Heterotrophic Nanoflagellates Research Articles

Community heterogeneity and single‐cell digestive activity of estuarine heterotrophic nanoflagellates assessed using lysotracker and flow cytometry

Heterotrophic nanoflagellates (HNFs) are an essential component of all aquatic microbial food webs, and yet the exploration of the numerical and single-cell responses of these organisms in mixed assemblages still represents a major technical challenge. LysoTracker Green staining combined with flow cytometry was recently proposed for the enumeration of aquatic HNFs. Here we show that LysoTracker Green not only allows the enumeration of HNFs in estuarine samples with a wide range of HNF abundances, but also allows the discrimination of distinct HNF populations in mixed assemblages. In addition, the resulting cytometric parameters can be used to characterize cell size and the level of activity of the cells in the different populations that are detected. LysoTracker Green accumulates preferentially in lysosomes, and we demonstrate that the green fluorescence emission from HNF cells stained with LysoTracker strongly correlates with cell-specific beta-glucosaminidase (beta-Gam) activity, a key digestive enzyme of lysosomal origin in eukaryotic cells. Our results further show that different populations that develop in estuarine regrowth cultures are characterized by different intrinsic ranges of size and of feeding activity, and that there is a wide range of single-cell responses within these HNF populations. We found a large degree of uncoupling between cell size and feeding activity, both between and within HNF populations, and there appears to be no clear allometric scaling of feeding activity. We were able to reconstruct the succession of distinct HNF populations that developed during the regrowth experiments, and explore the complex interactions that occurred between numerical (change in abundance of the cytometric populations) and single-cell HNF responses.

Relationships between bacteria and heterotrophic nanoflagellates in lake water examined by different techniques controlling grazing pressure

ABSTRACT: A dialysis bags experiment, involving the use of natural water from eutrophic LakeMiko8ajskie (Mazurian Lake District, Poland), was performed to assess the impact of grazing pressureby heterotrophic nanoflagellates (HNF; <10 µm) on bacterial abundance, their size distribution, tax-onomic composition and activity measured by bacterial secondary production (BP) and the contribu-tion of active bacteria with an intact membrane (MEM+). Three different techniques—size-fraction-ation (<1.0 µm pore size), dilution (10×) and selective eukaryotic inhibition (cycloheximide andcolchicine)—were applied to control HNF grazing. There were significant differences in the effec-tiveness of grazing pressure limitation between the different techniques employed. The most distinctchanges in the bacterial community were found in the control and the 10× diluted treatments; in both,a considerable increase in HNF abundance was noted. In these 2 treatments, a significant decreasein both bacterial numbers and contribution of MEM+ cells, as well as an increase in the proportion ofbacterial filaments (up to 50 µm long), was observed. In contrast, the use of cycloheximide andcolchicine in combination resulted in the lowest and an almost constant HNF abundance. In addition,high numbers of bacteria with a large proportion of MEM+ cells (30 to 40%) and exponential increaseof bacterial secondary production were found. These results suggest that eukaryotic inhibition is themost useful method of limiting HNF grazing pressure and involves minimal manipulation of the watersample. Close relationships between bacteria and HNF confirm the crucial role of nanoflagellates inshaping bacterial abundance, morphology and activity.KEY WORDS: Bacteria · HNF · Grazing pressure · Dialysis bags · Filtration · Dilution · Eukaryotic inhibition

Changes in microbial food web structure in response to changed environmental trophic status: A case study of the Vranjic Basin (Adriatic Sea)

