Review Article

Mediterranean Marine Science Volume 7/1, 2006, 87-118

Alien Marine in the Mediterranean - the 100 ‘Worst Invasives’ and their Impact

N. STREFTARIS and A. ZENETOS

Hellenic Center for Marine Research, Institute of Oceanography P.O. Box 712, 190 13, Anavissos, Attica, Greece e-mail: [email protected]

Abstract

A number of marine alien species have been described as invasive or locally invasive in the Medi- terranean because of their proliferation, and/or their geographical spread and/or impact on native populations. Based on that information and on the documented impact they have on the biodiversity and socioeconomics of the basin, a preliminary list of the 100 ‘worst’ Invasive Alien Species (IAS) in the Mediterranean has been produced and presented in this work along with details on their impact. Emphasis is given to their impact on socioeconomics (fisheries/aquaculture, health & sanitation, in- frastructure & building), documented for 43 species. Such selection of the ‘worst’ IAS was difficult and controversial and is expected to attract much attention and scientific criticism since not only can the documentation of the impact of IAS be controversial, but also their inventory can be biased towards the effort and resources devoted to the study of the impact of certain species/taxonomic groups. Thus, while marine plants (phytobenthos and phytoplankton) are fairly well studied, less attention has been paid to the impact of vertebrates and even less to invertebrates. Nevertheless, the list highlights the need for continued research on the issue (monitoring aliens and their impact for an integrated ecosystem based management approach over the entire area). The preliminary list can provide the basis for selecting indicator species within the Mediterranean and thus be the common ground to build cooperation about IAS within countries in the region.

Keywords: Worst Invasive Alien Species; Mediterranean; Impact; Biodiversity; Socioeconomics.

Introduction pendent on these ecosystems and/or human health (EPA, 2001). A number of definitions have been applied Biological invasions in marine habitats to describe the term Invasive Alien Species represent a recognized worldwide threat (IAS); in many of them the term invasive is to the integrity of native communities, to associated with established species which economy and even to human health. Invasive are agents of change and threaten native bio- species are believed to accelerate the decline logical diversity (IUCN, 2002), or with spe- of native populations already under environ- cies that threaten the diversity or abundance mental stress, leading to population losses of native species, the ecological stability of and extinctions on a local scale (RICCIAR- infested ecosystems, economic activities de- DI, 2004), but not globally (GUREVITCH

Medit. Mar. Sci, 7/1, 2006, 87-118 87 & PADILLA, 2004). The extent of the im- countries in the region. Moreover, it will give pact has been so severe that invasive species an idea of what priorities may be needed for are regarded as the second biggest cause of the different countries in developing control biodiversity loss after habitat destruction programs, and starting environmental moni- (BREITHAUPT, 2003), constituting one toring of IAS species. of the four greatest threats to the world’s oceans on local, regional and global scales Methods (IMO 2000-2004). This ‘biological pollu- tion’ (CARLTON & GELLER, 1993) can be Selecting ‘worst’ invasive species is a detrimental to the host ecosystem since un- difficult task and will be surely criticised like other forms of marine pollution where by scientists. Since no objective criteria ameliorative action can be taken and their are available at the moment, the choice of effects can be reversed, their impact is more ‘worst’ invasive species is subjective. De- often irreversible (CARLTON, 1989). pending on personal interest some species In general, however, the impact of most will be favoured over others. For a rapid invasive species remains unknown, and the assessment of this indicator, a preliminary predictability of their direct and indirect ef- list of ‘worst IAS’ of the Mediterranean by fects remains uncertain (RUIZ et al., 1997). taxonomic groups was compiled through a In most regional European Seas the altera- literature search. tions of marine ecosystems due to new intro- The criteria used for selecting the ‘worst ductions and the associated socioeconomic invasive species’ in the Mediterranean were impacts have been poorly studied with few based on the criteria used by the IUCN/ well-documented cases reported and rarely GISP for the list ‘100 of the World’s Worst quantified (LEPPAKOSKI et al., 2002). Invasive Alien Species’ and endorsed by the Among invasive alien species, the ‘worst’ SEBI2010 Working Group 5. In this task, we invasive species have been the focus of many have included species that have either a doc- environmental programs and initiatives. A umented impact and/or possess the potential list of ‘100 of the World’s ‘Worst IAS’ has to cause serious negative impacts on biologi- been compiled by IUCN/GISP, whereas a list cal diversity and socio-economy. Thus, as of the worst IAS threatening biodiversity in ‘worst IAS’ have been defined invasive spe- Europe has been endorsed by the SEBI2010 cies that have an impact on: Working Group 5. However, both lists are very generic, covering all environments (ter- Biodiversity restrial, freshwater, marine) at global or Pan- In general alien species pose a threat to European scale and the contribution of ma- biodiversity by impacting on: rine species is underestimated. • Native species The aim of this work is to give an over- • Ecosystems either directly (affecting hy- view of the situation in the Mediterranean drology, nutrient cycling, and other proc- by presenting a list of the ‘worst’ invasive esses, mainly by the so-called ‘ecosystem marine species which will be the common engineers’), or indirectly by changing ground to build cooperation about IAS within the whole ecosystem structure and func- tioning (introduced species often con-  As part of the SEBI2010 process (Streamlining sume or prey on native ones, overgrow European 2010 Biodiversity Indicators http:// them, compete with them, attack them, biodiversity-chm.eea.eu.int/information/indica- or hybridise with them). tor/F1090245995 ) the Expert group 5 on ‘Trends • Unique biodiversity of endemic species, in invasive alien species’ is developing a list of isolated (pristine) ecosystems and con- ‘Worst invasive species threatening biodiversity servation areas in Europe’.

88 Medit. Mar. Sci, 7/1, 2006, 87-118 Socio-economics tion, and/or their geographical spread and/or New incursions of marine alien species impact on native populations. ZENETOS continue and some existing species are ex- et al., (2005) presented some of the ‘worst’ tending their range. By doing so, they can be IAS per eco-functional/taxonomic group. detrimentally affect the socioeconomic val- Table 1 summarises the top ‘100 Worst IAS’ ues of an area by impacting on fisheries & based on the documented impact they have aquaculture, health & sanitation, and infra- on biodiversity and socioeconomic values. structure & building. By definition all introduced species have an • Fisheries & Aquaculture: Alien species, impact on biodiversity (SEBI2010: WG5). including imported livestock pests, re- However, only those having a serious impact duce yields drastically, either directly are selected for our preliminary list. The lit- (e.g. pests) or indirectly (e.g. clogging of erature upon the attributions of a species on nets). IAS may also greatly increase the the list is given below (brief notes on their effort required to clean fishing gear and geographical distribution in ZENETOS et aquaculture. al., (2005)). Details of their impact are pre- • Health & Sanitation: The unintentional sented in the relevant sections that follow. introduction of toxic species, parasites and pathogens has an impact on both the 1.1. Plants ecosystem and human health, Many authors have provided lists of in- • Infrastructure & Building: Alien species vasive macrophytes in the Mediterranean. may induce habitat modification and al- WALLENTINUS (2002) for example has teration of physical conditions. They may provided a different perspective in which also cause fouling (for example may clog 25 macroalgae are considered as invasive water pipes and/or foul propellers), and and nine as highly invasive. The current may become navigational hazards. list is based on the list of invasive species In general, it does not seem a great prob- produced by BOUDOURESQUE & VER- lem to separate biodiversity and economic LAQUE (2002b) and references therein and impact, although they sometimes go hand in on the list of invasive or potentially inva- hand. Nevertheless, in lists of ‘worst’ aliens sive exotic macroalgae which according to there are some ‘pest’ species with a negative a screening protocol, defined in the ALIENS economic impact or which affect human or project, is based on species with: a) large health, but without a known ecological and fast spread in Europe (e.g. Heterosipho- impact so far. In the preliminary list of ‘worst nia japonica); b) invasive behaviour in Eu- IAS’ of the Mediterranean presented in this rope (e.g. Sargassum muticum); c) high im- paper however, the impact has been clearly pact on recipient assemblages and/or human indicated on the two major categories: biodi- activities (e.g. Caulerpa spp.) (VERLAQUE versity and socioeconomics, with special at- et al., 2005). tention to the latter and its subdivisions (fish- Microscopic algal species (phytoplank- eries & aquaculture (F), health & sanitation ton) responsible for the occurrence of Harm- (H), and infrastructure & building (I)). ful Algal Blooms have been regarded as invasive by many authors. For details see Results section 3.2 ‘Impact on health’.

