Abstract: We investigated the effects of water depths (0.6 m (D1), 0.9 m (D2), 1.2 m (D3) and 1.5 m (D4)) on phytoplankton community structure in paddy fields with Procambarus clarkii from April to May 2021 in the Agricultural Science and Technology Park of Yangtze University in Jingzhou, Hubei Province. The results showed that a total of 106 phytoplankton species belonging to 8 phyla were identified across the four treatments. Chlorophyta was the most dominant group, which accounted for 50.67%, 46.83%, 46.91% and 46.38% of total phytoplankton species in D1, D2, D3, and D4 treatments, respectively. Schroederia nitzschioides, Chlorella sp., and Chroomonas caudata were the dominant species. The total phytoplankton abundance and biomass in the four treatments ranged from 0.82×10⁶ to 99.74×10⁶ cells·L^-1 and 0.77 to 27.21 mg·L^-1, respectively. The total phytoplankton abundance and biomass was lower in D1 than in other treatments, with the highest phytoplankton abundance in D4 treatment and biomass in D2 treatment. The Margalef, Pielou, and Shannon indices were higher in D1 treatment than in other treatments. Based on the phytoplankton diversity indices, water quality in paddy fields was at light to medium pollution level. Results of redundancy analysis showed that dissolved oxygen and water temperature greatly impacted dominant phytoplankton species in paddy fields of different water depths. Therefore, keeping shallow water is beneficial to phytoplankton growth and increase phytoplankton standing stocks in paddy fields.

Key words: phytoplankton, paddy field, water depth, Procambarus clarkii.