Page 4 - BIR_2017_Balistreri_etal

P. Balistreri et al.

5.0 a
4.5
4.0
(ind.km -2 ) 3.5
3.0
2.5
R. nomadica 2.0 1 st records
1.5
1.0
0.5
0.0
30 SN J M M J SN J M M J SN J M M J SN J M M J SN J M M J S 40
b
25 35
Temperature (°C) 20 30 Salinity

15

10
25
Figure 4. (a) Rhopilema nomadica 5 Temperature
individual abundance in Bizerte Salinity
Lagoon between 2011 and 2016, 0 20
along with (b) the variation in sea SN JM M J S N J M M J SN J M M J SN J M M J SN J M M J S
temperature ( C) and salinity values. 2011 2012 2013 2014 2015 2016
°

temperature recorded on the day was that of 21–22 °C. Tyrrhenian flow spreading northwards in an anti-
This sighting was made by the main SCUBA diving clockwise fashion along the Italian coast and into a
centre within the archipelago (Egadi Scuba Diving, south-bound flow traversing the Sicily Channel
based on the island of Favignana) and was obtained (Millot 1987), one can anticipate that further future
from social media with the owner’s permission. sightings of R. nomadica will be made within the
These two new records for Italian waters further Tyrrhenian Sea, especially along the south-western
support the invasive potential of R. nomadica and coast of the Italian peninsula.
the hypothesis that the Levantine current has a role Further south, within Tunisian waters, the Jellyfish
in the westward spread of the species in the survey conducted annually in Bizerte Lagoon between
Mediterranean (Deidun et al. 2011). By crossing over 2011 and 2016 showed a marked change over the
to the western half of the Mediterranean Basin, years in both the occurence period and abundance of
Rhopilema nomadica has joined an increasing list of Rhopilema nomadica individuals, since the first
Lessepsian migrants [e.g. Lagocephelaus sceleratus sighting of the species in the Gulf of Gabes in 2008.
(Gmelin, 1789), Saurida lessepsianus Russell, Golani Prior to the current study, the species was only
and Tikochinski, 2015, Sargocentron rubrum (Forsskal, sporadically recorded along different sections of the
1775), Fistularia commersonii Ruppell, 1838, Stepha- Tunisian coast (Daly Yahia et al. 2013). For instance,
nolepis diaspros Fraser-Brunner, 1940, Siganus the species was consistently recorded each summer
luridus (Ruppell, 1829), Melibe viridis Kelaart, 1858, since 2010 to the date of the Daly Yahia et al. (2013)
Cassiopea andromeda Forsskal, 1775 and Phyllorhiza publication within the Gulf of Tunis, whilst further
punctata von Lendenfeld, 1884] that have managed north along the Tunisian coast, within the Bizerte
to breach the Sicily Channel, which has traditionally area, the species was not recorded during the 2012
been viewed as a biogeographical barrier to the and 2013 summer seasons after its first record within
spread of such species, restricting them to the eastern the same location in September and October 2011
half of the Basin (e.g. Quignard and Tommasini (Figure 4). The latter phenonmenon could be due to a
2000). In view of the prevailing patterns of surface- pronounced decrease in water salinity (below 25)
water currents in the central Mediterranean, where the recorded within the Bizerte Lagoon at the start of
main Atlantic surface current bifurcates into a 2012.

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