Marine Ecology. ISSN 0173-9565 ORIGINAL ARTICLE Hydrozoan species richness in the Mediterranean Sea: past and present Cinzia Gravili1, Cristina Gioia Di Camillo2, Stefano Piraino1 & Ferdinando Boero1,3 1 Dipartimento di Scienze e Tecnologie Biologiche e Ambientali, Università del Salento, Lecce, Italy and CoNISMa -Consorzio Nazionale Interuniversitario per le Scienze del Mare 2 Dipartimento di Scienze della Vita e dell’Ambiente, Università Politecnica delle Marche, Ancona, Italy 3 CNR-ISMAR, Genova, Italy Keywords Hydrozoa; Mediterranean Sea; nonindigenous species; zoogeography. Correspondence Dr Cinzia Gravili, Laboratory of Zoology and Marine Biology, Dipartimento di Scienze e Tecnologie Biologiche e Ambientali, Di.S.Te.B.A., Università del Salento, Via Prov.le Lecce-Monteroni, 73100 Lecce, Italy. E-mail: cinzia.gravili@unisalento.it Accepted: 2 October 2012 doi: 10.1111/maec.12023 Abstract The Mediterranean hydrozoan fauna (Siphonophora excluded) comprises 400 species; most (68%) occur in the Atlantic Ocean, 20% are endemic to the Mediterranean, 8% are of Indo-Pacific origin, and 4% are non-classifiable. There are 69 nonindigenous (NIS) species in the basin: 44% of these are casual (recorded just one or very few times), 28% established (widely recorded in the basin), 6% invasive (established NIS that are able rapidly or largely to disseminate away from the area of initial introduction, having a noticeable impact on the recipient community), and 22% questionable (of doubtful taxonomic status). Entry through the Suez Canal and range expansion through the Gibraltar Strait, often enhanced by ship traffic, appear to be the main processes for recent species introductions, but uncertainties remain for many NIS. Species additions immediately result in larger local or regional species pools, but the newcomers might impact on populations of native species, altering extinction probabilities. A more reliable evaluation of the species pool can be accomplished by adding new species when they enter the taxonomic record (i.e. the records of any taxon in all types of literature), and by removing species that have not been found for a ‘reasonable’ time (e.g. several decades). Of the 400 non-siphonophoran hydrozoan species known to occur in the Mediterranean Sea, positive records in the last 10 years are available for 156 species (39%), whereas records of the remaining 244 species are older than a decade: 67 species have not been recorded for 41 years, 13 for 31–40 years, 79 for 21–30 years, and 85 for 11–20 years. Introduction Species lists and distribution records are fundamental to biodiversity research (Costello et al. 2001; Mora et al. 2011). Biodiversity research has a long history in the Mediterranean Sea, which is one of the best known seas globally. Yet, reliable fauna inventories and easily accessible regional species lists are only available for a few taxonomic groups. Lists of nominal species, such as the ERMS (European Register of Marine Species; Costello et al. 2001), do not provide resolution of records at the regional scale (Boero 2002; Occhipinti-Ambrogi et al. Marine Ecology 34 (Suppl. 1) (2013) 41–62 ª 2013 Blackwell Verlag GmbH 2011). Both historical and ecological factors contribute to high biodiversity in the Mediterranean (Bianchi & Morri 2000; Bianchi 2007). In particular, pronounced seasonality is thought to facilitate the spatial coexistence of species by creating niche differentiation in time, and by allowing the occurrence of species with temperate and tropical affinities in the same basin (Coma et al. 2000). The biodiversity of the Mediterranean Sea is changing dramatically, partly linked to global warming, which is thought to contribute to the establishment of tropical nonindigenous species in the basin (Coll et al. 2010; 41 Hydrozoan species richness in the Mediterranean Sea Lejeusne et al. 2010). The arrival of new species of tropical provenance increases the regional species pool, being possibly counterbalanced by regressions of resident species that are adapted to colder water (Boero et al. 2008). The diversity of the Hydrozoa in the Mediterranean Sea is well known (Bouillon et al. 2004, 2006; Schuchert 2006, 2007, 2008a,b, 2009, 2010), and Hydrozoa can be considered a good proxy for marine biodiversity, being widely represented both in the plankton and in the benthos. Here we limit our treatment to non-siphonophoran Hydrozoa (NSH); they are not a formally recognized taxon, but the Siphonophora have, traditionally, been studied separately. NSH, both as polyps and/or medusa stages, are common in all oceans and seas, and syntheses of their global distribution are available for the medusa stage (Kramp 1959, 1961, 1968). The aim of this paper is to review the knowledge about the diversity of Mediterranean NSH. We assess current estimates of the size of the species pool, and examine whether species might have become locally or regionally extinct. Material and Methods Our list of NSH species of the Mediterranean Sea is based on the monograph by Bouillon et al. (2004), on other taxonomic revisions (e.g. Schuchert 2001, 2006, 2007, 2008a,b, 2009, 2010), and on a revison of the Mediterranean NSH that is currently in preparation (Gravili C. & Boero F., unpublished data). We identified nonindigenous species (NIS), examining records from the 19th century to 2010, to trace the origin, date, method of introduction, current distribution and establishment status, and global distribution of NIS. With few exceptions, we named taxa according to Bouillon et al. (2006). NIS have been classified into five categories according to their establishment status, following Zenetos et al. (2010): casual (found just a few times), established (widely recorded in the basin), invasive (established NIS that are able to rapidly or largely disperse away from the area of initial introduction, having a noticeable impact on the recipient community), and questionable (of doubtful taxonomic status). We decided to discard the category cryptogenic (species whose probable introduction occurred in ‘early times’ and has not been witnessed, e.g. prior to the XIX century) because no species was ascribed to it in this analysis. The date and location of the first observation of each NIS in the Mediterranean Sea were extracted from the literature. Whenever possible, the actual date of first collection has been reported, along with the publication date of the paper first recording a NIS, since the two dates only rarely coincide. 42 Gravili, Di Camillo, Piraino, Boero The vectors of NIS introduction are the most probable mechanism by which a NIS reached the Mediterranean Sea; however, they are often just presumed and are factually demonstrated in only a very few cases. Mediterranean records of Indo-Pacific species, for instance, are often labelled as the result of Lessepsian immigration through the Suez Canal (Por 1978). In this article, however, Lessepsian immigrants (LI) are only the species with established populations in the Red Sea that have expanded their distribution to the Mediterranean Sea by using the new connection, whereas the species that are recorded from the Indo-Pacific but not from the Red Sea, are labelled as Possible Lessepsian immigrants (PLI). The difference implies that LI crossed the Suez Canal using natural means (i.e. own mobility, drifting, rafting, etc.), whereas PLI entered the Mediterranean via human vectors. The route of entrance of PLI, in fact, might have been the Suez Canal, but an Indo-Pacific species transported by a ship, for instance, would reach the Mediterranean even if the ship were to circumnavigate Africa, and hence the passage through the Canal would be only circumstantial. Our knowledge of the hydrozoan fauna of the Red Sea is unfortunately not as detailed as that of the Mediterranean