Abstract
Ciliates are pivotal components of the marine microbial food web, exerting profound impacts on oceanic biogeochemical cycling. However, the temporal dynamics of ciliate assemblages on a short time scale in the highly fluctuating estuarine ecosystem remain largely unexplored. We studied changes in the ciliate community during a short time frame in the high salinity waters (>26) of a subtropical estuary. Ciliate abundance, biomass, size and oral diameter structure, and community composition fluctuated considerably and irregularly over a few days or even a few hours. Spearman correlations and the generalized linear model revealed that heterotrophic prokaryotes (HPs) and viral abundances drove the dynamics of ciliate abundance and biomass. The structural equation model further identified a major path from the high-fluorescence content virus (HFV) to HPs and then ciliates. Given the substantial correlation between salinity and HPs/HFV, we proposed that the response of HPs and HFV to salinity drives the dynamics of ciliate biomass. Additionally, the Mantel test showed that phytoplankton pigments such as Lutein and Neoxanthin, phosphate, and pigmented picoeukaryotes were key covariates of the ciliate community composition. This study demonstrated the highly changing patterns of ciliate assemblages and identified potential processes regulating ciliate biomass and community composition on short timescales in a subtropical, hydrographically complex estuary.
Highlights
Microbial communities drive marine ecosystem functions (Fenchel, 2008; Worden et al, 2015)
Two ml of seawaters were pre-filtered through a 20μm mesh and fixed with ice-cold glutaraldehyde (0.5% final concentration) at room temperature for 15 min in the dark, flash-frozen in liquid nitrogen to determine the abundance of picoplankton, including pigmented picoeukaryotes (PPEs), heterotrophic prokaryotes (HPs), Synechococcus, and viral-like particles (VLPs)
The abundances of high-fluorescence content virus (HFV) and low fluorescence content virus (LFV) increased from 7.34 × and 5.27 × cells ml−1 (17:30 on Apr 9) to 1.44 × and 7.38 × 106 cells ml−1 (16:30 on Apr 16), whereas the HPs abundance increased from 7.18 × cells ml−1 (15:30 on Apr 3) to 3.10 × cells ml−1 (16:30 on Apr 16, ca. 30-fold increase)
Summary
Microbial communities drive marine ecosystem functions (Fenchel, 2008; Worden et al, 2015). Using techniques with high taxonomic resolution, in situ investigations have advanced our understanding of the diversity, distribution patterns, and potential driving mechanisms of estuarine ciliates, highlighting the influence of the water mass (as defined by salinity and temperature) and other environmental factors on the ciliate community (Sun et al, 2017, 2020, 2021; Yang et al, 2020; Gu et al, 2021). Due to their small size and fast growth rate, microbial communities cannot remain static throughout time and can respond rapidly to even mild perturbations (Faust et al, 2015). High-resolution investigations of short-term changes in ciliate abundance and community composition are highly desired to gain insights into the intricate temporal dynamics of ciliates and their driving factors
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