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Introduction

The dendronotacean nudibranchMelibe viridis has a wide distribution inthe tropical Indo-West Pacific(GOSLINER & SMITH, 2003); howeverit is not known from the Red Sea(DESPALATOVI et al., 2002; ZE-NETOS et al., 2004). It is also reportedfrom the Mediterranean where its occur-rence has been interpreted as due totransport via shipping, most likelythrough the Suez Canal (ZENETOS etal., 2004). The first Mediterraneanrecord of this species (as Melibe fimbria-

ta) was from the island of Cephalonia inthe Ionian Sea in 1970 (MOOS-LEITNER, 1986) and it has also beenrecorded from the coastal waters offpeninsular Greece, both the Ionian andTyrrhenian coasts of Calabria, the Straitof Messina, north-eastern Sicily, theisland of Djerba in the Gulf of Gabes(CATTANEO-VIETTI et al., 1990), andfrom the island of Hvar, Croatia in theAdriatic Sea (maps and references inDESPALATOVI et al., 2002; ZENE-TOS et al., 2004). Further records arefrom eastern Sicily (SCUDERI &RUSSO, 2003), the Gulf of Taranto

Mediterranean Marine ScienceVolume 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: patrick.j.schembri@um.edu.mt

Abstract

The alien dendronotacean nudibranch Melibe viridis (Kelaart, 1858), a tropical Indo-Pacific speciesthat seems to have been introduced by shipping into the Mediterranean via the Suez Canal, and which hasestablished populations in Greece, Turkey, Cyprus, Montenegro, Croatia, NW Sicily, southern peninsularItaly 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 islandof Comino (Maltese Islands). It is suggested that this species was introduced into Malta due to a naturalrange expansion of surrounding populations.

Keywords: Mollusca; Gastropoda; Nudibranchia; Dendronotina; Malta; Mediterranean; Dispersal.

Short Communication

(CARRIGLIO et al., 2004; MASTRO-TOTARO et al., 2004), Turkey (YOKES& RUDMAN, 2004), Montenegro(JANCIC, 2004) and Cyprus (SANCHEZVILLAREJO, 2007).

Mediterranean records of Melibewere originally referred to as Melibe fim-briata (Alder & Hancock, 1864), but aspointed out by GOSLINER & SMITH(2003) in their systematic review of thegenus, RUDMAN (1999) could find noconsistent characters for separatingMelibe fimbriata from Melibe viridis, andsuggested that the former be considereda junior synonym of the latter. TheMediterranean Melibe is now accepted as

Melibe viridis (Kelaart, 1858) (RUDMAN,2004; ZENETOS et al., 2008).

This note reports the presence ofMelibe viridis in Malta.

Methods

More than 10 individuals of Melibeviridis were encountered and pho-tographed by scuba divers on 30thSeptember, 2008, during a marine benthicsurvey off the western coast of the islandof Comino (Maltese Islands; Fig. 1). Thesite (centred on Latitude N36Æ 00’33.00"/Longitude E14Æ 19’ 27.05") wherethe nudibranch was recorded, is charac-

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Fig. 1: Maps showing the location of: (a) the Maltese Islands in the Mediterranean; (b) Comino in theMaltese Islands; and (c) the site (rectangle) off western Comino where the specimens of Melibe viridiswere recorded. The contour lines in figure (c) indicate the water depth in metres.

terised by a gently sloping bottom of grav-elly sand, with small stones and pebbles, ata water depth of 18-20 m. Extensive algalforests (on bedrock and large boulders),together with meadows of Neptune GrassPosidonia oceanica and of Lesser NeptuneGrass Cymodocea nodosa, surround thesoft bottom where the nudibranch wasencountered.

There is no doubt that this nudibranchis a species of Melibe, which, followingRUDMAN (2004), is referred to as Melibeviridis. The animals had all the gross mor-phological characteristics of this species asdescribed by GOSLINER & SMITH(2003), particularly the extremely charac-

teristic expanded buccal hood fringed withtentacles, the large cerata on the dorsalsurface, which are dorso-ventrally flat-tened at their distal ends, and thesheathed rhinophores (Fig. 2).

Results and Discussion

The specimens observed occurred ona bottom of gravelly sand with smallstones and pebbles at a depth of 18-20 m.Sparse patches of Cymodocea nodosawere present in the vicinity but none ofthe specimens were recorded fromamongst the seagrass. The individualsobserved ranged in length between 8 cm

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Fig. 2: Underwater photograph of a feeding Melibe viridis from western Comino, Maltese Islands, takenby Sarah Gauci Carlton on 30th September 2008 at a depth of 20 m. The animal in the photograph isabout 16 cm long (© Ecoserv 2008).

and 16 cm. A few solitary individuals wereobserved, but six were aggregated togeth-er within a 2 m2 area. The animals wereobserved feeding by the characteristicexpansion and contraction of the buccalhood as described by THOMPSON &CRAMPTON (1984), and creeping slowlyalong the substratum. They did not reactto the presence of the divers.

There seems to be a general consen-sus that Melibe viridis was introduced intothe Mediterranean via shipping since itdoes not occur in either the Red Sea orthe Levantine Sea, which is not what isexpected for Lessepsian immigrants thathave invaded the Mediterranean throughthe Suez Canal under their own power(ZENETOS et al., 2004). GALIL (2006)suggests that Melibe viridis was introducedvia ships’ ballast. Within the Mediter-ranean, the species seems to have spreadpartly by range expansion from centres ofestablishment (for example, the popula-tions around peninsular Italy) and partlyby internal transport via shipping (forexample, the Croatian population).

In the case of the Maltese population,although shipping may have been the vec-tor, this species may also have reached theislands through natural dispersal fromnearby populations, either those inTunisia or those on the eastern coast ofSicily, or from as yet unreported popula-tions closer to the Maltese Islands. Wecould find no information on the durationof the larval stage of Melibe viridis, howev-er, the veliger larvae of Melibe leoninametamorphose after 30-59 days in theplankton (RUDMAN, 2001); if Melibeviridis is similar, this is ample time for lar-val dispersal from known surroundingpopulations.

The large size and bizarre morpholo-gy of this animal makes it stand out and it

is unlikely that if it occurred in ports oryacht marinas or along coasts in the vicin-ity of shipping lanes in the MalteseIslands, it would have gone unnoticed,especially given the intense diving activitythat takes place along practically all theaccessible coastline of the islands. For thisreason, the arrival and establishment ofthis species is likely to have been fairlyrecent.

It is interesting to note that this is thesecond alien opisthobranch that has beendiscovered in the same general area (thechannel between the islands of Malta andGozo) within a few months in 2008. InJuly 2008, an individual of the anapsidAplysia dactylomela was photographed atCirkewwa, which is only some 2 km dis-tant from the site where Melibe viridis hasbeen recorded (SCHEMBRI, 2008). Thesignificance of this is obscure, although itmay be pure coincidence.

Acknowledgements

Thanks are due to Ms Sarah GauciCarlton (Ecoserv Ltd, Malta) for supply-ing photographs of Melibe viridis fromComino, and to Dr Argyro Zenetos (Hel-lenic Centre for Marine Research,Greece) for providing information on thedistribution of the species.

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Submitted: December 2008Accepted: March 2009

Published on line: June 2009