lecture 14 (phytoplankton eco-physiology)

Question 1

why are phytoplankton so important on earth?

Answer 1

they form large blooms,
influence atmospheric chemistry and biogeochemistry of nutrient cycling,
fix about 1/2 of total carbon fixed by photosynthesis,
represent the base of food chains supporting marine mammals, birds, and fisheries,
form oil and siliceous and limestone deposits

Question 2

describe the biological carbon pump:

Answer 2

CO2 is reduced in surface waters and fixed into organic matter by photosynthesis,
organic matter passes from producers to consumers through respiration and bacterial decomposition of organic matter
ultimate deposition locks the C away in sediments (carbon sequestration)
atmospheric CO2 -> algae -> consumers -> sink -> deposition/remineralization -> sequestration

Question 3

what is the difference between PP and phytoplankton biomass? how do you measure them?

Answer 3

primary productivity: the rate at which food is incorporated, yields biomass eg. g O2 produced/L, gC/m2/d (measured with fluorescence, satellites etc.)

phytoplankton biomass: standing stock (set number, not rate) eg. cells/L or chla/L

Question 4

what is NPP

Answer 4

net primary productivity (GPP-respiration)

Question 5

what is GPP

Answer 5

the total PP

Question 6

what is a phytoplankton bloom

Answer 6

an accumulation of phytoplankton biomass in a particular area

Question 7

how is size relevant to phytoplankton eco physiology?

Answer 7

as they grow larger, the SA:V ratio decreases, since SA increases to radius squared and thus it increases slower than volume. This is relevant since a high SA/V ratio allows for faster nutrient exchange

Question 8

why is a smaller size beneficial?

Answer 8

because it corresponds to a high SA/V ratio, allowing for faster and more nutrient exchange, and faster growth rates

Question 9

how does SA to volume ratio change with algal size

Answer 9

smaller size has a higher SA/V ratio
larger size has a smaller SA/V ratio
this is because Volume changes with radius cubed, and SA changes with radius Square

Question 10

how does size affect sinking?

Answer 10

larger cells sink faster, smaller cells are more buoyant

Question 11

what are adaptations to avoid sinking (5)

Answer 11

gas bubbles, lipids, oils, spines, chains

Question 12

explain the importance of considering spatial and temporal scales in phytoplankton ecology

Answer 12

different parts of phytoplankton ecology occur at different scales of time and space.
abundance of phytoplankton depends on time and space

Question 13

spatial scale

Answer 13

what volume or area (eg. how much volume)

Question 14

temporal scale

Answer 14

how often a bloom occurs (eg. what season)

Question 15

describe how certain aspects of the aquatic physical environment affects phytoplankton

Answer 15

density changes with temperature and salinity
increasing salinity increases density and lowers freezing point, keeping phytoplankton more buoyant
temperature increases lower density, causing phytoplankton to sink faster

Question 16

give four examples of nutrients essential for phytoplankton and their roles in physiology

Answer 16

Nitrogen -> amino acids, chlorophyll, nucleotides
Mg -> chlorophyll
Si -> diatom frustules, scales, stomatocyst walls,
S some amino acids, nitrogenase, thylakoid lipids, carrageenan, agar, DMSP, biotin

Question 17

how much light makes it to the surface

Answer 17

50% of light

Question 18

what wavelength penetrates deepest? shallowest?

Answer 18

blue penetrates deepest in water column
red is shallowest

Question 19

what impacts the depth that light reaches in the water column

Answer 19

clarity of the water (particulate/dissolved matter scatters light more quickly)
location (deeper in offshore, shallower in coastal)

Question 20

what is radience

Answer 20

the light that is visible

Question 21

what is the base of the euphotic zone

Answer 21

depth with 1% of incident light remaining

Question 22

draw a temperature profile, and a chlorophyll profile

Answer 22

both are straight down at surface (mixed layer), temperature decreases from then.
chlorophyll increases slightly below the surface, then decreases to 0 (too bright/no nutrients at surface, too dark further down)

Question 23

what is a langmuir cell

Answer 23

water with streaks of white lines parallel to one another
water masses spinning in localized area, upwelling and downwelling cells beside one another

Question 24

how does water motion impact phytoplankton

Answer 24

horizontal water motions concentrate/disperse phytoplankton patches
vertical motion affects sinking and nutrient supply
turbulence has species dependent effects

Question 25

define net growth rate

Answer 25

controlled by growth and loss

Question 26

define gross growth rate

Answer 26

rate of reproduction (only growth, does not include death rate)

