Ecological succession of zooplankton species in a temporary river in a semi arid region of Brazil

In the semi arid region of Brazil, the rivers and reservoirs are temporary, existing at times, even years, without water. The animal communities have to develop special strategies to survive when the environment is dry and to multiply, when water arrives. This study analyzed the zooplankton community upon the beginning of the rainy season in a temporary river (in remaining ponds) in Northeast Brazil. Ecological succession of species was analyzed throughout 9 months during which there was water in the river. During this period, samples were collected on days 15, 28, 37 and 43 after the start of raining and monthly afterwards. From diapause 28 rotifer species and 5 subspecies; 8 cladoceran species and 8 copepod species ecloded. The first cladoceran to appear was Moina minuta, which reached high densities, 1,234 ind.L-1, followed by Ceriodaphnia comuta, observed on day 28, and by Diaphanosoma spimilosum observed 37 days after the rain event. The first copepods to appear were Mesocyclops meridianus and Muscocyclops sp., both in the first sample (day 15). Of all the species, 21 were observed only once. Among the rotifers 10 species were observed in the first sample. This group was present in high densities e.g. Conochilus sp., with 20,403 ind.L-1, Keratella tropica with 9,392 ind.L-1 and K. lenzi with 1,149 ind.-1. Species densities were correlated with chlorophyll a, nitrate and ammonium. New ephippia production was related with total zooplankton densities, chlorophyll-a, nitrate and ammonium.