Transcript Trophic Structure & Food Webs

Zooplankton
Phytoplankton
Nutrients
What have we covered?
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Large-scale oceanography
Phytoplankton “box”
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Regulation of photosynthesis by light,
nutrients, temperature
Nutrient “box”
Redfield Ratios
 Growth rate & Redfield Ratio coupled
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What’s left?
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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
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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
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Top Down Control:
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Bottom Up Control:
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A single species (or small group of related species)
dominate a particular trophic level
Trophic Cascades
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Regulation of ecosystems by physics
Wasp-Waist Control:
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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
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Ecosystem: biotic community + environment
Producers
Consumers
Decomposers
Ecosystems and Energy Transfer
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Energy is always lost!
Ecosystems and Energy Transfer
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Trophic Levels: each level of organism
Trophic Transfer: percentage of energy
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Food Chains: short, direct transfer of energy
from phytoplankton to apex predators
Rules of Thumb
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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
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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
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Viruses can account for a
major source of
phytoplankton mortality
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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?
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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?
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Who’s there
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Flow Cytometry
Microscopy (with
stains)
SEM/TEM (viruses)
Chemical analysis
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Rates (producers)
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Rates (consumers)
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What’s there
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Chemical analysis
Radio-dating
NMR, mass spec, etc.
3H-Thymidine
3H-Leucine
Respiration
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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
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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