A Study on Spatio-Temporal Variations in Physicochemical Parameters and Ciliate Community Structure of Three Freshwater Bodies from Delhi, India.

The present investigation studied the spatial and temporal variation of the physicochemical parameters and their correlation with the ciliate community structure. Samples were collected from three freshwater sites viz., Okhla Bird Sanctuary (OBS), Sanjay Lake (SL) and Raj Ghat (RJ) in alternate months for one year from September 2018 to August 2019. Physicochemical parameters studied were temperature, pH, dissolved oxygen (DO), total dissolved solids (TDS), water hardness (WH), chloride, sulphate, phosphate, nitrite, nitrate and ammonia. Ciliate diversity, structure and abundance were studied using various diversity indices. Multiple statistical methods such as Pearson correlation coefficients, principal component analysis (PCA) and non-metric multidimensional scaling (NMDS) were applied to analyze the data. Maximum ciliate diversity, richness and evenness were observed in the OBS site. Maximum ciliate diversity was observed from class Spirotrichea (47%), followed by Oligohymenophorea (20%), Prostomatea (16%), Phyllopharyngea (6%), Colpodea (5%), Heterotrichea (3%), Litostomatea (2%) and Karyorelictea (1%). Maximum diversity was observed during the monsoon and post monsoon season and lowest during the winter and summer season. The present study on the dynamics of the environment driven community assembly suggests that ciliates are good indicators for assessing community-level responses and can be useful in predicting the water quality as well as environmental degradation in future.

Biogeographic Role of the Kuroshio Current Intrusion in the Microzooplankton Community in the Boundary Zone of the Northern South China Sea

Kuroshio Current intrusion (KCI) has significant impacts on the oceanographic conditions and ecological processes of the Pacific-Asian marginal seas. Little is known to which extent and how, specifically, the microzooplankton community can be influenced through the intrusion. Here, we focused on ciliates that often dominated the microzooplankton community and investigated their communities using high-throughput sequencing of 18S rRNA gene transcripts in the northern South China Sea (NSCS), where the Kuroshio Current (KC) intrudes frequently. We first applied an isopycnal mixing model to assess the fractional contribution of the KC to the NSCS. The ciliate community presented a provincial distribution pattern corresponding to more and less Kuroshio-influenced stations. Structural equation modeling revealed a significant impact of the KCI on the community, while environmental variables had a marginal impact. KCI-sensitive OTUs were taxonomically diverse but mainly belonged to classes Spirotrichea and Phyllopharyngea, suggesting the existence of core ciliates responding to the KCI. KCI-sensitive OTUs were grouped into two network modules that showed contrasting abundance behavior with the KC fraction gradient, reflecting differential niches (i.e., winner and loser) in the ciliate community during the Kuroshio intrusion scenarios. Our study showed that the Kuroshio intrusion, rather than environmental control, was particularly detrimental to the oligotrophic microzooplankton community.

Ciliates as bioindicators of environmental pressure in a karstic river

Ciliates (protozoa) are a very large and diverse group of microeukaryotes that occupy a central position in the trophic web of freshwater ecosystems. Ciliates exhibit high ecological sensitivity and have tremendous bioindicator potential, but they are largely ignored in routine biomonitoring, mainly due to limitations in morphological diagnosis, which is both time-consuming and costly. In this study, we combined molecular (Illumina sequencing of the hypervariable V9 region of the SSU rRNA gene) and morphological approaches to get a detailed insight into the periphytic ciliate community structure and function within a karst, tufa-precipitating hydrosystem (National Park Krka, Croatia). Periphyton (biofilm) was sampled from light- and dark-exposed lithified tufa/stones at four representative locations within the Krka River, including upstream, midstream, and downstream river sections. We identified hydrological parameters and saprobiological classification of the sampling locations as the main structuring factors for ciliate communities. The molecular approach showed a clear separation of sampling locations in beta diversity analyses, as confirmed by PERMANOVA test. In contrast, alpha diversity was mostly affected by light exposition of the lithified tufa/stones, as confirmed by morphological approach. Environmental conditions consistently affected ciliate community composition at all locations, resulting in clear separation of periphyton samples. Our results indicate that ciliates should be considered as important bioindicators in monitoring tufa-forming rivers and streams, and the molecular approach (V9 region) proved to be applicable because as it efficiently captured the diversity of ciliates in periphyton. Validation of such an approach would lead to significant progress in extending monitoring to a broader range of indicator organisms than those now included in standard monitoring.

Temporal Variability of Planktonic Ciliates in a Coastal Oligotrophic Environment: Mixotrophy, Size Classes and Vertical Distribution

