ANNALES • Ser. hist. nat. • 12 • 2002 • 2 original scientific paper UDC 574.5:582/.59(262.3-17) received: 2002-1 M 2 A TOPOGRAPHICAL SURVEY OF HABITAT TYPES IN THE AREA CHARACTERIZED BY SEACRASS MEADOW OF POStDONIA OCEANICA IN THE SOUTHERN PART OF THE GULF OF TRIESTE {NORTHERN ADRIATIC) Robert TURK Institute of the Republic of Slovenia foi Nature Conservation, 51-6330 Piran, Tartinijev tig 12 Martina ORLANDO BONACA, Tihomir MAKOVEC, Aleksander VUKOVIC & Lovrenc LlPtj Marine Biology Station, Nalion.il Institute of Biology, SI 6330 Hiran, rornace 41 E-mail: lipej@nib.si ABSTRACT According to the national legislation and by considering international documents on nature conservation, the Mediterranean endemic seagrass Posidonia oceanica was included in the latest edition or the Slovenian Red Lis! of Rare and Endangered Species. Moreover, the only Slovenian site with Posidonia ocean ica, which is also the only meadow along the West Istrian coast, was proposed to be declared <5 natural monument in 1904. However, besides some preliminary data on the topography and phenology of the meadow, very few data arc available regarding its fauna and flora. Being an area of great conservation interest, a non-destructive underwater inspection has been carried out. The fiorisdc and faunistic dala, together with accurate habitat type cartography, are presented. A special emphasis was given to ichthyofauna. Key words: Posidonia oceanica, North Adriatic, topographical survey, nature conservation, non destructive methods RILIEVO TOPOGRAFICO DEI TlPi DI HABITAT NELL'AREA CARATTERIZZATA DA UNA PRATFRIA DI POSIÜONIA OCEANICA NELLA PARTE MERtDIONALE DEL GOLFO Di TRIESTE (NORD ADRIATICO) SINTcSl Recentemente e stata inoltrata ¡a proposta per dicharare l'unico sito in cui ancora cresce una prateria di Posidonia oceanica in acque slovene Monumento Natúrale, vista la sua úntala e vulneiabiliia. Fino ad oggi la fauna e la flora della zona non fono state stvdiate a sufficienza. Vista l'imminente dichiarazione ufficiale del sito ad a rea pro-tetta, per il presente s tudio é stato usato un método di campionamento subaequeo non distruttivo. I. 'ai tico lo riporta i dati faunistici e floristici, nonché un'accurata cartografía dei tipi di habitat della zona. L'ittiofauna ha occupato un posto di rilievo nella ricetca. Parole chiave: Posidonia oceanica, Alto Adriático, rilievo topográfico, tutela della natura, metodi non distruttivi 2.36 ANNALES • Ser, hist. nat. • 12 • 2002 • 2 Robert 1 (.IRK et. a!.: A TOPOGRAPHICAL SURVEY OF 1 !A61TATTYPES IN THE AREA CHARACTERIZED BY SEAGRA55 MEADOW .... 191-202 INTRODUCTION Posidonia oceanic a (L) Delsle is an endemic sea-grass species in the Mediterranean. It forms seagrass meadows, which are nowadays considered to be amongst the most important habitat types in the infraik-toral zone of the Mediterranean Sea. Seagrass beds are known to be key nursery areas for coastal fisheries. According to some authors, the presence of P. oceanica should be also regarded as a good biological indicator of water quality due to its sensitivity to human activities (sensu Piazzi el a!., 2000). The isolated P. oceanica meadow in Slovenian coastal waters, between the towns of Izola and Koper (referred hereafter as the Koper meadow), was described by Vukovii: (1982}. Besides the tiny patch of app. 2 m" close to Grado, it seems that the Koper meadow is the only remnant of this marine phanerogam in the Gulf of Trieste and along the Istrian coast. According to Benacchio (1938), P. oceanica was quite common on the silted bottom of the inner part of the Gulf of Trieste, However, a drastic reduction in its distribution was recorded just about 30 years later by Si-monetti (1966) in his work dealing with distribution of the Zosteraceae in the Gulf. Although no specific mapping programme for seagrass meadows has been made in Slovenia so far, some data are available on different aspects of the distribution (Vukovic & Turk, 1995) and phenology (Turk & Vukovic, 1998) of