1. Records of ‘Worst Invasive’ Alien Species 1.2. Vertebrates A number of alien species have been Fish: Among the alien fish eighteen spe- described as invasive or locally invasive cies are characterised as successful invaders by different authors in different parts of the and of economic importance and twelve as Mediterranean because of their prolifera- very common or prevalent but of no eco-

Medit. Mar. Sci, 7/1, 2006, 87-118 89 nomic importance due to their small size Polychaeta: Alien polychaetes have been (GOLANI et al., 2002). However the term reported as invasive throughout the Mediter- invasive is not used when describing the ranean by KOÇAK et al., (1999), ZIBROW- impact of alien fish species due to the lack IUS (2002), ÇINAR et al., (2005), ÇINAR of reliable information on distribution and (2006). abundance prior to the opening of Suez Ca- Crustacea: our list has been compiled nal (GOLANI, 1998). The ‘Worst Fish IAS’ based on the alien that have been found in Table 1 are based on the works of reported as very abundant with recorded im- GOLANI et al., (2002; 2006); GOREN & pact on biodiversity and the socioeconomic GALIL, (2005), HARMELIN-VIVIEN et values of the area by GALIL 1986, GALIL al., (2005). et al., (2002 & 2006), ZIBROWIUS (2002), THESSALOU-LEGAKI et al., (2006). 1.3. Invertebrates Other invertebrates: When assessing the Mollusca: Many authors have provided scale and impact of ship-transported alien lists of invasive molluscs in the Mediter- fauna in the Mediterranean, invertebrate spe- ranean. The selected species in Table 1 are cies have been regarded as invasive primarily based on lists of invasive species produced based on their spread by ZIBROWIUS (2002), by OCCHIPINTI AMBROGI (2002a,b), ZI- and individual species were also regarded as BROWIUS (2002), GOFAS & ZENETOS such by GALIL et al., (1990), OCCHIPINTI (2003), ZENETOS et al., (2003) and in- AMBROGI (2000a,b), GALIL & ZENETOS dividual species reported in BLANCHARD (2002), HYAMS et al., (2002), MERIÇ et al., (1996) and HOPPE (2002). (2002), YOKES & MERIÇ (2004).

Table 1 The ‘100 Worst Invasive Species’ in the Mediterranean F:Fisheries/Aquaculture - H: Health & Sanitation - I: Infrastructure & Building.

Species Latin name Common name Biodiver- Socio- SEBI sity economy 2010 PLANTS F H I PHYTOBENTHOS Acrothamnion preissii A red alga + + + Antithamnion nipponicum A red alga + + + Asparagopsis armata Harpoon weed + + + Asparagopsis taxiformis Limu kohu + + Bonnemaisonia hamifera A red alga + Caulerpa racemosa Grape caulerpa + + + Caulerpa taxifolia Killer alga + + + Codium fragile Dead man’s finger + + + + Colpomenia peregrina A brown alga + + Desmarestia viridis A brown alga + + + Grateloupia turuturu A red alga + + Halophila stipulacea A sea grass + + Heterosiphonia japonica A red alga + + Lophocladia lallemandii A red alga + Polysiphonia morrowii A red alga + + + Sargassum muticum Jap weed + + + + Continued

90 Medit. Mar. Sci, 7/1, 2006, 87-118 Table 1 (Continued) Species Latin name Common name Biodiver- Socio- SEBI sity economy 2010 F H I Stypopodium schimperi A brown alga + + + Undaria pinnatifida Wakeme, Asian kelp + + + + Womersleyella setacea A red alga + + + PHYTOPLANKTON Alexandrium catenella A dinoflagellate + + + + Alexandrium taylori A dinoflagellate + + Coolia monotis A dinoflagellate + + + Ostreopsis ovata A dinoflagellate + + + VERTEBRATES FISH Alepes djedaba Shrimp scad + Callionymus filamentosus Dragonet + elopsoides Slender rainbow + Lagocephalus sceleratus Elongated pufferfish + + Fistularia commersonii Bluespotted + + Herklotsichthys punctatus Spotted herring + Pempheris vanicolensis Vanikoro sweeper + Plotosus lineatus Eel catfish + + Sargocentron rubrum Redcoat + Saurida undosquamis Brushtooth lizard fish + + Scomberomorus commerson Narrowbarred Spanish + mackerel Seriola fasciata Lesser amberjack + + + Siganus luridus Dusky spine foot + + + Siganus rivulatus Marbel spine foot + + + Sillago sihama Silver sillago + Sphoeroides pachygaster Blunthead puffer + + + + Sphyraena chrysotaenia Yellow stripe barracuda + Upeneus moluccensis Goldband goatfish + Upeneus pori Por’s goatfish + INVERTEBRATES MOLLUSCA Anadara demiri Arc shell + + Anadara inaequivalvis Arc shell + + Brachidontes pharaonis Variable mussel + + Bursatella leachi Ragged sea hare + Chama pacifica Large Pacific Chama + + Cerithium scabridum A gastropod + Crassostrea gigas Pacific giant oyster + + Crepidula aculeata Spiny Slippersnail + Crepidula fornicata Slipper limpet + + +

Continued

Medit. Mar. Sci, 7/1, 2006, 87-118 91 Table 1 (Continued)

Species Latin name Common name Biodiver- Socio- SEBI sity economy 2010 F H I Musculista senhousia Green bugmussel + + Mya arenaria Soft shell clam + + Pinctada radiata Pearl oyster + + Rapana venosa Veined rapa whelk + + + Rhinoclavis kochi A gastropod + Ruditapes philippinarum Manila clam + + + + Spondylus spinosus Shiro-toge-umi-giku + + Strombus persicus Persian Conch + Teredo navalis Shipworm + + Xenostrobus securis Little Brown Mussel + + POLYCHAETA Branchiomma luctuosum Tube worm + Ficopomatus enigmaticus Australian tube worm + + + Hydroides dianthus Tube worm + + Hydroides dirampha Tube worm + + Hydroides elegans Tube worm + + Hydroides heterocerus Tube worm + Hydroides homoceros Tube worm + Hydroides minax Tube worm + Hydroides operculatus Tube worm + + Hydroides branchyacanthus Tube worm + Leonnates persicus Mud worm + Polydora cornuta Mud worm + + + Pomatoleios kraussii Tube worm + + Pseudonereis anomala Mud worm + Spirobranchus tetraceros Tube worm + Spirorbis marioni Tube worm + + + Streblospio gynobranchiata Mud worm + CRUSTACEA Callinectes sapidus Blue crab + + Charybdis longicollis Swimming crab + + Charybdis helleri Spiny hands + Dyspanopaeus sayi + Erugosquilla massavensis Mantis shrimp + Elasmopus pectenicrus An amphipod Eriocheir sinensis Chinese mitten crab + + + + Marsupenaeus japonicus Tiger prawn Karuma + + Melicertus hathor A shrimp + Metapenaeus monoceros Speckled shrimp + Metapenaeus stebbingi Penegrine shrimp + Mytilicola orientalis Red worm + +

