Use of dried algae as a food source for zooplankton growth and nutrient release experiments

Zooplankton growth and nutrient recycling are key processes in theoperation of pelagic food webs. Most studies investigating these processesrely on complex methods and often require extensive laboratory facilities.Here we introduce a technique for preserving algae by rapid drying forlater use in laboratory- or field-based growth and nutrient recyclingexperiments. Chemostat-grown Scenedesmus acutus wasrapidly dried for later experiments evaluating its nutritional composition,suitability for animal growth and potential for use in nutrient releaseexperiments. Reconstituted dried algae had slightly lower nitrogen (N),Phosphorus (P) and protein content (% dry weight) than fresh algae, butlipid content did not differ and elemental ratios were in the rangeconsidered to indicate favorable food quality. These elemental andbiochemical differences did not appear functionally important, asDaphnia magna grew identically on fresh and driedfood. Freeze-dried S.acutus did not work as analternative to oven drying as it resulted in 100% mortality. NH4 and PO4concentrations did not change over 24 h when dried algae were resuspendedin normal media or boiled lake water. However, concentrations of PO4decreased over 24 h, suggesting chemical adsorption of PO4 to the driedalgae and reinforcing the need for animal-free controls in nutrient releaseexperiments using this approach. N and P release rates forD.magna and natural zooplankton communities wereestimated using dried algae, and values were comparable to published ones.Thus, dried algae may be a useful, simple technique for studying foodquality and nutrient release in environments where maintaining active algalcultures may not be practical and a constant supply of consistent qualityfood is needed.