P. oceanica as well as on epiphytes and its colonisation (Orlando & Bressan, 1998). Some (fata are also at hand on the impacts of motorway pollution on the ecological conditions of the site (Faganeli ef a/., 1997). One of the most interesting aspects of the Koper meadow - the possibility of being an ancient, post-glacial clone - is described in the work on genetic identity and homozygosity in Northern Adriatic populations of P. oceanica carried out by Ruggiero et ai. (2002). A decree for the protection of the meadow is being currently drafted by the government. The most important aspect of biodiversity is species composition, a checklist of a variety of species present in the area (Costelto, 2000). To assess the marine biodiversity of a protected site, a non-destructive methodology is more suitable than any other classical sampling technique. Almost 50 years have passed from the inception of the nondestructive underwater visual census technique (Brock, 1954) for the study of coral reef fish assemblages. Numerous studies throughout the world confirmed the usefulness of this technique, which is nowadays accepted as a useful methodology to gain coastal fish density estimate (Harmelin, 1987; Francour, 1991, 1994; Barmelin-Vivien & Francour, 1992; Patzner & Serrao Santos, 1993; Harmelin et a/., 1995; Castellarin et ai., 2001). Today, visual census data are recognised as a valuable source of information for other aspects of fauna (Peharda eta/., 2000), flora, habitat types and in broader meaning for conservation purposes as well (Edgar et a/., 2000). The present study aims to describe the habitat types occurring in the proposed protected area covered with P. oceanica seagrass meadows, and to assess the faunis-tic and floristic diversity of the area with non-destructive methods, Since this area is to be legally protected, such data can be very useful in the process of defining suitable conservation measures. Fig. 1: Location of transects in the proposed natural monument area near Koper. SI. 7: Lokacije transektov na predlaganem naravnem spomeniku hlizu Kopra. 192 ANNALES • Ser. hist. nat. • 12 • 2002 • 2 «obe« «UR* «"• .il: A TOPOGRAPHIC At SURVEY OF HABITAT TYPES IN Tilt AREA CHARACTERIZED BY SEACRASS MEADOW ..., 191-202 MATERIAL AND METHODS Study area i he study area is located between the towns of izola and Koper, with the only site of P. oceanica scagrass meadow along the northern and western coasts of ¡stria. As a rec ent sediment of Koper Bay it consists of sandy silt with up to 40% of sand and less than 15% of clay (Ogorelec d al., 1988). The area surveyed is a known tourist resort with many recreational facilities. This is particularly true of the eastern part, which is close to the r ity of Koper and densely inhabited, whereas towards the city of izola in the west the area is without any man-made structures but for the waterfront on< e used by the railway. On the other hand, trie area has been subjected to a certain extent to organic pollution from the nearby city of Koper. Although recent studies have shown benthic organisms contaminated with PAH and heavy metals, this has not been reflected in the area's benthic community (! aga-neli eta/., 1997). Materia! and methods Taking into account the vulnerability <;f the area, the underwater inspection of the area's flora, fauna and habitat types was carried oui by SCUBA divers in the summer of 2000 and in the summer and autumn of 2001 along five vertical transect lines (station 1-5). The distances between different stations are shown in fig. 1. During each survey we tried to get as much data as possible on the flora, fauna, habitat types and cryptobenihic fishes. A special emphasis was laid on the underwater mapping of different habitat types, occurring along the transect lines. Details about sighted animals and algae were written on a slate. Only the specimens, which were not determined during the sampling, were taken out in special bags and identified later in the laboratory and