CO2 Chemistry Effects on Benthic Calcifying Communities

Chris LangdonRosenstiel School of Marine and

Atmospheric ScienceUni. of Miami

How will rising CO2 impact benthic communities?

– pCO2 has increased by 32% between 1880 and 2000 (280 vs. 370 uatm) Houghton et al., 2002.

– Sea surface temperatures have risen by 0.6°C over the same period (Sheppard and Rioja-Nieto, 2005).

– Coral reef ecosystems are negatively affected by the increase of both temperature and pCO2.

• Increased temperature leads to loss of zooxanthellae (bleaching)

• Increased pCO2 leads to reduced calcification of corals and algae

What are the concerns?

• Reduced geographic range – As pCO2 rises, regions with a saturation state sufficient to support vigorous coral growth will shrink.

• Reduced tolerance to other environmental fluctuations – rising pCO2 may reduce thermal optimum for growth (Reynaud et al. 2003).

• Reduced rate of recovery following disturbance– Reduced skeletal growth to repair damage done by storms,

predators and humans– Reduced fecundity– Reduced survivorship of early life stages

• Accelerated phase shift from coral to algal dominance

Modes of manipulation

1. Constant TA. Adjust DIC with CO2 gas. (Simulates natural situation)

2. Constant DIC. Adjust TA with acid or base.

3. Constant pH. Adjust TA and DIC.

1600

1700

1800

1900

2000

200 400 600 800

pCO2, uatm

HC

O3

- , u

mo

l kg

-1

0

100

200

300

CO

32

- , u

mo

l kg

-1

HCO3-

CO32-

Natural situation: adding CO2 by diffusion

Artificial situation: changing TA by addition of acid or base without changing DIC

1600

1700

1800

1900

2000

200 400 600 800

pCO2, uatm

HC

O3

- , u

mo

l kg

-1

0

100

200

300

CO

32

- , u

mo

l kg

-1

Natural

Change TA

HCO3-

CO32-

1000

2000

3000

4000

200 400 600 800 1000

pCO2, uatm

HC

O3

- , u

atm

0

100

200

300

400

CO

32

- , u

mo

l kg

-1

Added HCO3

Natural

HCO3-

CO32-

HCO3-

CO32-

Artificial situation: adding Na2HCO3

both TA and DIC increase

What happens to the photosynthesis and calcification of a coral or alga when the carbonate chemistry is altered?

0

50

100

150

200

250

300

0 2000 4000 6000

TDIC, umol kg-1

CO

2 a

q a

nd

CO

32-,

um

ol k

g-1

0

1000

2000

3000

4000

HC

O3- , u

mo

l kg

-1

CO2

CO3

HCO3

Both photosynthesis and calcification increased

Ptns

Calcif

Borowitzka and Larkum 1976 looked at effect of increasing DIC on the photosynthesis and calcification of the green calcareous alga Halimeda tuna byadding Na2HCO3

0

200

400

600

800

1000

6 7 8 9 10

pH

CO

2 a

q a

nd

CO

32-,

um

ol k

g-1

0

1000

2000

HC

O3- , u

mo

l kg

-1

CO2

CO3

HCO3

pH

Ptns

Calcif

Photosynthesis increased and calcification decreased!

Borowitzka and Larkum 1976 also varied pH while holding DIC constant, mimicking thenatural situation

Conclusion: Ptns using CO2 aqand calcif. using CO3

2-

Reynaud et al. 2003 looked at the effects of temperature and CO2 on the photosynthesis, respiration and calcification of the coral Stylophora pistillata. Corals were grow for 5 weeks at each condition.

•Elevated pCO2 caused slight reduction in net photosynthesis.•Net photosynthesis increased with temperature as expected for this species.•Cell specific density was 24% higher at elevated pCO2 suggesting some disruption in the balance of growth rates of the algal and animal cells.•Dark respiration not effected by elevated pCO2 or temperature.

•Elevated pCO2 caused no significant change in calcification at 25°C but a 50% reduction at 28°C.

•The reduction in calcification was immediate and persisted unchanged over the 5 wk experiment.

•At normal pCO2, the increase in temperature caused an increase in calcification but at elevated pCO2 the increase in temperature caused a 34% reduction in calcification.

•One interpretation is that elevated pCO2 reduced the thermal optimum for this species.

Interesting interactions of temperature and CO2 on coral calcification

Experiment in an outdoor flowing seawater flume

•200 closely packed colonies of corals forming a patch 2.2 m2 in area simulating a patch of reef with 100% coral cover.

•Flowing seawater duplicates turbulent boundary conditions in the field.

•Receiving full natural sunlight

•Carbonate chemistry manipulated by addition of HCl or NaOH.

Langdon, C., and M.J. Atkinson, Effect of elevated pCO2 on photosynthesisand calcification of corals and interactions with seasonal change in temperature/irradiance and nutrient enrichment, J. Geophysical Res., in press.

