Sedimentary records of reduction in resting egg production of <Emphasis Type="Italic">Daphnia galeata</Emphasis> in Lake Biwa during the 20th century: a possible effect of winter warming |
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| Authors: | Narumi K Tsugeki Seiji Ishida Jotaro Urabe |
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| Institution: | (1) Center for Ecological Research, Kyoto University, 509-3, 2-chome, Hirano, Otsu Shiga, 520-2113, Japan;(2) Present address: Ecology and Evolutionary Biology, Graduate School of Life Sciences, Tohoku Universiy, Aramaki Aza Aoba, Sendai Miyagi, 980-8578, Japan;(3) Department of Biological Sciences, State University of New York at Buffalo, Buffalo NY, 14260, USA;(4) Graduate School of Life Science, Tohoku University, Aoba, Aramaki, Aoba-ku, Sendai 980-8577, Japan |
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| Abstract: | To clarify long-term variations in the resting egg production of Daphnia galeata in Lake Biwa during the 20th century, we examined an abundance of plankton remains and ephippia in a 26-cm sediment core
with a time resolution of approximately 2–6 years. Historical changes shown by these plankton remains indicated that the Daphnia population has not produced resting eggs since the 1980s, but it has remained the most abundant zooplankton species in the
lake. Plankton monitoring data collected from 1966 to 2000 revealed that the overwintering individuals (January–March) of
D. galeata plankters showed a significant increasing trend in recent years, such increase being negatively correlated with ephippial
abundance in the sediment samples. Further analyses showed that the dominant phytoplankton in winter has changed from large
inedible diatoms to edible flagellated algae, probably due to changes in vertical mixing regimes resulting from winter warming.
These changes that occurred in the last several decades suggest that global warming has improved winter food conditions and
thus enabled the Daphnia plankton to maintain its population without producing resting eggs in Lake Biwa. |
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| Keywords: | Daphnia Resting eggs Winter warming 20th century Lake Biwa Zooplankton |
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