Topic 21Productivity

GEOL 2503Introduction to Oceanography

Feeding Strategies

• Primary producers—make food– Photosynthesis– Chemosynthesis

• Consumers—don’t make their own food– Herbivores—eat plants– Carnivores—eat meat– Omnivores—eat both

• Decomposers—break down food by decay

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Algae-supported biotic community

Fig. 13.15

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A Simple Food Chain

Trophic Level

5. Killer Whale4. Seal3. Bony Fish2. Zooplankton 1. Phytoplankton

Energy

1 unit10100 10%

efficiency 1,000 at each level10,000 Solar Energy 500,000 2% efficiency

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CHARACTERISTICS OF ECOSYSTEMS

With progress through an ecosystem:

• 1. Biomass decreases• 2. Size of organisms increases• 3. Energy decreases• 4. Entropy (disorder) increases

Trophic Levels

• Each level represents a link in the food chain

• Primary producers are always the first trophic level

• Herbivorous zooplankton are second level, etc.

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TROPHIC PYRAMIDS

• Trophic levels vary between 2 – 8 with average of 5

• Average efficiency about 10% for each level in the open ocean

• Efficiency may be 15% near coasts and 20% in areas of upwelling

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Where does all the energy go?• If only 10% of energy is harvested at each trophic level,

where does the other 90% go?

Energy is lost to excretion, metabolism (respiration), and decomposition when organisms die uneaten

Food Chains and Webs

• Food chain implies linear relationship, but it is a much more complex interrelationship among organisms, called food web

• primary producers primary consumers secondary consumers top carnivore

• Example: organic molecules phytoplankton zooplankton anchovy tuna killer whale (decomposers)

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A Food Web

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Productivity versus 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

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Biomass pyramid

• Number of individuals and total biomass decrease at successive trophic levels

• Organisms increase in size

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Different Feeding Strategies• Large carnivores like

Toothed Whales, Seals & Sharks feed at top of food web

• Disadvantages – collapse of any trophic level affects all higher levels. Large prey less abundant than small prey.

• Advantage – larger prey provide more calories

• Baleen Whales feed low down on food web

• Disadvantage – must consume enormous volumes of small plankton

• Advantage – closer to energy source (less middle men)

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Regional productivity summarized

Fig. 13.14

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Upwelling and nutrient supply

Coastal upwelling brings nutrients and carbon dioxide up to the photic zone creating zones of high productivity

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A. open ocean (3.8% of total)

B. upwellings (20.9% of total)

C. tropical shelves (21% of total)

D. non-tropical shelves (35.6% of total)

E. coastal and coral (18.7% of total)

Contribution to the total world fishery by ecosystem

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A. Sunshine curve peaks during the summer monthsB. Phytoplankton curve reaches its highest peak in the springC. Nutrients curve peaks during the winter. D. Zooplankton (grazers) curve peaks during the late spring,

after microscopic plants, upon which they feed

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The equation for photosynthesis

6 CO2 + 6 H2O C6H12O6 + 6O2

carbon dioxide + water + light energy glucose + oxygen

Animal Feeding Strategies

• Heterotrophs–Herbivores – eat plants–Granivores – eat seeds–Frugivores – eat fruits–Foliovores – eat leaves–Carnivores – eat other animals–Piscivores – eat fish

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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 (gives that part of the production available to higher trophic levels)