Dynamic Changes of Phytoplankton Composition During Cyanobacteria Blooms in Aquaculture Ponds

Abstract:

In order to further understand the dynamics of phytoplankton and its physio-chemical variables during the development of cyanobacterial blooms in aquaculture ponds, water samples were collected and evaluated in an aquaculture pond during the cyanobacterial bloom (July to September, 2017) in Henan Normal University, Xinxiang, Henan (351938.363N, 1135409.482E). The results showed that during the study periods, in total, 25 phytoplankton species belonging to six phyla were identified, and the total phytoplankton abundance and biomass were (0.883~12.666) × 108 cells/L and 9.740~ 70.020 mg/L, respectively. Furthermore, the Shannon-Wiener index was determined, ranging between 0.05 and 1.15. Additionally, the total phosphorus (TP) and total nitrogen (TN) concentrations were 0.32~0.51 mg/L and 4.18~7.09 mg/L, respectively; the water temperature was 22.1~30.6℃. It was suggested that the high amount of TN and TP contents, combined with the high water temperature, might play important roles in this occurrence of cyanobacterial blooms and the low biodiversity in ponds. To further understand the key factors affecting phytoplankton composition, Redundancy analysis was applied. The results showed that cyanobacteria were closely related to the TP and TN concentrations and water temperature. In addition, in consideration of microcystin release due to the occurrence of Microcystis blooms, microcystin content was also determined in this study. At the end of the study periods, according to the ELISA, microcystin content was detected in algal cells and pond water, which were 0.686 µg/L and 0.040 µg/L, respectively. The World Health Organization suggested that the contents of microcystin should be no more than 1.0 µg/L in water samples. Thus, according to the present study, it suggested that the microcystin content was within the safety range in this bloom-occurring pond.