Study on macrozoobenthos diversity in Batang Toru River and its surrounding, North Sumatra, Indonesia

Abstract

Batang Toru River is one of the sizable rivers in North Sumatra, encompassing to south and west and stream down to the Indian Ocean. The river area has been used by the local community for several activities, i.e. fisheries and tourism. The macrozoobenthic community structure study was carried out for 3 months in April, July, and October 2019 at 13-17 stations from the upstream to the estuary. Observations were made on the type of macrozoobenthos, meanwhile, data analysis was performed on density, diversity index, evenness index, and dominance index. A total of 21 genera of macrozoobenthos was identified consists of 9 classes, namely Bivalvia (2 genera), Diptera (3 genera), Gastropoda (4 genera), Ephemeroptera (1 genus), Odonata (1 genus), Oligochaeta (6 genera), Plecoptera (1 genus), Tricoptera (2 genera), and Zygoptera (1 genus). Thiara sp. and Balanocochlis sp. were quite commonly found in the study area. The density of the macrozoobenthos during the study period varied between 11-957 ind/m2. The value of the diversity index, evenness index, and dominance index at each station varied from 0.722 to 2.419, 0.411 to 1.0, and 0.210 to 1.0, respectively. Based on these values, the condition of the Batang Toru river ecosystem expressed moderate ecological pressure.