Phytoplankton Nutrients Zooplankton

What have we covered? Large-scale oceanography Large-scale oceanography Phytoplankton “box” Phytoplankton “box” Regulation of photosynthesis by light, nutrients, temperature Regulation of photosynthesis by light, nutrients, temperature Nutrient “box” Nutrient “box” Redfield Ratios Redfield Ratios Growth rate & Redfield Ratio coupled Growth rate & Redfield Ratio coupled

What’s left? Moving towards the Zooplankton “box”… Moving towards the Zooplankton “box”… But before we get there, we’re going to expand on the concept of new, regenerated, and export production 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) These processes are driven by the microbial loop (or web)

Setting the Stage 1940’s-1950’s, end of World War II 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!) 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? 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 , 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 , simplified it to: dN/dt = N(Ph - R) - G Phytoplankton Nutrients Zooplankton

Trophic Terminology Top Down Control: Top Down Control: Regulation of ecosystems by predation Regulation of ecosystems by predation Bottom Up Control: Bottom Up Control: Regulation of ecosystems by physics Regulation of ecosystems by physics Wasp-Waist Control: Wasp-Waist Control: A single species (or small group of related species) dominate a particular trophic level A single species (or small group of related species) dominate a particular trophic level Trophic Cascades Trophic Cascades Influencing any one “box” cascades to other boxes, not always linearly Influencing any one “box” cascades to other boxes, not always linearly The concept of r-K strategy The concept of r-K strategy Food webs versus food chains Food webs versus food chains

r versus K strategies r versus K strategies Based on the concept of ‘maximizing’ reproductive efficiency by balancing offspring versus parenting r K Rapid GrowthSlow growth Multiple offspringFewer offspring Short LifeLong Life Small body sizeLarge body size Invasive/TransientEstablished GeneralistsSpecialist

Ecosystems and Energy Transfer Ecosystem: biotic community + environment Ecosystem: biotic community + environment Producers Producers Consumers Consumers Decomposers Decomposers

Ecosystems and Energy Transfer Energy is always lost! Energy is always lost!

Ecosystems and Energy Transfer Trophic Levels: each level of organism Trophic Levels: each level of organism Trophic Transfer: percentage of energy Trophic Transfer: percentage of energy

Food Chains: short, direct transfer of energy from phytoplankton to apex predators 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% 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 This has been tested several times— similar to things like the Redfield Ratio, it is surprisingly robust

Pauly & Christensen, Nature 374: , 1995

Light, nutrient, and fish effects on FCE (2-way ANOVA, n = 12, P = ) (A), herbivore efficiency (3-way ANOVA, n = 23, P = ) (B and C), and carnivore efficiency (2-way ANOVA, n = 12, P = ) (D). Dickman E M et al. PNAS 2008;105: ©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.

N ZP NPZ Models of Biology Circulation/physics Remineralization time Feeding efficiency Respiration, excretion Michaelis-Menten Respiration Temperature Light

Microbial Food Web First recognized by Azam, extended by others (Pomeroy, Wiebe, Hobbie) First recognized by Azam, extended by others (Pomeroy, Wiebe, Hobbie) 1977: Hobbie introduces Acridine Orange Direct Counts (AODC) 1977: Hobbie introduces Acridine Orange Direct Counts (AODC) 1980s-90s: Viruses discovered 1980s-90s: Viruses discovered 2000: Archaea! 2000: Archaea!

The Microbial Web Viruses can account for a major source of phytoplankton mortality Viruses can account for a major source of phytoplankton mortality Bacteria can provide 50% of phytoplankton nutrients Bacteria can provide 50% of phytoplankton nutrients Some ecosystems can be net heterotrophic 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) Biogeochemistry of Marine Dissolved Organic Matter. Academic Press.

Deep water DOC is ca 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

Cole et al. (1988) Mar. Ecol. Progr. Ser 43: 1-10 Bacterial Production and NPP are generally related

Bacterial Production (mg C m-2 d-1)

So what is the microbial web? About 50% of NPP goes through bacterial degradation (formation of DOM, respiration back to inorganic compounds) 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 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 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 Who’s there Flow Cytometry Flow Cytometry Microscopy (with stains) Microscopy (with stains) SEM/TEM (viruses) SEM/TEM (viruses) Chemical analysis Chemical analysis What’s there What’s there Chemical analysis Chemical analysis Radio-dating Radio-dating NMR, mass spec, etc. NMR, mass spec, etc. Rates (producers) 3H-Thymidine 3H-Leucine Respiration Rates (consumers) Fluorescently Labeled Bacteria (FLB) Grazer Dilution Infection/Lysis

Low diversity (acidic environ.) Medium diversity (plankton) High diversity (sediment) 100-clone library ARISA 454 or Illumina Fuhrman, Nature 459: , 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 In the 1970s, the importance of the ‘microbial loop’ (web) was discovered For each size class of producer, there is an equivalent consumer For each size class of producer, there is an equivalent consumer Approximately 50% of NPP goes through this cycle (regenerated production) Approximately 50% of NPP goes through this cycle (regenerated production) Biogeochemistry is controlled by these processes Biogeochemistry is controlled by these processes Boyd et al: in the absence of iron fertilization, HNLC regions are dominated by microzooplankton grazing Boyd et al: in the absence of iron fertilization, HNLC regions are dominated by microzooplankton grazing