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Spread of Rhopilema nomadica in the western Mediterranean

Since 2014, R. nomadica has been recorded Mediterranean sites, could be attributable to the
within Bizerte Lagoon during summer. While the peculiarities that such a lagoon environment presents,
occurences were restricted to summer and autumn both in trophic terms (less oligotrophic in nature that
seasons in 2014 (last recorded specimen during that the non-lagoon sites) and by virtue of the sheltered
year was in November 2014), the population recorded nature of the lagoon (compared to the intense hydro-
during summer 2015 was present until February dynamism of the non-lagoon sites). This viable
2016. In terms of abundance, while R. nomadica was population established along the northern extremity
sporadically observed in 2014, with individual abun- of Africa along the entrance to the western basin of
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dance values ranging between 0.1 and 0.3 ind. km , the Mediterranean is expected to serve as a spring-
the jellyfish were continuously observed between board for a further westward spread of the species.
August 2015 and February 2016 at higher abundance
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values, ranging from 0.1 to 1.1 ind. km . The Acknowledgements
highest individual abundance within Bizerte Lagoon
of R. nomadica after 2013 was recorded in July The authors thank M. Colombo, F. Boero, S. Piraino, A. M.
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2016, reaching 4.4 ind. km . Mannino and the Egadi Scuba Diving Centre in Favignana for all
It should be noted that no ephyrae of the species their help. The jellyfish survey conducted within the Bizerte
Lagoon (Tunisia) was supported by the European project
were ever identifed in the net samples, while speci- MEDJELLYRISK (ENPI – CBCMED (ref: I-A/1.3/098). The
mens observed during January and February 2016 authors are also grateful to two anonymous referees for greatly
were all juveniles (bell diameter <10 cm). During improving the manuscript through their useful comments.
the R. nomadica occurence period, the water surface
temperature ranged from 13 °C (January 2016) to References
28.1 °C (August 2015), and the water surface salinity Boero F, Putti M, Trainito E, Prontera E, Piraino S, Shiganova TA
varied from 37 to 38.2. (2009) First records of Mnemiopsis leidyi (Ctenophora) from the
Since the first records of Rhopilema nomadica in Ligurian, Thyrrhenian and Ionian Seas (Western Mediterranean)
the Bizerte area in 2011 (Daly Yahia et al. 2013), its and first record of Phyllorhiza punctata (Cnidaria) from the
annual occurrence between 2014 and 2016 within Western Mediterranean. Aquatic Invasions 4: 675–680,
https://doi.org/10.3391/ai.2009.4.4.13
the same area as well as the presence of juveniles of Crocetta F, Agius D, Balistreri P, Bariche M, Bayhan YK, Çakir M,
the species within the same waters indicate the Ciriaco S, Corsini-Foka M, Deidun A, El Zrelli R, Ergüden D,
establishment of a reproducing population. Rhopilema Evans J, Ghelia M, Giavasi M, Kleitou P, Kondylatos G, Lipej
nomadica is the third non-indigenous scyphozoan L, Mifsud C, Özvarol Y, Pagano A, Portelli P, Poursanidis D,
Rabaoui L, Schembri PJ, Taşkin E, Tiralongo F, Zenetos A
species established in the Bizerte Lagoon with (2015) New Mediterranean Biodiversity Records (October 2015).
Phyllorhiza punctata and Aurelia solida Browne, Mediterranean Marine Science 16: 472–488, https://doi.org/10.12
681/mms.1477
1905, being previously recorded from the same Daly Yahia MN, Daly Yahia-Kéfi O, Gueroun SKM, Aissi M,
waters (Gueroun et al. 2014; Gueroun 2016). The Deidun A, Fuentes VL, Piraino S (2013) The invasive tropical
late population onset of R. nomadica (two years after scyphozoan Rhopilema nomadica Galil, 1990 reaches the
the first record of the species) may be explained by a Tunisian coast of the Mediterranean Sea. BioInvasions Records
2: 319–323, https://doi.org/10.3391/bir.2013.2.4.10
possible competition with Phyllorhiza punctata, Deidun A, Arrigo S, Piraino S (2011) The westernmost record of
with whom it shares the same occurrence period Rhopilema nomadica (Galil, 1990) in the Mediterranean – off
(summer–autumn). Further investigation is needed to the Maltese Islands. Aquatic Invasions 6 (Suppl. 1): S99–S103,
https://doi.org/10.3391/ai.2011.6.S1.023
assess the factors that support Rhopilema nomadica Galil BS, Spanier E, Ferguson WW (1990) The Scyphomedusae of
proliferations as well as its impact on the Bizerte the Mediterranean coast of Israel, including two Lessepsian
Lagoon trophic resources and on other gelatinous migrants new to the Mediterranean. Zoologische Mededelingen
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It is interesting to note that whilst the occurrence Galil BS (2007) Loss or gain? Invasive aliens and biodiversity in the
of R. nomadica has only been documented through Mediterranean Sea. Marine Pollution Bulletin 55: 314–322,
https://doi.org/10.1016/j.marpolbul.2006.11.008
single individuals in the Maltese Islands, Pantelleria, Gambill M, Mcnaughton SL, Kreus M, Peck MA (2016)
and Sardinia, the species has attained viable popula- Temperature-dependent settlement of planula larvae of two
tions further west, within Tunisian waters, suggesting scyphozoan jellyfish from the North Sea. Estuarine Coastal
Shelf Science (in press), https://doi.org/10.1016/j.ecss.2016.08.042
that advection is the major driving force behind the Gueroun SKM (2016) Dynamique des populations et écologie
dispersal of the vagrant individuals observed along trophique des scyphoméduses du bassin sud méditerranéen:
the northern shores of the Sicily Channel. The Etude in situ et expérimentale de l’impact de la prédation
establishment of a viable R. nomadica population d’Aurelia sp. 8 et de Pelagia noctiluca sur le réseau trophique
pélagique. Thesis. Faculty of Science of Bizerte, Carthage
within the Bizerte lagoon, as opposed to a more University, 200 pp
ephemeral occurrence within the other central

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