Depik Jurnal Ilmu-Ilmu Perairan, Pesisir dan Perikanan (2021) 10(2): 174-179 DEPIK Jurnal Ilmu-Ilmu Perairan, Pesisir dan Perikanan Journal homepage: www.jurnal.unsyiah.ac.id/depik * Corresponding author. Email address: fx.widadi.padmarsari.s@faperta.untan.ac.id p-ISSN 2089-7790; e-ISSN 2502-6194 Received 20 June 2021; Received in revised from 9 July 2021; Accepted 5 August 2021 Available online 26 August 2021 This is an open access article under the CC - BY 4.0 license (https://creativecommons.org/licenses/by/4.0/) The diversity of plankton as bioindicators in Kakap River Estuary, West Kalimantan Widadi Padmarsari Soetignya * , Patricia Marniati, Mardan Adijaya, Yunita Magrima Anzani Department of Aquatic Resources Management, Faculty of Agriculture, University of Tanjungpura, Pontianak, West Kalimantan, Indonesia . ARTICLE INFO ABSTRACT Keywords: Phytoplankton Zooplankton Water quality DOI: 10.13170/depik.10.2.21303 Kakap River Estuary plays an essential role in the life organisms, but it is vulnerable to environmental changes and pollution caused by human activities. This study aims to assess the presence of plankton species, their abundance and diversity as aquatic ecological bio-indicators in Kakap River Estuary. Plankton and water samples were taken for three months, with a frequency of one sample per month, viz. in March, April and June 2020 from four sampling stations in Kakap River Estuary, West Kalimantan. A total of 34 species of plankton were observed from all sampling sites, and identified to belong to 18 classes. Chlorophyceae had the highest relative abundance among the phytoplanktons (40.10%), followed by Bacillariophyceae (21.86%) and Cyanophyceae (19.28%). Oscillatoria sp. and Hydrodictyon sp. were the most dominant phytoplankton species. There were 8 classes of zooplankton identified from all sampling stations throughout the research period. Hexanauplia had the highest relative abundance among the zooplanktons (36.56%) followed by Euglenophyceae (24.37%). The plankton diversity index (H ′) values ranged between 2.33 -3.11. The plankton evenness index value ranged from 0.79 to 0.89 which indicates high plankton evenness at all samping stations, and this is supported by a low dominance index value at all stations ranging from 0.06-0.16. Station 1 had high Shannon-Wienner diversity index score, while for station 2, 3, 4, their scores were in the moderate level. Overall. the diversity index of the plankton from all sampling sites indicated that the quality of the water had no pollution to light pollution level. Introduction Human activities affect the quality of water bodies including lakes, seas, rivers and estuaries (El-Zeiny and El Kafrawi 2017; Fadillah et al., 2017). The estuary is a transitional zone between land water bodies (rivers, streams) and the ocean where the mixing of freshwater and saltwater occurs, or a, giving this area unique characteristics (Hakiki et al., 2017). Estuaries are also a productive area, due to the increased input of organic matter from the land and upstream rivers. Estuaries also play an important role in the life of aquatic organisms, namely as a source of nutrients, as habitat and shelter for various biota, areas of food source, spawning grounds, and also as nursery ground for a number of shrimp and migratory fish species. Furthermore, estuaries are also a habitat for plankton and nekton. Estuaries are very dynamic areas that are vulnerable to environmental changes and pollution caused by human activities, including through the disposal of waste which can come from domestic area, industrial, and other public places (Suoth and Nazir, 2016). This condition is also present in the Kakap River Estuary. The estuary of Kakap River is located in Sungai Kakap District, Kubu Raya Regency, West Kalimantan. In this area, there are not only domestic activities going on. Due to the existence of a fishing port, there are also capture fisheries activities and a fish processing industry. Currently, the Kakap River Estuary seems to have been polluted by domestic waste, market waste, and fish waste. This condition can cause disruption of the ecosystem which then affects the life of the biota living in it, including plankton. Generally, water quality can be observed and measured by a variety of physical, chemical and biological methods. Examples of the biological