Vranjic Basin, in the eastern part of KaštelaBay (middle Adriatic Sea), received municipal wastewater until offshore submarine outfalls were finished in November 2004. To identify the responses of the microbial community to changes in the trophic status of the marine environment, two 4-year periods were compared: a eutrophic period (2001–2004) when the sewage waters entered the Basin and an oligotrophic period (2005–2008) after the outfalls were completed. The switch from eutrophic to oligotrophic conditions was accompanied by decreases in bacterial abundance, bacterial production and chlorophyll a, and increase in heterotrophic nanoflagellate (HNF) abundance and bacterial specific growth rate. Qualitative changes in the phytoplankton community manifested through dramatically decreased abundance of the diatom species Skeletonema costatum and Euglenophyta Eutreptiella spp. during the oligotrophic period. Furthermore, the percent contribution of pico–nano phytoplankton chlorophyll to total chlorophyll increased from less than 40% during the eutrophic period to more than 60% during the oligotrophic period. Changes in seasonal patterns of phytoplankton, bacteria and HNF abundance were also observed, with summer maxima during the eutrophic period and spring and autumn maxima during the oligotrophic period. Significant changes in the microbial food web were also identified. During eutrophic conditions, bacteria were dominantly under the phytoplankton-mediated bottom-up control whereas HNF were dominantly controlled by ciliate grazing (top-down control). In contrast, during the oligotrophic period, predominantly top-down control of bacteria by strong HNF grazing was observed. At the same time, HNF were spared from strong ciliate predation pressure because the ciliates apparently switched their dominant prey from HNF to the pico-nano phytoplankton fraction during that period.

Trophic linkages between grazers and ultraplankton within the microbial food web in subtropical coastal waters

To investigate the trophic linkages among different micrograzers and their preys and the possible occurrence of trophic cascades within the microbial food web, we combined the dilution technique and size-fractionation methods to monitor the grazing rates of different grazer assem- blages on various ultraphytoplankton cells in subtropical waters. The mortality rates of Synechococ- cus and picophytoeukaryotes (<2 µm) were often higher in dilution experiments set up with 5 µm pre- filtered seawater (containing only heterotrophic nanoflagellates (HNFs)) than in the <20 µm treatments (including both HNFs and small ciliates), indicating the effect of trophic cascading. In addition, similar grazing rates on Synechococcus and picophytoeukaryotes can be well related to the biomass of HNFs but not to that of total grazers. Growth and grazing rates of Synechococcus and picophytoeukaryotes mostly fell to a 1:1 relationship, suggesting grazing was the major loss pathway for picophytoplankton. The trophic linkages of micrograzers and their preys in coastal waters do not appear to differ substantially from those observed in open oceans.

The Role of Zooplankton Grazing and Nutrient Loading in the Occurrence of Harmful Cyanobacterial Blooms in Florida Bay, USA

Florida Bay is Florida’s (USA) largest estuary and has experienced harmful picocyanobacteria blooms for nearly two decades. While nutrient loading is the most commonly cited cause of algal blooms in Florida Bay, the role of zooplankton grazing pressure in bloom occurrence has not been considered. For this study, the spatial and temporal dynamics of cyanobacteria blooms, the microbial food web, microzooplankton and mesozooplankton grazing rates of picoplankton, and the effects of nutrients on plankton groups in Florida Bay were quantified. During the study, cyanobacteria blooms (>3 × 105 cells mL−1) persisted in the eastern and central regions of Florida Bay for more than a year. Locations with elevated abundance of cyanobacteria hosted microzooplankton grazing rates on cyanobacteria that were significantly lower (p < 0.001) and less frequently detectable compared to sites without blooms. Consistent with this observation, cyanobacteria abundances were significantly correlated with ciliates and heterotrophic nanoflagellates at low cyanobacteria densities (p < 0.001) but were not correlated during bloom events. The experimental enrichment of mesozooplankton abundance during blooms yielded a significant decrease in the net growth rate of picoplankton but had the opposite effect when blooms were absent, suggesting that the cascading effect of mesozooplankton grazing on the microbial food web was also altered during blooms. While inorganic nutrient enrichment significantly increased the net growth rates of eukaryotic phytoplankton and heterotrophic bacteria, such nutrient loading had no effect on the net growth rates of cyanobacteria. Hence, this study demonstrates that low rates of zooplankton grazing and low rates of inorganic nutrient loading contribute to the persistence of cyanobacteria blooms in Florida Bay.

