Macroinvertebrate Composition, Diversity and Richness in Relation to the Water Quality Status of Mananga River, Cebu, Philippines

Abstract

between February and December 2006 using selected physicochemical factors in combination with macroinvertebrate composition and diversity indices. Three sampling stations, each 100 m long, were established. Alkalinity, total phosphates and nitratenitrogen were similar in all sampling stations. The significant variation in stream depth, width and stream bed profile resulted in diminishing velocity but increasing discharge downstream. These physical characteristics led to increased total suspended solids, water temperature, and biological oxygen demand, but decreased pH and dissolved oxygen levels downstream. The physicochemical factors influenced the composition and diversity of macroinvertebrates in Mananga River. A total of 37 families representing 15 orders were recorded. Aquatic insects T (Class Hexapoda) made up 58.6% of total abundance followed by the gastropods (Class Gastropoda) at 39.9%. The order Ephemeroptera of Hexapoda had the highest abundance (47.6% of total) and highest richness (6 families). Family Thiaridae was the most persistent and the most abundant macroinvertebrate taxa followed by Caenidae. Almost all taxa were represented in the upper stations, except for Neritidae, Grapsidae and Nereididae, which were limited to the downstream station. Macroinvertebrate richness and diversity were significantly higher in the upper stations, but there was an apparent lack of seasonal variation. Signs of increasing water quality deterioration were evident in the results of the physicochemical analyses, and validated by the diversity index where the upper stations came out as moderately polluted, and the downstream station as moderately to highly polluted.