Influence of substrate embeddedness and canopy cover on the distribution of Ephemeroptera, Plecoptera and Trichoptera (EPT) in tropical rivers

The pattern of Ephemeroptera, Plecoptera and Trichoptera (EPT) distribution in rivers of Gunung Jerai catchment in Kedah, a northern state in Peninsular Malaysia, varied significantly among rivers (p < 0.005) coinciding with the substrate embeddedness and shaded areas of their habitats. Generally Ephemeroptera preferred a habitat with optimal embeddedness (0-25% substrates surrounded by fine sediments) while Trichoptera and Plecoptera preferred marginal (50-75% substrates surrounded by fine sediments) or suboptimal (25-50% substrates surrounded by fine sediments) conditions. The Kruskal-Wallis test indicated that the EPT abundance differed significantly among various categories of substrate embeddedness (chi(2) = 19.673, p < 0.005) and canopy cover (chi(2) = 20.723, p < 0.005). The Canonical Correspondence Analysis (CCA) ordination and the non-supervised artificial neural network (ANN) showed that distribution of Neoperla (Plecoptera), Hydropsyche and Setodes (Trichoptera) were strongly influenced by the embeddedness of rivers' substrates in the surrounding sand and silts in each river. In addition, the amount of canopy covering the water surface determined the associations of Kamimuria, Ecnomus, Macrostemum, Setodes and Ganonema with their habitats. These results showed that distribution of the EPT genera in these rivers was influenced by the availability of surface area on rocky substrates and the amount of light penetration into the water.