Growth and reproductive cycle of the zebra mussel in the River Rhine as studied in a river bypass |
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Authors: | B Jantz D Neumann |
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Institution: | Department of Zoology, Physiological Ecology, University of K?ln, Weyertal 119, D-50931 K?ln, Germany fax: 0221/470–5932; e-mail: bjantz@biolan.uni-koeln.de, DE
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Abstract: | In a Rhine River bypass built at a water pollution control station, the growth and reproductive cycle of the zebra mussel
(Dreissena polymorpha) were studied over a period of nearly 3 years. The experimental setup offered the possibility to manipulate the temperature
of the continuously passing river water and to calculate influences of temperature and food on the growth of individually
marked mussels. Shell growth rates were a function of algal density (measured as chlorophyll a). This function followed saturation
curves with temperature-dependent plateau levels, and saturation occurred at values above 40 μg/l chlorophyll a. The relationship
between shell growth rate and temperature followed the courses of bell-shaped curves with algal-food-dependent heights. No
clear correlations could be found between shell growth and other environmental factors such as dissolved organic matter, total
organic content, seston, and turbidity. Two spawning periods per year characterized the reproductive cycle of the zebra mussels
at the study site. The first one covered nearly 3 months (April to July) comprising several spawning events. The second shorter
one occurred in August. Young mussels of the first spawning period settled at the end of May, and they were able to reproduce
a few months later (end of August) when their shell length exceeded 9 mm. This first spawning period of the young-of-the-years
coincided with the second spawning period of the older generations. Through the combined analysis of the results of both body
weight determinations and shell growth experiments, it was possible to model mussel growth over a period of nearly 3 successive
years, and to suggest the presence of an endogenous factor that might be involved in determining the start of the annual shell
growth period.
Received: 8 April 1997 / Accepted: 3 November 1997 |
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Keywords: | Dreissena polymorpha River Rhine River bypass Growth Reproductive cycle |
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