are often difficult to distinguish based solely on external morphology. Since the presence in the Veerse Meer and the Grevelingenmeer has been confirmed through DNA, it suggests that the earlier (2019) observations of morphologically identical flatworms in the ports of Rotterdam, Vlissingen, and Zeebrugge also pertain to Prosthiostomum wagurensis [2].
The presence in the ports (Zeebrugge, Vlissingen, Rotterdam) and the inland waters of the Dutch Delta region (Veerse Meer, Grevelingen) strongly suggests that Prosthiostomum wagurensis was introduced via fouling communities on ship hulls. The species could have used the more sheltered areas of the ports as a staging ground for its further secondary spread. However, the initial location of the species' introduction remains uncertain [2].
The limited available information on this species means that no statements can currently be made about the temperature and salinity tolerance of this flatworm.
Due to the presence of a pelagic larval phase [2], there is a possibility that the species, once introduced to a new area, could further spread by drifting with prevailing currents (or in ballast water). However, the biology of polyclad flatworms remains largely unknown. There is a lack of knowledge about their developmental processes, feeding habits, distribution, and seasonality, which hinders the analysis of potential spread patterns and occurrences [4].
There is no information available regarding the effects or potential measures related to the presence of Prosthiostomum wagurensis.
Flatworms generally exhibit a cryptic lifestyle, which allows them to go unnoticed and spread via biofouling on ship hulls. Consequently, the presence of such species in a new area may also remain undetected for a long time. For example, the presence of another non-native flatworm, Notocomplana koreana, in the port of Vlissingen was detected through eDNA three years before the first physical specimens of the species were actually found in the Netherlands [2].
In contrast to most flatworm species in our region, Prosthiostomum wagurensis is generally spotted, while other local species are characterised by irregularly striped or mottled patterns. The color of the spots varies from light to dark orange/red [5].
[1] World Register of Marine Species (WoRMS) (2024). Prosthiostomum wagurensis Kato, 1944. https://www.marinespecies.org/aphia.php?p=taxdetails&id=483894 (2024-10-18).
[2] Gittenberger, A.; Rensing, M.; Faasse, M.; van Walraven, L.; Smolders, S.; Keeler Perez, H.; Gittenberger, E. (2023). Non-indigenous species dynamics in time and space within the coastal waters of the Netherlands. Diversity 15(6): 719. [https://www.vliz.be/nl/imis?module=ref&refid=365105]
[3] Kato, K. (1944). Polycladida of Japan . Journal of the Sigenkagaku Kenkyusyo 1(3): 257-318, 4 pls. [https://www.vliz.be/en/imis?module=ref&refid=394255]
[4] Tosetto, L.; McNab, J.M.; Hutchings, P.A.; Alonso Rodriguez, J.; Williamson, J.E. (2023). Fantastic flatworms and where to find them: Insights into intertidal polyclad flatworm distribution in southeastern Australian boulder beaches. Diversity 15(3): 393. [https://www.vliz.be/en/imis?module=ref&refid=393674]
[5] de Bruyne, R.; Meyling, A.G.; Oonk, B. (2023). Brainstormen over platwormen. Nature Today 15 okt.: online [https://www.vliz.be/en/imis?module=ref&refid=393668]
VLIZ Alien Species Consortium (2024). Prosthiostomum wagurensis. Introduced alien species of the Belgian part of the North Sea and adjacent estuaries anno 2024. Flanders Marine Institute (VLIZ). 4 pp.