Understanding the Interaction of Extractive and Fed Aquaculture Using Ecosystem Modelling

One of the most difficult tasks resource managers face is understanding the carrying capacity of coastal waters for aquaculture. Aquaculture, like many other human activities, can threathen coastal waters. Understanding eutrophication and the interaction of two diffierent types of aquaculture is very important to the safe and effective management of coastal aquaculture. The first type of aquaculture, producing shrimp and finfish depends on supplemental feeding and can contribute to eutrophication. The second type, involving bivalve molluscs and macroalgae, extracts plankton and nutrients from surrounding waters and can have a significant positive impact on moderately eutophic waters. These species depend on the water's basic productivity and will not grow effectively in water with low nutrient levels. Balancing extractive and fed aquaculture is of obvious importance to maximizing the safety and optimizing the carrying capacity of an embayment.

Ecosystem modelling offers a three-dimensional physical, chemical and biological simulation that can help scientist and managers understand and predict the eutrophic impact of aquaculture for a specific embayment. Such a model is being explored in China in research sponsored by the Sino-US Living Marine Resources Panel. In this study, two projects are using the model to simulate the impact of aquaculture on Jiaozhou Bay, Shangdong Province, and on Xincun Lagoon, Hainan Province. Jiaozhou Bay is in the temperate zone adjacent to the Yellow Sea.

There, a major port and industrial city, Qingdao, and scallop and shrimp aquaculture interact with the physical and biological components of the bay. The other modelled environment is very different. Xincun Lagoon is a small embayment (~22 km^2) in southeastern Hainan Island adjacent to the South China Sea. Aquaculture in Xincun Bay includes 6500 fish pens ( 3m X 3 m), 100 ha of shrimp ponds, pearl culture rafts and a new macroalgae culture operation that produced 3500 tonnes of Eucheuma in 1998-1999. The surrounding area has ~15,000 people and Xincun City is a major offshore fishing port (~500 vessels, > 10 m length) and Monkey Island Wildlife area with > 400,000 visitors annually. Extractive and fed aquaculture, along with the external activities, all have an impact on the carrying capacity of the bay for aquaculture.

These two models show much promise for simulating local eutrophic conditions and for increasing the general understanding  of the complex interactions of aquaculture and other human activities and eventually predict carrying capacity should become useful tools for resource managers.