Bioindication of the Ecotoxicity of the Nemunas River according to the Functional Changes in Bacteriocenoses of the Sediments and the Digestive Tract of Molluscs

Our studies revealed that hydrocarbon-degrading bacteria are found not only in water and sediments, but in the digestive tract of hydrobionts as well. Their abundance in the endosystem of hydrobionts is much higher than in the environment of the macrobionts. On the basis of functional changes in the bacteriocenoses of sediments and digestive tract of molluscs, we may state that the stretch of the Nemunas River near Merkinė is the safest locality for the populations of hydrobionts in comparison to other stretches of the Nemunas River. In this stretch of the Nemunas River, the abundance of hydrocarbon-degrading bacteria in sediments and the digestive tract of hydrobionts was the lowest. In other stretches of the Nemunas River (near Liškiava, Kulautuva, Rusnė and in Kaunas reservoir near Kapitoniškės), the number of hydrocarbon-degrading and intestinal bacteria in the bacteriocenoses of the digestive tract of hydrobionts and in sediments was high. That means the ecosystem of the river near those localities is polluted with sewage and petroleum products.