Wioślarki (Cladocera, Crustacea) jako źródło informacji w badaniach osadów jeziornych

Znaczenie analizy szczątków Cladocera w badaniach paleolimnologicznych potwierdzają zaprezentowane wyniki osiągnięte w Polsce i zagranicą. Opisano po krótce metodę preparacji i oznaczania szczątków. Podkreślono znaczenie stosowania mikroskopu skaningowego w celu prawidłowego oznaczenia gatunków. Często znajdowane są skorupki o różnej strukturze, a należące do tego samego gatunku, co prawdopodobnie związane jest z różnymi warunkami egzystencji. Przedyskutowano interpretację danych, wskazując na duże znaczenie form planktonowych, zwłaszcza gatunków z rodziny Bosminidae. Gatunki Chydoridae odzwierciedlające głównie stan strefy brzegowej przedstawiono według grup wskaźnikowych wydzielonych przez różnych badaczy.

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The chitinous fragments of Cladocera carapaces, frequently found in lacustrine sediments, are valuable material for palaeolimnological studies. On the basis of species composition of Cladocera it is possible to restore the development of the lake, including its trophic changes and water level fluctuations. The importance of analyses of subfossil Cladocera in palaeolimnological investigations is accentuated by the results hitherto obtained in many countries (Frey, 1986a; Korhola, 1990; Hofmann, 1993). A review of previous research in this domain is presented in this paper, alongside with the methodology of analytic works and interpretation of the results. The most frequently used and very useful method of preparation of Cladocera remnants from gyttja sediments is described (Frey, 1986a). It has been shown that determination of Cladocera remnants using biological microscope alone may lead to taxonomic errors. For instance, the present author has found that carapaces belonging to Chydorus sphaericus, when seen under scanning microscope, differed considerably in their structure. In my opinion, the differences in structure within the same species may be a result of various lake conditions. Hence, the need to use scanning microscope in solving taxonomic problems is emphasised (Figs. 1-4). The results of analyses of changes in the frequency and species composition of Cladocera are particularly useful in reconstructions of lake evolution. The planktonic forms, mainly the species of the Bosminidae family, are particularly important in determining trophic changes and water level fluctuations (Alhonen, 1970; Hofmann, 1986, 1993; Szeroczyńska, 1998a). The species of the Chydoridae family, characterising mainly the littoral environment, are presented according to the index groups established by some authors (Flössner, 1990; Hofmann, 1986; Korhola, 1990). Particular species of this family make a basis for determination of the diversity and equitability, as well as pH, providing to some extent climatic information (Frey, 1988b; Hofmann, 1986; Krause-Dellin, 1988; Whiteside, 1970).