Field Measurement and Modelling of the Material Cycle in the Cultivation Pond of Penaeid Shrimp Penaeus Japonicus

Abstract

Field measurement and modelling of the material cycle are carried out for the cultivation pond of penaeid shrimp Penaeus japonicus. The main purpose of the present study is to investigate the sustainability of coastal shrimp aquaculture, which is increasingly being questioned due to many problems like disease, excessive nutrient enrichment, and low levels of dissolved oxygen tension. Despite the great economic importance of shrimps and their suitability to aquaculture, little is known about the material cycle through the cultivation pond. Additionally, the collapse of shrimp aquaculture in most tropical countries may be attributed to the lack of ecological, biological, and environmental understanding. Hence field measurement of water quality is conducted in the shrimp cultivation pond, which locates in the Kyushu district of Japan. Various environmental factors such as water temperature, salinity, and the concentrations of dissolved oxygen, nutrients, and chlorophyll a are monitored for the water in the pond and that drawn from the outer sea during November and December of 2006. In addition to field measurement, one dimensional numerical model is developed for the shrimp cultivation pond to understand the material cycle through the pond in a quantitative manner. The numerical model consists of physical, lower trophic-level ecosystem, and shrimp growth submodels. The numerical values of physical and physiological parameters are calibrated to achieve the best agreement between observed and simulated results. By integrating results from field measurement and numerical simulation, it is revealed that the quality of water in the cultivation pond is quite different from that drawn from the outer sea. In particular the concentration of chlorophyll a is much higher in the cultivation pond due to large primary production. The results of the numerical simulation show that the high productivity is attributed partly to the activities of shrimps. The information from field measurement and the simulated results of the developed numerical model are useful to optimize the food quantity and quality, the population density of shrimps, and the design of watermills or the other equipments to improve the water quality for sustainable use of coastal shrimp cultivation pond.