Food spectrum of Branchinecta orientalis-are anostracans omnivorous top consumers of plankton in temporary waters?

Anostracans are key elements of temporary ponds, due to the high abundance and importance as food for waterbirds. Except for a few large species, they are generally considered to be herbivorous filter feeders. However, this assumption is not supported by empirical data. In fact, there is a lack of quantitative experimental studies on their trophic role in the food webs of temporary waters. Here, we briefly revise the available data about the feeding spectrum of anostracans. Moreover, we present experimental data on the feeding behaviour of a key species of soda pans, Branchinecta orientalis. We show that B. orientalis is able to ingest a wide range of prey items, ranging from picosized algae, to motile prey such as copepods, with no significant differences in the ingested biomass from the different food types. We do not find evidence for sex and size-specific differences in the ingestion rates in adult animals. Our results clearly show that B. orientalis is an omnivorous planktivore. Based on our data and existing studies, we suggest refuting the general theorem that most anostracans are herbivorous filter feeders. More empirical data from the field are needed to fully appreciate the trophic role of these key consumers of temporary waters.