Sea (see Table 1, for a list of Red Sea NSH). The Indo-Pacific species recorded from the Mediterranean Sea, but not yet from the Red Sea, are therefore just considered as PLI. The type locality, broad geographic distribution (comprising all historical records) and native range are given for each NIS. To identify species that have not been positively recorded for some time, records of all Mediterranean NSH were entered into a relational database whose entries can be arranged to list the collection localities of each taxon in chronological order. Taxonomic records (i.e. records of each taxon, in any kind of report) are reported on a time scale from the original description to the last citation in the literature. Mediterranean species were ranked according to the date of their last record in the basin: species not recorded for 41 years or more, species not recorded for 31–40 years, species not recorded for 21–30 years, species not recorded for 11–20 years, and species recorded in the last 10 years. Results How many species? Picard’s (1958) list of Mediterranean Antho- and Leptomedusae includes 191 species, Boero & Bouillon (1993) report 346 NSH species, and Bouillon et al. (2004) list 396 NSH taxa of 457 hydrozoan species (i.e. including the Siphonophora); this represents about 11% of the Marine Ecology 34 (Suppl. 1) (2013) 41–62 ª 2013 Blackwell Verlag GmbH Gravili, Di Camillo, Piraino, Boero Hydrozoan species richness in the Mediterranean Sea Table 1. Summary table of non-siphonophoran hydrozoan species of the Red Sea and neighbouring areas. Taxa Class Hydroidomedusae Subclass Anthomedusae Bougainvillia fulva Citations Locality Hartlaub (1909), Kramp (1968), Schmidt (1973) Eilat Bay, Red Sea, Gulf of Aqaba, Gulf of Aden Red Sea Bougainvillia muscoides Schmidt (1973) Bougainvillia muscus* Billard (1904) as Bougainvillia muscus, Billard (1926) as Bougainvillia ramosa muscus, Schmidt (1973) Schmidt (1973) Schmidt (1973) Schmidt (1973) Schmidt (1973) Schmidt (1972a, 1973) Schmidt (1973) Bougainvillia platygaster Köllikerina fasciculata* Köllikerina multicirrata Köllikerina octonemalis Thamnostoma eilatensis Pachycordyle conica Corydendrium parasiticum* Turritopsis dohrnii* Billard (1926, 1933) Cytaeis nassa Billard (1926) as Dendroclava dohrni, Schmidt (1973) as Turritopsis nutricula Vervoort (1967), Hirohito (1977) Cytaeis tetrastyla* Schmidt (1973) Hydractinia echinata* Hydractinia kaffaria Mergner & Wedler (1977) Schmidt (1972b) Hydractinia meteoris Schmidt (1973) as Podocoryne meteoris Podocoryne denhami? Podocorynoides minima* Allorathkea ankeli Distichopora violacea Stechow (1912) Schmidt (1973) as Podocoryne minima Schmidt (1972a) De Blainville (1834), Klunzinger (1879), Boschma (1959, 1968) Vanhöffen (1911) Vanhöffen (1911) Schmidt (1973) Calycopsis bigelowi Calycopsis chuni Heterotiara anonyma Eudendrium capillare* Eudendrium deciduum Eudendrium mucronatum Eudendrium ramosum Hirohito (1977) as Eudendrium tenellum Mergner & Wedler (1977) Billard (1926) as Eudendrium racemosum mucronatum Thornely (1908), Mergner & Wedler (1977), Mergner (1987) Marine Ecology 34 (Suppl. 1) (2013) 41–62 ª 2013 Blackwell Verlag GmbH Remarks Mediterranean Misidentifications of closely related species (see Schuchert 2007) Suez Canal, Red Sea, Gulf of Aden X Red Sea Red Sea, Gulf of Aden Red Sea Red Sea Eilat Bay, Red Sea Eilat Bay, Red Sea, Gulf of Aden Suez Canal X X X Suez Canal, Gulf of Aqaba, Red Sea Abiad Bay, Entedebir, Dahlak Archipelago, southern Red Sea, Eilat, Gulf of Aqaba Eilat Bay, Red Sea, Gulf of Aden Alexandria Gulf of Aqaba, Red Sea Eilat Bay, Red Sea, Gulf of Aden Gulf of Aden Red Sea, Gulf of Aden Eilat Bay, Red Sea Red Sea Gulf of Aden Gulf of Aden Eilat Bay, Gulf of Aqaba, Red Sea, Gulf of Aden Gulf of Aqaba X X X Doubtful status X X Around Perim, Gulf of Aden Suez Canal Khor Dongola, Suez Canal, Red Sea, around Perim, Gulf of Aden X 43 Hydrozoan species richness in the Mediterranean Sea Gravili, Di Camillo, Piraino, Boero Table 1. (Continued). Taxa Citations Locality Amphinema rugosum* Leuckartiara gardineri Leuckartiara octona* Merga violacea Schmidt Schmidt Schmidt Schmidt Pandeopsis ikarii? Proboscydactyla ornata* Protiara tropica Sphaerocoryne bedoti Zancleopsis gotoi Corymorpha annulata Corymorpha bigelowi Corymorpha forbesii* Schmidt (1973) as Pandeopsis scutigera Schmidt (1973) Corymorpha nutans* Dicodonium cornutum Schmidt (1973) as Steenstrupia nutans Haeckel (1879), Kramp (1968), Halim (1969) Eilat Bay, Red Sea Red Sea Red Sea Eilat Bay, Red Sea, Gulf of Aden Gulf of Aqaba, Red Sea Red Sea, Gulf of Aqaba, Gulf of Aden Gulf of Aqaba, Red Sea Around Perim Gulf of Aqaba, Red Sea Red Sea Red Sea Eilat Bay, Red Sea, Gulf of Aden Gulf of Aden Gulf of Suez, Red Sea Euphysilla piramidata Schmidt (1973) Euphysa aurata* Schmidt (1973) Pennaria disticha Thornely (1908) as Pennaria symmetrica, Billard (1926, 1933) as Pennaria disticha var. australis, Vervoort (1967) as Halocordyle disticha var. australis, Schmidt (1972b, 1973) as Halocordyle disticha var. australis, Hirohito (1977) as Halocordyle disticha, Mergner & Wedler (1977) as Halocordyle disticha var. australis, Mergner (1987) as Halocordyle disticha var. australis, Vervoort (1993) Schmidt (1973) Thornely (1908) as Ceratella crosslandi, Vervoort (1967) as Solanderia crosslandi and S. minima, Schmidt (1972b), Mergner & Wedler (1977) as as S. minima and S. secunda, Mergner (1987) as S. minima and S. secunda, Vervoort (1993) Schmidt (1972b) as Tubularia mesembryanthemum, Vervoort (1993) as Tubularia crocea Billard (1926) as Tubularia larynx, Schmidt (1972b) as Tubularia larynx Klunzinger (1879), Crossland (1941), Boschma (1968), Mergner (1987) Klunzinger (1879), Crossland (1941), Mergner (1987) Klunzinger (1879), Crossland (1941), Boschma (1968), Mergner (1987) Boschma (1968) as Millepora tenera Pennaria grandis Solanderia secunda Ectopleura crocea* Ectopleura larynx* Millepora dichotoma Millepora exaesa Millepora platyphylla Millepora tenella 44 (1973) (1973) (1973) (1973) Schmidt (1973) Mergner & Wedler (1977) Schmidt (1973) Schmidt (1973) as Euphysora annulata Schmidt (1973) as Euphysora bigelowi Schmidt (1973) as Vannuccia forbesii Eilat Bay, Gulf of Aqaba, Red Sea Eilat Bay, Red Sea, Gulf of Aden Gulf of Suez, Shab al Shubuk, Suakim, Umm Aabak, Dahlak Archipelago, southern Red Sea, Eilat, Gulf of Aqaba Remarks Mediterranean X X X X X X X X X Unrecognizable species (see Schuchert 2001) X X Gulf of Aden Port Sudan, Umm Aabak, Dahlak Archipelago, Djidda, Red Sea, Eilat, Gulf of Aqaba Eilat, Gulf of Aqaba, Red Sea X Suez Canal, Gulf of Aqaba, Red Sea Eilat, Gulf of Aqaba, Red Sea Red Sea X Red Sea, Eilat, Gulf of Aqaba Cundabilu, Dahlak Archipelago, southern Red Sea Marine Ecology 34 (Suppl. 