Calcification

1. Calcification

2. Calcification • Calcite • Aragonite • Magnesian calcite • DIC - dissolved inorganic carbon • CO2 (aq) • HCO3- • CO3--

3. 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--

4. 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

6. 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

7. 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

8. 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

9. 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

10. Environmental Effects of Calcification • When atmospheric [CO2] increases, what happens to calcification rate ? • goes down • more CO2 should help calcification ? • No • Look at the chemistry

11. 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

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

14. 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

15. 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.

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 19th 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):

28. Overall productivity of the reef: 4.1 - 14.6 gC/m2/d • includes • epilithic algae, on rock, sand etc., • few phytoplankton • seagrasses • coral etc.

29. Overall productivity of the reef: 4.1 - 14.6 gC/m2/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.