Effect of rice-crab culture system on zoobenthos diversity in paddy field

Rice-crab culture system is a new ecological complex that combines rice culture with that of Eriocheir sinensis. Zoobenthos communities play a critical role in this complex ecological system. To our knowledge, however, there little research has been conducted on zoobenthos diversity in rice-crab culture systems. Much research has been directed towards the rational selection of rice variety, cultivation and management measures of rice-crab culture systems. To determine the effects of rice-crab culture systems on zoobenthos diversity in paddy fields, periodic sampling was conducted in rice-crab culture systems with different crab densities (10 ind·m^-2, LD; 30 ind·m^-2, HD) and in conventional paddy field (CK) at four key growth stages (tillering stage, elongation stage, flowering stage and maturity stage). The samples (a total of four per time) were analyzed for species composition, average density and diversity. At tillering stage, the results revealed no significant difference in species number, average density, diversity index and Pielou evenness index of zoobenthos faunal groups in the three treatments (^P > 0.05). At elongation and flowering stages, zoobenthos species number and average density were inversely related with crab density. Species number and average density of zoobenthos under LD and HD treatments was lower than those under conventional treatment. Shannon-Wiener diversity index of conventional treatment was significantly higher than that of HD treatment in both periods (^P< 0.05). However, the Shannon-Wiener diversity index and Pielou evenness index of conventional treatment were only significantly higher than those of LD treatment at elongation stage (^P < 0.05). At maturity stage, species number and average density of zoobenthos under three treatments were at the lowest levels. The Shannon-Wiener diversity index revealed no significant difference among the three treatments (^P> 0.05) and the Pielou evenness index of HD treatment was significantly higher than that of the conventional treatment (^P < 0.05). The study provided additional theoretical guidance about zoobenthos diversity protection and sustainable development of rice-crab culture systems. It provided another means of promoting the development of rice-crab culture technology.