DOCSLIB.ORG

Examination of the Role of the Microbial Loop in Regulating Lake Nutrient Stoichiometry and Phytoplankton Dynamics

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Examination of the Role of the Microbial Loop in Regulating Lake Nutrient Stoichiometry and Phytoplankton Dynamics Biogeosciences, 11, 2939–2960, 2014 www.biogeosciences.net/11/2939/2014/ doi:10.5194/bg-11-2939-2014 © Author(s) 2014. CC Attribution 3.0 License. Examination of the role of the microbial loop in regulating lake nutrient stoichiometry and phytoplankton dynamics Y. Li1,2,3, G. Gal4, V. Makler-Pick5,6, A. M. Waite7,*, L. C. Bruce1,7, and M. R. Hipsey1,7 1Aquatic Ecodynamics, School of Earth & Environment, The University of Western Australia, Crawley WA 6009, Australia 2Department of Ecology, Jinan University, Guangzhou 510632, China 3School of Environmental Science & Engineering, Ocean University of China, Qingdao 266100, China. 4Kinneret Limnological Laboratory, Israel Oceanographic and Limnological Research, Migdal 14950, Israel 5Faculty of Civil and Environmental Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel 6Oranim Academic College of Education, Kiryat Tivon 36006, Israel 7The Oceans Institute, The University of Western Australia, Crawley WA 6009, Australia *current address: Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Am Handelshafen 12, 27570 Bremerhaven, Germany Correspondence to: M. R. Hipsey ([email protected]) Received: 8 July 2013 – Published in Biogeosciences Discuss.: 16 December 2013 Revised: 3 May 2014 – Accepted: 6 May 2014 – Published: 5 June 2014 Abstract. The recycling of organic material through bacteria cally amplifying internal phosphorus limitation due to bacte- and microzooplankton to higher trophic levels, known as the rial competition for phosphate to satisfy their own stoichio- “microbial loop”, is an important process in aquatic ecosys- metric requirements. Importantly, each configuration led to tems. Here the significance of the microbial loop in influenc- a unique prediction of the overall community composition, ing nutrient supply to phytoplankton has been investigated and we conclude that the microbial loop plays an important in Lake Kinneret (Israel) using a coupled hydrodynamic– role in nutrient recycling by regulating not only the quan- ecosystem model. The model was designed to simulate the tity, but also the stoichiometry of available N and P that is dynamic cycling of carbon, nitrogen and phosphorus through available to primary producers. The results demonstrate how bacteria, phytoplankton and zooplankton functional groups, commonly employed simplifying assumptions about model with each pool having unique C : N : P dynamics. Three mi- structure can lead to large uncertainty in phytoplankton com- crobial loop sub-model configurations were used to isolate munity predictions and highlight the need for aquatic ecosys- mechanisms by which the microbial loop could influence tem models to carefully resolve the variable stoichiometry phytoplankton biomass, considering (i) the role of bacterial dynamics of microbial interactions. mineralisation, (ii) the effect of micrograzer excretion, and (iii) bacterial ability to compete for dissolved inorganic nu- trients. The nutrient flux pathways between the abiotic pools and biotic groups and the patterns of biomass and nutrient 1 Introduction limitation of the different phytoplankton groups were quan- tified for the different model configurations. Considerable One of the principal objectives for water quality manage- variation in phytoplankton biomass and dissolved organic ment of freshwater bodies is to reduce the magnitude and matter demonstrated the sensitivity of predictions to assump- frequency of nuisance algal blooms. Excess nutrients are tions about microbial loop operation and the specific mech- generally implicated in the production of nuisance blooms anisms by which phytoplankton growth was affected. Com- since they fuel primary production and organic matter ac- parison of the simulations identified that the microbial loop cumulation (Elser, 1999). In trying to understand these pro- most significantly altered phytoplankton growth by periodi- cesses much work in limnology is based on the classic “N-P-Z-D” (nutrients-phytoplankton-zooplankton-detritus) Published by Copernicus Publications on behalf of the European Geosciences Union. 