Heterotrophic Nanoflagellates Research Articles

The interplay between short‐term, mild physicochemical forcing and plankton dynamics in a coastal area

Two intensive surveys were conducted in the coastal waters of Barcelona (northwest Mediterranean) to assess short‐term variations of biological parameters in relation to environmental conditions. Surveys lasted 1 week, with three to four samplings per day, and were carried out in autumn and spring. Rather than exploring extreme events, we aimed to study the effects of regular low or moderate perturbations, such as meteorological fronts, on the dynamics of the system. We focused on two attributes: wave height, as a proxy for mechanical energy entering the system, and nutrient inputs, whose variability in total load and relative composition is a central characteristic of coastal areas. The effects of the temporal coupling or uncoupling of both factors were examined. Sudden nutrient fluxes uncoupled from water motion tended to favor bacteria and heterotrophic nanoflagellates, while their concurrence with some water column mixing shaped a favorable scenario for large autotrophs. Ultimately, these two distinct biological responses pointed toward two main disturbance scenarios: episodes of nutrient enrichment uncoupled from mixing, mostly related to episodic water spills from the nearby city that contributed to high relative loads of ammonium and organic compounds; and episodes of increased wind caused by passing weather fronts that promoted some water column mixing and the entrainment of nutrients from bottom sediments or from adjacent water masses.

Effects of nitrogen and phosphorus on the abundance and cell size of planktonic nanoflagellate communities

AIM: We experimentally investigated the effects of nutrients (Nitrogen and Phosphorus) enrichment on the density, biomass, and cell size of pigmented and heterotrophic plankton nanoflagellates communities. METHODS: The experiment was done in mesocosms in a tropical reservoir during a 19-day period. Four different treatments were carried out: Control (non-nutrient addition - C), phosphorus additions (P), nitrogen addition (N) and phosphorus + nitrogen addition (N + P). Each treatment was performed in triplicate, sorted randomly, thus giving a total of 12 experimental carboys, which were placed transversely in the middle of the reservoir. RESULTS: In general, pigmented and heterotrophic nanoflagellates fractions responded to nutrient addition, increasing densities and biomass values at the fertilized treatments. Opposed to expected, enriched treatments resulted in a slight decrease in mean cell size of the pigmented fraction. Moreover, in nutrient-rich treatments, pigmented nanoflagellates had higher relative abundance than in the control. CONCLUSIONS: Our results indicate that: i) the density and biomass of nanoflagellates responded to the nutrient enrichment, mainly when N and P were added together; ii) the pigmented and heterotrophic fractions showed distinct time responses to fertilization; iii) the growth of nanoflagellate community seems to be co-limited by N and P; iv) the nutrient enrichment led to a greater pigmented than heterotrophic fraction contribution; and v) among the analyzed variables, nanoflagellate densities seem to be more sensitive to changes in nutrient availability than biomass or mean cell size.

Differential freshwater flagellate community response to bacterial food quality with a focus on Limnohabitans bacteria

Different bacterial strains can have different value as food for heterotrophic nanoflagellates (HNF), thus modulating HNF growth and community composition. We examined the influence of prey food quality using four Limnohabitans strains, one Polynucleobacter strain and one freshwater actinobacterial strain on growth (growth rate, length of lag phase and growth efficiency) and community composition of a natural HNF community from a freshwater reservoir. Pyrosequencing of eukaryotic small subunit rRNA amplicons was used to assess time-course changes in HNF community composition. All four Limnohabitans strains and the Polynucleobacter strain yielded significant HNF community growth while the actinobacterial strain did not although it was detected in HNF food vacuoles. Notably, even within the Limnohabitans strains we found significant prey-related differences in HNF growth parameters, which could not be related only to size of the bacterial prey. Sequence data characterizing the HNF communities showed also that different bacterial prey items induced highly significant differences in community composition of flagellates. Generally, Stramenopiles dominated the communities and phylotypes closely related to Pedospumella (Chrysophyceae) were most abundant bacterivorous flagellates rapidly reacting to addition of the bacterial prey of high food quality.

