1. Calcification

2. Calcite Aragonite Magnesian calcite DIC - dissolved inorganic carbon –CO 2 (aq) –HCO 3 - –CO 3 --

3. 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 --

4. 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

6. 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

7. 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

8. 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

9. 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

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

11. 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

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

14. 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

15. 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.

16. a major source of calcium deposition on the reef –the coral symbiosis However, CALCAREOUS ALGAE (greens & reds) also major contributors –the more flexible magnesian calcite last 20 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)

17. Most calcareous algae in the Phyla: –RHODOPHYTA (REDS) & CHLOROPHYTA (greens) –1 genus in PHAEOPHYTA (brown - Padina)

18. Many not considered to be “ plants ” until 19 th century –referred to as “ corallines ” –calcareous horny sea organisms 3 genera particularly important in creating reef structure: 1. Halimeda (global) 2. Penicillus (Caribean) 3. Tydemania (Indo-pacific)

19. Halimeda variety of substrates from sand to rock different species adapted to specific substrates –lagoon - large holdfast (1-5cm) deep into the sand –on rock - small (1cm) in crevices –sprawl across coral debris - attached by threadlike filaments

21. variety allows Halimeda to colonize all zones of the reef –except very high energy areas like reef crest, (find calcareous reds here) Halimeda particularly abundant in lagoon and the back- and fore-reef areas –so not much in Bonaire

22. Halimeda grows quickly produces a new segment overnight –a whitish mass –turns green in the morning –induction of chlorophyll synthesis by light –after greening, it lays down the magnesian calcite and stiffens up

24. Estimates from Great Barrier Reef –Halimeda doubles its biomass every 15d. –equates to 7g dry wt. per day per sq m. Segments get broken off –settle on lagoon floor –in sand grooves –adding solid material

25. Halimeda grows down to 150m –light intensity is 0.05% of surface –grows slowly here, uses different pigments –this is about the limit for the Chlorophyta –algae growing deeper than this are in the Rhodophyta Texts often say euphotic zone ends at 1% surface light –not the case, reds can be found as deep as 268m.

26. Productivity no single major contributor to primary production due to a mixture of organisms - can be different at different locations Includes: –Fleshy and calcareous macroalgae –Sea grasses –Zooxanthellae

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

28. Overall productivity of the reef: 4.1 - 14.6 gC/m 2 /d includes –epilithic algae, on rock, sand etc., –few phytoplankton –seagrasses –coral etc.

29. 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 greens and reds.

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