Benthic Microbial Food Web Research Articles

The Effects of Paroxetine on Benthic Microbial Food Web and Nitrogen Transformation in River Sediments.

Paroxetine is a common pharmaceutical to treat depression and has been found to pose threats to aquatic organisms. However, little is known about the effects of paroxetine on the nutrient cycle in aquatic environments. Therefore, DNA metabarcoding is used in this study to analyze the effects of paroxetine on multi-trophic microorganisms and nitrogen transformation in river sediments. Although paroxetine has no significant effect on the diversity of microbenthos, changes in benthic nitrogen-converting bacteria are consistent with the change in the various forms of nitrogen in the sediment, indicating that paroxetine affects the nitrogen conversion process by affecting nitrogen-converting bacteria. In addition, it is found that paroxetine has the ability to influence nitrogen transformation in an indirect way by affecting the trophic transfer efficiency of higher trophic levels (meiofauna and protozoa, protozoa and protozoa), subsequently affecting the growth of nitrogen-converting bacteria through a top-down mechanism (i.e., predation).The results show that paroxetine affects nitrogen transformation directly by affecting nitrogen-converting bacteria and indirectly through top-down effects, emphasizing that the assessment of paroxetine's ecological risks should consider species within different trophic levels.

Determining the effect of sertraline on nitrogen transformation through the microbial food web in sediments based on 15N-DNA-stable isotope probing

Antidepressants may influence the food web and alter the nitrogen cycle through top-down forces. However, the effect of antidepressants on the key nitrogen-using species in the benthic microbial food web remains unclear, particularly the resulting changes in the nitrogen transformation process within the microecosystems. Therefore, in this study, we employed DNA stable-isotope probing to detect nitrogen-converting organisms at various trophic levels and quantify the nitrogen transformation process for the first time. The input of sertraline greatly increased nitrogen-transforming microorganisms and promoted more species to participate in the nitrogen transformation process. 100 μg/L sertraline was observed to stimulate the predation of bacteria via protozoa and metazoan, increasing the total nitrogen flow flux through the microbial food web to 31.50%, 1.32 times that of the natural condition. The results confirm that at sertraline concentrations close to the lowest observable effect concentration in the meiobenthos (100 μg/L), key components in the microbial food web were largely interfered and exerted a long-term interference on the nutrient cycle in the river sediment ecosystem. These findings confirm that sertraline has negative effects on river ecosystems from the perspective of microbial food webs and open a new line of inquiry into assessing ecological risks of antidepressants.

Cascade dam impoundments restrain the trophic transfer efficiencies in benthic microbial food web

Determination of the effects of cascade dams on benthic microbial ecosystem is essential for dam regulation and ecological function protection. However, no comprehensive investigation has yet shown the ecosystem-level responses of microbiota to dam impoundments. This study conducted DNA metabarcoding and microbial food web analysis for multiple species and their interrelationships along a cascade dam-affected river. The composition, distribution and diversity of bacteria, protozoans and metazoans were obviously different between river and reservoirs, mainly controlled by hydrological (P < 0.01) and nutrient parameters (P < 0.05). Those three groups make up a co-occurrence network, with most edges direct from higher to lower trophic levels or vice versa and more than 50% keystones participate in the food web, indicating the significant role of predator-prey relationships. Based on the microbial food web analysis, the predator biomass, especially at higher trophic levels, decreased by about 10% from the riverine to the lacustrine system. The structural equation model illustrates that both bottom-up forces (environmental factors particularly velocity and nutrient concentrations) and top-down forces (higher trophic levels) critically control microbial food web patterns (P < 0.05). As a result of dam impoundments, the lower velocity in the reservoirs has direct negative effects on trophic transfer efficiencies that may be further magnified by nutrient accumulation, probably leading to an increase of eutrophication and posing a risk to water quality. The results suggest the potential ecological risk in the reservoirs and highlight the need to consider from the perspective of ecosystem during the operation of cascade dams.

Impact of Arenicola marina (Polychaeta) on the microbial assemblages and meiobenthos in a marine intertidal flat

