Research Article

Effects of salinity on species composition of zooplankton on Hau River, Mekong Delta, Vietnam

¹ Can Tho University and staff of Faculty of Agriculture and Food Science, Tien Giang University, Can Tho, Vietnam
² GRECO, Institute of Aquatic Ecology, Faculty of Sciences, University of Girona, Girona, Spain
³ College of Aquaculture and Fisheries, Can Tho University, Can Tho, Vietnam

^* Corresponding author: vnut@ctu.edu.vn

Received: 12 March 2020
Accepted: 15 July 2020

Abstract

The area surrounding the Hau River is one of the most important aquaculture and fisheries areas in the Mekong Delta, Vietnam. Fish, shrimp farms and fishers rely of the natural zooplankton production in the incoming water to sustain production. Zooplankton samples were collected from July 2017 to June 2018 using a zooplankton net with mesh size of 60 μm at 3 sites on Hau river at Tran De (river mouth), Dai Ngai (midpoint) and Cai Con (farthest salt intrusion area on Hau river). Qualitative and quantitative samples of zooplankton together with salinity level were determined monthly at each sites. The salinity was found to fluctuate from 0 to 20‰ in the study area. A total of 137 zooplankton species were recorded including 26 species of Protozoa (19%), 47 species of Rotifera (34%), 12 species of Cladocera (9%), 44 species of Copepoda (32%) and 8 other taxon (6%). Copepod and rotifer prevailed with high densities (19.9 × 10³ ind m⁻³ and 19.7 × 10³ ind m⁻³, respectively), whereas protozoa and cladocera were less abundant with 6.8 × 10³ ind m⁻³ and 4.9 × 10³ ind m⁻³, respectively. When salinity increased to more than 5, protozoa and copepods were more abundant and reached a peak at 20 with 25.0 × 10³⁶ ind m⁻³ and 53.0 × 10³ ind m⁻³, respectively. Regression analysis indicated that the density of zooplankton was significantly correlated to salinity variation. Protozoa and copepod were positively correlated with salinity, whereas cladocera and rotifer were negatively correlated with salinity. The impacts of climate change could exacerbate the seasonal fluctuations in salinity and zooplankton composition.