Weed-bed Macro-invertebrate Composition and Abundance in Relation to Water Hyacinth (Eichhornia crassipes (Mart) Solms) in the North-Eastern Lake Tana, Ethiopia

Abstract

The composition and abundance of weed-bed macro-invertebrates were assessed using data from Lake Tana from September, 2012 to May, 2013. Higher weed-bed macro-invertebrates density (6395ind/m 2 inaverage) was recorded in the weed-infested sites. Ephemeroptera was the dominant taxa in weed-infested sites while Hemiptera in the non-infested sites. Statistically there were no significant spatial variations in the density of weed-bed macro-invertebrates in the weed infested and non-infested sites except coleopteran. Seasonally, however, Ephemeroptera, Diptera and Coleoptera showed highest peak density during the dry season in the weed-infested site. While, Hemiptera and Basommatophora, during the rainy reason and Diptera during post rainy season showed peak density in the non-infested sites. The results obtained from Hilsenhoff-Family Level Biotic Index H-FBI categorized site Ribas the highest organic and nutrient polluted site while site Debre-Sinaas the least perturbed site. Though, the results of H-FBI did not show clear difference between the weed-infested and non-infested sites, the observed spatial disparity in taxa may be explained by the variation in the density of prey items, interstitial space for refuge, and presence of predators coupled with small variations in physico-chemical factors. Presence of higher density of beetle species of the families Dytiscidae and Hydrophylidae at the leaf and root interface of water hyacinth seemed to have association between them. Therefore, further investigation is recommended to see their effect and interactions with the weed so as to use those beetles as biological agent to control the weed.