1) (2013) 41–62 ª 2013 Blackwell Verlag GmbH Gravili, Di Camillo, Piraino, Boero Hydrozoan species richness in the Mediterranean Sea Table 1. (Continued). Taxa Citations Locality Porpita porpita Vervoort (1967) Velella velella Zanclea costata* Halim (1969) Vanhöffen (1911), Schmidt (1973) Landing Bay, Entedebir, Red Sea, Gulf of Aden Red Sea Red Sea Zanclea dubia Halocoryne orientalis Schmidt (1973) Hartlaub (1909) as Zanclea sp., Schmidt (1973) as Z. orientalis Eilat Bay, Red Sea Eilat Bay, Red Sea, Gulf of Aden Haeckel (1879) as Octocanna octonema, Schmidt (1973) as Aequorea aequorea Schmidt (1973) Schmidt (1973) Red Sea X Red Sea Eilat Bay, Red Sea, Gulf of Aqaba, Gulf of Aden Eilat Bay, Red Sea, Gulf of Aden Red Sea, Gulf of Aden Red Sea Aroun Perim X X Subclass Leptomedusae Aequorea forskalea* Aequorea australis Aequorea coerulescens Aequorea macrodactyla Aequorea parva Aequorea pensilis* Aglaophenia latecarinata* Cladocarpus alatus Cladocarpus dofleini Cladocarpus sewelli Gymnangium eximium Gymnangium eximium millardae n.var. Gymnangium gracilicaule Gymnangium hians var. balei Lytocarpia flexuosus Lytocarpus (?) hornelli Macrorhynchia balei Macrorhynchia meteor Schmidt (1973) Hartlaub (1909), Schmidt (1973) Halim (1969) Mergner & Wedler (1977) Rees & Vervoort (1987) Rees & Vervoort (1987) Rees & Vervoort (1987) Marktanner-Turneretscher (1890) as Halicornaria flabellata, Schmidt (1972b), Mergner & Wedler (1977), Mergner (1987), Rees & Vervoort (1987), Vervoort (1993), El Beshbeeshy (1995) El Beshbeeshy (1995) Gulf of Aden Gulf of Aden Gulf of Aden Gulf of Suez, Red Sea, Gulf of Aqaba, around Perim, Gulf of Aden Stechow (1912) as Halicornaria gracilicaulis, Jäderholm (1920) as Halicornaria gracilicaulis, Billard (1933) as Halicornaria gracilicaulis, as Vervoort (1967) as Halicornaria gracilicaulis, Mergner & Wedler (1977) as Gymnangium gracilicaulis Marktanner-Turneretscher (1890) as Aglaophenia balei, Mergner & Wedler (1977), Mergner (1987) Mergner & Wedler (1977) as Thecocarpus flexuosus var. flexuosus, El Beshbeeshy (1995) as Lytocarpia flexuosa flexuosa Thornely (1908) Mergner & Wedler (1977) as Lytocarpus balei El Beshbeeshy (1995) Gulf of Suez, Nocra, Cundabilu, Dahlak Archipelago, around Perim, Red Sea, Gulf of Aden Marine Ecology 34 (Suppl. 1) (2013) 41–62 ª 2013 Blackwell Verlag GmbH Remarks Mediterranean X Misidentifications based on polyp records only (see Schuchert 2010) X X Southern Red Sea Djidda, Red Sea, around Perim Southern Red Sea, Gulf of Aden Suez Bay Around Perim Doubtful status Southern Red Sea 45 Hydrozoan species richness in the Mediterranean Sea Gravili, Di Camillo, Piraino, Boero Table 1. (Continued). Taxa Citations Locality Suez Canal, Suakim Harbour, Gulf of Aqaba, Red Sea, around Perim, Gulf of Aden X Gulf of Aqaba, Eilat X Eilat Bay, Red Sea Red Sea Red Sea, Gulf of Aden X X Helgicirrha schulzei* Halecium beanii* Marktanner-Turneretscher (1890) as Lytocarpus philippinus, Thornely (1908) as Lytocarpus philippinus, Stechow (1919) as Lytocarpia philippina, Billard (1926, 1933) as Lytocarpus philippinus, Schmidt (1972b) as Lytocarpus philippinus, Mergner & Wedler (1977) as Lytocarpus philippinus, Mergner (1987) as Lytocarpus philippinus, Rees & Vervoort (1987) as Lytocarpus philippinus, Vervoort (1993) Mergner & Wedler (1977), Mergner (1987) Schmidt (1973) Schmidt (1973) Hartlaub (1909) as Irene pellucida, Kramp (1968), Schmidt (1973) Schmidt (1973) Schmidt (1973) Hartlaub (1909) as Octorchandra orientalis, Kramp (1968), Schmidt (1973) Schmidt (1973) Hartlaub (1909) as Eutimalphes modesta, Kramp (1968), Schmidt (1973) Hartlaub (1909) as Phialidium sp., Kramp (1968) Schmidt (1973) Billard (1933), Mergner & Wedler (1977) Halecium labiatum Billard (1933), Vervoort (1967) Halecium sessile* Antennella secundaria Billard (1933) Vervoort (1967), Mergner & Wedler (1977), El Beshbeeshy (1995) Halopteris alternata Thornely (1908) as Plumularia alternata Billard (1933) as Theocaulus campanula Billard (1904) as Plumularia catharina var. articulata, Stechow (1925) as Plumularia catharina Billard (1904) as Plumularia alternata, Thornely (1908) as Plumularia alternata Schmidt (1972b), Mergner & Wedler (1977) as H. glutinosa Mergner & Wedler (1977) as Hebella parasitica, Mergner (1987) as Hebella parasitica Macrorhynchia philippina Cuspidella humilis* Eirene kambara Eirene tenuis Eirene viridula* Eutima commensalis Eutima curva Eutima hartlaubi Eutima levuka Eutima modesta Eutonina scintillans* Halopteris campanula Halopteris catharina Halopteris diaphana* Halopteris platygonotheca Anthohebella parasitica* 46 Remarks Mediterranean Red Sea Red Sea Red Sea, Gulf of Aden Red Sea Red Sea, Gulf of Aden Gulf of Aden X Red Sea Gulf of Suez, Southern Red Sea, around Perim, Gulf of Aden Gulf of Suez, Umm Aabak, Dahlak Archipelago, southern Red Sea Gulf of Suez, Red Sea Landing Baym Entedebir, Dahlak Archipelago, southern Red Sea, around Perim, Gulf of Aden Khor Dongola X X Gulf of Suez Red Sea, Gulf of Aden Gulf of Aden, Khor Dongola, Red Sea Gulf of Aqaba, Red Sea, around Perim Around Perim, Djidda, Red Sea X X X X X Marine Ecology 34 (Suppl. 1) (2013) 41–62 ª 2013 Blackwell Verlag GmbH Gravili, Di Camillo, Piraino, Boero Hydrozoan species richness in the Mediterranean Sea Table 1. (Continued). Taxa Citations Locality Hebella dyssymmetra Billard (1933), Vervoort (1967) Hebella scandens Billard (1904) as Lafoea calcarata, Billard (1933) as Hebella calcarata, Vervoort (1967, 1993) Hebella venusta Mergner & Wedler (1977), Mergner (1987) Kirchenpaueria pinnata* Pycnotheca mirabilis Ventromma halecioides* Schmidt (1972b) Gulf of Suez, Nocra, Cundabilu, Dahlak Archipelago, southern Red Sea Gulf of Suez, Cundabilu, Dahlak Archipelago, Red Sea, Gulf of Aden Djidda, Red Sea, around Perim, Gulf of Aden Gulf of Aqaba, Red Sea Mergner & Wedler (1977) Thornely (1908) as Plumularia halecioides, Billard (1926) as Kirchenpaueria halecioides, Vervoort (1967) as P. halecioides, Vervoort (1993) Acryptolaria conferta* Filellum serratum* Zygophylax armata El Beshbeeshy (1995) Billard (1933), Rees & Vervoort (1987) Mergner & Wedler (1977) Zygophylax millardae El Beshbeeshy (1995) Laodicea fertilis Laodicea indica Schmidt (1973) Vanhöffen (1911) as Laodice maasi, Kramp (1968), Schmidt (1973) Billard (1933) as (?) Campanulina hincksii Schmidt (1973) Kramp (1968) Vanhöffen (1911) as Euchilota ventricularis Schmidt (1973) Schmidt (1973) Eucheilota Eucheilota Eucheilota Eucheilota maculata* menoni tropica ventricularis Lovenella assimilis Octophialucium indicum Mitrocomella polydiademata Nemertesia ramosa* Plumularia setacea* Plumularia strobilophora Plumularia wasini Abietinaria filicula Amphisbetia minima Diphasia digitalis Diphasia heurteli Billard (1926) as Cuspidella grandis Mergner & Wedler (1977) as Nemertesia ramosa var. plumularioides Thornely (1908), Billard (1933), Mergner & Wedler (1977), Mergner (1987) Billard (1933) as Plumularia strobilifera Mergner & Wedler (1977) El Beshbeeshy (1995) Thornely (1908) Mergner & Wedler (1977) Billard (1933) as Diphasia heurteli var. simplex Marine Ecology 34 (Suppl. 1) (2013) 41–62 ª 2013 Blackwell Verlag GmbH Around Perim Suez Canal, Gulf of Aqaba, Nocra, Dahlak Archipelago, southern Red Sea, Eilat, Gulf of Aqaba, Gulf of Aden Southern Red Sea Gulf of Suez, Gulf of Aden Around Perim, Hodeida (Red Sea) Southern Red Sea, Gulf of Aden Red Sea Red Sea, Gulf of Aden Gulf of Suez Red Sea Red Sea Red Sea Remarks Mediterranean X Doubtful status X X X X X X Red Sea Eilat Bay, Red Sea, Gulf of Aqaba Gulf of Suez Around Perim X Gulf of Suez, Khor Dongola, Djidda, Red Sea, around Perim Gulf of Suez X Around Perim Gulf of Aden Gulf of Suez Around Perim Gulf of Suez 47 Hydrozoan species richness in the Mediterranean Sea Gravili, Di Camillo, Piraino, Boero Table 1. (Continued). Taxa Citations Locality Diphasia mutulata Thornely (1908), Billard (1933), Mergner & Wedler (1977) Dynamena cornicina Billard (1926, 1933), Vervoort (1967), Schmidt (1972b), Mergner & Wedler (1977), Mergner (1987) Dynamena crisioides Marktanner-Turneretscher (1890) as Dynamena tubuliformis, Billard (1904) as Thuiaria tubuliformis, Thornely (1908) as Thuiaria tubuliformis, and as Synthecium maldivense, Billard (1926, 1933), Vervoort (1967) as Dynamena crisioides crisioides, Schmidt (1972b) as Dynamena crisioides crisioides, Hirohito (1977) Mergner & Wedler (1977), Mergner (1987) Mergner & Wedler (1977), El Beshbeeshy (1995) as Sertularella campanulata Billard (1933), Vervoort (1993), El Beshbeeshy (1995) Schmidt (1972b), Mergner & Wedler (1977), Mergner (1987), El Beshbeeshy (1995) Suez docks and Suez Bay, Djidda, Red Sea, around Perim Suez Canal, Nocra, Dahlak Archipelago, Red Sea, Eilat, Gulf of Aqaba, around Perim Gulf of Suez, Gulf of Aqaba, Landing Bay, Entedebir, Dahlak Archipelago, southern Red Sea, Gulf of Aden Dynamena