Phytoplankton Ecophysiology Flashcards
- Why are phytoplankton so important on Earth?
Form large blooms
Influence atmospheric chemistry and biogeochemistry of nutrient cycling
Fix ~1/2 of the total carbon fixed by photosynthesis on earth
Formed oil, siliceous and limestone deposits
Represent base of food chain supporting fisheries, marine mammals and bird populations
- Describe the biological carbon pump.
CO2 is fixed into organic matter by photosynthesis
Organic matter passes from producers to consumers a and can sink into deeper waters
Carbon returned to seawater: Respiration by animals and algae + Bacterial decay of organic matter
Ultimate deposition locks C away in sediments = C sequestration
Atmospheric CO2 –> Algae –> Consumers –> sink –>
deposition/remineralization –> sequestration
What is the difference between primary productivity and phytoplankton
biomass?
Biomass = the standing stock
Total phytoplankton in a given area or volume of water
(# of cells/L or g chlorophyll a / L
Primary Productivity: rate at which organic matter is produced by primary producers via photosynthesis (photosynthetic rate)
g of O2 produced per m^2 per day
g of C fixed per m^2 per day
How can you measure Chlorophyll?
In vivo fluorescence: a flow-through fluorometer either towed in the water as part of a CTD package
Emits blue light which causes chlorophyll to fluoresce red light, the intensity of which can be converted to an estimate of Chl a
In vitro fluorescence: Collect water sample and filter a known amount on a filter
Extract the chlorophyll a with acetone (or methanol) for 24 h Measure chlorophyll fluorescence in a fluorometer (like above) (not flow-through).
Sattelite sensors: Convert measures of ocean color into estimates of Chlorophyll a
Enables oceanographers to examine global patterns
Depth of water imaged ranges from 5-25 m.
How can you measure Primary productivity?
Variety of methods – as long as they measure rate
Special fluorescence instruments (Scale = Minutes/Single cells)
Incubations with isotopes (Scale = Days/Specific depths)
O2 mass balance (Scale = Weeks/Mixed layer)
Satellites (Scales = Months/Globally)
- Why is size relevant in phytoplankton eco-physiology?
It is the most important characteristic affecting phytoplankton eco-physiology
As they grow the volume grows faster than the SA
- How does the surface area to volume ratio (SA/V) vary with algal size?
As cells grow the volume increases by radius^3 and SA increases by radius^2
- Is SA/V related to growth rate? Explain how.
Yes as cells get larger they grow slower
Because at small size the SA/V is much higher and they have higher nutrient uptake so faster growth
- How does size affect sinking?
Small cells are more buoyant
Large cells tend to sink faster
Explain the importance of considering spatial and temporal scales in phytoplankton ecology
Nutrient regeneration/grazing: seconds to minutes over mm
Growth rates: hours to days
Phytoplankton patches: weeks and km
Succession of species: entire season across lake basins and oceans
So the problem is how to accurately determine the abundance
What volume or area to measure and how often
Describe how certain aspects of the aquatic physical environment (discussed in lecture) affect phytoplankton
The density of freshwater changes with the temperature
Salinity increases density and depresses the freezing point to -1.91 Celcius
- Give four examples of nutrients essential for phytoplankton and their role in their physiology.
Nitrogen: amino acids, nucelotides
Phosphorus: ATP,DNA
Silica: diatom frustules, silica skeletons
Magnesium: Chlorophyll
- Define net and gross growth rates.
Net growth rate is r and is the gross growth rate minus the death rate
Gross growth rate: lambda is the birth rate or rate of reproduction
How do you calculate the growth rate of a phytoplankton population by using exponential or logistic growth models? How do you calculate
doubling time and divisions per time (e.g. divisions per day)?
The exponential growth rate equation is defined as follows: N = No*e^rt
This can be done as a logistic equation as well:
ln(N) = rt + ln(No)
Doubling time: td = ln(2)/r
Divisions per time = 1/td
Describe, using a well-labeled graph, the relationship between phytoplankton photosynthesis (y-axis) and irradiance (x-axis)? Check your notes from lecture for all the parameters included in the graph.
