• Review– Seasonal cycle – spatial variation
• Food web and microbial loop
• Eutrophic vs. Oligotrophic food webs
• Biological pump
Phytoplankton biomassZooplankton biomass
Nutrients
Rel
ativ
e in
crea
se Mixing Mixing
Stratified
Light Temperature
Annual cycle in N. Atlantic
Spring bloom
Fall mini-bloom
Primary production and its seasonal cycle vary greatly in space
Chl a from SeaWIFS satellite
Atlantic Ocean
Pacific Ocean
Temperature
South pole Equator North Pole
South pole Equator North Pole
Mixed layer is deeper in Atlantic than in Pacific
Depth
(m)
Depth
(m)
Latitudinal variation in seasonal cycles driven by variation in irradiance
90o
N = N. Pole
60o
N ~Anchorage,AK
30o
N ~N. Florida
0o
N = Equator
[Also Irradiance]
Annual cycles in other regions
Try this on your own: Draw the vertical profiles of temperature and light and the critical depth for each region as we did in class for the North Atlantic.
Phytoplankton biomassZooplankton biomass
Chisholm, 2000
Biological Pump
Photosynthesis Respiration
SinkingRemineralization
On average, predators are ~10x bigger than prey
Hansen et al. 1994
ESD = Equivalent Spherical Diameter
What’s in a liter of seawater?
1 Liter of seawater contains:• 1-10 trillion viruses• 1-10 billion bacteria• ~0.5-1 million phytoplankton• ~1,000 zooplankton• ~1-10 small fish or jellyfish• Maybe some shark, sea lion,
otter, or whale poop
*The bigger you are, the fewer you are
This basking shark can filter ~25,000 L seawater per day!
phytoplankton
zooplankton
fish
Assume a trophic transfer efficiency of 10%
Biomass
10
100
1000
Efficiency
0.1
0.1
Trophic transfer efficiency = fraction of biomass consumed that is converted into new biomass of the consumer
Traditional view of simple food web:Small things are eaten by (~10x) bigger things
Siz
e (μ
m)
20,000
2,000
200
20
2
0.2
Heterotrophs Autotrophs
Have to add heterotrophic bacteria, heterotrophic protists, and autotrophic bacteria
Siz
e (μ
m)
20,000
2,000
200
20
2
0.2
Heterotrophs Autotrophs
Bacteria absorb organic molecules leaked by microbes and phytoplankton. This creates a microbial “loop.”
20,000
2,000
200
20
2
0.2
Siz
e (μ
m)
Heterotrophs Autotrophs
Dissolved organic matter
Microbial Loop
Chisholm, 2000
Zoom in on food web
Photosynthesis respiration
Phytoplankton are eaten by zooplankton
Plankton size structure is important
Diatoms, dinoflagellates
Coccolithophores, cyanobacteria
Importance of microbial loop depends on environmental conditions.
Microbial loop
Definitions
• Eutrophic environments have high nutrient concentrations and high productivity. Coastal upwelling regions and estuaries are Eutrophic.
• Oligotrophic environments have low nutrients and low productivity. Subtropical gyres (open ocean) are Oligotrophic.
• It takes a lot of mixing or a big nutrient influx to make an environment eutrophic. Stratified systems eventually must become oligotrophic.
Diatom bloom in Barents SeaClear water over Great Barrier Reef
Eutrophic-coastal-estuaries-upwelling-high latitudes
Oligotrophic-open ocean-central gyres
In eutrophic systems, large phytoplankton (diatoms) dominate and more biomass goes directly to large plankton and fish.
Temp.
Dep
th
Dcr
Microbial loop is less important
Temp.
Dep
th
Dcr
In oligotrophic systems, small phytoplankton (e.g. cyanobacteria) dominate and biomass goes through more levels of plankton to get to fish.
Microbial loop is key
Open Ocean
Tuna
Carniv. Fish
Carniv. Plankton
Herbiv. Plankton
Phytoplankton
5 Levels10% Efficiency
Coastal Ocean
Carniv. Fish
Carniv. Plankton
Herbiv. Plankton
Phytoplankton
4 Levels15% Efficiency
Upwelling Zone
Anchovies
Phytoplankton
2 Levels20% Efficiency
Oligotrophic Eutrophic
Draw biomass spectrum here
Area % of ocean area
Total Plant
Production
Transfer
Efficiency
Trophic
Levels
Estimated
Fish Production
(x109 metric tons carbon
per year)
(x106 metric tons
per year)
Open
Ocean
90.0 39 10% 5 4
Coastal
Ocean
9.9 8.6 15% 4 29
Upwelling
Zones
0.1 0.23 20% 2 46
Open ocean Coastal ocean Upwelling zones
=109 metric tons Cper year
=106 metric tons fish per year
5 Trophic levels10% Efficiency 4 Trophic levels
15% Efficiency2 Trophic levels20% Efficiency
Chisholm, 2000
Photosynthesis respiration
Food-web structure affects the export of carbon to deep ocean
How does organic matter get to the bottom of the ocean?
• Dead cells and fecal pellets (plankton poop) sink. Big ones sink faster.
• Dissolved organic matter, pieces of gelatinous animals etc. stick together and form bigger “marine snow” that sinks.
Organic debris is collectively known as Detritus.
Bigger plankton sink faster. They also have bigger, faster-sinking fecal pellets.
Marine snow
Large plankton and their fecal pellets
Small plankton and their fecal pellets
In eutrophic conditions, there are more, larger particles that sink into deep ocean.
Temp.
Dep
th
Large fecal pellets
Large Marine snow
Dcr
In oligotrophic conditions, there are fewer, smaller particles that sink more slowly into deep ocean.
Temp.
Dep
th
Dcr
small fecal pellets
Eutrophic vs. Oligotrophic summary
Eutrophic Oligotrophic
Mixed layer More mixing Cooler
More stratified Warmer
Nutrients High concentration
Newer
Low concentration
More recycled
Plankton Larger Smaller
Particles Larger
Faster-sinking
Smaller
Slower-sinking
Carbon Export More Less
Top Related