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Spread of Rhopilema nomadica in the western Mediterranean

Figure 2. Specimen of Rhopilema nomadica from
Poetto (Italy). Lower part of mouth arm divided in
two triangular flaps, each flap distally tripartite and
terminating in claw-like digitate processes
(photo: Alessandro Spiga).

a WTW multi-parameter probe (Cond 3110/SET
model, Xylem Analytics, Germany). Jellyfish abun-
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dance (ind. km ) was estimated through visual counts
of the numbers of jellyfish from a small boat. The
-1
boat was run at a constant speed (1.85 km h ) for a
fixed distance (4.54 km) and all medusae observed
were counted. Only individuals lying within two
meters on either side of the boat bow were counted.
Small individuals (bell diameter <15 cm) were
sampled by a hand net for taxonomic verification.
Vertical net tows using a WP2 net (0.56 m mouth
diameter, 200 µm mesh size) were also performed.
The net samples were immediately fixed with
buffered 4% formalin in sea water and analyzed
under a Leica MZ125 stereomicroscope so as to
detect the presence of ephyrae.

Results and discussion

On the 26 October 2015, a large specimen of R.
nomadica (with an umbrella of ~40 cm in diameter,
Figure 2) was sighted at the surface at Poetto
(Supplementary material Table S1). The specimen,
identified through observation and photographic
documentation, was recorded during the regattas of Figure 3. Specimen of Rhopilema nomadica spotted at the surface
the Techno 293 World Windsurfing Championship, within Cala Minnola on the island of Levanzo within the
Aegadian archipelago (photo: Martina Taddei, Egadi Scuba Diving).
with the sea temperature on the day being that of 26 °C.
The sighting of this single individual was reported in

a local newspaper on 27 October 2015 (http://lanuo
vasardegna.gelocal.it/cagliari/cronaca/2015/10/27/news On the 22 September 2016, a single R. nomadica
/avvistata-nelle-acque-della-sardegna-una-pericolosa- individual (shown in Figure 3), having an estimated
medusa-gigante-del-mar-rosso-1.12340691) and within bell diameter of 25 cm, was spotted at the surface
the non-scientific literature through the ICES within Cala Minnola on the island of Levanzo within
Working Group on Introductions and Transfers of the Aegadian archipelago off the western coast of
Marine Organisms (ICES 2016). Sicily (Supplementary material Table S1). The water

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