Long-term dynamics of the macrozoobenthos in the Kytai Lake (Danube River, Odessa region, Ukraine)

Abstract

Species composition and quantitative characteristics of the macrozoobenthos in the Kytai Lake were studied. During 2006–2012, 272 macrozoobenthic samples were collected from the littoral and sublittoral zones of the lake. A total of 66 species were identified in the collected samples. In 2006–2009, the number of species increased from the upper to the lower reaches of the lake, with all 66 species recorded in the latter. However, with increasing salinity and decreasing dissolved oxygen content, the total number of macrozoobenthic species dropped up to 12 in 2012, with the highest number observed at the lower reaches. The average annual macrozoobenthic abundance and biomass in the littoral zone (836±33.08 ind. m−2 and 19.7±0.78 g m−2, respectively) were comparable to those in the sublittoral zone (879±35.16 ind. m−2 and 9.19±0.36 g m−2, respectively). In summer 2012, during the period of maximum development, the macrozoobenthic abundance and biomass in the littoral zone were 346 ind. m−2 and 3.26 g m−2, respectively. The Shannon-Weaver diversity index reached 3.26 bits ind−1 in the littoral zone in 2006–2008 and then decreased to 2.34 bits ind−1 in 2010–2012. The Pielou evenness indices during these periods were 0.66 and 0.61, respectively. In August 2009–2012, the correlation coefficient between salinity and macrozoobenthic abundance was −0.97. In July 2006– 2012, the correlation coefficient between dissolved oxygen content and macrozoobenthic biomass was 0.89, whereas that between dissolved oxygen content and macrozoobenthic species number was 0.95. Results of the correlation and multiple regression analyses revealed the key role of oxygen depletion in decreasing the macrozoobenthic species richness and its development. Principal component analysis indicated that the first two principal components, related to transparency, oxygen, salinity, and temperature, explained most of the total variance of the data. Transparency, oxygen, and temperature positively influenced the macrozoobenthic species composition and quantitative characteristics, whereas salinity exerted a negative influence.