Ianiropsis serricaudis - Japanese marine isopod

The natural range of this species extends from the Sea of Okhotsk to the Sea of Japan (Japan, Korea, Russia) ^[2].
 

First observation in Belgium

The species was first recorded in September 2015 in the Verbindingsdok of the inner port area of Zeebrugge ^[3].
 

Distribution in Belgium

In the period after 2015, the species was recorded several more times in the inner port area of Zeebrugge (Verbindingsdok, Boudewijn Canal, and Old Ferry Dock) as well as in the marina ^[3,4]. In 2023, it was also observed in the Sluice dock of Ostend ^[5]. Due to its small size and the often complex diagnostic characteristics of species within the genus ^[2,6-9], the species is likely more widespread than has been documented to date ^[2,10].
 

Distribution in neighbouring countries

The first observation outside the natural distribution range of the species occurred in 1977, when it was identified in the fouling community in San Francisco Bay ^[2,11].

In the Netherlands, the Japanese marine isopod was first found in 2000 on a pontoon at Neeltje Jans in the Eastern Scheldt. Initially, it was considered to be Janiropsis breviremis, but later reclassified as Ianiropsis sp., with the note that it was a species unknown in the northeastern Atlantic Ocean ^[12-15]. In 2006, the species was found near the port of Rotterdam and has since been observed in several shallow subtidal and rocky intertidal zones, as well as on floating harbor and hydraulic structures ^[2].

In 2004, this isopod, initially misidentified as the native Janira maculosa, was recorded on a floating pontoon in Hamble Point Marina in Southampton (southern England) ^[2,16]. In 2011, the species was observed in the Bay of Ferrol (northwest Spain) ^[17]. In the Mediterranean region, it was discovered in 2012 in the Venice Lagoon (Italy), where it was already present in large numbers ^[10]. In 2013, it was found on the French Atlantic coast in the Bay of Arcachon. Since a large number of breeding females were found, it was suspected that the species had already established a presence and was likely introduced before 2013 ^[18]. In 2019, it was discovered in the port of Le Havre in the English Channel ^[19].

A potential introduction vector for this species is transport via shipping. The spread through ballast water or as a fouling organism on ship hulls are plausible pathways, which is supported by the common occurrence of this isopod in and/or near ports ^[2,10,15,19]. Another pathway, suggested in the context of introductions in the Venice Lagoon and the Bay of Arcachon, involves the import of commercial mollusk species for local shellfish farming ^[10,18]. Additionally, it was recently found that the Japanese marine isopod is one of the most common species on floating marine debris from the 2011 Japanese tsunami, which may facilitate further spread of the species throughout the Pacific region ^[20].

This marine isopod is found in the intertidal zone at depths of up to 7 meters. It occurs in water temperatures ranging from -0.5°C (winter) to 24°C (summer) ^[2,21,22] and tolerates salinity variations between 16.9 and 35 psu, but primarily inhabits environments with salinity levels between 24 and 35 psu ^[2]. This isopod is found on hard substrates, as well as on sponges, tunicates, corals, brown algae, and kelp ^[15,21-23]. Floating and submerged harbor infrastructure also provide suitable habitats for this isopod ^[19].
 

In addition to its known broad tolerance range for various physicochemical parameters, further research is needed to gather more information on the biological and ecological characteristics of this isopod that could facilitate its successful introduction and establishment worldwide.

Despite the fact that the species is now commonly found in fouling communities in some shallow marine habitats along Pacific and Atlantic coasts, there is little information available about its ecological role. There is no concrete data on the extent of potential competition with native species or on how it might serve as prey for certain species ^[19].

The observed males reached a maximum length of 3.2 mm, while females were up to 2.7 mm ^[2,21,22]. The animals often have dark red pigmented eyes and reddish-brown pigment spots on an otherwise translucent body. A distinctive pigmentation visible through the transparent body is associated with the digestive tract ^[2].

The sixth and seventh segments of the antennula are elongated. The specimens have two claws on the dactyli of pereopod 1 and two to three claws on pereopod 7. They also have three or four (sometimes up to seven) small teeth on the lateral margin of the pleotelson, along the posterior half of the edge. The maxilliped palps are elongated and visible in a dorsal view ^[2,6,9,10].

