Emergy Synthesis of Two Oyster Aquaculture Systems in Zhejiang Province, China

China is rich in oyster resources and has a long history of oyster aquaculture. Various forms of oyster aquaculture coexist in the coastal regions of China, which are dominated by raft aquaculture and long-line aquaculture. The objective of this study is to assess the environmental sustainability of the oyster aquaculture systems located in Jiantiao Bay, Zhejiang province, China. Emergy synthesis is used in the study to quantify the contributions of the natural and economic inputs to the oyster aquaculture systems, in order to better understand the sustainability. The results show that the raft oyster aquaculture system was high in emergy inputs and yield per unit area, whereas the long-line oyster aquaculture system was low in emergy inputs and yield per unit area. However, the transformities of the oysters from the raft oyster aquaculture system and the long-line aquaculture were similar, reflecting that both systems had a similar efficiency in using natural and economic resources. The oyster aquaculture systems had a different impact on the environment as inferred from the emergy indicators. The higher emergy yield ratio and low emergy loading ratio in the long-line oyster aquaculture system suggest that the system could gain more net benefit, and had a lower impact on the surrounding environment, than raft oyster aquaculture system, and can been considered to be more sustainable. Nevertheless, oyster aquaculture was a labor-intensive process and relied highly on purchased resources, such as labor and construction materials. If the construction materials could be used for a longer time, the oyster aquaculture systems might be more sustainable and environmentally friendly.