The benthic microbial food web can be responsible for a large proportion of benthic carbon cycling yet there are few data on the trophic interactions between this food web and macrobenthos. A large-scale field experiment was conducted to investigate effects of eliminating the polychaete Arenicola marina on benthic microbes (prokaryotes, heterotrophic and autotrophic protists) and metazoan meiofauna in a marine intertidal flat of the North Sea, Germany. Over a period of 2 years, quantity and composition of micro- and meiobenthos from unmanipulated sites were compared to those from sites deplete of lugworms. These grazer treatments were cross-classified with different sediment characteristics (low- and mid-intertidal areas). Lugworm removal resulted in an initial increase in abundance of prokaryotes and nanoflagellates, which became less pronounced in the second year. Ciliates were not affected quantitatively, but in the absence of lugworms, diversity and the proportion of carnivorous forms increased. Meiobenthos (nematodes, ostracods and copepods) were affected only moderately. The observed changes are probably due to a combination of release from grazing/predation pressure, changes in the species composition of higher trophic levels (namely large polychaetes) and altered environmental conditions (such as depth of the oxygenated layer and sediment grain size). Spatial differences between sites of different tidal exposure/grain size appeared to be as large as temporal differences during the 2 years following the manipulation of the system. We conclude that in intertidal sediments, indirect effects due to habitat transformation are as important as direct biological interactions (grazing pressure and competition) for the dynamics of the benthic microbial food web.

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.

Tracing carbon and nitrogen incorporation and pathways in the microbial community of a photic subtidal sand

The pathways and fate of C and N in the microbial compartment of a coastal permeable sandy sediment in the photic zone were studied in a pulse-chase experiment. 13 C-bicarbonate and 15 N-nitrate were added to the water column on top of 5 sediment cores incubated in 4 transparent and 1 opaque laboratory chambers. After 9 h of labelling in the light and dark, stable isotope incorpora- tion by microphytobenthos (MPB) and bacteria was quantified over a period of 4 d through the analy- sis of phospholipid-derived fatty acids (PLFA) and hydrolysable amino acids (HAA). 13 C was fixed by MPB, and more than 50% was directed to the production of extracellular polymeric substance (EPS). MPB 15 N incorporation was similar in the dark and in the light. Bacterial activity appeared to have 2 effects that depended on sediment depth: at the sediment surface, there was a steady increase of label in the bacterial PLFA, suggesting metabolism of label-containing EPS; in the subsurface layers, uniform enrichment started immediately after the labelling procedure, indicating continuous incor- poration of inorganic C by chemoautotrophic bacteria (Cbac). This experiment demonstrates the efficient transfer of inorganic C and N to the benthic community through the activities of photo- and chemoautotrophic microorganisms, and the role of EPS as a carrier of energy to the benthic microbial food web.

Bacteriological study of the superficial sediments of Guanabara bay, RJ, Brazil

Thirty sediment samples were collected in Guanabara Bay in August, November and December 2005. The material was analyzed for organic matter, total and faecal coliforms, heterotrophic bacteria, bacterial respiratory activity, esterase activity and electron transport system activity. The organic matter in the superficial sediments (2 cm) ranged from 4 to 6%. The highest level of total coliforms and faecal coliforms were 1.7 x 10(5) MPN/g and 1.1 x 10³ MPN/g, respectively. Heterotrophic bacteria presented the highest values at station 7 (4.1 x 10(6) CFU/g) and the lowest values at station 3 (7 x 10(4) CFU/g) (northwestern part of Guanabara Bay). Esterase enzyme activity showed activity in the sediment of all 30 stations. Electron transport system activity ranged between 0.047 muL O2/h/g and 0.366 muL O2/h/g at six stations. The benthic microbial foodweb is anaerobic. Anaerobic processes such as fermentation, denitrification and sulphate-reduction are responsible for the biogeochemical cycles in the sediment of Guanabara Bay. The input of untreated sewage in the Mangue Channel outflow in Guanabara Bay has favored the increase of the organic load, and the maintenance of the total coliforms and faecal coliforms in the sediment. Faecal coliforms have been reported to be a good indicator of aquatic pollution and organic contamination in the water column, but total coliforms may be an ideal candidate group for sediment quality tests as well.

Benthic microbial abundance and activities in an intensively trawled ecosystem (Thermaikos Gulf, Aegean Sea)

Abundance of benthic bacteria, heterotrophic nanoflagellates and ciliates, extracellular enzymatic activities, bacterial C production, C mineralisation and sediment community oxygen consumption rates were measured in the Thermaikos Gulf (Northeastern Mediterranean), before (September 2001), and during intense trawling activities (October 2001 and February 2002). The biochemical composition of sedimentary organic matter has revealed that bottom trawling had an effect on the trophic state of Thermaikos Gulf. Changes on the benthic microbial food web were also recorded, during the three sampling seasons. Even though trawling-induced sediment resuspension did not alter significantly the abundance of the microbial components, with the exception of the most impacted station, it determined changes regarding their relative importance. Thus, the ratios of bacterium to nanoflagellates and ciliate to nanoflagellates abundance increased in the trawled stations, causing a sudden increase in bacterial C production, in comparison to the non-trawled station. Four months later, the effects of trawling on the microbial food web were less evident, masked possibly by the drastic decrease in the water temperature. The results of the present work suggest that bottom trawling induces alteration of the sedimentological variables and can be considered as a factor affecting the function of the microbial food web in marine coastal ecosystems. These alterations cause faster mobilisation of organic C buried in the sediment and increase nutrient concentrations and availability in the system, thus inducing an effect that could lead to coastal eutrophication.

