Species composition and population dynamics of the phytoplankton community in Kotmale reservoir

Abstract

The present work was carried out in the Kotmale reservoir from April 1994 to April 1996 with the objective of studying the species composition and the seasonal,spatial and diurnal distribution of phytoplankton.The phytoplankton of the reservoir was composed of four major families:chlorophyceae,Bacillariophyceae and dinophyceae.Chlorophyceae dominated the phytoplankton,with staurastrum species forming the major component.The results show seasonal variation in the major phytoplankton types of the reservoir that correlates with the water level.During the wetmonths,Staurastrum species dominated the phytoplankton while in the dry months Microsystis aeruginosa became prominent especially in the upstream region of the reservoir.This periodic occurrence of M.aeruginosa bloom was a prominent feature of the impoundment.Although the filamentous diatom,Melosira species and the dinoflagellate,peridinium cinctum formed an important part of the plankton community,no contrasting periodicity was observed as in M.aeruginosa.A clear vertical and diurnal migration pattern was observed among the major phytoplankton types.Microcystis showed a downward movement during noon,while P.cinctum was very abundant in the surface during early morning.The phytoplankton forms a major part of the food consumed by the fish in the Kotmale reservoir and the knowledge gained through this investigation will help to improve the commercial fishery of the impoundment.