Assessment of zooplankton diversity in Iranamadu Reservoir, Kilinochchi in the Northern Province, Sri Lanka

Abstract

Zooplanktons serve as effective bio-indicators due to their rapid response to environmental fluctuations. The present study was undertaken to study the diversity and composition of zooplanktons in the Iranamadu reservoir, which is the largest tank in the Northern Province of Sri Lanka. This research aimed to provide detailed insights into the composition and density of zooplankton populations, utilizing rigorous methodologies for accurate taxonomic identification and density estimation. Monthly sampling was carried out at ten randomly selected locations from August 2022 to January 2023 including three monsoon periods (South West monsoon, Inter monsoon period, and North East monsoon). Water samples were collected from each location with the help of a 5 l plastic bucket, and filtered through the 64-micron mesh size zooplankton net. The plankton biomass was transferred to specimen bottles (10 ml) filled with 25% of alcohol. In this study, zooplankton observations were conducted using a binocular microscope, with specimens identified to the nearest taxonomic level using standard identification keys. Population density was quantified employing the drop count method. Altogether 10 zooplankton species were recorded, belonging to protozoa, arthropoda including amoebozoa and amoeboid protists. Of the observed species, Paramecium aurelia recorded at high densities throughout the three monsoon periods, however during the South West monsoon, no observations were made for Didinium faurei compared to other species. In the North East monsoon, Amoeba proteus was present at a density of 5 individuals/l. During the three monsoon periods, a total of 77 individuals of Vorticella citrina were recorded. These findings underscore the ecological impacts of seasonal monsoon variations on zooplankton species. The present study provides updated knowledge of zooplankton species diversity in the Iranamadu reservoir.