Ciliate Abundance Research Articles

The influence of environmental characteristics on the distribution of ciliates in two coastal areas in the Eastern Mediterranean Sea (Gulf of Gabes, Tunisia)

Spatial variability of ciliates in relation to chlorophyll a, nutrients, and environmental variables were studied in lagoon (Boughrara lagoon) and marine ecosystems (Ghannouch coast) in the surface layer and at the water–sediment interface during autumn. Results revealed a striking difference between the two ecosystems, with higher nutrient concentrations at the Ghannouch coast, except for ammonium. Ciliate abundance was five to six times higher in the lagoon (123.43–126.80×102cellsl−1) than at the marine coast (21.80–24.50×102cellsl−1) (ANOVA, P < 0.001). Loricate ciliate attained high abundance in Boughrara lagoon (88%–90% of total ciliates abundance) and decreased at Ghannouch coast (44%–51% of total ciliate abundance). The species richness of the loricate ciliates was higher in Boughrara lagoon (68 taxa at both surface layer and water–sediment interface) than at Ghannouch coast (32 taxa at the surface layer and 23 taxa at the water–sediment interface). Naked ciliates were poorly represented (10%–12% of the total ciliate abundance) in the lagoon stations but had substantial percentages (49%–56% of the total ciliate abundance) at Ghannouch coast. The spatial distribution patterns of ciliate communities at both sites were strongly influenced by nutrient heterogeneity. Small species (naked ciliates) are favoured by higher nutrient concentrations at Ghannouch coast, whereas the contribution of large species (loricate ciliates) increased with the lower nutrient concentrations in Bouhgrara lagoon. It has been suggested that nutrient changes could drive shifts in ciliate community structure and abundance. The deteriorated water quality of the Ghannouch coast likely induces the low loricate ciliate abundance and diversity and the higher relative abundance of naked ciliates compared to the less polluted Boughrara lagoon.

Water mass shapes the distribution patterns of planktonic ciliates (Alveolata, Ciliophora) in the subtropical Pearl River Estuary

Ciliates comprise essential components of microzooplankton in diverse marine environments. However, the extent to which environmental variables shape the distribution of planktonic ciliates in complex estuarine systems remains unclear. Here, 52 samples were collected from the Pearl River Estuary, China to reveal the influence of environmental variables on planktonic ciliate communities. Distinct community compositions of ciliates were found in three identified water masses: Pearl River diluted water mass, South China Sea surface water mass, and South China Sea bottom water mass. Significant differences in abundance, biomass, cell size, and oral diameter structure of ciliates were also detected among the three water masses. The partial Mantel test showed that water mass (as represented by water temperature and salinity) surpassed other environmental variables to be the primary factor driving the dynamics of the ciliate community. This study revealed the controlling mechanisms of planktonic ciliate communities in a subtropical, hydrographically complex estuarine ecosystem.

Spatial variations of planktonic ciliates, predator-prey interactions and their environmental drivers in the Gulf of Gabes-Boughrara lagoon system

Spatial variability of ciliates in relation to environmental variables and abundance of heterotrophic prokaryotes, picoeukaryotes, nanoeukaryotes, microphytoplankton and mesozooplankton were studied in the Gulf of Gabes- Boughrara lagoon system in the surface layer and at the water-sediment interface between 9 and April 15, 2017. Results revealed a striking difference between the two ecosystems, with higher temperature and salinity and high availability of nitrite and total nitrogen concentrations in the Boughrara lagoon, probably generated by limited exchanges of water with the Gulf of Gabes associated with disturbed areas in the lagoon. Ciliates abundance was slightly higher in the Gulf of Gabes (16–19 × 102 cells l−1) than in the Boughrara lagoon (13–16 × 102 cells l−1), but the species richness was significantly higher in the Boughrara lagoon (40 taxa in the surface layer and 35 taxa at the water-sediment interface) than in the Gulf of Gabes (35 taxa in the surface layer and 33 taxa at the water-sediment interface). The ciliate community was characterized by the predominance of Spirotrichea. Tintinnids were more abundant than naked ciliates in both sampled ecosystems, except in a few stations. Some tintinnid species, such as Tintinnopsis radix, T. nana and T. parvula, showed high abundance, indicating their tolerance to environmental pollution. The dominant species T. beroidea, T. nana and Strombidium compressum showed significant relationships with nutrient concentrations, illustrating their affinity for highly eutrophic sites. Regression and correlation analyses suggest food dependence of Spirotrichea and tintinnids up on picoeukaryotes, whereas naked ciliates appeared more controlled by the availability of nanoeukaryotes and microphytoplankton. Metazooplankton abundance showed no significant relationships with ciliate abundance.