quadridentata Calamphora campanulata Sertularella diaphana Sertularella mediterranea* Sertularella natalensis Sertularella polyzonias* Mergner & Wedler (1977) Sertularia distans* Billard (1933) as Sertularia distans var. gracilis Mergner & Wedler (1977) Mergner & Wedler (1977) Sertularia ligulata Sertularia trigonostoma Synthecium elegans Thyroscyphus fruticosus Campanularia denticulata Clytia ambigua Clytia arborescens Clytia hemisphaerica 48 Mergner & Wedler (1977), El Beshbeeshy (1995) Mergner & Wedler (1977), Mergner (1987), El Beshbeeshy (1995) Thornely (1908) as Campanularia juncea, Billard (1926) as Thyroscyphus vitiensis, Billard (1933), Vervoort (1967), Schmidt (1972b), Mergner & Wedler (1977), Mergner (1987), Vervoort (1993), El Beshbeeshy (1995) Remarks Mediterranean Djidda, Red Sea Southern Red Sea, around Perim, Gulf of Aden Gulf of Suez, Red Sea, Gulf of Aden Gulf of Aqaba, Eilat, Red Sea, around Perim, Gulf of Aden Nile Delta Southern Red Sea, around Perim, Gulf of Aden Gulf of Suez X X X Around Perim Around Perim Thornely (1908) Djidda, Red Sea, around Perim, Gulf of Aden Suez Canal, Gulf of Aqaba, Eilat, Khor Dongola, Umm Aabak, Nocra, Cundabilu, Dahlak Archipelago, Jebel Attair, Red Sea, around Perim Khor Shinab Schmidt (1973) as Phialidium ambiguum Billard (1933) Schmidt (1972b, 1973) as Phialidium hemisphaericum, Mergner & Wedler (1977) as Campanularia (Clytia) hemisphaerica Red Sea Suez Canal Gulf of Aqaba, Eilat Bay, Red Sea, around Perim X X Marine Ecology 34 (Suppl. 1) (2013) 41–62 ª 2013 Blackwell Verlag GmbH Gravili, Di Camillo, Piraino, Boero Hydrozoan species richness in the Mediterranean Sea Table 1. (Continued). Taxa Clytia latitheca Clytia linearis Clytia lomae Clytia malayense Clytia paulensis Gastroblasta timida Obelia bidentata Obelia dichotoma Obelia geniculata Obelia longissima ? Orthopyxis crenata Malagazzia carolinae Class Automedusa Narcomedusae Solmundella bitentaculata Cunina frugifera Cunina mucilaginosa Cunina octonaria Cunina peregrina Cunina tenella Pegantha aureola Pegantha clara Pegantha forskalii Pegantha laevis Pegantha martagon Pegantha triloba Solmaris flavescens Trachymedusae Geryonia proboscidalis Liriope tetraphylla Citations Locality Thornely (1908) as Campanularia denticulata, Mergner & Wedler (1977) as Campanularia (Clytia) latitheca, El Beshbeeshy (1995) Billard (1904) as Campanularia gravieri, Billard (1926) as Clytia (?) foxi, Billard (1933) as Laomedea gravieri, Vervoort (1967) as Campanularia (Clytia) gravieri, Schmidt (1972b) as Campanularia gravieri, Hirohito (1977), Mergner & Wedler (1977) as Campanularia (Clytia) gravieri, Mergner (1987) as Campanularia (Clytia) gravieri Kramp (1968) as Phialidium lomae Schmidt (1973) as Phialidium malayense Mergner & Wedler (1977) as Campanularia (Clytia) paulensis Keller (1883), Halim (1969) Thornely (1908) as Obelia bifurcata Thornely (1908) as Campanularia cheloniae, Billard (1926), Schmidt (1972b) as Laomedea (Obelia) dichotoma, Mergner & Wedler (1977) as Laomedea (Obelia) dichotoma, Mergner (1987) as Laomedea (Obelia) dichotoma Billard (1926) Billard (1904) Billard (1926) as Orthopyxis lennoxensis Schmidt (1973) as Phialucium carolinae Suez Canal, around Perim, Southern Red Sea Suez Canal Gulf of Aden Suez Canal Eilat Bay, Red Sea, Gulf of Aqaba X X X Schmidt (1973) Red Sea, Gulf of Aden X Schmidt (1973) Vanhöffen (1908) as Solmaris mucilaginosa Schmidt (1973) Schmidt (1973) Schmidt (1973) Haeckel (1879) as Solmoneta aureola, Halim (1969) Schmidt (1973) Haeckel (1879) as Polycolpa forskalii, Halim (1969) Schmidt (1973) Schmidt (1973) Red Sea, Gulf of Aden Gulf of Aden Gulf of Suez, Gulf of Tadjoura, Landing Bay, Entedebir, Nocra, Cundabilu, Dahlak Archipelago, Gulf of Aqaba, southern Red Sea, around Perim, Gulf of Aden X Red Sea Khor Shinab Khor Dongola, Red Sea, Suez Canal, Gulf of Aden, Gulf of Aqaba, Eilat Red Red Red Red Sea, Gulf of Aden Sea Sea, Gulf of Aden Sea Gulf of Aden Red Sea Schmidt (1973) Vanhöffen (1908) Schmidt (1973) Vanhöffen (1902), Hartlaub (1909) as Liriope rosacea, Halim (1969), Schmidt(1973) Gulf of Aqaba, Red Sea Eilat Bay, Red Sea, Gulf of Aqaba, Gulf of Aden Mediterranean X Red Sea Red Sea Around Perim Red Sea, Gulf of Aden Eilat Bay, Red Sea, Gulf of Aden Red Sea, Gulf of Aden Gulf of Aden Marine Ecology 34 (Suppl. 1) (2013) 41–62 ª 2013 Blackwell Verlag GmbH Remarks X X Doubtful status X Doubtful status Doubtful status X X X X 49 Hydrozoan species richness in the Mediterranean Sea Gravili, Di Camillo, Piraino, Boero Table 1. (Continued). Taxa Petasus eucope Aglaura hemistoma Amphogona pusilla Colobonema sericeum Pantachogon haeckeli Rhopalonema funerarium Rhopalonema velatum Sminthea eurygaster Citations Locality Remarks Haeckel (1879) as Petasata eucope Vanhöffen (1902), Furnestin (1958), Halim (1969), Schmidt (1973), Khalil & El-Rakman (1997) Hartlaub (1909) Schmidt (1973) Vanhöffen (1902) as Pantachogon rubrum Halim (1969), Schmidt (1973) Halim (1969), Schmidt (1973) Schmidt (1973) Red Sea Eilat Bay, Red Sea, Gulf of Aqaba, Gulf of Aden Gulf of Aden Red Sea, Gulf of Aden Red Sea, Gulf of Aden Red Sea, Gulf of Aden Red Sea, Gulf of Aden Red Sea Doubtful status Mediterranean X X X X X X Sources for distribution: Billard (1904, 1926, 1933); Boschma (1959, 1968); Crossland (1941); De Blainville (1834); El Beshbeeshy (1995); Furnestin (1958); Haeckel (1879); Halim (1969); Hartlaub (1909); Hirohito (1977); Jäderholm (1920); Keller (1883); Khalil & El-Rakman (1997); Klunzinger (1879); Kramp (1968); Marktanner-Turneretscher (1890); Mergner (1977, 1987); Mergner & Wedler (1977); Rees & Vervoort (1987); Schmidt (1972a,b, 1973); Stechow (1912, 1919, 1925); Thornely (1908); Vanhöffen (1902, 1908, 1911); Vervoort (1967, 1993). X, presence in Mediterranean. *species first recorded from the Mediterranean Sea, and even from boreal seas, and only later recorded in the Red Sea. 3702 nominal known species of the superclass Hydrozoa globally (Bouillon et al. 2006). New records of Mediterranean hydrozoans are continually improving our knowledge of the fauna (Schuchert 2001, 2006, 2007, 2008a,b, 2009, 2010; Galea 2007; Gravili et al. 2007, 2008; Morri et al. 2009), resulting in the most current estimate of 400 NSH species (Fig. 1). Most of these (68%) occur in the Atlantic Ocean and are subdivided into Mediterranean Atlantic (14%), tropical Atlantic (10%), boreal (12%), and circumtropical (21%), cosmopolitan (11%); 20% are endemic to the Mediterranean, 8% are of Indo-Pacific origin, and 4% are non-classifiable. How many nonindigenous species? Recent additions to regional faunal lists (e.g. Diphasia digitalis, Dynamena quadridentata, Sertularia thecocarpa, Campanularia morgansi) are almost invariably represented by nonindigenous species (NIS), whereas description of Fig. 1. Periods of last records in the taxonomic literature of all the non-siphonophoran hydrozoan Mediterranean species. 