Research Article Mediterranean Marine Science Indexed in WoS (Web of Science, ISI Thomson) and SCOPUS The journal is available online at http://www.medit-mar-sc.net DOI: http://dx.doi.org/10.12681/mms.15117

Benthic Hydrozoans as Potential Indicators of Water Masses and Anthropogenic Impact in the Sea of Marmara

NUR EDA TOPÇU1, LUIS FELIPE MARTELL1, 2, IZZET NOYAN YILMAZ3 and MELEK ISINIBILIR1

1Department of Marine , Faculty of Aquatic Sciences, Istanbul University, Turkey 2University Museum of Bergen, Department of Natural History, University of Bergen, Norway 3Institute of Marine Sciences and Management, Istanbul University, Turkey

Corresponding author: [email protected] Handling Editor: Carlo Bianchi

Received: 27 November 2017; Accepted: 23 March 2018; Published on line: 18 June 2018

Abstract Changes in the abundance and distribution of marine benthic hydrozoan are indicative of variations in environmental conditions in the marine realm. The comparative analysis of such assemblages can improve our understanding of environmental and ecological conditions in the Sea of Marmara, a strongly stratified and heavily populated inland sea connecting the Aegean and Black seas, on route of national and international maritime traffic. We compared the hydrozoan assemblages occurring in harbours with those developed at natural sites, as well as the assemblages associated with the Black Sea water mass versus the Mediterra- nean water mass in the vicinities of the Prince Islands, the north-easternmost section of the Sea of Marmara. Sampling took place at 12 stations, once in March 2015 and once in August 2015 in order to cover species with both warm and cold water affinities. Multivariate analyses showed that benthic hydroid assemblages with both affinities differed significantly between the heavily -traf ficked harbours of the Prince Islands (connected to the metropolis of Istanbul) and areas without human settlements and maritime traffic. In addition, highly distinct hydroid assemblages were found characterizing both areas with water of Mediterranean origin and areas with water from Black Sea origin. Based on our results, we discuss the potential for the use of these organisms as indi- cators of water masses and anthropogenic impact at the regional level.

Keywords: Hydroids; Prince Islands; harbours; Black Sea water; Mediterranean water; bioindicators.

Introduction 1972, 1977, 1987), as well as of climate change (Puce et al., 2009; González-Duarte et al., 2014), and anthro- Benthic hydrozoans are common components of bot- pogenic impact in harbours (Megina et al., 2013, 2016). tom communities in tropical and temperate shallow wa- Despite their ecological importance and advocated ters, where they form distinct and often characteristic potential as bioindicators, there are still only few studies assemblages in different marine habitats (Boero, 1984). focusing on hydrozoan assemblages from harbours ver- They have a high potential as monitor and indicator spe- sus assemblages on natural sites, and there is not enough cies of environmental conditions in the marine realm research intended to evaluate the suitability of benthic (Mergner, 1977), in part because of their ubiquity, but hydrozoans as indicators of important oceanographic also due to other life-history traits such as the sessility features such as water masses. In the Sea of Marmara in of their colonies (which prevent migration due to chang- particular, research on hydrozoans has historically been ing conditions), their differential sensitivity to stress, focused on the production of species inventories (e.g. Os- and their rather rapid response to disturbances (Gili & troumoff, 1896; Demir, 1954), with recent studies report- Hughes, 1995). Morphological modifications in individ- ing on the punctual presence of either pelagic (Isinibilir ual colonies of some benthic hydrozoans are indicative et al., 2010; Isinibilir et al., 2015a; Yılmaz et al., 2017) or of turbulent conditions (e.g. da Silveira & Migotto 1991) benthic (Albayrak & Balkıs, 2000; Marques et al., 2000; and heavy metals pollution (Karbe, 1972; Theede et al., Topçu et al., 2016) taxa. As a result, sixty-two species of 1979), while local changes in abundance and distribution hydrozoans have been recorded so far in the Sea of Mar- of hydrozoan species have been linked to variations in in- mara (see Isinibilir & Yılmaz, 2016 for a check-list), al- tensity and speed of water flow (Riedl 1966). As a group, though more can be expected as sampling effort increases these organisms have been used as indicators of partic- in the region. The documented hydrozoan diversity in the ular hydrodynamic conditions (Wedler, 1975; Mergner, neighbouring Aegean Sea was also not very high until