2940 Y. Li et al.: Microbial loop effects on lake stoichiometry paradigm, which assumes a relatively simple flow of nutri- organisms and the fluxes between them are in reality neither ents to autotrophic and then heterotrophic pools. However, uniform nor static (Elser and Urabe, 1999; Sterner and Elser, it is now well-documented both in oceanographic and, to a 2002). Whilst representation of microbial loop processes has lesser extent, in limnological applications, that higher order been developed in marine ecosystem models (e.g. Faure et predators such as crustacean zooplankton or fish can be sup- al., 2010), their uptake in freshwater ecosystem models has ported by two paths: the so-called “green” (algal-based) and been limited and none to our knowledge simultaneously re- “brown” (detrital-based) food web components (Moore et al., solve the microbial loop and the dynamic stoichiometry of 2004). The latter refers to the dynamics of the heterotrophic carbon (C), nitrogen (N) and phosphorus (P). bacteria and the microzooplankton grazers (defined here as As a background to this study, there have been several size less than 125 µm that account for rotifers, ciliates and attempts to incorporate the microbial loop into Lake Kin- juvenile macrograzers; Thatcher et al., 1993) – often termed neret ecosystem models. Initially, a steady-state C flux model the “microbial loop”. This has been shown to play an im- was developed to examine C cycling through the plank- portant role in shaping carbon fluxes in lakes and in enhanc- tonic biota, including consideration of the microbial loop ing nutrient cycling at the base of food webs (Gaedke et al., (Stone et al., 1993; Hart et al., 2000). A one-dimensional 2002), including in Lake Kinneret which is the focus in this (1-D) coupled hydrodynamic–ecosystem model (DYRESM- study (Stone et al., 1993; Hart et al., 2000; Hambright et al., CAEDYM) was presented by Bruce et al. (2006), which fo- 2007; Berman et al., 2010). cused specifically on the zooplankton dynamics and their Less well understood is how the microbial loop affects contribution to nutrient recycling. However, the model pre- phytoplankton growth and thus potentially shape patterns of sented by Bruce et al. (2006) had a simplistic representation phytoplankton succession. There are several main mecha- of the microbial loop dynamics, like many contemporary lake nisms by which microbial loop processes are thought to in- ecosystem models, and also did not individually simulate two fluence phytoplankton dynamics: (i) the provision of bacteri- important cyanobacterial species, Microcystis sp. and Aph- ally mineralised nutrients for phytoplankton growth; (ii) the anizomenon sp., which are important to the health of the excretion of readily available nutrients by micrograzers that ecosystem and sensitive to stoichiometric constraints within support primary production (Johannes, 1965; Wang et al., the food web (Zohary, 2004). Gal et al. (2009) expanded this 2009); (iii) the competition of bacteria with phytoplankton model to include a dynamic microbial loop parameterisation for inorganic nutrients when organic detritus becomes nutri- and accounted for the two cyanobacterial species listed above ent depleted (Barsdate et al., 1974; Bratbak and Thingstad, and validated the model approach against a comprehensive 1985; Stone, 1990; Kirchman, 1994; Caron, 1994; Joint et al., data set. The relationship between phytoplankton stoichiom- 2002; Danger et al., 2007). Additionally, a potential fourth etry and patterns in the stoichiometry of available nutrients indirect mechanism is that bacteria provide an alternative was further analysed by Li et al. (2013), who noted that the food source for micrograzers, thus alleviating some grazing microbial loop parameterisation approach could adjust both pressure from small primary producers. The relative signif- the quantity and stoichiometry of nutrient transfers. icance of each of these mechanisms, and in particular how This research builds on these studies and applies the val- they interact in a dynamic environment to shape microbial idated model with the general aim of isolating the signifi- community composition and influence net productivity re- cance of the microbial loop on the phytoplankton patterns mains unclear. within the lake. Specifically, three different microbial loop Models of lake ecosystems are increasingly common to model structural configurations were designed and analysed support management and analysis of water quality prob- to unravel how the microbial loop processes identified above lems, acting as ‘virtual’ laboratories for exploring ecosystem combine to