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P. Balistreri et al.

Figure 1. Geographical locations of the central
and western Mediterranean sites referred to in this
study, arranged in chronological order in terms of
year of first sighting of Rhopilema nomadica. 1 =
Gulf of Gabes, Tunisia (2008); 2 = Maltese Islands
(2011); 3 = Bizerte lagoon (2011); 4 = Pantelleria
Island (Italy, 2015); 5 = Poetto, Cagliari (Sardinia
Island, Italy, 2015); 6 = Levanzo (Aegadian
archipelago, Italy, 2016).

substrate availability (Holst and Jarms 2007; Liu et authors (PB, AS). This network operates by keeping
al. 2009; Purcell et al. 2012; Song et al. 2013; regular contact with coastal and marine stakeholders,
Gambill et al. 2016). For Rhopilema nomadica¸ such as organizers of recreational events and
temperature seems to control the strobilation process competitions at sea, fishermen, boat owners, and
(Lotan et al. 1994). Both Deidun et al. (2011) and SCUBA divers.
Daly Yahia et al. (2013) reconstructed the chrono- In Tunisia, within the framework of the Tunisian
geonomic map for Rhopilema nomadica in the National Program on jellyfish monitoring and the
Mediterranean. These maps need to be revised on MED-JELLYRISK project (2013–2015; www.jelly
the basis of findings reported in this study. risk.eu), the Laboratory of Aquatic Systems
Biodiversity and Functioning of the University of
Material and methods Bizerte conducted jellyfish stranding and outbreaks
monitoring in the Bizerte area (north Tunisia;
In Italy, an informal marine citizen-science campaign Figure 1). Surveys were conducted monthly to semi-
is maintained, parallel to more formal initiatives monthly in the Bizerte Lagoon, depending on the
such as Jellywatch (e.g. Boero et al. 2009), along weather conditions. For each survey, sea sub-surface
southern Italian shores (Figure 1) by some of the (−0.5 m) temperature, and salinity were recorded using

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