Elemental ratios in fresh-water plankton; implications for community structure and energy transfer in food webs

The transfer of energy through food webs will be determined by the "growth efficiency" in terms of carbon for the individual members of the foodweb. Recent studies have clearly confirmed that the elemental ratios of the food will be a major determinant to this energy transfer or "trophic efficiency". Consumers need a certain proportion of major elements in their diet to match their bodily demands. When the food source has too low proportions of P or N relative to C, the excess C cannot be utilized for gro wth, and the growth efficiency will decrease. Less C is diverted through the food web, slopes of trophic pyramids will decrease, and there will be less energy available for top trophic levels. Using cladocera as an example, "bottleneck" periods for reduc ed growth can be identified The present experiment will study how light and nutrients (P) alone and combined will affect C:P-ratios in phytoplankton, and how this will be manifested as changed flux of carbon and energy. This will have strong bearings for carbon import and export (sedimentation) in aquatic ecosystems. The Dr. scient. degree will be based on a combination of laboratory (chemostat) experiments and field (enclosure) studies.