Benthic heterotrophic flagellates in an Antarctic melt water stream

Investigations on the abundance, biomass and position of heterotrophic flagellates (HF) in the benthic microbial food web of a melt water stream on King George Island, Antarctic Peninsula, were undertaken during the Antarctic summer from 23rd December 1997 until 13th March 1998. Abundance and biomass of potential HF resources (picophotoautotrophic and non-photoautotrophic bacteria) as well as potential predators on HF (ciliates and meiofauna) were also investigated. HF abundance ranged from approximately 9 × 103 to 81 × 103 cells cm−3, values which fall into the same range as those found in lower latitudes. Numerically important benthic HF were euglenids, kinetoplastids, thaumatomastigids and especially chrysomonads. Most species identified have been shown to have a worldwide distribution. Abundance of the benthic ciliates ranged from 27 to 950 cells cm−3. Mean bacterial abundance was 1.9 × 107 and 5.2 × 108 cells cm−3 for picophotoautotrophic and non-photoautotrophic benthos, respectively. The well-developed microbial community was able to support the large number of nematods, gastotrichs, tardigrads and rotifers with abundances reaching more than 1000 individuals cm−3. The largest portion of heterotrophic biomass was formed by the meiofauna with a mean of 63 μg C cm−3, followed by that of the heterotrophic bacteria with 4.80 μg C cm−3. Picophotoautotrophic bacteria contributed a mean of 1.37 μg C cm−3. HF and ciliates mean biomass was 0.61 and 1.99 μg C cm−3, respectively, with the HF biomass comprising between <10 and 70% of the total protozoan biomass. The data obtained in this study identify the melt water stream as a hot-spot of heterotrophic microbial and meiofaunal activity during the austral summer. The HF in the melt water stream formed a diverse group in terms of taxa and potential feeding types. Chrysomonads, kinetoplastids, euglenids and thaumatomastigida were the most abundant taxa. A classification into feeding types identified an average of 34% of the total HF as bacterivorous while all others were able to utilise other, larger organisms as resources. Potential trophic interactions between HF and bacteria and higher trophic levels are discussed.

Benthic recruitment of zooplankton in an acidic lake

In recent years, most studies of the benthic microbial food web have either been descriptive or were restricted to the measurement of within sediment process rates. Little is known about benthic–pelagic coupling processes such as recruitment. We, therefore, developed an ex situ core incubation procedure to quantify the potential for microbial recruitment from the benthos to the pelagic in an acidic mining lake, Mining Lake 111 (ML 111; pH 2.6), in eastern Germany. Our data suggest that considerable zooplankton recruitment from the benthos takes place. Heliozoan and rhizopod recruitment in both summer and winter sediment cores was highest when they were incubated at 20 °C. Maximum heliozoan recruitment was 23 (±9 S.E.) individuals cm −2 day −1 (40% initial standing stock daily) in the winter 20 °C incubation. Maximum rhizopod recruitment was 6 (±2 S.E.) individuals cm −2 day −1 in the summer 20 °C incubation. Little or no recruitment was apparent for either taxa when winter cores were incubated at 5 °C, implying a temperature cue. Conversely, the rotifer, Cephalodella hoodi, exhibited a maximum recruitment of 6 (±2 S.E.) individuals cm −2 day −1 during the winter 5 °C incubation, representing 30% of initial standing stock daily, but little recruitment when incubated at 20 °C. Cephalodella may have responded to an increased winter benthic food supply; in situ winter Chl a concentrations in the benthos were 3.4 times higher than those in the summer. The importance of this was reinforced by the poor pelagic food supply available in ML 111. In situ, Heliozoa, rhizopods and Cephalodella were first observed in the epilimnion of ML 111 in spring or early summer, suggesting active or passive recruitment following lateral transport from littoral sediments. Benthic–pelagic coupling via recruitment is potentially important in understanding the pelagic food web in ML 111 and warrants further investigation in this and other aquatic environments.

