Mediterranean Marine Science Vol. 8, 2007 A critical review of records of alien marine species from the Maltese Islands and surrounding waters (Central Mediterranean) SCIBERRAS M. Department of Biology, University of Malta, Msida MSD2080 SCHEMBRI P.J. Department of Biology, University of Malta, Msida MSD2080 https://doi.org/10.12681/mms.162 Copyright © 2007 To cite this article: SCIBERRAS, M., & SCHEMBRI, P.J. (2007). A critical review of records of alien marine species from the Maltese Islands and surrounding waters (Central Mediterranean). Mediterranean Marine Science, 8(1), 41-66. doi:https://doi.org/10.12681/mms.162 http://epublishing.ekt.gr | e-Publisher: EKT | Downloaded at 25/09/2021 11:19:06 | Review Article Mediterranean Marine Science Volume 8/1, 2007, 41-66 A critical review of records of alien marine species from the Maltese Islands and sur- rounding waters (Central Mediterranean) M. SCIBERRAS and P. J. SCHEMBRI Department of Biology, University of Malta, Msida MSD2080, Malta e- mail: [email protected] Abstract An updated list of alien marine species recorded from the Maltese Islands and surrounding waters, compiled from scientific and ‘grey’ literature and from authenticated unpublished reports to the authors, is presented. The listed species are classified in one of four categories as regards establishment status: established, casual, invasive and questionable. Doubtful records are listed as ‘?’. A total of 48 species, including nine dubious ones, are included in the list. Of the accepted records, 64% are established, of which 15.4% are invasive, 18% are casual and 18% are questionable. The most represented groups are molluscs (14 species), fish (13 species) and macrophytes (10 species). Six species are classified as inva- sive in Maltese waters: Lophocladia lallemandii, Womersleyella setacea, Caulerpa racemosa var. cylin- dracea, Percnon gibbesi, Fistularia commersonii and Sphoeroides pachygaster; impacts of some of these species on local ecosystems are discussed. Since the early 1900s, there has been an increasing trend in the number of alien marine species reported from the Maltese Islands. Transportation via shipping and in connection with aquaculture, as well as the range expansion of Lessepsian immigrants, appear to be the most common vectors for entry, accounting for 20%, 11% and 32% respectively of the alien species included in this review. The general warming trend of Mediterranean waters and increasing marine traf- fic may be facilitating the spread of warm-water Atlantic and Indo-Pacific species to the central Mediter- ranean, including the Maltese Islands. Keywords: Alien species; Invasive species; Malta; Biodiversity; Aquaculture; Lessepsian immigrants. Introduction 1996). The environmental impact of inva- sive marine species may be so severe that Invasion of native biotas by non- the introduction of aliens has been identi- indigenous species is a threat to the fied as one of the four greatest threats to integrity of biotic communities, the econ- the world’s oceans (IMO, 2000-2007). omy and even human health that is recog- Alien species may affect recipient ecosys- nized worldwide (VITOUSEK et al., tems through predation, direct and indi- Medit. Mar. Sci., 8/1, 2007, 41-66 41 http://epublishing.ekt.gr | e-Publisher: EKT | Downloaded at 25/09/2021 11:19:06 | rect competition, contamination of the ber of non-indigenous species in the native gene pool by exotic genes (for Mediterranean Sea has been attributed to example, through hybridization), habitat such human activities as seafaring, com- modification, and through the introduc- merce, and tourism; to the occurrence of tion of new parasites and pathogens. numerous habitats susceptible to inva- Human communities may also be impact- sion, in particular those subject to anthro- ed in several ways. For example, in the pogenic disturbance such as lagoons, Mediterranean, the massive swarms of estuaries, and marinas; to aquaculture the voracious Indo-Pacific jellyfish, ventures; and to the opening of the Suez Rhopilema nomadica Galil that have Canal which has led to the introduction of appeared along the Levantine coast since hundreds of Lessepsian immigrants the mid-1980s, have adversely affected (CHU et al., 1997; COUTTS et al., 2003; tourism, fisheries and coastal installations OCCHIPINTI-AMBROGI & SAVINI, when large groups of the jellyfish draw 2003; GALIL, 2006; MINCHIN, 2007). close to the coast (GALIL & ZENETOS, Although temperature change scenarios 2002). On the contrary, Erythrean fish in Europe vary regionally, there is a clear (Upeneus moluccensis (Bleeker), U. pori trend towards overall warming Ben-Tuvia & Golani, Dussumieria acuta (SCHROTER et al., 2005). Consequent- Valenciennes in Cuvier & Valenciennes) ly, present day sea