Key drivers influencing the colonization of periphytic ciliates and their functional role in hydrologically dynamic floodplain lake ecosystem

We investigated the colonization process and community dynamics of periphytic ciliates in a floodplain lake. To elucidate the functional role of ciliates, we investigated variations in their functional traits during colonization. Our research revealed that ciliate colonization process differs significantly between spring and summer, mainly due to differences in water temperature and hydrological regime. The most pronounced influence of temperature-initiated differences was observed during the initial phase of colonization, during which faster colonization with different pioneer species, and more diverse and abundant ciliate community characterized the summer initial phase. Hydrological changes significantly affected periphytic communities during the intermediate and late phases, resulting in different patterns of the colonization process. Mitigation of suspended food particles during flooding periods led to a decrease in ciliate abundance and the dominance of mobile benthivore ciliates (raptorial and filter feeders), whilst during more stable periods of low water, sessile planktivores (filter feeders) that consume suspended particles, dominated. They are considered to be main representatives of periphytic ciliates in floodplain lakes, playing a significant role in the pelagic-benthic coupling. The results of the present study offer new insights into the ecology and functional role of periphytic ciliates in a floodplain ecosystems of temperate regions.

Impact of El Niño-Southern Oscillation on plankton ciliates from a saline lowland river in South America

We analyzed the structure and dynamics of plankton ciliates from the Salado River, Buenos Aires (Argentina), during El Niño-Southern Oscillation events, to evaluate their response to alterations of certain environmental variables during these climatic phenomena. The basin exhibits intense land use at the headwaters and fluctuating salinity along the main channel, canals and tributaries. During El Niño (1997-1998), heavy rainfall caused high discharge, and low mean conductivity values were recorded along with low mean abundances in the entire basin. During neutral (2004-2005) and La Niña (2007-2009) events, the discharge was reduced, and mean conductivity was double the values recorded during El Niño, with maxima of mean abundances and diversity at the headwaters and the lower basin. The most abundant ciliates were tintinnids, heterotrichs and peritrichs. Species replacement was detected along the river system, mainly during the neutral event. At the headwaters and canals, abundance peaks of certain species were attributed to the strong human impact (nutrients and sewage inputs) and increased salinity, allowing the establishment of euryhaline ciliates. In the middle basin, freshwater species predominated, although less abundantly due to higher water flow. The mouth sector showed abundance peaks of an estuarine tintinnid. Temperature, conductivity and suspended solids were the most important variables driving ciliate structure. High discharge as a result of heavy rainfall during El Niño negatively influenced ciliate assemblages. In contrast, low water conditions during the other events allowed the development of diverse assemblages, increasing species number and abundance of particular species.

СВОБОДНОЖИВУЩИЕ ИНФУЗОРИИ УСИНСКОГО ЗАЛИВА (КУЙБЫШЕВСКОЕ ВОДОХРАНИЛИЩЕ) В РАЗГАРЦИАНОБАКТЕРИАЛЬНОГО «ЦВЕТЕНИЯ»

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.

Progress in studies on the diversity and distribution of planktonic ciliates (Protista, Ciliophora) in the South China Sea.

