ANN ALES • Ser. hist. nat. - 13 • 2003 • 2 original scientific article UDK 595.142.2:391.9(262.3-16) received: 2003-10-20 SPATIAL DISTRIBUTION OF SOFT-BOTTOM POLYCHAETES ALONG WESTERN COAST OF THE NORTHERN ADRIATIC SEA (ITALY) Fioriarta ALEFFI, Nicola BETTOSO & Vivianne SOUS-WEISS Marine Biology Laboratory, Trieste, 1-34010 Trieste, Via A. Piccard 54 L-mail: aleffi@univ.irieste.it. ABSTRACT The composition and spatial distribution of soft bottoms poiychaetes in the northwestern Adriatic Sea are described. The basin is characterized by shallow depths (mean depths 3.3.5 mi, high river inputs along the western coast, large annual temperature variations and water stratification during the summer. The sediment composition varied from muds to sands. A total of 135 species, belonging to 37 families, were identified; the average density and biomass were respectively 313 ind. m'2 and 17.6 g WW m"\ The cluster analysis on abundance, data resulted in four-main groups of stations, characterized by different sets of organisms and sediment features. The river inputs and depth seem to be particularly important in structuring these bottom populations. Key words: poiychaetes, distribution, soft-bottom, Adriatic Sea DISTRIBUZIONE SPAZIALE DEI POLICHETI Di FONDI MOBILÍ LUNGO LA COSTA OCCIDENTALE DELL'ADRIATICO SETTENTRIONALE (ITALIA) SINTESl Nel presente lavoro viene descritta la composizione e la distribuzione dei policheti di fondi mobili nell'Adriatico Nord occidentale, li bacino è caratterizzato da profond/là non elevate, cospicui apport! fluvial i lungo il versante occidentale; ampie variazioni di temperatura e stratificazione délia colon na d'acqtia durante i'esta te. La composizione tessiturale del sedimento varia da fanghl a sabbie. Sono state identifícate 135 specie appaitenenti a 37 famiglie; la densith media e la b/omassa erario rispettivamente di 313 ind. m'" e '¡7.6 g m'1 di peso umido. L'analisi mu Iti varia ta sui dati di abbondanza ha rilevato quattro gruppi principali di stazioni, caratterizzati da una diversa composizione degíi organismi e dei sedimenti. Gli apporti continentali e la profondità sembrano particolarmente important/ ne/la caratterizzazione di queste comunith di fondo. Parole chiave: policheti, distribuzione, fondi mobili, Mare Adriático 211 ANNALES • Ser. hist. nat. • i 3 - 2003 • 2 F to rta ru AllfFl «t if.: SPATtAl. DISTRIBUTION Of SOFT-BOrTOM POlYCHAtTtS AtONG WESTERN COAST .... 21 !-222 INTRODUCTION The northern Adriatic Sea is characterized by shallow depths (mean depth 33.5 m and maximum depth 70 m) and considerable river inputs. These inputs are particularly important on the western coast where the Po River discharges 50% of the total freshwater flow in the northern Adriatic and is the most important ai-lochthonous source of organic matter and nutrients for the entire Mediterranean Sea (Pagnotta etal., 1999). The shores are predominantly sandy along the northwestern coast and the deposition of fine materia! from northern rivers is relatively poor, settling along a discontinuous narrow belt. In the area influenced by the Po River, the belt of fine bottom sediments becomes larger and extends southwards. Offshore shelf sands are present (Frigriani & I rascari, 1990). The main oceanographic features of the basin are the annual variation in the density structure of the water column, characterized by a strong summer stratification and a dynamic separation between the waters of the basin proper and the coastal zone (Franco & Michelato, 1992). The northern Adriatic Sea is undergoing considerable anthropic pressure due to nutrients loading (urban and agricultural development) (Degobbis et a/., 2000), commercial fishing and tourism, including the infrastructure to support it. Furthermore, oxygen depletion deriving from natural hydrologicnl processes and/or eutrophication mainly for the area influenced by the Po (Faganeli et a/., 1985; Degobbis