Diatom bloom trigger notable variations in microzooplanktonic ciliate composition, body-size spectrum and biotic-abiotic interaction in the Arctic Ocean.

How microzooplanktonic ciliate adaptative strategies differ across diatom bloom and non-diatom bloom areas in the Arctic Ocean remains poorly documented. To address this gap, two different situations were categorized in the Arctic Ocean at summer 2023: diatom bloom stations (DBS) (genus Thalassiosira, chain-like) and non-diatom bloom stations (nDBS). Total abundance of ciliate at 3 m and 25 m in DBS was 2.8 and 1.8 folds higher than in nDBS, respectively. Aloricate ciliates were singled out in both DBS and nDBS, whilst their average abundance and biomass of large size-fraction (>50 µm) in former were 4.5-5.6 folds higher than in latter. Regarding tintinnids, high abundance of Ptychocylis acuta (Bering Strait species) mainly occurred at DBS, coupled with distribution of co-occurring Pacific-origin species Salpingella sp.1, collectively suggested a strong intrusion of Pacific Inflow during summer 2023. Additionally, presence of high abundance of Acanthostomella norvegica and genus Parafavella in nDBS might indicate the trajectory of the Transpolar Drift. Alternatively, tintinnids can serve as credible bioindicators for either monitoring currents or evaluating microzooplankton Borealization. Average abundance of total ciliate within 15-135 µm body-size spectrum in DBS was higher than nDBS. Moreover, spearman's rank correlation between biotic and abiotic analysis revealed that temperature and dissolved oxygen at DBS determined tintinnid species richness and ciliate total abundance, respectively. The results clearly demonstrate that remarkable divergences in large size-fraction of ciliate abundance between DBS and nDBS validate their irreplaceable role in controlling phytoplankton outbreak and associated biological processes in polar seas.

Planktonic ciliate communities along an environmental gradient in the Nile Delta (Damietta region, Egypt).

The spatial patterns of planktonic ciliate communities were studied from May to June 2019 in the Nile Delta's Damietta region, southeastern Mediterranean. The ciliate communities were sampled from twenty-five sites of five stressed domains with spatial gradients of environmental status. A total of 32 ciliate taxa with six dominant species were identified, comprising 21 tintinnids and 11 aloricate ciliates. The abundance and richness of each ciliate group varied geographically and were most strongly influenced by salinity variations; tintinnid ciliates attained high abundance and richness at high salinity sites in the harbour and coastal region and decreased within the estuary upstream. Aloricate ciliates were poorly represented at most sites but were a substantial proportion of upstream estuarine sites. Multivariate/univariate analyses demonstrated that spatial patterns of the ciliate communities were significantly correlated with environmental variables, especially salinity, chlorophyll-a, and nutrients, either alone or in combination with one another. These results indicate that the ciliates can be useful bioindicators in stressed environments while also allowing the detection of impacts on short time scales by rapidly responding to environmental variations.

Upstream cascade reservoirs drive temporal beta diversity increases through species loss in a dammed river.

Changes in the biodiversity of aquatic environments over time and space due to human activities are a topic of theoretical and conservational interest in ecology. Thus, variation in taxonomic beta diversity of the planktonic ciliates community was investigated along a temporal and spatial gradient in two subsystems of a Neotropical floodplain, one impacted by dams (Paraná) and the other free of them along its course (Ivinhema). For the spatial analysis, the Paraná subsystem did not show a significant decrease in beta diversity, presenting a pattern like that observed for the Ivinhema subsystem. Therefore, biotic homogenization was not observed for the ciliate's community downstream of the dams. It was noted that there was a fluctuation in the relevance of the components of beta diversity, regardless of the subsystem analyzed. For the temporal analysis there was a significant change in species composition from the first to the last year investigated, essentially for the subsystem impacted by dams, and that this was determined mainly by species loss. Although spatial beta diversity remained high without a clear process of biotic homogenization, dams promoted remarkable changes in ciliate species composition over the years mainly by continuous loss of species.

Morphological and ribosomal DNA-based characterization of six Antarctic ciliate morphospecies from the Amundsen Sea with phylogenetic analyses.