50 new species is rarer. Sixty-nine nonindigenous species (NIS) of NSH have been recorded in the Mediterranean (Fig. 2; Table 2; Appendix 1): 30 are casual, 20 established, four invasive, and 15 questionable. No cryptogenic species are recognized. Nonindigenous taxa include Hydroidomedusae (Anthomedusae: 24 species; Leptomedusae: 34 species; Laingiomedusae: two species; Limnomedusae: three species), and Automedusae (Trachymedusae: six species) (Table 2). NIS were grouped into three main categories according to their distribution: recorded throughout the basin (27), recorded in the Levantine basin (27), recorded in the Strait of Gibraltar and/or Alboran Sea (15) (Table 2, Fig. 2). At the sub-regional scale, more NIS are found in the eastern basin (42 species), with a peak of 38 in the Levant Sea, followed by the Gulf of Lions and the Ligurian Sea (21 species), the Ionian and Adriatic Seas (19 species), the Strait of Gibraltar and nearby areas (22 species), the Tyrrhenian Sea (nine species), Algeria and North Tunisia (three species). Some NIS have been recorded in more than one of these areas. Fifteen NIS listed in Table 2 are considered as ‘questionable’, mainly due to uncertainties about their taxonomic status and distributional patterns. Twenty NIS are established, with self-maintaining and self-perpetuating populations unsupported by and independent of humans in at least one sector of the Mediterranean Sea (See Appendix 1), four (6%) are invasive species having overcome biotic and abiotic barriers to develop large populations in the Mediterranean waters, and for 30 species (43%) casual records have been reported from one or a few locations only. Modes of introduction are unknown for many NIS (36%). Nine per cent have been introduced by ships. Other probable ways of introduction are the Marine Ecology 34 (Suppl. 1) (2013) 41–62 ª 2013 Blackwell Verlag GmbH Gravili, Di Camillo, Piraino, Boero Hydrozoan species richness in the Mediterranean Sea F 3% 4/136 8% G E 11% 7/83 21/198 H 5% 4% D8/182 4/81 C 4% J 9/208 4% 2/45 A 16% B 6% 3/52 22/134 * * 0% M0/52 I 4% 4/109 K 4% 2/48 L 28% 38/137 Fig. 2. Distribution of nonindigenous species of Hydrozoans (excluding Siphonophora) in each biogeographic sector within the Mediterranean Sea. (A) Alborán Sea; (B) Algeria and North Tunisia coasts; (C) Southern Tyrrhenian Sea; (D) Balearic Sea to Sardinia Sea; (E) Gulf of Lions and Ligurian Sea; (F) Northern Adriatic Sea; (G) Central Adriatic Sea; (H) Southern Adriatic Sea; (I) Ionian Sea; (J) Northern Aegean Sea; (K) Southern Aegean Sea; (L) Levant Sea; (M) Strait of Messina (marked by asterisk). Biogeographic sectors according to Bianchi (2007). For each sector, nonindigenous species (NIS) percentage and NIS number/non-syphonophoran Hydrozoa (NSH) total number are shown. expansion of natural ranges through the Strait of Gibraltar (22%) and the Suez Canal (19% of Mediterranean NIS as Possible Lessepsian immigrants, and about 14% as Lessepsian immigrants). As an example of the expansion of a NSH-NIS in the Mediterranean we chose Clytia linearis (Thornely, 1900), a successful Lessepsian immigrant that, in the last decades, has been recorded to be abundant at almost every Mediterranean location surveyed, occurring from shallow waters to shaded rocky bottoms (Fig. 3). This species probably colonised the Mediterranean from the Suez Canal (the first Mediterranean record is by Billard in 1926), and then, from Gibraltar, it expanded its distribution to the Atlantic coast of Spain (Altuna Prados 1995; Boero et al. 2005). The Mediterranean–Red Sea relationship Red Sea species that have also been found in the Mediterranean are listed in Table 1. Many of them are Lessepsian immigrants to the Mediterranean, but many others (marked by an asterisk in Table 1) were first recorded from the Mediterranean Sea, and even from boreal seas, and were only later recorded in the Red Sea. Thirty species are casual, having seldom been recorded, possibly because they are not established in the basin, but their Marine Ecology 34 (Suppl. 1) (2013) 41–62 ª 2013 Blackwell Verlag GmbH inconspicuousness might have prevented proper records of their presence. How many species could we possibly have lost? Fewer than 160 species of NSH have been positively recorded in the last 10 years. Conversely, there are no positive records of 67 species in the last 40 years or longer. Four decades of absence might be long enough to suggest the possibility that regional extinction (or at least range contraction) may be considered. This period precedes the first signs of the impact of global warming on Mediterranean biota. However, species might have remained unrecorded simply because their descriptions were not sufficient to allow subsequent positive identification, or due to scant expertise on the taxon, with little sampling efforts. As an example, Tricyclusa singularis Schulze 1876, is case of a species that has been ‘absent’ for a very long time. It is a species of boreal affinity, after its original description from Trieste (the northernmost part of the Northern Adriatic and the coldest part of the Mediterranean); it has never been recorded again from the Mediterranean Sea (Fig. 4). Instead, it was recorded several times from Roscoff (Atlantic coast of France) (e.g. Bedot 1911; Teissier 1965), resulting in a disjunct distribution. The disappearance of T. singularis represents not 51 Hydrozoan species richness in the Mediterranean Sea Gravili, Di Camillo, Piraino, Boero Table 2. List of non-siphonophoran Hydrozoa NIS. Subclass NIS in the Mediterranean Sea, not restricted to Levantine or Alboran Seas Anthomedusae Garveia franciscana (I), Trichydra pudica (Q), Calycopsis simplex (C), Eudendrium carneum (E), Eudendrium merulum (E), Amphinema rubrum (C), Octotiara russelli (Q), Moerisia inkermanica (C), Corymorpha annulata (Q), Coryne eximia (E) Leptomedusae Gymnangium montagui (E), Cirrholovenia tetranema (E), Eutima mira (E), Filellum serratum (E), Eucheilota paradoxica (E), Campalecium medusiferum (E), Monotheca pulchella (E), Diphasia rosacea (C), Clytia hummelincki (I), Clytia linearis (I), Clytia mccrady (E) Laingiomedusae Limnomedusae Trachymedusae Gonionemus vertens (E), Scolionema suvaense (Q) Haliscera bigelowi (E), Haliscera racovitzae (C), Amphogona pusilla (C), Arctapodema australis (C) NIS present only in the Levantine waters Bougainvillia aurantiaca (Q), Bougainvillia niobe (Q), Nubiella mitra (Q), Cytaeis vulgaris (Q), Paracytaeis octona (C), Halitiara inflexa (C), Moerisia carine (E), Sphaerocoryne bedoti (C), Euphysa flammea (Q), Corymorpha bigelowi (Q), Ectopleura minerva (Q), Plotocnide borealis (Q) Aequorea conica (C), Macrorhynchia philippina (I), Laodicea fijiana (Q), Eucheilota ventricularis (E), Diphasia digitalis (C), Dynamena quadridentata (E), Sertularia thecocarpa (E), Sertularia marginata (E), Campanularia morgansi (C), Obelia fimbriata (C) NIS present in the Strait of Gibraltar, in the Alborán Sea or near areas (absent in the rest of the Mediterranean Sea) Russellia mirabilis (C), Tubularia ceratogyne (Q) Aglaophenia parvula (C), Cladocarpus multiseptatus (C), Cladocarpus pectiniferus (C), Cladocarpus sinuosus (C), Halecium sibogae (C), Pseudoplumaria marocana (C), Kirchenpaueria bonnevieae (C), Cryptolaria pectinata (C), Diphasia attenuata (C), Diphasia delagei (C), Diphasia margareta (C), Hydrallmania falcata (C), Sertularella robusta (Q) Fabienna oligonema (C), Kantiella enigmatica (C) Olindias singularis (E) Halitrephes maasi (C), Tetrorchis erythrogaster (E) Establishment success (C = Casual; E = Established; I = Invasive; Q = Questionable). Discussion Fig. 3. The distribution map of the species Clytia linearis. only the putative local extinction of a species but also the disappearance from the Mediterranean of the family Tricyclusidae that comprises just this single species and genus (Boero & Bonsdorff 2007). 52 Changes in the size and composition of regional species pools can provide important insights about environmental change. In general, species lists for an area are updated by adding new species as soon as they enter the taxonomic record (i.e. records of taxa from any source). These updates disregard the species that were in the previous lists and that have not been recorded anymore from the area for a reasonably long period, for instance more than 40 years, before the appreciation of the impacts of global change, as proposed here. An alternative approach, including putative loss of species, may indicate endangered or even extinct species, but these are usually charismatic and popular species, whereas inconspicuous taxa (the bulk of biodiversity) are usually disregarded. The Mediterranean Sea today represents a model basin for all oceans, being subjected to a period of temperature increase that is radically changing its biota (Bianchi 2007; Boero & Bonsdorff 2007; Lejeusne et al. 2010). Our analysis of records over time can provide ‘early warning Marine Ecology 34 (Suppl. 