“The open ocean is a biological desert.”. Primary Production Global chlorophyll concentrations...

“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?