Question 27

compare phytoplankton biomass in northern hemisphere tropic, temperate, and polar oceans over a year

Answer 27

tropical stays low all year round, stable
polar peaks only in summer (june, july/august) since usually not enough light (only enough for short period of time, when less ice)
temperate has spring and fall blooms (larger in spring, smaller in fall)

Question 28

draw how light, nutrients, and zooplankton effect/interact with the temperate ocean phytoplankton bloom cycle. label whether they are bottom up/top down

Answer 28

phytoplankton has a peak in spring and fall. nutrients are high in winter, lowered with bloom and low through summer until fall, when they start to go up again (plateauing briefly during fall bloom) -> bottom up
sunlight is low in winter, high over spring to fall (peak in summer) -> bottom up
zooplankton have lower, and slightly delayed blooms after phytoplankton blooms -> top down

Question 29

sketch logistic and exponential growth. how are these different? which occurs in nature/lab?

Answer 29

exponential growth: occurs in lab. biomass increases exponentially to infinity
logistic growth: occurs in nature, exponential increase to a certain carrying capacity (K), then plateaus, with an optimal yield of 1/2 K

Question 30

equation for net growth rate

Answer 30

r = mu-lambda
(net growth rate = gross growth rate - death rate)

Question 31

draw the relationship between photosynthesis and irradience in phytoplankton

Answer 31

increasing light to a certain point increases PP, and then PP decreases again (too much light causes photodamage)
when light is lowered, PP decreases, and reaches the compensation point where light is 1% of surface light and respiration and PP are equal

Question 32

what is the compensation point

Answer 32

when Respiration = Production, NPP=0
when <1% of visible light remains (compensation light intensity)

Question 33

describe the Michaelis-menten model

Answer 33

nutrient uptake from the environment (algae growth curve)
quick uptake to a certain point (saturation), then plateaus
x-axis = nutrients (concentration nutrient), y-axis = nutrient uptake/cell/min)

Question 34

describe the droop model

Answer 34

growth as a function of internal nutrient stores and quotas. quick growth until reaches max growth rate
Q0= minimal subsistence quota, Q = internal pool/quota of nutrient
y-axis = growth rate, x-axis = Qxmol/cell

Question 35

describe the Monod model

Answer 35

growth as a function of external nutrient supply
increases to a maximum growth rate.
x-axis = nutrient concentration, y-axis = growth rate

Question 36

how do you calculate net growth rate of phytoplankton population by using exponential or logistic growth models?

Answer 36

for exponential: gross growth rate - death or loss rate.
if no loss then net growth rate = gross growth rate. r can be estimated from slope of ln N vs time plot
for logistic growth: use (K-N/K) to estimate (as N approaches K, this approaches 0, when N is small, close to 1

Question 37

how do you calculate doubling time

Answer 37

for exponential growth:
doubling time (td) = ln2/r

Question 38

How do you calculate divisions per time?

Answer 38

for exponential growth,
divisions per unit time = 1/doubling time

Question 39

What parameters of the photosynthesis-irradiance relationship are commonly used to determine the success of some phytoplankton species relative to others?

Answer 39

amount of net production/uptake (maximum K), as well as the speed of uptake/growth

Question 40

how do you determine the compensation depth on a graph of photosynthetic rate vs depth?

Answer 40

the compensation depth is where the Respiration line and photosynthesis curve intersect (or where Net PP is 0)

Question 41

using a michaelis-menten model, how can you determine which species would out compete another for the limmiting nutrient?

Answer 41

depends on high or low nutrient concentrations.
when low nutrient concentrations, the one that uptakes faster will dominate.
when nutrients are high, the one that has higher overall growth/uptake rates will dominate

Question 42

describe general loss processes in phytoplankton populations (7)

Answer 42

grazing, perennation, sedimentation, death/morality, parasitism, washout, competition

Question 43

Compare the general relationships and the effects to energy transfer of a marine food web dominated by larger phytoplankton cells (e.g. diatoms) with one dominated by picophytoplankton. Where in the oceans are these different types of food webs commonly found?

Answer 43

the larger the phytoplankton (base of food chain), the shorter the food chain, and more efficient. (cold, temperate/boreal, coastal upwelling zones)
intermediately sized plankton have medium length chains, occur in subtropical gyres, summer/stratified temperate oceans
smaller cells (picoplankton) have longer, less efficient chains (coastal/eutrophic waters)