We characterized six tintinnid ciliates from Antarctic waters using molecular markers and morphological traits: Amphorellopsis quinquealata, Codonellopsis gaussi, Cymatocylis convallaria, Cy. calyciformis, Cy. drygalskii, and Laackmanniella prolongata. The 100% similarity in SSU-ITS1-5.8S rDNA-ITS2-partial LSU rDNA sequences among Cy. convallaria, Cy. calyciformis, and Cy. drygalskii is supportive of synonymy. Codonellopsis gaussi and L. prolongata also showed high levels of similarity in SSU rDNA (99.83%) and the D2 domain of LSU rDNA (95.77%), suggesting that they are closely related. Phylogenetic analysis placed Cymatocylis in the Rhabdonellidae, Amphorellopsis in the Tintinnidae and L. prolongata/Co. gaussi within the Dictyocystidae.

Full-depth vertical distribution of planktonic ciliates (Ciliophora) and a novel bio-index for indicating habitat suitability of tintinnid in the Arctic Ocean.

Despite the planktonic ciliate importance in the microzooplankton compartment, their full-depth vertical distribution in the Arctic Ocean was poorly documented as well as the related variations in different water masses. The full-depth community structure of planktonic ciliates was investigated in the Arctic Ocean during summer 2021. The ciliate abundance and biomass decreased rapidly from 200 m to bottom. Five water masses were identified throughout the water column and each one exhibited a unique ciliate community structure. Aloricate ciliates were singled out as the dominant group with average abundance proportion to total ciliates at each depth >95%. Large (>30 µm) and small (10-20 µm) size-fractions of aloricate ciliates were abundant in shallow and deep waters, respectively, which revealed an anti-phase relationship in vertical distribution. Three new record tintinnid species were found during this survey. Pacific-origin species Salpingella sp.1 and Arctic endemic species Ptychocylis urnula occupied the top abundance proportion in the Pacific Summer Water (44.7%) and three water masses (≥38.7%, Mixed Layer Water, Remnant Winter Water, Atlantic-origin Water), respectively. The habitat suitability of tintinnid abundant species was characterised by the Bio-index revealing a distinct death-zone for each species. Variations in survival habitat of abundant tintinnids can be regarded as indicators for the future Arctic climate change. These results provide fundamental data on the microzooplankton response to the intrusion of Pacific waters into the Arctic Ocean upon its rapid warming.

Sex in the wild: repeated observations of planktonic ciliate conjugation from field samples.

Ciliate conjugation is considered a rare event to encounter in the field and it is mostly reported from cultures. In this work, we describe a synchronized conjugation event of planktonic ciliates that was discovered twice; in September 2019, at two different locations in the Cretan Sea, Eastern Mediterranean, and in October 2020. In 2019, first, at 2 m depth of the coastal station POSEIDON-HCB, in samples fixed with acid Lugol and formaldehyde, we found 340 and 200 mating pairs L-1of different ciliate species, respectively; and second, at the Heraklion port, we found 220 mating pairs L-1 of Strombidinopsis sp. and 1960 mating pairs L-1 of Strombidium sp. At the Heraklion port visited again in 2020, we found 800 mating pairs L-1 of Strombidinopsis sp. and 200 mating pairs L-1 of Strombidium sp. Since detailed descriptions of conjugation in pelagic oligotrich ciliates are missing, our observations indicate that ciliate conjugation could be a frequent and periodic phenomenon, under specific conditions.

FISHing for ciliates: Catalyzed reporter deposition fluorescence in situ hybridization for the detection of planktonic freshwater ciliates.

Planktonic ciliate species form multiple trophic guilds and are central components of freshwater food webs. Progress in molecular analytical tools has opened new insight into ciliate assemblages. However, high and variable 18S rDNA copy numbers, typical for ciliates, make reliable quantification by amplicon sequencing extremely difficult. For an exact determination of abundances, the classical morphology-based quantitative protargol staining is still the method of choice. Morphotype analyses, however, are time consuming and need specific taxonomic expertise. Catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH) may represent a promising tool for the analysis of planktonic ciliates by combining molecular identification with microscopic quantification. We tested the applicability of CARD-FISH using nine cultured ciliate species. Eight species- and three genus-specific oligonucleotide probes were designed based on their 18S rRNA genes. The CARD-FISH protocol was adapted and the specificity of probes was established. We subsequently examined the precision of quantitation by CARD-FISH on single cultures and mock assemblages. Successful tests on lake water samples proved that planktonic ciliates could be identified and quantified in field samples by CARD-FISH. Double hybridizations allowed studying interspecific predator prey interactions between two ciliate species. In summary, we demonstrate that CARD-FISH with species-specific probes can facilitate studies on the population dynamics of closely related, small sized or cryptic species at high sampling frequencies.

