Study On The Effects Of Plankton And Zoobenthos In Rice-crab Culture System

Paddy field ecological new technology of planting and breeding isaccounted for a new type of ecological intercropping model. It is a kind oftypical three-dimensional ecological agriculture. Its characteristic isaccording to the rice and Eriocheir sinensis growth reproductivecharacteristics and biological characteristics, applying modern science andtechnology, the planting, breeding and relevant processing ably combinedto form the many species coexistence, multi-level configuration,multilevel energy circulation transformation of the stereo cultivation,breeding and supporting technology, to realize the economic, social andecological three benefits is harmonious and unified.To our knowledge, there has been no research into the plankton andzoobenthos diversity of rice-crab culture system as most research effortsare directed towards the rational selection of rice variety, cultivation andmanagement measures in this system. But plankton and zoobenthoscommunities play a very important role in this complex ecological system.In order to study the effect of rice-crab culture system on plankton andzoobenthos communities in paddy field, periodic sampling was conducted monthly from rice-crab culture system and conventional paddy field whenthe rice in four key growing stage (tilling stage, elongation stage,flowering stage and maturing stage) and the samplings totaled up to fourtimes, then analyzed their species composition, average density, averagebiomass and diversity. Crab larvae were stocked at the density of0ind m-2(the contrast check, namely CK),10ind m-2(the low density treatment,namely LD) and30ind m-2(the high density treatment, namely HD), eachwith three treatments respectively.We identified a total of61species belonging to8phyla and26genera.The average density and average biomass of the conventional treatmentwas significantly higher than the high density treatment in flowering stage(P<0.05). The average density and average biomass of the conventionaltreatment was significantly higher than the rice-crab culture system inmaturing stage (P<0.05). The Shannon-Wiener diversity indices calculatedfor all the treatments revealed no significant difference (P>0.05). TheShannon-Wiener diversity indices of the rice-crab culture system washigher than the conventional treatmentThe three treatments differed little in their species composition: the26of38species were common, and the same five species were dominant.The average density and average biomass of each zooplankton faunalgroup and their annual trends displayed similar patterns, except the average density of cladocera fauna between HD and CK in September(HD>CK, P<0.05), and the average biomass of rotifer fauna between HDand CK in September (CK>HD, P<0.05). The diversity indices calculatedfor cladocera group revealed significant difference among LD, HD andCK in August (CK>LD, CK>HD, P<0.05), and for rotifer group inSeptember (LD>CK, HD>CK, P<0.05).The results showed that the number of zoobenthos species andaverage density declined in rice-crab culture system and the stockingdensity of Eriocheir sinensis had a large effect on zoobenthos. TheShannon-Wiener diversity index and Simpson diversity index ofzoobenthos in the high density treatment were lower than those inconventional paddy field during the whole period, especially in elongationstage and flowering stage (P<0.05), but the evenness index was higherthan conventional paddy field, especially in maturing stage (P<0.05). Thezoobenthos diversity of the low density treatment was significantly lowerthan conventional paddy field only in elongation stage (P<0.05).