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Phytoplankton Bio-optics: Absorption, Pigments, Biomass. Homework: Chapter 2 in your reader: C. Miller “The phycology of phytoplankton”. Roles of Phytoplankton Light absorption & related heat budgets Inorganic to organic conversion of C, N, P, S, etc for consumption by food web
Homework: Chapter 2 in your reader: C. Miller “The phycology of phytoplankton”
Roles of Phytoplankton
Light absorption & related heat budgets
Inorganic to organic conversion of C, N, P, S, etc for consumption by food web
Formation of DOC (=DOM, of which cDOM is a component)
Sinking and loss of POC to the deep sea/ fossil fuel
ALL Biogeochemical Cycles
Harmful Algal Blooms
Cloud formation/Climate modification
Optical Signaling (satellites/moorings/submarines)
~ 40 % global photosynthesis and related primary productivity
A quantum of sunlight getting into surface water column is either absorbed, scattered and/or transmittedto deeper depths, due to water properties, phytoplankton, cDOM, particles, detritus etc.
Incident Light, Io = QPARo
Light Absorption and Scattering
Transmitted Light = Attenuated Light, Iz = QPARz
This and the next Lectures and readings emphasize that
Therefore, much can be learned about phytoplankton by looking at their effects on the underwater light field; hence, the study of the bio-optics of phytoplankton is central to aquatic ecology
2. Phytoplankton cellular components and their internal distribution in the cell largely determine how much of light getting into the cell is absorbed or transmitted.
Fundamental review, see readings for additional detail.
1. Phytoplankton shapes/sizes and surface composition/roughness largely control light scatter
3. Phytoplankton cell absorption of light occurs largely in photosynthetic lamellae (thylakoids) where ALL photosynthetic pigments are located. Thylakoids are in chloroplasts organelles within eukaryotic phytoplankton and located in cytoplasm (no organelles) of prokaryotic bacteria
Even at the organizational level of a chloroplast, incoming light can be scattered,
absorbed or transmitted.
Major differences in thylakoid arrangements exist in different phytoplankton groups and affect with how light energy is absorbed and utilized.
Optional excellent review of basic photosynthesis given as a self test (based upon green plants) http://ghs.gresham.k12.or.us/science/ps/sci/soph/energy/photorev/basics/rev.htm
Chl a-protein complexes
Chlorophyll a is only pigment required for photosynthesis
Because Chl a (C) is the only pigment that comprises the photochemical reaction centers of Photosystem I and Photosystem II
P700 = special Chl a dimer of Ps I
P680 = special Chl a dimer of Ps II
Note how depth is not in meters (Z) but scaled to light field as % surface QPAR …this approach allows distribution of Chl in euphotic zones of different depths to be intercompared.
Chl a is in all photosynthetic
phytoplankton and its
abundance in a water sample is
used to indicate the relative
BIOMASS of phytoplankton
Caveat:[Chl a] is imperfect measure of phytoplankton biomass & interpretations of findings must recognize the possible sources of error.
How would your view of phytoplankton distribution in the above graphs change if I told you that each phyto cells at 1%Qpar have 10x Chl of that of cells at the surface?
So, if Chl a is all that is needed for photosynthesis, what are all those other pigments doing and where are they located?
In vivo whole cell absorption
in organic solvent
They are absorbing light energy and passing the excitation energy on to Chl a-doinated PS I and PS II reaction centers to do photochemistry
As such they are called Antenna or Light-Harvesting Complexes (LHCs)
This is an example for a chlorophyte (green algae) LHCs, giving rise to a whole cell absorption spectrum that is a summation of the absorption properties of each of these pigments bound to proteins in the thylakoid membrane
Case I: Open Ocean
Cyanobacteria and some red algae
Found in large quantities in
red colored cyanobacteria
and in some red algae
LH Pigments evolved to efficiently capture aquatic QPAR(l) that Chl a does not absorb well
turning yellowish under
If phycoerythrin abundant,
then red colored
Reddish brown to golden brown
If phycocyanin abundant,
then blue colored
Phytoplankton pigments: types, function and taxonomic distribution
You need to know this information very well to study phytoplankton community ecology as well as regional differences in aquatic primary production
Transect of Santa Barbara Channel
West Front East
Chl a + Chl c (1+2) + fucoxanthin
Chl a + Chl c (2) + peridinin
Examples of phytoplankton absorption spectra for different phytoplankton groups
Chl a (which absorption peaks?) + phycobilin containing phytoplankton
In ocean, these are picophytoplankton that tend to dominate
phytoplankton communities of oligotrophic waters.
North Atlantic Ocean
Low phyto biomass in
Gyres of N. and S.
High phyto biomass
In coastal currents
How pigment data is used in oceanography
1. To map distribution of Chl a as proxy measure of phytoplankton biomass
But not all Chl is the same phytoplankton community.. How do we know which
Groups of phytoplankton are in which locations?