Feeding of tropical cladocerans (Moina micrura, Diaphanosoma excisum) and rotifer (Brachionus calyciflorus) on natural phytoplankton: effect of phytoplankton size-structure

摘要

The proliferation of large phytoplankton in tropical shallow freshwater ecosystems may be attributable to inefficient feeding by the dominant zooplankton (small cladocerans and rotifers) on large particles, but more information on the feeding behavior of tropical organisms is required to explore this hypothesis. In this study, food size selectivity and functional feeding responses of three major tropical freshwater zooplankton species (Moina micrura, Diaphanosoma excisum and Brachionus calyciflorus) were studied to test their ability to control phytoplankton. Eleven grazing experiments were performed, using natural phytoplankton assemblages as a food source. Moina micrura fed efficiently on a wide range of sizes of phytoplankton particles, from unicellular picoplankton Chlorella sp. (2-4 mu m equivalent spherical diameter, ESD) to large Coelastrum reticulatum coenobia (20-40 mu m ESD), but the selectivity depended on the nature and size distribution of the phytoplankton. Diaphanosoma excisum ingested only very small particles (Monoraphidium, Chlorella). Brachionus calyciflorus fed on a wide size range but showed a clear preference for the largest algae (Cyclotella sp, Scenedesmus opoliensis). These three species increased their ingestion rate linearly with the food concentration and the saturation point was reached for M. micrura within the range of experimental conditions. The results suggest a strong food partitioning between these three species and showed that B. calyciflorus and M. micrura were better able to exploit and control algal blooms than D. excisum, which was a more selective feeder controlled by the availability of small food particles.