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Abstract
The larvae of Propsilocerus lacustris were found at densities ranging from 30 to 150 ind. m−2 in the hypertrophic Lake Syczyńskie, eastern Poland. They burrowed in the top 5 cm of soft sediment at a water depth of ca. 1 m along the reed belt. The sediment was well decomposed, with fair contribution of organic matter (16.5 – 31.6%) and of neutral pH (6.5 – 7.7). Concentrations of total phosphorus in the sediments ranged from 1.64 to 5.04 mg g DW−1. The sediment pore water contained cyanobacterial microcystins (1 – 2 μg MC-LR eq. l−1). The analysis of subfossil remains indicates that the larvae appeared in the lake in the middle 1960s, i.e. a few years before the system switched from eutrophy to hypertrophy. Densities increased parallel to the increase in the lake trophic status, estimated as concentrations of organic matter and total chlorophyll in the sediment. The results suggest that P. lacustris, as its close relative P. akamusi, favours nutrient-rich lakes.
Acknowledgements
The study was supported by the State Committee for Scientific Research, project No. 2 P06S 001 27. The authors are indebted to Dr. Xinhua Wang for checking the identification of the larvae, to Dr. M. Gąsiorowski for dating the sediment, and Dr. hab. A. Tatur for providing us with data on concentrations of total phosphorus and organic matter in the sediments. Dr. Ramesh Gulati gave constructive comments on an earlier draft of the manuscript and Małgorzata Kornijów revised the language.