Effect of CO2

August 199927.3°C 37 E m-2 d-1

January 200023.4°C 19 E m-2 d-1

0

10

20

30

40

50

60

Calcif NP c NP o

mm

ol m

-2 h

-1

1.0X n=18

1.7X n=9

0

10

20

30

40

50

60

Calcif NP c NP o

mm

ol

m-2

h-1

1.0X n=3

1.4X n=2

2.0X n=1

Langdon and Atkinson, in press

Coral net carbon production may benefit from rise in pCO2

y = 2.64x + 75.83

R2 = 0.60

020

406080

100120

140160

0 5 10 15 20 25

[CO2] aq, mmol kg-1

NP

C,

% o

f ra

te a

t p

rese

nt

day

[C

O2]

aq

Decrease in coral calcification is not due to an adverse effect of acidification on the zooxanthellae.

Coral calcification decreases with decreasing saturation state

0

5

10

15

20

25

0 1 2 3 4

Wa

G,

mm

ol

CaC

O3 m

-2 h

-1

Aug-99

Jan-00

Model

G = (8±1)(Wa-1)r2=0.87

First-order rate law explains 87% of variability in calcification of this coral assemblage

Aragonite saturation state

Wa = [Ca2+][CO32-]/K’sp

where K’sp is the solubility product for the particular mineral phase of carbonate of interest, i.e. calcite, aragonite or high Mg-calcite

W has been found to be useful predictor of the rate of calcification in inorganic systems. The rate law R=k(W-1)n gives a good fit to many data sets.

Is it pH or Wa?

y = 0.48x + 2.80

R2 = 0.71

0

2

4

6

8

0 2 4 6

Wa

Cal

cif.

, mm

ol l-1

h-1

Calcification varied 3-fold at constant pH indicating that change in seawater pH not required to explain decrease in calcification.

TA DIC pCO2 pH sw Wa

832 697 190 7.91 0.81

1223 1068 311 7.92 1.16

1504 1343 427 7.90 1.37

2013 1792 491 7.91 2.06

3562 3222 863 7.96 3.82

4774 4270 950 8.01 5.91

6195 5591 1311 7.97 7.41

Langdon unpublished

Agegian 1985 found a linear relationship between linear extension of the red coralline alga Porolithon and saturation state

Red Sea coral Stylophora pistillata

0

20

40

60

80

100

120

0 2 4 6 8

Wa

Cal

cif.

, %

of

rate

at W

a=

4.6

Gattuso et al. 1998 variedCa

Reynaud et al. 2003 25Cvaried pCO2

Reynaud et al. 2003 28Cvaried pCO2

Pacific and Caribbean branching corals Porites compressa/P. porites/Montipora capitata

0

20

40

60

80

100

120

140

160

0 2 4 6 8

Wa

Cal

cif.

, %

of

rate

at W

a=

4.6 P. compressa (Marubini et al. 2001)

varied TA

P. compressa (Marubini and Atkinson1999) varied TA

P. porites (Marubini and Thake 1999)added HCO3

P. compressa/M. capitata (Langdonand Atkinson in press) 27.3C variedTAP. compressa/M. capitata (Langdonand Atkinson in press) 23.4C variedTA

G=16.1Wa+21.7R2=0.82

Pacific massive corals Porites lutea/Fungia sp.

0

50

100

150

200

0 2 4 6 8

Wa

Cal

cif.

, %

of

rate

at W

a=

4.6

P. lutea (Ohde andHossain 2004) varied TA

P. lutea (Hossain andOhde in press) varied TA

Fungia sp. (Hossain andOhde in press) varied TA

G=24.6Wa-11.7R2=0.81

Assortment of Red Sea corals of branching and foliose structure

0

20

40

60

80

100

120

0 2 4 6 8

Wa

Cal

cif.

, %

of

rate

at W

a=

4.6

G. fascicularis

P. cactus

T. reniformis

A. verweyi

Marubini et al. 2003

G=7.6Wa+65.2R2=0.96

Varied TA

Summary of coral and reef community response to saturation state

-150

-100

-50

0

50

100

150

0 2 4 6W

a

Ca

lcif

., %

of

rate

at W

a=4

.6

P. compressa/P. porites/M. capitata

P. lutea/Fungia sp.

A. verweyi/G. fascicularis/P. cactus/T.reniformis

S. pistillata

Monaco mesocosm Leclercq et al. 2000, 2002

B2 mesocosm Langdon et al. 2000, 2003

Bahama Banks Broecker and Takahashi 1966;Broecker et al., 2003

Okinawa reef Ohde and van woesik 1999

Shiraho Reef Suzuki et al. 1995

2065

Effect of a doubling in pCO2 on calcificationWide range of sensitivity

Species Source % decline by 2065

S. pistillata Gattuso et al. 1998 -3

P. compressa Marubini et al. 2001 -16

G. fascicularis Marubini et al. 2002 -11

P. cactus “ “ -13

T. reniformis “ “ -9

A. verweyi “ “ -13

S. pistillata (25C) Reynaud et al. 2003 +7

“ “ (28C) “ “ -57

P. lutea Ohde and Hossain 2004 -38

P. compressa/M. capitata Langdon and Atkinson in press

-41

P. lutea Hossain and Ohde, in press -33

Fungia sp. “ “ -60

-8%

-46%

Predictions based on pCO2 alone are probably underestimates because we also need to take

the temperature increase into account

• There is evidence that many corals are currently at or slightly above their thermal optimum.

