This appendix serves as an example of the wide variety of experimental studies on the effects of ocean acidification on calcifying marine organisms. We focus here on calcifying algae, corals, and carbonate-dominated systems, because more studies have been conducted on this collective group than on others. This table lists only those studies published through 2009 that used realistic carbonate chemistry manipulations; i.e., those that were consistent with projected changes in the carbonate chemistry of seawater due to natural forcing. Note that pCO2 is reported both in units of parts per million (ppm) and microatmospheres (μatm); the two units can be considered essentially equivalent.
Organism/System | Summary of findings | Reference |
Calcifying Algae Crustose coralline algae (unidentified species) |
Manipulation: Acid addition Duration: 7 weeks Design: Outdoor continuous-flow mesocosms: control at ambient reef pCO2 (average 380 ppm), others manipulated to ambient + 365 ppm. Recruitment and growth of crustose coralline algae were measured on clear acrylic cylinders after 7 weeks in control and manipulated flumes. Results: Under high CO2 conditions, CCA recruitment rate decreased by 78% and percentage cover decreased 92% relative to ambient; non-calcifying algae percent cover increased by 52% relative to ambient. |
Kuffner et al., 2008 |
Rhodoliths of mixed crustose coralline algae including Lithophyllum cf. pallescens, Hydrolithon sp. and Porolithon sp. | Manipulation: Acid addition Duration: 9 months Design: Outdoor continuous-flow mesocosms: control at ambient reef pCO2 (average 380 ppm), others manipulated to ambient + 365 ppm. Rhodolith growth was measured with buoyant weighing. Results: Rhodolith growth in control mesocosms was 250% lower than those in acidified mesocosms; that is, they experienced net dissolution. |
Jokiel et al., 2008 |
Porolithon onkodes | Manipulation: Bubbled CO2 Duration: 8 weeks Design: Algae placed in flow-through aquaria: 2 temperatures: 25–26°C and 28–29°C; 3 pH levels: 8. 0–8.4 (control) 7.85–7.95 and 7.60–7.70. Results: P. onkodes calcification rate in low pH treatment was 130% less (25–26°C) and 190% less (28–29°C) than in control (i.e., net dissolution). |
Anthony et al., 2008 |
Calcareous epibionts on seagrasses (Hydrolithon boreale, H. cruciatum, H. farinosum, Pneophyllum confervicola, P. fragile and P. zonale) | Manipulation: Bubbled CO2 and field observations Duration: 2 weeks Design: In field, calcium carbonate mass on seagrass blades was measured across a natural pH gradient. In lab, seagrass blades with 50–70% cover of crustose coralline algae were collected from the field and placed in aquaria of pH = 8.1 (control) or pH = 7.0. Coralline algal cover was estimated before and after treatments. Results: In field, coralline algal cover was highly correlated with pH, decreasing rapidly below pH = 7.8 and absent at pH = 7.0; in lab experiment, coralline algae were completely dissolved after two weeks at a pH of 7.0, whereas control samples showed no discernable change. |
Martin et al., 2008 |
Rhodoliths of Hydrolithon sp. | Manipulation: Both acid/base addition and bubbled CO2 Duration: 5 days Design: Acid/base additions used to alter pH to multiple levels (7.6, 7.8, 8.2, 8.6, 9.0, 9.4 and 9.8; control was 8.1); CO2 bubbling used to alter pH and DIC to 7.8. Results: Calcification rate was positively correlated with pH in both light and dark experiments; decreasing the pH to 7.8 with CO2 bubbling lowered calcification by 20%. |
Semesi et al., 2009a |
Hydrolithon sp. Mesophyllym sp. Halimeda renschii |
Manipulation: Drawdown of CO2 by seagrass photosynthesis Duration: 2.5 hours Design: In situ open-bottom incubation cylinders; pH and algal calcification rates measured in presence or absence of seagrasses. Results: Seagrass photosynthesis caused pH to increases from 8.3–8.4 to 8.6–8.9 after 2.5 hours; calcification rates increased > 5x for Hydrolithon sp., and 1.6x for Mesophyllum sp. and Halimeda sp. |
Semesi et al., 2009b |
