Calcification - growth of the reef

1. Calcification - growth of the reef

2. CO2 and seawater • What forms of C are available to the coral ? • Organic and inorganic forms • DIC - dissolved inorganic carbon • CO2 (aq) • HCO3- • CO3--

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 mmol/Kg • Average seawater pH = 8.0 - 8.2 • pH affects nature of DIC

5. Carbon and Seawater • normal seawater - more HCO3- than CO3-- • when atmospheric CO2 dissolves in water • only 1% stays as CO2 • rest dissociates to give HCO3- and CO3--

6. H2O + CO2 (aq) H2CO3 HCO3- + H+ (1) HCO3-CO3-- + 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++ + CO3-- CaCO3 (3) pulls equilibrium (2) over, more HCO3- dissociates to CO3-- HCO3-CO3-- + H+ (2) removes HCO3-,pulls equilibrium in eq (1) to the right H2O + CO2 (aq) H2CO3 HCO3- + H+ (1) more CO2 reacts with water to replace HCO3-, thus more CO2 has to dissolve in the seawater

9. Can re-write this carbon relationship: 2 HCO3-CO2 + CO3-- +H2O • used to be thought that • symbiotic zooxanthellae remove CO2 for PS • pulls equation to right • makes more CO3-- available for CaCO3 production by polyp • No

10. demonstrated by experiments with DCMU • stops PS electron transport, not CO2 uptake • removed stimulatory effect of light on polyp CaCO3 deposition • therefore, CO2 removal was not playing a role • also, in deep water stony corals • if more food provided, more CaCO3 was deposited • more energy available for carbonate uptake & CaCO3 deposition

11. Now clear that algae provide ATP (via CHO) to allow polyp to secrete the CaCO3 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 [CO2] increases, what happens to calcification rate ? • goes down • more CO2 should help calcification ? • No

13. Add CO2 to water • quickly converted to carbonic acid • dissociates to bicarbonate: H2O + CO2 (aq) H2CO3 HCO3- + H+ (1) HCO3-CO3-- + H+ (2) • Looks useful - OK if polyp in control, removing CO3--

14. Add CO2 to water • quickly converted to carbonic acid • dissociates to bicarbonate: H2O + CO2 (aq) H2CO3 HCO3- + H+ (1) HCO3-CO3-- + H+ (2) • Looks useful - OK if polyp in control, removing CO3-- • BUT, if CO2 increases, pushes eq (1) far to right

15. Add CO2 to water • quickly converted to carbonic acid • dissociates to bicarbonate: H2O + CO2 (aq) H2CO3 HCO3- + H+(1) HCO3-CO3-- + H+(2) • Looks useful - OK if polyp in control, removing CO3-- • BUT, if CO2 increases, pushes eq (1) far to right • [H+] increases, carbonate converted to bicarbonate

16. So, as more CO2 dissolves, • more protons are released • acidifies the water • the carbonate combines with the protons • produces bicarbonate • decreases carbonate concentration

18. Also, increase in [CO2] • leads to a less stable reef structure • the dissolving of calcium carbonate H2O + CO2 + CaCO3 2HCO3- + Ca++

19. Also, increase in [CO2] • leads to a less stable reef structure • the dissolving of calcium carbonate H2O + CO2 + CaCO3 2HCO3- + Ca++ • addition of CO2 pushes equilibrium to right • increases the dissolution of CaCO3

20. anything we do to increase atmospheric [CO2] leads to various deleterious effects on the reef: • Increases solubility of CaCO3 • Decreases [CO3--] 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 CO2 • principally through photosynthesis • chemosynthesis much less important. • All life on earth is directly or indirectly dependant on primary production.

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 productivityvalues (varies with location):

30. Overall productivity of the reef: 4.1 - 14.6 gC/m2/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. 1 m 106 nm 106 nm 10–5 nm 1 nm 10–3 nm 103 nm 103 m Micro- waves Radio waves Gamma rays X-rays UV Infrared Visible light 380 450 500 550 600 650 700 750 nm Shorter wavelength Longer wavelength Lower energy Higher 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 • mE.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. Mesophyll Chloroplast 5 µm Outer membrane Thylakoid Intermembrane space Thylakoid space Granum Stroma Inner membrane 1 µm

40. CO2 NADP ADP + P i CALVIN CYCLE [CH2O] (sugar) O2 An overview of photosynthesis H2O Light LIGHT REACTIONS ATP NADPH Chloroplast

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. Chlorophyll a Chlorophyll b Absorption of light by chloroplast pigments Carotenoids Wavelength of light (nm) 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, c1, c2 & d • a all green plants and algae • b Chlorophyceae • c1 & c2 Phaeophyceae • d Rhodophyceae