Maximum in the Middle: Nonlinear Response of Microbial Plankton to Ultraviolet Radiation and Phosphorus

The responses of heterotrophic microbial food webs (HMFW) to the joint action of abiotic stressors related to global change have been studied in an oligotrophic high-mountain lake. A 2×5 factorial design field experiment performed with large mesocosms for >2 months was used to quantify the dynamics of the entire HMFW (bacteria, heterotrophic nanoflagellates, ciliates, and viruses) after an experimental P-enrichment gradient which approximated or surpassed current atmospheric P pulses in the presence vs. absence of ultraviolet radiation. HMFW underwent a mid-term (<20 days) acute development following a noticeable unimodal response to P enrichment, which peaked at intermediate P-enrichment levels and, unexpectedly, was more accentuated under ultraviolet radiation. However, after depletion of dissolved inorganic P, the HMFW collapsed and was outcompeted by a low-diversity autotrophic compartment, which constrained the development of HMFW and caused a significant loss of functional biodiversity. The dynamics and relationships among variables, and the response patterns found, suggest the importance of biotic interactions (predation/parasitism and competition) in restricting HMFW development, in contrast to the role of abiotic factors as main drivers of autotrophic compartment. The response of HMFW may contribute to ecosystem resilience by favoring the maintenance of the peculiar paths of energy and nutrient-mobilization in these pristine ecosystems, which are vulnerable to threats by the joint action of abiotic stressors related to global change.

Heterotrophic microorganisms and viruses in the water of the Gorky reservoir during a period of anomalously high water temperature

During the anomalously hot summer of 2010, the water temperature in the Gorky reservoir reached 27–33°C. Pronounced cyanobacterial blooms occurred in the limnetic part of the reservoir. The average values for bacterioplankton abundance (11.58 ± 1.25 × 106 cell/mL), biomass (886 ± 96 mg/m3), and production [169 ± 32 mg C/(m3 day)] were twice as high as in the year with temperatures comparable to long-term average values. These parameters were higher in the limnetic part than in the river one. The abundance (4.86 ± 0.75 × 103 cell/mL) and biomass (138 ± 9 mg/m3) of heterotrophic nanoflagellates were 2.3 and 1.7 times higher, respectively, than in years with regular temperature regimes. The average number of plank-tonic viral particles (Nv) in 2010 was 48.89 ± 9.54 × 106 particles/mL, while virus-induced bacterial mortality (VMB) accounted for 26.9 ± 4.6% of the bacterial production. The Nv and VMB values in the limnetic part of the reservoir were, respectively, 1.5 and 1.8 times higher than in the river one.

Responses of microbial food web to increased allochthonous DOM in an oligotrophic subarctic lake

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 68:171-184 (2013) - DOI: https://doi.org/10.3354/ame01614 Responses of microbial food web to increased allochthonous DOM in an oligotrophic subarctic lake Laura Forsström1,3,*, Toni Roiha1,2, Milla Rautio1,2 1Department of Biological and Environmental Science, 40014 University of Jyväskylä, Finland 2Département des sciences fondamentales and Centre for Northern Studies (CEN), Université du Québec à Chicoutimi, Québec G7H 2B1, Canada 3Present address: Department of Environmental Sciences, 00014 University of Helsinki, Finland *Email: laura.forsstrom@helsinki.fi ABSTRACT: Climate-induced changes in catchment area vegetation and runoff alter the quality and quantity of carbon that enters lakes, with implications for food webs in recipient water bodies. The effect of dissolved organic matter (DOM) on the ratio between heterotrophic and autotrophic biomass and productivity was studied in a subarctic, clear water lake in northern Finland. In a mesocosm experiment, natural DOM from a subarctic bog and a boreal lake was added to the lake water, doubling the initial dissolved organic carbon (DOC) concentration. Optical indices suggested that the subarctic DOM addition was more bioavailable, which was in line with the greater increase in bacterial biomass and production observed in this treatment. Both DOM additions increased the abundance of heterotrophic nanoflagellates (HNF) and decreased primary productivity. They also led to lower ratios of primary to bacterial production, autotrophic to mixotrophic algae and pigmented nanoflagellates (PNF) to HNF relative to the control samples, indicating a shift from a primary production-based food web towards one based on bacterial production. A comparable increase in DOM in the natural environment would lead to a considerable decrease in the euphotic layer and loss of areas available for primary production, resulting in a shift towards a heterotrophic production based food web. KEY WORDS: Dissolved organic matter · Dissolved organic carbon · Subarctic · Microbial food web Full text in pdf format PreviousCite this article as: Forsström L, Roiha T, Rautio M (2013) Responses of microbial food web to increased allochthonous DOM in an oligotrophic subarctic lake. Aquat Microb Ecol 68:171-184. https://doi.org/10.3354/ame01614 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 68, No. 2. Online publication date: March 01, 2013 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2013 Inter-Research.

