Energetics of Marine Ecosystems Part I
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Transcript Energetics of Marine Ecosystems Part I
Section 3
Review
primary source of energy
for photosynthetic
organisms is the sun/light.
Food web
Food chain
Biomass
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
Energy Losses Along Food Chains
Of total energy from Sun, only
3 reasons:
Respiration/heat
Waste/feces
Excretion (feces) or egestion
(from cells)
Some parts of organism not
eaten
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
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 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
Ecological Pyramid
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)
4th, 5th, 6th, 7th
4th, 5th, 6th
4th, 5th, 6th
3rd, 4th
4th, 5th, 6th
3rd, 4th, 5th
3rd, 4th , 5th
2nd, 3rd
1st trophic level
3rd, 4th, 5th
2nd
4th, 5th
3rd, 4th, 5th
3rd, 4th
3rd
2nd
3rd, 4th
2nd
1st trophic level
3rd