As an important component of microzooplankton, ciliates play a key role in matter cycling and energy flow in marine planktonic ecosystems. Studies of planktonic ciliate have been extensive in the South China Sea (SCS) over the last 20years. Here, we summarize the recent progress on the diversity and distribution of this group in the SCS. This includes that in: (1) the waters covering the intertidal zone of the northern SCS, most studies have focused on taxonomy, with 71 species collected, identified, and described (with ~ 40% new species); (2) neritic waters distribution patterns have been examined at a regional scale, with ciliates displaying significant spatial variations and seasonal dynamics; (3) in oceanic waters, there has been a focus on ciliate distribution in north, centre, and south regions, where mesoscale physical processes play roles in controlling distributions, and noticeable vertical variations occur. More generally, some studies examine the influences of environment variables on ciliates, and indicate that chlorophyll a concentration is commonly positively correlated with ciliates abundance. In addition, some significant findings are summarized, the limitations of past studies are considered, and recommendations are made for future work on planktonic ciliates in SCS.

Spatial and seasonal variability of the planktonic ciliates assemblages along the Eastern Mediterranean Coast (Sfax coast, Tunisia)

In the present study we investigated the effects of restoration (northern coast) and anthropization (southern coast) on the spatial and seasonal distribution of ciliates communities in relation to environmental factors in coastal Sfax area. The low pH value was attributed to anthropogenic waste inputs around the southern coast. The nutrients concentrations, recorded in the southern coast, were higher than those recorded in the northern coast. Analyses demonstrated that ciliates communities’ structures showed significant differences between the northern and southern parts of the sampling coast (F = 6.54, df = 12, p < 0.001). Ciliates diversity was significantly more important in the southern coast (65 taxa) than in the northern coast (40 taxa). The ciliates abundance was 6.33 ×102±3.38× 102 cells L−1 in northern stations. The abundance of ciliates was high over the whole southern coast (12.12×102±3.78× 102 cells L−1), which increased during summer (27 × 102 cells L−1at station 1), and decreased during the spring (3 × 102 cells L−1at station 3). Tintinnids abundance was higher than naked ciliates abundance reported for all seasons, both in the north and south Sfax coast. Some tintinnids species, like Tintinnopsis beroidea, Tintinnopsis nana and Tintinnopsis parvula attained important abundance in the southern area, because they are able to survive under adverse conditions owing to its adaptive strategies. Tintinnidium balechi was a dominant and common species, with high occurrence and represented an important contributor to the ciliate communities. Pearson’s correlation coefficients showed that the seasonal ciliates variations were significantly correlated with nutrients (total nitrogen with tintinnids and orthophosphate plus total phosphate with naked ciliates).

Planktonic ciliates communities of hydrological natural monuments of the Southern Urals, the Lake Kandrykul and the Lake Aslykul, Russia

A comparative analysis of communities of plankton ciliates has been performed for two large clear-water, slightly alkaline lakes belonging to the hydrological natural monuments of the Southern Urals (Russia). The fauna of ciliates was typical for most oligo-mesotrophic reservoirs. However, in addition to tintinnids and strombidiids, small species of the genera Balanion, Urotricha, and Askenasia had higher abundance in the Lake Kandrykul, and large colonial Epicarchesium pectinatum, in the Lake Aslykul. In general, the ciliates abundance in the lakes did not exceed 789 Cells L1 and 8,978 Cells L1, the biomass, 45 mg m−3 and 70 mg m−3, respectively. The Lake Aslykul had higher water mineralization, a greater presence of mineral suspension, and a smaller area overgrown by higher aquatic vegetation; it was characterized by poor species composition, low taxonomic and structural diversity, and lower abundance and biomass of ciliates. The heterogeneity of the lake structural characteristics was less expressed in the Lake Kandrykul, due to the underwater associations of submerged aquatic plants, which smoothed the differences between ciliates communities in different ecotopes. The mixotrophic ciliates in both lakes contributed 20-25% of total abundance and 13-44% of total biomass. The degree of organic pollution corresponded to the (3-mesosaprobic in both lakes as followed by saprobity indicator species.

