Faunal trophic interaction in an oligotrophic-dystrophic lake (Shirakoma-ike, Japan)

 The trophic interaction in the pelagic food web of oligotrophic-dystrophic Lake Shirakoma-ike was investigated by a stable isotope technique. Carbon and nitrogen isotope analyses revealed the trophic interaction among Piona carnea (a water mite), Chaoborus sp. (a phantom midge), Daphnia longispina (a cladoceran), and Acanthodiaptomus pacificus (a calanoida copepoda). The δ¹³C values for estimating the relative contributions of D. longispina and A. pacificus to carnivores were used, and they were also used for the constraint of the trophic enrichment factor of δ¹⁵N. Both Chaoborus sp. and P. carnea were suggested to consume D. longispina and A. pacificus at almost the same ratio (1 : 1). However, both carnivores preferred A. pacificus to D. longispina, because D. longispina was much more abundant in the lake than A. pacificus. Omnivory of P. carnea was also analyzed by the mixing model. Received: February 28, 2002 / Accepted: July 10, 2002 Present address: Hydrospheric Atmospheric Research Center, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan Tel. +81-52-789-3434; Fax +81-52-789-3436 e-mail: lee@ihas.nagoya-u.ac.jp Present address: Research Institute for Humanity and Nauture, Kyoto, Japan Acknowledgments We would like to thank Professor Kikuo Kato for providing useful comments and colleagues in the Laboratory of Biogeochemical Data Analysis, Nagoya University, for their support with the sample collection. We are in debt to Dr. R. Coucett for the kind suggestion on the trophic enrichment factors for blood-sucking insects. We also thank the members of the Suwa Hydrobiological Station, Shinshu University, who kindly allowed us to use facilities for sampling in Lake Shirakoma-ike. The zooplankton samples were partly provided by Mr. Masataka Yoshida. Correspondence to:J.-Y. Lee