Algal Nutrient Limitation and Food Quality for Aquatic Herbivores

Nutrient limitation of algal growth provokes changes in the biochemical composition of the cells. This in turn affects the quality of algae as food for upper trophic levels. Models of the dynamics of the interaction of herbivores and their food thus should include such food quality effects. This research will explore the ways in which algal growth rate changes food quality. Laboratory demography studies of the freshwater cladoceran, Daphnia pulex, feeding on variously limited unialgal and multi- algal foods will be undertaken. These studies will ascertain the relationship between growth rate and quality in simple systems. In addition, food quality effects in natural populations will be examined through a set of experiments and measurements including 1. assessment of nature and degree of nutrient limitation in algal populations, 2. assessment of degree of food limitation in zooplankton populations, 3. measurement of assimilation efficiency of N and P in zooplankton. These data will then be used to explore in theoretical models how the stability and tendency for coexistence of herbivore and algae is influenced by food quality effects. Results will contribute to the conceptual basis of limnology and will add to the information base for managing aquatic resources.