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Biological Productivity inthe Ocean


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An ecosystem is the totality of theenvironment encompassing allchemical, physical, geological andbiological parts.

Ecosystems function by the exchange ofmatter and energy.

Plants use chlorophyll in photosynthesis toconvert inorganic material into organiccompounds and to store energy for growth

and reproduction. Plants are autotrophs and the primary producers in

most ecosystems.

All other organisms are heterotrophs, theconsumers and decomposers in ecosystems.

Herbivores eat plants and release the storedenergy.

10-1 Food Webs and TrophicDynamics


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Population size is dependent upon food

supply. Material is constantly recycled in the

ecosystem, but energy gradually dissipatesas heat and is lost.



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The word trophic refers tonutrition.

Trophic dynamics is the study of thenutritional interconnections amongorganisms within an ecosystem.

Trophic level is the position of an organismwithin the trophic dynamics.

Autotrophs form the first trophic level.

Herbivores are the second trophic level.

Carnivores occupy the third and higher trophic levels.

Decomposers form the terminal level.

A food chain is the succession of organismswithin an ecosystem based upon trophicdynamics. (Who is eaten by whom.)



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An energy pyramid is the graphic

representation of a food chain in terms of theenergy contained at each trophic level.

The size of each successive level is controlled by thesize of the level immediately below.



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As the primary producers, plantsrequire sunlight, nutrients, water andcarbon dioxide for photosynthesis.

Sunlight and nutrients are commonly thelimiting factor.

The formula for photosynthesis is:

Sunlight + 6 CO2 + 6 H2O C6H12O6 (sugar) + 6 O2.

Phytoplankton blooms are the rapidexpansion of a phytoplankton populationbecause light and nutrients are abundant.



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Bacteria are the decomposers; theybreak down organic material andrelease nutrients for recycling.

Few bacteria are capable of completely

degrading organic material into its inorganiccomponents. Most operate in succession withother bacteria to decompose material in aseries of stages.

Bacteria also serve as food for other

organisms either directly or indirectly. Two basic types of bacteria are Aerobic

bacteria and Anaerobic bacteria.

Most bacteria are heterotrophs, but twotypes are autotrophs: Cyanobacteria (blue-

green algae) and Chemosynthetic bacteria.



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Animals must consume pre-existingorganic material to survive.

Animals break down the organic compoundsinto their inorganic components to obtain thestored energy.

The chemical formula for respiration is:

C6H12O6 (sugar) + 6 O2 6 CO2 + 6 H2O + Energy.

The recovered energy is used for movement,reproduction and growth.

The food consumed by most organisms isproportional to their body size.

Generally, smaller animals eat smaller food and largeranimals eat larger food, although exceptions occur.

The basic feeding style of animals are:

Grazers, Predators, Scavengers, Filterfeeders, and Deposit feeders.



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Primary production is the total amount of carbon(C) in grams converted into organic material persquare meter of sea surface per year (gm C/m2/yr).

Factors that limit plant growth and reduce primaryproduction include solar radiation and nutrients as majorfactors and upwelling, turbulence, grazing intensity andturbidity as secondary factors.

Only .1 to .2% of the solar radiation is employed forphotosynthesis and its energy stored in organic compounds.

Macronutrients and Micronutrients are chemicals needed forsurvival, growth and reproduction.

10-2 General Marine Productivity


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Productivity varies greatly in different parts ofthe ocean in response to the availability ofnutrients and sunlight.

In the tropics and subtropics sunlight is abundant, but it

generates a strong thermocline that restricts upwellingof nutrients and results in lower productivity.

High productivity locally can occur in areas of coastal upwelling, in thetropical waters between the gyres and at coral reefs.

In temperate regions productivity is distinctly seasonal.

Polar waters are nutrient-rich all year but productivity isonly high in the summer when light is abundant.



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Upwelling and turbulence can returnnutrients to the surface.

Over-grazing of autotrophs can deplete thepopulation and lead to a decline inproductivity.

Turbidity reduces the depth of light

penetration and restricts productivity even ifnutrients are abundant.



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G


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Primary productivity varies from 25 to 1250 gmC/m2/yr in the marine environment and ishighest in estuaries and lowest in the openocean.

In the open ocean productivity distribution resembles a bullseye pattern with lowest productivity in the center andhighest at the edge of the basin.

Water in the center of the ocean is a clear blue because it is an area ofdownwelling, above a strong thermocline and is almost devoid of biologicalactivity.

Continental shelves display moderate productivity between 50and 200 gm C/m2/yr because nutrients wash in from the landand tide- and wave- generated turbulence recycle nutrientsfrom the bottom water.

10-3 Global Patterns of Productivity

Gl b l P f P d i i


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Polar areas have high productivity becausethere is no pycnocline to inhibit mixing.

Equatorial waters have high productivitybecause of upwelling.



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10 1 F d W b d T hi


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Food chains transfer energy from one trophic level to

another. Biomass is the quantity of

living matter per volume ofwater.

With each higher trophic level,the size of organisms generally

increases, but theirreproductive rate, number andthe total biomass decrease.

The two major food chains inthe ocean are the Grazing foodchain and the Detritus food

chain - non-living wastes formthe base of the food chain.

Only about 10-20% of energyis transferred between trophiclevels and this produces arapid decline in biomass at

each successive trophic level.



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10 3 Global Patterns of Productivity


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It is possible to estimate plant andfish productivity in the ocean.

The size of the plankton biomass is a good indicator of thebiomass of the remainder of the food web.

Annual primary production (APP) is equal to primaryproduction rate (PPR) times the area for which the rate isapplicable.

APP = PPR x Area (to which applicable )

Transfer efficiency (TE) is a measure of the amount ofcarbon that is passed between trophic levels and is used forgrowth.

Transfer efficiency varies from 10 to 20% in most food chains.




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Potential production (PP) at any trophic level is equal tothe annual primary production (APP) times the transferefficiency (TE) for each step in the food chain to the trophiclevel of the organism under consideration.

PP = APP x TE (for each step)

Although rate of productivity is very low for the openocean compared to areas of upwelling, the open ocean has

the greatest biomass productivity because of its enormoussize.

In the open ocean the food chains are longer and energytransfer is low, so fish populations are small.

Most fish production is equally divided between area of upwelling and

coastal waters.

Calculations suggest that the annual fish production isabout 240 million tons/yr.




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Over-fishing is removing fish from the oceanfaster than they are replaced byreproduction and this can eventually lead tothe collapse of the fish population.



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10 4 Biological Productivity of


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Upwelling of deep, nutrient-richwater supports large populations ofphytoplankton and fish.

The waters off the coast of Peru normally is

an area of upwelling, supporting one of theworlds largest fisheries.

Every three to seven years warm surfacewaters in the Pacific displace the cold,nutrient-rich water on Perus shelf in a

phenomenon called El Nino. El Nino results in a major change in fauna on

the shelf and a great reduction in fishes.

This can lead to mass starvation of organismsdependent upon the fish as their major food source.

10-4 Biological Productivity ofUpwelling Water


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Hot Vents and Cold Seeps


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Hot Vents and Cold Seeps


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Hydrothermal Vent Communities


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