MEASUREMENTS OF PRIMARY PRODUCTIVITY AND NITROGENASE ACTIVITY OF CORAL-REEF ALGAE IN A CHAMBER INCORPORATING OSCILLATORY FLOW

Diffusive limitation of C and nutrient uptake can be an important factor regulating metabolic processes in aquatic plants. Relationships between the flow regime and both primary productivity and nitrogenase activity (ethylene production) of coral reef algal components were studied via a productivity chamber that simulates oscillatory flow. Net primary productivity of algal turfs was increased significantly by flow speeds (steady flow equivalent) up to 16 cm s-1. The mode of water flow also was important; primary productivity of algal turfs increased by 21% under an oscillatory flow regime as compared to vortex flow created by stirring. Acanthophora spicifera exhibited increased primary productivity at flow speeds up to 10 cm s-1, while primary productivity of another rhodophyte, Coelothrix irregularis, increased up to 4 cm s-1. Rates of nitrogenase activity exhibited by algal turfs also were affected significantly by flow speed. These data indicate that diffusive limitation is important to varying degrees in reef algal turfs and macroalgae and suggest that primary productivity and rates of nitrogenase activity depend on ambient flow speeds and boundary-layer dynamics.