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Zooplankton Phytoplankton Nutrients What have we covered? Large-scale oceanography Phytoplankton “box” Regulation of photosynthesis by light, nutrients, temperature Nutrient “box” Redfield Ratios Growth rate & Redfield Ratio coupled What’s left? Moving towards the Zooplankton “box”… But before we get there, we’re going to expand on the concept of new, regenerated, and export production These processes are driven by the microbial loop (or web) Setting the Stage 1940’s-1950’s, end of World War II We started to realize that ocean productivity was not unlimited (we can run out of fish!) How do you link phytoplankton productivity to marine resources? Trophic Structure & Food Webs 1946, Riley published a simple food web model: PP = 153T - 120P - 7.3N - 9.1Z + 6713 1947, simplified it to: dN/dt = N(Ph - R) – G (this should look familiar!) Trophic Structure & Food Webs 1946, Riley published a simple food web model: PP = 153T - 120P - 7.3N - 9.1Z + 6713 Phytoplankton Zooplankton 1947, simplified it to: dN/dt = N(Ph - R) - G Nutrients Trophic Terminology Top Down Control: Bottom Up Control: A single species (or small group of related species) dominate a particular trophic level Trophic Cascades Regulation of ecosystems by physics Wasp-Waist Control: Regulation of ecosystems by predation Influencing any one “box” cascades to other boxes, not always linearly The concept of r-K strategy Food webs versus food chains r versus K strategies Based on the concept of ‘maximizing’ reproductive efficiency by balancing offspring versus parenting r < ---------------------------------------------------------------> K Rapid Growth Slow growth Multiple offspring Fewer offspring Short Life Long Life Small body size Large body size Invasive/Transient Established Generalists Specialist Ecosystems and Energy Transfer Ecosystem: biotic community + environment Producers Consumers Decomposers Ecosystems and Energy Transfer Energy is always lost! Ecosystems and Energy Transfer Trophic Levels: each level of organism Trophic Transfer: percentage of energy Food Chains: short, direct transfer of energy from phytoplankton to apex predators Rules of Thumb We often assume that trophic efficiency (the amount of carbon or energy that is transferred from a lower to higher trophic level) is ~10% This has been tested several times— similar to things like the Redfield Ratio, it is surprisingly robust Pauly & Christensen, Nature 374: 255-257, 1995 Light, nutrient, and fish effects on FCE (2-way ANOVA, n = 12, P = 0.0009) (A), herbivore efficiency (3-way ANOVA, n = 23, P = 0.0003) (B and C), and carnivore efficiency (2-way ANOVA, n = 12, P = 0.0138) (D). Dickman E M et al. PNAS 2008;105:18408-18412 ©2008 by National Academy of Sciences Results from a really interesting paper that shows trophic efficiency is ultimately controlled by light, nutrients, and food chain length (in other words, the food quality of phytoplankton influences higher trophic levels). High nutrients and low light increase trophic transfer by making the phytoplankton more nutritious. NPZ Models of Biology P Z Michaelis-Menten Feeding efficiency Respiration Respiration, excretion Temperature Light N Circulation/physics Remineralization time Microbial Food Web First recognized by Azam, extended by others (Pomeroy, Wiebe, Hobbie) 1977: Hobbie introduces Acridine Orange Direct Counts (AODC) • 1980s-90s: Viruses discovered • 2000: Archaea! The Microbial Web Viruses can account for a major source of phytoplankton mortality Bacteria can provide 50% of phytoplankton nutrients Some ecosystems can be net heterotrophic Up to 20% of the biomass in the oceans may be associated with archaea. What are they doing? Illustration by S. Cook, Scripps Institution of Oceanography Example 1: Nitrogen Cycling While we tend to focus on nitrate and ammonium (new and regenerated production) there are many other possible reactions that provide energy or N-compounds. All of these are found in the marine environment, mediated by microbes…. Example 2: Complex Biogeochemistry What is DOM? Operational definition: organic matter that passes a GF/F filter (nominal pore size of 0.7 µm) DOM = Dissolved Organic Matter; DOC = Dissolved Organic Carbon; DON= Dissolved Organic Nitrogen; DOP=Dissolved Organic Phosphorous Includes 1. All (most) viruses 2. 50% of bacteria 3. Some phytoplankton (chlorophyll) 4. Many "submicron particles," e.g. colloids Items 1-3 generally not big part of DOM pool. Hansell, D.A. and C.A. Carlson (ed) 2002. Biogeochemistry of Marine Dissolved Organic Matter. Academic Press. Deep water DOC is ca. 6000 years old. Same concentration of deep DOC is also in surface layer because oceans circulate on order of 1000 years • Divide the DOC pool into three components: 1) Refractory DOM 2) Semi-labile DOM 3) Labile DOM Bacterial Production and NPP are generally related Cole et al. (1988) Mar. Ecol. Progr. Ser 43: 1-10 Source of organic C 500 ) -1d -2 Indian 400 Lakes & Estuaries 300 Antarctica 200 N. Atlantic Equator NA Rings 100 Arctic N.Pacific Subarctic Bacterial Producti Bacterial Production (mg C m-2 d-1) Bacteria roughly follow phytoplankton Arctic 0 200 400 600 800 1000 Primary Production (mg C m-2 d-1) 1200 1400 So what is the microbial web? About 50% of NPP goes through bacterial degradation (formation of DOM, respiration back to inorganic compounds) For each size class of producer, there’s an equivalent consumer In terms of new versus regenerated production, the microbial web is HOW the material is regenerated, and the microbial community is WHO is responsible How do we measure it? Who’s there Flow Cytometry Microscopy (with stains) SEM/TEM (viruses) Chemical analysis Rates (producers) Rates (consumers) What’s there Chemical analysis Radio-dating NMR, mass spec, etc. 3H-Thymidine 3H-Leucine Respiration Fluorescently Labeled Bacteria (FLB) Grazer Dilution Infection/Lysis Low diversity (acidic environ.) 100-clone library ARISA 454 or Illumina Medium diversity (plankton) High diversity (sediment) Fuhrman, Nature 459: 193-199, 2009 Who Cares? • Air-Sea flux of: CO2, methane, DMS, oxygen, nitrogen gas • Regeneration of nutrients • Repackaging of organic matter • Recycling and oxidation (rather than export) Summary In the 1970s, the importance of the ‘microbial loop’ (web) was discovered For each size class of producer, there is an equivalent consumer Approximately 50% of NPP goes through this cycle (regenerated production) Biogeochemistry is controlled by these processes Boyd et al: in the absence of iron fertilization, HNLC regions are dominated by microzooplankton grazing