er al., 1991; justic, 1991; Voilenweider ft a/., 1992; Orel et ah, 1993a), periodically cause severe hypoxia and even anoxia in the bottom layers resulting in massive local benthos mortality (Aleffi ef al., 1992; Rinaldi et a!.r 199.3; Stachowitsch & Fuchs, 1995; Kollmann & Stachowitsch, 2001). In addition, the area is affected by occasional massive mucilage formations (Azam ef al., 1999; Degobbis et al., 1999) which, sinking to the bottom, asphyxiate the benthic fauna (Ore! ei at.. 1993b). Despite this environmental stress, the northern Adriatic Sea has Fjeen characterized by a rich benthic fauna and studied since the 19th century. In 1934-1936, Vatova (1949) sampled the macrobenthic communities of the northern and middle Adriatic and defined some ecological units as "zooce-noses", based on the dominant species. Subsequent studies on benthic communities have been either localized (Fedra etal,, 1976; Aleffi ei a/., 1996; Mancinelli et a/., 1998; Moodley ef al., 1998) or very general; in the latter, different data sets have been analysed together to achieve a comprehensive overview of the northern Adriatic benthos (Orel et al, 1987; Scardi et al., 2000). However, regarding the Polychaeta fauna, previous studies have been carried out only for some species and in narrow areas along the northwestern coast (Ambrogi ef al., 1993; Castelli et a/., 1999). On the contrary, along the northeastern coast, mainly characterized by rocky shores, the first surveys on poiychaetes started in the 19,h century (Grube, 1840, 1861), and were followed in the 20lh century by numerous taxonomic. studies; among the most important, wc can cite; Fauvel (1934, 1940), Amoureux & Katzmann (1971), Amoureux (1975, 1976), Bel Ian (1969) and Poiar-Domac (1978). The present study constitutes the first comprehensive survey carried out along the western coast of the northern Adriatic (from Trieste to Ancona) in order to determine the composition, structure and spatial distribution of the soft bottoms polychaetes. MATERIAL AND METHODS Within the framework of the PRISMA 1 Project (financed by the Italian Ministry of Research), carried out in May 1995, forty stations were sampled along the A w 'I 45' \ . ' V-'Vr^ " 1S;j ; RrvtRPo r; - Iv-yW ' - ty fcfie IS" 23. x'21 22ČL i ' * • .i.Sis '10. .9 i 2 V % \ « 3 v s . V* • V 44« s ... ... ,., 35 \ 311 32 W ' V 37s, 33 a>v 38 ' V ■ 3y\ v J ANCb^JA I _13! JA3 Fig; 1: Map of the study area showing the sampling stations. The four delimited areas (J, 2, 3, 4} correspond to the dendrogram groups. SI. 1: Zemljevid obravnavanega območja z vzorčeval-nimi postajami. Štiri označeni predeli (t, 2, 3, 4) ustrezajo skupinam v dendrograms 212 ANN ALES • Ser. hist. nat. - 13 • 2003 • 2 flori,ma AlEfTI et ¿t.: SPATIAL DISTRIBUTION OF SOFT-BOTTO-M POLYCHAETES ALONG WESTERN COAST ..., 211-722 western Adriatic coast, at depths ranging from 12 to 70 m (Fig. 1 ). At each station, five samples were collected with a 0.1 m" van Veen grab, sieved through a 1 mm mesh and preserved in buffered 4% formalin. Biomass (wet weight: WW) determinations were made by weighing fonnatin-preserved samples, following blotting on absorbent paper. Abundances were adjusted to 1 rrr. Species were grouped in feeding guilds according to Faucha Id & Jumars (1979). Four main groups were considered: suspension feeders (SF), surface-deposit feeders (SDF), subsurface-deposit feeders (SSDF) and carni-vores/ornnivores (C). The sediment texturai characteristics were taken both from Brambati et al. (1983) and Frascari ei al. (2000). The latter analysed the sediment features in the same PRISMA 1 Project. Univariate analyses used included: number of species, as a measure of alpha diversity, abundance and biomass. Multivariate analysis was performed using the Bray-Curtis similarity index on double square root transformed abundance data, using group-average clustering (PRIMER software package developed at the Plymouth Marine Laboratory) on the species determined for each station. RESULTS AND DISCUSSION At all stations, the polychaetes dominated in species number in comparison with other main macrobenthic taxonomic groups, such as molluscs, crustaceans and echinoderms (Fig. 2). A total of 6260 polychaetes were collected and 135 species were determined from 37 families. The dominant family in terms of species richness and abundance was by far Spionidae with 17 spe- 60 I 1 J 4 5 6 7 S 5 10 i| 13 I? 14 15 I« IJ I« 19 » Il 23 23 24 2? 