Phytoplankton Bio-optics: Absorption, Pigments, BiomassPhytoplankton Bio-optics: Absorption, Pigments, BiomassHomework: Chapter 2 in your reader: C. Miller “The phycology of phytoplankton”Homework: Chapter 2 in your reader: C. Miller “The phycology of phytoplankton”

Roles of PhytoplanktonRoles of Phytoplankton

1.1. Light absorption & related heat Light absorption & related heat budgetsbudgets

2.2. Inorganic to organic conversion Inorganic to organic conversion of C, N, P, S, etc for consumption of C, N, P, S, etc for consumption by food webby food web

3.3. Formation of DOC (=DOM, of Formation of DOC (=DOM, of which cDOM is a component)which cDOM is a component)

4.4. Sinking and loss of POC to the Sinking and loss of POC to the deep sea/ fossil fuel deep sea/ fossil fuel

5.5. ALL Biogeochemical CyclesALL Biogeochemical Cycles

6.6. Harmful Algal BloomsHarmful Algal Blooms

7.7. Cloud formation/Climate Cloud formation/Climate modificationmodification

8.8. Optical Signaling Optical Signaling (satellites/moorings/submarines)(satellites/moorings/submarines)

9.9. ~ 40 % global photosynthesis ~ 40 % global photosynthesis and related primary productivityand related primary productivity

A quantum of sunlight getting into surface water column is either A quantum of sunlight getting into surface water column is either absorbedabsorbed, , scatteredscattered and/or and/or transmittedtransmitted to deeper depths, due to water properties, phytoplankton, cDOM, to deeper depths, due to water properties, phytoplankton, cDOM, particles, detritus etcparticles, detritus etc..

Last Lecture and reading emphasized that

• A quantum of light reaching the surface a phytoplankton cell is also either A quantum of light reaching the surface a phytoplankton cell is also either scatteredscattered (mostly at cell surfaces)(mostly at cell surfaces), , absorbedabsorbed (PAR, mostly by pigments and cell metabolites: UVR by (PAR, mostly by pigments and cell metabolites: UVR by DNA and protein), orDNA and protein), or transmittedtransmitted through the cell to penetrate deeper in the water column.through the cell to penetrate deeper in the water column.

• In addition some absorbed light by pigments can be reemitted as light (= In addition some absorbed light by pigments can be reemitted as light (= fluorescencefluorescence) )

• The measurable proportionalities of incoming irradiance in theThe measurable proportionalities of incoming irradiance in the photon budget of a phytophoton budget of a phyto change with different taxonomic groupings, physiology, photosynthetic activity &cell growth.change with different taxonomic groupings, physiology, photosynthetic activity &cell growth.

This and the next Lectures and readings emphasize that

Therefore, much can be learned about phytoplankton by looking at their Therefore, much can be learned about phytoplankton by looking at their effects on the underwater light field; hence, the study of the effects on the underwater light field; hence, the study of the bio-optics of bio-optics of phytoplankton is central to aquatic ecologyphytoplankton is central to aquatic ecology

Transmitted Light = Attenuated Light, Iz = QIz = QPARPARzz

Incident Light, Io = QIo = QPARPARoo

Light Absorption and Scattering

1. Phytoplankton shapes/sizes and 1. Phytoplankton shapes/sizes and surface composition/roughness surface composition/roughness largely control largely control light scatterlight scatter

2. Phytoplankton cellular components and their 2. Phytoplankton cellular components and their internal distribution in the cell largely determine internal distribution in the cell largely determine how much of light getting into the cell is how much of light getting into the cell is absorbed absorbed or or transmittedtransmitted..

3. Phytoplankton cell 3. Phytoplankton cell absorptionabsorption of light occurs largely in photosynthetic lamellae (thylakoids) of light occurs largely in photosynthetic lamellae (thylakoids) where ALL photosynthetic pigments are located. Thylakoids are in chloroplasts organelles within where ALL photosynthetic pigments are located. Thylakoids are in chloroplasts organelles within eukaryotic phytoplankton and located in cytoplasm (no organelles) of prokaryotic bacteria eukaryotic phytoplankton and located in cytoplasm (no organelles) of prokaryotic bacteria

Fundamental review, see readings for additional detail.Fundamental review, see readings for additional detail.

Several kinds ofDinoflagellates

Even at the organizational level of a chloroplast, incoming light can be scattered,Even at the organizational level of a chloroplast, incoming light can be scattered, absorbed or transmitted.absorbed or transmitted.

CHLOROPLAST REVIEWCHLOROPLAST REVIEW• All photosynthetic pigments are in thylakoidsAll photosynthetic pigments are in thylakoids• Thylakoids give cell colorThylakoids give cell color• Photosynthesis light reactions in thylakoidsPhotosynthesis light reactions in thylakoids• Photosynthesis dark reactions in stroma;Photosynthesis dark reactions in stroma;

Major differences in thylakoid arrangements exist Major differences in thylakoid arrangements exist in different phytoplankton groups and affect with in different phytoplankton groups and affect with how light energy is absorbed and utilized.how light energy is absorbed and utilized.

