Marine Biology (1999) 135: 729±739 Ó Springer-Verlag 1999 C. Morri á C. N. Bianchi á S. Cocito á A. Peirano A. M. De Biase á S. Aliani á M. Pansini á M. Boyer F. Ferdeghini á M. Pestarino á P. Dando Biodiversity of marine sessile epifauna at an Aegean island subject to hydrothermal activity: Milos, eastern Mediterranean Sea Received: 20 January 1999 / Accepted: 25 August 1999 Abstract Sessile macroepifauna was sampled at six rocky sites between 2 and 90 m depth with a number of di€erent methods involving both underwater photography and collection of specimens. A total of 212 species (or varieties) were identi®ed, belonging to seven higher taxa: poriferans (24 species), cnidarians (32), molluscs (8), serpuloidean polychaetes (33), bryozoans (90), brachiopods (4) and ascidians (21). The combined use of a varied array of sampling methods was e€ective in obtaining a rich faunal inventory. Deep and o€shore sites tended to be richer in species than shallow and inshore sites. In all cases species richness was higher at sites closest to hydrothermal vents on the sea ¯oor. Although there are no comparable inventories of marine sessile epifauna in the Aegean, the high number of species found, with a relatively low sampling e€ort in a Communicated by R. Cattaneo-Vietti, Genova C. Morri (&) á M. Pansini DipTeRis (Zoologia), UniversitaÁ di Genova, via Balbi 5, I-16126 Genova, Italy C.N. Bianchi á S. Cocito á A. Peirano á F. Ferdeghini Marine Environment Research Centre, ENEA S. Teresa, P.O. Box 316, I-19100 La Spezia, Italy A.M. De Biase Centro Interuniversitario di Biologia Marina, piazzale Mascagni 1, I-57127 Livorno, Italy S. Aliani Istituto per lo studio dell'Oceanogra®a Fisica, CNR, Forte di Santa Teresa, I-19032 Pozzuolo di Lerici, La Spezia, Italy M. Boyer Indo-Paci®c Divers, P.O. Box 1014, Manado 95010, North Sulawesi, Indonesia M. Pestarino DiBiSAA (Sezione di Neuroendocrinologia e Biologia dello Sviluppo), UniversitaÁ di Genova, viale Benedetto XV 5, I-16132 Genova, Italy P. Dando School of Ocean Sciences, University of Wales, Bangor, Menai Bridge, Anglesey LL59 5EY, United Kingdom restricted area, indicates that the marine biodiversity of this sea is not as low as traditionally believed. Introduction Thanks to a tradition of study dating back at least to Renaissance time (®fteenth and sixteenth centuries), the marine ¯ora and fauna of the Mediterranean are among the best known in the world (Bianchi et al. 1995; Bianchi 1996). The data bank Medifaune (Fredj et al. 1988, 1992) has been collecting data over many years. The recent series of check-lists on Italian fauna (Ru€o 1996) comprises several volumes on marine taxa. Because of its central geographical position and extensive and varied coastline, Italy is likely to harbour the great majority of the marine species of the Mediterranean. Most of what we know about the marine fauna of the Mediterranean comes from studies done in the western basin and the Adriatic, while our knowledge of the fauna of the Aegean Sea is comparatively scarce (Eleftheriou 1992; Eleftheriou and Smith 1993). Apart from early investigation by Aristotle (Briggs 1974), modern research on the marine fauna of the Aegean began with Forbes (1844). In more recent times, information on fauna distribution has been collected by the Italians in the Dodecanese area (Issel 1928; Tortonese 1947; Bianchi and Morri 1983a, b); by the cruises of the French vessel ``Calypso'' in the whole Aegean between 1955 and 1964 (PeÂreÁs and Picard 1958; see also Zibrowius 1979 for a compendium and bibliography); by the cruises of the Russian vessel ``Academician Kowalevsky'' in the NE Aegean in 1958 to 1960 (Kisseleva 1983); by two British expeditions to Chios (Jones et al. 1968); by a Swiss expedition to eastern Crete (Hottinger 1974); and by a