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“The open ocean is a biological desert.”
Primary Production
Global chlorophyll concentrations for Oct. 2000
Feb 5, 1998: uniformly low pigment concentrations during all seasons
Primary productivity
• Primary productivity is the amount of carbon (organic matter) produced by organisms– Mostly through photosynthesis
• Energy source = solar radiation
– Also includes chemosynthesis• Energy source = chemical reactions
Photosynthetic productivity
Primary Producers
Common NameBlue-green algae (cyanobacteria)Red algaeBrown algaeGreen algaeCoccolithophoridsDinoflagellatesDiatomsSeagrass
Oceanic photosynthetic productivity
• Controlling factors affecting photosynthetic productivity:– Availability of nutrients
• Nitrates• Phosphates• Iron
– Amount of sunlight• Varies daily and seasonally• Sunlight strong enough to support photosynthesis
occurs only to a depth of 100 meters (euphotic zone)
Locations of maximum photosynthetic productivity
• Coastlines– Abundant supply of nutrients from land– Water shallow enough for light to penetrate
all the way to the sea floor
• Upwelling areas– Cool, nutrient-rich deep water is brought to
the sunlit surface
Upwelling
Coastal upwelling
The electromagnetic spectrum and light penetration in seawater
Water color and life in the ocean
• Ocean color is influenced by:– The amount of turbidity from runoff– The amount of photosynthetic pigment, which
corresponds to the amount of productivity
• Yellow-green = highly productive water– Found in coastal and upwelling areas (eutrophic)
• Clear indigo blue = low productivity water– Found in the tropics and open ocean (oligotrophic)
Table 1. Average net primary production and biomass of aquatic habitats. Data from R.H. Whittaker and G.E. Likens, Human Ecol. 1: 357-369 (1973).
Habitat Net primary Production
(g C/m2/yr)
Coral Reefs 2000
Kelp Bed 1900
Estuaries 1800
Seagrass Beds 1000
Mangrove Swamp 500
Lakes & streams 500
Continental Shelf 360
Upwelling 250
Open ocean 50
Productivity varies TEMPORALLY and SPATIALLY:
• generally highest over continental shelves; over the shelf itself it is highest just offshore
• seasonality more pronounced at high latitudes• at mid latitudes, productivity peaks both spring
and fall
Observations from September 1997 through July 2005
Thermocline
Temperature profile
depth
Regional productivity
• Photosynthetic productivity varies due to:
– Amount of sunlight – Availability of nutrients
• Thermocline (a layer of rapidly changing temperature) limits nutrient supply
• Examine three open ocean regions:1. Polar oceans (>60° latitude)2. Tropical oceans (<30° latitude)3. Temperate oceans (30-60° latitude)
Productivity in tropical, temperate, and polar oceans
Zooplankton
Productivity polar oceans
Productivity in tropical oceans
Productivity in temperate oceans
Plankton Sampling
picoplankton
nanplankton
Plankton Size
microplankton
• Picoplankton (.2-2 µm) • Nanoplankton (2 - 20 µm)• Microplankton (20-200 µm)• Macroplankton (200-2,000 µm)• Megaplankton (> 2,000 µm)
R=P
Primary Productivity• Gross Primary Productivity (GPP)
– The rate of production of organic matter from inorganic materials by autotrophic organisms
• Respiration (R)– The rate of consumption of organic matter
(conversion to inorganic matter) by organisms.
• Net Primary Productivity (NPP)– The net rate of organic matter produced as a
consequence of both GPP and R.
Primary Productivity
NPP = GPP - R
Light & Dark Experiments
Photosynthesis:light + 6CO2 + 6H2O C6H12O6 + 6O2
Respiration:C6H12O6 + 6O2
zooplanktonphytoplankton
decomposition6CO2 + 6H2O
dark bottle light bottle
photosynthesis + respirationrespiration
weight
Calculating Primary Productivity
(Light - Initial) = (10 - 8) = 2 mg/L/hr = (GPP - R) = NPP
(Initial - Dark) = (8 - 5) = 3 mg/L/hr = Respiration
(Light - Dark) = (10 - 5) = 5 mg/L/hr = (NPP + R) = GPP
Assume that our incubation period was 1 hour.
Measured oxygen concentrations:
Initial bottle = 8 mg O2 /L
Light bottle = 10 mg O2 /L
Dark bottle = 5 mg O2 /L
Environmental Factors Affecting Primary Production
(eutrophication)
Inquiry1. Why is the open ocean a biological desert?2. Where are the most productive regions located?3. Describe productivity in temperate, polar and
tropical water.4. Why does the zooplankton lag behind the
phytoplankton?5. If you want to catch microplankton, what size mesh
net do you need?6. Why can’t plants grow below the compensation
depth?7. Why does eutrophication sometimes result in mass
fish kills?