Daphnia community analysis in shallow Kenyan lakes and ponds usingdormant eggs in surface sediments

摘要

Water fleas of the genus Daphnia are considered rare in tropical regions, and information on species distribution and community ecology is scarce and anecdotal. This study presents the results of a survey of Daphnia species distribution and community composition in 40 standing waterbodies in southern Kenya. The study sites cover a wide range of tropical standing aquatic habitats, from small ephemeral pools to large permanent lakes between approximately 700 and 2 800 m a.s.l. This analysis combines data on Daphnia distribution and abundance from zooplankton samples and dormant eggs in surface sediments. Nearly 70% (27 of 40) of the sampled waterbodies were inhabited by Daphnia. Although their abundance in the active community was often very low, this high incidence shows that Daphnia can be equally widespread in tropical regions as in temperate regions. Analysis of local species assemblages from dormant eggs in surface sediments was more productive than snapshot sampling of zooplankton communities. Surface-sediment samples yielded eight Daphnia species in total, and allowed the detection of Daphnia in 25 waterbodies; zooplankton samples revealed the presence of only four Daphnia species in 16 waterbodies. Daphnia barbata, D. laevis, and D. pulex were the most frequently recorded and most abundant Daphnia species. Canonical correspondence analysis of species-environment relationships indicates that variation in the Daphnia community composition of Kenyan waters was best explained by fish presence, temperature, macrophyte cover and altitude. Daphnia barbata and D. pulex tended to co-occur with each other and with fish. Both species tended to occur in relatively large (>10 ha) and deeper (>2 m) alkaline waters (pH 8.5). Daphnia laevis mainly occurred in cool and clear, macrophyte-dominated lakes at high altitudes