subsequently released. Only epifauna was taken into consideration. for the assessment of coastal fish assemblage, a visual census technique was performed by two SCUBA divers along 60 m long transects. Coastal fish were counted up to 2 meter away from the transect rope by one or two divers. Two 30-m long measuring tapes were used. The average duration of a visual count transect was approximately 2C minutes. Additionally we used the data of one parallel census in P. oceanica habitat type at the station b. In addition, a narcotiser quinalcin (MS222) was used to detect some cryptobenthic fish species, which could be otherwise overlooked. t iabitat type cartography was carried out by filming with underwater Sony camera (Handicam Hi-8). The diver with the camera followed the transect rope and filmed all habitat types. Afterwards, some shots of spe- cific vegetation cover or peculiar habitat types in the neighbouring area were taken as well. Additionally, some specific habitat types were photographed with Su-beye underwater camera. In the laboratory the transect films were carefully analysed and used for drawing Habitat types. The coverage of each habitat type was estimated by calculating the area in habitat type distribution drawings. RESULTS AND DISCUSSION Floristic survey At least 58 algai species and 2 other phanerogams (Cymodocea nodosa and Zostera noltii) were recorded in the investigated area (Tab. 1}. Altogether 10 green macroalgae, 11 brown macroalgae and 37 red macroalgae were recorded. Twenty-four epibionts had been previously surveyed by Orlando & Bressan (1998). The vegetation cover in the area is strongly connected with the ecological conditions, such as the water quality and the seabed substrata. Iri somehow deeper area, the seabed is covered by sandstone rocks and cobbles, which are not suitable for algae, and by some bigger boulders, to which Alsidium corallinum and Anadyomene steiiata are attached. Faimistic survey Benthic invertebrate fauna At least 88 taxa of benthic invertebrates were recorded in the studied area (Tab. 2). The majority of them, 38 species, were mollusks, followed by crustaceans (16), sponges (8), cnidarians (7), echinoderms (6), pofychaets (6), tunicates (4) and bryozoans (3). At the station 1, at least 45 species were recorded, whereas at stations 2 and 3 at least 58 species were sighted. The invertebrates recorded were found mostly as fauna on rocks and boulders or as epibionts on Posidonia, Cymodocea and Cystoseira. The number of animals recorded is obviously far from complete, since only epifauna was taken into consideration. On the other hand, we used the technique of visual inspection mostly as it is a nondestructive method and at the same time very appropriate for protected areas. Many tiny and cryptic invertebrates could obviously not be recorded with such method. Numerous studies demonstrated the importance of Posidonia seagrass meadows for a variety of animal groups. It is characterized as a complex biotic community with high richness, in which many animals spend ail or part of their lives {sensu Garcia-Raso, 1990). According to Somaschini et ai. (1993), the poiychaete community of the P. oceanica bed is richer and more diversified than the neighbouring environment. 2.36 ANNALES • Ser. hist. nat. • 12 • 2002 • 2 Robed TURK rt. 4/.; A TOPOGRAPHICAL SURVFY OF HABITAT TYPrs IM THE ARFA CHARACTERISED BY Si:AGRASS MEADOW .... 