Short Communication Mediterranean Marine Science Volume 10/1, 2009, 131-136 Occurrence of the alien nudibranch Melibe viridis (Kelaart, 1858) (Opisthobranchia, Tethydidae), in the Maltese Islands J. A. BORG, J. EVANS and P. J. SCHEMBRI Department of Biology, University of Malta, Msida MSD2080, Malta e-mail: [email protected] Abstract The alien dendronotacean nudibranch Melibe viridis (Kelaart, 1858), a tropical Indo-Pacific species that seems to have been introduced by shipping into the Mediterranean via the Suez Canal, and which has established populations in Greece, Turkey, Cyprus, Montenegro, Croatia, NW Sicily, southern peninsular Italy and Djerba Island in the Gulf of Gabes, is recorded for the first time from Malta. A thriving popu- lation was observed on a soft sediment bottom at a depth of 18-20 m off the western coast of the island of Comino (Maltese Islands). It is suggested that this species was introduced into Malta due to a natural range expansion of surrounding populations. Keywords: Mollusca; Gastropoda; Nudibranchia; Dendronotina; Malta; Mediterranean; Dispersal. Introduction ta) was from the island of Cephalonia in the Ionian Sea in 1970 (MOOS- The dendronotacean nudibranch LEITNER, 1986) and it has also been Melibe viridis has a wide distribution in recorded from the coastal waters off the tropical Indo-West Pacific peninsular Greece, both the Ionian and (GOSLINER & SMITH, 2003); however Tyrrhenian coasts of Calabria, the Strait it is not known from the Red Sea of Messina, north-eastern Sicily, the (DESPALATOVI et al., 2002; ZE- island of Djerba in the Gulf of Gabes NETOS et al., 2004). It is also reported (CATTANEO-VIETTI et al., 1990), and from the Mediterranean where its occur- from the island of Hvar, Croatia in the rence has been interpreted as due to Adriatic Sea (maps and references in transport via shipping, most likely DESPALATOVI et al., 2002; ZENE- through the Suez Canal (ZENETOS et TOS et al., 2004). Further records are al., 2004). The first Mediterranean from eastern Sicily (SCUDERI & record of this species (as Melibe fimbria- RUSSO, 2003), the Gulf of Taranto Medit. Mar. Sci., 10/1, 2009, 131-136 131 (CARRIGLIO et al., 2004; MASTRO- Melibe viridis (Kelaart, 1858) (RUDMAN, TOTARO et al., 2004), Turkey (YOKES 2004; ZENETOS et al., 2008). & RUDMAN, 2004), Montenegro This note reports the presence of (JANCIC, 2004) and Cyprus (SANCHEZ Melibe viridis in Malta. VILLAREJO, 2007). Mediterranean records of Melibe Methods were originally referred to as Melibe fim- briata (Alder & Hancock, 1864), but as More than 10 individuals of Melibe pointed out by GOSLINER & SMITH viridis were encountered and pho- (2003) in their systematic review of the tographed by scuba divers on 30th genus, RUDMAN (1999) could find no September, 2008, during a marine benthic consistent characters for separating survey off the western coast of the island Melibe fimbriata from Melibe viridis, and of Comino (Maltese Islands; Fig. 1). The suggested that the former be considered site (centred on Latitude N36Æ 00’ a junior synonym of the latter. The 33.00"/Longitude E14Æ 19’ 27.05") where Mediterranean Melibe is now accepted as the nudibranch was recorded, is charac- Fig. 1: Maps showing the location of: (a) the Maltese Islands in the Mediterranean; (b) Comino in the Maltese Islands; and (c) the site (rectangle) off western Comino where the specimens of Melibe viridis were recorded. The contour lines in figure (c) indicate the water depth in metres. 132 Medit. Mar. Sci., 10/1, 2009, 131-136 terised by a gently sloping bottom of grav- teristic expanded buccal hood fringed with elly sand, with small stones and pebbles, at tentacles, the large cerata on the dorsal a water depth of 18-20 m. Extensive algal surface, which are dorso-ventrally flat- forests (on bedrock and large boulders), tened at their distal ends, and the together with meadows of Neptune Grass sheathed rhinophores (Fig. 2). Posidonia oceanica and of Lesser Neptune Grass Cymodocea nodosa, surround the Results and Discussion soft bottom where the nudibranch was encountered. The specimens observed occurred on There is no doubt that this nudibranch a bottom of gravelly sand with small is a species of Melibe, which, following stones and pebbles at a depth of 18-20 m. RUDMAN (2004), is referred to as Melibe Sparse patches of Cymodocea nodosa viridis. The animals had all the gross mor- were present in the vicinity but none of phological characteristics of this species as the specimens were recorded from described by GOSLINER & SMITH amongst the seagrass. The individuals (2003), particularly the extremely charac- observed ranged in length between 8 cm Fig. 2: Underwater photograph of a feeding Melibe viridis from western Comino, Maltese Islands, taken by Sarah Gauci Carlton on 30th September 2008 at a depth of 20 m. The animal in the photograph is about 16 cm long (© Ecoserv 2008). Medit. Mar. Sci., 10/1, 2009, 131-136 133 and 16 cm. A few solitary