A Preliminary Study on the Variation of Zooplankton Diversity, Abundance and Density in a Selected Branch of Diyawanna Oya Canal System

Zooplankton make the secondary level in aquatic ecosystems and provide a ready source of food for secondary consumers. Hence any fluctuation in their population will directly affect the food webs, and eventually the whole ecological system. This study was carried out along a main branch of Diyawanna Oya, during the period of February to July, 2003. The objectives of the study were to find out the variation in diversity, abundance and density of zooplankton present in a selected branch of Diyawanna Oya and their correlation with some environmental parameters. Zooplankton & water samples were collected monthly from six stations representing both edges and the middle of the canal. During the study, 39 species of rotifers, 9 species of cladocerans, 6 species of copepods, 5 species of ostracods, some larval stages of malacostracans, 2 species of large protozoans and one Tardigrade species were recorded. There was a significant monthly variation in the average density of zooplankton. It was positively correlated with the flow rate (r = 0.81), depth (r = 0.47) and temperature (r = 0.58) of water. And there was a significant variation in density and abundance among six sampling stations. Density values of stations were positively correlated with DO level (r = 0.72) while it was negatively correlated with total alkalinity (r = -0.78), total hardness (r = -0.67) and conductivity (r = -0.6). The highest average density of zooplankton was recorded from Kotte whereas the least was from Torrington. Additionally, the possibility of ousing Lacane sp., Philodina sp. and Moina micrura taxa as indicators was also noted.

OUSL Journal Vol.9 2015: 61-81