1. Productivity and the Coral Symbiosis II

6. Polyp can survive extended periods with no external food source Tight internal N-cycling and algal PS Polyp lays down extensive lipid reserves to be drawn on in times of starvation High light and high food availability –ejection of pellets containing viable algal cells Control of algal cell number ? Algae divide within host polyp

7. Analyze algal cell –C,H,O from PS –N,P,S, from host (normally limiting) Symbiosis controlled by host Polyp controls permeability of algal membrane “signal molecules”

8. Freshly isolated zooxanthellae Incubate in light with 14 CO 2 Release very little organic C into medium Add some polyp extract - releases lots of organic carbon into medium Other cnidarian extracts work

9. 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

10. 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

11. Alga stores CHO – starch Broken down at night Polyp stores lipid – fat bodies Energy reserve Algal PS: 90% fixed C to coral host Used for metabolic functions Growth, reproduction & Calcium deposition

12. Calcification - growth of the reef

13. 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

14. Calcification Calcite Aragonite Magnesian calcite (Mg carbonate)

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

16. 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

17. Calcification

18. 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 --

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

20. 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

21. 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 --

22. 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

24. 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

25. 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

26. 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

27. 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

28. 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

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

30. 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

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

33. 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

34. 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.