the open ocean - primary production II

Question 1

• Who are the producers?

Answer 1

○ Pelagic phytoplankton (95%) 
		○ Cyanobacteria 
		○ Benthic micro/macroalgae 
		○ Seed plants 
		○ Symbiotic algae in corals and animals

Question 2

Primary production varies by:

Answer 2

○ Organism (phytoplankton abundance) 
		○ Impacted by water motion linked to nutrient availability 
		○ Animal grazing effects 
		○ Termed phytoplankton patchiness 
`Seasonality

Question 3

look at temperate ex of primary producers

Answer 3

ok

Question 4

example of seaonality and pp? look at graph

Answer 4

ok. more stability in the tropics, arctic has more algae from march to september
temperate has highest algae from m-a, lowest july/june, peaks a bit from aug - s, falls again by nov

Question 5

Langmuir circulation: define, what does it create? look at diagram

Answer 5

water vortices created by wind driving water
○ Creates divergences and convergences moving plankton
○ Like a path - can also occur with islands/ larger structures

Question 6

gross pp?

Answer 6

• Gross primary production: total organic fixed - without loss

Question 7

net pp? how are net and gross measured?

Answer 7

• Net primary production: amount after respiration - some taken away
Both measured as g C/m^2/yr integrated over all deapths

Question 8

standing crop?

Answer 8

• Standing crop: total organism biomass in a given vol. of H2O at a given time

Question 9

compensation depth? how does it vary? limited by?

Answer 9

depth at which org. rate of respiration = photosynthetic rate
○ When can it compensate its metabolism w enough light
○ Varies by location, season, day, water clarity
○ Limited inshore by sediment and run off - worst
○ Lots of light is broken + scattered + absorbed fast

Question 10

look at figure of light irradiance and depth. Relationship?

Answer 10

irradience decreases exponentially w depth. • Clearest water = deeper light intensity to 1100 vs costal waters only to 300

Question 11

• Compensation light intensity: define, when does it occur

Answer 11

○ Light intensity at which rate of photosyn. = rate of respiration
○ Occurs approx. when light intensity = 1% of surface light
Varies similar to compensation depth

Question 12

describe marine pyramids:energy passed? Ocean Vs land?

Answer 12

• Food chain/ web with avg. of 10% energy passed on
• On land food web has more producers (higher biomass)
• In ocean it is inverted as compared to terrestrial ( more carnivores than herbivores)
If you look at actual production, a pyramid exists - closer to classic food web pyramid

Question 13

what are phytoplankton limited by? highest productivity where?

Answer 13

• Limited by N, P, and silica - availability of nutrients
○ May be higher in some areas due to human intervention/dumping, but generally limited
• Highest productivity in cold waters (temperate seas)
Higher levels in the organism than ocean - hoarding

Question 14

carbon cycle: describe acidification impact + why it happens

Answer 14

• Oceans are sinks for CO2
• Ocean acidification - changing pH, phytoplankton cannot adapt at an adequate rate - acidification + temp is bleaching the corals
•
○ Dissolves into the water creating carbonic acid = acidification
○ Primarily impacts plankton shells - requires more energy to make them or they dissolve if levels too high
○ Plankton = basic food source = affects fish = affects ppl

Question 15

what are measures of PP based on?

Answer 15

• Based on measuring rate of disappearance/appearance of photosynthesis compounds

Question 16

classic method to measure PP?

Answer 16

• Classical method - light/dark bottle method
○ 2 identical bottles, 1 opaque, 1 transparent
○ Filled with SW of known [O2]
○ Return to depth, let sit for known time
○ Remove, measure [O2] = approx. photosynth. Rate
• Gives net community photosynthesis - mix of plankton
○ Photosyn. In excess of resp.
○ Gross photosynth = lighPmax value - decrease after this t - dark

Question 17

look at graph w relationship btwn photosynth and light intensity

Answer 17

ok

Question 18

14 c method for measuring?

Answer 18

• Preferred, add 14C (H14CO3) to bottles, incubate at depth
• Filter and measure 14C on filter
•
• Problems/ confounding variables (underestimates) with method:
○ Bacteria growing on bottles
○ Phytoplankton behavior altered
○ Water pollution or 14C contamination
○ Low phytoplankton #s
○ Cell breakage on filters
○ 14C fixed but respired as 14CO2

Question 19

are newer methods preferred?

Answer 19

• Not preferred, just newer

Question 20

APAR method?

Answer 20

• Not preferred, just newer
• Net primary productivity (NPP) = APAR x e
Using satellite
e is average light utilization efficiency
Absorbed Photosynthetically Active solar Radiation = apar
• Ex. Assuming higher density of plankton = high productivity
• Measuring pigment

Question 21

standing crop assessment? problem with it?

Answer 21

easure [chlorophyll a] = #s of phytoplankton or photosyn. Org
• Assume # of chlorophyll = primary productivity
• Stimulate chloro. A to fluoresce or extract and measure directly from cells
• Problem - assumes chloro a is constant
○ Not all org.s use chloro a

Question 22

Crit. Depth definition

Answer 22

critical depth is defined as a hypothetical surface mixing depth where phytoplankton growth is precisely matched by losses of phytoplankton biomass within the depth interval.