Medit. Mar. Sci., 19/2, 2018, 273-283 273 recently, especially along the Turkish , but late is around 38.5, while the temperature is around 14-15°C reports highly increased the number of species, show- throughout the year. In the upper layer, the salinity is ing that the apparently low species richness was mainly around 20 at the north of the Sea of Marmara and the due to limited research effort in the area (Isinibilir et al., temperature varies between 8 and 24°C depending on the 2015b; Topçu et al., 2017). season. The Sea of Marmara offers a unique opportunity for The specific sampling area, the Prince Islands, are the evaluation of the potential of benthic hydrozoans as located in the northeast Sea of Marmara, very close to indicators of environmental conditions. It is a semi-en- the highly populated coasts of Istanbul, between Kadıköy closed sea, connecting the Black Sea to the Aegean Sea and Kartal (Fig. 1). The northern coasts of the larger via the Turkish straits system, and it is characterized by islands (facing Istanbul) are urbanized and have sever- a two-layer stratification, with the brackish surface lay- al harbours with different purposes, while the southern er formed by the Black Sea water mass flowing into the coasts are mainly uninhabited and pristine. The two Sea of Marmara through the Istanbul Strait (Bosphorus) north-easternmost sampled islands, Yassıada and Sivria- and the more saline Mediterranean Sea water entering da, are small islands with harbours and some buildings through the Çanakkale Strait (Dardanelles) and flowing used in past times, but they are currently uninhabited. approximately 20 m below the brackish layer (Beşikte- The depth at the northern coasts of the Prince Islands is pe et al., 1994). The Turkish straits system serves as an generally around 20 m and do not descend below 50 m in ecological barrier, a biological corridor and an acclima- the area between Istanbul and the archipelago; therefore tization zone for the biota of the Mediterranean and the the Mediterranean water layer (below 20-30 m) is almost Black Sea (Öztürk & Öztürk, 1996). These characteristics never reached in this part. The southern coasts are char- make the Sea of Marmara particularly interesting for the acterized by a descending profile that rapidly descends to study of benthic hydrozoans in relation to clearly defined 40-50 m. All sampling stations were characterized by a water masses. Within the Sea of Marmara, the Prince Is- lands (located at the north-easternmost sector) constitute a good example of a “natural laboratory” for the com- parative study of benthic communities, since they include both heavily trafficked small harbours and natural areas with high habitat heterogeneity and diver- sity of faunistic (e.g. octocoral) assemblages (Topçu & Öztürk, 2015), while at the same time they offer the op- portunity to observe the typical change of the Marmara vertical profile from Black Sea habitats to Mediterranean ones, including the coralligenous. In this sense, the dif- ferent anthropogenic pressure at the north and south of the islands allows for an interesting comparison between the fauna associated with harbours versus natural sites, while the effect of the water masses on the abundance and distribution of the species can be easily evaluated at the southern part of the archipelago. The aim of this study was therefore to investigate the assemblages of benthic hydrozoans associated with the typical water masses of the Sea of Marmara (Black Sea water mass vs Mediterra- nean water mass), and evaluate the specific characteristics of benthic hydroid assemblages developing in harbours in comparison with those developing in well-preserved, ad- jacent natural areas.

Material and Methods

Study Area and Sampling Design

The circulation in the Sea of Marmara is character- ized by a strong two-layer stratification, with a Black Sea Fig. 1: (A) Location of Prince Islands and sampling sites in originated brackish upper layer flowing southwards and a the Sea of Marmara. Squares represent harbours and circles lower Mediterranean layer flowing northwards. The two represent natural coasts. (B) Google Earth satellite picture of layers are separated by a permanent halocline, located Büyükada, Heybeliada and Burgazada, showing the urbaniza- at 15-30 m depth depending on the season and location tion at the northern coasts and locations of the harbours, in con- (Beşiktepe et al., 1994). In the lower layer, the salinity trast to the pristine southern coasts.

