Notocomplana koreana -

This polyclad flatworm naturally occurs in the northwestern part of the Pacific Ocean, near Korea ^[2,3].

First observation in Belgium

The species has not yet been observed in Belgian territory.

Distribution in Belgium

The species has not yet been observed in Belgian territory.

Distribution in neighbouring countries

The presence of Notocomplana koreana was confirmed in both 2020 and 2021 in the Veerse Meer and the Grevelingenmeer (the Netherlands), with species identification verified through DNA analysis. Additionally, this species was also found on navigation buoys in the Dutch part of the North Sea in 2021 ^[2]. The potential presence of this flatworm was suggested in 2017 based on eDNA analysis in the port of Vlissingen (Western Scheldt), although no specimens have been found at this location to date ^[4].

There is a strong suspicion that Notocomplana koreana was introduced to the Netherlands via fouling communities on ship hulls. Unlike the non-native Prosthiostomum wagurensis (which occurs in more sheltered waters), Notocomplana koreana is also found in exposed open sea habitats. This suggests that navigation buoys or other artificial structures (e.g., wind turbines) in the open sea could serve as potential stepping stones for further secondary spread of this species ^[2].

In its natural range, this flatworm has been found in the intertidal zone on the undersides of stones along sheltered rocky coasts and occasionally in mussel beds in exposed rocky areas ^[5]. The limited available information on this species means that no statements can currently be made regarding the temperature and salinity tolerance of this flatworm.

Due to the presence of a pelagic larval stage ^[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 development, feeding habits, distribution, and seasonality, which hinders the analysis of potential distribution patterns and occurrence ^[3].

There is no information available on the effects or potential measures related to the presence of Notocomplana koreana.

Flatworms typically exhibit a cryptic lifestyle. This not only makes the species susceptible to introductions via biofouling on ship hulls but also means that the presence of such species in a new area can remain unnoticed for a long time. For example, the presence of this flatworm in the port of Vlissingen was detected through eDNA three years before the first specimens of the species were actually found in the Netherlands ^[2].

The flatworm closely resembles Leptoplana tremellaris, though its eyes are characterised by somewhat different orientation and placement ^[6]. Live specimens measure 10 to 20 mm in length and 5 to 9 mm in width. The body is elongated oval, tapering towards the rear. The body color is whitish, with a general appearance ranging from yellowish khaki to golden yellow. Brown spots are scattered across the entire dorsal surface, except at the edges. Tentacular eye clusters consist of 17-41 eye spots. For a detailed description, refer to specialised literature ^[5].

[1]          World Register of Marine Species (WoRMS) (2024). Notocomplana koreana (Kato, 1937). https://www.marinespecies.org/aphia.php?p=taxdetails&id=483509 (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]          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] 

[4]          van der Hoorn, B.; Gittenberger, A. (2019). Environmental DNA Sloehaven: A multi-substrate metabarcoding approach for detecting non-indigenous species in a Dutch port. Naturalis rapport 2018_01. Naturalis Biodiversity Center: Leiden. 43 pp. [https://www.vliz.be/en/imis?module=ref&refid=393666] 

[5]          Oya, Y.; Kajihara, H. (2017). Description of a new Notocomplana species (Platyhelminthes: Acotylea), new combination and new records of Polycladida from the northeastern Sea of Japan, with a comparison of two different barcoding markers. Zootaxa 4282(3): 526-542. [https://www.vliz.be/en/imis?module=ref&refid=393663] 

[6]          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). Notocomplana koreana. Introduced alien species of the Belgian part of the North Sea and adjacent estuaries anno 2024. Flanders Marine Institute (VLIZ). 4 pp.