Spider Assemblages and Diversity in Rice–Crab Co-Cropping Production Fields

Rice–crab co-cropping refers to a new type of ecological aquaculture technology that involves raising crabs (Eriocheir sinensis H. Milne Edwards) in rice fields. To investigate whether crabs affect the community of spiders in the rice fields, we surveyed the species composition of spiders in two types of rice production fields—a rice–crab co-cropping paddy and a conventional paddy—over two growing seasons. The fields were representative of the rice fields in Panjin City, Liaoning Province, China. We collected a total of 3,406 spiders representing 27 genera and 10 families over the duration of the study. The number of spiders in rice–crab co-cropping paddy fields was significantly higher than in conventional paddy fields, but there was no significant difference in the types of spiders in the two types of paddy fields. An analysis of spider community diversity using Simpson's index, Shannon–Wiener diversity index, Pielou's index, and Margalef's index revealed no significant differences between the rice–crab co-cropping paddy and the conventional paddy throughout the survey period. The evenness index and the richness index exhibited a positive relationship, whereas the dominance index showed a negative relationship. The dominant species in the two cropping systems was Pirata subpiraticus Boes. et Str. (Araneae, Lycosidae). Overall, we found no impact of co-cropping with crabs on the composition and characteristics of the spider community.