productivity

Question 1

Who are the (primary) producers in marine ecosystems?

Answer 1

Phytoplankton

e.g. diatoms, dinoflagellates, green algae,
coccolithophores, photosynthetic bacteria

Seaweeds

Benthic microalgae and photosynthetic bacteria

Marine plants

e.g. eelgrass, surf grass, mangroves

Chemosynthetic bacteria (hydrothermal vents)

Question 2

What do “producers” produce?

Answer 2

Energy-rich organic compounds (e.g. glucose)
from inorganic materials (CO2 & H20) through
photosynthesis OR chemosynthesis

These energy rich compounds can be used in
respiration or to produce more of themselves
either through growth or reproduction

Question 3

what’s biomass and how is it measured?

Answer 3

“mass of organic material in organisms or ecosystems”

Measured after removal of water since water is not organic, contains no useable energy and varies over
time in organisms (unit area)

Inorganic material (other than water) is usually insignificant in terms of mass

Question 4

what’s primary productivity?

Answer 4

“the quantity of organic material produced, or
solar energy fixed, by photosynthesis in green
plants per unit time”

Question 5

what’s GPP? Gross Primary Productivity

Answer 5

Rate at which autotrophs synthesize organic
matter (glucose) = GPP
Quantity of organic matter produced (or solar
energy fixed) by autotrophs per unit area per
unit time

Result of photosynthesis (or chemosynthesis)

Question 6

what’s NPP?

Answer 6

Rate at which autotrophs synthesize new
biomass = NPP
Not all of the total productivity (GPP or energy) goes into making biomass (growth & reproduction)

Some productivity is used in the autotroph’s own life processes (respiration) and this energy is ultimately lost as heat

Question 7

explain how NPP = GPP - respiration

Answer 7

GPP less the biomass or energy used by
autotrophs in respiration

Respiration:

Glucose + O2 ⇒ CO2 + H2O +ATP (energy)

When energy is released from ATP it is lost
as heat (chemical ⇒ heat)

Question 8

How to measure primary productivity?

Answer 8

*Harvest method - measure biomass change over time and express as biomass per unit area
per unit time Destructive!

*CO2 assimilation - measure CO2 uptake in
photosynthesis (and release by respiration)
- Assume any CO2 removed is incorporated into
organic material by photosynthesis
- CO2 is difficult to measure in aquatic systems

*Oxygen production - Measure O2 production
and consumption
light and dark bottle experiments
Light bottle: photosynthesis + respiration
Dark bottle: respiration only
Measure O2 change in both bottles to determine GPP (photosynthesis) and NPP (GPP-R)

*Radioisotope method - use 14C tracer in
photosynthesis
- Incubate producers with a known quantity of 14C often as bicarbonate)
- Measure amount of radioactive glucose produced

Question 9

What are the factors that affect primary productivity?

Answer 9

Solar radiation:
- quality (colour) of light
↑quantity of light ⇒↑ productivity (to a point whentoo much light can inhibit photosynthesis)

Temperature: ↑temp. ⇒↑ productivity
(to a point when high temperatures can denature enzymes)

CO2: ↑ CO2 ⇒↑ productivity (since CO2 is an input)

H2O:↑ H2O ⇒↑ productivity (again, since H2O is an input)

Nutrients: ↑nutrients ⇒↑ productivity (nutrient = any food, chemical element or compound required by an organism to live, grow and reproduce

Examples of nutrients required by algae (& plants): iron, magnesium, calcium, nitrate,
phosphate, silicate