191-307 Tab. 7: Checklist of the flora associated with Posidonia ocean 1 ca seagrass meadow in the Žusterna-Moleto region (Legend: M - macroalgae, E ~ epiphyte, C - sea-grass, Me - mediolitoral, Z /Vie - upper mediolitoral, S Me = loner mediolitoral, I - infralittoral, Z I - upper infralitoral, S I = lower infralitoral). Tab. 1: Popis flore, povezane s travniki morske trave pozejdonke na območju med Moietom in Žusterno (Legenda: M - makroalge, E - epifit, C = morska travar Me = mediolitoral, Z Me - zgornji mediolitoral, S Me -spodnji Mediolitoral, I ~ infralittoral Z I - zgornji irt- Tab. 2: Checklist of benfhic invertebrates recorded in the area during the study period. Tab. 2: Seznam bentoških nevretenčarjev, opaženih na obravnavanem območju v obdobju vzorčevatija. Porifera Chondrosia reniformis Chondritis nucula Ctione celata Hippospongia communis Oscarella lobiíormis Spiraslrella cuncíaíhrix Tethya aurantium Verongia aerophoba Cnidaria A et in i a equina Aiptasia mutabilis Anernonia sulcata BaianophylUa italica Cladocora caespitosa Eudendrium sp. Paranemonia cinerea Mollusca Aplysia punctata Aporrhais pes pelecani Arca noae Astraea rugosa Bittium reticulatum Cerithium rupestris Cardium eduh Chiton oliváceas Chlamys varius Dendrodoris limbatus Elysia tímida Epilonium communis Gastrochaena dubia Courmya válgala Haliotis lamellosa Hinia costulata Hinia reticulata Hinia incrassata Uma h ians Littorina ne rito ides Lithophaga lithophaga Loripes tacteus Monodonta articulata Murex brandaris Mytilus galloprovincialis Mytilaster minimus O strea edulis Patella caerulea Pholas dactyhis Pinna nobilis Sepia officinalis Solecurtus strigillatus Thuridilla hopei Trunculariopsis trunculus Ven&rupis decussata fralitoral, S I - spodnji infralitoral). TAXON Beli Alsidium coralltnom M 1 Anadyomene síeiteta M 1 Antithainnion tenuissimim E 1 Ascocvctus orb/ctiíáris c; ! CaHiSbamníon consmboswv £ i Cerumium sp. M f f! 1 Ceramium cinjwlatum i Ceramium circinnaUnn t i Cer.tmium tenerrimum t i Chaetomorpha sp. M f f Me Chylocladia sp. £ ( Cbylocladia verticillata t 1 Chondría dasyphiila M ( Cladophora sp. M 1 Ctadophora echmus E 1 Cladophora prolitera M + E S Me +1 Cladosiphon cyltndricus r 1 Cladostephuí verticillaíus M Me + 1 Coraltiria yjan itera M + E Z 1 Coiatlina officinnlis M Z 1 Cvmnrlocca nodosa C i Cystmeira bar bata M 1 Cysloseira compressa M l Oictvota dichotoma M L 1 ! Dictyopleris membrana cea M S Me + Z u frithiotrichia campa i 1 1 fucus vino/des M Z Me Celidietta nizrescens M + t; 1 Celidiüm sp. M + E ! Cetidium spatbltláUim M 1 Gipartina sp. M I Ciraudya sphacetarioides E 1 Halopithys incurvus M Hotel osi chonta i vi irdema nmi E i Hycírolithon cruciatum C i Hydrolithon fariñ'ósiim F 1 Laurencia obtusa M S Me +1 Laurencio papillosa M 2 f iopbosíphonia scoptilorum E ~~ 1 Nitophyltum punctatum M Zi P.idiiia pavonica M S Me + 1 Peyssonnelia squamaria M S 1 Pneophyllum /rabile E 1 Polysiphonia denúdala E 1 Polysinhooia furcellata E 1 Poiysipiioma nigrescens E ! Posídonia ocean/ca C 1 Pseudoliihoplntlum expansum M S 1 Pterodadia car>Hlacea M S Me + 1 Sphacelaria cirrhosa M 1 Spyridi.i filamentosa M + E 1 i Stylortemu ahidii £ 1 Titanoderma corallrnae E ! titanoderma oosivIaUim £ 1 Udotea peíioiafa M 5 l t.ltva fp. M t- E SMe + l LHva rígida M + E S Me -t- I Ulyelta setchellií i I 1 Valoiva utriculms M + E ! i 1 Wranqeiia penicillara M + Í í i Zoílera nollii C 1 2.36 ANNALES • Ser. hist. nat. • 12 • 2002 • 2 Roben TURK«. «I: A TOPOGRAPHIC Al SURVEY OF HABITAT IVRfS IN THE ARIA CHARAOTRtZÍD BY StACRASS MÜAOOW..., 191-202 Venus verrucosa Vermetus triqueter Polydiaeta Bispira sp. Protula tubularia Poinaioceros fr/queter Serpula vermiformis Spirographs spallanzani Spirorbis pagenslecheri Crustacea Alpheus sp. Anilocra physodes Balanus sp. Cardnus aestuari Callianasa stebbingi Chlhamalus siellatus Eriphia spinifrons Gafathea sp. Ligia itaiica Maia verrucosa Macropodia rostrata Mysidae Pinnotheres sp. Porceifana platycheles Upogebia littoralis Bryozoa Membranipora me.branacea Electra posidoniat-. Schizoporefla sanguinea I'chtnodermala Amphiphoiis squan)ata Cucumaria elongata ! iclothuria tubulosa Ophiothrix cf. fragilis Paracentrotus iMdus Sphaerechinus granulans Tunica ta Ascidia sp. Oiplosoma spongiform? Microcosmos cf. sulcatus Phallusia fumigala Ichthyofauna Al least 33 coastal fish species were found to inhabit the studied area (Tab. 3). The number of species pet transect varied from 9 to 22. Only 5 species were recorded at all transects. )he majority of species (10) recorded were gobiids, followed by blennioids (8), sparids (6) and labrids (4). The dominant species were Atherina sp., Symphodus roissali and 5. cinereus. in the patches of Posidonia meadow, only juvenile specimens of Diplodus spp. were abundant. On the basis of a visual count, the highest density was recorded for Symphodus roissali with 9.8 specimens per 100 nv, followed by 5. cinereus with 3.08 per 100 m¿. However, it must be noted that the 60 in parallel census was carried out in the area, where almost 25% of the habitat type consisted of Cys tose ira spp. The dominant gobiid species were ascribed to the Cobius xa nthocep ha I us/fa flax group. Although the yellow markings on the head typical of the species G. xanthocephalus were quite distinct, we decided to use, for practical purposes, the group taxon, since the taxonómica! differentiation during the inspection of the transect is almost impossible in the area, where this species is sympatic with other similar gobiids. Small cryptobenthic fishes Lepadogaster candollei, Zebrus zebras arid Millerigobius macrocephalus were found in the Posidonia meadow (Tab. 3). As they were found under stones, they are not directly related to sea-grass meadows. The goby M. macrocepha/us has been till now recorded only at few sites in the Adriatic Sea (see jardas, 1996). In comparison with other areas in Slovenian coastal waters, the studied 3rea is poor. Fifty-two fish species were recorded for C.ape Madoria Natural Monument, 49 for Strunjan Nature Reserve and 36 for Debe! i rtic Natural Monument (Lipej & Orlando Bonaca, in prep.). The main reason for this lies in the fact lhat the data for other areas were obtained by the use of 90 m long vertical transects, due to which a broader variety of different habitats was obtained, which obviously affected the number of species, (t is well known that the spatial heterogeneity is an important factor, which affects the species diversity of the area. if we lake into consideration only the seagrass meadow of P. oceánica, then only few species can be considered true residents of this area. Bussotti & Guidetti (1999) studied the fish communities associated with P. oceanica on the one hand and Cymodocea nodosa and Zosters noltii seagrass meadows on the other with the visual census technique monthly in August I995 and August 1996 and never sighted more than 24 fish species. Bell & Harmelin-Vivien (1982) reported 49 fish species on Posidonia meadows with a trawl at a depth 16-18 rn. However, only 30 species of them were considered to be residents. The depth obviously had an effect on the species number as well. According to the study of Guidetti (2000) on the visual census data in the southern Adriatic, only three species, Spondylliosoma cantharus, Diplodus annularis and to a minor extent Symphodus ocellatus, were associated with P. oceanica. Since the number of samplings performed in the studied area is lower than in the other (above mentioned) three protected areas in Slovenian coastal waters, we can speculate that the number of species will increase with a further inspection of the area. 2.36 ANNALES • Ser. hist. nat. • 12 • 2002 • 2 Robert TURK el. a/.: A TOPOGRAPHICAL SURVEY OF HABITAT TYPES W THE AREA CHARACTERIZED BY SEACRASS M1-AOOW .... 191-202 Tab 3: Coastal fish assemblage in the studied area. The abundance of different fish species are presented in ranges: - = no specimen recorded, 1 = single specimen, 2 - 2-3 specimens, 3 - 3-5 specimens, 4 = 5-10 specimens and 5 = more than 10 specimens, Cryptobenthic species, which were recorded with the use of narcotic, are marked with asterisk. Tab. 3: Obrežna ribja združba na obravnavanem območju. Številko osebkov posameznih ribjih vrst je predstavljeno v rangih: - = noben osebek zabeležen, 1 = osebek, 2 - 2-3 osebki, 3 - 3-5 osebkov, 4 = 5-10 osebkov in 5 = več kot 10 osebkov. Kriptobentoške vrste vrste rib, ki smo jih potrdili z uporabo narkotičnega sredstva, so označene z zvezdico. St. Species/ station (transects) 4 5 6 1 3 1 Atherina sp. 5 5 5 - - Diplodus annularis - 1 3 - 2 3 Diplodus puntazzo 1 - - - 4 Diplodus sargus - 1 - - 1 5 Diplodus vulgaris 1 1 3 1 3 6 Cobit/s cobitis i i 1 - - -y / Cobius cruentatus i 1 -t i 1 1 8 Gobius paganellus 1 - - - - o j Cobius fallax/xanthoccphalus i - 3 5 10 Gobius niger - 1 - 1 3 11 Gobius roulei 1 - - 12 Lepadogaster candollei"' - 1 - - - | 13 iipophrys adriaticus - - - 1 14 i ipophrys dalmatinus 4 4 - - - 15 Millerigobius macrocephalus * - 1 1 - - 16 Oblada melanura 3 3 - _ - 1? Parablennius gattorugine 1 - - - 1 18 Parablennius incognitas 2 - - 1 19 Parablennius rouxi - 1 - - - 20 Parablennius sanguinolentas - - - 2 - 21 Pa rabien ri i us ten tacit la ris 1 i - - - 22 Pomatoschistus marrnoratus - - - - 5 23 Saipa salpa - - 1 - 5 24 Serranus hepatus 1 - - - 3 25 Serranas acriba 2 2 2 2 - 26 Symphodus cinéreos o A. 3 5 3 5 27 Symphodus ocellatus 3 3 1 3 2 28 Symphodus roissali 5 5 5 3 2 29 Symphodus tinea 2 2 - 2 - 30 Svngnathus acus 1 - 31 Tripterygion tripteronotus 2 - - - 32 Zosterissesor ophiocephalus 1 - - - - 33 Zebrus zebrus* - 2 - 5 - Total number of species 19 22 9 12 14 Habitat types The studied area is characterised by several different habitat types such as a iochthonous limestone boulders, photophilic algal population on roc-.ALSURVtV'r MAfllTAT TYPES M IHi AREA CHARACTCRIZČD BY Sf AC.HASS MEADOW .... 191-20.' Tab. 4: Habitat type distribution (expressed as percentage of the entire surveyed transect area) along five transects. The term fine sand indicates the area not covered by vegetation. Tab. 4: Razporeditev habitatnih tipov: apnenčasti balvani, terase peščenjaka, travnik cimodoccje, travnik poze-idonke„ fini pesek, mulj, prodnjaki in infralitoralni kamni in skale (izraženih v odstotkih celotne površine pregledanega območja) na 5 transektih. Z izrazom fini pesek označujemo predele, ki niso hiti poraščeni z vegetacijo. Habitat type/stations (transects) 1 2 3 4 5 Ailochthonous boulders 7.50 5.0 10.0 11.67 12.50 Sandstone terraces 0 0 21.67 7.50 0 ! Cyniodocea meadows 33.33 13.33 18.33 8.33 26.67 Posidonia meadows 0 11.67 2.50 0.80 52.50 Fine sand* 0 22.50 28.33 45.83 4.20 Mud 22.50 15.00 0 0 0 Pebbles 10.83 5.83 13.33 1 2.50 4.20 ! Infralittoral stones and rocks 25.83 20.83 5.83 13.33 0.0 spreads a dense meadow, whereas in other transects the density is very low. It seems that the ecological conditions are not the same at the five studied transects. Limestone boulders Ailochthonous limestone boulders were placed along the coastal trunk road to function as wavebreak-ers. Numerous niches are available on these boulders and between them, which has resulted in typical me-diolittoral fauna and flora. A broad and large belt on the ailochthonous limestone boulders is covered by the association Tucetum virsoidis, represented by Fucus vir-soides. Characteristic of ¡his belt are also some other common species, such as Chaelomorpha hnurn, Padina pavonica. Cladophora prolifera, Cladoslephus verticil-latus, Dictyopteris irtcmbranacea, and Ulva rígida. The last two also form the typical nitrophilic associations Dyctiopteretum membranáceas and Pterocladio-Ulve-tum, which normally develop in areas influenced by organic pollution. Pebbles Pebbles of irregular shapes were found at all 5 studied transects. Due to the constant wave action, they are not overgrown with vegetation. However, at all transects benthopleustonic alga Ulva rígida was round as very abundant. This nitrophilous green alga is probably connected with outlets of sewage water from the nearby tourist resort 7usterna. Most spec ies inhabiting this area are hidden under pebbles. The typica! fish species of this habitat type are Gobios paganellus, G. cobitis and Parablennius sanguinolentas. Photophilous algae Other parts of the ¡nfralitíoral belt are covered with dense algal phyla! consisting mainly of Cystoseira com- pressa and C. barbate, which are inhabited by some epiphytes such as: Corallina granifera, Ceramiurn sp., Gelidium sp., Polisiphonía furcellata, Spyridia