1. Calcification - growth of the reef

2. In ocean, mostly find 3 forms of CaC03 Calcite
Mostly of mineral origin
Aragonite
Fibrous, crystalline form, mostly from corals
Magnesian calcite
Smaller crystals, mostly plant origin

3. Calcification
Calcite
Aragonite
Magnesian calcite
(Mg carbonate)

4. Examples: organism CaCO3 Molluscs calcite & aragonite Corals
just aragonite
Some green algae
Red algae
magnesian calcite
Sponges
aragonite (with silica)
Some bryozoans
all 3

5. remove Ca++ & CO3-- from seawater Combines them to CaCO3
Corals
remove Ca++ & CO3-- from seawater
Combines them to CaCO3
transports them to base of polyp
Calcicoblastic epidermis
minute crystals secreted from base of polyp
Energy expensive
Energy from metabolism of algal PS products

6. Calcification

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

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

9. DIC in ocean constant over long periods
Can change suddenly on local scale
E.g. environmental change, pollution
Average seawater DIC = mmol/Kg
Average seawater pH =
pH affects nature of DIC

10. 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--

11. H2O + CO2 (aq) H2CO3 HCO3- + H+ (1)
HCO CO H+ (2)
equilibrium will depend heavily on [H+] = pH
relative amounts of different ions will depend on pH

13. dissolved carbonate removed by corals to make aragonite
Ca CO CaCO (3)
pulls equilibrium (2) over, more HCO3- dissociates to CO3--
HCO CO H+ (2)
removes HCO3-, pulls equilibrium in eq (1) to the right
H2O + CO2 (aq) H2CO HCO H (1)
more CO2 reacts with water to replace HCO3-, thus more CO2 has to dissolve in the seawater

14. 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

15. 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

16. 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

17. Environmental Effects of Calcification
When atmospheric [CO2] increases, what happens to calcification rate ?
goes down
more CO2 should help calcification ? No

18. H2O + CO2 (aq) H2CO3 HCO3- + H+ (1) HCO3- CO3-- + H+ (2)
Add CO2 to water
quickly converted to carbonic acid
dissociates to bicarbonate:
H2O + CO2 (aq) H2CO HCO H+ (1)
HCO CO H+ (2)
Looks useful - OK if polyp in control, removing CO3--

19. H2O + CO2 (aq) H2CO3 HCO3- + H+ (1) HCO3- CO3-- + H+ (2)
Add CO2 to water
quickly converted to carbonic acid
dissociates to bicarbonate:
H2O + CO2 (aq) H2CO HCO H+ (1)
HCO CO H+ (2)
Looks useful - OK if polyp in control, removing CO3--
BUT, if CO2 increases, pushes eq (1) far to right

20. H2O + CO2 (aq) H2CO3 HCO3- + H+ (1) HCO3- CO3-- + H+ (2)
Add CO2 to water
quickly converted to carbonic acid
dissociates to bicarbonate:
H2O + CO2 (aq) H2CO HCO H+ (1)
HCO CO 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

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

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

24. addition of CO2 pushes equilibrium to right
Also, increase in [CO2]
leads to a less stable reef structure
the dissolving of calcium carbonate
H2O + CO2 + CaCO HCO Ca++
addition of CO2 pushes equilibrium to right
increases the dissolution of CaCO3

25. Increases UV - DNA, PS pigments etc.
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.

26. Reef Photosynthesis

27. principally through photosynthesis
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. gC/m2/d
TropicalCoral Reef
Tropical open ocean
Mangrove
2.46
Tropical Rain Forest
5.5
Oak Forest
3.6

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

30. net productivity values (varies with location):
gC/m2/d
Calcareous reds
1 - 6
Halimeda
2 -3
Seagrass
1 - 7
N.S. kelp 5

31. 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

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

33. Light
Reflected
Chloroplast
Absorbed
light
Granum
Transmitted

34. 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

35. a very specific part of the EM spectrum
Photosynthetically Active Radiation nm

36. Gamma rays X-rays UV Infrared Micro- waves Radio 10–5 nm 10–3 nm 1 nm
380
450
500
550
600
650
700
750 nm
Visible light
Shorter wavelength
Higher energy
Longer wavelength
Lower energy

37. 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

38. 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.:

40. 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.

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

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

43. In the thylakoid membrane,
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

44. LHC = pigment molecules bound to proteins
funnel energy of photons to the reaction center
reaction-center chlorophyll absorbs energy
One of its electrons gets bumped up to a primary electron acceptor
electron transport
ATP & NADPH production

45. (INTERIOR OF THYLAKOID)
Photosystems
Primary election
acceptor
Photon
Thylakoid
Light-harvesting
complexes
Reaction
center
Photosystem
STROMA
Thylakoid membrane
Transfer
of energy
Special
chlorophyll a
molecules
Pigment
THYLAKOID SPACE
(INTERIOR OF THYLAKOID) e–

46. Light The visible light spectrum includes
the colors of light we can see
the wavelengths that drive photosynthesis
Photosymthetic pigments absorb light

47. Gamma rays X-rays UV Infrared Micro- waves Radio 10–5 nm 10–3 nm 1 nm
380
450
500
550
600
650
700
750 nm
Visible light
Shorter wavelength
Higher energy
Longer wavelength
Lower energy

48. Light
Reflected
Chloroplast
Absorbed
light
Granum
Transmitted

49. 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)

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

51. 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

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

54. Marine PS pigments 3 major groups of PS pigments in marine organisms
Chlorophylls
Phycobiliproteins
Carotenoids

55. 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

56. 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

57. Chlorophyll a Chlorophyll b Is the main photosynthetic pigment
Is an accessory pigment C CH
CH2 N
H3C Mg H
CH3 O
CHO
in chlorophyll a
in chlorophyll b
Porphyrin ring:
Light-absorbing
“head” of molecule
note magnesium
atom at center
Hydrocarbon tail:
interacts with hydrophobic
regions of proteins inside
thylakoid membranes of
chloroplasts: H atoms not
shown
Accessory pigments absorb different wavelengths of light and pass the energy to chlorophyll a

58. Also a wide range of carotenoids
C40 TETRATERPENES
very hydrophobic
sit in membranes
2 types of carotenoids
CAROTENES (hydrocarbons)
XANTHOPHYLLS (have 1 or 2 oxygens)

59. b-CAROTENE is the most common carotenoid in marine organisms
often see a mixture of b-CAROTENE & FUCOXANTHIN (another carotenoid) in the Phaeophyceae
gives the brown colour

60. PHYCOBILINS are linear tetrapyrroles attached to proteins
red pigments
no ring, no chelation of a metal
Only found in Rhodophyceae & Cyanophyceae
and a few species of Cryptophyceae