Ciliate Abundance Research Articles

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.

Multivariate control of heterotrophic bacterial abundance and zooplankton grazing in Labrador fjords (northeastern Canada)

This study was conducted in 4 Labrador fjords (Nachvak, Saglek, Okak, and Anaktalak) during the summers of 2007 and 2013, early fall 2010, and late fall 2009. Our results show that water temperature combined with the availability of nutrients and organic substrates are the main abiotic factors controlling the abundance of heterotrophic bacteria in Labrador fjords. Bacterivory also played a crucial role, with heterotrophic bacteria exerting a significant bottom-up control on the abundance of heterotrophic nanoflagellates (r = 0.35, p < 0.05) and ciliates (r = 0.70, p < 0.01). During summer 2013, the intrinsic phytoplankton growth rate varied between <0 and 0.64 d-1, with a mean value of 0.36 d-1. The herbivory rate was highly variable, ranging from 0.01 to 0.86 d-1, with a mean value of 0.31 d-1. Grazing mortality was 6-fold higher than phytoplankton growth rate. Mean phytoplankton growth and herbivory rates in Labrador fjords were comparable to the Barents and Bering seas. The intrinsic growth rate of total heterotrophic bacteria ranged between <0 and 0.68 d-1, with a mean value of 0.30 d-1. Bacterivory varied from 0.01 to 0.95 d-1, with a mean of 0.30 d-1. Mortality due to grazing was up to 2.3 times higher than total bacterial growth rate. This study improves our understanding of the factors influencing the dynamics of heterotrophic bacteria and indicates that herbivory and bacterivory exert substantial control on microbial communities in Labrador fjords.

Difference of planktonic ciliate communities of the tropical West Pacific, the Bering Sea and the Arctic Ocean

Ciliates are important components in planktonic food webs, but our understanding of their community structures in different oceanic water masses is limited. We report pelagic ciliate community characteristics in three seas: the tropical West Pacific, the Bering Sea and the Arctic Ocean. Planktonic ciliate abundance had “bimodal-peak”, “surface-peak” and “DCM (deep chlorophyll a maximum layer)-peak” vertical distribution patterns in the tropical West Pacific, the Bering Sea and the Arctic Ocean, respectively. The abundance proportion of tintinnid to total ciliate in the Bering Sea (42.6%) was higher than both the tropical West Pacific (7.8%) and the Arctic Ocean (2.0%). The abundance proportion of small aloricate ciliates (10–20 µm size-fraction) in the tropical West Pacific was highest in these three seas. The Arctic Ocean had higher abundance proportion of tintinnids in larger LOD (lorica oral diameter) size-class. Proportion of redundant species increased from the Arctic Ocean to the tropical West Pacific. Our result provided useful data to further understand ecology roles of planktonic ciliates in different marine habitats.

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 ± 0.12m (0.8 to 2.8m) 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.

A note on the differences found between examining whole water vs. phytoplankton net (52 μm mesh) samples to characterize abundance and community composition of tintinnid ciliates (marine microzooplankton)

AbstractMost tintinnid species have a shortest linear dimension < 50 μm. Hence, a priori, nets of mesh sizes ≥ 50 μm will likely under‐sample most tintinnid species. However, studies often appear (23 since 2015) using sampling with nets of meshes sizes ≥ 50 μm, reporting both tintinnid concentrations, and community composition. How biased are results from using coarse mesh nets? We provide a comparison of whole water vs. net sampling based on fortuitous, that is, unplanned, parallel sampling. Pairs of samples from a standard monitoring station in the Bay of Villefranche (N.W. Mediterranean Sea) taken on 44 dates from 2013 to 2018 were compared. Tintinnids were enumerated in settled material from a water column sample, an integration of six discrete depth samples between 5 and 70 m, prepared for analysis of phytoplankton composition and in material from a plankton net (52 μm mesh) tow from 70 to 0 m, taken the same day. Despite the large confidence limits due to low raw cell counts from whole water samples, cell concentration estimates were about an order of magnitude higher than those from plankton net samples and frequently biomass estimates as well. Community composition also differed. The most common species in whole water samples were small (diameter ≤ 20 μm), and some common forms were absent, or nearly, from the net samples. We show that, while valuable for collecting larger and rarer species, coarse net samples do not yield robust estimations of overall concentrations, nor allow identification of the dominant tintinnid species.