274 Medit. Mar. Sci., 19/2, 2018, 273-283 substrate composed of a mixture of rocks, sand and bio- Statistical Analysis concretions of dead shells/polychaete tubes/pebbles. S9 and S11 comprised dense facies of the yellow gorgonian Species richness, total hydroid abundance and di- Eunicella cavolini. versity (as measured by Simpson’s index 1-D) between The sampling was designed to compare benthic hy- the two layers and the two levels of anthropogenic im- drozoan assemblages: pact (harbours vs natural sites) for both warm-water and (1) in the upper layers of natural coasts (southern cold-water assemblages were compared by non-paramet- coasts) versus the harbours (northern coasts) of the Prince ric Kolmogorov-Smirnov tests performed with GraphPad Islands, Prism version 6.01 for Windows. (2) in the upper layer (Black Sea waters) versus the To test for differences in assemblage composition, lower layer (Mediterranean waters) of (southern) natural sample by species matrices were calculated for abun- coasts. dances of species at all sites. The abundance matrices Six sites at the north (harbours) and six sites at the were square-root transformed and the samples were south of the islands were thus selected for sampling, with compared on the basis of species abundances using the the sites at the south sampled at two depth layers. Upper Bray-Curtis similarity index. Non-Metric multidimen- layer samplings were performed at 1 – 6 m depth while sional scaling (nMDS) analyses were performed to visu- lower layer samplings were performed at 30 – 35 m depth. alize changes in the assemblages. Differences in the hy- The sampling took place once in March 2015 and once in drozoan assemblages according to the tested factors were August 2015 in order to cover species with both warm identified using permutational multivariate analysis of and cold water affinities. In each station, benthic hydroid variance (PERMANOVA, Anderson, 2001); while a sim- colonies from the bottom and fragments of diverse sub- ilarity percentage analysis (SIMPER) was performed to strates supporting or susceptible to support hydrozoan determine the contribution of each taxon to the observed colonies (e. g. algae, , etc.) were collected similarities and dissimilarities between groups. Based on by two trained SCUBA divers using visual collection the above-mentioned sampling design that contemplates techniques (Boero & Fresi, 1986; Megina et al., 2013). the differences between the northern and southern coasts One of the divers picked up all hydroid colonies or their of the islands, two different experimental designs were potential substrates from two randomly placed transects employed in the analysis, each including two factors: of 6 m2. The other diver conducted a visually-oriented Design 1) factors “anthropogenic impact” (fixed, two collection in order to obtain an efficient representation of levels: not impacted [southern coasts – upper layer] and hydroid species diversity in shallow coastal benthic hab- harbours [northern coasts – upper layer]) and “affinities” itats (Piraino et al., 2013), selectively collecting hydroid (fixed, two levels: cold and warm); and Design 2) fac- colonies or their potential substrates from a single, larger tors “water mass” (fixed, 2 levels: upper layer of southern homogeneous bottom belt (5m x 10 m length = 50 m2) at -not impacted- coasts [Black Sea water] and lower layer the targeted depth zone. [Mediterranean water]) and “affinities” (fixed, two- lev Samples were fixed immediately after collection in els: cold and warm). All the above analyses and diversity a 10% formalin-seawater solution. All hydrozoans were index computations were carried out with the Primer v6 sorted and identified in the laboratory to the lowest taxo- software (Clarke & Gorley, 2006). nomic level with the aid of specialized scientific literature (Bouillon et al., 2004, 2006). The identity of the taxa not Results previously recorded for the area was confirmed through a comparison with specimens included in the Forty-one hydrozoan taxa were found along the coasts Collection, University of Salento, Italy (accession num- of Prince Islands (Table 1). To our knowledge, 17 repre- bers for relevant species as in Gravili et al., 2015) and the sent first records for the Sea of Marmara, with 7 of them University Museum of Bergen, Norway (accession num- being also first records for the Turkish coastal area. In bers ZMBN 10781, 10788, 10789, 13283, and 13597). the case of sp., Halecium sp. 1 and sp. 2, For most of the species, hydroid abundance was calculat- Campanulinidae sp., Campanulina sp, Cuspidella sp., ed by counting the number of polyps in each site (see Me- Corynidae sp. 1 and sp. 2, and sp., iden- gina et al., 2013, González-Duarte et al., 2014); however, tification to species level was impossible, either because for large colonies (≥ 10 cm high) of dichotoma, of the small amount of material available or because of Kirchenpaueria pinnata and muscus the the lack of characters essential for identification. Species number of polyps was estimated by averaging the total richness of cold-affinity hydrozoans was not significantly number of polyps in 15 randomly selected colonies and different from that of warm-affinity hydrozoans, neither multiplying this number by the total number of colonies between the studied water masses nor in the unimpacted observed in the station (< 1% of the entries in the abun- sites or the harbours (Fig. 2). Conversely, the abundance dance matrix). of hydrozoans in both cold and warm-affinity assemblag- es were significantly different from each other in all cases

Medit. Mar. Sci., 19/2, 2018, 273-283 275 Table 1. Species found at Prince Islands coasts according to water masses (the upper layer (Black Sea waters) versus the lower lay- er (Mediterranean waters)), sites (natural versus impacted (harbours) and sampling time (March [M] or August [A]). First records for the Sea of Marmara are in bold. Species recorded for the first time inTurkey are marked with *.

