Leaf-litter preferences of the introduced freshwater shrimps Atyaephyra desmarestii and Neocaridina davidi

Detailed knowledge of the significance of shrimps in freshwater food webs is very limited. However, determination of the current potential invasion of shrimps into European freshwater systems requires information on their ecology and feeding behaviour. Atyaephyra desmarestii has established stable populations in Western and Central Europe, while the ornamental species Neocaridina davidi was released in 2009 into a small tributary of the Erft River (North Rhine Westphalia, Germany), where it has thrived. Both species use leaf-litter as a significant food source. In this study, we assessed a reproducible method to compare the preferences of this two shrimp species for decaying leaves of four different species of deciduous tree: alder (Alnus glutinosa), Italian poplar (Populus x canadensis), pedunculate oak (Quercus robur) and goat willow (Salix caprea). We also determined the relevance of A. desmarestii and N. davidi in leaf-litter breakdown. Adults of both species showed a significant preference for leaves of alder and Italian poplar, whereas juvenile individuals did not favour any particular leaf species. A. desmarestii and N. davidi adults exhibited higher night-time than daytime activity. Diurnal consumption rates were determined for N. davidi. It consumed 51.0% leaf litter dry weight per body dry weight per day. Alnus and Salix leaves (including biofilm) made up the majority of the diet of Neocaridina, followed by Populus and Quercus leaves. Our results demonstrate the distinct relevance of leaf-litter in the diet of freshwater shrimps, and their role in leaf-litter breakdown. While the invasion potential of A. desmarestii seems to be relatively low, at least for now, N. davidi has thus far been a very successful invader. This is supported by its high feeding rates on leaf litter of the regional vegetation. Since there is no indigenous shrimp species in the study area, the potential implications of the invasion process merit further investigation.