the open ocean environment: plankton, productivity and food webs of the sea chapters 7, 9, and 10
TRANSCRIPT
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The Open Ocean Environment:
Plankton, Productivity and
Food Webs of the Sea
Chapters 7, 9, and 10
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Plankton: Definitions
• Plankton: organisms living in the water column, too small to be able to swim counter to typical ocean currents. This term refers to both animals and plants living in the water column.
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Plankton: Definitions 4• Size classes
Ultraplankton < 2 m
Nannoplankton 2-20 m
Microplankton 20-200 m
Macroplankton 200-2000 m
Megaplankton > 2000 m
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Phytoplankton (only plants)
• Occur singly or form chains
• Size range of nanno to microplankton
• Encased in silica shell consisting of two valves (pillbox)
• Usually radially symmetrical
• Reproduce asexually by binary fission
• Also sexual reproduction
• Doubling once or twice per day usually
• Dominate the seas over the world.
Diatoms
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Phytoplankton
• Secrete organic test and have two flagellae• Size range of nanno and microplankton• Asexual and sexual reproduction• Often many life history stages• Many species are heterotrophic• Often abundant in tropics, mid-latitudes in
summer• A few species are the cause of red tides
Dinoflagellates
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Red Tides
Red tides are caused by an increase in nutrients in seawater that causes an increase in dinoflagellate populations. Species that cause red tides produce a neurotoxic substance, saxitoxin.
This substance is dangerous to people. Shellfish (filter feeders) ingest the dinoflagellates and the toxin. Their tissues also become toxic.
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Diatoms Dinoflagellates
Coccolithophore Flagellate Isochrysis
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ZooplanktonCopepods
Females of different species with eggs
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ZooplanktonCrustaceans - Euphausids (Krill)
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ZooplanktonGelatinous Zooplankton - Cnidaria
Note muscular bell and tentacles
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ZooplanktonGelatinous Zooplankton - Cnidaria
Siphonophores
By-the-wind-sailorVellela
Porpita (ca. 10 cm wide) Physophora (50 mm high)
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ZooplanktonGelatinous Zooplankton - Ctenophores
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Patchiness of the Plankton
• Plankton rarely distributed homogeneously in the water column
• Plankton occur in spatially discontinuous patches, sometimes distinct aggregations
• WHY?
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Diurnal Vertical Migration of Zooplankton
• Zooplankton rise to shallow water at night, sink to deeper water during the day
• Found in many different groups of zooplankton• Zooplankters usually start to sink before dawn,
and start to rise before dusk• Cycle is probably an internal biological clock that
must be reinforced by day-night light changes
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0 1 2 3
Night
Day
Twilight
0
100
200
300
400
Distance (km)
Dep
th (
m)
Vertical migration of planktonic shrimp Sergia lucens
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Review Questions:
1)Why does diurnal vertical migration occur?
2) Do plankton have high or low Reynolds numbers?
Explain what a Reynolds number is.
3) How does plankton’s Reynolds number influence feeding in copepods?
4) Define the term drag in marine hydrodynamics. What adaptations do plankton have to decrease drag?
5) Why might it be important for plankton to stay in surface waters and not sink to great depths?
6) In some marine environments, copepods have strong diurnal migration and it others it is very weak. Why??
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Critical Factors in Plankton Abundance
Chapter 9
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Spring Phytoplankton Increase(or Spring Diatom Increase)
In midlatitudes, phytoplankton increase inthe spring, decline in summer, and may increase to a lesser extent in fall.
Question: What factors may cause these seasonal increases and declines?
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Nutrientsat surface
SpringDiatomIncrease
Zooplankton
Availablesunlight
Winter Spring Summer Fall Winter
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Variations on the Spring Phytoplankton Increase
The spring phytoplankton peak and the later zooplankton peak are shortest and sharpest in high latitudes, becomingindistinct in the tropics
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Arctic
Temperate
Tropical
Phytoplankton
Phytoplankton
Herbivorezooplankton
PhytoplanktonHerbivorezooplankton
J F M A M J J A S O N D
Month
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Productivity and Food Webs in the Sea
Chapter 10
©Jeffrey S. Levinton 2001
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Productivity vs biomass
Biomass the mass of living materialpresent at any time, expressed as gramsper unit area or volume
Productivity is the rate of production of living material per unit time per unit areaor volume
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Productivity
Primary productivity - productivity due toPhotosynthesis.Secondary productivity - productivity due toconsumers of primary producers.
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Food Chain
Food chain - linear sequence showingwhich organisms consume which otherorganisms, making a series of trophic levels
Food web - more complex diagram showingfeeding relationships among organisms, notrestricted to a linear hierarchy
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Food Chain Abstraction
Adultherring
Phytoplankton
Barnaclelarvae
Mollusklarvae Small
copepodseuphausid tunicate
cladocerans
amphipodsand eel
Young herring
arrowworm
Largercopepod
Phytoplankton
Copepod
Herring
Food chain Food Web
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Transfer Between Trophic Levels
Transfer from one trophic level to thenext is not complete:
1. Some material not eaten2. Not all eaten is converted with 100% efficiency.3. 2% transferred from sunlight to primary producers; 10% transferred from primary producers, herbivores and up.
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Oceanic Food Webs
Food webs in the oceans vary systematically in food chain efficiency,number of trophic levels, primary production
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Oceanic Food WebsFood Chain
TypePrimary
Productivity
gCm-2y-1
Trophic Levels
Food Chain
Efficiency
Potential
Fish Production
mgCm-2y-1
Oceanic 50 5 10 0.5
Shelf 100 3 15 340
Upwelling 300 1.2 20 36,000
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Oceanic Food Webs
Note: Great potential of upwelling areasdue to combination of high primary production,higher food chain efficiency, lower numberof trophic levels
Why does lower number of trophic levels increase potential of production?
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Oceanic Food Webs
Stable, low nutrient Turbulent, high nutrient
Few trophic levels
Manytrophiclevels
Open ocean,gyre centers
Shelf, upwelling
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Primary production(mg C/m2/day) <100 100-150 150-250 >250
Asia
NorthAmerica
SouthAmerica
NorthAmerica
Antarctica
IndianOcean
NorthAtlantic
SouthAtlantic
NorthPacific
SouthPacific
Africa
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Satellite Images and marine sciences
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Measuring Primary Productivity
Gross primary productivity - total carbon fixedduring photosynthesis
Net primary productivity - total carbon fixed during photosynthesis minus that part whichis respired.
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Measuring Primary Productivity Satellite Approaches:
Satellites can use photometers specific towavelength to measure chlorophyll, Seawater temperature
Need ground truthing to get relationshipBetween chlorophyll concentration and primary production; varies with region
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sun
Satellite
Color scanner
IrradianceRadiance
Phytoplankton
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Satellite image of world productivity, from SeaWiFS satellite
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What’s in this image?
How do sensors collectsatellite images?
What do the colors represent?
How do we get these colors?
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Images are always collected in black and white first. A computer then adds color.
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Gulf stream image with pixels
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A satellite image of this Red tide event helped researchers determine the concentrations of diatoms and toxins in the water.