Grazing resistant freshwater bacteria profit from chitin and cell‐wall‐derived organic carbon

The rise of grazing resistant planktonic bacteria in freshwater lakes during vernal phytoplankton blooms is favoured by predation of heterotrophic nanoflagellates (HNF). The spring period is also characterized by increased availability of organic carbon species that are in parts derived from cellular debris generated during bacterivory or viral lysis, such as peptidoglycan, chitin and their subunit N-acetylglucosamine (NAG). We tested the hypothesis that two dominant grazing resistant bacterial taxa, the ac1 tribe of Actinobacteria (ac1) and filamentous bacteria from the LD2 lineage (Saprospiraceae), profit from such carbon sources during periods of intense HNF predation. The abundances of ac1 and LD2 rose in parallel with HNF, and disproportionally high fractions of cells from both lineages were involved in NAG uptake. Members of ac1 and LD2 were significantly more enriched after NAG addition to lake water. However, highest growth rates of both bacterial lineages were found on chitin and peptidoglycan. Moreover, the direct or indirect transfer of organic carbon from peptidoglycan to LD2 filaments could be demonstrated. We thus provide evidence that these taxa may benefit twofold from protistan predation: by removal of their competitors, and by specific physiological adaptations to utilize carbon sources that are released during grazing or viral lysis.

Effects of Chemically Enhanced Water-Accommodated Fraction of Iranian Heavy Crude Oil on Periphytic Microbial Communities in Microcosm Experiment

Exposure experiments were conducted to determine the effects of an oil spill on a periphytic microbial community with the chemically enhanced water-accommodated fraction (CEWAF) of Iranian Heavy Crude oil in a microcosm containing artificial benthic substrates. Bacteria and heterotrophic nano-flagellates (HNF) grew well in all the treatments, except for the 100% CEWAF exposure. However, periphyton did not adapt to concentrations of CEWAF ≥ 20%. Among the periphyton, Cylindrotheca spp. dominated under treatment conditions, and the response of Cylindrotheca spp. to CEWAF (i.e., particularly 10%) closely followed the changes in chlorophyll a concentration. The concentrations of petroleum hydrocarbons from 10% and 20% CEWAF seemed to have a negative effect on periphyton and a growth-promoting effect on bacteria and HNF, respectively.

Micro-grazer biomass, composition and distribution across prey resource and dissolved oxygen gradients in the far eastern tropical north Pacific Ocean