Characteristics of microbial eukaryotic community recovery in eutrophic water by using ecological floating beds

Ecological floating beds can rapidly remove nutrients (nitrogen and phosphorus) from eutrophic water, but we still know little about whether this process can simultaneously recover microbial eukaryotic communities. To fill this gap, planktonic microbial eukaryotic communities were investigated using 18S rRNA high-throughput gene sequencing during nutrient removal by floating beds of Canna indica L. We found that nutrient concentrations were high in both the control and treatment groups during period 1 (days 0–5) but rapidly decreased in the treatment group during period 2 (days 6–9) and period 3 (days 10–18). However, the microbial eukaryotic species richness and community compositions were similar between the control and treatment groups during periods 1 and 2 but showed small differences during period 3. The microbial eukaryotic co-occurrence networks between the control and treatment groups also showed similar degree centrality and interconnected eukaryotic members. We found that some abundant fungi species significantly responded to nutrient variations, but a large number of abundant ciliates were insensitive to nutrient removal. Our findings suggest that ecological floating beds can rapidly remove nutrients in eutrophic waters but that it is difficult to quickly and simultaneously improve microbial eukaryotic communities. This result reveals the critical influence of nutrient pollution on aquatic ecosystems and therefore on long-term and comprehensive aquatic habitat restoration, as aquatic macrophyte recoveries should be conducted after nutrient controls have been implemented.

Effect of Hydrographic Variability on the Distribution of Microbial Communities in Taiwan Strait in Winter

This study investigated the spatial variation in the components of a microbial food web (viruses, picoplankton, nanoflagellates, and ciliates) in different hydrographic environments in the Taiwan Strait during winter. Water temperature and salinity varied spatially, with lower temperatures (15.3–22.8 °C) and salinities (32.2–33.4 psu) in the northern part of the Taiwan Strait, largely affected by runoff from the coast of China. Concentrations of nutrients and Chl a were significantly higher in the northern part than that in the southern part of the study area. Synechococcus spp., nanoflagellate, and ciliate abundance also varied significantly, with the northern strait having higher abundances of these communities. In contrast, a higher abundance of bacteria was found in the southern part of the Taiwan Strait. The results of this study, which describes two different ecosystems in the Taiwan Strait, suggest that during winter, a “viral loop” might play an important role in controlling bacterial production in the southern part of the Taiwan Strait, while nanofalgellate grazing of picophytoplankton may contribute mainly to the flux of energy in the northern part.