Fatty acid composition of the heterotrophic nanoflagellate Paraphysomonas sp.: influence of diet and de novo biosynthesis

We compared the relative importance of dietary factors versus de novo synthesis in determin- ing the polyunsaturated fatty acid (PUFA) composi- tion of the heterotrophic nanoflagellate Paraphyso- monas sp. The flagellate was fed with different mutants of the picocyanobacterial strain Synechocystis PCC6803, which differ in their capability to synthe- size specific PUFAs. The desA, desB, and desD genes of Synechocystis PCC6803 encode lipid desaturases at the Δ12, Δ15, and Δ6 positions of 18C fatty acids (FAs), respectively. Thus, the use of desA - , desB - , desD - , and desA - /des D - mutants of Synechocystis PCC6803 as food sources permitted us to provide the heterotrophic flagellate with decreasing levels of unsaturated FAs. In each treatment, Paraphysomonas sp. exhibited the same FA composition pattern, i.e. high levels of 16:0 and 18:1, and significant amounts of 18C PUFAs and long-chain PUFAs such as 20:4(n-6), 20:5(n-3), and 22:6(n-3), which indicated that Paraphysomonas sp. is capable of synthesizing these PUFAs de novo. Results also showed that dietary 18C PUFAs seem to be preferentially accu- mulated in Paraphysomonas sp. lipids. This demon- strates that heterotrophic protists could play a key role in transferring essential compounds from pri- mary producers to metazoan consumers.

Distribution of Virus-Infected Bacteria in the Western Equatorial Pacific

Abstract: Viruses are generally considered an important agent of bacterial loss in diverse marine environments. However, the impact of viruses on bacteria is unknown in the western equatorial Pacific, where surface waters are warm and phytoplankton biomass is low (i.e., oligotrophic). Further, little is known about their importance in the mesopelagial, where bacteria and heterotrophic nanoflagellates are known to be metabolically active. To elucidate the ecological characteristics of viruses in the western equatorial Pacific, abundances of bacteria and viruses were measured, along with frequencies of visibly infected cells (FVIC) and frequencies of dividing cells (FDC) in epipelagic and mesopelagic samples at three stations near the equator from August to September 2002. Measurements of Secchi depth (20 m) and chlorophyll a concentrations (0.07– 0.4 µg chl a liter-1) indicated that the study area was oligotrophic during the investigation. FVIC ranged from 0.4% to 1.8% and 0.5% to 1.8% in the epipelagic an...

Community-level and species-specific responses of coastal phytoplankton to the presence of two mesozooplanktonic grazers

The response of phytoplankton to the presence of two mesozooplanktonic grazers was studied in a 44-h laboratory experiment from the phytoplankton perspective. The <45-μm-filtered plankton community, as well as females of the copepod Eurytemora affinis and nauplii of the barnacle Balanusimprovisus originated from the northern Baltic Sea. The phytoplankton community was dominated by the dinoflagellate Heterocapsa triquetra, which was preferred as food by the mesozooplanktonic grazers, especially E. affinis. Cryptophytes were eaten by the B. improvisus nauplii, while heterotrophic nanoflagellates increased in the presence of B. improvisus nauplii, and colonial cyanobacteria increased in the presence of E. affinis. Because of the strong selective feeding on the dominant, large-sized phytoplankton species, the negative effect of the mesozooplanktonic grazers on total chlorophyll a was stronger than any cascade effect releasing phytoplankton from protozoan grazing.

Erratum to: The significance of transparent exopolymeric particles in the vertical distribution of bacteria and heterotrophic nanoflagellates in Lake Pavin

Erratum to: The significance of transparent exopolymeric particles in the vertical distribution of bacteria and heterotrophic nanoflagellates in Lake Pavin

Response of the plankton community to herbicide application (triazine herbicide, simetryn) in a eutrophicated system: short-term exposure experiment using microcosms

