# Effects of Rice–Duck–Crayfish Integrated System on the Community Structure of Plankton and Its Relationships with Environmental Factors

## TL;DR

This study compares two farming systems and finds that integrating ducks with rice and crayfish improves water quality and plankton diversity.

## Contribution

The study reveals that the rice–duck–crayfish system enhances plankton diversity and reduces eutrophication compared to rice–crayfish systems.

## Key findings

- The RDCI system had higher plankton diversity and biomass compared to the RCCC system.
- Key environmental factors influencing plankton include water temperature, dissolved oxygen, and nitrogen levels.
- The RDCI system reduces eutrophication during crayfish stages and increases nutrients during rice stages.

## Abstract

To clarify plankton dynamics and improve water quality management in the rice–duck–crayfish integrated system (RDCI), we continuously monitored plankton and physicochemical parameters in the RDCI and the rice–crayfish continuous culture system (RCCC) (Mar 2022–Jan 2023). Key findings include the RDCI had 214 phytoplankton/92 zooplankton species (vs. 196/95 in the RCCC), with shared dominant groups (Chlorophyta, Bacillariophyta; Rotifera). Compared with the RCCC, the RDCI had lower plankton density, higher biomass in key stages, and significantly higher plankton diversity indices. Key influencing factors were water temperature, dissolved oxygen, total nitrogen, and ammonia nitrogen. The RDCI has a more stable plankton community, alleviates eutrophication in crayfish stages, increases rice-stage nutrients, and supports green agriculture.

To accurately manage precise feeding and water quality regulation in the rice–duck–crayfish integrated system (RDCI), the continuous monitoring of plankton and physicochemical parameters in the water was conducted from March 2022 to January 2023 in both the RDCI and the rice–crayfish continuous culture system (RCCC). The results showed that a total of 188 phytoplankton species and 92 zooplankton species were identified in the RDCI, whereas 152 phytoplankton species and 95 zooplankton species were detected in the RCCC. The phytoplankton community composition was similar between these two systems. For zooplankton, Rotifera was the dominant group. However, Chlorophyta and Bacillariophyta were the dominant phytoplankton groups. Compared with the RCCC, the RDCI exhibited lower plankton density during the crayfish-farming stage and overwintering stage, but higher plankton biomass during the crayfish-farming stage, overwintering stage, and rice maturity stage. The diversity indices, richness indices, and evenness indices of both phytoplankton and zooplankton in the RDCI were significantly higher than those in the RCCC. Correlation analysis indicated that water temperature, dissolved oxygen, total nitrogen, and ammonia nitrogen were the key environmental factors affecting plankton community structure. In summary, compared with the RCCC, the RDCI exhibits higher plankton diversity and better evenness, suggesting a more complex and stable community structure. The species composition of plankton and related indices indicate that the RDCI mitigates the degree of eutrophication in water during both the crayfish farming and the overwintering stages, while increasing nutrients levels during the rice planting stage. This approach is beneficial for reducing non-point-source pollution in agriculture and promoting green agricultural development.