A review of the impacts of invasive aquatic weeds on the biodiversity of some tropical water bodies with special reference to Lake Victoria (Kenya)

Abstract

Aquatic weeds may be defined as troublesome or unsightly plants growing in abundance in aquatic situations where they are not wanted. These plants are either adapted to continuous supplies of water or are at least tolerant to waterlogged soil conditions for substantial periods of time. The wide range of adaptation to varying amounts of water, and the impossibility of sharply distinguishing between aquatic and terrestrial environments, makes it difficult to precisely define an aquatic plant. The menace of water weeds is reaching alarming proportions in many parts of the world, especially in tropical water bodies where they have led to serious ecological and economic losses. Lake Victoria, Kenya, which is the largest freshwater body in the tropics, has undergone serious ecological changes including over-exploitation of its fishery resources, degradation of the catchment area, introduction of exotic fish species and invasion by the water hyacinth, Eichhornia crassipes (Mart.) Solms (Pontederiaceae), among others. The presence of the weed in the lake has led to many problems including blockage of water pumps, reduced fishing activities and increase in water borne diseases such as schistosomiasis. Positively, aquatic weeds constitute a free crop of great potential value; they are a highly productive crop that requires no tillage, fertilizer, seed, or cultivation. Moreover, these plants have the potential for exploitation as animal feed, human food, source of food to some aquatic organisms, soil additives, fuel production, wastewater treatment, source of raw materials and habitat to many organisms. This paper reviews the effects of aquatic weeds in aquatic systems with examples from some selected waterbodies and special reference to Lake Victoria.