Research in coral reef communities has been directed towards learning why single-celled algae, the zoothanthellae, live in animal cells such as those of corals and anenomes. A popular assumption has been that the host cell provides a high nutrient environment in otherwise nutrient poor waters. Drs. Cook and Muller-Parker have shown that zooxanthellae, the algal symbionts of corals and other reef invertebrates, can be limited by inorganic nutrients. This research project addresses the question of nutrient limitation with an emphasis on the effect of nutrient status on productivity of the zoothanthellae and on the relative contribution of dissolved versus host-derived sources to the nutrient budgets of these algae. Biochemical and physiological techniques will be applied to both laboratory cultures and in situ coral reef populations. Results will help answer questions relating to the regulation and control of symbiotic systems, mechanisms of nutrient transport and the roles of zooxanthellae in coral reef carbon and nutrient recycling processes.