Phytoplankton

Nutrients

Zooplankton

What have we covered?What have we covered?

Large-scale oceanographyLarge-scale oceanography Phytoplankton Phytoplankton ““boxbox””

Regulation of photosynthesis by light, Regulation of photosynthesis by light, nutrients, temperaturenutrients, temperature

Nutrient Nutrient ““boxbox”” Redfield RatiosRedfield Ratios Growth rate & Redfield Ratio coupledGrowth rate & Redfield Ratio coupled

WhatWhat’’s left?s left?

Moving towards the Zooplankton Moving towards the Zooplankton ““boxbox””…… But before we get there, weBut before we get there, we’’re going to re going to

expand on the concept of new, expand on the concept of new, regenerated, and export productionregenerated, and export production

These processes are driven by the These processes are driven by the microbial loop (or web)microbial loop (or web)

Setting the StageSetting the Stage

19401940’’s-1950s-1950’’s, end of World War IIs, end of World War II We started to realize that ocean We started to realize that ocean

productivity was not unlimited (we can run productivity was not unlimited (we can run out of fish!)out of fish!)

How do you link phytoplankton productivity How do you link phytoplankton productivity to marine resources?to marine resources?

Trophic Structure & Food Trophic Structure & Food WebsWebs

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 Trophic Structure & Food WebsWebs

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

Phytoplankton

Nutrients

Zooplankton

Trophic TerminologyTrophic Terminology Top Down Control:Top Down Control:

Regulation of ecosystems by predationRegulation of ecosystems by predation Bottom Up Control:Bottom Up Control:

Regulation of ecosystems by physicsRegulation of ecosystems by physics Wasp-Waist Control:Wasp-Waist Control:

A single species (or small group of related species) A single species (or small group of related species) dominate a particular trophic leveldominate a particular trophic level

Trophic CascadesTrophic Cascades Influencing any one Influencing any one ““boxbox”” cascades to other boxes, not cascades to other boxes, not

always linearlyalways linearly The concept of r-K strategyThe concept of r-K strategy Food webs versus food chainsFood webs versus food chains

r versus K strategiesr 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 Ecosystems and Energy TransferTransfer

EcosystemEcosystem: biotic community + environment: biotic community + environment ProducersProducers ConsumersConsumers DecomposersDecomposers

Ecosystems and Energy Ecosystems and Energy TransferTransfer

Energy is Energy is alwaysalways lost! lost!

Ecosystems and Energy Ecosystems and Energy TransferTransfer

Trophic Levels:Trophic Levels: each level of organismeach level of organism Trophic Transfer:Trophic Transfer: percentage of energy percentage of energy

Food Chains:Food Chains: short, direct transfer of energy short, direct transfer of energy from phytoplankton to apex predatorsfrom phytoplankton to apex predators

Rules of ThumbRules of Thumb

We often assume that trophic efficiency We often assume that trophic efficiency (the amount of carbon or energy that is (the amount of carbon or energy that is transferred from a lower to higher trophic transferred from a lower to higher trophic level) is ~10%level) is ~10%

This has been tested several times—This has been tested several times—similar to things like the Redfield Ratio, it similar to things like the Redfield Ratio, it is surprisingly robustis 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.

N

ZP

NPZ Models of BiologyNPZ Models of Biology

Circulation/physics

Remineralization time

Feeding efficiency

Respiration, excretion

Michaelis-Menten

Respiration

Temperature

Light

Microbial Food WebMicrobial Food Web

First recognized by Azam, extended by First recognized by Azam, extended by others (Pomeroy, Wiebe, Hobbie)others (Pomeroy, Wiebe, Hobbie)

1977: Hobbie introduces Acridine Orange 1977: Hobbie introduces Acridine Orange Direct Counts (AODC)Direct Counts (AODC)

• • 1980s-90s: 1980s-90s: Viruses discoveredViruses discovered

• • 2000: Archaea!2000: Archaea!

The Microbial WebThe Microbial Web

Viruses can account for a Viruses can account for a major source of major source of phytoplankton mortalityphytoplankton mortality

Bacteria can Bacteria can provide 50% of provide 50% of phytoplankton phytoplankton nutrientsnutrients

Some ecosystems Some ecosystems can be net can be net heterotrophicheterotrophic

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 Example 1: Nitrogen CyclingCycling

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 Example 2: Complex BiogeochemistryBiogeochemistry

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

Includes1. All (most) viruses2. 50% of bacteria3. 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

Cole et al. (1988) Mar. Ecol. Progr. Ser 43: 1-10

Bacterial Production and Bacterial Production and NPP are generally NPP are generally

relatedrelated

Bac

teri

al P

rodu

ctio

n (m

g C

m-2

d-1

)

So what is the microbial So what is the microbial web?web?

About 50% of NPP goes through bacterial About 50% of NPP goes through bacterial degradation (formation of DOM, degradation (formation of DOM, respiration back to inorganic compounds)respiration back to inorganic compounds)

For For eacheach size class of producer, there size class of producer, there’’s an s an equivalent consumerequivalent consumer

In terms of new versus regenerated In terms of new versus regenerated production, the microbial web is production, the microbial web is HOWHOW the the material is regenerated, and the microbial material is regenerated, and the microbial community is community is WHOWHO is responsible is responsible

How do we measure it?How do we measure it?

WhoWho’’s theres there Flow CytometryFlow Cytometry Microscopy (with Microscopy (with

stains)stains) SEM/TEM (viruses)SEM/TEM (viruses) Chemical analysisChemical analysis

WhatWhat’’s theres there Chemical analysisChemical analysis Radio-datingRadio-dating NMR, mass spec, etc.NMR, mass spec, etc.

Rates (producers)Rates (producers) 3H-Thymidine3H-Thymidine 3H-Leucine3H-Leucine RespirationRespiration

Rates (consumers)Rates (consumers) Fluorescently Labeled Fluorescently Labeled

Bacteria (FLB)Bacteria (FLB) Grazer DilutionGrazer Dilution Infection/LysisInfection/Lysis

Low diversity (acidic environ.)

Medium diversity (plankton)

High diversity (sediment)High diversity (sediment)

100-clone libraryARISA

454 or Illumina

Fuhrman, Nature 459: 193-199, 2009

Who Cares?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)

SummarySummary In the 1970s, the importance of the In the 1970s, the importance of the ‘‘microbial microbial

looploop’’ (web) was discovered (web) was discovered For each size class of producer, there is an For each size class of producer, there is an

equivalent consumer equivalent consumer Approximately 50% of NPP goes through this Approximately 50% of NPP goes through this

cycle (regenerated production)cycle (regenerated production) Biogeochemistry is controlled by these Biogeochemistry is controlled by these

processesprocesses Boyd et al: in the absence of iron fertilization, Boyd et al: in the absence of iron fertilization,

HNLC regions are dominated by HNLC regions are dominated by microzooplankton grazingmicrozooplankton grazing