Increased Production and Water Remediation by Land-Based Farm-Scale Sequentially Integrated Multi-Trophic Aquaculture Systems—An Example from Southern Taiwan

Wastewater effluent from aquaculture ponds can affect aquatic ecosystems. To mitigate this problem, we designed 2 sets (southern and northern) of land-based and farm-scale sequential integrated multi-trophic aquaculture (IMTA) systems in order to reduce water pollution and to diversify and optimize aquaculture products in coastal southern Taiwan. In each system, the 1st pond cultivated milkfish as the main aquaculture product, the 2nd pond cultivated Portuguese oysters as the product to reduce suspended particles, and the 3rd pond cultivated the seaweed Gracilaria sp. as feed and to absorb nutrients. Photosynthetic bacteria (PSB) were added to the southern system in order to reduce nutrients. The objective of this study was to evaluate and compare performance parameters of the compartments and the overall IMTA systems preliminarily. Our results showed that the southern system with the addition of PSB had lower PO4-P, slightly higher turbidity, and higher brown algal biomass than the northern system. In the southern system, PO4-P and cyanobacteria levels were lowest at the end of the seaweed pond. In the northern system, NO2-N and phytoplankton levels were lowest at the end of the seaweed pond. Turbidity was reduced in the oyster pond and further reduced in the Gracilaria pond in both systems. The high seaweed yield in the northern system indicated substantial nutrient absorption. Advantages and limitations in terms of water purification and aquaculture production of these IMTA systems are evaluated in the present paper.