Continued

92 Medit. Mar. Sci, 7/1, 2006, 87-118 Table 1 (Continued) Species Latin name Common name Biodiver- Socio- SEBI sity economy 2010 F H I Penaeus semisulcatus Green tiger prawn + Percnon gibbesi Nimble spray crab + + Portunus pelagicus Blue swimming crab + OTHER INVERTEBRATES Amphistegina lobifera A foraminiferan + Amphisorus hemprichii A foraminiferan + Asterina burtoni A starfish + Microcosmus exasperatus An ascidian + + Oculina patagonica A stony coral + Rhopilema nomadica A jelly fish + + + + + Tricellaria inopinata A bryozoan + +

2. Impact on biodiversity have been reported (HOLMER et al., 2004). Despite the abundant scientific reports avail- 2.1 Plants able no efforts have yet been made to eluci- date the role of ecosystem biodiversity in the Caulerpa species susceptibility of Mediterranean macrophyte Caulerpaceae - Caulerpa taxifolia and assemblages to impacts by invasive Caul- Caulerpa racemosa var. cylindracea - are erpa species (MARBÀ et al., 2005). perhaps the most notorious invaders in the Mediterranean; in many cases their invasive Caulerpa racemosa var. cylindracea spread has radically altered the structure Thirteen years after the first record in and function of native ecosystems causing a the early 1990’s of the invasive variety of C. decrease in biodiversity and representing a racemosa var. cylindracea (for identification very serious ecological problem in the Medi- see VERLAQUE et al., 2003), nearly the en- terranean (GRAVEZ et al., 2001). They are tire Mediterranean basin was reported colo- considered particularly invasive since they nized, reaching as far as the Canary Islands; are good colonisers of unvegetated sedi- by 2005 it has colonised the coasts of 11 ments, have wide tolerance of stress and are nations (Albania, Croatia, Cyprus, France, unaffected by nutrient and light limitation. In Greece, Italy, Libya, Malta, Spain, Tunisia other words, they possess a high capacity for and , and all major Mediterranean is- vegetative growth and population persistence lands), growing on all kind of substrata, both (WILLIAMS, 1990; MEINESZ et al., 1995; in polluted and unpolluted areas, between CHISHOLM et al., 1996; DELGADO et al., 0 and 70 m depth, demonstrating an exces- 1996; CECCHERELLI & CINELLI, 1999a; sive rate of proliferation (VERLAQUE et PIAZZI & CINELLI, 1999; WILLIAMS & al., 2000, 2003, 2004; PIAZZI et al., 2001a, GROSHOLSZ, 2002). 2005; BOUDOURESQUE & VERLAQUE, The mechanisms, by which Caulerpa spp. 2002b; MEINESZ et al., 2003; RUITTON might affect native vegetation, especially the et al., 2005). seagrasses, are still unclear (CECCHEREL- The invasive ability and strong com- LI & CINELLI, 1997). A correlation with petitive characteristics of C. racemosa have sediment environment has been suggested as been demonstrated in many works (CEC- extremely high sulfate reduction rates, and CHERELLI & CINELLI 1997; PIAZZI sulfide concentrations in colonised sediments et al., 1997, 2001a; PIAZZI & CINELLI,

Medit. Mar. Sci, 7/1, 2006, 87-118 93 1999; CECCHERELLI et al., 2000; CEC- CINELLI 1997; CECCHERELLI & CAM- CHERELLI & CAMPO, 2002). First indi- PO, 2002). Conversely, a positive influence cations of the impacts suggested alarming was found on the Zostera noltii shoots (CEC- changes in community structure both on phy- CHERELLI & CAMPO, 2002). tobenthos as well as on zoobenthos (see be- low). However, when examining the impact Caulerpa taxifolia on the zoobenthos in Cyprus, ARGYROU The invasive proliferation of Caul- et al., (1999) demonstrated contradictory erpa taxifolia, the ‘killer alga’ (MEINESZ, effects (decreased abundance of gastropods 1999), is the most infamous example of the and crustaceans, but increased abundance of impact of invasive species. In the Mediter- polychaetes, bivalves and echinoderms). ranean, the alga is causing a ‘major ecologi- Experimental work (PIAZZI et al., 2001a; cal event’ (BOUDOURESQUE et al., 1995). PIAZZI & CINELLI, 2003; BALATA et al., Even though C. taxifolia is not considered 2004) has shown that C. racemosa var. cy- as so invasive as C. racemosa var. cylin- lindracea invasions have a great impact on dracea (PIAZZI et al., 2001b; BALATA et Mediterranean macroalgal assemblages on al., 2004), it has reached high abundances dead mattes of Posidonia oceanica and rocky (MEINESZ et al., 1995; CECCHERELLI bottoms, with greater impact on the former. & CINELLI 1997, 1998). The small colony Within 6 months the alga had completely of 1m2 (accidentally introduced in 1984 by overgrown the substrata and had impover- the Oceanographic Museum of Monaco) had ished the algal assemblages by reducing the spread to more than 6,000 hectares by 1996 species cover, number of species and diver- (MEINESZ et al., 1998). It covered more sity (affecting primarily turf and encrusting than 13000 hectares along 191 km of coast- species, compared to erect species); the im- line in six countries (Monaco, France, Italy, pact was so extensive that the algal assem- Spain, Croatia and Tunisia) by 2000. The area blage did not seem to recover even when C. colonized along the Mediterranean French racemosa diminished following a seasonal coast increased from 77.3 km² to 122.7 km² cycle. between 2001 and 2004, and the species is Interestingly, whereas the dead matte of still expanding, out-competing native species P. oceanica appears to be the most favora- and seriously reducing diversity (MEINESZ ble substratum for colonization, no coloniza- et al., 2001, 2004). Yacht anchors and fish- tion has been observed on dense meadows in ing gears appear to have carried it over great many other Mediterranean regions; dense P. distances (MADL & YIP 2003). oceanica meadows seem to prevent C. race- Caulerpa taxifolia is known to have a mosa var. cylindracea invasion (PIAZZI & major impact on marine ecosystems, which CINELLI, 1999, 2003; CECCHERELLI et is mainly attributed to a toxic nature (synthe- al., 2000; PIAZZI et al., 2001a, 2005; RUIT- sis of terpenoids), an ability to colonize all TON et al., 2005). Nevertheless other studies parts of the littoral zones and all substrata, have demonstrated some changes in the veg- and a high ecological fitness. The toxic ter- etative cycle and production of P. oceanica penoids synthesized in higher concentrations (DUMAY et al., 2002). than in tropical waters (GUERRIERO et al., Contrasting results have emerged when 1992) inhibit the growth of Cystoseira bar- the impact on other native seagrasses was bata and Gracilaria bursa-pastoris (FER- investigated. Some results suggest reduction RER et al., 1997), and can explain the su- in the distribution of Cymodocea nodosa perior competitiveness of Caulerpa against as a result of competitive displacement by native macroalgae. They also negatively C. racemosa: C. nodosa shoot density was affect several phytoplanktonic organisms reduced even by 50% (CECCHERELLI & (LEMEE et al., 1997). Lastly they protect

