Application of a nutrient-saturated growth model to phytoplankton management in freshwater prawn ( Macrobrachium rosenbergii) ponds in Hawaii

Abstract

With significant modification in only two of nine parameter values, a model of nutrient-saturated growth of Chlorella was found to give an excellent description of experimental data collected from six large experimental tanks and one earthern production pond. The results indicate that in order to maintain system stability with respect to oxygen fluctuations, primary production rates in other commercial ponds are usually kept well below levels that could be attained under optimal conditions. Application of the model to field data shows that phytoplankton populations in prawn ponds should be kept between 150 and 400 mg·m −3 Chl a in order to prevent anoxia in worst case situations such as calm nights. Due to a negative correlation between light-limited growth rates and Chl a concentrations, there is little increase in photosynthesis if Chl a concentrations are raised above 2 g·m −3, and there is a negative correlation between photosynthesis and Chl a concentrations for Chl a > 5 g·m −3. Therefore even under ideal conditions 1-m deep ponds should probably be operated with Chl a concentrations < 2 g·m −3. The success of the light-limited model in describing data from both monospecific continuous culture systems and from diverse populations in prawn ponds suggests that the model may have wide applicability in algal mass culture systems.