long-term project started in the 1970s by the University of Thessaloniki in the North Aegean Sea (Matsakis 1975; Koukouras 1979). Twenty years ago, Bacescu (1979) observed that the knowledge of the marine biodiversity of Greece was extremely poor, especially in relation to the cultural and 730 economic importance that the sea has for Greece. Thanks to extensive work by Greek universities, the National Centre for Marine Research (see Anastasakis 1988 for references) and the Institute of Marine Biology of Crete (Karakassis and Eleftheriou 1997), the situation has now greatly improved, and check-lists exist for several major marine taxa (e.g. Zenetos 1997 and references therein). Epifaunal taxa living on hard substrata remain the least known, although comprising many important and diverse groups. Ledoyer (1969) and Simboura et al. (1995) provided lists of mobile species, while sessile species have received even less attention. In this paper, we report on the sessile species collected on a variety of hard substrata o€ the south-east coast of the Island of Milos, one of the Cyclades. The sea ¯oor in the study area is rich in hydrothermal vents (Botz et al. 1995; Dando et al. 1995a; Fitzsimons et al. 1997). Previous studies on the marine biota living in this area took into account algae (Coppejans 1974; Diapoulis et al. 1994; Lazaridou 1995; Sartoni and De Biase 1999), infauna (Dando et al. 1995b; Thiermann et al. 1997; Fig. 1 Geographical setting of the study area and location of the six sampling sites: SR, E, CR, ST, VS and S. SR, CR and VS were close to hydrothermal vent systems on the sea ¯oor of the area Gamenick et al. 1998), meiofauna (Thiermann et al. 1994) and seagrass meadows (Aliani et al. 1998). Giaccone (1968) dredged algae and Zenetos et al. (1991) collected molluscs and other benthic macrofauna at a few, deeper stations o€ Milos. Materials and methods Sessile macroepifauna was sampled at various depths in six sites o€ the SE coast of Milos (Fig. 1). Site SR was located in shallow water (about 2 to 12 m) inside Palaeochori Bay. Site E corresponds to infralittoral (7 to 13 m depth) rocks at Spathi Point, Sites ST (9 to 31 m depth) and CR (25 to 32 m depth) to rocky shoals. Site VS was situated on rocky and/or biogenic banks, mostly at 41 to 44 m depth (but a few samples from 50 and 90 m were also included). Site S was at two o€shore rocks called Vrakoi Ktenia, at 15 to 41 m depth. Although all sites were located in a hydrothermally active area, SR, CR and VS were closest to the actual vents, and continuous emission of ¯uid was observed there during sampling. Samples were taken in June 1996 (plus a few additions in September 1996 and June 1997) with a number of di€erent methods to enhance the species inventory. Specimens were collected by snor- 731 Table 1 List of sessile macroepifaunal taxa found at the six sampling sites (SR, E, ST, CR, S and VS: see Fig. 1) with di€erent methods: SCUBA diving (D), fouling (F), indirect sampling gears (G), under water photographs (P), snorkelling (S). Asterisks mark the sites closest to hydrothermal vents SR* E ST CR* S Porifera Aaptos aaptos (Schmidt) Agelas oroides (Schmidt) Axinella damicornis (Esper) Axinella verrucosa (Esper) Chondrosia reniformis Nardo Cliona copiosa SaraÁ Cliona rhodensis Rutzler & Bromley Cliona nigricans (Schmidt) Corticium candelabrum Schmidt Crambe crambe (Schmidt) Dysidea avara (Schmidt) Erylus euastrum (Schmidt) Geodia cydonium (Jameson) Hymeniacidon sp. Ircinia foetida (Schmidt) Ircinia oros (Schmidt) Ircinia variabilis (Schmidt) Leuconia sp. Mycale lingua (Bowerbank) Mycale retifera Topsent Petrosia ®ciformis (Poiret) Phorbas tenacior (Topsent) Spongia ocinalis L. Sycon sp. ± D ± ± D ± S ± ± ± ± ± D ± DS ± DS D ± D ± D D D ± P ± P P ± ± ± ± P ± ± ± P P P ± ± ± ± P ± ± D P P ± P P P ± ± ± P DP ± ± P ± P D ± ± ± DP P P ± P D ± ± ± D D P ± P D ± D D ± P D ± P ± D P ± D ± D D ± ± ± ± D ± P ± ± ± P ± D D ± ± ± P P P D Cnidaria Aglaophenia elongata Meneghini Aglaophenia octodonta (Heller) Aglaophenia picardi Svoboda Antennella secundaria (Gmelin) Balanophyllia europaea (Risso) Bougainvillia muscus (Allman) Caryophyllia inornata (Duncan) Caryophyllia smithi Stokes & Broderip Clavularia ochracea von Koch Clytia hemisphaerica (L.) Clytia noliformis (Mc Crady) Condylanthidae gen. sp. Cornularia cornucopiae (Pallas) Eudendrium armatum Tichomiro€ Eudendrium glomeratum Picard Eudendrium racemosum (Gmelin) Eudendrium ramosum (Pallas) Halecium mediterraneum Weismann Halopteris catharina (Johnston) Hoplangia durotrix Gosse Kirchenpaueria pinnata (L.) Leptopsammia pruvoti Lacaze-Duthiers Madracis pharensis (Heller) Mitrocoma annae Haeckel Obelia bidentata Clarke Obelia dichotoma (L.) Phyllangia mouchezi (Lacaze-Duthiers) Plumularia obliqua (Thompson) Plumularia setacea (L.) Polycyathus muellerae (Abel) Sertularella ellisii (Deshayes & Milne-Edwards) Sertularia distans Lamouroux ± D D ± D ± ± ± D DF ± ± S ± ± D ± ± ± ± ± ± D F ± F ± ± ± ± D ± ± ± ± D D ± P ± ± ± ± ± ± ± ± ± ± ± D ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± P ± ± ± ± ± ± D ± ± ± ± ± ± ± P P ± ± ± DP ± ± D ± ± ± ± ± ± ± ± DP ± D ± D ± ± D ± ± ± ± ± D ± P P ± ± ± P D ± ± D ± ± ± ± ± ± ± DP ± ± ± ± ± ± ± ± ± ± ± ± ± ± P P ± ± ± ± ± ± D ± ± G ± ± ± ± G ± F ± G ± G ± ± G ± D G ± ± D ± D G F G ± ± D ± D D Mollusca Anomia ephippium L. Barbatia barbata (L.) Hiatella arctica (L.) Lithophaga lithophaga (L.) Modiolarca subpicta (Cantraine) ± ± D ± S ± ± ± ± ± ± ± ± ± ± ± D ± D ± ± ± D ± ± F D DGF ± ± P P P P P P VS* P P P P D ± ± G ± ± ± ± D ± D D G ± ± ± ± F D ± ± ± ± DF F F F GF F (cont. overleaf) 732 Table 1 (Continued) SR* E ST CR* S VS* ± D ± ± ± ± ± ± ± P ± D ± ± D D ± ± Polychaeta: Serpuloidea Apomatus similis Marion & Bobretsky Filogranula calyculata O. G. Costa Filogranula gracilis Langerhans Hydroides norvegicus Gunnerus Hydroides pseudouncinatus pseudouncinatus Zibrowius Janita ®mbriata (Delle Chiaje) Janua pagenstecheri (Quatrefages) Janua pagenstecheri gnomonica (Bailey) Josephella marenzelleri Caullery & Mesnil Metavermilia multicristata (Philippi) Neodexiospira pseudocorrugata (Bush) Nidi®caria clavus (Harris) Pileolaria heteropoma (Zibrowius) Pileolaria militaris ClapareÁde Pomatoceros triqueter (L.) Protolaeospira striata (QuieÂvrieux) Protula tubularia (Montagu) Salmacina dysteri (Huxley) Semivermilia agglutinata (Marenzeller) Semivermilia crenata (O. G. Costa) Semivermilia pomatostegoides (Zibrowius) Semivermilia torulosa (Delle Chiaje) Serpula concharum Langerhans Serpula sp. Serpula lobiancoi Rioja Serpula vermicularis L. Serpula vermicularis echinata MoÈrch Spirobranchus polytrema (Philippi) Vermiliopsis infundibulum (Philippi) Vermiliopsis labiata (O. G. Costa) Vermiliopsis monodiscus Zibrowius Vermiliopsis striaticeps Grube Vinearia koehleri (Caullery & Mesnil) ± D D ± D ± D D D ± S ± ± ± ± D ± DS ± D ± ± D ± ± D ± DSF D D D DS D ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± D ± ± D ± ± ± D ± ± ± ± ± ± ± P ± ± ± ± ± ± ± ± ± ± D ± D ± ± ± ± D ± ± D D ± ± D D D ± ± ± ± D DP D ± D D ± D ± ± ± D D ± D ± ± D ± ± ± ± ± ± D ± D ± ± D ± ± ± ± P DP ± D ± ± D ± ± D ± D ± D ± ± ± F D ± G ± D D D D D D D D G F ± F D D D ± G ± D G D F D D D G ± D Bryozoa Adeonella polystomella (Reuss) Aetea lepadiformis Waters Aetea sica (Couch) Aetea truncata (Landsborough) Amathia lendigera (L.) Amathia pruvoti Calvet Anarthropora monodon (Busk) Annectocyma major (Johnston) Beania hirtissima cylindrica (Hincks) Beania hirtissima hirtissima (Heller) Bowerbankia gracilis Leidy Bugula fulva Ryland Caberea boryi (Audouin & Savigny) Calpensia nobilis (Esper) Cellepora pumicosa (Pallas) Celleporina globulosa (D'Orbigny) Celleporina hassallii hassallii (Johnston) Celleporina hassallii tubulosa (Hincks) Celleporina lucida (Hincks) Chlidonia pyriformis (Bertoloni) Chorizopora brongniartii (Audouin & Savigny) Crassimarginatella maderensis (Waters) Crisia sp. Diplosolen obelia (Johnston) Disporella hispida (Fleming) Escharina dutertrei (Audouin & Savigny) Escharina hyndmanni (Johnston) Escharina sp. Escharina vulgaris (Moll) ± ± ± D ± ± ± D D D ± ± ± D ± ± ± ± D ± ± ± D ± ± D ± ± ± ± ± ± D ± ± ± ± ± D D ± ± ± ± ± ± ± ± ± ± ± D ± ± ± ± ± ± ± ± ± D ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± P D D D D ± ± D ± ± ± ± ± ± D D ± D ± D ± D D ± ± ± ± ± D ± ± ± D ± ± ± D ± ± ± ± ± D ± D ± D ± ± ± ± D D D ± ± D D D D ± D ± G D D ± D ± D G F ± D D ± D ± G G D ± D ± D ± D Serpulorbis arenaria (L.) Spondylus gaederopus L. Vermetus (Thylacodus) granulatus (Gravenhorst) F G G G G G GF GF F GF G G G GF G F GF F G G G 733 Table 1 (Continued) Escharoides coccinea (Abildgaard) Fenestrulina malusii (Audouin & Savigny) Haplopoma impressum (Audouin & Savigny) Hemicyclopora multispinata (Norman) Hincksina ¯ustroides ¯ustroides (Hincks) Hippaliosina depressa (Busk) Hippopodina feegensis (Busk) Hippopodinella lata (Busk) Hippoporidra picardi Gautier Idmidronea sp. Lichenopora radiata (Audouin & Savigny) Mecynoecia sp. Metroperiella lepralioides (Calvet) Microporella umbracula (Audouin & Savigny) Mimosella gracilis Hincks Mimosella verticillata (Heller) Mollia multijuncta (Waters) Mollia patellaria (Moll) Monoporella nodulifera Hincks Myriapora truncata (Pallas) Nolella gigantea (Busk) Onychocella marioni Jullien Parasmittina tropica (Waters) Pherusella tubulosa (Ellis & Solander) Plagioecia sp. Platonea stoechas Harmelin Puellina (Cribrilaria) hincksi (Friedl) Puellina (Cribrilaria) radiata (Moll) Puellina (Cribrilaria) sp. Puellina (Grabrilaria) orientalis orientalis Harmelin Puellina (Puellina) gattyae (Landsborough) Puellina (Puellina) setosa (Waters) Reptadeonella violacea (Johnston) Retevirgula akdenizae Chimenz, Nicoletti & Boncampi Rhynchozoon neapolitanum Gautier Rhynchozoon pseudodigitatum Zabala & Maluquer Rhynchozoon sp. 1 sensu Hayward Rhynchozoon sp. Savignyella lafontii (Audouin & Savigny) Schizobrachiella sanguinea (Norman) Schizomavella auriculata auriculata (Hassall) Schizomavella discoidea (Busk) Schizomavella hastata (Hincks) Schizomavella mamillata (Hincks) Schizomavella rudis (Manzoni) Schizoporella longirostris Hincks Schizoporella unicornis (Johnston in Wood) Scrupocellaria delilii (Audouin & Savigny) Scrupocellaria reptans (L.) Scrupocellaria scrupea Busk Scrupocellaria scruposa (L.) Scrupocellaria sp. Sertella septentrionalis Harmer Smittina cervicornis (Pallas) Smittoidea reticulata (Mac Gillivray) Tubulipora plumosa Harmer Tubulipora sp. Tubuliporidae indet. Turbicellepora camera (Hayward) Umbonula ovicellata Hastings Valkeria tuberosa Heller Brachiopoda Argyrotheca cordata (Risso) Argyrotheca cuneata (Risso) Megathiris detruncata (Gmelin) Neocrania anomala (O. F. MuÈller) SR* E ST CR* S VS* ± D ± ± ± ± ± D ± ± D D ± ± D D ± D ± D ± ± ± S ± ± ± ± ± ± ± ± D ± D S D ± ± D D D ± ± ± DS ± ± D ± D ± D ± ± ± DS ± S ± ± ± ± ± ± ± ± D ± ± ± D ± ± ± ± ± ± ± ± ± D ± ± ± ± ± D ± ± ± ± ± DP D ± ± DP ± ± D D ± ± D ± DP D ± ± ± D ± ± ± ± ± D ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± P ± ± ± ± ± ± ± ± ± ± ± ± P ± ± ± P ± ± ± ± ± ± ± D P ± ± ± ± ± ± P P ± ± ± ± ± ± ± D D D ± ± D ± ± ± ± D D D ± ± D D ± ± P ± ± P D ± ± D ± ± ± D ± ± ± D ± P ± D P P ± ± ± ± P ± D ± ± D D P P ± ± D ± ± D ± D D D ± ± ± ± ± ± ± D ± ± ± ± ± ± ± D DP ± D ± ± ± ± ± D ± ± ± D P ± ± ± DP ± ± ± D ± ± ± ± DP ± ± ± ± ± ± ± ± ± ± ± ± ± ± D G ± ± G D ± ± ± D F G ± ± G D D ± D D D ± ± D ± G D D D G G ± G ± ± D ± ± G G ± D G D ± ± D ± D D D D ± F D D F G G ± D D ± ± ± ± ± ± ± ± ± ± ± ± ± ± D ± D D ± ± DG DG G DG F G G G GF G F F GF F G F G (cont. overleaf) 734 Table 1 (Continued) Ascidiacea Aplidium sp. Ascidia mentula MuÈller Ascidia sp. Ascidia virginea MuÈller Ascidiella aspersa (MuÈller) Didemnum maculosum (Milne-Edwards) Diplosoma listerianum (Milne-Edwards) Halocynthia papillosa (L.) Microcosmus sabatieri Roule Microcosmus savignyi C. Monniot Microcosmus vulgaris Heller Molgula manhattensis (De Kay) Molgula occulta Kupfer Phallusia mammillata (Cuvier) Polycarpa gracilis Heller Polycarpa sp. Polyclinum aurantium Milne-Edwards Pyura microcosmus (Savigny) Pyura squamulosa (Alder) Pyura tessellata (Forbes) Sydnium sp. SR* E ST CR* S VS* ± ± ± ± ± DS ± D ± ± D ± D ± ± ± ± D ± ± D ± ± ± ± ± ± ± P ± ± ± ± ± ± ± ± ± ± ± ± ± DP ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± P DP D D ± ± DP ± P D D ± ± ± ± D ± D ± ± DP ± ± ± ± ± ± DP ± P ± ± ± ± ± ± ± ± ± ± ± ± ± F F ± F F DGF F D ± D ± D F F D D ± DF D D ± to seven main groups: Porifera, Cnidaria (Hydrozoa and Anthozoa), Mollusca (®xed Bivalvia and vermetid Gastropoda), Polychaeta (Serpuloidea only), Bryozoa, Brachiopoda and Ascidiacea. No barnacles (Crustacea: Cirripedia) were found. Bianchi and Morri (1983b) proposed extreme oligotrophy as an explanation for the lack of the common Mediterranean barnacle Balanus perforatus from the shallow sublittoral zone of the Island of Kos, SE Aegean Sea. Bryozoans, with 90 species (or subspeci®c taxa), were by far the most species-rich group. Nearly all of them were found by divers in samples collected by scraping. The reason for this was that most of them were smallsized species, living cryptically within the interstices of the substratum or as epiphytes on large algae (especially Sargassum and Cystoseira). Large encrusting (e.g. Reptadeonella violacea and Schizoporella longirostris) or erect species (Myriapora truncata, Sertella septentrionalis, Smittina cervicornis, etc.), recognisable on photographs, were few. The same observation also applies to the other taxa, so that more than 80% of the species were found in collections by divers (Table 2). Fouling samples, indirect kelling in shallow waters and by SCUBA diving in deeper waters, down to about 40 m. SCUBA divers also took wire-framed photographs of the epibenthos covering rocky substrata. Additional deeper samples (50 to 90 m) came from indirect sampling gears (anchor and box-corer). The macrofouling fauna that settled on oceanographic instruments left in situ for about 3 months (June 1996 to September 1996) or 9 months (September 1996 to June 1997) was also collected. Species were identi®ed by di€erent specialists, and species names mostly follow those used in the check-list of Italian fauna (Avian et al. 1995; Balduzzi and Emig 1995; Bedulli et al. 1995; Bodon et al. 1995; Castelli et al. 1995; Fredj et al. 1995; Pansini 1995). Species richness at the various sites was compared through a rarefaction method. The number of species from each site was summed cumulatively over all samples taken at that site (irrespective of the technique employed), and plotted against the number of samples. The number of samples varied from a minimum of 12 (Site VS) to a maximum of 20 (Site CR). The resulting plot has the usual aspect of a species±individuals or species±area curve commonly used in marine biodiversity studies (for examples see Gray 1995; Edinger et al. 1998). Results A total of 212 taxa (species, subspecies or varieties) of sessile animals were identi®ed (Table 1). They belonged Table 2 Number of species (or subspeci®c taxa) belonging to the major sessile macroepifaunal groups sampled with di€erent methods SCUBA diving Porifera Cnidaria Mollusca Polychaeta Bryozoa Brachiopoda Ascidiacea Total Snorkelling