Some notes on Brachionus rotundiformis (Tschugunoff) in Lake Palaeostomi

Abstract

In 1933 a connection was formed between the Black Sea and Lake Palaeostomi (Georgia) after which the latter became a brackish-water take with water salinity up to 13‰. Water salinity is variable, depending first of all on the direction and strength of the wind. Brachionus rotundiformis (Tschugunoff) (with 20% or more of total zooplankton abundance) was the dominant zooplankton species in the samples collected in 1977 (July, Aug) and 1996 (July) from this take. The morphology and ratio of physiological types of female and the population density of dominant species were studied. The lorica length of females was 105-250 μm, its widest part 95-250 μm. The average abundance fluctuated between 5 and 2,600 x 103 ind m-3. A positive correlation was revealed between the occurrence of B. rotundiformis and water salinity (r = 0.7; P < 0.0001). B. rotundiformis formed 84% of the abundance of rotifers and 49% of the numbers of total zooplankton. Several types of egg bearing female were detected. The proportions of females with egg types (M + F), (F + M) and (D/F) were 0.13, 0 and 0.01% in 1977 and 0.14, 0.01 and 0.01% in 1996, respectively.