How do microplastics affect the marine microbial loop? Predation of microplastics by microzooplankton.

Protozoans play an integral role in the microbial loop, an important process of material and energy transfer in marine ecosystems. The number of microplastics in the marine environment has greatly increased, but the potential impacts of small nanoplastics and microplastics on marine organisms remain unclear. Here, we conducted a series of feeding experiments with various concentrations of microplastic beads (ca. 1 µm) to characterize the response of the planktonic ciliated protozoan Strombidium sulcatum to microplastics and a set of additional exposure experiments with four different particle diameters of microplastics to explore whether the feeding response exhibited size selectivity. As the microplastic concentration increased, the number, body size, and biomass of ciliates decreased sharply during the exposure period. Predator biomass in all microplastic treatments was markedly reduced relative to the microplastic-free control. For example, at 72 h of exposure, the biomass in the highest microplastic concentration treatment was observed to decrease by 96.59% relative to the control. There was no obvious difference in the biomass of ciliates exposed to various diameters of microplastics; however, compared with the free bead control, the biomass still significantly decreased. These findings suggest that microplastics in the ocean negatively affect the growth of protozoan microzooplankton that might have accidentally ingested these tiny particles during the feeding process. Generally, this study provides basic and novel data for understanding the effect of microplastics on the microbial loop in marine ecosystems.

Overview of the Diversity, Phylogeny and Biogeography of Strombidiid Oligotrich Ciliates (Protista, Ciliophora), With a Brief Revision and a Key to the Known Genera.

Strombidiids are common free-living ciliates that have colonized coastal and open oceanic waters across the world. In recent years, numerous new taxa and gene sequences of strombidiids have been reported, revealing a large diversity of both their morphologic and genetic features. Here, we compare the taxonomic characters of all genera in the family Strombidiidae, provide a key to their identification, and investigate their molecular phylogeny. In addition, we analyze their regional distribution based on faunal data accumulated in China and attempt to infer their global distribution based on SSU rRNA gene sequence data. The current work revises the systematics of strombidiids based on morphologic, phylogenetic, and biogeographic evidence and provides a genus-level review of marine strombidiids.

Harmful algal blooms of Heterosigma akashiwo and environmental features regulate Mesodinium cf. rubrum abundance in eutrophic conditions.

Functional drivers of phytoplankton that can potentially form harmful algal blooms (HABs) are important to understand given the increased prevalence of anthropogenic modification and pressure on coastal habitats. However, teasing these drivers apart from other influences is problematic in natural systems, while laboratory assessments often fail to replicate relevant natural conditions. One such potential bloom-forming species complex highlighted globally is Mesodinium cf. rubrum, a planktonic ciliate. This species occurs persistently in the Sundays Estuary in South Africa yet has never been observed to "bloom" (> 1,000 cell.ml-1). Modified by artificial nutrient-rich baseflow conditions, the Sundays Estuary provides a unique Southern Hemisphere case study to identify the autecological drivers of this ciliate due to artificial seasonally "controlled" abiotic environmental conditions. This study utilised a three-year monitoring dataset (899 samples) to assess the drivers of M. cf. rubrum using a generalised modelling approach. Key abiotic variables that influenced population abundance were season and salinity, with M. cf. rubrum populations peaking in summer and spring and preferring polyhaline salinity regions (>18) with pronounced water column salinity stratification, especially in warmer months. This was reflected in the diel vertical migration (DVM) behaviour of this species, demonstrating its ability to utilise the optimal daylight photosynthetic surface conditions and high-nutrient bottom waters at night. The only phytoplankton groups clearly associated with M. cf. rubrum were Raphidophyceae and Cryptophyceae. Although M. cf. rubrum reflects a niche overlap with the dominant HAB-forming phytoplankton in the estuary (the raphidophyte, Heterosigma akashiwo), its reduced competitive abilities restrict its abundance. In contrast, the mixotrophic foraging behaviour of M. cf. rubrum exerts a top-down control on cryptophyte prey abundance, yet, the limited availability of these prey resources (mean < 300 cells ml-1) seemingly inhibits the formation of red-water accumulations. Hydrodynamic variability is necessary to ensure that no single phytoplankton HAB-forming taxa outcompetes the rest. These results confirm aspects of the autecology of M. cf. rubrum related to salinity associations and DVM behaviour and contribute to a global understanding of managing HABs in estuaries.