Diatoms,DinoflagellatesAnd other chromophytes

Green algae

thylakoid

stroma

Optional excellent review of basic photosynthesis given as a self test (based upon green plants) 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.htmhttp://ghs.gresham.k12.or.us/science/ps/sci/soph/energy/photorev/basics/rev.htm

Chlorophyll a Chlorophyll a is only pigment is only pigment requiredrequired for photosynthesis for photosynthesis

Chl a

Because Chl a (C) is the only pigment that comprises the Because Chl a (C) is the only pigment that comprises the photochemical reaction photochemical reaction centerscenters of of Photosystem IPhotosystem I and and Photosystem IIPhotosystem II

P700 = special Chl a dimer of Ps IP700 = special Chl a dimer of Ps I

P680 = special Chl a dimer of Ps IIP680 = special Chl a dimer of Ps II

PS I Ejects electronEjects electron

Chemical Chemical electron electron acceptoracceptor

Chl a Chl a is in all photosyntheticis in all photosynthetic phytoplankton and its phytoplankton and its

abundance in a water sample is abundance in a water sample is used to indicate the relative used to indicate the relative BIOMASS of phytoplanktonBIOMASS of phytoplankton

Chl a

Common Method for Determining Chl Biomass:Common Method for Determining Chl Biomass:• Filter phytos (can size fraction)Filter phytos (can size fraction)• Extract Chl with organic solventsExtract Chl with organic solvents• Measure magnitude of Chl red peak absorptionMeasure magnitude of Chl red peak absorption• Convert to Convert to [concentration units][concentration units] of ng/L =mg/m3 of ng/L =mg/m3

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?

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.

So, if Chl a is all that is needed for photosynthesis, what are all those other So, if Chl a is all that is needed for photosynthesis, what are all those other pigments doing and where are they located?pigments doing and where are they located?

They are absorbing light energy and passing the They are absorbing light energy and passing the excitation energy on to Chl a-doinated PS I and PS excitation energy on to Chl a-doinated PS I and PS II reaction centers to do photochemistryII reaction centers to do photochemistry

As such they are called Antenna or As such they are called Antenna or Light-Harvesting Complexes (LHCs) Light-Harvesting Complexes (LHCs)

orLHCs

This is an example for a This is an example for a chlorophyte (green algae) LHCs, chlorophyte (green algae) LHCs, giving rise to a whole cell giving rise to a whole cell absorption spectrum that is a absorption spectrum that is a summation of the absorption summation of the absorption properties of each of these properties of each of these pigments bound to proteins in the pigments bound to proteins in the thylakoid membranethylakoid membrane

In vivo whole cell absorption

Pure pigment in organic solvent

LH Pigments evolved to efficiently capture aquatic QLH Pigments evolved to efficiently capture aquatic QPAR(PAR() ) that Chl that Chl aa does not absorb well does not absorb well

Case I: Open OceanCase I: Open Ocean Case II: Coastal waters/most lakes Case II: Coastal waters/most lakes

400 nm400 nm 700 nm700 nm

Cyanobacteria and some red algaeFound in large quantities in

red colored cyanobacteria and in some red algae

Phytoplankton pigments: types, function and taxonomic distributionPhytoplankton pigments: types, function and taxonomic distribution

If phycoerythrin abundant, then red colored

If phycocyanin abundant, then blue colored

Reddish brown to golden brown

Forest green under low light, turning yellowish under High light

You need to know this information very well to study phytoplankton community You need to know this information very well to study phytoplankton community ecology as well as regional differences in aquatic primary productionecology as well as regional differences in aquatic primary production

Microflagellates

Transect of Santa Barbara ChannelWest Front East

Diatoms Phytoflagellates

Phytoplankton Biomass Chlorophytes, Prochloron?

Dep

th (

met

ers)

Dep

th (

met

ers)

Examples of phytoplankton absorption spectra for different phytoplankton groups

Chl a + Chl c (1+2) + fucoxanthin

Chl a + Chl c (2) + peridinin

aa

c

c

fuco

Phycocyanin, PC Phycoerythrin, PE

Chl a (which absorption peaks?) + phycobilin containing phytoplankton

In ocean, these are picophytoplankton that tend to dominate phytoplankton communities of oligotrophic waters.

How pigment data is used in oceanography

1. To map distribution of Chl a as proxy measure of phytoplankton biomass

Dense spring bloom in North Atlantic Ocean

Low phyto biomass in Gyres of N. and S. Atlantic Ocean

High phyto biomassIn coastal currents

But not all Chl is the same phytoplankton community.. How do we know whichGroups of phytoplankton are in which locations?