Use of degraded coastal wetland in an integrated mangrove–aquaculture system: a case study from the South China Sea
Abstract The coastal wetlands of the South China Sea are highly productive and, in 2004, the capture fishery and aquaculture of this area contributed around 8% and 54% of world production, respectively. However, the coastal zone is characterized by high population density and rapid development such that mangrove conversion and reclamation is one of the main threats to coastal wetlands. Globally, about 26% of the mangrove has disappeared since the 1980s much of it being converted to aquaculture ponds. In an attempt to achieve the target of combining mangrove conservation and aquaculture, the Integrated Mangrove Aquaculture System (IMAS) was established in 2002 in southern China. This system was directed towards three goals: mangrove replanting; water purification; and more ecologically friendly aquaculture. Different aquaculture ponds were planted with one of four mangrove species and the aquaculture production, water quality and mangrove growth and survival were compared with control ponds. It has been found that the mangrove species Aegiceras corniculatum is the best for planting in aquaculture ponds given its high tolerance of long-term inundation and its effectiveness in purifying the aquaculture water body in both laboratory and in situ experiments. Following planting with mangrove, the aquaculture ponds can become self-purifying through nutrient uptake by the mangrove. Aquaculture harvests of some mangrove-dependent species, such as red drum (Sciaenops ocellatus), and oyster (Crassostrea rivularis), were increased by over 10% in the presence of mangroves. The food chain, traced by stable isotope analyses, indicates that mangrove litterfall contributes between 1 and 26% of the diet of cultured fishes. The two replicated trials implemented in Shantou and Shenzhen displayed similar results of water purification. Further replication of the use of the IMAS should be attempted at other sites of southern China.