affect (a) the stoichiometry of nutrient trans- processes particularly for questions where empirical studies fers through the planktonic food web, and (b) phytoplank- would be difficult to undertake (Van Nes and Scheffer, 2005; ton growth and community composition. The results high- Mooij et al., 2010). In most models published to date it is light the importance of resolving the variable stoichiometry generally assumed that the biomass of heterotrophic bacteria of microbial interactions in aquatic models and suggest that is fairly stable and that the majority of bacterial production commonly used simplifying assumptions may compromise is lost to respiration (Cole, 1999). As a result, most quan- model function. titative models of carbon and nutrient fluxes in freshwater ecosystems essentially
Load more

Recommended publications
  • Response of Marine Food Webs to Climate-Induced Changes in Temperature and Inflow of Allochthonous Organic Matter
    Response of marine food webs to climate-induced changes in temperature and inflow of allochthonous organic matter Rickard Degerman Department of Ecology and Environmental Science 901 87 Umeå Umeå 2015 1 Copyright©Rickard Degerman ISBN: 978-91-7601-266-6 Front cover illustration by Mats Minnhagen Printed by: KBC Service Center, Umeå University Umeå, Sweden 2015 2 Tillägnad Maria, Emma och Isak 3 Table of Contents Abstract 5 List of papers 6 Introduction 7 Aquatic food webs – different pathways Food web efficiency – a measure of ecosystem function Top predators cause cascade effects on lower trophic levels The Baltic Sea – a semi-enclosed sea exposed to multiple stressors Varying food web structures Climate-induced changes in the marine ecosystem Food web responses to increased temperature Responses to inputs of allochthonous organic matter Objectives 14 Material and Methods 14 Paper I Paper II and III Paper IV Results and Discussion 18 Effect of temperature and nutrient availability on heterotrophic bacteria Influence of food web length and labile DOC on pelagic productivity and FWE Consequences of changes in inputs of ADOM and temperature for pelagic productivity and FWE Control of pelagic productivity, FWE and ecosystem trophic balance by colored DOC Conclusion and future perspectives 21 Author contributions 23 Acknowledgements 23 Thanks 24 References 25 4 Abstract Global records of temperature show a warming trend both in the atmosphere and in the oceans. Current climate change scenarios indicate that global temperature will continue to increase in the future. The effects will however be very different in different geographic regions. In northern Europe precipitation is projected to increase along with temperature.
    [Show full text]
  • Microbial Loop' in Stratified Systems
    MARINE ECOLOGY PROGRESS SERIES Vol. 59: 1-17, 1990 Published January 11 Mar. Ecol. Prog. Ser. 1 A steady-state analysis of the 'microbial loop' in stratified systems Arnold H. Taylor, Ian Joint Plymouth Marine Laboratory, Prospect Place, West Hoe, Plymouth PLl 3DH, United Kingdom ABSTRACT. Steady state solutions are presented for a simple model of the surface mixed layer, which contains the components of the 'microbial loop', namely phytoplankton, picophytoplankton, bacterio- plankton, microzooplankton, dissolved organic carbon, detritus, nitrate and ammonia. This system is assumed to be in equilibrium with the larger grazers present at any time, which are represented as an external mortality function. The model also allows for dissolved organic nitrogen consumption by bacteria, and self-grazing and mixotrophy of the microzooplankton. The model steady states are always stable. The solution shows a number of general properties; for example, biomass of each individual component depends only on total nitrogen concentration below the mixed layer, not whether the nitrogen is in the form of nitrate or ammonia. Standing stocks and production rates from the model are compared with summer observations from the Celtic Sea and Porcupine Sea Bight. The agreement is good and suggests that the system is often not far from equilibrium. A sensitivity analysis of the model is included. The effect of varying the mixing across the pycnocline is investigated; more intense mixing results in the large phytoplankton population increasing at the expense of picophytoplankton, micro- zooplankton and DOC. The change from phytoplankton to picophytoplankton dominance at low mixing occurs even though the same physiological parameters are used for both size fractions.