Upper Layer Species Natural Impacted Lower layer Sampling time Aglaophenia octodonta Heller, 1868 M-A Amphinema dinema (Péron & Lesueur, M-A 1810)* Antennella secundaria (Gmelin, 1791) M-A Anthoatecata sp. A (Allman, 1863) M-A Campanularia hincksii Allder, 1856 M Campanulina sp. A Campanulinidae sp. M Clytia viridicans (Leuckart, 1956) * M Clytia gracilis (Sars, 1850) M Clytia hemisphaerica (Linnaeus, 1767) M-A Clytia linearis (Thorneley, 1900) M-A Clytia paulensis (Vanhöffen, 1910) M-A Coryne eximia Allman, 1859 M Corynidae sp.1 M Corynidae sp.2 A Cuspidella sp. A Ectopleura larynx (Ellis & Solander, 1786) M Eudendrium armatum Tichomiroff, 1890 M Eudendrium glomeratum Picard, 1952 M Eudendrium racemosum (Cavolini, 1785) M Eudendrium sp. A Filellum serpens (Hassall, 1848) M-A Halecium beanii(Johnston, 1838) M-A Halecium sp.1 M Halecium sp.2 A Halecium tenellum Hincks, 1861 M Kirchenpaueria halecioides (Alder, 1859) M Kirchenpaueria pinnata (Linnaeus, 1758) M-A Lafoeina tenuis Sars, 1874 M Laomedea calceolifera (Hincks, 1871) M-A Laomedea flexuosaAlder, 1857 A Nemertesia tetrasticha Meneghini, 1845 A (Linnaeus, 1758) M-A Plumularia setacea (Linnaeus, 1758) A Podocoryna exigua (Haeckel, 1879)* A Proboscidactyla ornata (McCrady, 1859) * M Racemoramus panicula (G. O. Sars, 1874) M * Sertularella polyzonias (Linnaeus, 1758) M-A Stylactis inermis Allman, 1872* M Zanclea giancarloi Boero, Bouillon & M Gravili, 2000*

276 Medit. Mar. Sci., 19/2, 2018, 273-283 Fig. 3: MDS of the samples based on the cold/warm affinity hydroid species composition of the upper and lower layers.

Fig. 2: Box and whiskers plot of species richness, abundances and Simpson indices; of cold- and warm-affinity hydrozoan -as semblages in the lower layer, and in the upper layer of natural coasts and harbours.

(in the lower layer versus upper layer, and in the unim- pacted sites versus harbours, respectively), cold-affinity Fig. 4: MDS of the samples based on the cold/warm affinity hydrozoans being generally more abundant. Diversity, hydroid species composition of natural coasts and harbours. species richness and abundance of hydrozoans in the upper and lower layers were significantly different from each other, with Simpson diversity indices being much abundance at some sites. The two groups of seawater lay- higher in the lower layer. Species richness, abundance ers had strong dissimilarity (84%). and diversity were also significantly different between The hydrozoan assemblages in the natural, not impact- the unimpacted sites and the studied harbours, except for ed sites were significantly different from the assemblages species richness in the cold-affinity assemblage. developed in the harbours (PERMANOVA comparisons, The PERMANOVA comparisons revealed that the Table 2). In turn, the corresponding nMDS plot reflects assemblages in the upper and lower layers were sig- with a well goodness of fit the distinction between cold nificantly different from each other, with the cold-water and warm assemblages, but that of localities was less evi- assemblages being also significantly different from the dent (Fig. 4). The “harbours” were grouped together with warm-water ones (Table 2; Table S1). In addition, the a similarity of 67% according to the SIMPER analysis, nMDS plot showed the groupings of upper and lower lay- mainly due to Obelia dichotoma, which typically occurs er samples with a fair goodness of fit (Fig. 3). The SIM- in the harbours (Table 4). The two tested groups had a PER analyses suggest that the average similarity in the dissimilarity of only 46%. The group of cold-affinity -hy group of “upper layer” is rather high (80 %) and the main drozoan assemblages had a strong similarity (85%) re- species responsible for this similarity is Obelia dichoto- gardless of the impact of each site, due mainly to Obe- ma with a contribution of 87 % (Table 3). The group of lia dichotoma which contributed 91 % of the similarity “lower layer” revealed only a fair similarity (44 %), due alone. The group of “warm-affinity” hydrozoan assem- mainly to Bougainvillia muscus that had a relatively high blages had a less strong similarity (62%), associated to

Medit. Mar. Sci., 19/2, 2018, 273-283 277 Table 2. Results of the PERMANOVA testing for the effects of (A) the seawater layer (upper [Black Sea originated] and lower [Mediterranean originated]) and affinity (cold and warm) and (B) anthropogenic impact (not impacted versus harbours) and af- finity(cold and warm) on the hydrozoan assemblages.

PERMANOVA (A) Source df SS MS Pseudo-F P(perm) Layer 1 38307 38307 35.769 0.0001 Affinity 1 18404 18404 17.185 0.0001 Layer x Affinity 1 24871 24871 23.223 0.0001 Res 44 47121 1070.9 Total 47 1.287E5 Pairwise comparisons Within level ‘Upper’ of factor ‘Layer’ Within level ‘Lower’ of factor ‘Layer’ Groups t P(perm) Groups t P(perm) Cold, Warm 9.2267 0.0001 Cold, Warm 2.5088 0.0001 Within level ‘Cold’ of factor ‘ Affinity ‘ Within level ‘Warm’ of factor ‘ Affinity ‘ Groups t P(perm) Groups t P(perm) Upper, Lower 5.6639 0.0001 Upper, Lower 5.2539 0.0001