Composition and distribution of planktonic ciliates with indications to water quality in a shallow hypersaline lagoon (Pulicat Lake, India).

Planktonic ciliate composition and distribution together with physicochemical variables were investigated in a shallow hypersaline lagoon, Pulicat, India, during three seasons, i.e., pre-monsoon (PRM), monsoon (MON), and post-monsoon (POM). The low freshwater inflow, evaporation, and closure of the lake mouth were the main factors for the hypersaline conditions in Pulicat Lake. The average depth and salinity were 1.8 ± 0.12 m (0.8 to 2.8 m) and 35.3 ± 1.68 (12.5 to 61), respectively. A total of 29 ciliate taxa belonging to 18 genera and five classes were identified. Strombidium conicum (24%) was the dominant species followed by Euplotes sp. (10.7%) and Stenosomella sp. (7.02%). Spirotrichea (84%) was the dominant class followed by Oligohymenophorea (9.6%) and Heterotrichea (5.8%). Fabrea salina, a typical species in hypersaline systems, was abundant at locations where the salinity was more than 35. Multivariate analysis using the Bray-Curtis similarity, followed by SIMPROF (Similarity Percentage Analysis), on ciliate abundance data revealed three ciliate assemblages characterizing south, central, and north of the lake at 40% similarity (SIMPROF, cophenetic correlation = 0.622, P = 5%). Both ciliate abundance and chlorophyll-a were positively correlated with salinity. Species richness and evenness were higher in the south sector when compared with those in the other two sectors. Biotic-environmental interaction through canonical correspondence analysis (CCA) inferred that the combined effects of salinity, chlorophyll-a, and nutrient levels are the key factors responsible for the distribution of the ciliate species, suggesting that ciliates can be considered to be potential bioindicators of water quality.

Seasonality of Planktonic Freshwater Ciliates: Are Analyses Based on V9 Regions of the 18S rRNA Gene Correlated With Morphospecies Counts?

Ciliates represent central nodes in freshwater planktonic food webs, and many species show pronounced seasonality, with short-lived maxima of a few dominant taxa while many being rare or ephemeral. These observations are primarily based on morphospecies counting methods, which, however, have limitations concerning the amount and volume of samples that can be processed. For high sampling frequencies at large scales, high throughput sequencing (HTS) of freshwater ciliates seems to be a promising tool. However, several studies reported large discrepancy between species abundance determinations by molecular compared to morphological means. Therefore, we compared ciliate DNA metabarcodes (V9 regions of the 18S rRNA gene) with morphospecies counts for a 3-year study (Lake Zurich, Switzerland; biweekly sampling, n = 74). In addition, we isolated, cultivated and sequenced the 18S rRNA gene of twelve selected ciliate species that served as seeds for HTS analyses. This workflow allowed for a detailed comparison of V9 data with microscopic analyses by quantitative protargol staining (QPS). The dynamics of V9 read abundances over the seasonal cycle corroborated well with morphospecies population patterns. Annual successions of rare and ephemeral species were more adequately characterized by V9 reads than by QPS. However, numbers of species specific sequence reads only partly reflected rank orders seen by counts. In contrast, biomass-based assemblage compositions showed higher similarity to V9 read numbers, probably indicating a relation between cell sizes and numbers / sizes of macronuclei (or 18S rRNA operons). Full-length 18S rRNA sequences of ciliates assigned to certain morphospecies are urgently needed for barcoding approaches as planktonic taxa are still poorly represented in public databases and the interpretation of HTS data depends on profound reference sequences. Through linking operational taxonomic units (OTUs) with known morphospecies, we can use the deep knowledge about the autecology of these species.

Spatial variations in annual cycles of body-size spectra of planktonic ciliates and their environmental drivers in marine ecosystems.

