The study was conducted to survey the phytoplankton composition and abundance from intensive whilewhite shrimp (Litopenaeus vannamei Boone, 1931) culture in earthen ponds in Cai Nuoc district, Ca Mau province. Phytoplankton samples were collected once every 7 days until the harvest period, with a total of 13 sampling times. The results of this study showed that 77 phytoplankton species were identified that belonged to 4 phyla, Cyanobacteria, Chlorophyta, Bacillariophyta and Dinophyta. Among these diatoms were the dominant communities with 53 species (69%), whereas the remaining phyla contained fewer candidates in a range of 3 to 13 species (4 to 17%). The phytoplankton population ranged from 15 to 31 species throughout the study period, and the abundance of phytoplankton was around 12,080,036 to 181,150,577 ind./l. Bacillariophyta possessed the highest number of species while Chlorophyta was the most abundant group in this study. The green algae and dinoflagellate densities were obtained the highest in Pond 1 compared to those in Pond 2 and Pond 3. The most prevalence of cyanobacteria was found in Pond 3, whereas Diatoms were the most abundant in Pond 2 rather than others. In addition, Chlorella sp. and Nannochloropsis sp. reached the most abundant species in this study with means of 12,083,467 ± 7,260,148 ind./l and 22,581,921 ± 24,220,920 ind./l, respectively.