PERMANOVA (B) Source df SS MS Pseudo-F P(perm) Impact 1 16407 16407 30.336 0.0001 Affinity 1 61229 61229 113.21 0.0001 Impact x Affinity 1 4608.4 4608.4 8.5208 0.0001 Res 44 23797 540.84 Total 47 1.0604E5 Pairwise comparisons Within level ‘Cold’ of factor ‘ Affinity ‘ Within level ‘Warm’ of factor ‘ Affinity ‘ Groups t P(perm) Groups t P(perm) Natural. Harbour 4.2036 0.0004 Natural, Harbour 4.4536 0.0001 Within level ‘Natural’ of factor ‘Impact’ Within level ‘Harbour’ of factor ‘Impact’ Groups t P(perm) Groups t P(perm) Cold, Warm 9.2267 0.0001 Cold, Warm 6.9163 0.0001

Kirchenpaueria pinnata, the abundance of which highly Mediterranean Sea (Isinibilir & Yılmaz, 2016; Gravili et increased in the warm period. The two groups of affini- al., 2013), and the lack of research effort in the area is ev- ties had a dissimilarity of 80 % due to the change in the idenced by the fact that almost every study dealing with dominant species. hydrozoans in the area includes at least one new record or documents the extension of the distribution range of a Discussion species (confer Isinibilir & Yılmaz, 2016 and referenc- es therein). Our survey, despite the relatively small area The scarcity of records of hydrozoan species in the Sea covered, represents an increase higher than 20% in the of Marmara contrasts sharply with the general view of the number of hydrozoan species reported for the Sea of Mar- Mediterranean Sea as a well-studied region in terms of mara, and greatly elevates the number of recorded species its hydrozoan diversity (Bouillon et al., 2004). Both the in the area. Not surprisingly, most of the new records ob- number of species documented and the number of studies served in our study fill up distributional gaps for well- focused on hydrozoans are lower in the Sea of Marma- known, typical Mediterranean species such as Campanu- ra than in comparable regions in the western and central laria hincksii, Clytia linearis, Clytia paulensis, Lafoeina

278 Medit. Mar. Sci., 19/2, 2018, 273-283 Table 3. Results of the SIMPER analyses showing similarities within groups of layer (upper and lower) across affinities (warm and cold) and similarities within groups of affinities across all layer groups; dissimilarities between pairs of groups and the species mostly responsible for the observed differences.

Group Upper: Average similarity: 79.77 Group Cold: Average similarity: 67.70 Species Av.Sim Sim/SD Contrib% Cum.% Species Av.Sim Sim/SD Contrib% Cum.% Obelia dichotoma 69.39 2.83 86.99 86.99 Obelia dichotoma 54.5 1.43 80.51 80.51 Kirchenpaueria 9.99 0.51 12.53 99.52 Bougainvillia muscus 9.77 0.82 14.43 94.94 pinnata

Group Lower: Average similarity: 44.05 Group Warm: Average similarity: 56.12 Species Av.Sim Sim/SD Contrib% Cum.% Species Av.Sim Sim/SD Contrib% Cum.% Bougainvillia muscus 16.7 2.06 37.92 37.92 Obelia dichotoma 24.91 1.02 44.38 44.38 Obelia dichotoma 10.02 1 22.75 60.67 Kirchenpaueria pinnata 10.01 0.51 17.84 62.22 Nemertesia tetrasticha 5.84 0.51 13.26 73.93 Bougainvillia muscus 7.23 0.94 12.89 75.11 Sertularella polyzonias 3.54 0.52 8.03 81.96 Nemertesia tetrasticha 5.93 0.52 10.56 85.67 Halecium beanii 2.54 0.35 5.77 87.73 Sertularella polyzonias 3.19 0.47 5.68 91.35 Filellum serpens 1.74 0.59 3.94 91.68 Groups Cold & Warm: Average dissimilarity = 73.59 Groups Upper & Lower: Average dissimilarity = 84.33 Species Av.Diss Diss/SD Contrib% Cum.% Diss/ Species Av.Diss Contrib% Cum.% Obelia dichotoma 35.65 1.22 48.44 48.44 SD Obelia dichotoma 32.2 1.28 38.18 38.18 Nemertesia tetrasticha 7.03 0.73 9.56 58 Bougainvillia muscus 10.87 2.12 12.89 51.07 Kirchenpaueria pinnata 4.92 0.79 6.68 64.68 Nemertesia tetrasticha 7.84 0.7 9.3 60.37 Sertularella polyzonias 4.2 0.68 5.7 70.38 Halecium beanii 5.92 0.66 7.02 67.39 Halecium beanii 3.96 0.56 5.38 75.76 Sertularella polyzonias 5.69 0.77 6.74 74.13 Bougainvillia muscus 3.61 0.91 4.91 80.67 Kirchenpaueria 5.29 0.74 6.27 80.4 Antennella secundaria 1.96 0.46 2.67 83.34 pinnata Antennella secundaria 2.49 0.5 2.95 83.35 Anthoatecata sp. 1.87 0.3 2.54 85.88 Filellum serpens 2.42 0.82 2.87 86.22 Filellum serpens 1.62 0.7 2.21 88.09 Anthoatecata sp. 2.2 0.3 2.61 88.83 Campanulina sp. 1.29 0.63 1.75 89.83 Eudendrium Campanulina sp. 1.58 0.63 1.87 90.7 0.83 0.38 1.13 90.96 glomeratum