• This means that any increase in the average annual temperature will result in reduced calcification.

• Estimating the temperature effect is complicated because some species possess the ability to acclimate to new temperature regime while others do not.

Temperature dependence of coral calcification

0

20

40

60

80

100

120

18 20 22 24 26 28 30 32

Temperature, °C

Rel

ativ

e C

alci

f. R

ate

M. verrucosa Coles andJokiel 1978

M. verrucosa Houck et al.1977

P. lobata Houck et al.1977

P. damicornis Houck etal. 1977

Marshall and Clode 2004

S. pistillata Reynaud-Vaganay et al. 1999

Acropora sp. Reynaud-Vaganay et al. 1999

P. damicornis 28CClausen and Roth 1975

P. damicornis 23CClausen and Roth 1975

Optimum temperature for calcification is at or below current peak summer temperatures for many species.

Bleaching threshold

Data for Pacific corals

• Cellular mechanism underlying the response of coral calcification to an elevation of pCO2 in the external environment is poorly understood.

• Calcification is known to occur within a membrane enclosed space. Ca2+ and HCO3

- ions are thought to be actively transported across the membrane and into the calcifying space.

• In this scenario it is not obvious how changes in external pH or [CO3

2-] would influence the rate of calcification.• The explanation may be that the calcifying space (CS) is

leaky and some Ca2+, HCO3- and CO3

2- ions may arrive via leakage of seawater into the CS.

• In this scheme corals that have a tight CS would exhibit little sensitivity to change in the chemistry of the external environment and corals with a leakier CS would exhibit more sensitivity.

Role in the global carbon cycle

• Calcification (shallow water and pelagic) and volcanism are the main sources of CO2 to the atmosphere that counter-balance the removal of CO2 via weathering of silicate rock and burial of organic matter in deep sea sediments.

• As atmospheric CO2 rises the magnitude of the CO2 flux from calcification is going to diminish and at some point it will switch and become a sink as carbonate deposits start to dissolve.

• If we lose calcifying organisms we will also lose a negative feedback control on atmospheric CO2.

-50

0

50

100

150

0 100 200 300 400

CO32-, mmol/kg

Cal

cif.

mm

ol/m

2 /d

1200 500 250

pCO2, matm

Response of Biosphere 2 coral reef mesocosm

Dissolution

Role of coral reefs as a source of CO2 could reverse

y = 8.92x - 17.16

R2 = 0.67

-10

-5

0

5

10

15

20

0 1 2 3 4 5

Warag

Eff

lux,

mm

ol

CO

2/m

2/d

Unpublished data from Biosphere 2 experiment

Conclusions We need to understand the the temporal

and spatial changes of the carbon system in the global oceans and their impacts on biological communities and ecosystems.

There is a need for longer term experiments to see if marine calcifying organisms are able to acclimate to elevated CO2

and/or temperature if given sufficient time.There is a need to understand why certain species are able to adapt to life in low saturation state water.There is a need for manipulative experiments to look at the effects of high CO2 on coral calcification, reproduction, settlement, and reattachment of fragments.Need to know about the effect of high CO2 on the processes that recycle the reef framework, i.e. bioerosion and dissolution.

Fossil fuel emissions are acidifying the ocean

After Turley et al., 2005AAAS Annual MeetingWashington, D.C., 2005

Observations at the Hawaiian Ocean Time Series (HOTS) station confirming

ocean acidification

7.9

8.0

8.1

8.2

1/1/90 1/1/92 1/1/94 1/1/96 1/1/98 1/1/00

Date

pH

sw

s

-0.03±0.01 units per decade

Changes in CO2 chemistry based on IPCC “Business as usual”

(percent change from pre-industrial)

Glacial Pre-industrial

Present day

Future

2XCO2

Future

3XCO2

pCO2 180 (-56) 280 380 (36) 560 (100) 840 (200)

CO2 7 (-29) 9 13 (44) 18 (100) 25 (178)

HCO3- 1666 (-4) 1739 1837 (5) 1925 (11) 2004 (15)

CO32- 279 (-20) 222 186 (-16) 146 (-34) 115 (-48)

pH sws 8.32 8.16 8.05 7.91 7.76

Wa 4.26 (-19) 3.44 2.90 (-16) 2.29 (-33) 1.81 (-47)

Modified from Feely et al., (2001)

Why are some corals more sensitive to changes in external [CO3

2-]?

Seawater reaches the calcifying spacevia diffusion thru porous skeleton,junctions between cells or exocytosisof vacuoles.

Light-activated Ca-ATPase pumps Ca2+ into the calcifying space (CS) during the day. However, its main role is to transport H+ out of the CS thereby maintaining a pH favorable to the conversion of CO2 to CO3

2-.CS

Cohen and McConnaughey 2003

Corals with strong Ca-ATPase activitywould be predicted to be less sensitiveto a decrease in ambient [CO3

2-] whilecorals depending more on passive transport would be more sensitive.