Aurelia coerulea - Asian moon jelly

The natural origin of the Asian moon jelly is not entirely certain, but it is most likely in the northwestern part of the Pacific Ocean (Japanese coast). This is based, among other things, on the fact that specimens around Japan show higher molecular diversity compared to other regions (California (USA), Australia, and Europe) ^[2]. It is presumed that the species has recently expanded its natural range towards Korea, where it was not found before 2000 ^[3]. It is certain that the occurrences in Australia and Europe are the result of anthropogenic introductions ^[2,3].

First observation in Belgium

In July and August 2022, moon jellies were observed for the first time in the Visserijdok and Vuurtorendok in Ostend. This in itself is not entirely unusual, as the moon jelly Aurelia aurita is commonly found along the Belgian coast from May to July. However, these jellies normally disappear almost entirely after July. Yet in 2022, the moon jellies were observed (in decreasing numbers) until October 5 ^[4]. DNA research in the Netherlands, where they have been observing a similar phenomenon since 2020, confirms that this is a new exotic species: Aurelia coerulea, or the Asian moon jelly ^[5].
 

Distribution in Belgium

Official observations have so far been limited to the port of Ostend ^[4], although recent beach reports in 2023 along the central and eastern coasts suggest that the species is already more widespread ^[6].
 

Distribution in neighbouring countries

In July 2020, large groups of Asian moon jellies were found in the canals of the Dutch city of Middelburg ^[4]. A similar phenomenon occurred in July 2021 in the Veerse Meer ^[7]. Despite suspicions that it was a new exotic species, it wasn't until 2023 that molecular research could confirm this, as both types of moon jellies are morphologically indistinguishable (cryptic species) ^[4,5]. Additionally, the Asian moon jelly has also been confirmed through DNA analysis in Roscoff (France) and Büsum (Germany) ^[4]. Furthermore, the Asian moon jelly has an established presence in semi-enclosed brackish water systems in the Mediterranean region ^[3,8-10].

Based on the locations of occurrence, it can be assumed that the Asian moon jelly was likely introduced to Europe via shipping (ballast water or hull fouling) or through the import of shellfish (e.g., the also non-native Japanese oyster Crassostrea/Magallana gigas) for aquaculture purposes ^[3,8].

The specific temperature and salinity requirements of the Asian moon jelly are not well known, but it is known that they primarily occur in lagoons, harbors, and semi-enclosed brackish water systems with variable temperature and salinity ^[11].

There is debate regarding the natural dispersal potential of the Asian moon jelly, with some studies suggesting that these jellyfish might occasionally cross the Pacific Ocean naturally. However, modeling of ocean currents and the life cycle of these jellyfish indicates that populations would not be able to sustain long-term natural dispersal across the Pacific to North America ^[2].

The Asian moon jelly can bypass its polyp stage and directly produce ephyrae (young jellyfish) from planula larvae. This capability allows it to quickly achieve high population densities in the short term. Together with the invasive American comb jelly Mnemiopsis leidyi, the Asian moon jelly can significantly reduce animal plankton in late summer, disrupting normal plankton concentrations ^[4,12]. Additionally, it can pose issues for fisheries and cause blockages in the cooling water intakes of nuclear power plants ^[3,4].

The specific ecological impact of this species is not well understood due to confusion with native cryptic species ^[11], but competition with native jellyfish, comb jellies, or suspension feeders is plausible ^[11,13].

Mature individuals of the Asian moon jelly are disc-shaped and possess numerous small whitish tentacles at the bell margin. The disc is opaque white to brownish-pink. The medusae can reach a disc diameter of up to 260 mm ^[8,11]. The Asian moon jelly is noted to have dark orange or brownish ephyrae, whereas those of native moon jellyfish are white ^[4]. For a detailed description, please refer to the literature ^[8].

[1]          World Register of Marine Species (WoRMS) (2024). Aurelia coerulea von Lendenfeld, 1884. https://www.marinespecies.org/aphia.php?p=taxdetails&id=292506 (2024-10-18). 