Indirect sampling gears Fouling Photographs Total 22 21 5 27 76 4 17 3 1 1 4 5 0 1 2 9 1 14 33 4 1 2 8 2 9 15 0 9 18 4 1 2 10 0 5 24 32 8 33 90 4 21 172 15 64 45 40 212 735 sampling gears and photographs provided similar numbers of species, around 20% of the total each. Snorkelling, which was limited to shallow rocks, gave only 7% of the species. The sponges were a partial exception to what is stated above. They comprised 24 species in total, of which 22 (91.7%) were sampled by the divers and 18 (75%) seen on the photographs. Most sponges were large and colourful species, erect (Axinella damicornis, Axinella verrucosa), massive (Agelas oroides, Chondrosia reniformis, Cliona nigricans, Ircinia sp. p., Petrosia ®ciformis) or encrusting (Phorbas tenacior, Crambe crambe), and thus easily seen and recognised on photographs. Cnidarians and serpuloideans were represented by 32 and 33 species (or subspeci®c taxa), respectively. Among cnidarians, hydroids and scleractinians were the most species-rich groups. Only the latter included species (Caryophyllia inornata, Leptopsammia pruvoti, Madracis pharensis, Phyllangia mouchezi) easily recognised in photographs. In the case of serpuloideans, the total of 32 Fig. 2 Number of sessile macroepifaunal species (or subspeci®c taxa) of the di€erent higher taxa at the six sites (SR, E, CR, ST, VS and SS: see Fig. 1). Asterisks mark the sites closest to hydrothermal vents species (or subspeci®c taxa) corresponds to nearly half of those recorded in the Mediterranean (see Bianchi 1981 for comparison). They were commonly seen on photographs, but only two species (Protula tubularia and Salmacina dysteri) were recognisable with sucient certainty. Ascidians comprised 21 species, of which nine (42.9%) were recorded among the fouling fauna. Four species (Ascidia virginea, Ascidiella aspersa, Diplosoma listerianum and Phallusia mammillata) were found exclusively in the fouling. Didemnum maculosum and Halocynthia papillosa were the only two species recognised on photographs. Sessile molluscs comprised eight species: six bivalves and two vermetid gastropods. Among the latter, Serpulorbis arenaria was seen only on photographs. Brachiopods were the least species-rich group, with only four species in total. All of these were cryptic and found only within rock or bioconcretion fragments collected by divers or indirect sampling gears. At nearly all of the six sampling sites, bryozoans were the richest group, the only exception being Site ST where 736 Fig. 3 Cumulative number of sessile macroepifaunal species (or subspeci®c taxa) plotted against the number of samples at each of the six sites (SR, E, ST, CR, S and VS: see Fig. 1). Asterisks mark the sites closest to hydrothermal vents they were surpassed by the sponges. Sponges were species-rich also at Sites E and S, serpuloideans at Sites SR, CR and VS. Cnidarians were important at most sites, whereas the remaining groups were sparsely represented. Site VS showed the greatest evenness, all groups being proportionately represented (Fig. 2). Site VS also provided the greatest number of species: 133 (i.e. 60% of the total). There, the cumulative number of species (Fig. 3) still showed a tendency to increase after 12 samples, suggesting that the local diversity may even be higher. At all the other sites, the species-samples curve ¯attened out after about ten samples, indicating exhaustive sampling and thus adequate evaluation of their epifaunal richness. Discussion In contrast with the terrestrial fauna, which has been rather well investigated (Matsakis 1983), the marine fauna of the Cyclades is poorly known. The present Fig. 4 Species richness (number of species in ten samples: see Fig. 3) versus bottom depth and distance from shore of the six sampling sites (SR, E, ST, CR, S