STUDY OF ECOSYSTEM OF THE SUKHUM BAY WITH EMPHASIS ANTHROPOGENIC IMPACT, ABKHAZIAN BLACK SEA COAST

For the first time in thirty years, baseline comprehensive studies plankton and zoobenthos of the Sukhum Bay were conducted and an assessment of its current environmental status was given. The summer phytoplankton abundance of the port of Sukhum was represented mainly by coccolithophorids Emiliania huxleyi and diatoms algae, among the latter, the common species in polluted or eutrophic brackish waters were recorded. The presence of euglenic algae and cyanobacteria indicates a higher nutrient status, pollution and desalination of the sea area. The alien species Peridinium quinquecorne Abé (Dinophyceae) was recorded in the Abkhazian coastal waters for the first time. Totally, 7 species of tintinnids belonging to 3 genera Favella, Tintinnopsis, Eutintinnus were established from the Sukhum Bay. Among them, the non-indigenous species Eutintinnus tubulosus and E. apertus were noticed. Tintinnid ciliates accounted for ca. 5% of total ciliates abundance. The values of the abundance of aloricated ciliates were comparable to the values obtained from offshore of bays and ports of the northeastern Black Sea. As the pressure of predators is reduced the well-pronounced peaks of holo- and meroplankton biomass were recorded in the last summer – early autumn. A significant part of total holoplankton biomass – 66.5 % (up to 1.1 g/m3) was composed of cladocerans Penilia avirostris. The meroplankton was dominated by larvae of bivalve mollusks Mytilaster lineatus, polychaetes Polydora cornuta and cirripede barnacle Amphibalanus improvisus. The number of meroplankton in the open Sukhum port was 10–15 times lower above than a level of values obtained for ports and bays of the northeastern Black Sea. Among ichthyoplankton, the dominant species were Mullus barbatus ponticus, Diplodus annularis, Trachurus mediterraneus, Engraulis encrasicholus and Sciena umbra. Mean abundance of ichthyoplankton in vertical catches was 5–10 times lower than in offshore of Anapa and Gelendzhik of the northeastern Black Sea. And the proportion of dead eggs was 2 – 3 times higher than areas of these resort cities. The composition of macrozoobenthos was drastically depleted and resembled that of the polluted port complexes of the northeastern Black Sea. Heteromastus association dominated in mud bottom sediments. Among spionid polychaetes, the worst invaders Streblospio gynobranchiata and Polydora cornuta have been recorded in soft bottom communities. Depletion of benthic communities, loss from the structure of the trophic web of the macrophyte community and appearance of cyanobacteria and a new alien species in the planktonic and benthic communities leads inevitably to imbalance of the structure of the Sukhum port ecosystem.

Abundance and seasonal variability of aloricate ciliates and tintinnids in a eutrophic coastal lagoon system of the Gulf of California, Mexico

The heterotrophic ciliates, mainly composed of aloricate (naked) ciliates, are the dominant size fraction and play an important role in low impacted subtropical coastal systems of central region of the Gulf of California, México, by consuming up to 70% of phytoplankton biomass (pico- and nanoplankton). However, there is no information concerning microzooplankton populations for lagoons highly impacted by anthropogenic activities. This study established a baseline of regional abundance and spatio-temporal variability of aloricate ciliates and tintinnids, in the eutrophic lagoon system Topolobampo-Santa María-Ohuira. Their total abundance ranged from 10 to 56.1×103 org L−1 for ciliate, and 10 to 14.80×103 org L−1 for tintinnids. Aloricate ciliates mean abundances were approximately four times higher than that of tintinnids, with higher values occurring in winter–spring and punctuated by minor spurts during the rainy months. The study found that eutrophication levels (6.5 to 7.3 TRIX units) were the main factor contributing to their abundance, though tropic interactions and lagoon hydrological characteristics were also relevant. Their distribution revealed that substantial population increases resulted from nutrient enriched residual agricultural drainage at Santa María and Ohuira that exacerbated eutrophication conditions. Canonical correspondence analysis identified that lower values of salinity was due to the influence of wastewater effluent discharge and was the main variable that was related with tintinnids; while dissolved oxygen and chlorophyll-a, variables associated to large primary production, were related to ciliates. The deteriorated water quality of Santa María and Ouhira lagoons likely delineated the low macro-zooplanktonic biomasses and consequently the higher aloricate ciliates and tintinnids abundances.

Long-term changes in abundance and diversity of tintinnids in the Gulf of Trieste (Northern Adriatic Sea)

