![Figure 2. Geographical positions of sampling stations in Türkiye Eastern Black Sea Basin is between 40 o 15'-41 o 34' north latitudes and 36 o 43'-41 o 35' east longitudes in the northeast of Türkiye. This basin, which extends to the east of the Black Sea in the north, the Kaçkar Mountains in the east, the Yamanlı, Soğanlı, Kemer, and Iğdır Mountains in the south, and the Çarşamba Plain in the west, constitutes 2.92% of Türkiye with an area of 2,284,439 ha. Almost all of the streams flow vertically into the sea in narrow and deep valleys. The highest peak of the mountains extending parallel to the coast is 3,937 m high on the Kaçkar Mountains [6]. The Western Black Sea Basin is located between 40 o 34' 42"-4 1o 27' 52" north latitudes and 30 o 52' 33"-35 o 12' 12" east longitudes. The Western Black Sea Basin is bounded by the Sakarya Basin in the southwest, the Kızılırmak Basin in the southeast, and the Black Sea in the north. The Western Black Sea Basin, which covers approximately 3.7% of Türkiye's surface area, has a precipitation area of 28,855 km 2 [7]. The circumference of the Kızılırmak Basin, which has a precipitation area of 82 221 km 2 , which is approximately 10.49% of Türkiye's surface area, is 3 546 km and the length of the basin is 293 km [8].](https://www.researchgate.net/profile/Deniz-Mercan-4/publication/364075227/figure/fig1/AS:11431281110423554@1672509977366/Geographical-positions-of-sampling-stations-in-Tuerkiye-Eastern-Black-Sea-Basin-is-between_Q320.jpg)
September 2022
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Biological Diversity and Conservation
Commonly found in terrestrial and aquatic ecosystems, Gastropoda members are the class with the highest number of species within the Mollusca. Freshwater Gastropods which are generally listed in primary consumer play a crucial part in aquatic environments by feeding numerous fish species and vertebrate species. They include species that are widely distributed in rivers and lakes and are used as indicators in aquatic systems monitoring studies. In Turkey, the Black Sea Region is also a privileged geography in terms of its topography and historical development history of aquatic systems, rich in rivers and lakes. In this research, field studies were conducted from 20 different stations in the Black Sea region in 2017-2018. Benthic macroinvertebrate samples were collected from lakes and rivers with an Ekman grab sampler and hand net. Samples were washed in situ and fixed with 70% ethyl alcohol. Totally 10442 benthic macroinvertebrate members belong to 21 taxa were determined in the study. In the region, Oligochaeta was the dominant taxa with 56.80% dominancy value and followed by Chironomidae and Gastropoda with 18.26 and 8.24, respectively. As third dominant taxa, Gastropoda members were consist of 870 individuals belong to 11 taxa. It was determined that Gyraulus elenae and Radix labiata from Gastropoda were widely distributed in the region. These species have broad tolerance to pollution. In the study, it was determined that both densities of species and population were increased in the regions of the rivers that are far from the settlement areas or that have not been intervened and in the littoral parts of the lakes. In general, a decrease was observed not only in the Gastropoda members but also in the expected population density of the macrozoobenthos members in the parts of the streams that are under pressure.