1. Productivity and the Coral Symbiosis IV: Reef Photosynthesis

2. Productivity the production of organic compounds from inorganic atmospheric or aquatic carbon sources – mostly CO 2 principally through photosynthesis –chemosynthesis much less important. All life on earth is directly or indirectly dependant on primary production.

3. gC/m 2 /d TropicalCoral Reef4.1 - 14.6 Tropical open ocean0.06 - 0.27 Mangrove2.46 Tropical Rain Forest5.5 Oak Forest3.6

4. Productivity no single major contributor to primary production on the reef a mixture of photosynthetic organisms –can be different at different locations

5. net productivity values (varies with location): gC/m 2 /d Calcareous reds1 - 6 Halimeda2 -3 Seagrass1 - 7 N.S. kelp5

6. Overall productivity of the reef: 4.1 - 14.6 gC/m 2 /d from –epilithic algae, on rock, sand etc., –few phytoplankton –seagrasses –Zooxanthellae (in coral etc.) –Fleshy and calcareous macroalgae

7. One obvious differences between different algae is their colour Different colours due to the presence of different photosynthetic pigments

8. The visible light spectrum includes –the colors of light we can see –the wavelengths that drive photosynthesis Photosynthetic pigments absorb light

9. Light Reflected Light Chloroplast Absorbed light Granum Transmitted light

10. Light and Photosynthesis Air & water both absorb light –a plant at sea level receives 20% less light than a plant on a mountain at 4,000m –this reduction occurs faster in seawater –depends a lot on location get 20% light reduction in 2m of tropical seawater get 20% light reduction in 20cm of Maritime seawater

11. Photosynthesis uses a very specific part of the EM spectrum PAR Photosynthetically Active Radiation 350-700 nm

12. Gamma rays X-raysUVInfrared Micro- waves Radio waves 10 –5 nm 10 –3 nm 1 nm 10 3 nm 10 6 nm 1 m 10 6 nm 10 3 m 380450500550600650700750 nm Visible light Shorter wavelength Higher energy Longer wavelength Lower energy

13. Gamma rays X-raysUVInfrared Micro- waves Radio waves 10 –5 nm 10 –3 nm 1 nm 10 3 nm 10 6 nm 1 m 10 6 nm 10 3 m 380450500550600650700750 nm Visible light Shorter wavelength Higher energy Longer wavelength Lower energy

14. Measure it as IRRADIANCE –moles of photons per unit area per unit time –mol.m -2.s -1 –E = Einstein = 1 mole of photons  E.m -2.s -1

15. As light passes through seawater it gets ABSORBED & SCATTERED –= ATTENUATION (a reduction in irradiance) pure water –attenuation lowest at 465nm –increases towards UV and IR ends of spectrum TRANSMITTANCE is highest at 465nm not dealing with pure water –seawater has all kinds of dissolved salts, minerals, suspended material etc.:

17. Attenuation is different in different locations - different light transmittance spectra: To fully exploit a particular location, marine plants have a wide variety of PS pigments they can use.

18. Chloroplast Mesophyll 5 µm Outer membrane Intermembrane space Inner membrane Thylakoid space Thylakoid Granum Stroma 1 µm

19. CO 2 CALVIN CYCLE O2O2 [CH 2 O] (sugar) NADP  ADP + P i An overview of photosynthesis H2OH2O Light LIGHT REACTIONS Chloroplast ATP NADPH

20. Light Reactions In the thylakoid membrane, –chlorophyll molecules, other small molecules & proteins, are organized into photosystems –photosystems composed of a reaction center surrounded by a number of light-harvesting complexes (LHC) LHC = pigment molecules bound to proteins

21. funnel energy of photons to the reaction center reaction-center chlorophyll absorbs energy –One of its electrons gets bumped up to a primary electron acceptor –electron transport –ATP & NADPH production

22. Photosystems Primary election acceptor Photon Thylakoid Light-harvesting complexes Reaction center Photosystem STROMA Thylakoid membrane Transfer of energy Special chlorophyll a molecules Pigment molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID) e–e–

23. different pigments have different absorption spectra combine in different amounts in different species to give each a unique absorption spectrum tells us which wavelengths of light are being absorbed (and thus it’s colour)

24. Absorption of light by chloroplast pigments Chlorophyll a Wavelength of light (nm) Chlorophyll b Carotenoids Absorption spectra of pigments

25. doesn’t tell us what the alga is doing with the light For this you need to look at the ACTION SPECTRUM –measures photosynthesis at different wavelengths

26. The action spectrum of a pigment –show relative effectiveness of different wavelengths of radiation in driving photosynthesis Plots rate of photosynthesis versus wavelength

28. Marine PS pigments 3 major groups of PS pigments in marine organisms –Chlorophylls –Phycobiliproteins –Carotenoids

29. Chlorophyll a is essential –find it in all plants and algae the other pigments are accessory pigments –in the antennae complexes –funnel electrons to chlorophyll a in the reaction centres

30. 5 types of chlorophyll commonly found in marine organisms all are tetrapyrrole rings with Mg ++ in the middle chlorophyll a, b, c 1, c 2 & d a all green plants and algae b Chlorophyceae c 1 & c 2 Phaeophyceae dRhodophyceae

31. Chlorophyll a –Is the main photosynthetic pigment Chlorophyll b, c, d –Are accessory pigments C CH CH 2 C C C C C CN N C H3CH3C C C C C C C C C N C C C C N Mg H H3CH3C H C CH 2 CH 3 H C H H CH 2 H CH 3 C O O O O O CHO in chlorophyll a in chlorophyll b Porphyrin ring: Light-absorbing “head” of molecule note magnesium atom at center Hydrocarbon tail: interacts with hydrophobic regions of proteins inside thylakoid membranes of chloroplasts: H atoms not shown Accessory pigments absorb different wavelengths of light and pass the energy to chlorophyll a

32. Also a wide range of carotenoids –C40 TETRATERPENES –very hydrophobic –sit in membranes 2 types of carotenoids –CAROTENES (hydrocarbons) –XANTHOPHYLLS (have 1 or 2 oxygens)

33.  -CAROTENE is the most common carotenoid in marine organisms often see a mixture of  -CAROTENE & FUCOXANTHIN in the Phaeophyceae –gives the brown colour

34. PHYCOBILINS are linear tetrapyrroles attached to proteins –red pigments –no ring, no chelation of a metal Only found in Rhodophyceae & Cyanophyceae –and a few species of Cryptophyceae

35. Algae from different locations will often have different absorption and action spectra –CHROMATIC ADAPTATION difference in pigment composition due to a difference in light quality most pronounced when comparing algae grown at different depths Allows for optimal PS with the different wavelengths of light seen at different depths

36. occurs within and between species In general, less light means more pigment e.g. Sea Lettuce (Ulva spp) move from high to low light –10x less: 300 to 30  E.m -2.s -1 chl a,b & c go up 700%

37. One pigment doesn’t respond in this way FUCOXANTHIN –yellowish pigment found in brown algae –probably because it performs 2 functions light harvesting protection from high light levels