    [Show full text]
  • Developments in Aquatic Microbiology
    INTERNATL MICROBIOL (2000) 3: 203–211 203 © Springer-Verlag Ibérica 2000 REVIEW ARTICLE Samuel P. Meyers Developments in aquatic Department of Oceanography and Coastal Sciences, Louisiana State University, microbiology Baton Rouge, LA, USA Received 30 August 2000 Accepted 29 September 2000 Summary Major discoveries in marine microbiology over the past 4-5 decades have resulted in the recognition of bacteria as a major biomass component of marine food webs. Such discoveries include chemosynthetic activities in deep-ocean ecosystems, survival processes in oligotrophic waters, and the role of microorganisms in food webs coupled with symbiotic relationships and energy flow. Many discoveries can be attributed to innovative methodologies, including radioisotopes, immunofluores- cent-epifluorescent analysis, and flow cytometry. The latter has shown the key role of marine viruses in marine system energetics. Studies of the components of the “microbial loop” have shown the significance of various phagotrophic processes involved in grazing by microinvertebrates. Microbial activities and dissolved organic carbon are closely coupled with the dynamics of fluctuating water masses. New biotechnological approaches and the use of molecular biology techniques still provide new and relevant information on the role of microorganisms in oceanic and estuarine environments. International interdisciplinary studies have explored ecological aspects of marine microorganisms and their significance in biocomplexity. Studies on the Correspondence to: origins of both life and ecosystems now focus on microbiological processes in the Louisiana State University Station. marine environment. This paper describes earlier and recent discoveries in marine Post Office Box 19090-A. Baton Rouge, LA 70893. USA (aquatic) microbiology and the trends for future work, emphasizing improvements Tel.: +1-225-3885180 in methodology as major catalysts for the progress of this broadly-based field.
    [Show full text]
  • Controls and Structure of the Microbial Loop
    Controls and Structure of the Microbial Loop A symposium organized by the Microbial Oceanography summer course sponsored by the Agouron Foundation Saturday, July 1, 2006 Asia Room, East-West Center, University of Hawaii Symposium Speakers: Peter J. leB Williams (University of Bangor, Wales) David L. Kirchman (University of Delaware) Daniel J. Repeta (Woods Hole Oceanographic Institute) Grieg Steward (University of Hawaii) The oceans constitute the largest ecosystems on the planet, comprising more than 70% of the surface area and nearly 99% of the livable space on Earth. Life in the oceans is dominated by microbes; these small, singled-celled organisms constitute the base of the marine food web and catalyze the transformation of energy and matter in the sea. The microbial loop describes the dynamics of microbial food webs, with bacteria consuming non-living organic matter and converting this energy and matter into living biomass. Consumption of bacteria by predation recycles organic matter back into the marine food web. The speakers of this symposium will explore the processes that control the structure and functioning of microbial food webs and address some of these fundamental questions: What aspects of microbial activity do we need to measure to constrain energy and material flow into and out of the microbial loop? Are we able to measure bacterioplankton dynamics (biomass, growth, production, respiration) well enough to edu/agouroninstitutecourse understand the contribution of the microbial loop to marine systems? What factors control the flow of material and energy into and out of the microbial loop? At what scales (space and time) do we need to measure processes controlling the growth and metabolism of microorganisms? How does our knowledge of microbial community structure and diversity influence our understanding of the function of the microbial loop? Program: 9:00 am Welcome and Introductory Remarks followed by: Peter J.
    [Show full text]
  • 01 Delong 2-8 6/9/05 8:58 AM Page 2
    01 Delong 2-8 6/9/05 8:58 AM Page 2 INSIGHT REVIEW NATURE|Vol 437|15 September 2005|doi:10.1038/nature04157 Genomic perspectives in microbial oceanography Edward F. DeLong1 and David M. Karl2 The global ocean is an integrated living system where energy and matter transformations are governed by interdependent physical, chemical and biotic processes. Although the fundamentals of ocean physics and chemistry are well established, comprehensive approaches to describing and interpreting oceanic microbial diversity and processes are only now emerging. In particular, the application of genomics to problems in microbial oceanography is significantly expanding our understanding of marine microbial evolution, metabolism and ecology. Integration of these new genome-enabled insights into the broader framework of ocean science represents one of the great contemporary challenges for microbial oceanographers. Marine ecosystems are complex and dynamic. A mechanistic under- greatly aid in these efforts. The correlation between organism- and habi- standing of the susceptibility of marine ecosystems to global environ- tat-specific genomic features and other physical, chemical and biotic mental variability and climate change driven by greenhouse gases will variables has the potential to refine our understanding of microbial and require a comprehensive description of several factors. These include biogeochemical process in ocean systems. marine physical, chemical and biological interactions including All these advances — improved cultivation, environmental genomic thresholds, negative and positive feedback mechanisms and other approaches and in situ microbial observatories — promise to enhance nonlinear interactions. The fluxes of matter and energy, and the our understanding of the living ocean system. Below, we provide a brief microbes that mediate them, are of central importance in the ocean, recent history of marine microbiology and outline some of the recent yet remain poorly understood.
