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Subfossil shell margins and tail spines of Daphnia in Finnish lake sediments - is Daphnia underrepresented in cladocera analysis?

 Kaarina Sarmaja-Korjonen

Department of Geology, P.O. Box 64, FIN-00014 University of Helsinki, Finland, e-mail: kaarina.sarmaja-korjonen@helsinki.fi

 Abstract

One of the shortcomings of the analysis of subfossil Cladocera (water flee) remains is that preservation of remains is selective. Of Daphnia spp. which are very common in zooplankton assemblages of lakes, usually only postabdominal claws and ephippia are found. In the present paper I describe Daphnia shell margins and some tail spines from the Holocene sediments of a lake in southern Finland where the margins were much more abundant than the postabdominal claws, indicating that postabdominal claws may be underrepresented. Daphnia claws, shell margins and tail spines were found also in surface samples of 17 Finnish lakes and thus the abundance of tail spines could be compared with that of postabdominal claws. The results showed that in most cases the tail spines are more abundant than postabdominal claws and may give a closer estimate of the true abundance of Daphnia. However, in some lakes claws were clearly more frequent than tail spines. Apparently, there are differences in preservation of different types of Daphnia remains between lakes, possibly connected with water chemistry. Overall, the results indicate that probably Daphnia remains are always underrepresented in lake sediments.