Daily and vertical dynamics of rotifers under the impact of diatom blooms in the Three Gorges Reservoir, China

Abstract

The Three Gorges Dam was built in 2005 with a storage capacity of 39.3 billion m 3 , ranking 22nd in the world. However, since the impoundment of the reservoir, serious blooms of phytoplankton have occurred. Rotifers, having a key role in the freshwater aquatic food web, are important grazers of phytoplankton and an essential food resource to higher trophic consumers. To explore the impacts of phytoplankton blooms on the rotifer community, daily and vertical surveys of rotifers were conducted in a bay of the Three Gorges Reservoir (Xiangxi Bay). Altogether 46 rotifer species were registered, and Synchaeta tremula, Polyarthra vulgaris, and Brachionus calyciflorus were the most abundant species accounting for 36, 26, and 16% of the mean rotifer densities, respectively. Although these dominant species always prevailed in the rotifer community, their proportions changed significantly from non-bloom phase to bloom phase, e.g., the significance of S. tremula deceased from 46.8 to 33.2%, while P. vulgaris and B. calyciflorus increased from 23.9 and 13.9% to 26.2 and 16.2%, respectively. In the vertical water column, all the rotifer following phytoplankton displayed an aggregated distribution, concentrating at the upper layers (0.5-5 m), especially during the bloom phase. From the non-bloom phase to the bloom phase, rotifer densities, the dominant rotifers, Shannon-Wiener and Margalef's diversity increased significantly, while the evenness displayed the opposite trend. Non-metric multidimensional scaling analysis (NMDS) revealed that the samples in the non-bloom phase were well separated from those in the bloom phase. This means that the outbreak of the diatom bloom in the Xiangxi Bay had significant impacts on the rotifer community. Further investigations are needed to address the impacts of the changes of rotifer community on higher trophic levels.

Assessing the Effects of Phytoplankton Structure on Zooplankton Communities in Different Types of Urban Lakes

“…On the other hand, zooplankton grazers respond to the environmental changes as primary consumers of phytoplankton. First, as a food source, phytoplankton defines the structural features of zooplankton and conversely controls algal growth, with particular effects on water quality [60]. In addition, these communities, through the fast turnover, capture the ecosystem changes in a very short time.…”

Under‐ice mesocosms reveal the primacy of light but the importance of zooplankton in winter phytoplankton dynamics

“…Zooplankton significantly decreased total phytoplankton biovolume, cryptophyte biovolume, and diatom abundance, suggesting that zooplankton selectively grazed larger cryptophytes (specifically Cryptomonas ) and smaller or non‐colonial diatoms. Diatoms and cryptophytes are known food sources for both rotifers and crustacean zooplankton (Mohr and Adrian 2002; Zhou et al 2011; Tõnno et al 2016). Furthermore, we found higher SRP and ammonium with high zooplankton levels, which is likely the result of zooplankton excretion (Oliver et al 2015).…”

Under-ice mesocosms reveal the primacy of light but the importance of zooplankton in winter phytoplankton dynamics

“…Zooplankton significantly decreased total phytoplankton biovolume, cryptomonad biovolume, and diatom density, suggesting that zooplankton selectively grazed larger cryptophytes (specifically Cryptomonas ) and smaller or non-colonial diatoms. Diatoms and cryptophytes are known food sources for both rotifers and crustacean zooplankton (Hansen 2000, Mohr and Adrian 2002, Zhou et al 2011, Tõnno et al 2016). Furthermore, nutrients showed signals of zooplankton activity through increases in SRP, ammonia, and TN with increased zooplankton.…”