Lithophyllum cabiochae | Manipulation: Bubbled CO2 Duration: 1 year Design: Algae were maintained in aquaria at ambient or elevated temperature (+3°C) and at ambient (~400 ppm) or elevated pCO2 (~700 ppm). Results: No clear pattern of reduced calcification at elevated pCO2 alone, but combination of elevated pCO2 and temperature led to high rates of necroses and death. The dissolution of dead algal thalli at elevated pCO2 was 2–4x higher than under ambient pCO2. |
Martin and Gattuso, 2009 |
Corallina sessilis | Manipulation: Bubbled CO2Duration: 30 days Design: Controlled laboratory experiments to investigate the interactive effects of pCO2 and UV radiation on growth, photosynthesis, and calcification. 2 pCO2 levels (280 and 1000 ppmv), combined with 3 light conditions: PAR alone (solar radiation wavelengths > 395 nm); PAR+UVA (> 320 nm); PAR+UVA+UVB (> 295 nm). Results: Under PAR alone, elevated pCO2 decreased net photosynthetic rate by 29.3%, and calcification rate by 25.6% relative to low pCO2. Elevated pCO2 exacerbated the effects of ultraviolet radiation in inhibiting rates of growth (from 13% to 47%), photosynthesis (from 6% to 20%), and calcification (from 3% to 8%). The authors suggest that the decrease in calcification in C. sessilis at higher pCO2 levels increases its susceptibility to damage by UVB radiation. |
Gao and Zheng, 2009 |
Halimeda incrassata (green alga) and Neogoniolithon spp. (coralline red alga) | Manipulation: CO2 bubbling Duration: 60 days Design: Controlled laboratory experiment to examine changes in calcification under Ωarag = 3.12, 2.40, 1.84, and 0.90 (approx. pCO2 = 409, 606, 903, 2856 ppmv, respectively). SST maintained at 25°C. Results: Calcification rates in both species were higher at Ωarag = 2.40, then declined at lower saturation states. |
Ries et al., 2009 |
Corals Stylophora pistillata |
Manipulation: Altered Ca2+ ion concentration1 Duration: 2.5 hours Design: Controlled laboratory experiment; aragonite saturation changes from 98 to 390% were obtained by manipulating the calcium concentration. Results: Nonlinear increase in calcification rate as a function of aragonite saturation level. |
Gattuso et al., 1998 |
Porites compressa | Manipulation: Acid addition Duration: 5 weeks Design: 760 and 3980 µatm (pH = 8.2 versus 7.2); nitrate additions as well Results: Corals grown in low pH water grew half as fast. |
Marubini and Atkinson, 1999 |
Porites compressa | Manipulation: Acid addition Duration: 10 weeks Design: Controlled laboratory experiments: measured calcification at pCO2 = 199 and 448 µatm, at 3 light levels. In Biosphere 2 coral mesocosm: measured calcification at pCO2 = 186, 336, and 641 µatm. Results: Calcification decreased 30% from pCO2 = 186 to 641, and 11% from pCO2 = 336 to 641 µatm, regardless of light level. |
Marubini et al., 2001 |
Galaxea fascicularis | Manipulation: Altered Ca2+ ion concentration while maintaining pH at 8.11–8.12; temperatures maintained at ambient temperature of collections site1 Duration: Hours Design: Calcium additions to estimated Ωarag from 3.88 (present-day) to 4.83 and 5.77; calcification rate measured with 14C incorporation in skeleton. Results: Calcification rate increased 30–60% at Ωarag = 4.83 and 50–80% at Ωarag = 5.77 relative to Ωarag =3.88. |
Marshall and Clode, 2002 |
Stylophora pistillata | Manipulation: Bubbled CO2 Duration: 5 weeks Design: 2 pCO2 values (460 and 760 µatm) and 2 temperatures (25 and 28°C) Results: Calcification under normal temperature did not change in response to an increased pCO2. Calcification decreased by 50% when temperature and pCO2 were both elevated. |
Reynaud et al., 2003 |
Acropora verweyi Galaxea fascicularis Pavona cactus Turbinaria reniformis | Manipulation: Acid/base addition Duration: 8 days Design: 2 pCO2 values (407–416 and 857–882 µatm), 26.5°C Results: calcification rate in all 4 species decreased 13–18% |
Marubini et al., 2003 |
Porites compressa + Montipora capitata | Manipulation: acid/base addition Duration: 1.5 hours Design: Corals placed in flumes, multiple summer experiments at pCO2 = 460 and 789 µatm; multiple winter experiments at pCO2 = 391, 526, and 781 µatm; additional experiments included additions of PO4 and NH4. Results: Summer calcification rate declined 43% with increase in pCO2 from 460 to 789 µatm; winter rates declined 22% from 391 to 526 µatm; and 80% from 391 to 781 µatm. |