1) (2013) 41–62 ª 2013 Blackwell Verlag GmbH Gravili, Di Camillo, Piraino, Boero Fig. 4. The distribution map of the species Tricyclusa singularis. signals’ of species that may face higher probabilities of local or regional extinction. The increased number of tropical species recently recorded from the Mediterranean Sea has been called tropicalisation and also occurs in other taxa (Bianchi 2007). Twenty-eight of the 45 species with tropical affinity have been cited first from the Levant basin and most of them are of Indo-Pacific biogeographic affinity. The rest (17) are tropical Atlantic species. All the Indo-Pacific species have been usually labelled as Lessepsian immigrants and, thus, as having entered through the Suez Canal by the expansion of their natural range. This assumption, however, is correct only if the species in question have been recorded from the vicinities of the Suez Canal or, at least, from the Red Sea. Only 11 of 34 NIS species of Indo-Pacific origin have been recorded from the Red Sea and only these, thus, can be considered Lessepsian immigrants with some confidence. Thirty-eight species recorded from the Red Sea are typically Mediterranean (Table 1). They might represent misidentifications, but might also be anti-Lessepsian migrants or cryptogenic hydrozoan NIS for the Mediterranean Sea. Twenty-four of 69 NSH-NIS are of Atlantic affinity; eight are of these are restricted to the Gibraltar region or, at least, to the Alboran Sea and 16 expanded further into the Western Mediterranean Basin (see Appendix 1). These species might not even be NIS, having been present, albeit unnoticed, at these locations for a long time. These species might be removed from the list but, as literature reports are very scant for this part of the Mediterranean Sea, their status remains a matter of pure speculation. The number of NIS (69) matches closely the number of species that have not been recorded for more than 40 years (67). If the latter are removed from the species pool, introduction of new species would not result in a Marine Ecology 34 (Suppl. 1) (2013) 41–62 ª 2013 Blackwell Verlag GmbH Hydrozoan species richness in the Mediterranean Sea net increase. This is also suggested by data about a hydroid fauna that has been studied over the long term by Puce et al. (2009): the number of species tends to remain stable but the composition of the species assemblage changes. In spite of wide speculation about the impact of global warming on marine biodiversity, the work by Puce et al. (2009) is cited as the only report on the effects of global warming on populations of marine invertebrates in a recent review on this topic (Burrows et al. 2011). The cumulative species list thus shows an increase in biodiversity but this may not correspond to the number of species actually present at any given time. Our data suggest that the regional species pools tend to remain stable, and that the tropical NIS colonising the Mediterranean Sea are probably filling the gaps of species that are becoming rarer than before (thus not being recorded) or are even locally extinct. It is debatable whether lack of records is due to scant sampling effort (which, however, has led to recording of the NIS), or to impact of either abiotic (i.e. rising temperatures) or biotic (i.e. competition or predation) factors, or of a blend of the three possible causes. The processes of species extinction operate at different paces and involve different mechanisms at different spatial scales (Carlton et al. 1999). Red lists of endangered species almost invariably deal with charismatic species (a negligible minority) and disregard the bulk of marine biodiversity, i.e. inconspicuous species. We propose here the lack of records of a species for several decades as an operational tool to recognize putative extinctions. Obviously, the fact that a species is unrecorded from a given area does not mean that it is extinct in that area. Decades of absence of records, however, might allow one to raise hypotheses of putative extinctions that need to be tested with focussed samplings, increasing the bearing of biodiversity estimates in terms of species pools. The Hydrozoa are well studied along the northern coast of the Western Mediterranean Sea and the Adriatic Sea, but records are scant for the rest of the basin. Hence, the present figures might not accurately reflect biodiversity for the entire Mediterranean. It is probable that more hydrozoan invaders will arrive from tropical regions, as the Mediterranean basin is going through a period of tropicalisation (Bianchi 2007). Moreover, the species with the ability to become dormant under adverse conditions will be favoured (Boero 2002), as well as those with the ability to reverse their life cycle, surviving long journeys in ballast water (Miglietta & Lessios 2009); such ontogeny reversal is more widespread across cnidarians than previously thought (Piraino et al. 2004). The origins of Mediterranean hydrozoan NIS have not been investigated with molecular tools so far. Molecular approaches will, hopefully, improve our understanding of 53 Hydrozoan species richness in the Mediterranean Sea the origin of NIS and their modes of dispersal (e.g. Miglietta & Lessios 2009). The number of NIS in the Mediterranean Sea is probably underestimated. Especially for the Hydrozoa, the key areas for species introductions (i.e. the eastern basin and the Gibraltar Strait) are still understudied. It is probable that, at least for shallow waters, the additions to the Mediterranean hydrozoan fauna will mostly consist of NIS, as demonstrated for fish assemblages of the Levantine shallow marine ecosystems (Goren & Galil 2005). The results shown here suggest that species lists are dynamic, requiring continual updating that considers both additions of introduced species and putative subtractions of species with historical but not contemporary records. Without these subtractions, the species lists will never show possible biodiversity crises at the level of species pools, as biodiversity is always on the rise due to the arrival of NIS. Acknowledgements Work supported by Ministero dell’Università e della Ricerca Scientifica e Tecnologica (COFIN, PRIN and FIRB projects) and Ministry of Environment and Protection of Land and Sea (Italy-Israel Cooperation, R & D. Proposal 2007), by the CONISMA-CMCC project ‘The impacts of biological invasions and climate change on the biodiversity of the Mediterranean Sea’ and by the European Commission Seventh Framework Programme (FP7) projects ‘Vectors of Change in Oceans and Seas Marine Life, Impact on Economic Sectors’ (VECTORS), ‘Towards coast to coast networks of marine protected areas (from the shore to the high and deep sea), coupled with seabased wind energy potential’ (COCONET), and ‘Policyoriented marine Environmental Research in the Southern European Seas’ (PERSEUS), and by the Igeam SrlMATTM project ‘Sistema Ambiente 2010’. The publication of this paper is supported by CONISMA, the Italian National Interuniversity Consortium for Marine Sciences and the Flagship project RITMARE. Conflicts of Interest None of the authors have any potential conflicts of interest. References Altuna Prados A. 