The feeding habits of this isopod are not well known, but it is presumed to feed on the fecal matter of colonial invertebrates (tunicates, sponges, etc.) and on the surface microbiota and detritus from these organisms and algae ^[24]. Reproductively mature females carry between 7 and 32 eggs (an average of 18) ^[2,22].
 

[1]          World Register of Marine Species (WoRMS) (2024). Ianiropsis serricaudis Gurjanova, 1936. https://www.marinespecies.org/aphia.php?p=taxdetails&id=255999 (2024-10-18).

[2]          Hobbs, N.-V.; Lazo-Wasem, E.; Faasse, M.A.; Cordell, J.R.; Chapman, J.W.; Smith, C.S.; Prezant, R.; Shell, R.; Carlton, J.T. (2015). Going global: the introduction of the Asian isopod Ianiropsis serricaudis Gurjanova (Crustacea: Peracarida) to North America and Europe. Aquatic Invasions 10(2): 177-187. [https://www.vliz.be/nl/catalogus?module=ref&refid=282171]

[3]          Faase, M. (monitoring eCOAST, periode 2015-2019) (2019-10-02 en 2024-03-10). Persoonlijke mededeling.

[4]          Waarnemingen.be. Ianiropsis serricaudis Gurjanova, 1936. https://waarnemingen.be/species/717917/ (2024-02-02).

[5]          Jonckheere, I.; Kerckhof, F. (2024). Waarnemingen gedaan tijdens de SWG-excursie naar de Spuikom van Oostende op 9 juli 2023 met vondsten van verschillende nieuwe geïntroduceerde soorten voor de Belgische fauna. De Strandvlo 44(2): 33-41.  [https://www.vliz.be/nl/imis?module=ref&refid=394050] 

[6]          Doti, B.L.; Wilson, G.D.F. (2010). The genera Carpias Richardson, Ianiropsis Sars and Janaira Moreira & Pires (Isopoda: Asellota: Janiridae) from Australia, with description of three new species. Zootaxa 2625(1): 1-39. [https://www.vliz.be/en/imis?module=ref&refid=393389] 

[7]          Wilson, G.D.F. (1994). A phylogenetic analysis of the isopod family Janiridae (Crustacea). Invertebr. Taxon. 8(3): 749-766. [https://www.vliz.be/nl/imis?module=ref&refid=140551] 

[8]          Wilson, G.D.F.; Wägele, J.W. (1994). A systematic review of the family Janiridae (Crustacea, Isopoda, Asellota). Invertebr. Taxon. 8(3): 683-747. [https://www.vliz.be/nl/imis?module=ref&refid=140634] 

[9]          Morales-Núñez, A.G.; Chigbu, P. (2018). First record of Ianiropsis cf. serricaudis in Maryland Coastal Bays, USA (Crustacea, Peracarida, Janiridae). ZooKeys 747: 115-139. [https://www.vliz.be/nl/imis?module=ref&refid=396122]

[10]        Marchini, A.; Ferrario, J.; Occhipinti-Ambrogi, A. (2016). Confirming predictions: the invasive isopod Ianiropsis serricaudis Gurjanova, 1936 (Crustacea: Peracarida) is abundant in the Lagoon of Venice (Italy). Acta Adriatica 57(2): 331-336. [https://www.vliz.be/en/imis?module=ref&refid=353966] 

[11]        Carlton, J.T. (1979). History, biogeography, and ecology of the introduced marine and estuarine invertebrates of the Pacific coast of North America. PhD Thesis. University of California: Davis. 904 pp. [https://www.vliz.be/en/imis?module=ref&refid=393390] 

[12]        Faasse, M.A. (2007) De zeepissebed Ianiropsis sp. (Crustacea: Isopoda: Janiridae) geïntroduceerd in Nederland. Het Zeepaard 67(4): 125–127 [https://www.vliz.be/nl/imis?module=ref&refid=114199] 

[13]        Faasse, M.A. (2001). De zeepissebed Janiropsis breviremis Sars, 1899 autochtoon in Nederland. Het Zeepaard 61(1): 7-8. [https://www.vliz.be/en/imis?module=ref&refid=393443] 