Abundance and composition of the planktonic tintinnid ciliates were studied in the Gulf of Trieste (Northern Adriatic Sea, NE Mediterranean Sea) from July 1998 to July 2016. Tintinnids were collected biweekly-monthly from the LTER station C1 (200 m offshore, 17.5 m depth) at four depths (surface, 5 m, 10 m and 15 m). The maximum tintinnid abundance reached 4476 ind. L-1 at surface in February 2016. The tintinnid community comprised a maximum of 35 species and was dominated by the genera Stenosemella, Tintinnopsis, Codonellopsis, Salpingella and Eutintinnus. The most abundant species were Stenosemellanivalis, Tintinnopsisnana, Codonellopsisschabi, Salpingellarotundata and Eutintinnusapertus. We found a species-specific correlation with the abiotic factors considered, i.e., temperature and salinity. Temperature was positively correlated with S.rotundata and E.apertus and negatively with S.nivalis. Salinity was negatively correlated with the majority of the detected species. Agglutinated species presented winter maxima while hyaline species showed higher abundance in summer-autumn. Some key species were present over the whole period studied. Significant differences within the water column were not seen in the species composition, but were seen in the relative abundances of the same species at different depths. Stenosemellanivalis, S.ventricosa and Tintinnopsisberoidea can be considered as keystone species in the area and their possible loss can be seen as a signal of changes in the structure of the entire planktonic system.

Rearing of the Pacific white shrimp Litopenaeus vannamei (Boone, 1931) in BFT system with different photoperiods: Effects on the microbial community, water quality and zootechnical performance

In Biofloc Technology (BFT) Systems, there are changes in microbial communities during a shrimp culture cycle; usually, heterotrophic bacteria are replaced by a photoautotrophic or chemoautotrophic community, depending on the management employed. When the water is exposed to sunlight, it can abruptly change from a heterotrophic system (dominated by bacteria and protozoa) to a predominantly photoautotrophic system, with a dominance of microalgae. However, there is little information on the characterization and quantification of the microbial community in the culture of the Pacific white shrimp Litopenaeus vannamei in a BFT system with light restriction, especially the contribution of these microrganisms to the zootechnical performance of shrimp. The aim of this study was to evaluate the microbial community in a rearing environment with light restriction. The study was conducted in 12 tanks (800 L) with a storage density of 500 shrimp m−3 and an initial shrimp weight of 0.053 g. The experiment was designed with three treatments and four replicates distributed into the following groups: i) natural photoperiod - 12 h light/12 h dark (NP); ii) 24 h light (24hLI); and iii) 24 h dark (24hDA). Significant differences were found in water quality parameters (lower values of ammonia and nitrite in the 24hDA treatment), and higher values of CO2, light (Ix) and chlorophyll were observed for the NP and 24hLI treatments than for the 24hDA treatment (p < .05). Zootechnical performance registered higher values in final weight, final biomass, weekly growth rate and survival in the NP and 24hLI treatments than in the 24hDA treatment (p < .05). Proximal analysis of the biofloc showed higher concentrations of proteins and lipids in the NP and 24hLI treatments than in the 24hDA treatment (p < .05), and there was a greater abundance of bacteria (attached coccoid, free filamentous, and attached filamentous bacteria, Vibrio and Bacillus) in NP and 24hLI than in 24hDA (p < .05). There was a greater abundance of photoautotrophic flagellates, heterotrophic flagellates, ciliates, dinoflagellates, rotifers and nematodes in NP and 24hLI than in 24hDA (p < .05). The results show that light restriction favored nitrification. However, light exposition promoted an increased abundance of microrganisms, providing an additional food source and reflecting a lower rate of feed conversion, higher survival and better growth performance for L. vannamei.

Oceanography of Harmful Algal Blooms on the Ecuadorian Coast (1997–2017): Integrating Remote Sensing and Biological Data

