WWW.WAS.ORG • WORLD AQUACULTURE • MARCH 2015 27 cucumber Apostichopus japonicus, sea urchin Strongylocentrotus nudus, ark shell Scapharca broughtonii, Manila clam Ruditapes philippinurum and seaweeds Laminaria japonica was studied in a demonstration area of 665 ha located in the south cape of Sungo Bay (5-15 m depth). In the study area, natural seagrass (covering about 400 ha) and seaweed are abundant. Each spring, around 300,000 sea cucumber and 150,000 abalone juveniles are released into the area while other species recruit naturally. In 2009, the total production in the demonstration area was 1.5 t of abalone, 20 t of sea cucumber, 200 t of Manila clam, 80 t of ark shell, and 2.5 t of sea urchin with a total value of more than 10,450 yuan RMB/ha. Almost half of the revenue was derived from sales of sea cucumber. IMTA for Suspended Mariculture in Sungo Bay Open-water culture of finfish, bivalves and kelp. Marine fish cage farming releases organic and inorganic wastes into the environment in the form of uneaten food, faeces, and other excretory products. The accumulation of nutrients, particularly nitrogen, in the environment can cause eutrophication and other environmental problems, which may introduce serious effects on the sustainable development of aquaculture. To reduce the environmental impacts of cage culture, extractive species (bivalves, seaweed) are cultured simultaneously with fed species (marine finfish) as a means of using the waste resource and reduce pressure on the environment (Chopin et al. 2001, Neori et al. 2007). In such systems bivalves function as a filter to remove suspended particulate organic matter, originating from fish faeces, smallsized residual feed and phytoplankton. Bivalves only filter particles of a certain size range, so other deposit feeders (such as polychaetes or sea urchins) can be included to maximize nutrient recovery efficiency in finfish-based IMTA systems because those species ingest other size fractions of the available particulate material. Seaweeds are used to remove and transform dissolved inorganic nutrients from the excretions of finfish and bivalves and in return provide dissolved oxygen to those animals. To evaluate the optimal densities for simultaneous culture of finfish and seaweeds, a field study was conducted (CONTINUED ON PAGE 28) TABLE 2. Annual yield of sea ranching in Zhangzidao Island. Species Sea ranching area (ha) Annual yield (t) Scallop Patinopecten yessoensis 200,000 50,000 Abalone Haliotis discus hannai 1,000 100 Sea cucumber Apostichopus japonicus 1,000 400 Sea urchin Strongylocentrotus nudus 1,000 300 Ark shell Scapharca broughtonii 3,000 500
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