| Recently, the industry of shellfish and seaweed raft culture has been facing different kinds of severe challenges, because of bad management, seeking high production rate and high output value, lopsidedly and ignoring the social and ecological effectiveness, resulted in being over developed, overloaded and severely self-polluted in the marine farming areas, and the ecosystem shows disequilibrium, the diseases of the cultured organisms are aggravated, and cultured shellfish small in size, and high in mortality rate, and lower output. Polyculture is a better way to settle these problems. More effects produces mutually beneficial mechanism, more significant results attains the polyculture. And now, a criterion to evaluate the mechanism is necessary to be set up.Focusing on the criterion above, the polyculture pattern of scallop (Chlamys farreri) and kelp (Lamniaria japonica), which were stocked with different densities, were designed and established with two control ecosystems, according to the findings of shellfish experimental ecology in laboratory and the investigation results from practice. After being measured and assessed, some farming patterns are found they have more outputs and their environment is more optimized than other patterns. Making a future research on the mechanism of optimized pattern, a criterion to evaluate the mechanism will be set up. And checking the practicality, the possibility to benefit aquaculture can be understood. The main results of this study are listed as fellows:1 The first stage in 2000-2001: This study on the polyculture of scallop and kelp was undertaken in Maidao Experimental Station, by the means of experimental ecology to evaluate the mutually beneficial mechanism. The experimental items in this study are environmental parameter, nutrients, phytoplankton and the growth of scallop and kelp. Results from this study indicate that, the concentrations of TIN, SiO4-Si and PO4-P in PatternIII is lower than in Pattern I and Pattern II, and the content of NH4-N among the TIN in Patternlll is 69%, which is lower than in Pattern I and Pattern II. In the meantime, the total numbers of phytoplankton in Patternlll is decreased by 13.872 x 103cell per liter, and the content of chlorophyll is decreased by 1.96mg per cubic meter. (Pattern I : 6.045 x 103cell per liter, 1.79 mg Pattern II: 12.995 x 103cell, 1.78mg). Based on this experimental condition, scallops in Patternlll have a more significant growth compared with scallops in Pattern I and Pattern II .So, the effect of ecological culture in Patternlll is better than other patterns. Relatively the mutually beneficial mechanism in Patternlll is reasonable.2 The second stage in 2001-2002: This study designed three kinds of effective factors on the environmental, nutrient and livable levels to evaluate the mutually beneficial mechanism on the base of the results of the first stage. And the relationship between these effective factors and cultural output is analyzed. Moreover, theoptimized pattern of the first stage is checked again to seek for more accurate ratio of polyculture. Under conditions of the experiment, Pattern SK.2 has more output than other patterns and effective factors is more limiting to cultural output than other patterns in Pattern SK3. On the effective-factors level, the order of relative importance between each effective factor and cultural output is as follow: nutrient composite index > livable composite index > environment composite index > utilization coefficient of phytoplankton > production of phytoplankton > livable composite index > NHt-N > DO in Pattern SKi, nutrient composite index > production of phytoplankton > environment composite index > utilization coefficient of phytoplankton > NH4-N > DO.3 The control-temperature study in 2001: The temperature of polyculture was kept 9.27 + 0.82C. From cultural-output aspect, Pattern SK2 and SK3 get higher production than Pattern SK1 and SK4, which is same with that result from second stage in 2001-2002. But during similar period, the gr...
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