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Patterns of frequency in main Mediterranean sectors (sensu Zenetos et al. 2010) ExtraMediterranean distribution Papua New Guinea Indo-Pacific Bougainvillia niobe Mayer, 1894 Bahamas, Atlantic Ocean Atlantic Garveia franciscana (Torrey, 1902) Nubiella mitra Bouillon, 1980 Cytaeis vulgaris Agassiz & Mayer, 1899 San Francisco Bay, NE Pacific Papua New Guinea Circumtropical Indo-Pacific Paracytaeis octona Bouillon, 1978 Fiji Islands, South Pacific Ocean Seychelles, Indian Ocean Trichydra pudica Wright, 1857 Scotland, NE Atlantic Atlantic, Indo-Pacific Calycopsis simplex Kramp & Damas, 1925 Eudendrium carneum Clarke, 1882 Norway Atlantic Virginia, USA (Atlantic Ocean) Circumtropical Medes Isles: 1983 (Gili 1986) Eudendrium merulum Watson, 1985 SW Pacific (Australia) Circumtropical Amphinema rubrum (Kramp, 1957) Antarctic (South Orkney Islands) SW Pacific (Australia) Antarctic (Atlantic section) Indo-Pacific Portofino (Ligurian Sea, Italy): 1984 (Bavestrello & Piraino 1991) Villefranche-sur-Mer: 1963 (Goy 1973) Halitiara inflexa Bouillon, 1980 Papua New Guinea Indo-Pacific Heterotentacula mirabilis (Kramp, 1957) Antarctic Moerisia carine Bouillon, 1978 Papua New Guinea Antarctic, Atlantic (West Indies) Indo-Pacific Taxa Class Hydroidomedusae Subclass Anthomedusae Bougainvillia aurantiaca Bouillon, 1980 Marine Ecology 34 (Suppl. 1) (2013) 41–62 ª 2013 Blackwell Verlag GmbH Octotiara russelli Kramp, 1953 Indo-Pacific Indo-Pacific Western Mediterranean Central Mediterranean including Ionian Sea Adriatic Sea Eastern Mediterranean 1st Mediterranean record Distribution in Mediterranean Way of introduction Lebanon: survey from 1969 to 1989 (Goy et al. 1991) Lebanon (Goy et al. 1988) as Bougainvillia platygaster Venice lagoon (Italy): 1978 (Morri 1979) Lebanon (Goy et al. 1990) Lebanon (Goy et al. 1990) Leb PLI Questionable (see Schuchert 2007) Leb U Questionable (see Schuchert 2007) Adr, MedI S Leb PLI Leb U Questionable (see Schuchert 2007) Questionable Lebanon: survey from 1970 to 1982 (Lakkis & Zeidane 1985) Croatia (Adriatic Sea): collected in 1973– 1974 (Schmidt & Benovic 1979) Villefranche-sur-Mer: 1966 (Goy 1973) Leb PLI Casual Cro, Leb U Fr ENR Casual MedI, Tyrr, Lig, Fr, Cro, Lev, Leb Lig, Tyrr, Cro, Chaf, Fr, Ion, Lev LI Established S Established Fr, BlIs ENR Casual Fr U Questionable (see Schuchert 2007) Leb PLI Alb S Leb PLI Bay of Villefranche-surMer: 1954 (Goy 1973) as Octotiara violacea Lebanon: survey from 1969 to 1989 (Goy et al. 1991) Alborán Sea: 1997 (Pagès et al. 1999) Lebanon: survey from 1970 to 1982 (Lakkis & Zeidane1985) Invasive Red Sea and neighbouring areas Invasive Established Questionable Questionable (see Schuchert 2009) Established Established Established Established Casual Casual Established + Gravili, Di Camillo, Piraino, Boero Type locality and original description Hydrozoan species richness in the Mediterranean Sea 58 Appendix 1 Patterns of frequency in main Mediterranean sectors (sensu Zenetos et al. 2010) Type locality and original description ExtraMediterranean distribution Moerisia inkermanica PaltschikowaOstroumova, 1925 Sphaerocoryne bedoti Pictet, 1893 Coryne eximia Allman, 1859 Black Sea Atlantic, IndoPacific Malay Archipelago Atlantic, IndoPacific Atlantic and Pacific Oceans Corymorpha annulata (Kramp, 1928) Sunda Strait, IndoPacific Indo-Pacific Corymorpha bigelowi (Maas, 1905) Malay Archipelago and Australia, W Pacific Bear Island (Norway) Indo-Pacific Taxa Euphysa flammea (Hartlaub, 1902) British Isles Ectopleura minerva Mayer, 1900 Tortugas, Florida (Atlantic Ocean) Plotocnide borealis Wagner, 1885 White Sea Arctic circumpolar, Atlantic, IndoPacific Indo-Pacific Arctic and Subarctic, circumpolar, Atlantic, IndoPacific Northeastern Atlantic Way of introduction Western Mediterranean Gulf of Pozzuoli: BrinckmannVoss (1987) as Ostroumovia inkermanica Lebanon: survey from 1969 to 1989 (Goy et al. 1991) Ligurian Sea (polyp): Puce et al. 2003; medusa: doubtful records in the Mediterranean Sea (see Schuchert 2001) Adriatic Sea, Croatia: 1973– 1974 (Schmidt & Benovic 1977) Lebanon (Goy et al. 1988) Tyrr, Lev U Casual Leb LI Fr?, Lig, Leb? U Cro, Adr LI Leb LI Questionable (see Schuchert 2010) Lebanon: survey from 1969 to 1989 (Goy et al. 1991) Leb ENR Questionable (see Schuchert 2010) Lebanon: collected between 1969 and 1989 (Goy et al. 1990) Lebanon (Goy et al. 1988) Leb, Lig U Leb U Strait of Gibraltar and nearby areas of Gulf of Cádiz (Medel & López-González 1996) SG ENR Established + + Questionable (see Schuchert 2010) Questionable (see Bouillon et al. 2004; Schuchert 2010) Indo-Pacific Lebanon (Goy et al. 1988) Leb PLI Eastern Atlantic, S Australia SG U Casual Cladocarpus multiseptatus (Bale, 1915) Great Australian Bight, Australia N Spain, Australia Alb U Casual Cladocarpus pectiniferus Allman, 1883 Porto Praya, St. Iago (Cape Verde Islands, Atlantic Ocean) Off Durban, South Africa Northeastern Atlantic, from Iceland to Morocco Eastern Atlantic (coasts of Africa), Indian Ocean (south Africa) Eastern Atlantic Caños de Meca (near Strait of Gibraltar): 1991 (Medel & Vervoort 1995) Alboràn Sea, off the coast of Morocco: 1984 (Ramil & Vervoort 1992) Straits of Gibraltar, Alboràn Sea, near the coast of Morocco (BALGIM): 1984 (Ramil & Vervoort 1992) Alboràn Sea near the coast of Morocco: 1984 (Ramil & Vervoort 1992) SG, Alb ENR Casual Alb U Casual Fr, SG ENR Established Questionable (see Schuchert 2010) Casual 59 Hydrozoan species richness in the Mediterranean Sea Banyuls-sur-Mer (Redier 1962) + Questionable (see Schuchert 2001) Questionable (see Schuchert 2010) Questionable (see Schuchert 2010) Red Sea and neighbouring areas Casual Casual Ceylon, Indian Ocean SW Pacific (Australia) Roscoff, eastern Atlantic Ocean Eastern Mediterranean Distribution in Mediterranean Pas-de-Calais (Boulonnais), Atlantic Ocean Gymnangium montagui (Billard, 1912) Adriatic Sea 1st Mediterranean record Tubularia ceratogyne Pérez, 1920 ? (probably conspecific with Tubularia indivisa, see Schuchert 2010) Subclass Leptomedusae Aequorea conica Browne, 1905 Aglaophenia parvula Bale, 1882 Cladocarpus sinuosus Vervoort, 1966 Central Mediterranean including Ionian Sea Gravili, Di Camillo, Piraino, Boero Marine Ecology 34 (Suppl. 1) (2013) 41–62 ª 2013 Blackwell Verlag GmbH Appendix 1 (Continued). Patterns of frequency in main Mediterranean sectors (sensu Zenetos et al. 2010) Type locality and original description ExtraMediterranean distribution Macrorhynchia philippina (Kirchenpauer, 1872) Manila, Philippines, W Pacific Cirrholovenia tetranema Kramp 1959 Eutima mira Mc Crady, 1859 (= E. orientalis) Halecium sibogae Billard, 1929 Indo-Pacific Tropical Atlantic, Pacific and Indian Oceans Atlantic, IndoPacific Atlantic, IndoPacific Indo-Pacific, Eastern Atlantic warm waters Pseudoplumaria marocana (Billard, 1930) Off the coast of Morocco (east Atlantic) Trondhjem Fiord, Norway and two localities between the Faroes and Shetland Islands, North Atlantic Off New Zealand Taxa Kirchenpaueria bonnevieae (Billard, 1906) Cryptolaria pectinata (Allman, 1888) South Carolina, USA Indonesia Tropical temperate Eastern Atlantic North Atlantic, Indo-Pacific, Indian Ocean Western Mediterranean Central Mediterranean including Ionian Sea Adriatic Sea SC, Leb, Trk, Lev LI Gulf of Naples (Italy): 1963 (Brinckmann 1965) Haifa Bay, coast of Israel: 1956 (Schmidt 1973) Straits of Gibraltar, Alboràn Sea, off the coast of Morocco: 1984 (Ramil & Vervoort 1992) San Garcı́a, Algeciras Bay, Strait of Gibraltar: 1991 (Medel & Vervoort 1995) Alborán Sea, close to the coast of Morocco (BALGIM): 1984 (Ramil & Vervoort 1992) Tyrr, Fr, Leb PLI Established Casual Isr, Leb, Egy, Tn SG, Chaf U Casual Established U Casual SG ENR Casual Alb ENR Casual Casual Naples, Secca della Gajola; Ischia, Nisida (Stechow 1923) S Established Indo-Pacific Lebanon: Goy et al. (1988) Tyrr, Egy, Trk, Sp, Fr, BlIs, SG, Alb, Chaf, Lev, Lig Leb Atlantic, Eastern Pacific Port-Vendres, Cap Abeille (Western Mediterranean Sea): Motz-Kossowska (1911) Near Dubrovnik (S Adriatic Sea): 1967 (Schmidt & Benovic 1977) Lebanon: between 1970 and 1982 (Lakkis & Zeidane 1985) Murcia (Spain): 1968 (Garcı́a Corrales et al. 1978 as Plumularia femina) Lig, Tyrr, Adr, Ion, Fr, Sp U Established Established Established Adr, Alb, Leb, Fr, Tn U Casual Casual Casual Leb LI Sp, BlIs U Eucheilota paradoxica Mayer, 1900 Tortugas, Florida Atlantic, IndoPacific Eucheilota ventricularis McCrady, 1959 South Carolina, USA Circumtropical Monotheca pulchella (Bale, 1882) Indo-Pacific Atlantic coasts of the Strait of Gibraltar, IndoPacific, Atlantic coast of Argentine Established U + Questionable Established Established Established + Gravili, Di Camillo, Piraino, Boero Marine Ecology 34 (Suppl. 