The temporal variability of planktonic ciliates was studied in an extreme oligotrophic environment with special focus on trophic modes and size classes. Abundance, biomass, size classes, mixotrophy vs. heterotrophy, and species composition of planktonic ciliates were investigated focusing on temporal (samples collected on a monthly basis during 2019) and vertical (7 depth layers in the euphotic zone, from surface to 120 m) distribution at a coastal station in the oligotrophic Eastern Mediterranean. Abundance was in general very low (20 to 1150 cells L–1), except for September, which presented the highest abundance and biomass. Aloricate species dominated the ciliate community in all months and depths (% contribution from 77% in September to 99% in April). In general, oligotrichs presented maximum abundance at 2–10 m (except for June, July, and November: 100–120 m) whereas choreotrichs were more homogeneously distributed [and showed maxima at deep chlorophyll maximum (DCM)]. Small heterotrophs dominated the ciliate community at all depths and months, on average by 76% (they were 3 times more abundant than mixotrophs in terms of abundance and 2.5 times in terms of biomass). They were equally distributed both vertically and seasonally (and also in terms of size classes). In contrast, mixotrophs were found mainly at the surface layer to 20 m throughout the year, except for June and July (max at 100, 50 m). On average, 63% of integrated aloricate abundance was species <30 μm, of which 25% were mixotrophs. During the stratification period of May to November, the very small (<18 μm) and small (18–30 μm) mixotrophic species were distributed throughout the water column whereas the >50 μm mixotrophic species were found only above the DCM. In contrast, during the mixing period of December to May, mixotrophic ciliates were very few and were dominated by small and medium-sized species. It seems that mixotrophic and heterotrophic ciliates, on one hand, and the four size classes, on the other, are very distinct groups characterized by different distributions both vertically and seasonally. This may have important consequences for the structure and function of the microbial food web of which they are part, as well as for the carbon flow to the higher trophic levels of this oligotrophic environment in which ciliates are the main grazers.

FREE-LIVING CILIATES DURING THE PERIOD OF THE GREATEST CYANOBACTERIAL WATER BLOOM IN THE USINSKY BAY (KUIBYSHEV RESERVOIR)

The study of free-living ciliates in the Usinsky bay (the Kuibyshev reservoir) during the period of mass development of cyanobacteria are presented. The diversity of the ciliate species structure and spatial distribution were studied in summer. The abundance of ciliates varied from 124 to 1176 103ind./m3, biomass – from 6.9 mg/m3 to 104.9 mg/m3 during the study period. No significant differences in the communities of ciliates in different ecotopes of the bay (riverbed, open and overgrown by macrophytes coastal areas) were found. However, on average, in the riverbed part, all indicators of species richness and diversity, and quantitative developmentwere higher than in the littoral zone. The massive development of representatives of s/cl. Peritrichia (up to 51% of abundance and 66% of biomass): single cells species associated with planktonic algae (genera Vorticella, Vaginicola), and colonial free-floating Epistylisprocumbens Zacharias, 1897, was the distinctive feature of ciliate community in the UsinskyBay during the period of greatest cyanobacterial bloom. Water bloom significantly changed the trophic structure of the ciliate community: the role of algophages and nonselective omnivores, ordinary trophic groups of the Reservoir was significantly reduced, and bacterio-detritophages became absolutely dominated. It was shown that the dominant species of cyanobacteria had a significant effect on the ciliate community during the cyanobacterial water bloom.

Relationship between ciliates and environmental parameters in a restored carbonate fen

Wetlands restoration has been implemented on sites exploited for agricultural for over a decade in Eastern Europe. However, little is known about microbial diversity in this region. Microbial processes and patterns can be used as sensitive indicators of changes in environmental conditions. The responses of ciliates wetlands restoration are largely unexplored. Based on the results of a long-term study in fen of the Poleski National Park (Poland), we assumed that restoration causes changes in the physicochemical properties of fen water and sought to answer the question of how ciliate communities react to these changes and whether these microorganisms can play a significant role as bioindicators in evaluating the restoration process. Twenty taxa were recorded in the ciliate community, with 16 taxa found prior to restoration and 12 after restoration. Restoration clearly modified the taxonomic composition and abundance of ciliates. This was reflected in a decrease in the abundance and in the density of these protozoa and in a significant increase in the proportion of euplanktonic species. Before restoration, the most common ciliates were Cinetochilum margaritaceum and Strombidium viride, while the proportion of Paramecium bursaria increased after restoration. We also observed that the improvement in hydrological conditions, and hence the transformation of the vegetation structure in the peat bog, causes changes in the trophic structure of ciliates. The RDA analysis showed that all variables together accounted for 86.9% of the total variance. However, variables that significantly explained the variance in ciliate communities were water level, temperature, pH, and nutrients. Our results suggest that an indicator species approach based on functional groups may be appropriate for biomonitoring fens restoration.

Plankton ciliate community responses to different aquatic environments in Nan'ao Island, a representative mariculture base in the South China Sea

The temporal variation and spatial distribution of plankton ciliate communities were investigated in Shen’ao Bay, South China Sea. In all, 35 species belonging to 17 genera and 7 orders were identified. The number of ciliate species was lower in spring than in summer, whereas ciliate abundance was higher in spring than in summer. Spatially, the number of ciliate species and ciliate abundance were higher in the oyster–algae mixed culture area and non-aquaculture area, and lower in the caged fish culture area. Multivariate and univariate analyses demonstrated that ciliate communities were associated with environmental factors (e.g. temperature, chlorophyll (Chl)-a, nutrient levels). In addition, two dominant species, namely Mesodinium rubrum and Tintinnopsis beroidea, were significantly positively correlated with Chl-a. Three dominant species, namely Strombidium globosaneum, Tintinnopsis minuta and Strombidium conicum, showed more sensitivity to dissolved oxygen, pH and chemical oxygen demand, whereas Tintinnopsis parvula and Tintinnopsis chinglanensis were significantly related to NO2–. Ciliate species diversity, species evenness and species richness were higher in the oyster–algae mixed culture area and non-aquaculture area and lower in the caged fish culture area. Therefore, the results of this study suggest that the ciliate community is significantly correlated with its aquatic habitat and the dominant species can be considered a favourable bioindicator of the marine water environment.