Ocean climate drivers and phytoplankton life strategies interact in a complex dynamic to produce harmful algal blooms (HABs). This study aims to integrate historical biological data collected during “red tide” events along the Ecuadorian coast between 1997 and 2017 in relation to five ocean variables derived from satellite remote sensing data to explain the seasonal drivers of coastal processes associated with HABs dynamics. Seasonality of the occurrence of HABs was assessed in relation to oceanographic variables by applying multiple correspondence analysis (MCA) to the Ecuadorian central coast (Zone 1) and at the outer and inner Gulf of Guayaquil (Zone 2). Sixty-seven HABs events were registered between 1997 and 2017. From a total of 40 species of phytoplankton identified, 28 were identified as non-toxic and the remaining 12 are well known to produce toxins. Dinoflagellates were the taxonomic group most highly associated with potential HABs events along the entire Ecuadorian coast. HABs appear to be constrained by the Humboldt coastal upwelling, high precipitation, and associated coastal runoff, with higher biomass abundance in the Gulf of Guayaquil than in the central coast. Results from the MCA reveal that in the central Ecuadorian coast (oligotrophic system), toxic HABs occurred with low abundance of dinoflagellates, while in the Gulf of Guayaquil (eutrophic system), toxic HABs corresponded to a high abundance of dinoflagellates. In both cases, high values were found for sea surface temperature, precipitation, and irradiance—characteristic of wet seasons or El Nino years. Non-toxic HABs occurred with a high abundance of dinoflagellates, ciliates, and centric diatoms, corresponding to colder waters and low levels of precipitation and irradiance. These findings confirm that dinoflagellates display several strategies that enhance their productive capacity when ocean conditions are warmer, allowing them to produce toxins at high or at low concentrations. Considering that the Gulf of Guayaquil is essential to tourism, the shrimp industry, fisheries, and international shipping, these findings strongly suggest the need to establish an ecosystem health research program to monitor HABs and the development of a preventive policy for tourism and public health in Ecuador.

Recent changes in the spring microplankton of Lake Baikal, Russia

Lake Baikal is facing several environmental stressors, including climate change and nearshore eutrophication. To assess recent ecological changes in Lake Baikal and provide a baseline for future comparisons, we sampled spring plankton communities from the pelagic zone of the lake in 2016 and compared these data with unpublished and published historical information going back to 1990. In 2016, one pelagic long-term monitoring station was sampled in early spring (March) during ice cover and 21 long-term monitoring stations located throughout the lake were sampled in late spring (May-June). We measured water chemistry parameters at most stations and the abundance, taxonomic composition and biomass of bacteria, ciliates and phytoplankton at several locations in different areas of the lake. Biotic parameters from 2016 were compared with historical data, showing significant changes in the spring pelagic microbial community since the 1990s. We show increased quantities of small species, mixotrophic ciliates, and the appearance (or increasing number) of small coloured and colourless flagellates. We also show substantially decreased densities of formerly dominant heavily silicified diatoms such as Aulacoseira spp. Since 2007, Synedra acus subsp. radians, a smaller and weakly silicified diatom, has dominated the spring plankton of the lake. These results suggest that Lake Baikal’s pelagic plankton community may be changing, with climate likely playing a dominant role in these changes.

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.

Experimental evidence for crustacean zooplankton grazing activity on mixotrophic ciliates

Abstract With their ultraoligotrophic status, the Chilean North Patagonian lakes have mixotrophic ciliates in their pelagic environments as producers, whereas the primary consumers are crustaceans that are low in abundance and species numbers. The aim of the present study was to determine the potential grazer role of mixotrophic ciliates on crustacean zooplankton collected in a lake without mixotrophic ciliates. Three experiments were conducted; one had a control with mixotrophic ciliates and an experimental treatment including the copepod Boeckella gracilipes obtained from Caburgua lake, whereas the second and third experiments had a control without zooplankton, and three treatments with the addition of Daphnia pulex and Mesocyclops araucanus, and a third treatment with equal amounts of both species. The results revealed grazing effects on the mixotrophic ciliates in the experimental treatments. This finding supports the evidence from the field and experiments suggesting that, in the transition from oligotrophy to mesotrophy with consequent changes in zooplankton, species number and abundance of mixotrophic ciliates decrease in their abundance.