1) (2013) 41–62 ª 2013 Blackwell Verlag GmbH U Fiji Islands (S Pacific Ocean) Long Beach (California), Pacific coast of North America + Suez (Stechow 1919) as Lytocarpia philippina SG Laodicea fijiana Agassiz & Mayer, 1899 Campalecium medusiferum Torrey, 1902 Invasive Way of introduction Strait of Gibraltar: 1984 (Ramil & Vervoort 1992) Near Havana, Cuba Red Sea and neighbouring areas Distribution in Mediterranean Deep waters of the Atlantic and Pacific Oceans Circum(sub)tropical Filellum serratum (Clarke, 1879) Eastern Mediterranean 1st Mediterranean record Hydrozoan species richness in the Mediterranean Sea 60 Appendix 1 (Continued). Patterns of frequency in main Mediterranean sectors (sensu Zenetos et al. 2010) Type locality and original description ExtraMediterranean distribution Diphasia attenuata (Hincks, 1866) British Isles, E Atlantic Ocean Diphasia delagei Billard, 1912 E Atlantic Ocean Mainly records from temperate and tropical eastern Atlantic, but also several records from the Pacific Temperate and tropical eastern Atlantic Diphasia digitalis (Busk, 1852) Prince of Wales Channel, Torres Strait, Australia N Atlantic Ocean Taxa Diphasia margareta (Hassall, 1841) Diphasia rosacea (Linnaeus, 1758) Brighton, Sussex (English Channel) Dynamena quadridentata (Ellis & Solander, 1786) African coast (more likely Atlantic Ocean) near Ascension Island Kent, English Channel Hydrallmania falcata (Linnaeus, 1758) Circumtropical Temperate and subtropical northeastern Atlantic Eastern and Western Atlantic Circumtropical Sertularella robusta Coughtrey, 1876 New Zealand Sertularia marginata (Kirchenpauer, 1864) Pacific Ocean Circumtropical Sertularia thecocarpa (Jarvis, 1922) Campanularia morgansi Millard, 1957 Clytia hummelincki (Leloup, 1935) Madagascar Indo-West Pacific False Bay, South Africa South Africa, Madagascar Circumtropical West Indies, Caribbean Sea (Atlantic Ocean) Distribution in Mediterranean Way of introduction Western Mediterranean Strait of Gibraltar (Isla de Tarifa, Punta Saudiño, Benzù, Punta Almina): 1984 (Medel Soteras et al. 1991) SG ENR Casual Only found at the Strait of Gibraltar (Tarifa, Spain): 1984 (Ramil & Vervoort 1992) Levant Sea, Hadera: 2004 (Morri et al. 2009) SG ENR Casual Lev LI Levante, Spain (Garcı́a Corrales et al. 1980) Sp, SG ENR Casual 1929 (collections of the RBINS – Leloup’s specimen; see Bouillon et al. 1995) Levant Sea, around Selaata: 1999 (Morri et al. 2009) Lig, SG ENR Casual Lev LI Strait of Gibraltar (the west side): 1984 (Ramil & Vervoort 1992) SG ENR Casual Levante, Spain: collected between 1968 and 1971 (Garcı́a Corrales et al. 1980) Syria Coast: collected between 1929 and 1930 (Billard 1931) Levant Sea, Jbail northward: 1999 (Morri et al. 2009) Israel coast: 2009 (De Vito et al. 2010) Copanello (Calabria, Italy): 1996 (Boero et al. 1997) Sp U Questionable Syr, Isr, Trk, Lev, Sp PLI Established Lev PLI Isr PLI Ion, Adr, BalIs, Tyrr, Lig S Adriatic Sea Eastern Mediterranean Red Sea and neighbouring areas Casual + Established + Established Established Casual Invasive Invasive Invasive 61 Hydrozoan species richness in the Mediterranean Sea Mainly North Atlantic (western and eastern), but also records from South Africa (probably doubtful) and from North Pacific Ocean, Arctic Seas (White, Kara and Barents Sea) Indo-Pacific, S Atlantic 1st Mediterranean record Central Mediterranean including Ionian Sea Gravili, Di Camillo, Piraino, Boero Marine Ecology 34 (Suppl. 1) (2013) 41–62 ª 2013 Blackwell Verlag GmbH Appendix 1 (Continued). Patterns of frequency in main Mediterranean sectors (sensu Zenetos et al. 2010) 1st Mediterranean record Distribution in Mediterranean Way of introduction Western Mediterranean Central Mediterranean including Ionian Sea Circumtropical Suez Canal (Billard 1926) as Clytia foxi LI Invasive Invasive Bahama Islands, Atlantic Ocean Scotland Circumtropical Villefranche-sur-mer (Bougis 1963) Lebanon: collected between 1969 and 1989 (Goy et al. 1991) SC, Egy, Fr, Lig, Tyrr, Sp, Trk, Alb, MedI, BalIs, Gr, Ion, Chaf, Tn, Adr, Ion, Lev Fr, Lig, Tyrr, Leb Leb ENR Established ENR Casual Gulf of Guinea (W Africa) Seychelles Islands, Indian Ocean Atlantic Lebanon (Goy et al.1988 as Pochella oligonema) Lebanon (Goy et al. 1988) Leb U Casual Leb PLI Casual Maldives, Indian Ocean Puget Sound, Pacific coast of North America Fiji Islands, S Pacific Indo-Pacific Egyptian Mediterranean Sea: 1984 (Zakaria 2004) Trieste (Joseph 1918) as Gonionemus vindobonensis Egy PLI Adr, Lig, Fr, Tyrr S Established Indo-Pacific Villefranche-sur-Mer: 1950 (Picard 1951) Fr, Lig, Tyrr U Established E tropical Pacific Atlantic, IndoPacific, Arctic Adr, Sp, BlIs U Established Haliscera racovitzae (Maas, 1906) Bellingshausen Sea, Antarctic Fr U Casual Halitrephes maasi Bigelow, 1909 Amphogona pusilla Hartlaub 1909 Arctapodema australis (Vanhöffen, 1912) Tetrorchis erythrogaster Bigelow, 1909 Off coast of Peru Atlantic, IndoPacific, and in the Antarctic and Sub-Antarctic Atlantic, IndoPacific, Antarctic IndoPacific Antarctic, IndoPacific Indo-Pacific, Atlantic Dubrovnik (S Adriatic Sea): 1965 (Schmidt & Benovic 1977) Planier canyon (NW Mediterranean): 1994 (Gili et al. 1998) Lebanon (Goy et al. 1988) Leb PLI Villefranche-sur-Mer (Ligurian Sea): 1964 (Goy 1973) Dubrovnik (S Adriatic Sea) (Schmidt & Benovic 1977) Lebanon: survey from 1970 to 1982 (Lakkis & Zeidane 1985) Lig, Fr LI Casual Adr, SG, Fr U Casual Leb U Type locality and original description ExtraMediterranean distribution Clytia linearis (Thornely, 1900) New Britain (Papua New Guinea), Indo-Pacific Clytia mccrady (Brooks, 1888) Obelia fimbriata (Dalyell, 1848) Taxa Subclass Laingiomedusae Fabienna oligonema (Kramp, 1955) Kantiella enigmatica Bouillon, 1978 Subclass Limnomedusae Olindias singularis Browne, 1905 Gonionemus vertens A. Agassiz, 1862 Gulf of Aden, Arabian Sea Antarctic E tropical Pacific Indo-Pacific Circumboreal Eastern Mediterranean Red Sea and neighbouring areas Invasive Invasive + Established Established Established Established Casual + Established Established Taxa: Class, subclass, species. Distribution in the Mediterranean Sea: Adr = Adriatic Sea; Alb = Alborán Sea; BlIs = Balearic Islands; Chaf = Chafarinas Islands; Cro = Croatia; Egy = Egypt; Fr = Corsica and France; Gr = Greece; MedI = Medes Isles; Ion = Ionian Sea; Isr = Israel; Leb = Lebanon; Lev = Levant Sea; Lig = Ligurian Sea; SC = Suez Canal; Sp = Spain; SG = Strait of Gibraltar; Syr = Syria coast; Tn = Tunisia; Trk = Turkey; Tyrr = Tyrrhenian Sea. Way of introduction: ENR - Expansion Natural Range; LI = Lessepsian Immigrant; PLI = Possible Lessepsian Immigrant; S = Shipping; U = unknown. Red Sea and neighbouring areas: + (present), (absent). See text for the sources for the Mediterranean distribution, and Table 1 for the sources for the Red Sea and neighbouring areas. Gravili, Di Camillo, Piraino, Boero Marine Ecology 34 (Suppl. 1) (2013) 41–62 ª 2013 Blackwell Verlag GmbH Scolionema suvaense A. Agassiz & Mayer, 1899 Class Automedusa Subclass Trachymedusae Haliscera bigelowi Kramp, 1947 Atlantic and Pacific Oceans Adriatic Sea Hydrozoan species richness in the Mediterranean Sea 62 Appendix 1 (Continued).