94 Medit. Mar. Sci, 7/1, 2006, 87-118 C. taxifolia against grazers (RUITTON & Impoverishment has also been reported in BOUDOURESQUE, 1994). Caulerpa taxi- faunal assemblages. Polychaeta and mainly folia can drastically reduce marine biodiver- amphipod abundance (and to a lesser degree sity (mainly by displacing native algae and species richness) has been reduced), where- altering seagrass beds) (BOUDOURESQUE as the molluscan community appears either et al., 1992; VERLAQUE & FRITAYRE, to be benefited or to be impacted the least 1994a,b; de VILLELE & VERLAQUE, (BELLAN-SANTINI et al., 1994, 1996). De- 1995; CECCHERELLI & CINELLI 1997, creases have been observed in fish species in 1999a), disturb zoobenthos (BELLAN-SAN- number, density and biomass (HARMELIN- TINI et al., 1994; HARMELIN-VIVIEN et VIVIEN et al., 1996; GELIN et al.,, 1998; al., 1996) and modify organic and inorganic RELINI et al.,, 1998) along with an increase components of the sediment (CHISHOLM in numbers of green forms of labrid fish in & MOULIN 2003). The C. taxifolia im- populations living within C taxifolia mead- pact differs also according to the sensitiv- ows (ARIGONI et al., 2002). In contrast, ity and susceptibility of macrophyte assem- other authors (FRANCOUR et al., 1995; blages (PIAZZI et al., 2001a; VERLAQUE GELIN et al., 1998) have suggested that no & FRITAYRE, 1994a, b; de VILLELE & simple relation exists between the presence VERLAQUE, 1995; BALATA et al., 2004). of C. taxifolia and fish community. Dramatic decreases (with impoverishment reaching up to 75%) have been observed in Sargassum muticum photophilic subtidal assemblages of rocky The macrophyte Sargassum muticum substrates, which appear particularly vulner- reported in the Venice lagoon, Italy (RIB- able to invasions (VERLAQUE & FRITAY- ERA SIGUAN, 2002) and the Thau lagoon RE 1994a, b; KLEIN et al., 2005). Caul- and other parts of the Languedoc-Rous- erpa taxifolia, like C. racemosa, especially sillon coast, France (BOUDOURESQUE, colonizes the Cymodocea nodosa meadows 1994; VERLAQUE, 2001) is known to have and sparse Posidonia oceanica beds, caus- a direct impact on the indigenous floral as- ing the decay and regression of seagrasses semblages. It inhibits their recruitment and (MEINESZ & HESSE 1991;, BOUDOUR- growth (CRITCHLEY, 1983), even leading ESQUE et al., 1992; MEINESZ et al., 1993; to the eradication of many species e.g. Cys- CECCHERELLI & CINELLI, 1997, 1998, toseira barbata in Venice (OCCHIPINTI 1999a). In invaded P. oceanica meadows, AMBROGI, 2002b) and in the Thau lagoon the percentage of dead shoots can reach up (GERBAL et al., 1985; BOUDOURESQUE, to 45% and the living shoots possess abnor- 1994). It is also reported to have altered the mal yellowish leaves (de VILLELE & VER- vegetal landscape of canals in the Venice LAQUE, 1995). Even a facilitative effect of lagoon, together with other invasive algae seagrasses on C. taxifolia has been demon- (CURIEL et al., 1999), imposing a burden strated, which may cause indirect negative on the economy. effects on seagrasses (CECCHERELLI & CINELLI, 1997, 1998). Invasion appears to Womersleyella setacea, Acrothamnion be successful when seagrass meadows are preissii already experiencing a decline as a result of Mediterranean turfs are largely composed deteriorated environmental quality. There are of two introduced Rhodophyta: Acrothamni- suggestions that C. taxifolia is not capable of on preissii, colonising many parts of the west- invading the dense and healthy P. oceanica ern basin (BOILLOT et al., 1982; CINELLI meadows (MARBÀ et al., 1996, 2005; CEC- et al., 1984; FERRER et al., 1994; PIAZZI et CHERELLI & CINELLI, 1999b; JAUBERT al., 1996, 2002), and Womersleyella setacea et al., 1999; PEIRANO et al., 2005). colonising wide zones throughout the Medi-

Medit. Mar. Sci, 7/1, 2006, 87-118 95 terranean Sea (AIROLDI et al.,1995; ATHA- pinnatifida, and Antithamnion nipponicum NASIADIS, 1997). (= pectinatum) on coastal lagoon ecosystems These turfs have an adverse impact on have also been reported (CURIEL et al., Posidonia oceanica meadows in the W. 1998). Proliferations of Laminaria japonica Mediterranean: the diversity of the epiphytic have been reported in the Thau lagoon where macroalgal community of the rhizomes has its accumulation and decomposition have re- been found to decrease as the result of in- sulted in anoxia during summer (ANONY- vading filamentous Rhodophyta (PIAZZI MOUS, 1982). & CINELLI, 2000). In a study area in the Ligurian Sea (Italy) both total percentage 2.2. Vertebrates cover and diversity were found to be lower in invaded areas than in control areas: the Notwithstanding, definite changes in fish invasive Rhodophyta were reported to con- communities in the Levantine ecosystem stitute more than 90% of the epiphyte cover have been attributed to Lessepsian migrants. in P. oceanica rhizomes and along with C. According to OREN (1957) populations racemosa were discovered to occupy about of red mullet (Mullus barbatus) and hake 50% of macroalgal cover on dead P. oce- (Merluccius merluccius) have been forced anica mattes, throughout the year (PIAZZI to migrate to deeper waters by the aliens Up- & CINELLI, 2003). Similar high values eneus moluccensis and Saurida undosquamis, have been recorded for Womersleyella seta- respectively. However GOLANI (1998, and cea abundance in the area (AIROLDI et al., personal communication) argues against the 1995). evidence of such displacement as ‘it is diffi- Womersleyella setacea is also known to cult to determine whether the colonisers dis- have an impact on the coralligenous commu- placed the local species or whether the latter nities, as it has been found to form a mono- occupied the same bathymetric niche prior specific layer covering the coralligenous to its confamiliar colonisation’. According substrata in the Scandola reserve (Corsica) to GOLANI (1998) there are these two cases (RIBERA & BOUDOURESQUE, 1995). that deserve further study. The populations of narrow-barred Spanish mackerel Scombero- Asparagopsis armata, Codium fragile morus commerson and the dragonet Calliony- These have been reported as forming mus filamentosushave dramatically increased monospecific coverages, dominating many at a time when the indigenous meager Argyro- algal assemblages. Asparagopsis armata is somus regius (once of the most common com- known to cover 100 % of the upper infralitto- mercial species in Israel) and three other con- ral (0-10 m depth) in winter in the NW Medi- familial to the C. filamentosus species, have terranean and to dominate many infralittoral almost completely disappeared. assemblages in the Marseilles area along with Along the Lebanese rocky coasts, the Codium fragile (RIBERA & BOUDOUR- Lessepsian migrants represent 13% of the ESQUE, 1995). The dense populations of species richness and 19% of the total abun- A. armata are maintained, probably because dance of individuals (HARMELIN-VIVIEN the main Mediterranean herbivores, i.e. the et al., 2005), while almost half of the trawl sea urchin Paracentrotus lividus and the fish catches on the Mediterranean coast of Israel Sarpa salpa, avoid it (SALA & BOUDOUR- consist of alien fish species (GOLANI & ESQUE, 1997). BEN TUVIA, 1995). Similarly invading spe- cies have been found to comprise 62% of the Undaria pinnatifida, Desmarestia viridis, demersal fish biomass in the Gulf of Iskend- Antithamnion nipponicum erun, Turkey (GÜCÜ & BINGEL, 1994). Impacts of Desmarestia viridis, Undaria The invasive fish dominate the structure and