2(i 27 lu 3U ïl 12 33 34 33 3('i 37 39 -10 stations Fig. 2: Number of species of the main macrobenthic taxa (polychaetes, molluscs, crustaceans, echinoderms) at each station. SI. 2: Število vrst glavnih makrobentoških taksonov (mnogoščetinci, mehkužci, raki in iglokožci) na posamezni postaji. c.ies and a total of 702 organisms (11.3% of the total), followed by Maldanidae and Sabellidae both with nine species and 507 (8.1%) and 273 (4.3%) individuals respectively, The most frequent species were Lumbrineris gracilis (75%), Ampharete acutifrons (63%), Spiophanes kroyeri (63%), Levinsenia gracilis (60%), Spiochaeto-plerus costarum (58%) and Melinna palmata (58%) (Append. 1). The number of species varied from 51 in st. 10 to only 3 species in st. 25. The highest values were found in zones A and B (Fig. 3). The average density was 313 ind. irC with maximum values of 1,420 ind. m'2 (st. 9) and minimum values of 56 irtd. rrr (st. 25); the highest densities were observed in the same two areas (A and B), in which the highest number of species was found (Fig. 4). These two zones are characterized by mixed sediments where sands dominate (Brambati ei a/., 1983), constituting a quite heterogeneous habitat and thus favouring higher species richness than fine and homogeneous sediments (Gray, 1974). Despite this fact, in A and B both the number of species and density are higher than would have been expected, since they are located offshore in deeper areas (25-30 m in A and 40-50 rn in B) while tn general, shallow coastal zones directly influenced by river inputs, where organic matter content is high, as in the vicinity of the Po delta, could be thought to be more favourable for the development of those populations. In addition, zone A is considered an area of sedimentary instability, due to the effects of anthropic factors, such as trawling fisheries and the long term effects of dumping operations carried out for years and stopped a couple of years before this study was initiated. 213 ANNALES • Ser. hist. nat. • i 3 - 2003 • 2 Floridi» ALtFfl ei al.: SI'AIIAL DISTRIBUTION OF SOFT-fiOTTOM TOIVCHAFTES ALONG WtSlfRN COAST .. .. 211-222 (t V ; . „ v ■n. .. ... . . 2.\f rieste (45' " 30 V 18 19. 20 21 22 O^. % RAVENNA- I 26 / 25^24 23 S>V l-l ■ 30 v B % ■ -27-V28. 29 ^0 > , , ^ . . 31 ••• 32 -v.. Fig. J: Contours of the species richness; A and H indicate the zones of highest values. SI. 3: Vrstna ftestrost; A in B označujeta cone z največjo gostoto. The average biomass was 17.6 g WW m" , with considerable differences among the stations. The highest value was 172.8 g WW m"~ in st. 1, due to the presence of the tube-dwelling poiychaete Chaetopterus variope-datus, whereas the minimum value of 1.73 g WW rrr was found at st. 15, where density was also low. The biomass values can help explain the evident differences found between muddy and prevalently sandy bottoms, since densities are highest in fine sands, but with lower values of biomass than in stations characterized by muddy sediments; this is mainly due to the prevalence of small size polychaetes. Over the whole area, the dominant species were: Owenia fusiformis, characteristic of sandy sediments, Maldaneglebifex, characteristic of muddy bottoms, and L. gracilis, without any definite preference for a specific type of sediment. Cluster analysis on abundance data evidenced four main groups of stations (Fig. 51 characterized by different community types and different sediment, features. Area 1 (Fig. 1) was located along the coastline in muddy bottoms influenced by the main North Adriatic rivers inputs (Isonzo, Tagliamento, Piave, Adige, Po). The most abundant and frequent species of this community were: M. glebtfex, L. gracilis, S. costarum and A. acutifrons (Tab. 1). The mean species richness in this group was 21 Species, while average density was 260 ind. its \ The biomass was the highest (27 g WW m~~), due to large species such as C. variopedatus, Marphysa sanguines and Clycera unicornis. Inside this wide group, differences were clear between stations located north and south of the Po River deita. The mean species number and density of the northern stations (st. 1-13) were, respectively, 27 species and 358 ind. m"J, whereas lower values for both parameters (16 species, 182 ind. m ") were recorded at the stations influenced by the Po. In the latter zone, high sedimentation rates, high organic matter inputs and periodic hypoxic conditions prevail so that the community is affected by environmental instability (Creima el a/., 1991; Tahey ei at, 1996). In Area 2 (Fig. 1) sandy sediments dominated and diversity and density had the highest values, with averages of 38 species and 554 ind. m"2 (Tab. 2), while the biomass values were low due to the presence of smaller polychaetes than those found in Area 1. The most, representative species were: O. fusiformis, Myriochele ocu-lata, and Nothria conchylega, which prefer medium size muddy sands with shell debris (Glemarec, 1991; Am-brogi et al., 1995). In the deepest stations (60-70 m) Aponuphis fauveli was dominant (310 ind. m'2 in st. 35) and replaced A. bilineata also found in the stations of this group, but at a maximum depth of 40 m. The third group of stations (Area 3) is located along the offshore border of Area 1, south of the Po River delta, Muddy bottoms dominate as in Area 1, but in deeper waters (mean depths of 33 m versus 20 m in Area 1) and with lower organic matter content in the sediments (I rascari et al., 2000). The dominant species were: Sthenolepis yhleni and the burrowing poiychaete Sternaspis scutate, which jointly represented 69% of the polychaetes abundance and 83% of the biomass. Diversity and density values were lower than in the other groups and reached an average value of 8 species and 84 ind. m"2; the biomass values were the lowest there. Stations 3 and 8 (Area 4) constitute the smallest group in the dendrogram and are located in the area between the Isonzo River arid the Gulf of Venice, at 10 to 25 m depth (Ore! et al., 1987). This zone is characterized by coarse sandy bottoms with beachrocks, defined as medium to fine sandstones with carbonate cement by Brambati ei al. (1983). The dominant species were A. bilineata and Prionospio caspersi; the latter was 214 ANN ALES • Ser. hist. nat. - 13 • 2003 • 2 Hotteln ALHTI et ;•' V.-^Trieste v . - .. '-'IRAN VENEZ^ g a . •-:1.1?- '14 W 45°t ■ . "I '• . 17- .-.L r RIVER. PQ ' l6 'jg» v. 9 19. 20 21 22 ,: % ■ •ZS. 25 24. 23.'- « ! t /" -V o V _L \ / . v \ Monticellina dorsobranchialis 1 1 ? Grratulidae indet. 116 25 1.2,3,4 DorviMcfidae Schislomerit)gos neglectus 1 1 i £. Se is to me ringos rudo Iph i i 4 3 1,2 Eunicidae Eunice vittata 101 14 1,2,3 Lvsidice ninetta 3 ■J A 1,4 Marphysa bellii 57 13 1,2,3 Maiphysa sanguínea (0 G 1 Nematanereis unicornis 29 4 2 FSabefligeridae Pherusa monoüfera 6 3 1,2 Pherusa plumosa 7 ■j 1,2 Piromis eruca i 1 2 Ciyceridae Glycera alba 7 4 2,3 Glycera capita ta 9 4 2,3 Glycera rouxii 36 17 1,2,3 Glycera sp. 15 8 1,2 Glycera tesselata 1 1 2 Glycera tridactyla 9 4 2,4 Glycera unicornis 58 19 1,2,3,4 Goniadidae Geniada tnaculata 61 9 1,2,4 Glycinde nordmanni 1 1 •i Heslonidae Gvptis propinqua 5 3 ~t Ophiodromus flextiosus 3 3 1,2,4 Hesionidae indet. 