The methylthiotriazine herbicide, simetryn, is commonly used in Japan, and its concentration in surface water is often high enough to affect natural phytoplankton. To estimate how the plankton community in eutrophic systems respond to short-term exposure of realistic concentrations of simetryn, we collected plankton from a eutrophic lake and exposed them to low (20 μg l−1) and high (100 μg l−1) concentrations of simetryn for 12 days in microcosm tanks (50 l). High concentrations significantly lowered total phytoplankton biomass, particularly green algal density. Consequently, the species composition was severely modified by simetryn application. However, there was no apparent impact of simetryn on microbial food-web components, bacteria, heterotrophic nanoflagellates (HNF), and ciliates. Despite the decreased abundance of algal food, the zooplankton community showed subtle changes with simetryn application. The results indicate that the direct impact of simetryn on planktonic organisms other than phytoplankton, particularly on microbial food-web components, is weak. The indirect impact of simetryn on zooplankton through the change of food quality and quantity was also small. It has been suggested that the persistence of microorganisms, alternative food for zooplankton, probably dilutes the indirect impact of simetryn on zooplankton by compensating for the loss of food phytoplankton. Consequently, the plankton community in eutrophicated systems is resistant to the herbicide at a feasible concentration for a short period of time.

Full-depth profiles of prokaryotes, heterotrophic nanoflagellates, and ciliates along a transect from the equatorial to the subarctic central Pacific Ocean

Studies in epipelagic waters report higher heterotrophic microbial biomass in the productive high latitudes than in the oligotrophic low latitudes; however, biogeographical data are scarce in the deep ocean. To examine the hypothesis that the observed latitudinal differences in heterotrophic microbial biomass in the epipelagic zone also occur at depth, abundance and biomass of heterotrophic prokaryotes, nanoflagellates (HNF), and ciliates were determined at depths of 5-5000 m in the central Pacific between August and September of 2005. Heterotrophic microbial biomass increased from the tropical to the subarctic region over the full water column, with latitudinal differences in prokaryotic biomass increasing from 2.3-fold in the epipelagic zone to 4.4-fold in the bathypelagic zone. However, the latitudinal difference in HNF and ciliate biomass decreased with depth. In the mesopelagic zone, the vertical attenuation rate of prokaryotic abundance, which was calculated as the linear regression slope of log-log plot of abundance versus depth, ranged from -0.55 to -1.26 and was more pronounced (steeper slope) in the lower latitudes. In contrast, the vertical attenuation rate of HNF in the mesopelagic zone (-1.06 to -1.27) did not differ with latitude. In the subarctic, the attenuation rate of HNF was 1.7 times steeper than for prokaryotes. These results suggest the accumulation of prokaryotes in the deep subarctic Pacific, possibly due to low grazing pressure. Although the vertical attenuation rate of ciliates was steepest in the bathypelagic zone, HNF abundance did not further decrease at depths below 1000 m, except for at 2000 m where HNF was lowest across the study area. Ciliate abundance ranged 0.3-0.8 cells l -1 at 4000 m, and were below the detection limit ( < 0.1 cells l -1 ) at 5000 m. To our knowledge, this study presents the first data for ciliates below 2000 m.

Emerging concepts on microbial processes in the bathypelagic ocean – ecology, biogeochemistry, and genomics

This paper synthesizes recent findings regarding microbial distributions and processes in the bathypelagic ocean (depth >1000 m). Abundance, production and respiration of prokaryotes reflect supplies of particulate and dissolved organic matter to the bathypelagic zone. Better resolution of carbon fluxes mediated by deep microbes requires further testing on the validity of conversion factors. Archaea, especially marine Crenarchaeota Group I, are abundant in deep waters where they can fix dissolved inorganic carbon. Viruses appear to be important in the microbial loop in deep waters, displaying remarkably high virus to prokaryote abundance ratios in some oceanic regions. Sequencing of 18S rRNA genes revealed a tremendous diversity of small-sized protists in bathypelagic waters. Abundances of heterotrophic nanoflagellates (HNF) and ciliates decrease with depth more steeply than prokaryotes; nonetheless, data indicated that HNF consumed half of prokaryote production in the bathypelagic zone. Aggregates are important habitats for deep-water microbes, which produce more extracellular enzymes (on a per-cell basis) than surface communities. The theory of marine gel formation provides a framework to unravel complex interactions between microbes and organic polymers. Recent data on the effects of hydrostatic pressure on microbial activities indicate that bathypelagic microbial activity is generally higher under in situ pressure conditions than at atmospheric pressures. High-throughput sequencing of 16S rRNA genes revealed a remarkable diversity of Bacteria in the bathypelagic ocean. Metagenomics and comparative genomics of piezophiles reveal not only the high diversity of deep sea microbes but also specific functional attributes of these piezophilic microbes, interpreted as an adaptation to the deep water environment. Taken together, the data compiled on bathypelagic microbes indicate that, despite high-pressure and low-temperature conditions, microbes in the bathypelagic ocean dynamically interact with complex mixtures of organic matter, responding to changes in the ocean’s biogeochemical state.

