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]
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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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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. References AZZURRO E., ANDALORO F. (2004) - A new settled population of the lessepsian migrant Siganus luridus (Pisces: Siganidae) in Linosa Island, Sicily Strait. J. Mar. Biol. Assoc. UK, 84: 819-821. DI SILVESTRO D., GARZOLI L., LODOLA A. (2010) - Colonization status of the Mediterranean Sea by the tropical sea hare Aplysia dactylomela (Opisthobranchia, Anaspidea). 5th International Student Conference “Biodiversity and functioning of aquatic ecosystems in the Baltic Sea region”. 6-8 October 2010, Palanga (Lithuania). OCCHIPINTI-AMBROGI A., MARCHINI A., CANTONE G., CASTELLI A., CHIMENZ C., CORMACI M., FROGLIA C., FURNARI G., GAMBI M.C., GIACCONE G., GIANGRANDE A., GRAVILI C., MASTROTOTARO F., MAZZIOTTI C., ORSI-RELINI L., PIRAINO S. (2011) - Alien species along the Italian coasts: an overview. Biol. Invasions, 13 (1): 215-237. RAINERI P., ADRIANI A., PIRONI L., SAVINI D., OCCHIPINTI-AMBROGI A., BIANCHI C.N. (2011) - The invasive alien crab Percnon gibbesi (H. Milne-Edwards, 1853) in the Marine Protected Area of Linosa island (Central Mediterranean Sea). World Conference on Marine Biodiversity. 26-30 September 2011, Aberdeen, Scotland (UK). RAINERI P., SAVINI D. (2010) - Percnon gibbesi (H. Milne Edwards, 1853) in Linosa Island ten years after its first record. Rapp. Comm. int. Mer Médit., 39: 643. RELINI M., ORSI L., PUCCIO V., AZZURRO E. (2000) - The exotic crab Percnon gibbesi (H. Milne Edwards, 1853) (Decapoda, Grapsidae) in the central Mediterranean. Sci. Mar., 64: 337-340.
