engleski

Aquatic nematodes of Sakadaš lake (Kopački rit Nature Park, Croatia)

Aquatic free-living nematode assemblages were investigated between January 1998 and November 2000. The investigation was conducted in the sandy sediment of the deepest part of the central area of Sakadas lake (Kopacki rit Nature Park, Croatia). A total of 24 nematode species belonging to 18 genera was found. The dominant species was Tobrilus gracilis, with the relative abundance ranging from 22.2% to 98.4% of the total nematofauna. Nematode abundance was correlated to the following environmental factors: water-level fluctuation, depth, transparency, seasonal temperature variations and concentration of dissolved oxygen. A correlation analysis showed that the abundance of Mononchus aquaticus depended on the concentration of dissolved oxygen in the water. Furthermore, significant correlations existed between the abundance of Brevitobrilus stefanskii and the water level, and between the abundance of B. stefanskii and the water depth. Significant correlations were also found between the dissolved oxygen concentration and the number of species recorded (S), as well as between the dissolved oxygen concentration and the Shannon-Wiener index of diversity (H'). Sakadas lake, the deepest water depression in the Nature Park Kopacki rit, is naturally eutrophicated. During the recorded periods of hypoxia a low number of species and their low abundance was determined, but there was a high relative abundance of the tolerant species T. gracilis. The shape of the nematode abundance - biomass comparative curve (ABC) indicates a moderately disturbed investigation site in the lake.

Aquatic free-living nematodes; Abiotic water parameters; Lake; Croatia

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