The ecology of micro-grazers (Mg) was investigated across prey and dissolved oxygen (DO) gradients in the eastern tropical north Pacific Ocean (ETNP) during October–November 2007. Surface (<200m) chlorophyll a (Chl a) across a ∼1700km north–south transect ranged between the seasonal average of 0.2μgChlaL−1 to 1.8μgChlaL−1 in an extensive Chl a-rich patch in the center of the transect. Limiting (<20μmolkg−1 O2) DO concentrations were encountered as shallow as 24m. Biomass of Mg in waters above the upper oxycline (UO) ranged between 5.6μgCL−1 and 36.6μgCL−1, with highest Mg biomass observed in locations with highest Chl a. Heterotrophic dinoflagellates contributed most, on average, to Mg biomass (41% to 53%), followed by aloricate spirotrich ciliates (24% to 29%) and heterotrophic nanoflagellates (11% to 33%). Biomass of Mg decreased, on average, over 96% in waters below the UO, but this decrease did not appear to be regulated by DO; Mg biomass more strongly correlated with Chl a (r=0.83, P<0.001) and temperature (r=0.76, P<0.001) at discrete depths than with DO (r=0.67, P<0.001). Using a multiple stepwise regression model, Chl a alone accounted for 68% Mg biomass variability, whereas Chl a and temperature combined accounted for 84%. In two Mg grazing experiments we found that Mg removed 33% and 108% of surface primary production in the upper mixed layer. These estimates of Mg grazing, while limited in scope, fall within estimates from other regions of the equatorial Pacific Ocean, and help reinforce the paradigm that Mg are influential in regulating organic carbon dynamics in the eastern tropical Pacific. A primary finding from this study was that observations of Mg biomass are higher than previously reported for the ETNP. This observation suggests that the region’s complex air–sea interactions and the resultant positive influence on primary production and phytoplankton biomass can episodically support high biomass of a diverse Mg community.

Abundance and trophodynamics of surface microbial loop populations in the northern Red Sea

The population densities of filter feeding ciliates in the water of the three marine protectorates of Ras Mohammed, Nabq and Abu Galoum in the northern Red Sea, were calculated during the period from November 2006 to November 2007. Also, autotrophic nanoflagellates, heterotrophic nanoflagellates and heterotrophic bacteria were enumerated to gain some indication of the food resources available for ciliates. The abundance of ciliates in the three protectorates were found to follow an annual cycle with the highest ciliate numbers of 25.3 cells ml−1 observed in the spring, and the lowest numbers of 2.1 cells ml−1 in the summer. Abundances were at times 8-fold higher than those found in comparable studies on nutrient-poor pelagic systems and, astonishingly, approached those observed in coastal waters and in more productive open ocean systems. Nanoflagellates that could provide a food supply for the filter feeding ciliates were especially numerous in the spring, while the production of bacteria was presumably a more important component at the base of this food chain in the three protectorates’ water. The filtration activities of heterotrophic flagellates and filter feeding ciliates were compared with the population densities of bacteria, nanoflagellates and ciliates in spring and summer. Moreover, filtration rates from the literature were used to calculate the potential rate of capture of prey of different categories, as well as to calculate the time required for the whole water body to be filtered by heterotrophic nanoflagellates and filter feeding ciliates.

C-Biomass of Bacteria, Fungi, and Protozoan Communities in Arctic Tundra Soil, Including Some Trophic Relationships

The ecology of tundra terrestrial environments has gained increasing attention due to potential major changes resulting from global warming and climate change. However, the composition of terrestrial microbial communities and their role in the biogeochemical carbon cycle are less well studied. This is the first report of the C-biomass of bacteria, fungi, and representative protozoa (heterotrophic nanoflagellates, naked amoebae, and testate amoebae) in Alaskan tundra soil samples, and the effects of glucose solution enrichment in laboratory studies simulating release of soluble organic compounds as may occur during permafrost melt and increased plant root exudates due to global warming. The data for three moss-rich surface samples, two in spring and one in summer (2011), are reported for C-supplemented (8,000 μg glucose-C) and non-supplemented treatments in laboratory culture. Seven days after supplementation, fungal C-biomass in the glucose-treated and untreated samples were similar in the range of 5 to 11 mg g–1 soil dry weight, the highest values in the summer samples. The bacterial C-biomass was the next highest in the range of 20 to 120 μg g–1 soil dry weight, followed by heterotrophic nanoflagellates (2 to 14 μg g–1 soil dry weight). The naked amoebae (0.13 to 0.94 μg C g–1 soil dry weight) and testate amoebae (2 to 20 ng C g–1 soil dry weight) contributed the least C-biomass. All of the bacterial and protozoan treatments showed increased biomass with glucose supplementation. Based on size, and C-biomass estimates, the phagotrophic protozoa appear to be organized in a classical bacterial-based trophic hierarchy (i.e. bacteria – nanoflagellates – naked amoebae – testate amoebae, in ascending order). Correlations of the C-biomass of bacteria to each of the protozoa, provided further evidence of a trophic pyramid; bacteria vs. nanoflagellates (r = –0.986), indicating top-down control by predatory flagellates, bacteria vs. naked amoebae (r = –0.361) and bacteria vs. testate amoebae (r = –0.131), each of decreasing magnitude as would be predicted for higher level consumers. Estimates of bacterial predation indicated strong predatory pressures on bacteria by the protozoa, greater with C-supplementation compared to the non-supplemented treatments.