ГЕТЕРОТРОФНЫЙ МИКРОПЛАНКТОН ЮЖНОЙ ОКОНЕЧНОСТИ ЖЕЛОБА СВЯТОЙ АННЫ В ОСЕННИЙ ПЕРИОД (КАРСКОЕ МОРЕ)

The paper concerns the pelagic microbial community of the southern part of the St.Anna trough in the late vegetation period. in 2007 and 2011. The abundance, biomass and production of bacterioplankton, as well as the abundance and species composition of heterotrophic flagellates and ciliates were analyzed. The abundance and bacterial production values observed in the trough were significantly lower than the values typical of the surface brackish water layer above the Kara Sea shelf. The bacterioplankton abundance values of the upper warm layer in 2007 were several times lower than in 2011 (10-60*103 cells/ml and 24-147*103 cells/ml, respectively). In the deeper water layers, this difference diminished. The interannual differences in the values of bacterioplankton production were also most pronounced in the upper 60-meter layer: 0-0.17 and 0.05-0.87 mgC/m3 per day in 2007 and 2011, respectively. The distribution of the abundance of heterotrophic flagellates and ciliates is significantly influenced by the contour current along the slope of the trench. In the area of its influence in 2007, high values of the number of flagellates (154 ± 29 cells/ml) were observed throughout the water column, whereas in 2011 maximal values were confined to the upper 50-meter layer, exceeding almost twice the abundance at neighboring stations (810 ± 102 and 481 ± 61 cells/ml, respectively).The results of multifactor analysis showed that the number of heterotrophic flagellates, as well as the number of protozoan species decreased with depth. However in the euphotic layer there was a difference between two years of observations: in 2007, the abundance of consumers depended on the state of primary producers, whereas in 2011 the main factor affecting their abundance was the number of bacteria. Analysis of the species composition of heterotrophic flagellates suggests that the complex vertical hydrophysical structure of the water column does not affect substantially the microbial community of the region. However the influence of main currents of the area under consideration may be traced regarding the distribution of the abundance and species composition of heterotrophic microorganisms.

Parasitic protozoan interactions with bacterial microbiome in a tropical fish farm

The bacterial microbiome is an important component of any aquaculture environment. The interaction between the bacterial microbiome and other microorganisms (e.g. parasites, viruses, or other bacteria) in aquaculture systems can prevent or contribute to disease outbreaks. This study characterised the bacterial composition associated with the abundance of a ciliated protozoan parasite, Chilodonella hexasticha, in gills and freshwater ponds of barramundi, Lates calcarifer, farm in tropical Queensland, Australia, over one year. An environmental DNA (eDNA) approach was used to estimate the abundance of C. hexasticha (copies/μl) in water through SSU-rDNA gene qPCR and the relative abundance of bacterial species in water and fish gills through 16S rRNA V3 and V4 metabarcoding. The overall bacterial community diversity, dominated by Actinobacteria (42%), Proteobacteria (28%), Bacteroidetes (10%) and Cyanobacteria (6%), was stable among ponds over the study period (p > .05). Of those that could be identified to species, Flavobacterium columnare, Veillonella dispar and Bdellovibrio bacteriovorus abundance correlated with both high C. hexasticha levels in pond water and high observed fish mortalities (p < .05). Results also revealed significantly higher levels of F. columnare, B. bacteriovorus, Plesiomonas shigelloides, Prostecobactor debontii and Oxalobacter formigenes (p < .05) in gills of fish with high infection levels of C. hexasticha compared to fish with no detected parasite infection. This study demonstrated, for the first time, a link between increased parasitic ciliate abundance, bacterial composition and fish mortalities in a freshwater aquaculture environment and the application of eDNA to investigate pathogen, host and environment interactions.

Impact of the Słupia River waters on microbial communities in the port of Ustka and adjacent Baltic Sea waters

Abstract The distribution of bacterial and ciliate abundance, ciliate community composition and other parameters were studied during summer along a transect from the mouth of the Słupia River to offshore waters (southern Baltic Sea). Bacteria were examined under an epifluorescence microscope and ciliates were observed under an inverted microscope. Two water masses were identified along the transect. Less saline waters in the river mouth and in the surface layer in the port of Ustka were characterized by high bacterial abundance (5.51–6.16 × 106 ml−1) and low ciliate abundance (0.34–0.90 cells ml−1). More saline waters in the near-bottom zone in the port of Ustka and in the surface layer outside the port contained smaller numbers of bacteria (0.99–2.14 × 106 ml−1) and larger numbers of ciliates (2.65–5.40 cells ml−1). The differences were statistically significant. The separation of the two water masses indicated that the Słupia River exerted a minor impact on the marine waters. The ciliate community composition changed along the transect studied. The main statistically significant difference observed was the low contribution of oligotrichs and choreotrichs to ciliate biomass (3–4%) in less saline waters and their dominance (45–80% of ciliate biomass) in more saline waters.