96 Medit. Mar. Sci, 7/1, 2006, 87-118 function of littoral ecosystems on the Levan- Manila clam, Ruditapes philippinarum is tine coast, representing 50-90% of the fish surely the most well-adapted and widespread biomass (GOREN & GALIL, 2005). species. The species was introduced into the lagoon in 1983, to enhance the depressed fish- 2.3. Invertebrates eries and aquaculture activities. At present, Italy is the largest clam producer in Europe, In the Mediterranean, fast expanding in- with an estimated production in 1998 of 40 vaders outcompete local species. This can 000 MT. The exploitation of the clam banks have a major impact on the ecosystem as represents one of the main sources of envi- many sudden changes in faunal community ronmental disturbance in the Venice lagoon. diversity and structure are attributed to this About 600 boats equipped with mechanical competition. Another alarming issue is the dredges, operate without any management number of unintentional introductions of strategies, causing heavy stress on benthic pathogens and parasites, with species im- communities:a single fishing haul can- af ported for aquaculture. fect the macrozoobenthos organism density: (PRANOVI et al., 2004) and the whole la- Mollusca goon ecosystem (PRANOVI et al., 2003; In coastal lagoons Musculista senhousia SFRISO et al., 2003). has been found to alter native benthic com- As for Crassostrea gigas, that is also munities (CROOKS, 1998). Enormous pro- intensely cultivated in the brackish lagoons liferations of Anadara inaequivalvis in the N. of Southern France. Collecting methods are Adriatic (RINALDI, 1985), replacing the na- not as impacting as in the case of burrow- tive Cerastoderma glaucum (OCCHIPINTI ing clams but mostly related to the influence AMBROGI, 2000), and of Mya arenaria in on particulate matter dynamics between the the Berre lagoon, Marseilles, (ZIBROWIUS, water column and the bottom (OCCHIPINTI 2002) have been reported. The predatory gas- AMBROGI, 2000). tropod Rapana venosa was initially regarded to have potential impact on native bivalves Polychaeta and on the environment in the Northern Adri- Fouling serpulid worms have become a atic (ZENETOS et al., 2003), but no clear cut nuisance in ports and marinas throughout the sign of impacts in the Northern Adriatic Sea Mediterranean. Hydroides elegans, H. dian- has been recorded (OCCHIPINTI AMBRO- thus, H. elegans, H. dirampha, Ficopoma- GI 2000, 2001a; SAVINI & OCCHIPINTI tus enigmaticus and Spirorbis marioni are AMBROGI, 2006). known to foul harbours throughout the Med- Imported mollusca for aquaculture pur- iterranean and are regarded as major foulants poses on artificial surfaces (KOÇAK et al., 1999; Imported bivalves for aquaculture pur- ZIBROWIUS, 2002). poses (especially oysters and clams) are According to a recent study of the Levan- among the best-known examples of negative tine coasts of Turkey ‘the alien serpulid spe- impacts of alien species in European seas in cies dominated rocks, molluscs (Brachidon- general and in Mediterranean in particular tes pharaonis, Thais rugosa and Spondylus as the case of the Venice lagoon has demon- gaederopus) and artificial substrates (i.e. strated. The Manila clam Ruditapes philip- dock’s pilings, ropes and tires), comprising pinarum and the Pacific oyster Crassostrea more than 95% of the specimens found in gigas are considered as the most spectacular these habitats. On the algae such as Ulva sp. invasions in the lagoon of Venice (OCCHIP- and Cystoseira sp. sampled in this study, al- INTI AMBROGI, 2000). ien species accounted for more than 85% of Among alien species in the lagoon, the the specimen’ (ÇINAR, 2006).

Medit. Mar. Sci, 7/1, 2006, 87-118 97 The serpulid worm Hydroides elegans ice and outcompeting the native species in was found to comprise 65 % of the popu- adapting to the altered physical and chemical lation in the polluted marinas but was only parameters of the ecosystem. (OCCHIPINTI infrequently found in the non-polluted AMBROGI, 2000; OCCHIPINTI AMBRO- (KOÇAK et al.,, 1999). Similarly spionid GI & SAVINI, 2003). However, the synergy worms now constitute the key indicators of between the invader and the stress already polluted areas. According to ÇINAR et al., imposed in the ecosystem is not clear (OC- (2005) in Izmir bay (Turkey) Streblospio CHIPINTI AMBROGI, 2000). gynobranchiata and Polydora cornuta have Invasive displacement has also been re- replaced dominant indicator species such as ported in echinoderms. The sea star Asterina Malacoceros fuliginosus and Capitella capi- burtoni has increased in number in the East- tata reaching maximum densities of 34,270 ern Mediterranean, causing a rapid decrease ind m-2 and 3170 ind m-2, respectively, and in the population of the native A. gibbosa accounting for more than 60% of total faunal (GALIL & ZENETOS, 2002). populations in the majority of samples col- When assessing the scale and impact of lected in winter. Their impact becomes more ship-transported alien fauna in the Mediter- significant when considering that they con- ranean, ZIBROWIUS (2002) reported the stitute more than 90% of the total individuals vast spread of the Scleractinian coral Ocu- and 50% of total biomass at some stations. lina patagonica in Spain, the Ligurian coast of Italy, Alexandria, Lebanon, Israel, Tuni- Crustacea sia (recently it was also reported in Greece, GALIL & ZENETOS (2002) while re- SALOMIDI et al., 2006) and the dense pop- viewing impacts of exotics on the eastern ulations of the ascidian Microcosmus exas- Mediterranean populations reported the peratus in Mediterranean harbours. rapid decrease of populations of the prawn The Lessepsian foraminifer Amphistegina Melicertus kerathurus and the shrimp Al- lobifera appears to be the worst invasive spe- pheus dentipes, attributed to invasive dis- cies in Turkey changing all the habitat type placement by Marsupenaeus (=Penaeus) and coastal structure (MERIÇ et al., 2002; japonicus. A fisheries commodity, the shrimp YOKES & MERIÇ, 2004). It is actually re- Squilla mantis has been displaced into deep- garded as a ‘very good example to show how er waters by the mantis shrimp Erugosquilla much a ‘harmless’ alien species can actually massavensis. have the potential to destroy an ecosystem’ Τhe crab Dyspanopeus sayi was reported (YOKES pers. commun.) A. lobifera popu- as very abundant in the lagoon of Venice lations in Turkey have expanded to such an (OCCHIPINTI AMBROGI, 2000) with a po- unprecedented extent that the dead tests are tential impact on native crabs (GALIL et al., locally accumulated as a 30-60 cm thick lay- 2002) but already in 2001 it had almost dis- er on the sea bed [Antalya, Kas, Kekova, Bes appeared in the canal of Venice (OCCHIPIN- Adalar and Uc Adalar] (MERIÇ et al., 2002) TI AMBROGI, 2001b) and now its presence reaching densities of more than 350 speci- is limited to the marine sectors of the lagoon mens/g of sediment (YOKES & MERIÇ, near the mouths (MIZZAN et al., 2005). 2004) suggesting a deposition rate of 2,5-4 cm/year. In Israel A. lobifera appears to be Other Invertebrates: Echinoderms, Bryo- the most abundant of foraminiferans in hard zoans, Corals and Foraminifera substrata, reaching densities of almost 180 The bryozoan Tricellaria inopinata was specimens /g (HYAMS et al., 2002). Am- discovered to have a profound impact on phisorus hemprichii is also considered inva- the bryozoan community by colonizing all sive in Turkish waters (YOKES pers. com- possible hard substrata in the lagoon of Ven- mun.) where it has been spreading rapidly in