Feeding and Growth Characteristics of a Diatom-Feeding Flagellate Isolated from the Bottom Sediment of Onagawa Bay, Northeastern Japan

In recent years, several marine heterotrophic nanoflagellates have been reported to feed on diatoms much larger than themselves. However, very little is known about the grazer-prey relationships between heterotrophic nanoflagellates and diatoms in aquatic ecosystems. A diatom-feeding flagellate was discovered in the bottom sediment of OnagawaBay. It fed and proliferated on diatoms, especially Skeletonema costatum sensu lato. This study determined growth and ingestion rates of the flagellate on Skeletonema costatum s.l. under laboratory conditons. Its grazing pressure on the sinking flux of S. costatum s.l. was calculated by combining field data. Specific growth rate of the flagellate increased with increasing prey concentration. The maximum specific growth rate was 0.79 d–1 and maximum ingestion rate of the flagellate was 0.66 ng·C·grazer–1·d–1. Calculated grazing pressure of the flagellate on S. costatum s.l. flux was up to 25.6%. The results imply that the flagellate has a considerable grazing impact on S. costatum s.l. flux at least in a restricted season of the year. Therefore, the present study suggests that this benthic flagellate plays an important role in pelagic-benthic coupling inOnagawaBay.

Are Small Grazers and/or Viruses a Structuring Factor of the Free-Living Bacterial Community in Lake Geneva?

Two experiments were conducted to test whether viruses, small auto- and heterotrophic nanoflagellates were key factors regulating at relatively short-term (4 days) and nearby periods (April vs. May) the bacterial community in surface waters of Lake Geneva. 2.5 L containing polycarbonate bottles were incubated in situ with either μm filtered water with additions of either virus-free water or a viral concentrate. Abundances of viruses, prokaryotes and small autotrophs were obtained each day using flow cytometry, while bacterial richness was assessed using 16S rDNA PCR-DGGE and auto- and heterotrophic flagellates counted with epifluorescence microscopy at t0 and t96. Transmission electron microscopy was also used to assess virus-induced bacterial mortality at the start and the end of the experiments. Cloning-sequencing was applied on PCR products obtained after excision of selected DGGE bands to highlight more specifically the identity of bacteria of interest in the context of the experiment. The autotrophs and grazer presence and/or the virus enrichment resulted in different effects on the structure of the bacterial community and the impact was also different with the period. In May, bacterial structure changes seemed to be related to the impact or influence of the eukaryotes (including nanoflagellate grazers), while viruses might have a higher impact on the bacterial community structure the month before. This study provides new persuasive evidence that the presence of viruses and small eukaryotes are likely to drive bacterial community composition and shifts on the short-term in lacustrine ecosystems. More interestingly, such effects seem to be different between viruses and grazers, the ones sustaining, the others reducing bacterial community composition.

