The Louisiana crayfish (Procambarus clarkii) has been proposed as a biological control agent for the intermediate snail hosts (Bulinus and Biomphalaria spp.) of human schistosomes (Schistosoma haematobium and S. mansoni) in Kenya. Using laboratory and field experiments, we examined the potential non-target effects such introductions might have on native Kenyan aquatic biota. In an eight-week laboratory mesocosm experiment, crayfish decreased water clarity and reduced populations of slow-moving, benthic invertebrates including non-target snails, chironomid larvae and oligochaetes. Similar declines in invertebrates occurred in an unreplicated 35-day whole-pond experiment. In addition, water lilies disappeared from the pond into which crayfish were introduced, while water lilies remained abundant in the pond without crayfish. Given the large impacts of crayfish on native invertebrate and macrophyte communities in our experiments, promotion of this crayfish as a biological control agent should not proceed without additional assessment of the risks posed to native biota, including fishes (which were not addressed in our experiments). If crayfish colonised the large natural lakes of East Africa, globally important freshwater biodiversity resources might be at risk.
Keywords: introduced, invasive, invertebrates, Kenya, macrophytes, snails
African Journal of Aquatic Science 2005, 30(2): 119–124