    [Show full text]
  • Microbial Loop Carbon Cycling in Ocean Environments Studied Using a Simple Steady-State Model
    AQUATIC MICROBIAL ECOLOGY Vol. 26: 37–49, 2001 Published October 26 Aquat Microb Ecol Microbial loop carbon cycling in ocean environments studied using a simple steady-state model Thomas R. Anderson1,*, Hugh W. Ducklow2 1Southampton Oceanography Centre, Waterfront Campus, European Way, Southampton SO14 3ZH, United Kingdom 2College of William and Mary School of Marine Science, Rte 1208, Box 1346, Gloucester Point, Virginia 23062, USA ABSTRACT: A simple steady-state model is used to examine the microbial loop as a pathway for organic C in marine systems, constrained by observed estimates of bacterial to primary production ratio (BP:PP) and bacterial growth efficiency (BGE). Carbon sources (primary production including extracellular release of dissolved organic carbon, DOC), cycling via zooplankton grazing and viral lysis, and sinks (bacterial and zooplankton respiration) are represented. Model solutions indicate that, at least under near steady-state conditions, recent estimates of BP:PP of about 0.1 to 0.15 are consistent with reasonable scenarios of C cycling (low BGE and phytoplankton extracellular release) at open ocean sites such as the Sargasso Sea and subarctic North Pacific. The finding that bacteria are a major (50%) sink for primary production is shown to be consistent with the best estimates of BGE and dissolved organic matter (DOM) production by zooplankton and phytoplankton. Zooplank- ton-related processes are predicted to provide the greatest supply of DOC for bacterial consumption. The bacterial contribution to C flow in the microbial loop, via bacterivory and viral lysis, is generally low, as a consequence of low BGE. Both BP and BGE are hard to quantify accurately.
    [Show full text]
  • The Role of Bacterioplankton in Lake Erie Ecosystem Processes: Phosphorus Dynamics and Bacterial Bioenergetics
    THE ROLE OF BACTERIOPLANKTON IN LAKE ERIE ECOSYSTEM PROCESSES: PHOSPHORUS DYNAMICS AND BACTERIAL BIOENERGETICS A dissertation submitted to Kent State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy by Tracey Trzebuckowski Meilander December 2006 Dissertation written by Tracey Trzebuckowski Meilander B.S., The Ohio State University, 1994 M.Ed., The Ohio State University, 1997 Ph.D., Kent State University, 2006 Approved by __Robert T. Heath___________________, Chair, Doctoral Dissertation Committee __Mark W, Kershner_________________, Members, Doctoral Dissertation Committee __Laura G. Leff_____________________ __Alison J. Smith____________________ __Frederick Walz____________________ Accepted by __James L. Blank_____________________, Chair, Department of Biological Sciences __John R.D. Stalvey___________________, Dean, College of Arts and Sciences ii TABLE OF CONTENTS Page LIST OF FIGURES ………………………….……………………………………….….xi LIST OF TABLES ……………………………………………………………………...xvi DEDICATION …………………………………………………………………………..xx ACKNOWLEDGEMENTS ………………………………………………………….…xxi CHAPTER I. Introduction ….….………………………………………………………....1 The role of bacteria in aquatic ecosystems ……………………………………………….1 Introduction ……………………………………………………………………….1 The microbial food web …………………………………………………………..2 Bacterial bioenergetics ……………………………………………………………6 Bacterial productivity ……………………………………………………..6 Bacterial respiration ……………………………………………………..10 Bacterial growth efficiency ………...……………………………………11 Phosphorus in aquatic ecosystems ………………………………………………………12
    [Show full text]
  • Microbial Loop in an Oligotrophic Pelagic Marine Ecosystem: Possible Roles of Cyanobacteria and Nanoflagellates in the Organic Fluxes
    MARINE ECOLOGY - PROGRESS SERIES Vol. 49: 171-178, 1988 Published November 10 Mar. Ecol. Prog. Ser. Microbial loop in an oligotrophic pelagic marine ecosystem: possible roles of cyanobacteria and nanoflagellates in the organic fluxes A. Hagstrom*, F. Azam**, A. Andersson*, J. Wikner*, F. Rassoulzadegan Station Marine de Villefranche-Sur-Mer, Station Zoologique. Universite P. et M. Curie, F-06230 Villefranche-Sur-Mer. France ABSTRACT: In an attempt to quantify the organic fluxes within the microbial loop of oligotrophic Mediterranean water, organic pools and production rates were monitored. The production of cyanobac- teria and its dynamics dominated the overall productivity in the system. The largest standing stock was that of the bacterioplankton and its growth consumed 8.3 pg C 1-' d-', hence about 60 % of the primary production was required for bacterial growth. Using