3 2 1,2 219 ANNALES • Ser. hist, nal. - 13 • 2003 • 2 Flc.fi.nis ALEfft ci Hi. SPATIAI DISTRIBUTION Of SOfT-BOTTOM POLVCHA£Tf:S AlONC Wi$ItftN COAS1 .... 211-122 Family Species Tot. abund. Frequency Area Uimbrinencfae Lumbrineris gracilis 456 30 1,2,3,4 L umbrineris telreiiHi 86 17 1,2,4 tumbrineris sp. 2 1,3 Lumbrineris tetraura 31 13 1,2,3 Ninoe kinbergi 3 1 2 Magelonidae Mageicna alleni 24 11 1,2,3 Magetona minula 8 4 2 Magelona sp. 5 5 1,2 Maldanidae Clymenura clypeata 11 4 1,2 Euclymene lumbricoides 4 2 2 F. udyrnene oerstedi 34 4 1,2 Euclymene paletmitana 66 15 1,2,4 Maldane gtebifex 377 20 1,2 Metasychis gotoi I 1 T JL Pdaloproctus terricolus 1 1 2 Praxillella affinis 11 3 2 Praxillella lophosela 2 2 Maldanidae indet. 106 16 1,2,3,4 Nephtydae Microriepthys sp. 4 3 1,2,4 Nepthys hombergi 13 6 2 Nepthys hysiricis 79 20 1,2,3 Nepthys incisa 28 6 1,2,3 Nepthys sp. 14 4 1,2,3 Nereididae Ceratonereis costae 1 1 1 Nereis lame/loss 21 11 1,2,3 Nereis rava 6 2 1,4 Nereis sp. 5 4 1,2 Perinereis sp. 9 5 1,2 Onuphidae Aponuphis bilineata 142 12 1,2,4 Aponuphis fauveli 302 5 2,3 Diopatra neapolitaria 3 2 1 Nothria conchylega 195 8 1,2 Onuphis quadricuspis 5 1 1 Onuphis sp. 74 4 2 Opheliidae Ophelina cylindricaudata 13 4 2 Orbiniidae Orblnia cuvie/i 2 2 1,4 Phylo foetida 3 2 1 Scolopios armiger 2 1 2 Oweniidae Mvriochele oculata 172 17 1,2,3 Owertia fusiformis 547 20 1,2,3,4 Paraiacydoniidae Paralacydonia paradoxa 73 11 1,2 Paraonidae Aricidea claudiae 3 1 2 Aricidea mariannae 157 1 4 Cirrophorus furcatus 3 2 2 Levinsenia gracilis 130 24 1,2,3,4 Paradoneis lyra 58 14 1,2 Paraonides neapolitana 2 2 1,2 Paraonidae indet. 366 28 1,2,3,4 Recti nariidae Pectinaria auricoma 37 10 1.2 Pectinaria belgica 3 3 1,2 Pectinaria koreni 12 8 1,2 220 ANNALtS • Ser. hist. nat. • 13 • 2003 ■ 2 f lofian.a ALEFFI « a/.; ŠPATpU DISTRIBUTION Of SOFT-BOTTOM POLVir.HAFTFS A!ONG WESTERN'COAST .... 21 i-22J Family Species Tot. abund. Frequency Area Phyllodocidae Mysts pic ta 10 4 1,2 PhvHodoce Hneata 7 7 1,2 Phyllodoce sp. 2 2 1,2 Phyllodocidae indet. 2 2 2 Pilargiidae Andstrosyllis groenlandica 77 14 1,2,3,4 Pilargis verrucosa 9 8 1,2,3 Poecilochaetidae Poecilochaetus serpens .38 18 1,2,3,4 Poiynoidae Harmothoe sp. 3 2 3 Poiynoidae indet. 55 24 1,2,4 Sabellidae Chone acustica 1 1 2 Chone coHan's 22 7 1,2 Chone duneri 109 13 1,2,4 Euchone rosea 89 10 1,2 Euchone rubrocincta 12 7 2.3 Jasmine ira caudata 2 2 2 fasmineira elegans 24 7 2,4 Megalomma vesiculosum 11 8 1,2 Myxicoia infundibulum 3 1 4 Sabellidae indet. 16 3 2 ScaiibreRmatidae Seal ¡bregma inflatum 10 2 2 Serpulidae Dilrupa arielina 2 1 2 Hydroides norvegicus 1 1 2 Pomatoceros triqueter 4 2 1 Serpula concharum 3 2 2 Serpu/a vermicularis 3 3 1,4 Sigalionidae Psammolvce arenosa 1 1 2 Sthenelais boa 3 2 2,4 Sthenelais limicola 16 4 2 Sthenelais minor 3 1 i Sthenelais sp. 1 1 3 Sthenohpis yhleni 211 21 1,2,3 Spionidae Laonice cirrata 164 12 1,2 Polvdora caeca 1 1 1 Po!vdora flava 26 10 1,2,4 Polvdora sp. 2 2 1 Prionospio caspersi 73 8 1,2,4 Prionospio cirrifera 47 10 1,2 Prionospio malmgreni 149 16 1,2,4 Prionospio sp. 3 1 2 Prionospio steenstrupi 4 2 '> Pseudopolydora antenna!a 2 2 1,2 Scolelepis cantabra 1 1 2 Scolelepis tr¡denials 3 0 A. 2,4 Spio decoratus 2 1 ? Spio iilicornis 5 3 1,2,4 Spio multioculata 14 4 5,4 Spiophanes bombyx 3 2 1.4 Spiophanes kroyeri 203 25 1,2,3 Spionidae indet. 10 5 1,2 Sternaspidae Stemaspis scutata 197 22 1,2,3 221 ANNALES • Ser. hist. nat. -13 2003 • 2 FiDfians ALEFFI et aJ.; SPATIAL DISTRIBUTION Ot SO! f IJOITOM KHYCHAIITF5 ALONG WFSTFRN COAST .... 211-322 Family Species Tot. aburtd. Frequency Area Syilidae Syllis atmilhris 3 3 2,4 Syllis coma ta 15 5 1,2 Syllis sp. 2 2 1,2 Terebellidae Amphitrite cirrata 3 2 1 Amphitrite edwarsi 2 1 1 Amphitrite sp. 16 3 2 Lanic.e conchylega 23 9 1,2,3 Pista cris! at a 27 8 1,2 Poiycirrus sp. 11 5 2 Strebhsoma bairdi 4 3 2 Terebellidae Indet. 17 6 1,2 Trichobranchiidae Terebeilides stroemi 36 16 1,2,3 Trichobranchus glacialis 1 1 2