アメリカザリガニ
"Gomphonema gracile" is an epiphytic diatom found on "N. caerulea" in high elevation Lake Naivasha, Kenya. In Kenya, "N. caerulea" is positively associated with the freshwater snail "Biomphalaria pfeifferi", which is a main host of human schistosomiasis. The edible American crayfish "Procambarus clarkii" eliminates the mollusc, as well as feeding on the water-lily. The crayfish was first introduced to Kenya in 1966 as a species with which to enhance the local fisheries. In Lake Naivasha, "N. caerulea" was extremely common until the 1970s, and there is still a seedbank around the shores of the lake. "Procambarus clarkii" was introduced to the lake in 1970, and now supports an annual harvest of a few thousand kilograms, but it may have been responsible for eliminating not only the water-lily in the main lake by 1983, but "all" native aquatic plant species in this water body. It is not the only potential culprit; invasive mats of exotic floating vegetation have also taken over the lake, two different commercially fishable fish species have been introduced, and the new fisheries upon these three species could all be responsible, or a combination.