Macrofauna of Rajang River, Sarawak, Malaysian Borneo

Abstract

Surveys were carried out in the main Rajang River and its tributaries to record the community structure of macrofauna. Samplings were done in nine sampling stations using Van Veen Grab sampler and modified kick nets. Six phylla of macrofauna (Mollusca, Annelida, Arthropoda, Nematoda, Brachiopoda and Echinordermata) were recorded in which include 22 species of gastropods, three species of bivalves, 16 species of polychaetes, 10 species of oligochaetes, 51 species of insects, six species of crustacean, one species of nematode, one species of branchiopod and one species of echinoderm. The species number of aquatic insects group was high at freshwater stations while annelids groups were found to be dominant at the estuarine stations. The density of macrofauna ranged from 70-1550 individuals per m2. The Shannon–Weaver diversity and Pielou’s evenness indices ranged from 2.19-3.60 and 0.56-0.85 respectively. Based on the taxa richness values, the conditions of the aquatic ecosystem in Rajang River tributaries are good indicating recovery process in post-logging areas upstream of the sampling stations. However, water in the main Rajang River is loaded with fine silt and almost permanently turbid suggesting possible effects either detrimentally or otherwise to the range of resident fauna within the river system.