Estuarine microbial community characteristics as indicators of human-induced changes (Senegal River, West Africa)

Understanding how human-induced management interacts with and affects the structure and functioning of large estuarine ecosystems is a major research challenge. In West Africa, human intervention on the Senegal River Estuary was intended to reduce the impact of major flooding by opening a new mouth in October 2003, 25 km to the north of the existing mouth. This study describes the effects of the new environmental conditions on the physical and biochemical characteristics of the water column and on microbial communities (bacteria, phytoplankton by size class and heterotrophic nanoflagellates (HNF)) in comparison with the situation in 2002. In 2006, seventeen stations were sampled, during both neap and spring tides, at a depth of 0.5 m along a salinity gradient from freshwater to marine conditions. Inorganic nutrient levels were often low but there were high levels of chlorophyll a in the estuarine area (mean of 13.7–20.7 μg L −1 in spring and neap tide conditions, respectively) producing a eutrophic status in this estuary. Average HNF abundances were lower (mean of 108 and 174 cells l −1 during neap and spring tides, respectively) compared to the situation in 2002 (mean between 2.5 and 6.7 × 10 4 cells l −1). Three biological indicators for assessing environmental changes are discussed: ratio of bacteria to heterotrophic flagellate abundances, ratio of picophytoplankton to nanophytoplankton, and the density of thermo-tolerant coliforms (TTC) and faecal streptococci. It is demonstrated that man-made alteration of the hydrologic regime can modify the microbial community structure and cause the health status of the estuary to deteriorate.

Morphology, Ultrastructure, and Small Subunit rDNA Phylogeny of the Marine Heterotrophic Flagellate Goniomonas aff. amphinema

Marine goniomonads have a worldwide distribution but ultrastructural information has not been available so far. An isolate of the heterotrophic marine nanoflagellate Goniomonas (G. aff. amphinema) from North Wales (UK) has been studied, providing information on its morphology and cellular structure using video, electron, laser scanning confocal microscopy (LSCM), and atomic force microscopy. Here, we describe a new feature, a granular area, potentially involved in particle capture and feeding. The binding of the lectin wheat germ agglutinin to the granular area of cells with discharged ejectisomes indicates the adhesive nature of this novel feature. The presence of a microtubular intracellular cytopharynx, apparently also used for feeding, has been revealed by LSCM. The small subunit rRNA gene of the isolate has been sequenced (1,788 bp). Phylogenetic results corroborate significant genetic divergence within the marine members of Goniomonas. This work highlights the need for integrated morphological, ultrastructural, and molecular investigation when describing and studying heterotrophic nanoflagellates.

An Evaluation of the Use of the LSU rRNA D1-D5 Domain for DNA-based Taxonomy of Eukaryotic Protists

Diagnostic signature DNA sequences are important tools for the identification of species. There is an active debate in the literature on the choice of the best markers applicable for a broad range of organisms. Protists have seldom been included in these evaluations. Mitochondrial gene sequences are inappropriate for protists since several groups do not possess mitochondria. Here we studied the application of the large subunit (LSU) rRNA gene fragments (D1-D5) regarding their usefulness to discriminate between a wide range of heterotrophic nanoflagellates. Phylogenetic analyses based on the LSU rRNA fragments showed similar results compared to phylogenetic trees based on the small subunit (SSU) rRNA. The data set indicates the power of the use of the D1-D5 region as a marker for a DNA-based taxonomy. Our results, together with the available sequences in Genbank, form a comprehensive database for unicellular eukaryotes, especially heterotrophic flagellates. It is now possible to assign new sequences to the different groups of heterotrophic flagellates which we have tested for different closely related Cercomonas and Paracercomonas strains from groundwater.

