Characteristics of bacterioplankton in the Kuyalnyk estuary development in 2015-2017

Purpose. To study changes in the Kuyalnik Estuary bacterioplankton number in 2015-2017 under the influence of abiotic factors in conditions of controlled experiment consisting at the estuary refilling with marine water. Methods. Number of microorganisms in the Kuyalnyk Estuary and the adjacent water-bodies/watercourses has been studied. Method of direct count of microorganisms under microscope has been used. Results. Bacterioplankton number in the Kuyalnyk Estuary varied within very broad limits (1.4∙106 cell/ml - 140∙106 cell/ml); it was 1-2 orders of magnitude higher than in marine water and fresh watercourses entering the estuary. Dynamics of the two years’ set of observations has shown sharp changes of bacterioplankton number in the estuary; in 2016 it decreased in the average 2.2 times compared with 2015. Bacterioplankton number distribution in the estuary has shown quantitative prevalence in the bottom layer, which evidences arrival of microorganisms into the bottom layer from bottom sediment. Results. To our mind the sharp changes in bacterioplankton number in the Kuyalnyk Estuary were connected with several factors: on one hand intensive archaea development in 2015 could have been provoked by the changes in the environment caused by the estuary refilling with marine water; on the other hand, sharp decrease in microorganisms number in 2016 were caused by gypsum sedimentation and gypsum crust forming on the estuary floor, which practically suspended all the exchange processes between water and the bottom for some time.