filamentosa, Ulva rígida, Valonia utricularis. On such substrata, Halopithys incurvus, Laurencia papulosa and L. obtusa, Wrangelia pen ici I lata, Dictyota dichotoma are commonly distributed as well. In this habitat type, the ma jority of fishes occurred. Some boulders can be found at somewhat greater depth, forming substrata for dense algal cover and different sponges, sea anemones, vermetiri snails and other molluscs. Wrasses such as Symphodus roissali and 5. cinéreos predominated in the fish assemblage of this particular habitat type. Boulders are also inhabited by different fish species, which are using shelters made by endolitliic bivalves such as Lithophaga lithophaga or live in the boulders' cracks and crevices. The majority of them are blennies (Lipophrys dalmatinus, Parablennius incognitas) and gobies (Gobius cf. xanlhocephalus, Zebrus zebrus). Posidonia meadow in the transition zone, the patches of P. oceanica are situated between stony coastline and mud at a depth interval of 0.5 m to 4 m. The area is approximately 1 km long and 50 m wide (Fig. 1), with the maximum depth between 2 and 4 m. It shows patchy distribution, e.g. it is restricted to small islets ("leopard spots") (Vukovic, 1982; VukoviC & Semroud, 1984; Vukovic & Turk, 1995), embraced by C. nodosa. The Posidonia shoot density varies between 360 and 588 shoots/m*, or 460 shools/m on average (Turk & Vukovic, 1998). In the shady parts of the Posidonia shoots or stones some rhodophycean algae such as Pseudolithophyllum expansum and Peyssonnelia squamaria, which are typical of coralltgenous formations, were recorded. Only few fish species were sighted in this habitat type, but with the use of quinaldine we detected some interesting ciyptobenthic species, such as Millerigobius macro-cephalus and Lepadogaster candollei. 197 ANNALES • Ser. hist. nat. • 12 • 2002 • 2 Robert TURK el. al.: A TOPOGRAPHICAL SURVEY OF HABITAT TYPES IN THE AREA CI IARACTERIZEO BY SEAGRASS MEADOW .... 191-202 2.36 ANNALES • Ser. hist. nat. • 12 • 2002 • 2 Fig. 2: Habitat type distribution at 5 linear transects in the study area (see Fig. 1). SI. 2: Razporeditev habitatnih tipov na 5 linearnih transektih na obravnavanem območju (glej tudi SI. 1). 2.36 ANNALES • Ser. hist. nat. • 12 ■ 2002 ■ 2 Roberl tURK et. «JL: A TOPOGRAPHICAL SURVEY OF HABITAT TYPES IN THE AREA CHARACIERlZlcD BY 5EACRAS MEADOW .... 191-102 Cymodocea meadow Close to the coast is also (he C. nodosa seagrass meadow, occurring either in small patches in the sandy area or almost completely covering the entire transect area. A low number of Zostera noitii plants were found intermingling with C. nodosa. The mean density of C. nodosa shoots was 69 shools/m7 (Vukovic & Semroud, 1984). The Cymodocea seagrass meadow is extending to a depth of 6 to 8 m. Only few specimens of Pinna nobiiis were found. In this seagrass meadow, the typical goby Zosterissesor ophiocephalus was sighted, although it was not abundant. "Naked" boulders and sandstone terraces These habitat types were found at transects 1, 2 and 3 between Moleto and Zusterna. Infra-littoral stones and boulders were poorly overgrown with vegetation (the so-called algal turf). The dominant invertebrate species were the sponge Verongia aerophoba and, to a minor extent, Cladocora caespitosa. Sandstone terraces form a peculiar habitat type, which provides a number of suitable niches for different invertebrates and littoral fishes. They lie horizontally and thus give an impression of a man-made platform. The terraces are overgrown with corraligenous red algae Pseudohthophyl/um expansum, from which the terraces obtained their colour. Dominant invertebrates were poly chads of the genera Protula and Serpula, verrnetid gastropod Vermetus triqueter and sponges V. aerophoba and Chondrilla nucula. In little crevices and cracks between terraces, Gobius cf. xanthocephalus was established as the dominant littoral tish. Sa/jd> and muddy habitat types Some species were sighted only in sandy patches or at