Factors controlling bacteria and protists in selected Mazurian eutrophic lakes (North-Eastern Poland) during spring

BackgroundThe bottom-up (food resources) and top-down (grazing pressure) controls, with other environmental parameters (water temperature, pH) are the main factors regulating the abundance and structure of microbial communities in aquatic ecosystems. It is still not definitively decided which of the two control mechanisms is more important. The significance of bottom-up versus top-down controls may alter with lake productivity and season. In oligo- and/or mesotrophic environments, the bottom-up control is mostly important in regulating bacterial abundances, while in eutrophic systems, the top-down control may be more significant.ResultsThe abundance of bacteria, heterotrophic (HNF) and autotrophic (ANF) nanoflagellates and ciliates, as well as bacterial production (BP) and metabolically active cells of bacteria (CTC, NuCC, EST) were studied in eutrophic lakes (Mazurian Lake District, Poland) during spring. The studied lakes were characterized by high nanoflagellate (mean 17.36 ± 8.57 × 103 cells ml-1) and ciliate abundances (mean 59.9 ± 22.4 ind. ml-1) that were higher in the euphotic zone than in the bottom waters, with relatively low bacterial densities (4.76 ± 2.08 × 106 cells ml-1) that were lower in the euphotic zone compared to the profundal zone. Oligotrichida (Rimostrombidium spp.), Prostomatida (Urotricha spp.) and Scuticociliatida (Histiobalantium bodamicum) dominated in the euphotic zone, whereas oligotrichs Tintinnidium sp. and prostomatids Urotricha spp. were most numerous in the bottom waters. Among the staining methods used to examine bacterial cellular metabolic activity, the lowest percentage of active cells was recorded with the CTC (1.5–15.4%) and EST (2.7–14.2%) assay in contrast to the NuCC (28.8–97.3%) method.ConclusionsIn the euphotic zone, the bottom-up factors (TP and DOC concentrations) played a more important role than top-down control (grazing by protists) in regulating bacterial numbers and activity. None of the single analyzed factors controlled bacterial abundance in the bottom waters. The results of this study suggest that both control mechanisms, bottom-up and top-down, simultaneously regulated bacterial community and their activity in the profundal zone of the studied lakes during spring. In both lake water layers, food availability (algae, nanoflagellates) was probably the major factor determining ciliate abundance and their composition. In the bottom waters, both groups of protists appeared to be also influenced by oxygen, temperature, and total phosphorus.

How fast can plankton feed? Maximum ingestion rate scales with digestive surface area

Allometric scaling rules have been classically used in plankton ecology to describe how the maximum ingestion rate (Imax) under steady-state conditions changes with the body size of the consumer. Empirical and theoretical concerns, however, motivate a more accurate and mechanistic description of size–ingestion relations. Here, I propose to relate Imax to the digestive surface area, which expresses the capacity in preprocessing and digesting food items. This surface area depends on both the body size and the optimal prey size of the consumer. The allometry in Imax, hence, includes a second major variable which describes different feeding modes within a consumer size class. Species with a small optimal-prey-to-predator-size ratio and, thus, a small “internal” surface-to-volume ratio, as is typical for filter feeders, have large intra-body transport lengths and lower Imax than raptorial-feeding species of the same body size. Digestive surface scaling tries to mechanistically accommodate feeding ecology, physiology and geometry. It does not explicitly resolve further possible factors affecting maximal ingestion such as nutritional quality. Still, digestive surface scaling explains the variability in published data compilations better than classical approaches when applied to the entire plankton size range. This is corroborated in further applications where the theory precisely fits anomalously steep scaling relations reported for heterotrophic nanoflagellates, ctenophores and a scyphomedusa. By introducing feeding mode and related morphological diversity into the size-dependency in ingestion rates, digestive surface scaling can be expected to improve the accuracy of size-based plankton models.