Changes in the plankton community along the length of the River Rhine: Lagrangian sampling during a spring situation

The development of the planktonic microbial community [bacteria, heterotrophic nanoflagellates (HNF) and ciliates] was investigated along a 660 km stretch of the River Rhine using Lagrangian sampling in May 2000, and by taking the influence of the main tributaries into account. The relative importance of the components of the microbial food web (HNF, ciliates) increased in the course of the German river stretch, whereas the absolute abundance of protozooplankton decreased and phytoplankton abundance increased. Bacterial abundance remained relatively constant throughout the river stretch investigated. The taxonomic composition of phytoplankton changed from a dominance of cryptophytes to a dominance of diatoms, whereas flagellates, ciliates and metazooplankton showed no shift in species composition. Some tributaries had higher abundances of planktonic organisms than the Rhine itself, but only the River Moselle contributed significantly to the plankton load of the Rhine. However, even after its confluence with the River Rhine abundances of the heterotrophic plankton (HNF and ciliates) remained low and decreased further downstream. The shifts in the composition of the pelagic microbial food web along the river stretch are discussed in the context of group-specific growth and loss processes.

Seasonal variation in viral-induced mortality of bacterioplankton in the water column of a large mesotrophic lake (Lake Biwa, Japan)

Viruses are ubiquitous and abundant in aquatic systems, yet knowledge of virus-bacteria interactions in thermally stratified water columns of large lakes is limited. We explored the possible factors that affect viral abundance, infection rate, and the relative importance of viral lysis to heterotrophic nanoflagellate (HNF) grazing as a mortality factor of bacterioplankton in the upper (euphotic zone, 5 m) and deeper (aphotic zone, 50 m) layers of the large mesotrophic Lake Biwa,Japan. Data obtained for a full seasonal cycle indicated that bacterial abundance was the best predictor (r2 = 0.85) of viral abundance (range 1.0 × 1010 to 4.1 × 1010 viruses l-1), yielding an average virus:bacteria ratio of 8.2 ± 1.3 (SD). Variation in the frequency of visibly infected cells (range 1.8 to 4.1%) was largely accounted for by the linear combination of bacterial production and HNF abundance (r2 = 0.81, p < 0.001, n = 24). The percentage of daily bacterial production destroyed by viruses was estimated to be high (52.7 ± 16.2%) in the upper layer during the stratification period, which was on average 3.0-fold greater than the percentage of bacterial production consumed by HNF in that layer. In contrast, the corresponding value in the deeper layer was moderate (13.6 ± 5.2%), being 0.6- fold lower than the percentage of bacterial production consumed by HNF. Our data suggest that carbon and nutrient flux patterns controlled by viruses and HNF vary with depth in thermally stratified water columns of Lake Biwa.

The significance of transparent exopolymeric particles in the vertical distribution of bacteria and heterotrophic nanoflagellates in Lake Pavin

The abundance, size distribution, and bacterial colonization of Transparent Exopolymeric Particles (TEP) were examined in two consecutive years during the spring diatom development throughout the water column of the deep meromictic Lake Pavin, France. TEP concentrations ranged from 1.9 to 13.4 × 105 particles l−1 and their distribution and size spectra indicated that these particles are the main factor in governing the transport of diatoms to the deep hypolimnion of the lake. The majority of TEP was colonized by bacteria that constituted 0.4–8.9% of total DAPI-stained bacteria. The intensity of bacterial colonization was strongly related to temperature and decreased with particle size. A more important colonization of small particles in the hypolimnion during thermal stratification suggested that bacterial colonisation also increased with the age of the particle. The abundance of heterotrophic nanoflagellates (HNF) was more significantly related to the density of particles than to the density of total bacteria and the intensity of bacterial colonization of TEP. Our results therefore suggest that TEP are a more important factor for HNF development than attached and free bacteria. We conclude that TEP are involved not only in sedimentation processes but also in the dynamics of bacteria and protozoa in freshwater pelagic environments.

