Seasonal variations in the abundance of phytoplankton in the shallow waters of Cua Be river estuary, Nha Trang bay, Central Viet Nam

Abstract

Thirty-seven species of dinoflagellates and 60 species of diatoms were the main components of the phytoplankton community in the shallow waters of Cua Be river estuary. The key species in the study area in terms of both biomass and frequency of occurrence were Gonyaulax spp., Protoperidinium spp., and Peridinium quinquecorne (dinoflagellates), and centric diatom Coscinodiscus spp., Skeletonema costatum and Rhizosolenia spp. The species composition changed markedly between the dry and rainy seasons. Temperature and salinity were the two main factors affecting the seasonal shifts of species. Peaks of diatoms and dinoflagellates occurred together. Dinoflagellates were abundant throughout the year with highest concentrations in the middle of the dry season and at the beginning of the rainy season. Concentrations of nutrients such as nitrate-nitrogens and ortho-phosphate-phosphorus were strongly related with salinity, but the relations between dinoflagellates and diatoms and nutrients were not clear.