Dynamics of prokaryotic picoplankton community in the central and southern Adriatic Sea (Croatia)

This paper addresses the dynamics of the prokaryotic picoplankton community in the coastal and open sea areas of the central Adriatic and in the coastal area of the southern Adriatic. This involved the study, from January to December 2005, of bacteria (total number of non-pigmented bacteria; high nucleic acid content (HNA) bacteria; low nucleic acid content (LNA) bacteria), cyanobacteria (Synechococcus and Prochlorococcus) and heterotrophic nanoflagellates. During the warmer seasons, in the mainly oligotrophic area under investigation into the Adriatic Sea, bacterial densities and bacterial production have shown an increase in values and domination of the LNA group of the bacterial population. In contrast, in those areas influenced by karstic rivers, the domination of HNA bacteria in total abundance of non-pigmented bacteria and high values of bacterial production was estimated throughout the investigated period. Our results show the importance of both HNA and LNA bacterial groups in the total bacterial activity throughout the investigated area. The biomass of bacteria was mostly predominant in the prokaryotic community, while within the autotrophic community Synechococcus biomass mostly predominated. During the warmer seasons, an increase in autotrophic biomass was observed in relation to non-pigmented biomass. The importance of predation in controlling bacteria by heterotrophic nanoflagellates was pronounced during the warmer period and in the coastal areas.

Long‐term effects of warming and nutrients on microbes and other plankton in mesocosms

Summary1. We followed microbial and other planktonic communities during a 4‐month period (February–May) in 12 outdoor flow‐through mesocosms designed to elucidate the effect of global warming and nutrient enrichment. The mesocosms were established in 2003.2. Warming had a smaller effect than nutrients on the biomass of the microbial and planktonic communities, and warming and nutrients together exhibited complex interactions.3. We did not find direct effects of warming on the biomass of bacterioplankton or ciliates; however, warming significantly added to the positive effect of nutrients on these organisms and on heterotrophic nanoflagellates (HNF). No warming effects on any of the other planktonic groups analysed were detected.4. The zooplankton: phytoplankton biomass ratio was lowest, and the HNF: bacteria and rotifer: bacteria biomass ratios highest in the heated, nutrient‐rich mesocosms. We attribute this to higher fish predation on large‐bodied zooplankton, releasing the predation on HNF and competition for rotifers.5. The proportion of phytoplankton to the total plankton biomass increased with nutrients, but decreased with warming. The opposite pattern was observed for the proportion of phytoplankton to the total microbial biomass.6. As climate warming may lead to eutrophication, major changes may occur in the pelagic food web and the microbial community due to changes in trophic state and in combination with warming.

Species‐dependent effects of crustacean plankton on a microbial community, assessed using an enclosure experiment in Lake Taihu, China

A mesocosm experiment was performed to evaluate the species‐dependent effects of crustacean plankton on the microbial community in Lake Taihu, a large shallow eutrophic lake in China. Four dominant species of crustacean plankton (Daphnia galeata, Bosmina longirostris, Neodiaptomus schmackeri, and Mesocyclops dissimilis) in Lake Taihu were selected as predators. Denaturing gradient gel electrophoresis and cloning and sequencing of polymerase chain reaction–amplified ribosomal ribonucleic acid gene fragments were applied to analyze the microbial eukaryotic community composition (MECC) and bacterial community composition (BCC). The changes in the abundance of bacteria, heterotrophic nanoflagellates, ciliates, and phytoplankton were also measured. Crustacean plankton had a significant effect on phytoplankton biomass, the abundance of ciliates and bacteria, and the percentage of filamentous bacteria among total bacteria. Nonmetric multidimensional scaling analysis showed that the MECC and BCC in the treatments involving the same species were generally more similar to each other than to those in treatments with other species on both days 7 and 15. The MECC were clustered into two distinct groups between the cladoceran and copepod treatments on days 7 and 15. A phylogenetic analysis revealed that alveolates, chlorophytes, and fungi were the most important groups in the microbial eukaryotic clone libraries. Crustacean plankton had a significant species‐dependent effect on the microbial eukaryotic community and might have both trophic and nontrophic effects on the bacterial community.

