Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Record number 321102
Title Fo-spectra of chlorophyll fluorescence for the determination of zooplankton grazing
Author(s) Lürling, M.F.L.L.W.; Verschoor, A.M.
Source Hydrobiologia 491 (2003). - ISSN 0018-8158 - p. 145 - 157.
Department(s) Aquatic Ecology and Water Quality Management
Publication type Refereed Article in a scientific journal
Publication year 2003
Keyword(s) rotifer brachionus-calyciflorus - fresh-water zooplankton - microcystis-aeruginosa - planktonic rotifers - population-dynamics - loosdrecht lakes - clearance rates - feeding rates - growth-rate - food
Abstract In the PHYTO-PAM phytoplankton analyzer the minimal fluorescence of dark-adapted samples (F-0) was assessed, which gives direct information on the chlorophyll-a content. Clearance rates (CR) of Daphnia and Brachionus were calculated from a decrease in chlorophyll-a concentration using the PHYTO-PAM fluorometer for non-sacrificial sampling of chlorophyll-a. Clearance rates of Daphnia were measured and compared with those based on the cell-counts method using an electronic particle counter ( Coulter counter). Chlorophyll fluorescence-based CR for Daphnia magna were very strongly correlated with Coulter-based CR, signifying the potential suitability of the PHYTO-PAM in grazing experiments. A procedure for determination of rotifer clearance rates was developed and the effects of rotifer density, duration of the grazing period, and food concentration on CR were investigated. Between 10 and 30 rotifers in 2.5 ml food suspension (i.e. 4 - 12 rotifers per ml) appeared optimal for calculating CR. The application of the deconvolution of F-0-spectra in food selectivity experiments was evaluated using various mixtures of the green alga Scenedesmus obliquus and the cyanobacterium Microcystis aeruginosa fed to Brachionus. CR for Brachionus on M. aeruginosa were lower than on S. obliquus but this was not caused by toxicity, because no mortality was observed. The higher CR on Scenedesmus than on Microcystis in the mixtures suggested selectivity. The importance of digital suppression of background fluorescence is highlighted in additional experiments with Daphnia feeding on mixtures of Microcystis and Scenedesmus, or on Microcystis alone. Without background correction of filtered samples, negative clearance rates were obtained for the 'blue' Microcystis signal. Soluble fluorescing compounds of cyanobacterial origin, phycocyanin, were released from the Daphnia and contributed 40% to the overall-fluorescence. Deconvolution of F-0-spectra for the determination of chlorophyll-a using the PHYTO-PAM appears to be a suitable tool for determination of rotifer CR even at very low food concentrations. A drawback of the method is that rather high rotifer densities are required. The required grazing period, however, is shorter than for cell-count methods, the method is sensitive, clearance rates can be measured at low food concentrations (
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