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

Zooplankton growth and nutrient recycling are key processes in the operatio n of pelagic food webs. Most studies investigating these processes rely on complex methods and often require extensive laboratory facilities. Here we introduce a technique for preserving algae by rapid drying for later use in laboratory- or field-based growth and nutrient recycling experiments. Chem ostat-grown Scenedesmus acutus was rapidly dried for later experiments eval uating its nutritional composition, suitability for animal growth and poten tial for use in nutrient release experiments. Reconstituted dried algae had slightly lower nitrogen (N), phosphorus (P) and protein content (% dry wei ght) than fresh algae, but lipid content did not differ and elemental ratio s were in the range considered to indicate favorable food quality. These el emental and biochemical differences did not appear functionally important, as Daphnia magna grew identically on fresh and dried food. Freeze-dried S.a cutus did not work as an alternative to oven drying as it resulted in 100% mortality. NH4 and PO4 concentrations did not change over 24 h when dried a lgae were resuspended in normal media or boiled lake water. However, concen trations of PO4 decreased over 24 h, suggesting chemical adsorption of PO4 to the dried algae and reinforcing the need for animal-free controls in nut rient release experiments using this approach. N and P release rates for D. magna and natural zooplankton communities were estimated using dried algae, and values were comparable to published ones. Thus, dried algae may be a u seful, simple technique for studying food quality and nutrient release in e nvironments where maintaining active algal cultures may not be practical an d a constant supply of consistent quality food is needed.