Comparison of Kızılırmak and Yeşilırmak (Southern Black Sea) estuarine ecosystems based on macrobenthic biodiversity and environmental variables and new records for the macroinvertebrate fauna of Turkey

Abstract This study investigates the Kızılırmak and Yeşilirmak estuarine ecosystems in Turkey, which provide significant freshwater and nutrient inputs to the Samsun Shelf area along the midsouthern Black Sea. The objective was to determine the current ecological status and to detect any significant differences between two estuarine ecosystems (restored—Kızılırmak—and natural—Yeşilırmak) in terms of macrobenthic invertebrates and environmental variables. Macrobenthic invertebrates were collected with a 500 µm mesh size kick-net. A total of four samplings, one in each season, were collected during February, May, August, and November of 2017. A total of 90 taxa, mainly oligochaetas and chironomids, were identified, composed of 51 species in Kızılırmak and 60 in Yeşilırmak. Orthocladius (Orthocladius) dentifer , O. (O.) clarkei , O. (O.) dorenus , O. (O.) wetterenesis , O. (O.) mixtus , and Mystacides longicornis were found to be new records for Turkey. The distribution of macrobenthic invertebrates was compared between season, estuary, grain size and stations. In Kızılırmak and Yeşilırmak, the region characterized as estuarine was found to be small transitional waters. In Kızılırmak, a high similarity was observed among stations, accompanied by relatively low diversity across sampling sites. This phenomenon is thought to be a natural consequence of the reconstruction activities along the river, which have deleteriously affected the ecosystem. The Yeşilırmak estuary has a more diverse macrobenthic community and appeared to be better preserved than the Kızılırmak area.