Zooplankton succession on seasonal floodplains: surfing on a wave of food

Floodplains represent ecotones with frequent high productivity mediated by regular shifts between aquatic and terrestrial ecosystems. We examined interaction along this intercept on a seasonal floodplain of the Okavango Delta, Botswana. We focused on the zooplankton communities in order to gain knowledge on the energetic and stoichiometric interplay of the two systems involved. A conspicuous horizontal migration and pulsed biomass increase was found for the dominant zooplankton species (Moina micrura, Daphnia laevis, Mesocyclops leuckarti), culminating in truly extreme numbers before a final collapse. There was a distinct succession in the peak abundance of these species, apparently subsidized by hatchlings from the seed bank of resting eggs as the flood proceeded over the savannah. The high productivity of the system seems to be driven by a strong coupling of the terrestrial and aquatic phase of the floodplains via a mobilization of terrestrially derived nutrients, through nutrients from grazing ungulates during dry periods. Carbon of terrestrial origin, however, appeared to be of minor importance for the planktonic part of the food web. Handling editor: S. Dodson