Langdon and Atkinson, 2005 |
Acropora cervicornis | Manipulation: Bubbled CO2 Duration: 16 weeks total Design: Nubbins cultured for 1 week at pCO2=367 µatm, 2 weeks at 714–771 µatm, 1 week at 365 µatm Results: 60–80% reduction in calcification rate at 714–771 µatm relative to controls (357–361 µatm); note that calcification rate did not substantially recover with return to normal pCO2 during 4th week. |
Renegar and Riegl, 2005 |
Acropora eurystoma | Manipulation: Acid/base addition Duration: Hours Design: Separation of effects of different carbonate chemistry parameters by maintaining a) constant total inorganic carbon, b) constant pH, or c) constant CO2; temperatures = 23.5–24.5°C Results: calcification rate was correlated with [CO32−]: 50% decrease in calcification with 30% decrease in [CO32−]; 35% decrease in calcification with increase in pCO2 from 370 to 560 ppm. |
Schneider and Erez, 2006 |
Porites lutea and Fungia sp. | Manipulation: Acid/base addition Duration: 3 hours (night-time) and 6 hours (day-time) Design: Coral colonies were acclimated for several months, then subjected to seawater adjusted to one of 3 Ωarag levels: 1.56, 3.43, 5.18 (note that ambient Ωarag was 3.43); temperature was constant at 25°C. Results: Both day and night calcification decreased with decreasing pH; calcification rate at 2x preindustrial CO2 level (Ωarag = 3.1) was reduced by 42% relative to preindustrial level (Ωarag = 4.6). |
Ohde and Hossain, 2004; Hossain and Ohde, 2006 |
Montipora capitata | Manipulation: Acid addition Duration: 10 months Design: Corals places in flumes: control at ambient reef pCO2 (average 380 ppm), others manipulated to ambient + 365 ppm. Results: Calcification decreased 15–20% with a doubling of pCO2 (380 to 380+365 ppm). |
Jokiel et al., 2008 |
Porites astreoides (larvae/juveniles) | Manipulation: Acid addition Duration: 21–28 days Design: Flow-through seawater system; 3 aragonite saturation states: Ωarag = 3.2 (control), 2.6 (mid), and 2.2 (low); constant temperature at 25°C Results: Lateral skeletal extension in larvae was positively correlated with saturation state (P=0.007); juveniles in mid Ωarag treatment grew 45–56% slower than controls; those in low Ωarag treatments grew 72–84% slower than controls. |
Albright et al., 2008 |
Porites lobata Acropora intermedia | Manipulation: Bubbled CO2 Duration: 8 weeks Design: Corals placed in flow-through aquaria: 2 temperatures: 25–26°C and 28–29°C; and 3 pH levels: 8. 0–8.4 (control) 7.85–7.95 and 7.60–7.70. Results: Acropora intermedia and Porites lobata calcification rates were 40% lower at low pH treatment than in control. |
Anthony et al., 2008 |
Favia fragrum (larvae/juveniles) | Manipulation: Acid addition Duration: 8 days Design: Newly settled coral larvae reared in a range of Ωarag from ambient (3.71) to 3 treatments (Ωarag = 2.40, 1.03, 0.22); culture temperatures =25°C. Results: Aragonite was secreted by all corals even in undersaturated conditions; however, in Ωarag = 2.40 treatment, cross-sectional area of skeletons was more than 20% less than the control, and average weight of skeletal mass was 26% less than control. Similar trends occurred in the more extreme treatments. |
Cohen et al., 2009 |
Madracis mirabilis | Manipulation: Acid/base addition and bubbled CO2 Duration: 2 hour incubations following 3-hour acclimation period Design: Separation of effects of different carbonate chemistry parameters by manipulating chemistry to reflect 6 combinations of normal, low and very low pH, with normal low and very low [CO32−]; temperature maintained at 28°C Results: For pH/[CO32−] combinations that simulate natural ocean acidification (pCO2 = 390, 875 and 1400 µatm), calcification rate was not correlated with [CO32−], but rather with [HCO3-]. |
Jury et al., 2009 |
Oculina arbuscula (temperate coral) | Manipulation: CO2 bubbling Duration: 60 days Design: Controlled laboratory experiment to examine changes in calcification under Ωarag = 3.12, 2.40, 1.84, and 0.90 (approx. pCO2 = 409, 606, 903, 2856 ppmv, respectively). SST maintained at 25°C. Results: Calcification rate remained unchanged Ωarag > 1.84, then declined rapidly at Ωarag = 0.90. |
