Study on community structure and seasonal dynamics of zooplanktons and macrobenthos in Rice-Fish Symbiotic System in Qingtian, Zhejiang Province

Zooplanktons and macrobenthos are the main consumers and decomposers, and are also the important natural feeds for fish, in the rice-fish complex ecosystem. To explore the effect of fish in the Rice-Fish Symbiosis System in Qingtian, Zhejiang province, which was recognized as the Globally Important Agricultural Heritage System by the FAO in 2005, we investigated the community structure and seasonal dynamics of zooplanktons and macrobenthos in the specific rice paddy eco-system, by giving a comparison among those in the rice-carp field (RC), the rice-Chinese hooksnout carp field (RCHC), and the rice field without fish (RWF), in December 2020, and in April, July and September 2021, respectively. The results in the study showed that 30 species of zooplankton (including 16 species of rotifers, 6 species of cladocerans and 7 species of copepods) and 10 species of macrobenthos (including 2 species of oligochaetes, 3 species of chironomids, and 3 species of gastropods) were identified. In zooplanktons, Cyclops vicinus, Microcyclops intermedius, and Brachionus calyciflorus were annual dominant species, and Scapholeberis mucronata, Pleuroxus laevis, and Euchlanis dilatata were seasonal dominant species. In macrobenthos, Branchiura sowerbyi, Limnodrilus hoffmeisteri, and Chironomus flaviplumus acted as the dominant species throughout the year. The variation range of Shannon Weiner index (H′₁), Simpson diversity index (D₁) and the Pielou evenness index (J′₁) of zooplanktons in each of the three rice paddy systems during the experiment was 2.9-4.1, 0.81-0.93 and 0.52-0.75, respectively. The highest values of H′₁ and D₁ in RC and RCHC appeared in April, and for RWF in September, while the lowest value in RC and RCHC appeared in December, and RWF in July. The value of J′₁ in each of the three types of paddy fields was the highest in April and the lowest in December. In the other hand, the Shannon-Weiner index (H′₂), the Simpson diversity index (D₂) and the Pielou evenness index (J′₂) of macrobenthos varied from 1.46 to 2.24, 0.56 to 0.77 and 0.52 to 0.75, respectively, during the experiment. The peaks of H′₂ and D₂ appeared in September in all three paddy fields, while the lowest values in RC and RCHC appeared in April, and of RWF in July. The peak of J′₂ appeared in September in RC, and in December in RCHC and RWF. The lowest value of J′₂ appeared in April in RC and RCHC, but in July in RWF. It was found in our study that the number of species, the density, the biomass and the diversity indexes of zooplankton and macrobenthos in the rice-fish system were significantly different (all P<0.05) among various seasons. At the same season, the density and biomass of zooplankton and macrobenthos in RC and RCHC were lower than those in RWF, however, all of the difference between them were not significant (all P>0.05). In all, to illustrate the community structure and seasonal dynamics of zooplankton and macrobenthos in the rice-fish symbiosis system will be helpful to reveal the intrinsic mechanisms of the mutually beneficial symbiosis of rice and fish, and to promote the development and the comprehensive improvement of the cropping-breeding coupled mode of rice and fishery.