Effects of the invasive red swamp crayfish ( Procambarus clarkii ) on eelgrass-dominated clearwater lakes: the role of bioturbation

The invasive red swamp crayfish Procambarus clarkii (Girard, 1852) can affect freshwater ecosystems, their macrophyte communities in various ways. To examine the effects of red swamp crayfish on clearwater macrophyte-dominated lakes, we performed a 28-day mesocosm experiment, without and with presence of red swamp crayfish, with or without access to sediments using netting. All in the presence of one of the following three different submerged macrophytes: Myriophyllum spicatum L., Vallisneria denseserrulata (Makino) Makino, or Hydrilla verticillate (L.f.) Royle . This experimental design allowed a partial separation of the effects of disturbing the sediment using netting from other factors such as excretion and direct harm of the plants. Nutrients and total suspended solids concentrations were lower in the crayfish-with-net than in the crayfish-without-net treatments but had similar concentrations in the crayfish-with-net and crayfishless-without-net treatments. Compared to the crayfish-with-net treatment, there were more broken leaves in the crayfish-without-net treatments for V. denseserrulata and H. verticillata , while no difference was found for M. spicatum , likely reflecting their different growth forms. Our results suggest that the sediment disturbance by the crayfish was more important than their plant handling/consumption and nutrient excretion for an observed water quality change from clear to turbid.