Ries et al., 2009 |
Lophelia pertussa (cold water coral) | Manipulation: Acid addition Duration: 24 hours Design: On-board incubations of deep-water corals at ambient pH, ambient pH − 0.15 units, and ambient pH − 0.3 units. Calcification rates measured using 45Ca labeling. Results: Calcification rates were reduced by 30% and 56% at pH reduced by 0.15 and 0.3 units, respectively, as compared to calcification rate at ambient pH. Calcification in young polyps showed a stronger reduction than in old polyps (59% reduction versus 40% reduction, respectively). |
Maier et al., 2009 |
Carbonate-dominated systems Gr. Bahama Banks | Manipulation: NA; field measurements Duration: Days Design: Measured changes in pCO2, DIC, temperature salinity, and residence time of Bahama Banks waters. Results: CaCO3 precipitation rate correlated with CaCO3 saturation state. |
Broecker and Takahashi, 1966; Broecker et al., 2001 |
B2 mesocosm | Manipulation: Acid/base and CaCl2 additions and natural alkalinity draw-down Duration: Days to months/years (3.8 years total) Design: Biosphere 2 coral reef mesoscosm; time series of net community calcification measurements in relation to carbonate chemistry. Results: Calcification rate well correlated with saturation state; calcification rate decreased 40% between preindustrial and doubled CO2 conditions. |
Langdon et al., 2000; Langdon et al., 2003 |
Monaco mesocosm | Manipulation: Bubbled CO2 Duration: 24-hour incubations Design: Coral community mesocosm subjected to continuous flow with a range of pCO2 values (134–1813 µatm; temperature maintained at 26°C Results: Community calcification was reduced by 21% between preindustrial and double pCO2 levels. |
Leclercq et al., 2000 |
Monaco mesocosm | Manipulation: Bubbled CO2 Duration: 9–30 days Design: Coral community mesocosm subjected to continuous flow with mid (647 µatm) pCO2 for 12 weeks, low (411 µatm) for 4 weeks, and high (918 µatm) for 4 weeks; temperature maintained at 26°C Results: Daytime community calcification was reduced by 12% between low and high treatments. |
Leclercq et al., 2002 |
Molokai Reef System | Manipulation: Natural alkalinity drawdown by organisms Duration: Several days Design: Large benthic chambers placed on reef bed; in situ carbonate chemistry, salinity, temperature, and net calcification/dissolution measured continuously. Results: Calcification and dissolution were linearly correlated with both CO32− and pCO2. Threshold pCO2 and CO32− values for individual substrate types showed considerable variation. Results indicate that average threshold for shift to net dissolution for Molokai reef is when pCO2 = 654 ±195 µatm. |
Yates and Halley, 2006 |
Northern Red Sea Reef | Manipulation: NA; field measurements Duration: 2 years Design: Eulerian measurements of carbonate system in seawater and community calcification/dissolution rates as a function of saturation state; adjusted for residence time of water. Results: Based on seasonal differences in calcification rate, determine that net reef calcification rate was well-correlated with precipitation rates of inorganic aragonite; projected a 55% decrease in reef calcification at 560 ppm CO2 and 30°C relative to 280 ppm and 28°C |
Silverman et al., 2007 |
Calcifying community dominated by Montipora capitata | Manipulation: Acid addition Duration: 24 hours Design: See Jokiel et al., 2008 and Kuffner et al. 2008. Compared Net ecosystem calcification (NEC) in coral community mesosms exposed to ambient pCO2 (380 ppm) and 2x ambient (380+365 ppm). NEC was determined every 2 hours by accounting for changes total alkalinity in the entire system. Results: NEC was 3.3 mmol CaCO3 m−2 h−1 under ambient and −0.04 mmol CaCO3 m−2 h−1. |
Andersson et al., 2009 |
1These studies manipulated Ca2+ rather than the carbon system. They are included here for completeness and because they provide insights into calcification mechanisms, but the results should not be strictly interpreted as a response to ocean acidification.
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