Crustacean zooplankton communities, mixotrophic cililates, and optical properties in North Patagonian lakes, investigated by remote sensing

Abstract North Patagonian lakes are characterized by their oligotrophic or oligo-mesotrophic status. These conditions bring with them, respectively, the presence of abundant mixotrophic ciliates and a low species number of crustacean zooplankton under oligotrophic status, and low numbers of mixotrophic ciliates and a high species number of zooplankton under oligo-mesotrophic status. The aims of the present study are, (1) to use remote sensing techniques for determining abundances of mixotrophic ciliates and crustacean zooplankton, and (2) to characterize these mixotrophic and zooplankton communities by using null models. The sensing was accomplished from a satellite, i.e., by measuring the reflectance of the sunlight on a waterbody, which result will vary according to the contents of the water column. The results of Principal Component Analysis (PCA) revealed that sites with low reflectance of all bands have a high abundance of Stentor accompanied by low zooplankton absolute abundance, whereas a markedly opposite situation was observed under high reflectance, where Stentor has low abundance in conjunction with high zooplankton absolute abundances. The null models revealed that the communities in the studied sites do not have structured species associations, and that there is an overlap of niches. These results obtained agree with similar observations for Argentinean Patagonian lakes.

Spatial distribution of planktonic ciliates in the western Pacific Ocean: along the transect from Shenzhen (China) to Pohnpei (Micronesia).

Planktonic ciliates have been recognized as major consumers of nano- and picoplankton in pelagic ecosystems, playing pivotal roles in the transfer of matter and energy in the microbial loop. However, due to the difficulties in identification, the species composition of ciliate assemblages, especially for the small, fragile, and naked species that usually dominate the ciliate communities in the oceanic waters, remains largely unknown. In the present study, 22 stations along the transect from Shenzhen (China) to Pohnpei (Micronesia) were sampled for the enumeration of picoplankton and nanoflagellates. In addition, pigment analysis of major phytoplankton groups along with the measurements of environmental variables including temperature, salinity, and nutrients were also carried out. Ciliates were identified at species level using quantitative protargol stain to reveal the species composition and their distribution patterns from off-shore to open ocean. Ciliate abundance was positively correlated with phosphate, silicate, and pico-sized pigmented eukaryotes (PPEs), whereas the biomass was closely related with PPEs, heterotrophic nanoflagellates, and chlorophytes. The combination of silicate and pigmented nanoflagellates was identified as the major factor driving the ciliate community composition. The close relationship between silicate and ciliate abundance and community structure needs further validation based on more data collected from oceanic waters. Our study showed the necessity of using techniques that can reveal the community composition at higher taxonomic resolutions in future studies on ciliates.

The effect of climate warming on microbial loop function in peat pools and Sphagnum hollows: Mesocosm experiments

AbstractClimate change models predict a possible increase in air temperature of 2–8°C. This means that global warming will significantly affect the functioning of various types of hydrogenic ecosystems. However, the effect of the temperature increase on microbial loop function in small water bodies associated with peat ecosystems (peat pools and Sphagnum hollows) is still unknown. We used mesocosm experiments (control and treatments with a 2°C, 4°C and 8°C temperature increase) to determine the response of bacterioplankton, flagellates, testate amoebae and ciliates to simulated temperature changes, taking into account seasonal variation in the temperate climate zone. The simulated increase in climate warming increased the species richness of ciliates and the abundance of bacteria, flagellates and ciliates. In contrast, there was a decrease in the species number and abundance of testate amoebae, the top predators in peat ecosystems. The sensitivity of the various microbial groups to temperature was size‐dependent; large‐sized testate amoebae declined under warming. These shifts caused a decrease in the predator–prey mass ratio. An increase in the abundance of top predators promotes increased abundance of ciliates, and thus changes the architecture of the food web. At the same time, we observed the increase in phycoflora biomass thus can cancel the potential negative effects of warming on heterotrophic microbial activity. So, the potential effect of warming on the C budgets of peat pools and hollows is evident. A better understanding of what regulates microbial populations and activity in small reservoirs in peat bogs and unravelling of these fundamental mechanisms are particularly critical to more accurately predict how peat bogs will respond to climate disturbances.

