Phytoplankton Bio-optics: Absorption, Pigments, Biomass Phytoplankton Bio-optics: Absorption, Pigments, Biomass Homework: Chapter 2 in your reader: C. Miller “The phycology of phytoplankton” Roles of Phytoplankton 1.Light absorption & related heat budgets 2.Inorganic to organic conversion of C, N, P, S, etc for consumption by food web 3.Formation of DOC (=DOM, of which cDOM is a component) 4.Sinking and loss of POC to the deep sea/ fossil fuel 5.ALL Biogeochemical Cycles 6.Harmful Algal Blooms 7.Cloud formation/Climate modification 8.Optical Signaling (satellites/moorings/submarines) 9.~ 40 % global photosynthesis and related primary productivity

A quantum of sunlight getting into surface water column is either absorbed, scattered and/or transmitted to deeper depths, due to water properties, phytoplankton, cDOM, particles, detritus etc. Last Lecture and reading emphasized that A quantum of light reaching the surface a phytoplankton cell is also either scattered (mostly at cell surfaces), absorbed (PAR, mostly by pigments and cell metabolites: UVR by DNA and protein), or transmitted through the cell to penetrate deeper in the water column. A quantum of light reaching the surface a phytoplankton cell is also either scattered (mostly at cell surfaces), absorbed (PAR, mostly by pigments and cell metabolites: UVR by DNA and protein), or transmitted through the cell to penetrate deeper in the water column. In addition some absorbed light by pigments can be reemitted as light (= fluorescence) In addition some absorbed light by pigments can be reemitted as light (= fluorescence) The measurable proportionalities of incoming irradiance in the photon budget of a phyto change with different taxonomic groupings, physiology, photosynthetic activity &cell growth. The measurable proportionalities of incoming irradiance in the photon budget of a phyto 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 effects on the underwater light field; hence, the study of the bio-optics of phytoplankton is central to aquatic ecology Iz = Q PAR z Transmitted Light = Attenuated Light, Iz = Q PAR z Io = Q PAR o Incident Light, Io = Q PAR o Light Absorption and Scattering

1. Phytoplankton shapes/sizes and surface composition/roughness largely control light scatter 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. 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 Fundamental review, see readings for additional detail. Several kinds of Dinoflagellates

Even at the organizational level of a chloroplast, incoming light can be scattered, absorbed or transmitted. absorbed or transmitted. CHLOROPLAST REVIEW All photosynthetic pigments are in thylakoids All photosynthetic pigments are in thylakoids Thylakoids give cell color Thylakoids give cell color Photosynthesis light reactions in thylakoids Photosynthesis light reactions in thylakoids Photosynthesis dark reactions in stroma; Photosynthesis dark reactions in stroma; Major differences in thylakoid arrangements exist in different phytoplankton groups and affect with how light energy is absorbed and utilized. Diatoms, Dinoflagellates And other chromophytes Green algae thylakoid stroma Optional excellent review of basic photosynthesis given as a self test (based upon green plants)

Chlorophyll a is only pigment required for photosynthesis Chl a 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 PS I Ejects electron Chemical electron acceptor

Chl a is in all photosynthetic phytoplankton and its phytoplankton and its abundance in a water sample is used to indicate the relative BIOMASS of phytoplankton Chl a Common Method for Determining Chl Biomass: Filter phytos (can size fraction) Filter phytos (can size fraction) Extract Chl with organic solvents Extract Chl with organic solvents Measure magnitude of Chl red peak absorption Measure magnitude of Chl red peak absorption Convert to [concentration units] of ng/L =mg/m3 Convert to [concentration units] 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 Q PAR …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 pigments doing and where are they located? 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) or 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 In vivo whole cell absorption Pure pigment in organic solvent

LH Pigments evolved to efficiently capture aquatic Q PAR( ) that Chl a does not absorb well Case I: Open Ocean Case II: Coastal waters/most lakes 400 nm 700 nm Cyanobacteria and some red algae Found in large quantities in red colored cyanobacteria and in some red algae

Phytoplankton 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 ecology as well as regional differences in aquatic primary production Micro flagellates

Transect of Santa Barbara Channel West Front East Diatoms Phytoflagellates Phytoplankton BiomassChlorophytes, Prochloron? Depth (meters)

Examples of phytoplankton absorption spectra for different phytoplankton groups Chl a + Chl c (1+2) + fucoxanthin Chl a + Chl c (2) + peridinin a a c c fuco

Phycocyanin, PCPhycoerythrin, 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 biomass In coastal currents But not all Chl is the same phytoplankton community.. How do we know which Groups of phytoplankton are in which locations ?