[14]        van Bragt, P.H. (2016). Een Japanse zeepissebed in Nederland. Nature Today 17 jan: online  https://www.naturetoday.com/intl/nl/nature-reports/message/?msg=22397 [https://www.vliz.be/en/imis?module=ref&refid=393657] 

[15]        van Moorsel, G. (2015). De Japanse zeepissebed Ianiropsis serricaudis. Zoekbeeld: nieuwsbrief van Stichting Anemoon 5(2): 11-14. [https://www.vliz.be/en/imis?module=ref&refid=393438]  

[16]        Arenas, F.; Bishop, J.D.D.; Carlton, J.T.; Dyrynda, P.E.J.; Farnham, W.F.; Gonzalez, D.J.; Jacobs, M.W.; Lambert, C.; Lambert, G.; Nielsen, S.E.; Pederson, J.A.; Porter, J.S.; Ward, S.; Wood, C.A. (2006). Alien species and other notable records from a rapid assessment survey of marinas on the south coast of England. Journal of the Marine Biological Association of the United Kingdom 86(6): 1329-1337. [https://www.vliz.be/nl/imis?module=ref&refid=119308] 

[17]        Martinez-Laiz, G.; Ros, M.; Guerra-García, J.M. (2018). Marine exotic isopods from the Iberian Peninsula and nearby waters. PeerJ 6: e4408. [https://www.vliz.be/en/imis?module=ref&refid=353970] 

[18]        Gouillieux, B. (2018). First record of the invasive species Ianiropsis serricaudis Gurjanova, 1936 (Crustacea: Isopoda) in Arcachon Bay, Bay of Biscay (NE Atlantic). Bioinvasions Records 7(2): 171-176. [https://www.vliz.be/en/imis?module=ref&refid=353968]    

[19]        Raoux, A.; Pezy, J.-P.; Dauvin, J.C. (2020). First record of the non-indigenous isopod Ianiropsis serricaudis Gurjanova, 1936 along the French coast of the English Channel. Bioinvasions Records 9(4): 745-752. [https://www.vliz.be/en/imis?module=ref&refid=353967]  

[20]        Murray, C.C.; Therriault, T.W.; Maki, H.; Wallace, N. (Ed.) (2019). The effects of marine debris caused by the Great Japan Tsunami of 2011. Pices Special Publication, 6. North Pacific Marine Science Organization (PICES): Sidney. ISBN 978-1-927797-33-4. viii, 270 pp. [https://www.vliz.be/en/imis?module=ref&refid=353969] 

[21]        Kussakin, O.G. (1962). On the fauna of Janiridae (Isopoda, Asellota) from the USSR seas. Trudy Zoologicheskogo Instituta Rossijskoj Akademii Nauk = Proceedings of the Zoological Institute, Russian Academy of Sciences 30: 17-65. [https://www.vliz.be/en/imis?module=ref&refid=393386] 

[22]        Kusakin, O.G. (1982). Morskie i solonovatovodnye ravnonogie rakoobraznye (Isopoda) kholodnykh i umerennykh vod severnogo polushariia : Podotriady Anthuridea, Microcerberidea, Valvifera, Tyloidea = Marine and brackish-water isopod Crustacea of cold and temperate waters of the Northern Hemisphere. “Nauka” Leningradskoe otdelenie: Leningrad. 461 pp. [https://www.vliz.be/en/imis?module=ref&refid=394259] 

[23]        Gurjanova, E.F. (1936). Beitrage zur Kenntnis der Isopodenfauna des Pazifischen Ozeans. IV. Neue Isopodenarten aus dem Japanischen und Beringmeer. Zoologischer Anzeiger 114(9): 250-265. [https://www.vliz.be/en/imis?module=ref&refid=393388]  

[24]        Nemesis. Ianiropsis serricaudis. https://invasions.si.edu/nemesis/species_summary/544802 (2024-02-01)

VLIZ Alien Species Consortium (2024). Ianiropsis serricaudis. Introduced alien species of the Belgian part of the North Sea and adjacent estuaries anno 2024. Flanders Marine Institute (VLIZ). 5 pp.