Conversion from rice–wheat rotation to rice–crayfish coculture increases net ecosystem service values in Hung-tse Lake area, east China

Paddy field farms are being converted to provide both grain and aquatic products. Presently, China has 1.11 million ha of rice–crayfish farming system which is growing. Conversion from paddy field-based farming to rice–crayfish coculture systems requires field engineering to excavate ditches for breeding. However, the net ecological benefits of this conversion remain unknown. To address this gap, this study used unmanned aerial vehicle surveillance to monitor the proportion of area of different types of ditches (circle, U-shaped, L-shaped, and I-shaped ditch) of the total field area in 140 rice–crayfish fields in the Hung-tse Lake area. Then the ecosystem service (ES) values were evaluated after the conversion to rice–crayfish coculture. The results showed that the average proportions of area covered by circular, U-shaped, L-shaped, and I-shaped ditches of the total field area were 26.29%, 17.38%, 9.63%, and 1.92%, respectively. Conversion to rice–crayfish coculture increases the net ES value by 145.3–176.9%, but also negatively impacts the ecological environment which should not be ignored. Indeed, with a decrease in the proportion of the ditch, the net ES value increased. Overall, the study suggested that rice–crayfish coculture fields with L- and I-shaped ditches produce substantial crayfish yields and stable rice yields, whereas those with circular and U-shaped ditches squeeze the rice planting area and reduce rice yield. The study provides vital information to avoid the blind expansion and development of rice–crayfish farming from the perspective of the ecological environment, and provides policy suggestions for sustainable development.