Abstract:
The plankton communities in Trat Bay, Trat Province were studied. The plankton
samples were collected 3 times in each station, from 10 stations in February, May and August
2018. The results showed 3 phytoplankton divisions, consisting of the Chlorophyta (green algae
division) Cyanophyta Division (Blue-Green Algae) and Chromophyta Division (Golden-Algae)
which found that Chromophyta Division Bacillariophyceae (Diatom) was the most diversity. In
total, 9 zooplankton were found in 29 groups. The zooplankton, Calanoid copepod, was a
dominant group throughout the study. The average density of phytoplankton in February, May
and August was 35,771, 532,120 and 855,820 cells per liter, respectively. The result indicated
that only in August, phytoplankton was found in the green algae group. The average density of
zooplankton in February, May and August was 7,765, 4,412 and 10,815 individuals per cubic
meter, respectively, in terms of the structure of plankton in the area of Trat Bay. Each mouth
found the changes with the density of phytoplankton in the diatom group Dinoflagellate group,
the group of blue-green algae and zooplankton were found in the group of Calanoid copepod,
Arrow worm, Comb jellyfish and Cnidaria Larva during high salinity. The density of
phytoplankton in the group of green algae, the Dinoflagellate group and the Calanoid copepod
zooplankton during the low salinity water period were also found. In this study, both salinity and
nutrients were the main factors affecting the structural changes and distribution of
phytoplankton and zooplankton.