1. The Open Ocean Environment:
Plankton, Productivity and
Food Webs of the Sea
Chapters 7, 9, and 10

2. 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.

3. Plankton: Definitions 4
Size classes
Ultraplankton
< 2 m
Nannoplankton
2-20 m
Microplankton m
Macroplankton m
Megaplankton
> 2000 m

4. Phytoplankton (only plants)
Diatoms
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.

5. Phytoplankton Dinoflagellates
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

6. 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.

7. Diatoms
Dinoflagellates
Coccolithophore
Flagellate Isochrysis

8. Zooplankton
Copepods
Females of different species with eggs

9. Zooplankton
Crustaceans - Euphausids (Krill)

10. Zooplankton Gelatinous Zooplankton - Cnidaria
Note muscular bell and tentacles

11. Zooplankton Gelatinous Zooplankton - Cnidaria Siphonophores
By-the-wind-sailor
Vellela
Porpita (ca. 10 cm wide) Physophora
(50 mm high)
Siphonophores

12. Zooplankton
Gelatinous Zooplankton - Ctenophores

13. Patchiness of the Plankton
Plankton rarely distributed homogeneously in the water column
Plankton occur in spatially discontinuous patches, sometimes distinct aggregations
WHY?

14. 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

15. Night
100
Depth (m)
200
Day
300
Twilight
400
Distance (km)
Vertical migration of planktonic shrimp Sergia lucens

16. 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??

17. Critical Factors in Plankton Abundance
Chapter 9

18. Spring Phytoplankton Increase (or Spring Diatom Increase)
In midlatitudes, phytoplankton increase in
the spring, decline in summer, and may increase to a lesser extent in fall.
Question: What factors may cause these seasonal increases and declines?

19. Nutrients
at surface
Spring
Diatom
Increase
Available
sunlight
Zooplankton
Winter Spring Summer Fall Winter

20. Variations on the Spring Phytoplankton Increase
The spring phytoplankton peak and the
later zooplankton peak are shortest and
sharpest in high latitudes, becoming
indistinct in the tropics

21. Month Arctic Phytoplankton Herbivore zooplankton Temperate
Tropical
Herbivore
zooplankton
Phytoplankton
J F M A M J J A S O N D
Month

22. Productivity and Food Webs in the Sea Chapter 10
©Jeffrey S. Levinton 2001

23. Productivity vs biomass
Biomass the mass of living material
present at any time, expressed as grams
per unit area or volume
Productivity is the rate of production of
living material per unit time per unit area
or volume

24. Productivity Primary productivity - productivity due to
Photosynthesis.
Secondary productivity - productivity due to
consumers of primary producers.

25. Food Chain Food chain - linear sequence showing
which organisms consume which other
organisms, making a series of trophic levels
Food web - more complex diagram showing
feeding relationships among organisms, not
restricted to a linear hierarchy

26. Food Chain Abstraction
Food chain Food Web
Herring
Adult
herring
Young herring
arrowworm
amphipod
sand eel
Copepod
Larger
copepod
cladocerans
Barnacle
larvae
Mollusk
larvae
tunicate
Small
copepods
euphausid
Phytoplankton
Phytoplankton

27. Transfer Between Trophic Levels
Transfer from one trophic level to the
next is not complete:
1. Some material not eaten
2. Not all eaten is converted with 100% efficiency.
3. 2% transferred from sunlight to primary producers; 10% transferred from primary producers, herbivores and up.

28. Oceanic Food Webs Food webs in the oceans vary
systematically in food chain efficiency,
number of trophic levels, primary
production

29. Oceanic Food Webs Food Chain Type Primary 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

30. Oceanic Food Webs Note: Great potential of upwelling areas
due to combination of high primary production,
higher food chain efficiency, lower number
of trophic levels
Why does lower number of trophic levels increase potential of production?

31. Oceanic Food Webs Open ocean, Shelf, gyre centers upwelling Many
trophic
levels
Few trophic
levels
Stable, low nutrient Turbulent, high nutrient

32. Asia Indian Ocean Antarctica North America Africa South America North
Atlantic
North
Pacific
Africa
South
America
Indian
Ocean
South
Pacific
South
Atlantic
Antarctica
Primary production
(mg C/m2/day)
< >250

33. Satellite Images and marine sciences

34. Measuring Primary Productivity
Gross primary productivity - total carbon fixed
during photosynthesis
Net primary productivity - total carbon fixed
during photosynthesis minus that part which
is respired.

35. Measuring Primary Productivity
Satellite Approaches:
Satellites can use photometers specific to
wavelength to measure chlorophyll,
Seawater temperature
Need ground truthing to get relationship
Between chlorophyll concentration and
primary production; varies with region

36. sun
Satellite
Color
scanner
Irradiance
Radiance
Phytoplankton

37. Satellite image of world productivity, from SeaWiFS satellite

38. What’s in this image?
How do sensors collect
satellite images?
What do the colors
represent?
How do we get these
colors?

39. Images are always collected
in black and white first.
A computer then adds color.

40. Gulf stream image with pixels

43. A satellite image of this Red tide event helped researchers determine the concentrations of diatoms and toxins in the water.