tenuis, Halecium tenellum, Podocoryna exigua, Kirchen- lower than temperatures at similar depths elsewhere in paueria pinnata, Plumularia setacea, and the large spe- the Mediterranean) (Çoban-Yıldız et al., 2000), and this cies of Eudendrium; all taxa already documented has been advocated as one of the main explanations for in the neighbouring Aegean and/or Black seas (Marino- the presence of deep-water cnidarians species at shallow poulos, 1979; Çınar et al., 2014; Isinibilir et al., 2015b); depths in the area (Topçu & Öztürk, 2015). The same while other records (e.g. Clytia viridicans, Stylactis iner- phenomenon may be involved in the maintenance of pop- mis, Amphinema dinema, Zanclea giancarloi) constitute ulations of Racemoramus panicula and Proboscidactyla range extensions for species previously collected some- ornata around the Prince Islands. To our knowledge, the where else in the eastern Mediterranean (Adriatic, Ionian, only previous record of polyps of P. ornata in the Med- or Levantine coasts) but not reported hitherto from the iterranean Sea is that of Brinckmann &Vannucci (1965) Aegean or the Black seas. who found it in high numbers in depths of ca. 100 m in Conditions similar to those of higher depths in the the Bay of Naples, but we found several polyps growing Mediterranean Sea can be found in shallower waters in on tubes of Branchiomma sp. off Burgazada at shallower the Sea of Marmara due to a combination of regional depths (around 30 m). The unexpected finding of colonies oceanographic features (high turbidity preventing day- of R. panicula at 30 m off Büyükada and Sivriada, on the light at very shallow depths, temperatures below 20 m other hand, contrasts with the typically deep distribution

Medit. Mar. Sci., 19/2, 2018, 273-283 279 Table 4. Results of the SIMPER analyses showing similarities within groups of anthropogenic impact (natural coasts and har- bours) across affinities (warm and cold) and similarities within groups of affinities across all anthropogenic impact; dissimilarities between pairs of groups and the species mostly responsible for the observed differences.

Group Natural: Average similarity: 79.77 Group Cold: Average similarity: 84.59 Species Av.Sim Sim/SD Contrib% Cum.% Species Av.Abund Av.Sim Sim/SD Contrib% Cum.% 69.39 2.83 86.99 86.99 Obelia 299.85 76.94 4.57 90.96 90.96 Obelia dichotoma dichotoma Kirchenpaueria 9.99 0.51 12.53 99.52 pinnata Group Warm: Average similarity: 62.50 Group Harbour: Average similarity: 67.32 Species Av.Abund Av.Sim Sim/SD Contrib% Cum.% Species Av.Sim Sim/SD Contrib% Cum.% Kirchenpaueria 59.62 28.23 1.4 45.17 45.17 pinnata 32.1 1.02 47.69 47.69 Obelia 33.75 24.55 0.99 39.28 84.45 Obelia dichotoma dichotoma

Kirchenpaueria 18.24 0.92 27.09 74.77 Aglaophenia 23.81 7.8 0.52 12.49 96.94 pinnata octodonta Aglaophenia 14.82 0.85 22.01 96.78 octodonta Groups Cold & Warm: Average dissimilarity = 79.75

Groups Natural & Harbour: Average dissimilarity = 45.60 Species Av.Diss Diss/SD Contrib% Cum.%

Species Av.Diss Diss/ Contrib% Cum.% Obelia 54.06 3.98 67.78 67.78 SD dichotoma

Aglaophenia 15.57 1.33 34.14 34.14 Kirchenpaueria 11.39 1.75 14.29 82.07 octodonta pinnata 12.23 1.61 26.83 60.97 Aglaophenia 7.82 0.76 9.8 91.87 Obelia dichotoma octodonta Kirchenpaueria 8.69 0.58 19.06 80.03 pinnata