Temperature effects on the heterotrophic bacteria, heterotrophic nanoflagellates, and microbial top predators of the NW Mediterranean

Prokaryotes and protists are important players in the carbon biogeochemistry of mar- ine ecosystems, and temperature is one of the physical factors most influential in the metabolism and composition of plankton communities. Small changes in temperature can change the flow of carbon and the community structure of planktonic ecosystems, and climatological models predict a rise in temperature of 2 to 5°C toward the end of the century in the NW Mediterranean. Labora- tory culture experiments have shown that warming can increase the transfer of carbon between bacteria and protists and alter the community composition of microbial top predators (i.e. ciliates and dinoflagellates) by increasing the abundance of bacterivores and producing the extinction of herbivores. Here, we tested whether a small rise in temperature would produce these effects in the coastal Mediterranean. Between March 2003 and February 2004, we established 12 micro- cosm experiments with water from the Bay of Blanes. The samples were incubated for 48 h at ambient and warmer temperatures (~2.7°C higher than in situ values), and the net and gross growth rates of bacteria and heterotrophic nanoflagellates (HNF) were measured using unfiltered and 0.8 µm filtered treatments. Warming increased the rates of bacterial gross production and bacterial losses to grazing with a clear seasonality; the largest increments in the rates were observed during the cooler months of the year. Warming did not change the net growth rates of dinoflagellates. It decreased the net production of HNF and the net growth rates of ciliates but did not promote the extinction of herbivorous protists. Temperature changed the microbial food web function in NW Mediterranean waters, with small alterations in the community composition of microbial top predators.

Ross Sea deep-ocean and epipelagic microzooplankton during the summer-autumn transition period

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 67:123-137 (2012) - DOI: https://doi.org/10.3354/ame01588 Ross Sea deep-ocean and epipelagic microzooplankton during the summer-autumn transition period Karl A. Safi1,*, Karen V. Robinson2, Julie A. Hall3, Jill Schwarz3, Elizabeth W. Maas3 National Institute of Water and Atmospheric Research, 1PO Box 11-115, Hamilton, 2PO Box 8602, Christchurch, and 3Private Bag 14901, Wellington, New Zealand *Email: k.safi@niwa.co.nz ABSTRACT: Microzooplankton populations are key participants in the transfer, recycling and export of carbon in epipelagic waters, but little is known about their role, abundance and diversity at depth, especially in the Antarctic region. We surveyed microzooplankton populations and their potential prey in the Ross Sea area from 66° S to 77° S during the New Zealand IPY-CAML survey, 12 February to 11 March 2008. Samples were taken throughout the available water column at depths between ~5 and 3400 m, allowing us to compare deeper, largely unknown, mesopelagic and bathypelagic waters with the traditionally studied epipelagic zone. Microzooplankton diversity and abundance were highest in the high chlorophyll a, diatom-dominated waters of the epipelagic zone, but occasionally, peaks did occur in the upper mesopelagic before populations declined with depth. Ciliates and dinoflagellates declined more rapidly than heterotrophic nanoflagellates, which led to the latter dominating at depth. Ciliate populations in epipelagic waters were correlated with bacteria, picophytoplankton and chlorophyll a, but these potential prey did not correlate well with heterotrophic nanoflagellates in deeper or low-biomass waters. Despite their rapid decline with depth, due to the large volume of deeper waters, the total integrated microzooplankton biomass exceeded that found in the epipelagic zone. This indicates that the deeper waters of the Ross Sea, at this time, contained a significant pool of microzooplankton biomass. These deeper populations are likely to aid in the recycling and remineralisation of sinking phytoplankton biomass traditionally thought to be exported to the ocean floor. KEY WORDS: Microzooplankton · Protists · Mesopelagic · Bathypelagic · Epipelagic · Ross Sea Full text in pdf format PreviousNextCite this article as: Safi KA, Robinson KV, Hall JA, Schwarz J, Maas EW (2012) Ross Sea deep-ocean and epipelagic microzooplankton during the summer-autumn transition period. Aquat Microb Ecol 67:123-137. https://doi.org/10.3354/ame01588 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 67, No. 2. Online publication date: October 02, 2012 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2012 Inter-Research.