Body-size spectra has proved to be a useful taxon-free resolution to summarize a community structure for bioassessment. The spatial variations in annual cycles of body-size spectra of planktonic ciliates and their environmental drivers were studied based on an annual dataset. Samples were biweekly collected at five stations in a bay of the Yellow Sea, northern China during a 1-year cycle. Based on a multivariate approach, the second-stage analysis, it was shown that the annual cycles of the body-size spectra were significantly different among five sampling stations. Correlation analysis demonstrated that the spatial variations in the body-size spectra were significantly related to changes of environmental conditions, especially dissolved nitrogen, alone or in combination with salinity and dissolve oxygen. Based on results, it is suggested that the nutrients may be the environmental drivers to shape the spatial variations in annual cycles of planktonic ciliates in terms of body-size spectra in marine ecosystems.

Planktonic ciliate community structure in shallow lakes of lowland Western Europe.

Temperate shallow meso- to eutrophic lakes can exist in one of two alternative states with contrasting foodwebs, referred to as the clear-water and the turbid state. We describe the planktonic ciliate communities of such lakes based on a survey of 66 northwestern European lakes. Ciliates were enumerated and identified to species level according to the quantitative protargol staining technique. Ciliate biomass was on average twice as high in the turbid than in the clear-water lakes. The ciliate communities were dominated by oligotrichs and protostomatids, and no differences in functional composition or α-diversity could be detected between turbid and clear-water lakes, although ß-diversity tended to be higher in the latter. At the species level, however, community structure strongly differed between turbid and clear-water lakes, and several indicator species could be identified for the different lake categories. Variation partitioning showed that nutrient status did not explain ciliate community structure independent of the alternative states, while lake area was identified as an additional structuring factor for the ciliate communities. These results stress the importance of the ecosystem structure in shaping ciliate communities in temperate shallow lakes and suggest that nutrient status has little direct effect on ciliate community structure in such lakes.

Factors driving the seasonal distribution of planktonic and epiphytic ciliates in a eutrophicated Mediterranean lagoon.

We studied the distribution of planktonic and epiphytic ciliates coupled with environmental factors and microalgae abundance at five stations in Ghar El Melh Lagoon (Tunisia). Planktonic ciliates were monitored for a year and epiphytic ciliates were sampled during summer 2011 in concordance with the proliferation of the seagrass Ruppia cirrhosa. Ciliate assemblage was largely dominated by Spirotrichea followed respectively by Tintinnida of and Strombidiida. No significant difference was found in the distribution of ciliate species among the stations. Redundancy analysis indicates that abiotic factors (temperature and nutriments) have a significant effect on the dynamics of certain ciliates. For epiphytic ciliates, 4 species were identified: Tintinnopsis campanula, Aspidisca sp., Strombidium acutum and Amphorides amphora. Based on PERMANOVA analyses, ciliates exhibit significant correlations among months and stations. According to ACP, epiphyte distribution follows roughly those of R. cirrhosa and pH. Significant correlations were found between harmful dinoflagellates and both planktonic and epiphytic ciliates.

Spatial and temporal patterns of ciliate species composition (Protozoa: Ciliophora) in the plankton of the Upper Paraná River floodplain

Spatial and temporal patterns of plankton ciliates species composition in the Paraná River floodplain were investigated. Samplings were carried out in twelve environments in two distinct hydrological periods (limnophase and potamophase). A total of 61 species of ciliates were recorded, and among them 21 are classified as pelagic while 40 are considered preferentially as littoral species. The registered species belong to eleven orders, and among them, Prostomatida was the most specious followed by Hymenostomatida and Peritrichida. The ciliate species composition was significantly distinct between periods, but not among environments. In this way, typically pelagic species characterized the ciliate community during the limnophase period, while the littoral species were predominant during the potamophase period. Our results strongly support the idea of the flood pulse as the main factor driving the composition pattern of the planktonic ciliates community in the Paraná River floodplain.

