Seasonal patterns of food limitation in Daphnia galeata

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separating food quantity and food quality effects .... Studies of growth and production of zooplankton in the field cannot separate the limiting ...... the eutrophic Loosdrecht lakes, with notes on other P sources for phytoplankton requirements.
Journal of Plankton Research Vol.18 no.7 pp.1137-1157.19%

Seasonal patterns of food limitation in Daphnia galeata: separating food quantity and food quality effects Dorthe Miiller-Navarra1 and Winfried Lampert Max-Planck Institutfiir Limnologie, Abteilung Okophysiologie, Postfach 165, D-24302 Plon, FRG 'Present address: Scripps Institution of Oceanography, Hanue Biology Research Division 0202, LaJolla, CA 92093, USA

Introduction

Natural populations are shaped by mutual action of top-down and bottom-up control. For zooplankton communities the functioning of top-down control can be easily explained with the size-efficiency hypothesis (Brooks and Dodson, 1965) however, bottom-up control is more obscure. For bottom-up control, food is the important factor, which influences the reproductive output and, thus, the birth rate and potential abundance of a population (Lampert, 1985). Therefore it is crucial to determine the degree of food limitation of zooplankton and relate it to measurable food parameters. Food quantity can easily be measured for example as biovolume (e.g. Berquest et al., 1985), chlorophyll (e.g. Vijverberg, 1976) or the elemental composition (Behrendt, 1990), like carbon and nitrogen (Checkley, 1980), or protein (Guisande and Serrano, 1989). But in particular, food accessibility (including interference in the feeding process) and its nutritional value are food quality parameters that cannot be determined so easily (Schindler, 1970; Pechenik and Fischer, 1979, Matveev and Balseiro, 1989). For example, zooplankton growth also depends on the biochemical content of the algal food. For example, eicosapentaenoic acid (20:5w3) seems to be of great importance for Daphnia growth on seston (Miiller-Navarra, 1993). However, the biochemical content differs between algal species, but also changes with the physiological state of the alga, resulting in differences in food quality (Ahlgren etal., 1990; Checkley, 1980; Ki0rboe, 1989; Giani, 1991; Groeger et al., 1991). However, even knowing the nutritional value of biochemical compon© Oxford University Press

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Abstract. Food limitation for the cladoceran Daphnia galeata was measured growing them with natural lake seston for one growing season under standardized conditions in the laboratory. Growth rates were related to several measures of food quantity. Paniculate organic carbon (POC) . = 1.08 x [1-e-"" • - • '">]; r-' = 0.52*** g, [ ] CS = 5.4 x [i_e-»'-iiw -»»>]; r- = 0.62*** 5CS = 7.6x [1-e-" • " ^ ' " " ] : r- = 0 . 5 8 "

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