the MiniCap technique, we measured a predation on bacteria of 2 6 X 104bacteria ml-' h-'. This was in good agreement with the bacterial production rate of 2.3 X 104 cells rnl-' h-' Thus, growth and predation were balanced for heterotrophic bacterioplank- ton. Almost all of this predation on bacteria was due to organisms passing a 12 vm Nuclepore filter. This raises the question of what mechanisms channel 60 % of primary production into bacteria. We therefore outlined a mass-balance model to illustrate routes that could explain this transfer. According to our model the main flux route is cyanobacteria and concomitantly consumed heterotrophic bacteria carbon into bacterivores. A substantial fraction of the bacterivore and the microplankton carbon is released by excretion and/or cell lysis, to be used by the heterotrophic bacterioplankton.
    [Show full text]
  • Microbial Food Webs & Lake Management
    New Approaches Microbial Food Webs & Lake Management Karl Havens and John Beaver cientists and managers organism’s position in the food web. X magnification under a microscope) dealing with the open water Organisms occurring at lower trophic are prokaryotic cells that represent one (pelagic) region of lakes and levels (e.g., bacteria and flagellates) of the first and simplest forms of life reservoirs often focus on two are near the “bottom” of the food web, on the earth. Most are heterotrophic, componentsS when considering water where energy and nutrients first enter meaning that they require organic quality or fisheries – the suspended the ecosystem. Organisms occurring at sources of carbon, however, some can algae (phytoplankton) and the suspended higher trophic levels (e.g., zooplankton synthesize carbon by photosynthesis or animals (zooplankton). This is for good and fish) are closer to the top of the food chemosynthesis. The blue-green algae reason. Phytoplankton is the component web, i.e., near the biological destination of (cyanobacteria) actually are bacteria, but responsible for noxious algal blooms and the energy and nutrients. We also use the for the purpose of this discussion, are it often is the target of nutrient reduction more familiar term trophic state, however not considered part of the MFW because strategies or other in-lake management only in the context of degree of nutrient they function more like phytoplankton solutions such as the application of enrichment. in the grazing food chain. Flagellates algaecide. Zooplankton is the component (Figure 1c), larger in size (typically 5 that provides the food resource for Who Discovered the to 10 µm) than bacteria but still very most larval fish and for adults of many Microbial Food Web? small compared to zooplankton, are pelagic species.
    [Show full text]
  • Microbial Loop
    Microbial loop The microbial loop describes a trophic pathway in the marine microbial food web where dissolved organic carbon (DOC) is returned to higher trophic levels via its incorporation into bacterial biomass, and then coupled with the classic food chain formed by phytoplankton-zooplankton-nekton. The term microbial loop was coined by Farooq Azam and Tom Fenchel et al.[1] to include the role played by bacteria in the carbon and nutrient cycles of the marine environment. In general, dissolved organic carbon (DOC) is introduced into the ocean environment from bacterial lysis, the leakage or exudation of fixed carbon from phytoplankton (e.g., mucilaginous exopolymer from diatoms), sudden cell senescence, sloppy feeding by zooplankton, the excretion of waste products by aquatic animals, or the breakdown or dissolution of organic particles from terrestrial plants and soils (Van den Meersche et al. 2004). Bacteria in the microbial loop decompose this particulate detritus to utilize this energy-rich matter for growth. Since more than 95% of organic matter in The microbial loop is a marine trophic marine ecosystems consists of polymeric, high molecular pathway which incorporates dissolved weight (HMW) compounds (e.g., protein, polysaccharides, organic carbon into the food chain. lipids), only a small portion of total dissolved organic matter (DOM) is readily utilizable to most marine organisms at higher trophic levels. This means that dissolved organic carbon is not available directly to most marine organisms; marine bacteria introduce this organic carbon into the food web, resulting in additional energy becoming available to higher trophic levels. Recently the term "microbial food web" has been substituted for the term "microbial loop".