warming favours the and penaeid prawns (Marsupenaeus occurrence and establishment of warm- japonicus (Bate), Metapenaeus monoceros water species, whether alien or native, in (Fabricius), M. stebbingi Nobili), consti- the Mediterranean Sea (BIANCHI, 2007; tute most of the catches along the Egypt- OCCHIPINTI-AMBROGI, 2007). The ian and Israeli coasts (GALIL & number of macroscopic marine species ZENETOS, 2002). inhabiting the Mediterranean is today estimated at about 12,000 Invasion by non-indigenous species (BOUDOURESQUE, 2004), of which may be a natural phenomenon whereby around 745 species are alien to the region an organism is dispersed into a region (ZENETOS et al., 2005). Immigration where it did not exist before by means of through the Suez Canal and transporta- natural mechanisms. Such invasions have tion by ships are the two vectors con- been termed ‘range expansions’ by MORI tributing largely to introductions into the & VACCHI (2002). The problem with Mediterranean (STREFTARIS et al., human-facilitated introductions is that, 2005). more often than not, these occur at rates The fate of immigrants is decidedly higher than the natural rate of range mixed. Those which survive the multitude expansion (MACK et al., 2000), often of physical stressors during the immigra- overcoming many natural barriers to dis- tion or transportation processes, and suc- persal, such as distance or currents ceed in reaching a suitable new environ- (SCHEMBRI & LAFRANCO, 1996; ment, may survive to reproduce and RUIZ et al., 1997). Consequently, existing become established, and some become equilibria between the native biota and invasive. The degree of success of the their physical and biological environ- introduced species depends on a multitude ments may be disrupted. The high num- of physical and biological factors, such as 42 Medit. Mar. Sci., 8/1, 2007, 41-66 http://epublishing.ekt.gr | e-Publisher: EKT | Downloaded at 25/09/2021 11:19:06 | the availability of vacant, under- or un-uti- assess the reliability of the available infor- lized niches, escape from biotic constraints mation as a prelude to future studies. (competitors, predators, parasites and dis- eases), low resident-community species Methods richness, disturbance before or upon immigration to the recipient environment, Records of alien species from the Mal- as well as the physico-chemical require- tese Islands and their surrounding waters, ments of the invader and its community taken to be the sea area within the 25 NM interactions (RUIZ et al., 1997; MACK et Fisheries Management Zone established al., 2000; TORCHIN et al., 2001). by the European Union (CAMILLERI, Because of their location on or close to 2003), were searched for in scientific, grey, the biogeographic boundary between the and popular literature. Unpublished western and eastern Mediterranean bio- reports to the authors by other workers, regions (BIANCHI, 2007), the Maltese fishers, sea users and others were also Islands are an important station for moni- included if these records were supported toring the entry and spread of alien marine by physical evidence such as specimens or species in this sea. With increasing marine photographs. The reliability of each record traffic, both commercial and tourist (cruise was assessed, and where possible, the liners, yachting), the Maltese Islands face establishment status of the species in the the ever increasing threat of alien species Maltese area was determined, using the arriving in ballast water or on ship hulls. terminology that follows. Due to their position, the Maltese Islands may act as a stepping stone for already Indigenous: A species which occurs established alien species to expand their naturally in a particular place – in the pres- range from west to east or vice versa. ent case, the Maltese Islands and sur- Moreover, the Maltese Islands are at the rounding waters as defined here; (synony- meeting point of Atlantic-derived aliens mous term: native, autochthonous). with those originating from the Red Sea and Indo-Pacific, providing an interesting Alien: Species or infraspecific taxon, opportunity to study the interactions of inclusive of parts, gametes or propagules, alien species of different biogeographic that may survive and subsequently repro- affinities. duce and spread outside of its historically However, records of alien marine known range (geographical area occupied species from the Maltese Islands are naturally) and beyond its natural dispersal sparse and scattered; the most recent potential (due to minor climatic oscilla- review, that by SCHEMBRI & tions) as a result of deliberate or acciden- LANFRANCO (1996), is now outdated. tal introduction by humans; (synonymous The aim of the present work is to present terms: non-native, non-indigenous,