Bougainvillia 3.54 0.66 7.76 87.79 muscus

Laomedea 2.25 0.4 4.93 92.72 flexuosa

of this species in temperate regions (70-5200 m, but distribution of Obelia dichotoma corresponded particu- mostly below 500 m) (Schuchert et al., 2017). larly well with the studied water masses, so the species The studied hydrozoan fauna reflected exceptionally became a useful aid in the identification of the influence well the double-layered structure of the Sea of Marma- of Black Sea or Mediterranean waters in each particular ra, with highly distinctive assemblages, characteristic of site. Colonies of Obelia spp. are common throughout the the Black Sea and the Mediterranean Sea water masses. entire Mediterranean Sea (Bouillon et al., 2004), but they Low diversity and species richness, combined with high reach remarkably high abundances in the Bosphorus strait abundances were consistently observed in the upper lay- and the Black Sea (e. g. Wijsman et al., 1999; Albayrak er, effectively signalling the water masses originating & Balkıs, 2000; Revkov et al., 2002), which is congruent from the Black Sea and flowing into the Sea of Marma- with the observed pattern of high numbers of dominant, ra through the Istanbul Strait. In turn, high diversity and large colonies of Obelia dichotoma in the upper layer of species richness together with relatively low abundances the Sea of Marmara (Black Sea water masses) and scarc- were characteristic of the lower layer, indicating water er, smaller colonies of the same species in the lower layer masses originating from the Aegean Sea and flowing into (Mediterranean water masses). the Sea of Marmara through the Çanakkale Strait. The The differences between impacted and natural sites effects of the strong stratification of the Sea of Marmara were also clearly indicated by the composition of the have been previously documented in such diverse taxa as hydrozoan assemblages in the area. The harbour as- diplonemids (Lara et al., 2009), foraminiferans (Kirci-El- semblages were characterized by the dominance of few mas, 2013), and octocorals (Topçu & Öztürk, 2015), but large species (Obelia dichotoma, Kirchenpaueria pinna- direct observations regarding benthic hydrozoans have ta, Bougainvillia muscus and Aglaophenia octodonta). not hitherto been performed. Variations in abundance and Again, the hydroid Obelia dichotoma was in large part