98 Medit. Mar. Sci, 7/1, 2006, 87-118 southwestern coasts over the past two years. The mollusc Crepidula fornicata has been It has is also been observed in Israel recently found to compete with commercial shellfish (HYAMS et al., 2002). (BLANCHARD, 1996). Rapana venosa, be- ing an active predator of epifaunal bivalves, 3. Impact on socio-economic values poses a serious threat to cultivated (as well as natural) populations of oysters and mussels 3.1 Impact on Fishery/Aquaculture (ZENETOS et al., 2003). (Including Pests) Crustaceans have also been regarded as economic pests (GALIL et al., 2002). Dys- Many cases of economic losses to fisher- panopeus sayi reported abundant in the Ven- ies and aquaculture associated with invasive ice lagoon feeds on bivalves and may affect species have been reported local clam farming (although its presence Caulerpa taxifolia infestations are also is now regarded as limited ( OCCHIPINTI renowned for their negative impact on fish- AMBROGI, 2001b; MIZZAN et al., 2005)). ing, both commercial and recreational (e.g.: Eriocheir sinensis reported in the Narbonne tourism and SCUBA diving activities). Wom- littoral lagoons is capable of causing con- ersleyella setacea clogs up fishing nets in siderable damage to fisheries by consuming France (VERLAQUE, 1989) and the same netted fish and by cutting nets. Callinectes happens with Acrothamnion preissii and fish- sapidus has also been reported to affect nets ing gear in Italy (CINELLI et al., 1984) and and netted fish, and finally Charybdis longi- with Asparagopsis armata (M. VERLAQUE collis hampers trawl fishermen. The parasitic pers. commun). Similarly, Antithamnion copepod Mytilicola orientalis has been found nipponicum (=pectinatum), Caulerpa taxi- to infect the indigenous oyster Ostrea edulis folia, Codium fragile, Colpomenia pereg- (STOCK, 1993) as well as the blue mussel, rina, Heterosiphonia japonica, Desmarestia Mytilus edulis and is considered a serious viridis, Grateloupia turuturu, Polysiphonia pest (HOLMES & MINCHIN, 1995). morrowii, Sargassum muticum and Undaria The mass swarms of the jellyfishRhopilema pinnatifida foul shellfish aquaculture facili- nomadica reported along the Levantine coast ties in coastal lagoons and (VERLAQUE, and as far north as the southeastern coast of Tur- 1994, 2001; CECERE et al., 2000; M. VER- key, imposed a financial strain on fisheries (as LAQUE pers. commun.). well as tourism, and coastal installations, see Dinoflagellate blooms of Alexandrium 3.2. and 3.3) (GALIL & ZENETOS, 2002). taylori, Alexandrium catenella, Ostreopsis ovata and Coolia monotis have an impact on 3.2 Impact on health the economy by impacting on fisheries (as well as on human health and tourist activi- Ηarmful Algal Blooms (HABs) are in- ties) (see 3.2.). creasing both in intensity and frequency Displacement of native fish and prawns in the (GARCÉS et al., (due to Upeneus moluccensis and Saurida 2000; PENNA et al., 2005). HABs pose a undosquamis, Erugosquilla massavensis re- significant and expanding threat to marine ported in section 2) has also economic im- ecosystems and socioeconomic values (hu- plications, as these are fishery com- man health, amenities and fishery resources) modities which now require more effort for either as toxin producers (toxic HABs) or as their harvesting. Abundant populations of causatives of anoxic conditions (High-Bio- fish of no economic importance are another mass HABs). However, the mechanisms of example of economic burden to fishermen as the insurgence of blooms of toxic strains in fish are caught in fishing gear and have to resident populations are poorly known, even de discarded, as in the case of Sphoeroides if it is suspected that long range transport pachygaster (GOLANI et al., 2002).

Medit. Mar. Sci, 7/1, 2006, 87-118 99 of cysts and propagules with ballast water thermore, shellfish andArbacia sp. mortality might be involved. has been observed during Ostreopsis ovata Recurrent blooms of the non-toxic dino- blooms on Marina di Massa reefs and addi- flagellate Alexandrium taylori have been de- tional studies have indicated the presence of tected in the western Mediterranean (Catalan DSP-like and ciguatoxin-like toxins (SIMO- coast, Balearic Island, Sicily and Italian west NI et al., 2004). Potentially toxic epiphytic coast) over the past 15 years. High biomass assemblages comprising the Coolia monotis blooms during summer have led to deterio- (and genera Ostreopsis, Prorocentrum and ration of water quality for recreational uses, Amphidinium) which have impacts not only and to economic losses for the tourist indus- on molluscs’ safety but also on tourist activi- try (PENNA et al., 2001; GIACOBBE & ties as well, were recorded in Greek coastal YANG, 1999; GARCÉS et al., 1999, 2000; waters in 2003 (STRATEGY Workshop, 2002; BASTERRETXEA et al., 2005). Sim- 2004). ilar surface water discolorations have been In general, dinoflagellate blooms (such observed in the Eastern Mediterranean (Am- as those of Alexandrium taylori, Alexandri- vrakikos Bay, Greece, STRATEGY Work- um catenella, Ostreopsis ovata and Coolia shop, 2004). monotis in addition to their direct impact on Toxic red tide species are on the rise in human health, impact on tourist activities in many parts of the Mediterranean. A new PSP the areas where they occur. toxin in the Mediterranean strain of Alex- The jellyfish Rhopilema nomadica re- andrium andersonii, previously reported as ported along the Levantine coast and as far non-toxic, has been detected in Italy (Gulf north as the southeastern coast of Turkey, is of Naples) raising concern about potential most certainly a health issue to swimmers toxic events (CIMINIELLO et al., 1999). in the area, and has an impact on tourism Similar concern has been raised in Alexan- (GALIL & ZENETOS 2002). dria () as a result of the detection of Al- Invading fish also constitute a health threat exandrium catenella (MIKHAIL, 2001). A. to humans. Following the recent occurrence catenella is known to cause toxic events in of Lagocephalus sceleratus (Gmelin, 1789) the western Mediterranean. In spring 1998, in the Mediterranean Sea, (AKYOL et al., the first toxic event was detected, covering 2005), new findings revealed that the spe- 100 km of the Catalan coast (GARCÉS et cies is now very common along the Levan- al., 2000) reccurring in 1999 (VILA et al.,, tine coasts of Turkey (BILECENOGLU et 2001). A bloom observed in 1994 in Valencia al., 2006) and the south Aegean (CORSINI was later attributed to this species (GÓMES et al., 2006). The species is a potential risk to et al., 1996). The presence of Gymnodinium humans, since it contains tetrodotoxin (TTX) catenatum in the western Mediterranean has that may be a source of food poisoning. Two also been perceived as a probable ‘protago- cases of poisoning of people who had con- nist of future red tide events’ (GÓMEZ & sumed this fish were reported from Israel and CLAUSTRE, 2001). Lebanon (GOLANI et al., 2006). Ostreopsis ovata and Coolia monotis Plotosus lineatus is notorious for being have been detected in the Tyrrhenian Sea, highly venomous, with venom glands lo- (Tuscany coast and the islands of Elba, Gi- cated along the dorsal and pectoral spines annutri, and Giglio), in Sicily, Sardinia and (GOLANI, 2002). Several cases of injury also in the Ionian Sea (O. ovata in Bari). The were followed by hospitalization in Israel outbreaks of these red tides have been con- (GOLANI et al., 2006). Other not so se- sidered responsible for inflammation of the vere threats include: Siganus luridus, a food upper respiratory tract and conjunctivitis in fish that is occasionally poisonous (with all swimmers (SIMONI et al., 2003, 2004). Fur- spines slightly venomous), with very pain-

