Testing a model of zooplankton secondary production in cultures of Daphnia magna

TESTING A MODEL OF ZOOPLANKTON SECONDARY PRODUCTION IN CULTURES OF Daphnia magna M. Gómez* , I. Martínez* , I. Mayo*, J.M. Morales*& T.T. Packard* * Laboratorio de Oceanografía Biológica, Facultad de Ciencias del Mar, Universidad de Las Palmas de Gran Canaria, Campus Universitario de Tafira 35017, Las Palmas de Gran Canaria, Islas Canarias, España Contacto: [email protected] Harvest Size measurement Freezer -20ºC Parameters measurements Dry mass (Lovegrove,1966) Growth rate Condition factor CF = (a · W)/L3 Mother culture (20L) Phytoplankton culture (Scenedesmus sp. +Ankistrodesmus sp.) Corn flour culture (comercial) Yeast culture (comercial) Different cultures of D. magna were grown on phytoplankton, baker’s yeast, or corn flour at 18-21°C. Growth rates were calculated from time courses of size (Fig.1) and dry mass (Fig. 2 ). MATERIAL AND METHODS RESULTS Table 1. Characteristics of the different D. magna cultures Kind of food Maximum size Lmax(mm) Age of Lmax (days) Maximum weight Wmax(µg) Age of Wmax (días) Gorwth rate (d-1) Condition factor (CF) Temperature (ºC) Phytoplankton mixture 1.42 ± 0.19 18 153 13 0.203±0.03 (r2=0.77) 5.78 20.9 ± 1.1 Yeast 2.01 ± 0.14 17 110 12 0.317±0.03 (r2=0.94) 1.19 20.1 ± 0.5 Corn Flour 1.38 ± 0.07 19 150 19 0.136±0.01 (r2=0.72) 4.51 19.2 ± 1.2 Table 2. Regression analysis for size and dry-mass. W=dry-mass, in µg; L=size, in mm (*) p<0.0001 Kind of food Equation r2 Phytoplankton mixture Ln W = 1.39 Ln L + 4.51 0.92 (*) Yeast Ln W = 2.68 Ln L + 2.67 0.98 (*) Corn flour Ln W = 1.02 Ln L + 4.46 0.93 (*) CONCLUSIONS  Although the highest global growth rates were obtained with yeast (0.317d-1), the highest values of the condition factor (5.778) and secondary production (508 µg dry mass·d-1) as well as the maximum weight were found in daphnia fed on phytoplankton. This mixture seems to be the optimal food for culturing Daphnia.  The Huntley and López (1992) model overestimates the secondary production by 174%.  On a utilitarian basis, because size is such a good index of biomass, it provides a simple and more reliable measure of growth-rate than dry-mass. BIBLIOGRAPHY: Huntley, M.E. & M.D.G López, 1992. Temperature-dependendent production of marine copepods: a global synthesis. American Naturalist, 140:201-242 Vijverberg, J., 1989. Culture techniques for studies on the growth development and reproduction of copepods and cladocerans under laboratory and in situ conditions: a review. Freshwater Biology 21:317-373 Fig. 2 and Fig. 3 .- D. magna growth illustrated by the dry-mass time-course and daily growth rate, respectively. A: Fed on phytoplankton mixture; B: Fed on yeast; C: Fed on corn flour. Dashed lines represent the 95% confidence intervals. INTRODUCTION Secondary production is the product of biomass and growth rate. The key to its estimation is a good measurement of growth rate. Principal factors controlling this rate in zooplankton are the amount, and the quality of food (Vijverberg, 1989). Here, we measure the daily and overall growth rate in the Cladoceran, Daphnia magna, raised under different food regimes. We then used the measurements as a reference standard to model zooplankton secondary production in natural populations. Fig.1 .- D. magna growth illustrated by the size time-course. A: Fed on phytoplankton mixture; B: Fed on yeast; C: Fed on corn flour. Fig.1 Fig.2 Fig.3 Secondary production values (period of 12 days) Phytoplankton culture (µg dry mass·d-1) Yeast culture (µg dry mass·d-1) Corn flour culture (µg dry mass·d-1) 508.88 307.46 328.26 Using the expression P = B 0.0455 e0.111T (Huntley and López, 1992) Phytoplankton culture (µg dry mass·d-1) Yeast culture (µg dry mass·d-1) Corn flour culture (µg dry mass·d-1) 1379.32 776.75 943.16 (B = biomass, T = temperature) In comparison, our measurements are approximately 60% lower than the HuntleyLópez model predict. Its seems that their equation may overestimate the secondary production in our culture system. Yeast Corn flour Mixture of Scenedesmus sp. Ankistrodesmus sp. mixture Daphnia magna