No presente estudo foram investigados os padrões espaciais e temporais da composição de espécies de ciliados planctônicos na planície de inundação do Alto Rio Paraná. As amostras foram obtidas em 12 ambientes, em dois períodos hidrológicos distintos (limnofase e potamofase). Foram registradas 61 espécies de ciliados entre as quais 21 foram classificadas como pelágicas enquanto 40 foram consideradas preferencialmente litorâneas. As espécies registradas pertencem a 11 ordens, sendo Prostomatida foi a mais especiosa, seguida por Hymenostomatida e Peritrichida. A composição de espécies de ciliados foi significativamente distinta entre os períodos hidrológicos, enquanto que entre os ambientes, diferenças na composição não foram evidenciadas. Dessa forma, espécies tipicamente pelágicas caracterizaram a comunidade de ciliados na limnofase, enquanto que espécies litorâneas foram preponderantes para a composição de ciliados na potamofase. Os resultados suportam a idéia do pulso de inundação como principal fator controlador dos padrões de composição da comunidade de ciliados planctônicos na planície de inundação do Alto Rio Paraná.

Spatial and temporal patterns of ciliate species composition (Protozoa: Ciliophora) in the plankton of the Upper Paraná River floodplain / Padrões espaciais e temporais da composição de espécies de ciliados (Protozoa: Ciliophora) no plâncton da planície de inundação do Alto Rio Paraná

Spatial and temporal patterns of plankton ciliates species composition in the Paraná River floodplain were investigated. Samplings were carried out in twelve environments in two distinct hydrological periods (limnophase and potamophase). A total of 61 species of ciliates were recorded, and among them 21 are classified as pelagic while 40 are considered preferentially as littoral species. The registered species belong to eleven orders, and among them, Prostomatida was the most specious followed by Hymenostomatida and Peritrichida. The ciliate species composition was significantly distinct between periods, but not among environments. In this way, typically pelagic species characterized the ciliate community during the limnophase period, while the littoral species were predominant during the potamophase period. Our results strongly support the idea of the flood pulse as the main factor driving the composition pattern of the planktonic ciliates community in the Paraná River floodplain.

No presente estudo foram investigados os padrões espaciais e temporais da composição de espécies de ciliados planctônicos na planície de inundação do Alto Rio Paraná. As amostras foram obtidas em 12 ambientes, em dois períodos hidrológicos distintos (limnofase e potamofase). Foram registradas 61 espécies de ciliados entre as quais 21 foram classificadas como pelágicas enquanto 40 foram consideradas preferencialmente litorâneas. As espécies registradas pertencem a 11 ordens, sendo Prostomatida foi a mais especiosa, seguida por Hymenostomatida e Peritrichida. A composição de espécies de ciliados foi significativamente distinta entre os períodos hidrológicos, enquanto que entre os ambientes, diferenças na composição não foram evidenciadas. Dessa forma, espécies tipicamente pelágicas caracterizaram a comunidade de ciliados na limnofase, enquanto que espécies litorâneas foram preponderantes para a composição de ciliados na potamofase. Os resultados suportam a idéia do pulso de inundação como principal fator controlador dos padrões de composição da comunidade de ciliados planctônicos na planície de inundação do Alto Rio Paraná.

Planktonic ciliates from an oligotrophic South Andean lake, Morenito Lake (Patagonia, Argentina)

In this contribution we have studied the planktonic ciliates from Morenito Lake, an oligotrophic lake situated in the South Andes of Argentina. Six species that are new records for South America or Argentina are described and illustrated. Besides, population dynamics of the ciliate species were studied during a spring--summer period. Strobilidium lacustris and Balanion planctonicum were the most abundant species, showing a maximum in mid summer. Paradileptus elephantinus was present all over the period while Urotricha furcata was observed in late summer samples. Strobilidium lacustris and S. humile were found to be occasional species during the studied period. The recorded ciliate assemblage with oligotrichs and prostomates as dominant indicate the oligotrophic condition of the lake.

Nesta contribuição estudamos os ciliados planctônicos do Lago Morenito, um lago oligotrófico localizado nos Andes do Sul (Argentina). São descritas e ilustradas seis espécies registradas pela primera vez na Argentina e na América do Sul. Durante o período de primavera--verão foram estudadas as dinâmicas populacionais dessas espécies de ciliados. Strobilidium lacustris e Balanion planctonicum foram as espécies mais abundantes, mostrando um máximo na metade do verão. Paradileptus elephantinus esteve presente durante todo o período e Urotricha furcata foi observado em amostras no final do verão. Strobilidium lacustris e S. humile foram espécies ocasionais durante o período estudado. O grupo de ciliados registrados com dominância de oligotricos e prostomados indica a condição oligotrófica do lago.