the end of transects, where the stony bed is replaced by mud. In these peculiar habitat types, more specimens of Pinna nobiiis were found than in the meadows, but the majority of them were dead. In our opinion, this should be attributed mainly to the high sedimentation rate in this area. The typical sand species Pomatoschis-tus marmoratus was found on sand at a depth range from 2 to 4 m between patches of Posidonia or Cymodocea seagrass meadows. Cobius roulei, a recently rediscovered gobiid species in the Adriatic sea (Kovacic, 1995}, was more or less restricted to coarse sand, whereas C. rt/ger preferred muddy areas. NATURE CONSERVATION VALUE The different aspects of the importance of P. oceanica meadows were confirmed in the last decades by numerous authors. The meadows are the base of the richness of the coastal waters of the Mediterranean (Mo-iinier & Picard, 1952; Cinelii eta!., 1974; Boudouresque & Meinesz, 1982), This is due to the great surface of the sea bottom of the Mediterranean they cover, to the great quantities of organic materia! and oxygen they produce, to their contribution to the stability of the sea bottom and, last but not least, to the fact that the meadows host more than a thousand species of marine organisms. Tor all this reasons, the meadows of P. oceanica and the species themselves are legally protected in several countries around the Mediterranean. Besides, the contracting parties to the Barcelona convention included P. oceanica in Annex II ~ List of endangered or threatened species of the Protocol concerning specially protected areas and biological diversity in the Mediterranean (see Lipej et ai, 2000), Last but not least, the meadows of P. oceanica are listed as a priority habitat type in the EU Directive 92/43 on the conservation of natural habitats and on wild fauna and flora. The importance of the tiny Koper meadow and consequently the need for a strict protection go even beyond the reasons listed in the previous paragraph. The total absence of genetic variability in the meadow, stated in the work by Ruggiero ef al. (2002), is another strong cause of major concern for conservation of the species in this northernmost part of the Adriatic. Low levels of genetic variability and habitat fragmentation can influence species fragility by lowering populations resilience to increasing levels of ecosystem disturbance, either of anthropogenic origin or not (Meffe & Carroll, 1997). Legal protection of the Koper meadow as the only remnant of P, oceanica in the Gulf of Trieste and introduction of efficient conservation measures, together with a suitable long-term monitoring, should be regarded as issues of high priority. The regression of the meadow would not only jeopardise the survival of the species in the North Adriatic but would also add a hundred or more to the Slovene Red Lists of rare arid endangered species. 200 ANNALES • Ser. hist. nat. • 12 ■ 2002 ■ 2 Kobili TURC.rt.ji.. A TO!'OCRAl>mCAL SUKVfcY Of HAP.HA1. TVPES IN VHf Akt A CHARAC: t KiZf D BY SCAGRASS MtAOOW-T5Ü202-- TOPOGRAFSKI PREGLED HAB1TATNIH TIPOV NA OBMOČJU RASTIŠČA POZEJDONKE POS/DONIA OCEANICA, V jUŽNEM DELU TRŽAŠKEGA ZALIVA (SEVERNI JADRAN) ' Robert TURK 7 a vod RS za varstvo narav-, Območna enota Piran, Sl-6330 Piran, Tartlnij'ev trg 12 Martin* ORLANDO BONACA, Tfho/mr MAKOV!.C, Aleksander VUKOVIČ A Lovrenc LIPE J Morska biološka postaja, Nacionalni inSrittrt za biologijo, Sf-6330 Piran, Fomačp 2 Guidetti, P. (2000): Differences among fish assemblages associated with nearshore Posidonia oceanica seagrass beds, rocky-algal reefs and unvegetated sand habitats in the Adriatic Sea. Habitats. Estuar., Coast. Shelf Sci., SO, 515-529. Harmelin, j. G. (1987): Structure et variabilité de l'ich-thyofaune d'une zone rocheuse protégée en Méditer-anée (Parc national de Port-Cros, France). P.S.Z.N.I.: Mar. Ecol., 8(3), 263-284. Harmelin-Vivien, M. L. & P. Francour (1992): Trawling or Visual Censuses? 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