and VS: see Fig. 1). Asterisks mark the sites closest to hydrothermal vents paper, reporting 212 sessile animals from Milos, is one of the ®rst accounts. There has been no previous inventory of marine sessile fauna to such an extent for the Aegean Sea, although lists of sessile, among other, animals can be found in benthic ecological papers (e.g. Kocatas 1976; Bogdanos and Satsmadjis 1983, 1987; Zenetos and Bogdanos 1987; Simboura et al. 1995) or in publications on single faunal groups: sponges (e.g. VoultsiadouKoukoura and Koukouras 1993), cnidarians (e.g. Marinopoulos 1979; Zibrowius 1979; Va®dis et al. 1994), bivalves (e.g. Zenetos 1996), serpuloideans (e.g. Knight-Jones et al. 1991; Simboura and Nicolaidou 1994), barnacles (e.g. Kattoulas et al. 1972), bryozoans (e.g. Harmelin 1969; Hayward 1974; UÈnsal 1975) and ascidians (e.g. Uysal 1976; Koukouras et al. 1995). More than 200 species, collected with a relatively low sampling e€ort in a restricted area, can be considered quite a high number: this contrasts with the lower number of infaunal species (152) reported from shallow water in this zone by Dando et al. (1995b). Our results con®rm the opinion of Zenetos (1997) that the marine biodiversity of the Aegean is higher than traditionally believed (Tortonese 1951; Fredj et al. 1992). The highest numbers of species were found at the deepest Site VS. Samples from VS included fouling organisms and material taken with indirect gears (but no photographs). Taking into account only the number of species collected by SCUBA diving, VS remains the richest site, with 80 species. With the exception of the rich and shallow Site SR, deep sites were in general richer than shallow sites. This pattern conforms to the view that marine zoobenthic diversity increases with depth, at least within a sublittoral to bathyal range (Lambshead 1993; Angel 1996). This view, however, has recently been questioned (Gray 1994; Gray et al. 1997). Species richness also tended to increase with distance from the shore, contrasting the basic prediction of island biogeography that remote localities are species-poorer, as con®rmed by many studies (Manne et al. 1998). All the rocky shoals studied here, however, are located on 737 the shelf and are not suciently far from each other to be treated as ``islands'', even with respect to the limited dispersal capabilities of sessile benthos. It has also been mentioned in the literature that o€shore habitats tend to have a greater species richness than inshore habitats (Levinton 1995; Arntz et al. 1998). Irrespective of depth and distance from shore, biodiversity was proportionally higher at sites closest to hydrothermal vents (Fig. 4). These ®ndings apparently contradict the impression that the number of species of shelf macrobiota is reduced near vents (Fricke et al. 1989; Tarasov and Zhirmunskaya 1989; Kamenev et al. 1993) and clearly deserve further investigation. As a comparison, within the submerged Kraternaya Caldera of the Kurile Islands, Tarasov and Zhirmunskaya (1989) reported approximately 200 species of macrozoobenthos, compared with more than 360 species reported to date o€ Palaeochori Bay, Milos (Dando et al. 1995b; present study). Tarasov et al. (1999) found that both epifauna and infauna were sparse at the shallow-water hydrothermal vents in the Rabauls Caldera (New Britain Island, Papua New Guinea), but areas adjacent to the vents showed the richest benthic communities. At Milos, all the species found exclusively at the sites closest to actual vents are already known from ``normal'' sites in the Mediterranean Sea and, therefore, no ventobligate species could be recognised. The seven epifaunal groups were di€erently represented, in terms of the relative number of species, at the six sampling sites, con®rming that