    [Show full text]
  • Dissolved Organic Matter and the Microbial Loop
    Microbial cycling of dissolved organic matter MOG Lecture 8 March 1st, 2011 8.1 Microbial cycling of dissolved organic matter • The inclusion of microbes in marine food webs • Microbial production (from 2 perspectives) • Microbial consumption (from 2 perspectives) • Discuss Cottrell & Kirchman and Kujawinski review • Recitation date/time 8.2 “I presume that the numerous lower pelagic animals persist on the infusoria, which are known to abound in the open ocean: but on what, in the clear blue water, do these infusoria subsist?” - Charles Darwin (1845) Pomeroy Bioscience 1974 “Basic to the understanding of any ecosystem is knowledge of its food web, through which energy and materials flow. If microorganisms are major consumers in the sea, we need to know what kinds are the metabolically important ones and how they fit into the food web.” - Lawrence Pomeroy 8.3 Microbial Dominance in the Sea • Ca. 1 billion microbes per liter (includes viruses) • More estimated bacteria in the ocean (1029) than stars in the universe (1021) • Total biomass of marine bacteria is greater than the combined mass of all zooplankton and fishes • Metabolic rate of a 1um bacterium = 100,000 times that of a human • Microbes dominate fluxes of energy and biologically-relevant chemical elements in the oceans 8.4 (simplified) Microbial Loop DOM CO2 CO2 8.5 Quantifying the microbial loop Global fluxes in Gt C/year; Nagata 2ne ed Kirchman 2008 8.6 Bacterial carbon demand and growth efficiency Bacterial Carbon Demand (BCD) = Bacterial Production (BP) + Bacterial Respiration (BR) BP measured w/ incubation of 3thymidine and/or 3leucine BR measured as either O2 consumption or CO2 production -or calculated using an assumed BGE… Bacterial Growth Efficiency (BGE) = BP/BCD 8.7 Bacterial carbon demand and growth efficiency Church 2ne ed Kirchman 2008 Carlson BMDOM 2002 8.8 Kujawinski Ann.
    [Show full text]
  • Planktonic Food Webs: Microbial Hub Approach
    Vol. 365: 289–309, 2008 MARINE ECOLOGY PROGRESS SERIES Published August 18 doi: 10.3354/meps07467 Mar Ecol Prog Ser OPENPEN ACCESSCCESS REVIEW Planktonic food webs: microbial hub approach Louis Legendre1, 2,*, Richard B. Rivkin3 1UPMC Univ Paris 06, UMR 7093, Laboratoire d’Océanographie de Villefranche, 06230 Villefranche-sur-Mer, France 2CNRS, UMR 7093, LOV, 06230 Villefranche-sur-Mer, France 3Ocean Sciences Centre, Memorial University of Newfoundland, St. John’s, Newfoundland A1C 5S7, Canada ABSTRACT: Our review consolidates published information on the functioning of the microbial heterotrophic components of pelagic food webs, and extends this into a novel approach: the ‘micro- bial hub’ (HUB). Crucial to our approach is the identification and quantification of 2 groups of organ- isms, each with distinct effects on food-web flows and biogeochemical cycles: microbes, which are generally responsible for most of the organic carbon respiration in the euphotic zone, and metazoans, which generally account for less respiration than microbes. The key characteristics of the microbial- hub approach are: all heterotrophic microbes are grouped together in the HUB, whereas larger heterotrophs are grouped into a metazoan compartment (METAZ); each food-web flow is expressed as a ratio to community respiration; summary respiration flows through, between, and from the HUB and METAZ are computed using flows from observations or models; both the HUB and METAZ receive organic carbon from several food-web sources, and redirect this carbon towards other food- web compartments and their own respiration. By using the microbial-hub approach to analyze a wide range of food webs, different zones of the world ocean, and predicted effects of climate change on food-web flows, we conclude that heterotrophic microbes always dominate respiration in the euphotic zone, even when most particulate primary production is grazed by metazoans.
    [Show full text]