1. Energetics of Marine Ecosystems Part II
Section 3

2. Review
primary source of energy for photosynthetic organisms is the sun/light.
Food web
Food chain
Biomass

3. 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 = GPP
respiration (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

4. Energy Losses Along Food Chains
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 surfaces
Pass straight through a producer – not absorbed
Inefficiencies of photosynthesis
NPP = GPP – R
3 reasons:
Respiration/heat
Waste/feces
Excretion (feces) or egestion (from cells)
Some parts of organism not eaten

5. Energy Flow in a Food Chain

6. 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

7. 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)

8. Example
3.5%
Show work! [1 point]

9. 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

10. Ecological Pyramids Graphical representation of food chain
Producers at base
Horizontal bars represents successive trophic levels
Width of bar proportional to numbers, biomass or energy
Impossible to have more energy in higher trophic levels

11. Ecological Pyramid

12. Example Draw 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)

13. 4th, 5th, 6th, 7th
4th, 5th, 6th
4th, 5th, 6th
3rd, 4th
4th, 5th, 6th
3rd, 4th, 5th
3rd, 4th , 5th
3rd, 4th, 5th
2nd, 3rd
2nd
1st trophic level

14. 4th, 5th
3rd, 4th, 5th
3rd, 4th
3rd
3rd
2nd
2nd
3rd, 4th
1st trophic level