100 Medit. Mar. Sci, 7/1, 2006, 87-118 ful stinging but not lethal; several cases of Both formed layers of 1m thick which cov- ciguatera-like effects have been attributed to ered about 7 % and 1.5% of the lagoon area consumption of S. luridus (FISHBASE); Si- respectively (BIANCHI & MORRI, 2001). ganus rivulatus which has a very painful, but Pomatoleios kraussii together with an al- non-lethal, sting: all spines are slightly ven- ien bivalve species, Brachidontes pharaonis, omous (FISHBASE); Seriola fasciata, is as- may form a calcareous belt the thickness of sociated with reports of ciguatera poisoning which reaches approximately 3-5 cm. Rocks (FISHBASE) and Sphoeroides pachygaster in 0-1 m depths in Iskenderun harbour were which can be poisonous, due to its capacity largely covered with this species. In Mersin to produce tetrodotoxin (nevertheless, some Bay, the population density of Hydroides puffers are successfully exploited around the operculatus was very high. These two spe- world and are highly valued as food). cies were also observed on hulls of fishing boats in harbours, indicating that they have 3.3 Impact on Infrastructure a potential to cause economic trouble to ship owners and others using sea-water intake A financial burden associated with the pipes (ÇINAR, 2006). proliferation of alien species is the mechani- The bivalvia mollusca Spondylus spino- cal removal of accumulated material on the sus, Chama pacifica, Crassostrea gigas, beaches and the nuisance to tourism, as in the which live on hard substrata, can thrive in case of the removal of Codium fragile from harbour environments. The dense aggrega- the coasts of Marseille in the1960s (BOU- tions they form, may act as ‘ecosystem engi- DOURESQUE, 1994) and the Cladophora neers’ generating solid reefs. sp. proliferation along the coasts of Cyprus Fouling/clogging is also a problem with (RIBERA & BOUDOURESQUE, 1995). the mass swarms of the jellyfish Rhopile- Sargassum muticum, Undaria pinnatifida and ma nomadica reported along the Levantine Antithamnion nipponicum (=pectinatum) are coast and as far north as the southeastern regarded as navigational hazards to the users coast of Turkey where they are reported to of the canals along many of the Venice la- have clogged coastal installations (GALIL goon canals as they alter the sea bed and ca- & ZENETOS, 2002). Finally, the nal landscape and entangle boats (RIBERA Eriocheir sinensis has a documented impact & BOUDOURESQUE, 1995; OCCHIPINTI by damaging river banks through burrowing AMBROGI & SAVINI, 2003). Stypopodim (GALIL et al., 2006). schimperi has also been reported to have an impact on infrasructure facilities. The species Discussion is large ecosystem engineer and seasonally huge quantities are cast ashore on the Syrian In the Mediterranean the impact of inva- beaches. (M. VERLAQUE pers. commun.). sive species on biodiversity (from species Fouling serpulid worms have become a to community to ecosystem level) and to a nuisance in ports and marinas throughout the lesser extent on socioeconomic values and Mediterranean. Hydroides elegans, H. dian- health have been partially covered in vari- thus, H. dirampha, Ficopomatus enigmati- ous syntheses (BOUDOURESQUE, 1994; cus and Spirorbis marioni are known to foul BOUDOURESQUE & RIBERA, 1994; harbours throughout the Mediterranean and VERLAQUE, 1994; RIBERA & BOU- are regarded as major foulants of artificial DOURESQUE, 1995; GOLANI, 1998; surfaces (KOÇAK et al., 1999; ZIBROW- GALIL, 2000a&b; OCCHIPINTI AMBRO- IUS, 2002). Ficopomatus enigmaticus and GI, 2000, 2001a, 2002a,b; ZIBROWIUS, H. dianthus are building extensive reefs in 2002; BOUDOURESQUE & VERLAQUE, the lagoon of Orbetello (Tuscany, Italy). 2002a; GALIL & ZENETOS, 2002; GO-

Medit. Mar. Sci, 7/1, 2006, 87-118 101 Fig. 1: Numbers of ‘worst IAS’ impacting on socioeconomy per taxonomic group.

FAS & ZENETOS, 2003; OCCHIPINTI- ible designation of alien phytoplankton spe- AMBROGI & SAVINI, 2003; GOREN & cies related to HABs. Less attention has been GALIL, 2005). paid to the impact of vertebrates and even A preliminary list of the 100 ‘worst IAS’ less to invertebrates. Exceptions are the stud- in the Mediterranean by taxonomic groups ies on Ruditapes philippinarum (review by (Table 1) was compiled through a literature OCCHIPINTI AMBROGI 2002b) and on search. All 100 ‘worst IAS’ have an impact polychaetes (ÇINAR, 2006). on biodiversity (35 documented cases and Another issue that has to be emphasized the rest pose a potential threat) and 43 of is that absence from the list does not imply them have a documented impact on socio- that a species poses a lesser threat. It must economic values. Considering that the most be pointed out that some of the species that recent inventory of marine alien species in have been nominated as among 100 of the the Mediterranean has documented the exist- ‘World’s Worst’ invaders (ISSG, 2006), al- ence of 745 aliens, out of which 385 are es- though present in the Mediterranean, are not tablished (ZENETOS et al., 2005), the list of included in our preliminary list of ‘worst ‘worst IAS’ is expected to increase IAS’, mainly because of their sporadic re- The impact of the ‘worst IAS’ on socio- cording and minimal dispersal. These are: economical values is shown graphically in Mnemiopsis leidyi: Known for causing Figure 1. anoxia in bottom-near waters due to massive The Figure however is rather biased to- deposition of dead individuals and serious wards the effort and resources (both human economic losses due to the imposed decline and financial) devoted to the study of the in fisheries stock, as well as clogging water impact of certain species/taxonomic groups. intakes in the Black Sea. It has recently in- Thus, although the marine plants (phytob- vaded the Baltic Sea and North Sea (JAVID- enthos and phytoplankton) are fairly well POUR et al., 2006). In the Mediterranean studied, it has to be noted that taxonomic it has been reported in Turkey (UYSAL & difficulties often prevent the incontrovert- MUTLU, 1993) and Greece (SHIGANOVA

102 Medit. Mar. Sci, 7/1, 2006, 87-118 et al., 2001) in low numbers, where it is not 1991 (associated with a fish fry imported for known to have any impact. aquaculture) has been responsible for fish Liza haematocheila (Temminck & Sch- mortalities due to Pasteurellosis. From 1990 legel, 1845) [=Mugil soiuy Basilewsky, it has caused economic losses in different 1855]: One of the six alien species which Mediterranean countries including France, have a significant impact on the Black Sea Italy, Spain, Greece, Turkey and Malta (BA- ecosystem. Although present in the Mediter- KOPOULOS et al.,1995, 1997; CANDAN ranean, no impact has been reported. et al., 1996) affecting primarily gilthead sea Gambusia affinis: potential pest accord- bream (Sparus aurata), seabass (Dicentra- ing to FISHBASE. Present in Greece, Italy rchus labrax) and sole (Solea spp.). (1919-21), Spain (1921), Cyprus (1988), Al- On the other hand, recent studies have bania, Turkey, Malta, Bosnia, Slovenia, but demonstrated a lesser impact of species that no impact has been reported. had been initially considered to have a seri- Abundant populations of alien fish with- ous impact on biodiversity in the Mediterra- out direct economic use are also not included nean (e.g. Rapana venosa and Dyspanopae- in the ‘worst IAS’ despite the fact that they us say in the Venice lagoon: MIZZAN et al., can be considered as pests, an economic bur- 205; SAVINI, & OCCHIPINTI AMBROGI, den to fishermen who have to discard them 2006). from their gear (GOLANI et al., 2002). As pointed out above, selecting the ‘worst’ These are: Cynoglossus sinusarabici, Steph- IAS is a difficult task that attracts much at- anolepis diaspros, Lagocephalus spadiceus tention and scientific criticism. The debate and Lagocephalus suezensis. is ongoing since even the documentation of Bacteria (but also other parasites and the impact of IAS can be controversial, be- disease causing organisms) associated with cause of the lack of clear evidence on the aquaculture are also not included despite nature of such impacts and on the interaction the fact that they are considered a major between invaders and other anthropogenic threat connected with the development of stressors that influence such impact (RUIZet the worldwide transport of marine biota and al., 1999). Invasive success (and impact) de- hence of paramount importance when deal- pends not only on the invaders’ competitive ing with alien species. One of the reasons is advantage over native enemies/competitors, that with the exception of a few studies (e.g. but also on the environmental characteris- the parasite Perkinsus atlanticus and the tics of the host ecosystem (primarily spe- bacterium Photobacterium damselae subsp. cies richness and disturbance) and the level Piscicida), there is little data on the Mediter- of stress already imposed on it (RIBERA ranean alien bacteria/parasites. & BOUDOURESQUE, 1995; COHEN & The parasite Perkinsus atlanticus, first CARLTON, 1998; GOODWIN et al., 1999; detected in Spain in 1990 (SANTMARTÍ et OCCHIPINTI AMBROGI, 2000; KEANE al., 1995), had been widely distributed along & CRAWLEY, 2002). These environmental the Catalan coast by 1994, where it has been characteristics that render an environment or found in Ruditapes decussatus and Rudi- habitat vulnerable or resistant to biological tapes philippinarum in the Ebro river delta introductions are the focus of debate. The hy- (RIERA et al., 1995). It was associated with pothesis known as Elton’s ‘biotic resistance high mortalities of both bivalve species in hypothesis’ (ELTON, 1958), which assumes 1990 and also of Ostrea edulis and Crassost- that a species- rich ecosystem will be more rea gigas (SANTMARTÍ et al., 1995). resistant to introductions than a species-poor The bacterium Photobacterium damselae one, has been verified by several researchers subsp. piscicida (formerly Pasteurella pis- (LOOPE & MUELLER-DOMBOIS, 1989; cicida) reported in the Mediterranean since PIMM, 1989; REJMÀNEK, 1989; SIM-

