Macrozoobenthic community structure of İğneada region in Turkey (the southwestern Black Sea)

İğneada is a small town located in the northwestern part of Turkey, in the district of Demirkoy, the Kirklareli Province, Turkey. The İğneada region is located on a coastal plain of the European and Turkish zones of the Black Sea, approximately 5 km south of the Rezovo River, which forms the border with Bulgaria. The area is of ultimate importance to the biological diversity by providing habitats for many floristic and faunistic species. The urban population is small in this region compared to other parts of Turkey (as well as compared to Bulgaria), therefore the anthropogenic impact on this coastal ecosystem is very limited. Ozturk et al. (2013) suggested this region as the most appropriate location for a transboundary protected area. The proposed potential area comprises the İğneada coastal inshore marine area and a terrestrial component, Strandja, located between Bulgaria and Turkey. The terrestrial part of İğneada is already protected due to its unique floodplain forests, wetlands on alluvial soils and coastal sands (Ozturk et al. 2013).

The Turkish coast of the Black Sea was poorly investigated in terms of dynamics and structure of zoobenthic communities compared to the Turkish Aegean and Mediterranean coasts. The studies performed along the Turkish coast of the Black Sea were generally focused on the specific taxonomic groups such as Polychaeta (Marinov 1959; Dimitrescu 1960; 1962; Rullier 1963; Gillet & Ünsal 2000; Çinar & Gonlugur-Demirci 2005; Agirbas et al. 2008; Gozler et al. 2009; Kurt Sahin & Çinar 2012; Kus & Kurt-Sahin 2015; Kurt Sahin et al. 2017), Crustacea (Kocatas & Katagan 1980; Mutlu et al. 1992; Sezgin et al. 2001; Kirkim et al. 2006; Sezgin & Katagan 2007; Bilgin et al. 2007), Mollusca (Mutlu et al. 1993; Gonlugur-Demirci 2005; Ozturk et al. 2004) and meiobenthic taxa such as Nematoda, Harpacticoida and Kinorhyncha (Ürkmez et al. 2015; Ürkmez et al. 2016b; Ürkmez et al. 2016c). The studies on the zoobenthic dynamics of the Turkish Black Sea coast are scarce (Jakubova 1948; Caspers 1968; Uysal et al. 2002; Sezgin et al. 2010; Ürkmez et al. 2016a). In addition, there is no comprehensive study on the zoobenthic diversity and structure from the İğneada region. The work carried out by Ongan et al. (2009) dealt with zoobenthos of the study area, but it focused on the Holocene sediments of the southwestern Black Sea and presented a species list of Mollusca and Ostracoda. On the other hand, Ürkmez et al. (2016c) investigated meiobenthic assemblages in the area within the scope of the same project (MISIS) as the present work. The authors listed species of free-living nematodes and harpacticoid copepods occurring on İğneada coasts, with several new records for the Turkish Seas.

The objective of the present work was to obtain data on the biodiversity of the macrozoobenthic community in the region and to determine possible seasonal changes in the communities of the area. The present study is important because it provides the first data on the macrozoobenthic biodiversity of the area. The results of this study will provide a basis for future research.

Benthic sampling for the present study was carried out during the project “MSFD (Marine Strategy Framework Directive) Guiding Improvements in the Black Sea Integrated Monitoring System-MISIS” supported by the European Union. Benthic samples were collected seasonally at nine stations located at three different depths (5, 10, 20 m) of three transects using the Van Veen grab sampler between November 2012 and October 2013 (Table 1, Figure 1). Soft-bottom samples were sieved on board through 0.5 mm mesh and the retained material was transferred to separate jars containing 4% seawater formaldehyde solution. In the laboratory, samples were rinsed in freshwater, sorted into taxonomic groups under a stereomicroscope, and preserved in 70% ethanol. Next, macrozoobenthic species were identified and counted under stereo- and compound microscopes. In order to determine the water quality in the area, temperature, salinity, pH and dissolved oxygen concentration (DO) were recorded at each station in situ using the YSI 6600 V2 Water Quality Probe.