Fatty acid composition in the endemic Humboldt Current krill, Euphausia mucronata (Crustacea, Euphausiacea) in relation to the phytoplankton community and oceanographic variability off Dichato coast in central Chile

Fatty acids (FA) have been used as diet biomarkers. They have proven to be a valuable method of defining food web relationships, trophic positioning, and the dietary behaviors of marine species. The endemic krill species of the Humboldt Current System (HCS), Euphausia mucronata, is the most abundant krill species over the continental shelf, usually associated with coastal upwelling zones. This study aimed to quantify the changes in the FA composition of E. mucronata in the coastal upwelling zone off Dichato in central Chile concerning the phytoplankton community and environmental variability. We hypothesized that E. mucronata changes its FA composition according to the functional species groups that structure the phytoplankton community as well as environmental variability. Krill, phytoplankton, and environmental datasets were analyzed using multivariate analyses, considering samplings from January 2013 to August 2014. The total concentration of FAs was 550.5 ng/g (n = 42) of which the 77% corresponded to six FAs: palmitoleic acid (16:1n7), palmitic acid (16:0), vaccenic acid (18:1), oleic acid (18:1n7), eicosapentaenoic acid (EPA, 20:5n3) and docosahexaenoic acid (DHA, 22:6n3). FA composition did not change according to neither the season nor sampling date. Seasonal changes were observed in both community structure of the phytoplankton (i.e. species composition and functional groups) and sea temperature. EPA/DHA ratio, PUFA/SFA ratio and carnivory variability were seasonally different suggesting that E. mucronata had mostly a diatom-based herbivorous habit during austral spring and summer and, it could have omnivore or carnivore habits during austral autumn and winter. Diatom and ciliate abundances and, sea temperature were the best predictor variables explaining 64% of the total variation in the FA composition. This study suggests that, despite seasonal environmental variation (biotic and abiotic), this krill species fed mainly diatoms and could shift its trophic habit to carnivory according to season of the year.

Ice-on and ice-off dynamics of ciliates and metazooplankton in the \u0141ucza\u0144ski Canal (Poland)

The ciliate–metazooplankton trophic coupling is well documented from both laboratory and field experiments. The knowledge about these relationships during winter ice-covered periods is very scarce. The abundance and composition of planktonic ciliates, rotifers and crustaceans were studied during the ice-covered and ice-free periods in the Łuczański Canal (Masurian Lakeland, Poland). We hypothesised that in winter, rotifers play a major role in the top-down control of ciliates and that ciliate–metazooplankton relationships differ not only between the ice-covered and ice-free periods, but also between ice-covered months. Our study showed that ciliates formed a significant part of zooplankton biomass during the winter ice-covered period when crustaceans occurred in very low abundances. Despite cold water temperature and the presence of ice cover, time was probably a cue that initiates zooplankton development. The ciliate, rotifer and crustacean numbers and biomass, as well as chlorophyll a concentrations, were lower in February than in ice-free periods. In the winter month with ice cover, bottom-up control by resources was more important than top-down control by zooplankton grazing in regulating ciliates. In the spring month with ice cover, crustaceans and rotifers may include ciliates as an important part of their diets. In April, the studied groups of organisms were not related to each other in contrast to the summer, when zooplankton communities were closely related to each other. In autumn, rotifers may play an important role in controlling ciliates. The abundance, composition and ciliate–metazoan relationships can vary considerably not only across seasons, but also across ice-covered months.