280 Medit. Mar. Sci., 19/2, 2018, 273-283 responsible for the differences observed between -natu Aknowledgements ral and impacted (harbour) sites. This is a common and abundant species often encountered in disturbed sites and The authors thank Volkan Narcı, Bülent Tüzel and fouling communities in harbours (Megina et al., 2013), Anıl Durmaz for their help during field work. N.E. Topçu where it predominates over other species (Standing, and L.F. Martell contributed equally to this work. This 1976; Witt et al., 2004). While the colonies of O. dicho- work was supported by the Scientific Research Project toma may also be common in natural sites, their abun- Coordination Unit of Istanbul University under grants no dance and frequency tends to be higher in harbours and 50649 and 51140. marinas (Megina et al., 2013), similarly to the observed pattern for this species and Bougainvillia muscus in the References Sea of Marmara. According to Megina et al. (2013), for example, B. muscus was a characteristic species in West Albayrak, S., Balkıs, N., 2000. Hydroid polyps of the Bospho- Mediterranean harbours, besides being completely absent rus. Turkish Journal of Marine Sciences, 6, 41-53. from comparable natural sites, but in the present study Anderson, M.J., 2001. A new method for non-parametric mul- colonies of this species were observed in both impacted tivariate analysis of variance. Austral Ecology, 26, 32-46. and natural sites although with different abundance. Pop- Beşiktepe, Ş.T., Sur, H.İ., Özsoy, E., Latif, M.A., Oǧuz, T. et al., 1994. The circulation and hydrography of the Marmara ulations of benthic hydrozoans from harbours and natu- Sea. Progress in Oceanography, 34 (4), 285-334. ral areas, although belonging to the same species, could Boero, F., 1984. The ecology of marine hydroids and effects of however represent different genetic pools adapted to dif- environmental factors: a review. Marine Ecology, 5, 93-118. ferent environmental conditions, as has been shown for Boero, F., Fresi, E., 1986. Zonation and evolution of a rocky other benthic invertebrates in the Mediterranean (Turon bottom hydroid community. Marine Ecology, 7, 123-150. et al., 2003), so the observed differences between natu- Bouillon, J., Medel, M., Pagès, F., Gili, J., Boero, F. et al., ral and impacted sites based on hydrozoan assemblages 2004. Fauna of the Mediterranean Hydrozoa. Scientia Ma- could actually be larger than previously thought. rina, 68, 1-449. Seasonality was also a major factor determining the Bouillon, J., Gravili, C., Gili, J.M., Boero, F., 2006. An intro- specific composition and abundance of the observed hy- duction to Hydrozoa. Mémoires du Muséum national d’Hi- stoire naturelle volume 194. Publications scientifiques du drozoan assemblages in both layers and natural and im- Muséum, Paris, 591 pp. pacted sites. Comparatively higher competition for space Brinckmann, A., Vannucci, M., 1965. On the life-cycle of between hydrozoans and algae (Ulva spp. in particular) Proboscidactyla ornata (Hydromedusae, Proboscidacty- was expected during the warm season in the upper lay- lidae). Pubblicazioni della Stazione Zoologica di Napoli, er stations, when the algae proliferate tremendously at 34, 357-365. shallow sites resulting in lower abundances of benthic Clarke, K., Gorley, R., 2006. PRIMER v6: User Manual/Tuto- hydroids. For the lower layer in the Sea of Marmara, rial. PRIMER-E, Plymouth, 91pp. however, we were not expecting to find a large influence Çınar, M.E., Yökeş, M.B., Açık, Ş., Bakır, K., 2014. Check-list of seasonality in the studied assemblages because the of and from the coasts of Turkey. Tur- kish Journal of Zoology, 38, 677-697. temperature there is almost constant throughout the year Çoban-Yıldız, Y., Tuğrul, S., Ediger, D., Yılmaz, A., Polat, C., (Beşiktepe et al., 1994). However, cold and warm affinity 2000. A comparative study on the abundance and elemen- hydrozoan assemblages in the lower layer were signifi- tal composition of POM in three interconnected basins: the cantly different. That was probably a biased result, due to Black, the Marmara and the Mediterranean Seas. Mediter- the excessive increases of O. dichotoma and B. muscus ranean Marine Science, 1, 51-63. following an unexpected event of mass mortality that im- Da Silveira, F.L., Migotto, A.E., 1991. The variation of Ha- pacted the Prince Islands coasts (Topçu et al., 2016). locordyle disticha (Cnidaria, Athecata) from the Brazilian In general, considering both the upper and lower lay- : an environmental indicator species? Hydrobiologia, ers and the different natural / harbour habitats sampled, 216 (1), 437-442. the hydroid assemblages constituted useful indicators of Demir, M., 1954. Boğaz ve Adalar sahillerinin omurgasız dip hayvanları. İstanbul Üniversitesi Fen Fakültesi Hidrobiyo- environmental conditions in the study area. The multivar- loji Araştırma Enstitüsü Yayınları no: 3, İstanbul, 615 pp iate structure of the assemblages diverged significantly (In Turkish). and the differences seem to be more influenced by the Gili, J.M., Hughes, R.G., 1995. The ecology of marine benthic quantitative (abundance) and not the qualitative (specif- hydroids. Oceanography and Marine Biology - An Annual ic) composition, with few species being exclusive of one Review, 33, 351-426. habitat or the other. The benthic assemblages developing González-Duarte, M.M., Megina, C., Piraino, S., 2014. Looking in harbours and natural areas, as well as those character- for long-term changes in hydroid assemblages (Cnidaria, istic of the upper and lower layers in the Sea of Marma- Hydrozoa) in Alboran Sea (South-Western Mediterranean): ra, exhibit some particular and interesting characteristics a proposal of a monitoring point for the global warming. Helgoland marine research, 68 (4), 511-521. that would make them a good bioindicator group, helping Gravili, C., Di Camillo, C.G., Piraino, S, Boero, F., 2013. Hy- to reduce the effort needed for the comparison of differ- drozoan species richness in the Mediterranean Sea: past and ent types of habitats and providing a useful tool for both present. Marine Ecology, 34 (1), 41-62. scientists and policy-makers. Gravili, C., De Vito, D., Di Camillo, C.G., Martell, L., Piraino,

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282 Medit. Mar. Sci., 19/2, 2018, 273-283 Appendix 1

Results of the Kolmogorov-Smirnov (K-S) test. S: species richness; N: abundances; 1-D: Simpson index; ns: no-significant.

Hydrozoan assemblages DI K-S “D” p value P value summary S 0,08333 > 0,9999 ns in the upper layer N 1 < 0,0001 **** (natural coasts) 1-D 0,6667 0,0097 **

Cold water S 0,25 0,8475 ns vs in the lower layer N 0,6667 0,0097 ** warm water 1-D 0,4167 0,2485 ns S 0,5 0,0996 ns in the harbours N 1 < 0,0001 **** 1-D 0,8333 0,0005 *** S 0,8333 0,0005 *** cold-affinity N 1 < 0,0001 **** U p p e r l a y e r 1-D 1 < 0,0001 **** vs lower layer S 1 < 0,0001 **** warm-affinity N 0,75 0,0023 ** 1-D 1 < 0,0001 **** S 0,4167 0,2485 ns cold-affinity N 0,6667 0,0097 ** Natural coasts 1-D 0,8333 0,0005 *** vs harbours S 0,6667 0,0097 ** warm-affinity N 1 < 0,0001 **** 1-D 0,8333 0,0005 ***

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