Rhabdostylid Ciliates (Ciliophora, Peritrichia, Epistylididae) as Epibionts on Chironomid Larvae: Evidence of High Specificity and Association with Organic Pollution.

Although epibiont ciliates make up a significant part of the biomass in aquatic ecosystems and may cause perceptible alterations in the population dynamics of their hosts, studies on the extrinsic and intrinsic factors that control the abundance of these microorganisms are scarce in literature. In the present study, we investigated the colonization site and intensity of rhabdostylid epibiont upon chironomid larvae and assessed the influence of organic pollution and chironomid communities on the prevalence and abundance of epibiont ciliates at five sampling stations (two in rural areas and three in urban areas) along a neotropical urban stream over a period of 12 months. Among the 24 genera of chironomids found and the 31,976 larvae analyzed, 96.12% belonged to the Chironomus genus, of which 16.95% (5212) were colonized by Rhabdostyla aff. chironomi. The infestation intensity varied from one to 67 individuals per host with an average intensity of 4.86 (± 33.45). Ciliates were only found colonizing the chironomids' ventral tubules. The high number of chironomid larvae, high host- and site-specificity, low infestation intensity, and absence of apparent structural damage to hosts evidence an intimate relationship between epibiont and basibiont as well as a possibly long coevolutionary history. Both prevalence and abundance of epibiont ciliates were correlated to the pollution rate of the studied stream. There was an alteration in the composition and structure of the chironomid community along the sampling stations. Numeric dominance of Chironomus-tolerant chironomids and its direct correlation to infestation prevalence and to ciliates abundance highlights the predilection of both peritrich ciliates and Chironomus larvae for organically-enriched environments.

Plankton distribution within a young cyclonic eddy off south-western Madagascar

Mesoscale eddies are major features in ocean dynamics that significantly influence ocean production depending on their polarity, life-stage, location and time of formation. Eddies in the south-west Indian Ocean have been the focus of many studies, especially in the Mozambique Channel where southward-moving cyclonic and anticyclonic eddies feed into the Agulhas Current. However, eddies formed south of Madagascar that move westwards towards the coast of South Africa have been much less studied, despite their significant contribution to the Agulhas Current. This study aims to understand how the plankton communities (i.e. pico-, nano-, phyto-, microzoo- and mesozooplankton) are distributed in a cyclonic eddy generated off southern Madagascar. We also investigate a possible link between the Madagascar shelf and the eddy. Temperature, salinity, fluorescence and plankton abundance were measured at 25 stations spaced at 18.5 km intervals across a young (~ 1 month old) cyclonic eddy, and at three locations on the Madagascar shelf, in July 2013. A patch of enhanced chlorophyll a concentration was found at four stations in the eddy, homogeneously distributed vertically in the upper mixed layer and characterised by a higher proportion of diatoms compared to the other stations. Abundances of picoplankton, nanoplankton, ciliates and dinoflagellates were very similar within and outside the eddy. Zooplankton followed a contrasting pattern with higher biomass at four stations just to the west of this high diatom patch. The mesozooplankton composition at these four stations revealed greater species similarities with the Madagascar shelf than with the other stations, suggesting a link between the shelf and the western side of the eddy. The periphery of the eddy seems to have been primarily influenced by a strong geostrophic current propagating from the southern shelf of Madagascar which then wrapped itself around the eddy. This filament may be the source of the high zooplankton biomass in the eddy periphery, which would account for the similarities in zooplankton community composition between the eddy periphery and the shelf.