Terrestrial versus oceanic ecosystems

15 important questions on Terrestrial versus oceanic ecosystems

Where do you find a lot and where less nitrate in the oceans?

High concentration in upwelling currents
Low concentration in mid-ocean gyres

How much accounts oceanic GPP for the global GPP?

About 50%

What is mainly responsible for the GPP of the oceans?

Phytoplankton
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Why does phytoplankton have higher photsynthetic rates per gram biomass compared to vegetation?

- Algae are single celled don’t need to invest biomass in roots etc, so higher efficiency per biomass.

How does photosynthesis occur in phytoplankton?

Direct diffusion, no stomata
C3 is most common but other variants also happen y is unknown.

What is the euphotic zone?

The photic zone (or euphotic zone, epipelagic zone, or sunlight zone) is the uppermost layer of a body of water that receives sunlight, allowing phytoplankton to perform photosynthesis. It undergoes a series of physical, chemical, and biological processes that supply nutrients into the upper water column. The photic zone is home to the majority of aquatic life due to the activity (primary production) of the phytoplankton. The thicknesses of the photic and euphotic zones vary with the intensity of sunlight as a function of season and latitude and with the degree of water turbidity

What is blue carbon?

Natural capacity of vegetated coastal ecosystems to sequester C

A disproportionally important C sink
Conservation important to prevent C loss

What is noticable about decomposition in the ocean vs terrestrial?

Fragmentation is not as important in oceanic ceomposition. Grazers select food more on size rather than composition in oceanic. Grazing can even result in larger fragments which than get heavier and can then sink.


80-95% is decomposed in the surface ocean. 

the litter quality and decomposition rate is high, terrestrial is variable, low.

What limits nutrient uptake by plankton in nutrient-poor waters?

Diffusion

Where do you see more large and where smaller plankton?

Smaller phytoplankton in nutrient-poor waters (open ocean)
● High surface-to-volume ratio leads to less diffusion limitation 

▪ Larger phytoplankton in nutrient-rich waters (e.g. coasts)
● Diffusion less limiting; nutrients can be stored internally
● Less prone to grazing than small phytoplankton

Why does the size matter to grazing of phytoplankton?

Smaller phytoplankton get eaten by other plankton

What is the proximate limiting nutrient for phytoplankton

Marine Nitrogen

How can N2 be fixated in the ocean?

Cyanobacteria (blue green algue)
only bacteria containing chlorophyll-a

There are some areas with high N and P yet little phytoplankton, how come?

Micronutrients limiting (often Fe)

Where comes most available N in the oceans come from?

Regenerated/decomposed of existing N

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