Energetics of Marine Ecosystems Part II

Section 3

Reviewprimary source of

energy for photosynthetic organisms is the sun/light.

Food webFood chainBiomass

Gross Primary Production (GPP)calculate the % of incident light energy which

appears as energy of newly synthesised organic substances

The total energy captured by primary producers = GPPrespiration (R)Net primary production (NPP) - Remaining organic

substances Transferred to higher trophic levels

NPP = GPP – R~10% energy available at one trophic level is

transferred to the next trophic level

Energy Losses Along Food Chains

3 reasons:Respiration/heatWaste/feces

Excretion (feces) or egestion (from cells)

Some parts of organism not eaten

Of total energy from Sun, only a small percentage is captured and used for synthesis (NOT ALL ENERGY BECOMES AVAILABLE AS NET PRODUCTION)Reflected back from

surfacesPass straight through a

producer – not absorbedInefficiencies of

photosynthesisNPP = GPP – R

Energy Flow in a Food Chain

BIG reason why RARELY have more than 5 levels

Energy losses between trophic levels

“loss of heat energy”

Insufficient energy available to transfer to more than 5 trophic levels

Efficiency of Energy transfer between trophic levels

Net productivity of plants in a food chain is 36,000 kJ/m2 per year

Net production of herbivores is 1,700 kJ/m2 per year

Efficiency of transfer of energy from the producers to herbivores

(1,700 / 36,000) x 100 = 4.72%Energy losses: heat from respiration, losses in

urine, undigested plant material (fecal matter)Energy of production of herbivores represent

total energy available to carnivores (next trophic level)

Example

3.5%Show work! [1 point]

Productivity can be measured as mass of carbon incorporated into biological molecules per unit area per unit time

The primary productivity of the phytoplankton in this food web is 90 g of carbon per m2 per year.

The efficiency of transfer between phytoplankton and herbivores is approximately 10%.

Assuming that zooplankton and bottom-feeding herbivores eat equal quantities of phytoplankton, calculate the amount of carbon incorporated into zooplankton per m2 per year. Show your working.

....................................................... g C m–2 year–1 [2]

Answer: 90/10% = 9/2 = 4.5

Ecological PyramidsGraphical representation of food chainProducers at base

Horizontal bars represents successive trophic levels

Width of bar proportional to numbers, biomass or energyImpossible to have more energy in higher

trophic levels

Ecological Pyramid

ExampleDraw a pyramid of biomass for the following food

chain:Phytoplankon krill fish penguins killer

whales [2]

Answer:pyramid with 5 levels;each level named; (trophic)

1st trophic level

2nd2nd, 3rd

3rd, 4th, 5th 3rd, 4th , 5th

4th, 5th, 6th

4th, 5th, 6th, 7th

4th, 5th, 6th

3rd, 4th, 5th

4th, 5th, 6th

3rd, 4th

1st trophic level

2nd

2nd3rd, 4th

3rd

3rd3rd, 4th

3rd, 4th, 5th4th, 5th