Effects of resuspension and mixing on population dynamics and trophic interactions in a model benthic microbial food web

The effects of resuspension and mixing on the population dynamics and trophic inter- actions in a simple benthic microbial food web were studied during 3 plankton wheel experiments of 9 to 15 d duration. The food web consisted of a mixed bacterial assemblage, the heterotrophic flagel- late Bodo designis, the ciliate Euplotes balteatus and the rhizopod Vannella platypodia. The diatom Amphora coffeaeformis was included to maintain oxygen concentrations. B. designis, E. balteatus, V. platypodia and A. coffeaeformis are hereafter referred to by genus name alone. Population dynamics in 500 ml microcosms on rotating and non-rotating plankton wheels were compared. Final abun- dances of Amphora increased in suspension in all experiments. Resuspension increased initial growth rates and final abundances of Euplotes and Vannella during a whole-community experiment and a community subset experiment during which resuspension effects with and without the top predator Euplotes were compared. During the community subset experiment, suspended Bodo grew faster and reached higher final abundances than non-resuspended Bodo when Euplotes was absent, but experienced higher loss to Euplotes when the ciliate was present. Individual consumption rates of Bodo by Euplotes were estimated to be higher in suspension (5.5 vs 3.6 Bodo Euplotes -1 h -1 ), which could not be explained by higher abundance of Bodo alone. Similar but non-significant trends were found for bacteria. During a third experiment, Euplotes did not benefit from resuspension at low food concentrations. Our results show that resuspension and mixing can enhance population growth of autotrophic and heterotrophic protists, and that the trophic coupling between flagellates and ciliates, and possibly between other microbial food web components, can become closer in suspension when the food supply is sufficient. This suggests that subsidiary energy input by resuspension and mixing may increase the biomass turnover in benthic microbial food webs.

Seasonal abundances and community structure of benthic rhizopods in shallow lagoons of the southern Baltic Sea

Summary In order to assess the quantitative importance and community structure of benthic rhizopods in brackish lagoons of the southern Baltic Sea, their abundance, biovolume, and taxonomic composition were studied by using a liquid cultivation method. Seasonal dynamics in the superficial sediment of station Bak (Hiddensee Island) were investigated during eleven sampling campaigns between March and November 1996. Additional samples from three sediment layers were taken at two other stations. Rhizopod abundances at station Bak ranged from 2,800-10,900 cells cm-3. A seasonal trend with a summer maximum and minima in early spring and late autumn was observed. 46 morphotypes of rhizopods were found, 27 of which were identified to species. Gymnamoebia and Schizopyrenida always dominated the rhizopod community numerically, whereas testate and naked filose rhizopods sometimes contributed the major part to community biovolume. Typical marine and freshwater rhizopods coexisted in the study area. In addition to bacterivorous forms, high contributions of herbivores and omnivores were found. Our results suggest that the hitherto little-studied rhizopods are a major component of benthic protistan communities of shallow coastal waters. The high contributions of herbivorous and omnivorous forms to the rhizopod community indicate a complex trophic role of rhizopods within the benthic microbial food web.

Biomass partitioning of benthic microbes in a Baltic inlet: relationships between bacteria, algae, heterotrophic flagellates and ciliates

The structure of a benthic microbial food web and its seasonal changes were studied in the shallow brackish waters of the island of Hiddensee, northeastern Germany, at two sites in close proximity by monthly or bimonthly sampling from July 1995 to June 1996. Abundance and biomass of phototrophic and non-phototrophic bacteria, heterotrophic flagellates (HF) and ciliates as well as the biomass of microphytobenthos were determined in the upper 0.3 cm sediment layer. Abundance of organisms showed strong positive correlation with water temperature, with the exception of the bacteria. Non-phototrophic bacterial numbers ranged from 7 × 108 to 6.7 × 109 cells cm−3 and phototrophic bacterial abundance from 4 × 107 to 2.7 × 108. Heterotrophic protist abundance ranged from 8 × 103 to 104 × 103 ind cm−3 for HF and from 39 to 747 ind cm−3 for ciliates. The biomass partitioning demonstrated the primary importance of non-phototrophic bacteria (min. 0.83, max. 84.87 μg C cm−3), followed by the microphytobenthos (min. 1.32, max. 50.93 μg C cm−3). The heterotrophic protists contributed roughly the same fraction to the total microbial biomass, with the biomass of the HF being slightly higher (HF 0.23 to 1.76 μg C cm−3, ciliates 0.04 to 1.17 μg C cm−3). Taxonomic classification of the benthic HF revealed the euglenids to be the most important group in terms of abundance and biomass, followed by thaumatomastigids and kinetoplastids. Other important groups were apusomonads, cercomonads, pedinellids and cryptomonads. The structure of the HF assemblage showed strong seasonal changes with euglenids being the most abundant taxa in summer, while apusomonads and thaumatomastigids were predominant in winter. Similar to the pelagic microbial food web, benthic picophototrophic bacteria were occasionally abundant, and the feeding modes of heterotrophic protists exhibited a great variety (predominantly omnivores, bacterivores, herbivores or predators). Filter-feeding HF were of little importance. Contrary to the pelagic environment, a top-down control on total benthic bacterial numbers by HF seemed unlikely at the studied stations which were characterised by muddy sand.