Succession of cladocerans in a northern Italian ricefield

The seasonal succession of cladocerans was studied in an experimental ricefield (never treated with biocides) located on the Po River Plain (Province of Reggio Emilia) in 1982, the first year of rice cultivation, and in two later years, 1984 and 1986. A total of 26 species were identified; some of them were found in Northern Italy for the first time. The finding of Latonopsis australis Sars is discussed in detail. A trend of increasing specific diversity during the rice cultivation season was not recurrent every year. The most significant trends emerge when the three years are compared. The total number of species was 14 in 1982, 16 in 1984, and 20 in 1986. Diversity, too, increased strongly over the years: this trend was sustained chiefly by the increase in richness of Chydoridae species associated with the growth and decomposition of a large biomass of weeds and microalgae during the summer.