Response of lower trophic organisms to nutrient input and effects on carbon budget: a mesocosm experiment

The roles of heterotrophic organisms (microzooplankton, mesozooplankton, bacteria and heterotrophic nanoflagellates) were examined during a nutrient enrichment experiment using a mesocosm in Saanich Inlet, British Columbia, Canada. Grazing rates of microzooplankton, copepods, and Noctiluca scintillans were respectively estimated by the dilution method, from the egg production, and the apparent growth rate. The primary production increased by about 11 times during the initial 3 days, and the grazing rate by zooplankton also increased by 7.4 times. The primary production exceeded the grazing rate during the initial 5 days, after that, almost balanced rates were observed. Biomass peaks of bacteria and HNFs (heterotrophic nanoflagellates) were observed after the decline of the phytoplankton bloom. Bacterial production and HNF bacterivory gradually increased from the beginning to the end of the experiment. Microzooplankton consistently removed about half of the primary production. The contribution of microzooplankton to grazing was largest during the initial 7 days. Heterotrophic dinoflagellates were the most dominant component of the microzooplankton, but oligotrich ciliates showed the fastest growth response to phytoplankton production. Noctiluca scintillans became an important grazer after the bloom. Overall, the contribution of microzooplankton grazing was the largest of the processes through which phytoplankton were lost. Cell sinking was a minor component contributing to loss of phytoplankton. Thus, oligotrich ciliates and heterotrophic dinoflagellates were the most plausible organisms contributing to the steady state of phytoplankton concentrations.

Effects of snail grazers and light on the benthic microbial food web in periphyton communities

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 61:163-178 (2010) - DOI: https://doi.org/10.3354/ame01449 Effects of snail grazers and light on the benthic microbial food web in periphyton communities Tanja Burgmer1, Julia Reiss1,2, Stephen A. Wickham3, Helmut Hillebrand1,4,* 1Erken Laboratory, Department of Limnology, Evolutionary Biology Centre, Uppsala University, Norr Malma 4200, Norrtälje 761 73, Sweden 2Department of Life Sciences, Roehampton University, London SW15 4JD, UK 3Organismal Biology, Institute for Zoology, Hellbrunnerstr. 34, Salzburg 5020, Austria 4Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl-von-Ossietzky University Oldenburg, Schleusenstr. 1, Wilhelmshaven 26382, Germany *Corresponding author. Email: hillebrand@icbm.de ABSTRACT: Periphyton harbours a complex microbial food web with different trophic levels, but little is known about trophic interactions within this food web and its response to factors that potentially control the entire community. We used natural periphyton communities from Lake Erken (Sweden) in 2 experiments manipulating grazer presence. In addition to an ungrazed control, we included natural densities of either of 2 snail species (Theodoxus fluviatilis and Bithynia tentaculata) in order to test how generalist consumers affect different components of the periphyton. In the second experiment, we additionally manipulated light supply to alter the heterotroph–autotroph ratio in the periphyton and thus potentially the trophic interactions. In both experiments, grazer presence decreased algal biomass immediately and shifted the community composition from dominance of large filamentous forms to dominance of prostrate and motile unicellular species. Biomass of bacteria, heterotrophic nanoflagellates, ciliates and meiofauna also decreased with grazing, but with differentiated temporal dynamics and effect strength. In the ungrazed control, first heterotrophic protists and later meiofaunal biomass increased, indicating strong bottom-up and top-down propagation of trophic interactions in the microbial food web. High light increased the biomass of mixotrophic ciliates and nanoautotrophs but not total algal biomass. Grazer presence decreased algal richness in the second experiment, but increased evenness of the algal community under high light conditions. We conclude that grazer presence puts different pressure on the components of the periphyton, which are further linked by direct or indirect internal trophic processes. KEY WORDS: Periphyton · Microbial food web · Protozoa · Algae · Grazer · Light Full text in pdf format PreviousNextCite this article as: Burgmer T, Reiss J, Wickham SA, Hillebrand H (2010) Effects of snail grazers and light on the benthic microbial food web in periphyton communities. Aquat Microb Ecol 61:163-178. https://doi.org/10.3354/ame01449 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 61, No. 2. Online publication date: October 20, 2010 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2010 Inter-Research.