Figure 1

Table 1

Coordinates, depth and biotope of the sampling stations

Soyer’s Frequency Index (F) was applied to the abundance data to identify the characteristic species of the area. In order to interpret the quantitative data, Shannon-Weaver’s diversity index (H’) and Pielou’s evenness index (J’) were applied to the species abundance data. The pooled species abundance data, obtained per sampling station in each season, were analyzed using cluster techniques based on the Bray-Curtis similarity from the PRIMER 5 package (see Clarke and Warwick 2001).

Macrozoobenthic community structure and changes in the benthic fauna of the İğneada region of the Black Sea are documented for the first time through the present study. The species composition of zoobenthos on the western Black Sea coast in Turkey was studied by Jakubova (1948), Caspers (1968), Uysal et al. (2002) and Ürkmez et al. (2016c) who studied the meiobenthic community structure in the area. In the central Turkish Black Sea (Sinop), the seasonal dynamics of the meiobenthic assemblages were studied (Ürkmez et al. 2016a). The eastern coast was considered only by Sezgin et al. (2010). So far, 768 macrozoobenthic species were identified from the Turkish coast of the Black Sea (Açik 2014; Bakir et al. 2014; Çinar 2014; Çinar et al. 2014a,b; Evcen et al. 2016; Koçak & Onen 2014; Oztoprak et al. 2014; Ozturk et al. 2014; Topaloglu & Evcen 2014; Kus & Kurt-Sahin 2015; Kurt Sahin et al. 2017). The number of macrozoobenthic species reported from the Turkish coast of the Black Sea increased to 789, including the new species reported in the present study. Since no detailed study on the macrozoobenthos in the İğneada region is available, the results of the present study could not be compared with any other studies. However, Uysal et al. (2002) studied the prebosphoric region of the Black Sea and reported 29 macrozoobenthic species. Stoykov and Uzunova (2001) analyzed macrozoobenthic organisms of the southern Bulgarian coast and identified 96 species. Uzunova (2010) examined the zoobenthos of the eelgrass (Zostera spp.) of Sozopol Bay, Bulgaria and reported 69 species. In the present study, we identified 154 species on the coast of İğneada, including Anadara kagoshimensis – an alien species transported to the Aegean and Black Seas from the Pacific Ocean via ship ballast waters. The species was first reported from the Turkish coast of the Black Sea by Albayrak (2003). Rapana venosa was the other alien mollusk species from the Pacific Ocean. It was introduced to the Black Sea in the 1940s and expanded its distribution toward the Azov Sea, the Caucasus, and the Crimea. The species was first reported from the Turkish Black Sea coast in 1960 by Fischer-Piette (1960).

Salinity levels in the study area were at 16 PSU in May and July; they were slightly higher (18 PSU) in October and November. Sea currents induced by winds increase the influence of freshwaters introduced into the sea near the study area. Salinity levels are lower in the area under these circumstances.

In general, Polychaeta is the dominant taxon in the Black Sea, both in terms of the number of individuals and the number of species. The present study indicates that Polychaeta is the most diverse taxon, but mollusks are dominant and account for 82% of the total number of individuals. The dominant taxon is the mollusk Bittium reticulatum. No detailed ecological information on this species is available for the Black Sea, even though it is known that it forms dense populations in vegetated habitats. In general, they live as epiphytic grazers on the Zostera leaves. As supporting evidence, patchy Zostera beds are found to be abundant on the soft bottoms of the study area.

The present study was supported by the MISIS project, the objective of which was e.g. to deal with issues related to the establishment of the Transboundary Protected Area Strandzha – İğneada located on the border between Bulgaria and Turkey. Strandzha had the status of Natura 2000 SCI under the Habitats Directive before the study area was designated as a protected area (BG0001007). The İğneada marine area had no status of protection, except that it indirectly benefited from its location in very close proximity to Longoz Forest National Park (designated in 2007). Therefore, the project focused on thorough investigation of its current biological and ecological status for future designation of the marine part of the İğneada region as a Marine Protected Area under the Habitats Directive. The present study contains the results of the research on marine diversity in the İğneada area in order to gain knowledge about the ecological value and the current status of its biological and ecological aspects. In accordance with these objectives, macrozoobenthic fauna and its ecological status were determined to support the work carried out in the area aimed at creating a marine protected zone. In order to better understand the distributional and ecological features of the species occurring in the area, more samplings should be designed at various depths and representing different habitats.