1. Coral Structure and Function II

2. Alga donates most of it’s fixed C to polyp –used for resp, growth, etc. Polyp respires –releases CO 2 to alga Polyp excretes N waste - NH 3 –used by alga Polyp also releases PO 4 -, SO 4 -, NO 3 - to alga –1000x more conc. than in seawater –Algae grow faster - helps polyp

3. FOOD CHOProtein AAsSugarsFatty acids Alga Polyp NH 3 CO 2 O2O2 O2O2 NH 3 AAs Protein AAsSugars CHO Lipid ATP NADPH Fatty acids Growth & metabolism Growth & metabolism glycerol H2OH2OH2OH2O LIGHT PO 4 - SO 4 - ATP

4. Mar Drugs. 2010; 8(10): 2546–2568.

5. Alga stores CHO – starch Broken down at night Polyp stores lipid – fat bodies Energy reserve Algal Photosynthesis base of reef productivity Energy source for reef building

6. Overall productivity of the reef: 4.1 - 14.6 gC/m 2 /d this is organic carbon production must also consider carbonate production (deposition of physical structure of the reef) –Get about half of this from the coral symbiosis –the rest from the calcareous green & reds algae

7. CALCAREOUS ALGAE (greens & reds) are major contributors to reef calcification –the more flexible magnesian calcite last 25 years - role of these algae receive more attention –play a much bigger role in calcium deposition than previously thought 10% of all algae CALCIFY (about 100 genera)

8. Calcification - growth of the reef

9. In ocean, mostly find 3 forms of CaC0 3 Calcite –Mostly of mineral origin Aragonite –Fibrous, crystalline form, mostly from corals Magnesian calcite –Smaller crystals, mostly plant origin

10. Calcification Calcite Aragonite Magnesian calcite (Mg carbonate)

11. Examples: organismCaCO 3 Molluscscalcite & aragonite Coralsjust aragonite Some green algaejust aragonite Red algaemagnesian calcite Spongesaragonite (with silica) Some bryozoansall 3

12. Corals remove Ca ++ & CO 3 -- from seawater Combines them to CaCO 3 transports them to base of polyp –Calcicoblastic epidermis minute crystals secreted from base of polyp Energy expensive –Energy from metabolism of algal PS products

13. Calcification

14. 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 --

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

16. 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

17. 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 --

18. 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

20. 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

21. 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

22. 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

23. 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

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

25. 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 --

26. 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

27. 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

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

30. 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 ++

31. 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

32. 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.

33. Productivity and the Coral Symbiosis: Reef Photosynthesis

34. 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.

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

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

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

38. 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

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

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

41. Light Reflected Light Chloroplast Absorbed light Granum Transmitted light

42. 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

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

44. 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

45. 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

46. 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.:

48. 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.

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

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

51. 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

52. 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)

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

54. 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

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