biodiversity hotspots do not always correspond across taxa (Reid 1998). Cryptic species (brachiopods, bivalves, most serpulids, many bryozoans and some anthozoans) were better represented at VS and CR, within anfractuosities and small cavities of the bioconstructions of the coralline alga Mesophyllum lichenoides (Cocito et al. 1999). Bryozoans, hydroids and spirorbids also included many small epiphytic species, and these taxa were therefore species-rich at sites dominated by algal communities (Bianchi et al. 1997), such as SR, E and S. As a general rule, biodiversity was higher at sites where constructional or frondose algae formed a secondary substratum. Habitat provision by biologically generated complexity has been demonstrated to play an important role in enhancing biodiversity (Thompson et al. 1996). The combined use of a varied array of sampling methods was e€ective in completing the faunistic survey (Bianchi et al. 1999). The collection of substratum fragments through snorkelling and SCUBA diving, or with indirect sampling gears, provided the cryptic species and the species living as epiphytes on algae. Recovered instruments provided additional species of hydroids, serpulids, bryozoans and ascidians in high abundance with respect to the short deployment period. SCUBA diving was the most successful collection method, providing the great majority of the species. Balduzzi et al. (1989) stated that this is due to the diver having the possibility of taking visually oriented samples, which is of great importance to establishing inventories of species. Photographs gave fewer species than physical samples, but they were e€ective in providing further data on the depth and site distribution of conspicuous species, easily recognised on the photographs. Massive sponges were more easily seen on the photographs and comparatively poorly collected in the samples, so that the number of species of sponges identi®ed from photographs approached that from samples. Similarly, species of sponges (e.g. Crambe crambe) and bryozoans (e.g. Reptadeonella violacea and Schizoporella longirostris) encrusting barren infralittoral rocks were dicult to collect by scraping, but easily recognised on photographs. Shooting photographs was faster than scraping the substratum to survey sessile animals: photographs allowed more samples to be taken per dive. Clearly, photography and physical collection of specimens are complementary, not alternative, methods (Gili and Ros 1985; Bianchi et al. 1991). The former was able to detect the biodiversity living directly on the primary substratum, the latter provided information about the biodiversity associated with the secondary substrata: when used together they allowed for more complete and accurate set of results. Acknowledgements This study was part of the Project AG-HY-FL of the European Community (Contract MAS3-CT95-0021). We wish to thank S. Varnavas, for organising the logistics in Milos; the captains and crews of the vessels ``Pantocratos'' and ``Vasilios G''; the scienti®c diving supervisors A. Bruhn and K. Eichstaed; the deep-divers S. Schwabe and the late R. Palmer; F. Degl'Innocenti (La Spezia), R. Meloni (La Spezia) and all the other partners for their help with ®eld work. The following people helped with species identi®cation: G. Bavestrello (Genova), Eudendrium; C. Chiantore (Genova), Bivalvia; S. Schiaparelli (Genova) and D. Scuderi (Catania), Vermetidae. A. M. Alinat (BibliotheÁque du MuseÂe OceÂanographique, Monaco) assisted with the bibliographical search, whereas A. Balduzzi (Genova), C. Bogdanos (Hellenikon), G. Fassari (Catania), J. Geister (Bern), J. G. Harmelin (Marseille), A. Koukouras (Thessaloniki), A. Serhat (Istanbul), A. Zenetos (Hellenikon) and H. 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