[2]          Dawson, M.N.; Gupta, A.S.; England, M.H. (2005). Coupled biophysical global ocean model and molecular genetic analyses identify multiple introductions of cryptogenic species. Proc. Natl. Acad. Sci. U.S.A. 102(34): 11968-11973. [https://www.vliz.be/en/imis?module=ref&refid=394081] 

[3]          Ki, J.-S.; Hwang, D.-S.; Shin, K.; Yoon, W.D.; Lim, D.; Kang, Y.S.; Lee, Y.; Lee, J.-S. (2008). Recent moon jelly (Aurelia sp.1) blooms in Korean coastal waters suggest global expansion: examples inferred from mitochondrial COI and nuclear ITS-5.8S rDNA sequences. ICES J. Mar. Sci./J. Cons. int. Explor. Mer 65(3): 443-452. [https://www.vliz.be/nl/imis?module=ref&refid=214502] 

[4]          De Blauwe, H. (2023). De Aziatische oorkwal in Belgische en Nederlandse wateren. Natuurpunt. https://www.natuurpunt.be/nieuws/de-aziatische-oorkwal-belgische-en-nederlandse-wateren-20230628 (2024-02-08)

[5]          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] 

[6]          waarnemingen.be. Aurelia coerulea von Lendenfeld, 1884. https://waarnemingen.be/species/1177732 (2024-05-22)

[7]          Gittenberger, A.; Rensing, M.; Faasse, M.A.; Keeler Perez, H.; Gittenberger, E. (2021). Native and non-native species of the Veerse Meer 2020 - 2021. GiMaRIS Rapport, 2021_07. Office for Risk Assessment and Research, Netherlands Food and Consumer Product Safety Authority: Sassenheim. 153 pp. [https://www.vliz.be/en/imis?module=ref&refid=394080] 

[8]          Scorrano, S.; Aglieri, G.; Boero, F.; Dawson, M.N.; Piraino, S. (2017). Unmasking Aurelia species in the Mediterranean Sea: an integrative morphometric and molecular approach. Zool. J. Linn. Soc. 180(2): 243-267. [https://www.vliz.be/nl/imis?module=ref&refid=292091] 

[9]          Scorrano, S. (2014). Impacts of Aurelia sp. 1 outbreaks in a Mediterranean coastal lagoon (Varano, SE Adriatic coast). PhD Thesis. Università degli Studi della Tuscia, Dipartimento di Scienze Ecologiche e Biologiche: Viterbo. 157 pp. [https://www.vliz.be/en/imis?module=ref&refid=394079] 

[10]        Belmonte, G.; Scirocco, T.; Denitto, F. (2011). Zooplankton composition in Lake Varano (Adriatic Sea coast, Italy). Ital. J. Zoolog. 78(3): 370-378. [https://www.vliz.be/en/imis?module=ref&refid=394077] 

[11]        Nemesis. Aurelia coerulea. https://invasions.si.edu/nemesis/species_summary/-265 (2024-02-08)

[12]        Van Lente, I.; de Bruyne, R.; Gmelig Meyling, A.; Verkuil, J.; Postma, A.; Haarsma, M. (2023). Intens blauwe en nieuwe kwallen. Nature Today 6 august: online. https://www.naturetoday.com/intl/nl/nature-reports/message/?msg=31124 [https://www.vliz.be/en/imis?module=ref&refid=394076] 

[13]        Riisgård, H.U.; Barth-Jensen, C.; Madsen, C. (2010). High abundance of the jellyfish Aurelia aurita excludes the invasive ctenophore Mnemiopsis leidyi to establish in a shallow cove (Kertinge Nor, Denmark). Aquat. Invasions 5(4): 347-356. [https://www.vliz.be/en/imis?module=ref&refid=394075]

VLIZ Alien Species Consortium (2024). Aurelia coerulea – Asian moon jelly. Introduced alien species of the Belgian part of the North Sea and adjacent estuaries anno 2024. Flanders Marine Institute (VLIZ). 4 pp.