Effects of tidal events on the composition and distribution of phytoplankton in Merbok river estuary Kedah, Malaysia

Abstract

The impact of tidal events on water quality and on the species composition and distribution of phytoplankton at three stations along Merbok river estuary, Malaysia were investigated. Bacillariophyta was the most dominant group, followed by, in decreasing order, Dinophyta, Chlorophyta, Euglenophyta, Cyanophyta and Cryptophyta. Spring tides had higher total cell number and richness but neap tides had higher diversity (except Station 2) and evenness of phytoplankton at all stations. Spring tides also led to higher salinity, conductivity, total suspended solids, nitrate and orthophosphate but lower pH, dissolved oxygen, transparency, chlorophyll-a and nitrite. No significant effects of tidal changes were observed on temperature, light intensity and ammonia. Oscillatoria spp. was dominant at Station 1, while Cylindrotheca spp. and Cyclotella spp. occurred at all stations and were dominant at Stations 2 and 3, respectively. Higher abundance of phytoplankton at Station 1 corresponded to significantly higher nitrate and ammonia but lower temperature, pH, dissolved oxygen, salinity, conductivity, transparency, total suspended solids, nitrite and orthophosphate. Water quality varied according to the tidal events, which subsequently affected the composition and distribution of phytoplankton, thus reflecting the importance of biotic and abiotic parameters in understanding the overall ecological status of the Merbok river estuary.