individuals were is unlikely that if it occurred in ports or observed, but six were aggregated togeth- yacht marinas or along coasts in the vicin- er within a 2 m2 area. The animals were ity of shipping lanes in the Maltese observed feeding by the characteristic Islands, it would have gone unnoticed, expansion and contraction of the buccal especially given the intense diving activity hood as described by THOMPSON & that takes place along practically all the CRAMPTON (1984), and creeping slowly accessible coastline of the islands. For this along the substratum. They did not react reason, the arrival and establishment of to the presence of the divers. this species is likely to have been fairly There seems to be a general consen- recent. sus that Melibe viridis was introduced into It is interesting to note that this is the the Mediterranean via shipping since it second alien opisthobranch that has been does not occur in either the Red Sea or discovered in the same general area (the the Levantine Sea, which is not what is channel between the islands of Malta and expected for Lessepsian immigrants that Gozo) within a few months in 2008. In have invaded the Mediterranean through July 2008, an individual of the anapsid the Suez Canal under their own power Aplysia dactylomela was photographed at (ZENETOS et al., 2004). GALIL (2006) Cirkewwa, which is only some 2 km dis- suggests that Melibe viridis was introduced tant from the site where Melibe viridis has via ships’ ballast. Within the Mediter- been recorded (SCHEMBRI, 2008). The ranean, the species seems to have spread significance of this is obscure, although it partly by range expansion from centres of may be pure coincidence. establishment (for example, the popula- tions around peninsular Italy) and partly Acknowledgements by internal transport via shipping (for example, the Croatian population). Thanks are due to Ms Sarah Gauci In the case of the Maltese population, Carlton (Ecoserv Ltd, Malta) for supply- although shipping may have been the vec- ing photographs of Melibe viridis from tor, this species may also have reached the Comino, and to Dr Argyro Zenetos (Hel- islands through natural dispersal from lenic Centre for Marine Research, nearby populations, either those in Greece) for providing information on the Tunisia or those on the eastern coast of distribution of the species. Sicily, or from as yet unreported popula- tions closer to the Maltese Islands. We References could find no information on the duration of the larval stage of Melibe viridis, howev- CARRIGLIO, D., FANELLI, G. & er, the veliger larvae of Melibe leonina RUBINO, F., 2004. First record of the metamorphose after 30-59 days in the alien gastropod Melibe fimbriata (Opis- plankton (RUDMAN, 2001); if Melibe tobranchia: Tethyidae) in the Taranto viridis is similar, this is ample time for lar- seas (Mediterranean Sea). Journal of val dispersal from known surrounding the Marine Biological Association of the populations. United Kingdom, 84: 1067-1068. The large size and bizarre morpholo- CATTANEO-VIETTI, R., CHEMELLO, gy of this animal makes it stand out and it R. & GIANNUZZI-SAVELLI, R., 134 Medit. Mar. Sci., 10/1, 2009, 131-136 1990. Atlas of Mediterranean nudi- Available from http://www.seaslugfo- branchs. Roma, Italy: La Conchiglia; rum.net/factsheet.cfm?base=meliviri. 264pp. Retrieved: November 30, 2008. DESPALATOVIC’, M., ANTOLIC’, B. , RUDMAN, W.B., 2001 (Jan 12). Com- GRUBELIC’, I. & ULJEVIC’, A., ment on Re: Melibe from Alaska by 2002. First record of the Indo-Pacific William Cullen. [In] Sea Slug Forum. gastropod Melibe fimbriata in the Australian Museum, Sydney. Avail- Adriatic Sea. Journal of the Marine able from http://www.seaslugforum. Biological Association of the United net/find.cfm?id=3511. Retrieved: De- Kingdom, 82: 923-924. cember 6, 2008. GALIL, B., 2006. Shipwrecked - shipping SANCHEZ VILLAREJO, F., 2007 (Jul 20). impacts on the biota of the Mediter- Melibe 'fimbriata' from Cyprus. [Mes- ranean Sea. In: Davenport, J. & sage in] Sea Slug Forum. Australian Davenport, J.L. (eds.) The ecology of Museum, Sydney. Available from transportation: managing mobility for http://www.seaslugforum.net/find.cfm?i the environment. pp. 39-69. Springer: d=20207 Dordrecht. SCHEMBRI, P.J., 2008. Occurrence of GOSLINER, T.M. & SMITH, V.G., the alien sea hare Aplysia dactylomela 2003. Systematic review and phyloge- Rang, 1828 (Opisthobranchia, Aplysi- netic analysis of the nudibranch idae) in Malta. Mediterranean Marine genus Melibe (Opisthobranchia: Science 9(2): 113-116 Dendronotacea) with descriptions of SCUDERI, D. & RUSSO, G. F., 2003. three new species. Proceedings of the Due nuovi gasteropodi per le acque California Academy of Sciences, italiane: Melibe fimbriata Alder e 54(18): 302-355. Hancock, 1864 e Tricolia tingitana JANCIC, G., 2004 (Feb 26). Melibe from Gofas, 1982 (Mollusca: Gastropoda). the Adriatic. [Message in] Sea Slug Biologia Marina Mediterranea, 10(2): Forum.