1. Calcification - growth of the reef

2. CO 2 and seawater What forms of C are available to the coral ? Organic and inorganic forms DIC - dissolved inorganic carbon –CO 2 (aq) –HCO 3 - –CO 3 --

3. DIC comes from: –Weathering –Dissolution of oceanic rock –Run-off from land –Animal respiration –Atmosphere –etc.

4. DIC in ocean constant over long periods Can change suddenly on local scale –E.g. environmental change, pollution Average seawater DIC = 1800-2300  mol/Kg Average seawater pH = 8.0 - 8.2 pH affects nature of DIC

5. Carbon and Seawater normal seawater - more HCO 3 - than CO 3 -- when atmospheric CO 2 dissolves in water –only 1% stays as CO 2 –rest dissociates to give HCO 3 - and CO 3 --

6. H 2 O + CO 2 (aq) H 2 CO 3 HCO 3 - + H + (1) HCO 3 - CO 3 -- + H + (2) equilibrium will depend heavily on [H + ] = pH relative amounts of different ions will depend on pH

8. dissolved carbonate removed by corals to make aragonite Ca ++ + CO 3 -- CaCO 3 (3) pulls equilibrium (2) over, more HCO 3 - dissociates to CO 3 -- HCO 3 - CO 3 -- + H + (2) removes HCO 3 -, pulls equilibrium in eq (1) to the right H 2 O + CO 2 (aq) H 2 CO 3 HCO 3 - + H + (1) more CO 2 reacts with water to replace HCO 3 -, thus more CO 2 has to dissolve in the seawater

9. Can re-write this carbon relationship: 2 HCO 3 - CO 2 + CO 3 -- + H 2 O used to be thought that –symbiotic zooxanthellae remove CO 2 for PS –pulls equation to right –makes more CO 3 -- available for CaCO 3 production by polyp No

10. demonstrated by experiments with DCMU –stops PS electron transport, not CO 2 uptake removed stimulatory effect of light on polyp CaCO 3 deposition therefore, CO 2 removal was not playing a role also, in deep water stony corals –if more food provided, more CaCO 3 was deposited –more energy available for carbonate uptake & CaCO 3 deposition

11. Now clear that algae provide ATP (via CHO) to allow polyp to secrete the CaCO 3 and its organic fibrous matrix Calcification occurs 14 times faster in open than in shaded corals Cloudy days: calcification rate is 50% of rate on sunny days There is a background, non-algal-dependent rate

12. Environmental Effects of Calcification When atmospheric [CO 2 ] increases, what happens to calcification rate ? –goes down –more CO 2 should help calcification ? –No

13. Add CO 2 to water –quickly converted to carbonic acid –dissociates to bicarbonate: H 2 O + CO 2 (aq) H 2 CO 3 HCO 3 - + H + (1) HCO 3 - CO 3 -- + H + (2) Looks useful - OK if polyp in control, removing CO 3 --

14. Add CO 2 to water –quickly converted to carbonic acid –dissociates to bicarbonate: H 2 O + CO 2 (aq) H 2 CO 3 HCO 3 - + H + (1) HCO 3 - CO 3 -- + H + (2) Looks useful - OK if polyp in control, removing CO 3 -- BUT, if CO 2 increases, pushes eq (1) far to right

15. Add CO 2 to water –quickly converted to carbonic acid –dissociates to bicarbonate: H 2 O + CO 2 (aq) H 2 CO 3 HCO 3 - + H + (1) HCO 3 - CO 3 -- + H + (2) Looks useful - OK if polyp in control, removing CO 3 -- BUT, if CO 2 increases, pushes eq (1) far to right [H + ] increases, carbonate converted to bicarbonate

16. So, as more CO 2 dissolves, more protons are released acidifies the water the carbonate combines with the protons produces bicarbonate decreases carbonate concentration

18. Also, increase in [CO 2 ] –leads to a less stable reef structure –the dissolving of calcium carbonate H 2 O + CO 2 + CaCO 3 2HCO 3 - + Ca ++

19. Also, increase in [CO 2 ] –leads to a less stable reef structure –the dissolving of calcium carbonate H 2 O + CO 2 + CaCO 3 2HCO 3 - + Ca ++ addition of CO 2 pushes equilibrium to right – increases the dissolution of CaCO 3

20. anything we do to increase atmospheric [CO 2 ] leads to various deleterious effects on the reef: Increases solubility of CaCO 3 Decreases [CO 3 -- ] decreasing calcification Increases temperature, leads to increased bleaching Increases UV - DNA, PS pigments etc.

21. Great Barrier Reef: Calcification of Porites down 14% since 1990 –328 Porites corals sampled at 69 locations –compared several growth parameters over 400 years - 1572 to 2005.

22. Great Barrier Reef: Calcification of Porites down 14% since 1990 –328 Porites corals sampled at 69 locations –compared several growth parameters over 400 years - 1572 to 2005.

25. Productivity and the Coral Symbiosis: Reef Photosynthesis

26. 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.

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

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

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

30. 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

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

32. 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

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

34. 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

35. 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

36. 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.:

38. 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.

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

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

41. 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 its colour)

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

43. 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

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

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

47. 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

48. 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