Medit. Mar. Sci, 7/1, 2006, 87-118 103 BERLOFF, 1989; LODGE, 1993). ern Mediterranean both in aquaculture and In the Mediterranean, there is evidence in fisheries as wild populations have been supporting the theory as environments under established. The species is also exploited by stress (polluted or physically degraded) ap- fishermen in the Levantine where it invaded pear to be more prone to invasion than pris- via the Suez Canal (GALIL et al., 2002). tine sites (RIBERA & BOUDOURESQUE, However, considering the high perme- 1995; KoÇak et al., 1999; GALIL, 2000b; ability of aquaculture facilities, all introduc- OCCHIPINTI AMBROGI, 2000; OCCHIP- tions for the purpose of aquaculture should INTI-AMBROGI & SAVINI, 2003; see also be regarded and administered as possible, references in 2.1 Impact on Biodiversity - even probable, introductions into the wild. Caulerpa species). In addition, the fact that To reduce environmental and other risks, the environments that are known for their low ministries responsible and the aquaculture in- biodiversity (lagoonal or estuarine habitats dustry need to pursue management practices and polluted harbours) are recipient areas that prevent escapes and reduce the number for IAS related to mariculture and vessel- of inadvertent releases. Proper decision pro- transported aliens respectively (ZIBROW- tocols, containment, contingency planning, IUS, 1992), provide further support for this and end-user education are proactive means theory. However there are suggestions of of coping with potentially invasive species the opposite. When examining the frequency (ICES 2005; HEWITT et al., 2006). of introduced macrophytes in the shallow Even unintentionally introduced species subtidal macrophytic assemblages along the that have exhibited an invasive character French Mediterranean coast, no relationship have become locally of commercial impor- was established between the number of in- tance. Not surprisingly invading prawns troduced species, the species richness of the make up most of the catches along the coasts host macrophyte assemblages and distur- of Egypt and Israel (GALIL, 1993). bances (KLEIN et al., 2005). Examples of alien species that have be- While recent attention has focused on the come fishery resources in the Levantine area adverse impacts of accidentally introduced are: the gastropod Strombus persicus; the species, beneficial aspects of introductions prawns Marsupenaeus japonicus, Metap- are also known, as alien species have become enaeus monoceros, M. stebbingi, Penaeus fisheries commodities for the aquaculture semisulcatus and Melicertus hathor; the and fishing community and industry. Inten- crabs Portunus pelagicus, and Callinectes tionally introduced species have significantly sapidus (EEA, 1999; GALIL et al.,, 2002, contributed to aquaculture production (FAO GALIL & ZENETOS, 2002) and species of DIAS 1998), as well as fisheries (stock- fish such as the mullids Upeneus moluccen- ing) and recreational angling (MINCHIN & sis and U. pori, the obtuse barracuda ROSENTHAL, 2002). Sphyranea chrysotaenia, the clupeids Dus- A well known example is the success- summieria elopsoides and Herklotsichthys ful stocking of the Venice lagoon with the puncatus, the brushtooth lizard fish Saurida introduction of the oyster Crassostrea gigas undosquami as well as the Etrumeus teres, and the clam Tapes philippinarum in order Hemiramphus far, Atherinomorus lacuno- to replace depleted populations of two native sus, Sargocentron rubrum, Sillago sihama, species. Both species are fully acclimatised Alepes djedaba, Liza carinata, Gymnam- and exploited by fishermen (OCCHIPINTI modytes semisquamatus, Siganus luridus, S. AMBROGI, 2002a) Similarly, Marsupenae- rivulatus, Scomberomorus commerson and us japonicus, initially imported for aquacul- Solea senegalensis (GOLANI et al., 2002). ture, has become commercially important Protection against invasive species has in the Aegean Sea and the Central and West- been the focus of many environmental pro-

104 Medit. Mar. Sci, 7/1, 2006, 87-118 grams, initiatives and policies and strategies. seen that individual fact sheets on worst inva- The Bern Convention on the Conservation of sive species and their impact on biodiversity European Wildlife and Natural Habitats has and socio-economy will be produced for the developed a European Strategy on Invasive Mediterranean and the Black Sea. Alien Species, which offers specific advice to countries and international organisations Acknowledgements on measures to combat the threat. In Feb- ruary 2004, the International Maritime Or- The work was initiated under the auspices ganisation (IMO) adopted the International of the SEBI2010 - Streamlining European Convention for the Control and Management 2010 Biodiversity Indicators - Expert Group of Ship’s Ballast Water and Sediments. The 5: Numbers and costs of invasive alien spe- Convention will in the short term require cies. The programme is performed in collab- ships to exchange their ballast water in the oration between EEA, ECNC (the European open sea. Later, ballast water quality stand- Centre for Nature Conservation) and UNEP- ards will come into force. Ratification is WCMC. We would like to thank the partici- unfortunately only proceeding slowly and pants of the SEBI WG5 (Melanie Jossefson, it seems unlikely that the Convention will Jose Rico, Franco Andaloro, Franceso Pas- come into force in the near future. The im- sarelli, and MA. Pancucci-Papadopoulou), plementation of the EU Marine Strategy Di- who have substantially contributed to the rective, currently under development, should nomination of some Worst Invasive Species. include measures to limit the spread of IAS Special thanks are due to A. Occipinti Am- in European Seas. brogi and M. Verlaque whose constructive The information value of the preliminary criticism and suggestions have improved the list regards not only pressure on biodiversity manuscript. but is increased through the focus on socio- economic impacts at the species level. As References such, it provides the basis to examine the fea- sibility of endorsing indicator species within AIROLDI, L., RINDI, F. & CINELLI, F., the Mediterranean for monitoring aliens and 1995. Structure, seasonal dynamics and their impact for an integrated ecosystem- reproductive phenology of a filamentous based management approach over the entire turf assemblage on a sediment influenced, area. Considering the high number of new rocky subtidal shore. Botanica Marina, introductions in the Mediterranean (ZENE- 8: 227-237. TOS et al., 2005), it is inevitable that new AKYOL, O., ÜNAL, V., CEYHAN, T. & invaders with detrimental effects will pop up BILECENOGLU, M., 2005: First record in the basin. Keeping records up to date is of the Silverside Blaasop, Lagocephalus difficult and highlights the need for continu- sceleratus (Gmelin, 1789), in the Medi- ous research on the issue, not only recording terranean Sea. Journal of Fish Biology, the distribution of species but focusing on 66: 1183-1186. the impacts of the most invasive ones. ANoNYMOUS, 1982. Status (1980) of in- The work will continue under the Integrat- troduction of non-indigenous marine spe- ed Project (IP) SESAME (Southern European cies to North Atlantic waters. ICES Co- Seas: Assessing and Modelling Ecosystem operative Research Report, 116: 1-87. Changes). The list of ‘worst IAS’ is consid- Argyrou, M., Demetropoulos, ered a good management tool in order to as- A. & Hadjichristophorou, M., sess both the current status of the ecosystem 1999. Expansion of the macroalga Caul- of the region and the impact of climate change erpa racemosa and changes in soft bot- and anthropogenic activities. Thus, it is fore- tom macrofaunal assemblages in Moni

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