Trophic Ecology and Ecological Function for Oriental River Prawn ( Macrobrachium nipponense ) in the South-to-North Canal System

The South-to-North Canal System (SNCS) is the largest water diversion project in the world, and it transports water from water-sufficient southern and central to water-deficient northeastern China. The oriental river prawn is the most adaptable prawn species in this ecosystem and a dominant member of the benthic community. In this study, in order to obtain more information regarding the ecological functions of the prawn in the benthic food webs of the SNCS ecosystem, the trophic ecology of the prawn from the canal and the upstream reservoir was compared in the two ecosymtems. The prawn stable isotopic compositions of different prawn sizes (large, medium and small), niche spaces and the trophic positions were compared between the two ecosymtems. Results showed that in the main canal, particulate organic matter (POM) composed more than 40% of the food consumed by all three size prawns. Compared to small prawn, the diet of medium and large prawns were proportionally higher in POM and zooplankton. In the upstream reservoir, large prawn fed primarily on benthic microalgae, which composed 72.8% of the prawn diet. The pelagic food webs provided 93.5% food source for the canal prawn, while the benthic food webs afforded 72.4% food source for the reservoir prawn. Thereafter, the ecological functions of the prawn in the two ecosystems were also different due to their varied food diet. Careful considerations were suggested when using biomanipulation in the SNCS ecosystem.