Biol. Mar. Mediterr. (2012), 19 (1): 257-258
A. Lodola1,2, D. Savini1,2, A. Occhipinti-Ambrogi1,2
Dipartimento di Scienze della Terra e dell’Ambiente, Università di Pavia,
Via S. Epifanio, 14 - 27100 Pavia, Italia.
2
Associazione FOR-MARE, Italia.
[email protected]
1
ALIEN SPECIES IN THE CENTRAL MEDITERRANEAN SEA:
THE CASE STUDY OF LINOSA ISLAND (PELAGIAN ISLANDS, ITALY)
SPECIE ALIENE NEL MAR MEDITERRANEO CENTRALE:
IL CASO STUDIO DELL’ISOLA DI LINOSA (ISOLE PELAGIE, ITALIA)
Abstract - Linosa is a small volcanic island of the Pelagian Archipelago, a Marine Protected Area
located in the Central Mediterranean Sea (Sicilian Channel - Italy). It is subjected to the arrival of both
alien species from the Indo-Pacific region through the Suez Canal and species of tropical Atlantic origin
through the Strait of Gibraltar. The ongoing acclimatization of non-native thermophilic species, mainly
macroalgae, invertebrates and fishes on the island is presented.
Key-words: Linosa Island, Sicilian Channel, alien species.
Introduction - Linosa is a small volcanic island of the Pelagian Archipelago, a
Marine Protected Area (MPA) located in the Central Mediterranean Sea (Sicilian
Channel - Italy). Despite the very low anthropogenic impact (i.e. no industries,
nor agriculture, low tourism) and the reduced importance of ship traffic and
aquaculture, Linosa is recognized as one of the main hotspots of introduction of
alien species in Italy (Occhipinti-Ambrogi et al., 2011). The origin of these species is
mainly the Indo-Pacific region as they have been previously reported in the eastern
Mediterranean upon their entrance through the Suez Canal, whereas a few fish species
of tropical Atlantic origin seem to have entered through the Strait of Gibraltar. Due
to its location at the biogeographical boundary between the western and eastern
Mediterranean, Linosa island may act as stepping stone for secondary dispersal of
non-native species from west to east or vice versa. Moreover, it represents a meeting
point of Atlantic species with those from the Red Sea and Indo-Pacific, providing
an interesting opportunity for studying the interactions of alien thermophilic species
of different biogeographic origin.
Materials and methods - In two consecutive summers (2010-2011) the infralittoral
fringe was surveyed by underwater visual census, by both scuba diving and
snorkeling, in a depth range of 0-20 m with the aim of collecting updated data on
alien species distribution and abundance along transects of different size, depending
on the species considered. Survey sites were chosen according to their location inside
and outside the boundaries of the MPA, equally spaced and evenly covering the
whole perimeter of the island.
Results - Results showed the acclimatization of six alien species along the superior
infralittoral fringe of the island: the algae Caulerpa racemosa and Asparagopsis
taxiformis, the crab Percnon gibbesi, the opistobranch Aplysia dactylomela, the fish
Siganus luridus, and the bivalve Pinctada imbricata radiata. Caulerpa racemosa was
widespread in the summer of 2010 and has slightly increased its abundance in almost
all the survey sites in the summer of 2011. Asparagopsis taxiformis, which in 2010 was
confined to the northeastern coast, has increased its distribution having been found
also in sites along the southwestern coast. Percnon gibbesi showed higher densities
(mean: 25±34 individuals per 10 m2 of seabottom) in sites characterized by the
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A. Lodola, D. Savini, A. Occhipinti-Ambrogi
optimal habitat of the species, constituted by large boulders encrusted with coralline
algae (i.e. Mesophyllum sp. and Amphiroa sp.). Aplysia dactylomela was recorded in
both years only on the eastern coast. The fish S. luridus was detected only along
the northeastern coast in summer 2010 and also found along the western coast in
the summer of 2011 with relatively high densities (southern coast: 6±5 individuals
per 500 m2; northern and eastern coast: 1±1 individuals per 500 m2). The bivalve P.
imbricata radiata, absent in 2010, was detected along the northern and eastern coast
in 2011.
Conclusions - This study provides evidence of the ongoing acclimatization of alien
thermophilic species, mainly macroalgae, invertebrates and fishes. The abundance
and distribution of these species along the island coasts are increasing. Both C.
racemosa and A. taxiformis are successfully established and colonize rocky bottoms
starting from the surface to –20 m depth. Furthermore, A. taxiformis dominates
areas with strong hydrodynamism. Percnon gibbesi is an example of a very rapid
and successfull colonization. The crab was found in Linosa in 1999 for the first
time in the Mediterranean (Relini et al., 2000) and it is now widespread along the
superior infralittoral fringe as reported by recent studies (Raineri & Savini, 2010;
Raineri et al., 2011). Aplysia dactylomela was recorded for the first time in Linosa
in the summer of 2009 (Di Silvestro et al., 2010) and the subsequent records in 2010
and 2011 in the same locality on the eastern coast of the island, suggest that this
species is probably at an initial phase of colonization. The fish S. luridus was first
reported in Linosa in 2003 (Azzurro & Andaloro, 2004). It is now established, having
been found everywhere except along the southern coast. The finding of P. imbricata
radiata is the first report of the species in the island. These data highlight the key
role of Linosa for understanding the expansion of alien thermophilic species in the
Mediterranean Sea.
Acknowledgements: Authors thank the MPA of The Pelagian Islands that authorized this research.
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