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222 Mannino & Balistreri: An updated overview of invasive Caulerpa taxa ...

But later, Galil (2000) replaced the term “Lessepsian migration” with the original term
“Erythrean invasion” because she considered this inflow of tropical species an invasion more
than a migration (“cyclical and predictable movement between two geographic areas that is
related to the spatio-temporal distribution of resources or the reproductive cycle”).
In recent decades a conspicuous increase of introductions, essentially due to escape
from confinement, transport-stowaway and corridor (i.e. Suez Canal) entries (categories
according to CBD 2014), was registered. The Suez Canal is considered to be one of the
main vectors for the introduction of alien species into the Mediterranean Sea. However,
some authors (e.g. Por 2009) considered the current high settlement of tropical species
coming from the Suez Canal, mainly due to the ongoing sea-warming, as a re-colonization
by Tethyans descendants more than an invasion of alien species. As far as marine macro-
phytes are concerned, a total of 133 species (23 belong to Chlorophyta, 79 to Rhodophyta,
30 to Ochrophyta, and 1 to Tracheophyta) have been recently listed as possible aliens in
the Mediterranean Sea (Verlaque & al. 2015). This number is likely to increase as proved
by the recent record of Halimeda incrassata (J. Ellis) J.V. Lamouroux in the waters off
Mallorca Island (Alós & al. 2016).
Invasive Alien Species (IAS) are considered to be among the most serious threats, after
habitat losses, to biodiversity and natural ecosystem functioning (Bax & al. 2003;
Wallentinus & Nyberg 2007). Among the IAS recorded in the Mediterranean Sea, the fol-
lowing three Caulerpa taxa have raised serious concern due to their potential or ascer-
tained impact on the native communities (Boudouresque & al. 1995; Klein & Verlaque
2008; Katsanevakis & al. 2014).
Caulerpa cylindracea Sonder: even though it was reported along the coast of Tunisia by
Hamel (1926), the occurrence off the coasts of Libya in 1990 (Nizamuddin 1991) is gen-
erally accepted as the first record for the Mediterranean Sea. It was initially considered a
“Lessepsian migrant” (Alongi & al. 1993; Giaccone & Di Martino 1995a), but, recently,
Belton & al. (2014) concluded that this species has been introduced from Australia and
New Caledonia. Until Belton & al. (2014) it was reported in the literature as Caulerpa
racemosa var. cylindracea (Sonder) Verlaque, Huisman and Boudouresque, a new combi-
nation proposed by Verlaque & al. (2003).
Caulerpa taxifolia (M. Vahl) C. Agardh (invasive aquarium strain): this strain, first
recorded in the Mediterranean in 1984 (Meinesz & Hesse 1991), is genetically identical to
the strain cultivated in aquaria of western Europe (Jousson & al. 1998). According to
Meusnier & al. (2001), the first strain introduced in the Mediterranean is native to South-
Eastern Australia.
Caulerpa taxifolia (Vahl) C. Agardh var. distichophylla (Sonder) Verlaque, Huisman and
Procaccini: this alga, native to South Western Australia, was first reported in the Mediterranean
Sea as C. taxifolia from the coasts of South Turkey (2006, by Cevik & al. 2007).
Within the Mediterranean Sea, Sicily and circum-Sicilian Islands, as a consequence of
their strategic position both from a geographical and a transport-stowaway point of view,
including fisheries and recreational fleets, are particularly vulnerable and suitable to bio-
logical marine invasions (Occhipinti-Ambrogi & al. 2011a, b; Coll & al. 2012;
Katsanevakis & al. 2014; Mannino & al. 2014, 2015, 2017; Celesti-Grapow & al. 2016).
Since reliable and accessible information (literature, online inventories and databases) on
the spread dynamics, the introduction pathways and the invasiveness of marine alien