Grazing by microzooplankton and copepods on the microbial food web in spring in the southern Yellow Sea, China

Assessment of microzooplankton and copepods grazing pressure on picoplankton is a key requirement for resolving the microbial food web efficiency. Although microzooplankton grazing on picoplankton has been extensively studied, the impact of microzooplankton on different groups of picoplankton, i.e., heterotrophic bacteria, Synechococcus and picoeukaryotes have rarely been compared. Furthermore, in the very few existing studies there is no consistent evidence of an enhancing or restraining effect of copepods on picoplankton. More studies are needed to improve our understanding of the influence of microzooplankton and copepod on picoplankton. Dilution incubations and copepod addition incubations were performed during a cruise to the southern Yellow Sea on May 16–29, 2007. The bulk grazing of microzooplankton and the calanoid copepod Calanus sinicus on phytoplankton, flagellates and picoplankton was estimated. Stations were divided into either eutrophic or oligotrophic according to the nutrient and biological parameters. Picoplankton comprised a large part of the diet of microzooplankton in the central oligotrophic area, while phytoplankton was the main food of microzooplankton in the coastal eutrophic area. In the central oligotrophic area, microzooplankton preferred grazing on Synechococcus. After copepod addition, ciliate abundance decreased while Synechococcus abundance increased (382%, 64% and 64% at three experimental stations, respectively), indicating strong grazing pressure of microzooplankton on Synechococcus. Our results suggest that Synechococcus might be an essential carbon source the planktonic food web in the oligotrophic waters of southern Yellow Sea.

Use of a broad β-diversity measure of pelagic ciliate communities for assessing vertical heterogeneity of water columns in the Pacific Arctic Ocean.

Multivariate dispersion has proven to be a broad β-diversity measure that shows the heterogeneity of environmental conditions. The dispersion patterns of pelagic ciliate communities were investigated at eight water depths in the northern Bering Sea of the western Arctic Ocean and Chukchi Sea. Multivariate analysis indicated that (1) pelagic ciliates showed significant variability in multivariate dispersion on a vertical scale, (2) dispersion patterns were shaped by both the species composition and individual abundance, (3) vertical variation in species occurrence was significantly related to nutrients and chlorophyll a, and (4) the dispersion measures at both species occurrence and species abundance resolutions were significantly negatively related to salinity and dissolved oxygen. This suggests that multivariate dispersion measures driven by both species composition and the individual abundance of pelagic ciliates may be a useful indicator of environmental heterogeneity in marine ecosystems.

Seasonal and Spatial Variation of Ciliate Abundance in Lake Lanao along Wato-Balindong, Lanao Del Sur, Philippines

Ciliated protozoans are one-celled eukaryotes characterized by hair-like structures called cilia. Ciliate abundance has been used as bioindicators of organic pollution in a freshwater system. This study was conducted to determine the spatio-temporal variation of ciliate abundance in Lake Lanao, Philippines, along Wato-Balindong’s littoral and pelagic zones during dry (May 2018) and wet (August 2018) seasons. It intended to assess the trophic state of the lake based on planktonic ciliate abundance. In each zone, three sites were sampled for ciliates using a conical plankton net. The ciliates were fixed with formalin-acidified logul’s Iodine for microscopic observation and counting. Spatially, the data on ciliate abundance did not vary between littoral and pelagic zones. However, it did vary significantly between seasons; ciliates had higher abundance in the wet season than in the dry season. This variation could be attributed to a possible increase of nitrogen and phosphorus washed into the lake by rain. Bioindication using ciliate abundance revealed that Lake Lanao in Wato-Balindong is ultraoligotrophic, i.e., the lake is pristine, well-oxygenated and low in nutrients during sampling.

Changes in protistan abundance and bacterial activity in response to the addition of eukaryotic inhibitors to natural lake water

Abstract Two short-term (24 h and 48 h) microcosm experiments using natural waters from three eutrophic lakes (Masurian Lake District, Poland) were performed to assess the impact of eukaryotic inhibitors (a combination of cycloheximide and colchicine) on the abundance of nanoflagellates and small ciliates in the &lt;15 µm fraction. The results showed that eukaryotic inhibitors were not completely effective against either group of protists; however, they reduced their numbers considerably. At 24 h of the experiment, 41, 15, and 7% of nanoflagellate and 48, 23, and 3% of ciliate abundances were not lysed, depending on the lake from which water was taken. However, after 48 h of incubation, only below 7% of nanoflagellates and 33, 40, and 17% of ciliates were present in the treatments with inhibitors. Our results suggest that inhibitors may indirectly change bacterial growth and activity, but they do not definitively inhibit these processes. It was concluded that eukaryotic inhibitors are more effective against small nanoflagellates than larger nanoflagellates and ciliates. Concentrations of inhibitors higher than 200 and 100 mg l−1 for cycloheximide and colchicine, respectively, and an incubation time longer than 24 h also seemed to be more appropriate to achieve the complete inhibition of protists.

Major imprint of surface plankton on deep ocean prokaryotic structure and activity.

Deep ocean microbial communities rely on the organic carbon produced in the sunlit ocean, yet it remains unknown whether surface processes determine the assembly and function of bathypelagic prokaryotes to a larger extent than deep-sea physicochemical conditions. Here, we explored whether variations in surface phytoplankton assemblages across Atlantic, Pacific and Indian ocean stations can explain structural changes in bathypelagic (ca. 4,000m) free-living and particle-attached prokaryotic communities (characterized through 16S rRNA gene sequencing), as well as changes in prokaryotic activity and dissolved organic matter (DOM) quality. We show that the spatial structuring of prokaryotic communities in the bathypelagic strongly followed variations in the abundances of surface dinoflagellates and ciliates, as well as gradients in surface primary productivity, but were less influenced by bathypelagic physicochemical conditions. Amino acid-like DOM components in the bathypelagic reflected variations of those components in surface waters, and seemed to control bathypelagic prokaryotic activity. The imprint of surface conditions was more evident in bathypelagic than in shallower mesopelagic (200-1,000m) communities, suggesting a direct connectivity through fast-sinking particles that escape mesopelagic transformations. Finally, we identified a pool of endemic deep-sea prokaryotic taxa (including potentially chemoautotrophic groups) that appear less connected to surface processes than those bathypelagic taxa with a widespread vertical distribution. Our results suggest that surface planktonic communities shape the spatial structure of the bathypelagic microbiome to a larger extent than the local physicochemical environment, likely through determining the nature of the sinking particles and the associated prokaryotes reaching bathypelagic waters.

Spatial and seasonal variations of dinoflagellates and ciliates in the Kongsfjorden, Svalbard

AbstractAbundance and assemblages of dinoflagellates and ciliates were studied in water samples collected from three different depths at five locations in the Kongsfjorden, during summer (June 14–21, 2011) and fall (September 15–27, 2012). Generally, athecate dinoflagellates were ubiquitously dominant during both seasons. Surface dinoflagellates abundance ranged from 1.87 × 103 cells/L (KF1) to 11.62 × 103 cells/L (KF4) and column integrated abundance ranged from 20.3 × 106 cells/m2 (KF1) to 126 × 106 cells/m2 (KF2) during summer. Dinoflagellate abundance was relatively lower during fall ranging from 0.02 × 103 cells/L (KF5) to 0.66 × 103 cells/L (KF3) at surface, and correspondingly, a low column integrated abundance ranging from 2.34 × 106 cells/m2 (KF5) to 19.1 × 106 cells/m2 (KF1) was observed. Amphidinium sp., Gyrodinium fusiforme, Gyrodinium estuarile dominated during summer, while Gymnodinium sp. was dominant during fall. Among ciliates, aloricate ciliates were more dominant than loricates. Ciliates at surface ranged from as low as 0.069 × 103 cells/L (KF1) to 3.69 × 103 cells/L (KF4) during summer. Ciliate abundance increased with depth (up to 20 m). Strombidium spp. (55.28%) and Mesodinium rubrum (36.66%) were dominant during summer. Among the loricates and the aloricates, Strombidium spp. (85.72%) and Tintinnid spp. (92.15%) dominated in fall. The presence of dominant aloricates with characteristic cleptochloroplasts reflected high grazing activity in these waters during both seasons. Diversity study indicates that the dinoflagellates and ciliates are well represented during both seasons. Statistical analyses of the dinoflagellates and ciliates with hydrographic data do not show dominant role of any hydrographical parameters on their diversity, and the same is discussed vis‐à‐vis Atlantification of the fjord.